Iron and steel have played a leading role in the development of human civilization and their techniques. Together with its derivative, steel, iron has no real rival in its particular fields of application and has become a synonym of progress, being an essential element in mankind greatest technological achievements. It was at the origin of the industrial and scientific revolutions and at the heart of all the great discoveries which have marked the history of humanity from the manufacture of high quality swords in ancient times to today architectural wonders. Steel is an alloy that consists mostly of iron and has carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten. Rolling is a metal forming process in which metal stock is passed through a pair of rolls. Rolling is classified according to the temperature of the metal rolled. Steelmaking is the second step in producing steel from iron ore. Processing of steel results in special steel product with required properties, for example; vacuum treated steel for forging ingots; pre strengthened stress relieved elongated steel, metallurgical addition product, forging powder alloy steels, etc. Fasteners are used to join and hold two or more pieces of metal either temporarily or more pieces of metal either temporarily or permanently. Some of the most common are bolts, screws, nuts, rivets and pins. Packaging steels differ from other sheet products particularly in terms of their thickness, mechanical properties and coatings, together with their aptitude to satisfy specific industrial and marketing requirements related to high production rates, design factors etc. Small gage welded tubes have an extremely wide range of applications, including metallic roof frames, mechanical construction in public work and industrial engineering sector, agricultural machinery, fluid distribution circuits, piston, etc. India is among the top producers of all forms of steel in the world. Easy availability of low cost manpower and presence of abundant reserves make India competitive in the global setup. The steel industry in India has witnessed an increase in demand due to expanding oil and gas sector, huge spending on infrastructural facilities coupled with growth in housing, consumer durables and auto sectors.
This book basically deals with structural changes in steel during hot rolling, structural changes during reheating, kinds of grain restoration process, dynamic restoration process, static restoration process, effect of initial grain, size of static re crystallization, effects of temperature and micro alloying, fundamental principles of the metal rolling process, preparing and heating the initial materials, preparations for rolling heating before rolling operations, bolt and nut manufacturing technology, casting of steel for flat products etc.
The present book covers different important aspects of steel processing with the casting method of steel for flat products, rolling of rails, wheels and rings, rolling of different steel products, production of fasteners, welded pipes, steel products for the building trade and many more.
The book is very useful for everybody who wants the thorough study on steel and steel products or wants to diversify in to this field.
Structural Changes in Steel During Hot Rolling
Structural Changes During Reheating
of the consequences of
reheating process is grain coarsing. The control of grain coarsing
steels is an important step in the design of thermomechemical process
to achieve fine grained products.
microalloyed steels, the
reheating temperature should be high enough to provide solubility of
particles. If the stable particles remain undissolved, the beneficial
precipitation hardening effects cannot be obtained.
of aluminum, niobium,
vanium, titanium, etc., produces abnormal type of grain growth (Fig. 1)
involves the growth of very few grains in relatively unchanged fine
matrix. The abnormal grain growth occurs at the temperatures, which are
significantly lower than the microalloying solution temperature. The
temperature that corresponds to commencing of the abnormal grain growth
sometimes referred to as grain coarsing temperature.
The grain size distribution
has a complicated
dependence on the reheating temperature as depicted in Fig. 2 in
Nb V microalloyed steel. When reheating temperature is equal to 1200ºC
(2192ºF), the maximum area fraction of the steel microstructure
the grain size of approximately 0.12 mm (0.0048/in.). When the
temperature is lowered to 1150ºC (2102ºF), the grain size occupying the
area fraction is reduced to 0.06 mm (0.0024 in.). However, further
reheating temperature to 1050ºC (1922ºF) produces two pronounced peaks
distribution of the grain size, one of each is at the grain size of
mm (0.0072 in.) and the second one is at 0.022 mm (0.0009 in.).
affects a formation of so called deformation bands which play an
during subsequent grain restoration processes. As can be seen from Fig.
higher reheating temperature the smaller amount of deformation bands
formed and with less uniformity after the same reduction.
While it does not appear that the
final average austenite
grain size after deformation is strongly dependent on the reheated
it is likely that the distribution of the grain sizes above average is
smaller when the reheating temperature is kept below the grain coarsing
Kinds of Grain Restoration Process
Prior to the start of hot
rolling, the steel
microstructure consists of coarse equiaxed grains of austenite. During
through the rolls, the austenite grains are getting flattened and
the average each austenite grain undergoes a dimensional change
to that of the work piece as a whole. The deformation bands may also be
within the grains as illustrated in Fig. 4.
three following kinds of
restoration process are associated with hot rolling
1. Dynamic restoration process—This
process starts and
completes during deformation.
2. Metadynamic restoration
process—This process starts
during deformation and completes after deformation.
3. Static restoration process—This
process starts and
completes after deformation.
When steel is deformed in the
austenitic state at
high temperature, the flow stress rises to a maximum and then falls to
state as shown in Fig. 5a.
Dynamic restoration process
recovery and dynamic recrystallization.
Dynamic recovery is a
reduction of work hardening
effects without motion of large angle grain boundaries. It occurs in a
strain less than that for peak stress.
takes place in the range
of strain that corresponds to steady state of flow stress.
of dynamic recrystallization
of austenite in practical rolling of C Mn steels is small. It is due to
fact that a critical strain required for achieving the steady state of
stress is very large, even at high temperatures. The grain refinement
steels is usually achieved by static recrystallization.
Static Restoration Process
The microstructures developed
by dynamic restoration
are not stable and at the elevated temperatures are modified by
static restoration processes. The latter processes may include static
static recrystallization and metadynamic recrystallization as shown in
In hot rolling, static
recrystallization may start
spontaneously. Nuclei of recrystallization take place preferentially at
elongated grain boundaries and interfaces of deformation bands.
Softening by static recovery
occurs at the rates which depend on the prior deformation conditions
holding temperature. The recrystallization curves generally follow an
equation of the form.
Fundamental Principles of the Metal Rolling Process
The chief departments of a
operating on a complete ore to finished product cycle are the blast
steel making and rolling departments (Fig. 1).
all the steel that is
produced in the steel making department passes through the rolling
only a small portion is used for making castings and forgings. The
process, in which the finished product is produced, is the concluding
finished product of such a
plant is rolled stock of various types, designed for various purposes,
rails beams channels angles round, square or strip steel special
shapes, plate the sheet tubes, etc.
initial material supplied to
the rolling mill is the ingot, which may be either square or
cross section. In certain cases round ingots are employed (in the
tubes, wheels and types).
The rolling process in a
modern metallurgical plant
comprises two stages 1) rolling the ingot into the semi finished
product and 2)
rolling the semi finished into the finished product.
It is not expedient to roll
small blooms or billets
in heavy blooming mills since this lowers the productive capacity and
considerably increases power consumption of the mills.
A blooming mill can operate
efficiently if it rolls
ingots into blooms of large cross section, from 200 × 200 to 350 × 350
size. These blooms are subsequently rolled into billets of various
suit the production schedules of the mills rolling the finished
mills are usually located
adjacent to the blooming mills. This arrangement enables small billets
rolled from heavy ingots in a single heating. This is obviously good
from the economical point of view.
rolling of billets in two
mills has proved to be highly efficient. The larger the final cross
the bloom, the higher the blooming mill output will be. On the other
smaller the cross section of the billet supplied to the mill rolling
finished product, the simpler the design of this mill will be and the
its productive capacity. Another factor is the higher size accuracy and
of a finished product rolled from small billets or blanks.
department, producing semi finished products, may contain only a
or a blooming mill with a continuous billet mill. The preferable
depends on the production facilities of the section rolling department.
In modern metallurgical plants, the
production of sheet
and plate also comprises two stages 1) rolling ingots into slabs and 2)
slabs into plate or sheet.
Advantages of this two stage
procedure over that practiced
in old metallurgical plants, where sheet and plate were rolled directly
the ingot, are
Output of sheet
and plate mills is increased because the billets they roll is of
small thickness and because the top and bottom of the ingot are cut off
(2) The quality of the rolled plate
and sheet is improved
since the slabbing mill reduces the ingot on all sides and the slabs
inspected after rolling so that defects may be removed.
Slabs may be produced either
in blooming or in
slabbing mills. The ever increasing production of plate and sheet
conjunction with the development of continuous sheet and plate mills,
facilitated the widespread use of powerful slabbing mills, designed
for this purpose. The chief advantage of the slabbing mill, in
the blooming mill, is that the former has two vertical rolls in
addition to its
horizontal rolls. This enables the width to be rolled without turning
ingots on edge.
The slabbing mill is the
chief breaking down or
primary mill in plants designed for the large volume production of
plate. However, because of their narrower filed of application,
are much more seldom installed than blooming mills. In the majority of
it is necessary for the primary mill to roll both blooms and slabs.
blooming mill will serve this purpose.
The main requirements in
rolling the finished product are
To obtain a finished product of the
specified size and
shape at the highest possible rate of production and the lowest cost
To obtain a finished product of the
quality concerning, not only its physical and mechanical properties,
its surface condition.
requirements may be met
only if the processing schedule for all operations in producing the
rolled product is strictly followed.
The number of operations
comprising the rolling
process depends on the specifications stipulated for the shape
physical and mechanical properties, surface condition and macro and
microstructures of the rolled metal. The more exacting these
are, the more complicated the rolling procedure will be and the more
it will comprise.
The chief operations in metal rolling
initial material for rolling
initial material before rolling
including cutting, cooling, straightening, removing surface defects etc.
The preparation of the
initial material for rolling
consists in the removal of various surface defects. This is a very
operation, especially in rolling high quality carbon and alloy steels,
ensures a high output of proper quality with minimum rejects.
Strict observance of the
prescribed conditions for
heating the metal before rolling, proper determination of the
the beginning and end of the rolling process and determination of an
draughting schedule are of vital importance and directly influence the
of the finished product.
The prescribed procedure to
be followed in cooling
the metal after rolling may be quite significant in many cases. If it
observed, the rolled product obtained may have defects such as flakes
or it may have unsatisfactory properties.
It is necessary as well to
observe the prescribed
conditions for all of the remaining finishing operations, which ensure
finished product of the specified quality.
Fig. 2 shows a flow diagram
of rolled stock
production from the ingot to the finished product in modern rolling
departments. It represents the production of ordinary and quality
and alloy steel stock.
Proper control over the
rolling process and quality
control of the finished product are of primary importance.
One quality control procedure
practised in modern
rolling mill departments is melt inspection on the basis of which the
of the steel is determined and the melt is assigned for rolling. The
this inspection depends upon the requirements made to the grade of
Melt inspection begins in the
department where samples of the melt are taken to determine the average
chemical composition of the steel in each melt. Usually two samples are
from each ladle. The second sample serves to additionally check the
analysis. This is done in cases when it is necessary to check the
certain elements or if such inspection is stipulated by special
the customer. In certain cases, the samples for this analysis are taken
rolling mill department from the billet or the finished product. In the
years, many elements are determined by spectrographic analysis, which
become one of the most widespread physical methods of determining the
composition of metals and alloys.
Further melt inspection may
include determining the
quality of the melt by its macro and/or microstructure and longitudinal
fracture determining the grain size of the steel determining the
properties and hard enability and other tests. For this purpose one or
control ingots are selected. In the latter case, one ingot is selected
first tap and the second from the last tap. Control ingots of high
steels are selected from each tap. These ingots are rolled into billets
sometimes into finished products) either separately or together with
of the whole melt.
Samples for melt inspection
tests are selected from
bars rolled from the steel just under the top of the control ingot. In
cases, samples are taken from bars rolled from definite sections of the
in height, for example, from the top, middle and bottom sections.
Macrostructure inspection of
steel enables gas holes
(not permissible in killed steel) to be revealed as well as shrinkage
porosity, segregations, hairline cracks, flakes and other defects.
defects are evaluated by standard scales.
Longitudinal fracture enables the
degree of slatiness and
the grain size to be determined it reveals such defects as seams,
cavities, porosity, inclusions, stone like appearance, naphthalene
and other defects that can be seen by visual inspection.
inspection, the amount of
nonmetallic inclusions, grain size, depth of the decarburized layer and
factors are determined.
The second type of control is
over the rolling
process. It should ensure proper heating procedure for the initial
proper observation of the pass schedule for rolling the given section
the specified tolerances and proper finishing of the rolled material.
The marking on the initial
material must be
carefully checked in the storehouse before charging it into the heating
The temperature of hot ingots
should be measured
before placing them into the soaking pits. This will prevent thermal
Processing instructions usually list the minimum permissible
temperature of the
ingot surface and the maximum soaking pit temperature. The heating
and flame temperatures are checked during heating by appropriate
In rolling metal it is
necessary, first of all, to
check the initial and final rolling temperatures, as well as the pass
The setting of the rolls is checked continuously by measurements of the
sections the condition of the roll grooves and roll gear is also
frequently. Lately much attention has been paid to determining the
the rolls and the torques applied in rolling by means of load cells and
instruments. This enables the available power of the mills to be
correctly and fully.
Mechanization and automation
of rolling mills allow
the rolling speed to be considerably increased, particularly for
mills, and enable more attained in cold rolling sheet steel in
mills, for example, became possible only after instruments were
contactless continuous gauging of the strip. Such instruments include
strip thickness gauges based on the use of gamma or beta radiation.
isotopes are utilized as the source of energy. By means of a strip
control system, these instruments actuate the roll adjusting and strip
devices. In the very latest installations, computers and television
have also been
Steels for Magnetic Applications
steels metallurgy and properties
Together with nickel, cobalt
and a few other
elements, iron is one of the rare ferromagnetic metals. This property
intimately related to the electronic structure of the iron atom and a
explanation can only be given in terms of quantum mechanics. However,
consequence is that the spins of certain electrons are aligned,
resulting in an
overall magnetic moment, which is in the same direction throughout
of the crystal structure. Iron and the ferrite steels are, therefore,
of small saturated magnetic domains, each corresponding to a
magnet. The magnetization is not always obvious on a macroscopic scale,
the fact that the magnetization directions of individual domains tend
compensate one another. The magnetization directions of adjacent
(Weiss) domains are different, and often opposite, and they are
bound aries called Block walls (Fig. 1). When an external magnetic
applied, the magnetization directions tend to reorient and domains more
favorably oriented tend to grow at the expense of the others by
movement of the
Block walls, so that the individual magnetic fields no longer cancel
magnetically soft materials, the microstructure is such that
the Block walls is facilitated, enabling the metal to respond rapidly
external excitation, and to transmit the magnetic flux with minimum
losses. On the contrary, in magnetically hard materials (magnets), the
to conserve a strong macroscopic magnetization (remanent induction)
with a high
coercive force or coercivity (the external field necessary to overcome
remanent induction). Figure 2 shows the typical shape of a hysteresis
illustrating the fundamental parameters Bs (saturation induction). Br
induction or remanence) and He (coercivity). The magnetic permeability,
reflects the ability of the metal to transmit the magnetic flux,
the slope of the initial magnetization curve. A good electrical steel
must have a high permeability and minimum coercivity, together with
properties, which will be described in detail later.
Utilization and Property Requirements
Transformer sheets are sold
in the finished or semi finished
conditions and are used in the form of lamination stacks, mainly in
motors, alternators and compressors, depending on their properties. The
form the magnetic core of the apparatus concerned. The sheets must
several, sometimes contradictory, requirements, whose priorities depend
specific application, such as high magnetic permeability, low
(i.e. low power consumption) and ease of cutting to shape. Electrical
come in two principal categories, the oriented and non oriented grades.
Grain oriented sheets are
obtained by a complex
processing cycle and give excellent results in terms of permeability
losses in certain conditions, particularly in unidirectional fields,
such as in
transformers. The particular feature of these materials is their
consisting of very coarse grains, oriented with the cube edge parallel
rolling direction (110) ( the so called Goss
texture). The crystallographic
direction is a direction of easy magnetization, so
that when the
sheet is magnetized in the rolling direction, its permeability will be
high and its coercive force very low. Figure 3 shows the magnetic
iron and illustrates the advantage of having a
to the exciton field. In contrast, because of their planer anisotropy,
sheets have much poorer performance in rotating machinery, such as
where the excitation field rotates in the plane of the sheet. They are
difficult to blank because of their large grain size. In France, they
manufactured by the Ugine S.A. company.
Non oriented sheets are
produced by a much more
conventional process, and can be subdivided into two categories
Fully processed grades are delivered
in the finished
condition and are alloyed with silicon. They are continuously annealed
temperature, and sometimes varnished. Although their magnetic
properties in the
rolling direction are not as good as in grain oriented sheets, they are
less textured, making them better suited for use in rotary fields. They
good blankability, which depends on the silicon content, the grain
possibly on the coating.
Semi processed grades are
continuously annealed at a lower
temperature and are delivered after a significant skin pass reduction
%). They have good blankability, but must be given a final annealing
by the user to develop their magnetic properties. This treatment has
effects. Firstly, it produces a coarse grain size, due to the critical
(1 5%) imparted by the skin pass, leading to relatively few
nuclei, enhancing the magnetic properties. Secondly, decarburization is
promoted by the use of a controlled atmosphere. Thirdly slight
producing a bluish tinge, provides electrical insulation between the
laminations in a stack, limiting the formation of eddy currents in
current machines. The uses of semi processed grades are similar to
fully processed materials, even though the clients are often different.
top semi processed grades are roughly equivalent to mid range fully
Optimization of Magnetic Properties
The remainder of this article
will concentrate on semi
and fully processed non oriented sheet.
Among other characteristics,
a good electric motor
must have a high maximum speed (or torque) and high efficiency. The
circuit design and the choice of metal have a decisive influence on
properties. Power losses, which affect the efficiency, have two major
resistive losses in the copper windings, and core losses due to induced
and magnetic hysteresis. The resistive losses are proportional to the
the induction current, and can be decreased if the coupling between the
and the rotor is increased, i.e. if he core has a high permeability.
applied fields associated
with alternating currents are sinusoidal, so that the hysteresis cycle
repeated 50 times per second at the normal mains frequency. The energy
by this process alone is equal to the area inside the hysteresis loop.
hysteresis is caused by internal magnetic friction associated with the
of the Block walls. To reduce the losses, it is necessary to lower the
force, which correlates to high domain wall mobility. This can be done
eliminating as far as possible all precipitate particles, particularly
cementite, requiring extremely low carbon contents. The fully processed
are decarburized either in the melting shop or by strand annealing
rolling. The semi processed grades are decarburized by the user during
annealing after cutting to shape.
very low solubility of carbon
in ferrite at room temperature makes these steels highly sensitive to
aging, which can lead to increased power losses due to the natural
precipitation of fine carbide particles. The final carbon content must
therefore be less than or equal to 20 ppm. Figure 4 shows the
increase in power losses with carbon content after simulated aging in a
grade. Manganese sulfide and aluminum nitride particles are less
due to their large size (induced by appropriate metallurgical control).
way of reducing
hysteresis losses is to decrease the coercive force by increasing the
size, since grain boundaries are effective obstacles to the movement of
walls. In non oriented grades, cold rolling is performed in a single
of about 70%. Fully processed steels are continuously annealed at high
temperature to obtain coarse grain sizes of the order of 4 to 8 ASTM
um). Semi processed sheets are given a slightly smaller cold reduction,
by strand annealing at lower temperature and skin pass following
to a strain of less than 10%. Critical strain recrystallization during
final high temperature annealing treatment carried out by the customer
typical grain sizes of about 0 to ASTM (80 300 um), strongly
hysteresis losses. The skin pass reduction enables the blankability to
optimized. The electric motor manufacturers or blanking shops usually
YS/UTS ratios greater than 0.85 in order to improve productivity and
tool wear. The amount of cold work required to obtain such ratios is
few percent higher than the critical recrystallization strain. Figure 5
typical example of the variation of YS/UTS ratio with skin pass
accompanying micrographs illustrate the as annealed grain sizes. For
strains, recrystallizaion does not occur and the grain size remains
strains of a few percent lead to coarse recrystallized grains.
density of dislocations and
other mechanical defects is also important. Semi annealed sheets are
after blanking and therefore have very low dislocation densities. In
fully processed sheets can contain local regions of high strain after
This is particularly true at notches in the stator, where the
most severe. Since the purpose of these notches is to transmit the
flux from the stator to the rotor, certain users perform a stress
treatment at about 800ºC to produce local recovery or even
Finally, another useful way to
reduce hysteresis losses to
modify the texture, enhancing the density of (100) and (110) planes,
significantly raises the low flux density permeability and sharply
coercivity. The texture can be modified by adapting certain stages of
processing, but the operations involved are relatively complex.
Eddy current losses
other important source of
core losses is the resistive heating associated with induced eddy
latter are caused by interaction between the magnetic field and the
electrons of the metal. The losses due to this phenomenon are
the square of the frequency and the thickness of the sheet (the current
appear in the sheet section perpendicular to the magnetic flux, and
counter field which opposes the induction field). Apart from reducing
working frequency, which is rarely possible, there are three ways of
Decreasing the sheet thickness is
common practice, since
magnetic cores are generally composed of stacks of thin sheets, less
than 1 mm
thick. This approach is limited by productivity considerations.
Efficient inter lamellar electrical
obtained by oxidation (bluing) in semi processed grades, at the end of
final annealing treatment performed by the user, and by varnishing for
products. The latter technique is much more effective.
The use of alloying elements such
as silicon, phosphorus,
aluminum and manganese has the advantage of considerably increasing the
resistivity. This significantly decreases the intensity of the eddy
and the associated power losses. Silicon can be incorporated in the
appreciable amounts, up to 3.5%, with appropriately adapted processes.
this level, excessive brittleness prevents cold rolling. Furthermore,
reduces the saturation induction of the steel, and hence its
medium and high flux densities. Steels and hence its permeability at
high flux densities. Steels with more than 0.5% silicon have various
technological disadvantages. After continuous casting, the slabs must
transferred hot to the rolling mills, due to their tendency to crack on
cooling, and silicon containing sheets are difficult to weld. However,
of these drawbacks, the functional benefits of silicon containing
steels have led to their widespread use, due to the critical importance
power consumption, especially in large motors.
Type of electrical steel
oriented electrical steel
sheets are covered by three French standards, depending on whether they
semi or fully processed. Semi processed products are described by the C
and 28 926 standards, while NF C 28 900 treats fully processed sheet.
cases, only the magnetic properties are guaranteed, particularly the
specific losses at a given magnetization level and the induction level
given applied field, in both the transverse and rolling directions. For
sheet, after a reference heat treatment, the metal must guarantee a
consumption less than a specified value, together with a minimum
level for a given applied field. The reference heat treatment
annealing for two hours at 790ºC in a decarburizing atmosphere. The
used for the measurement is called in Epstein frame and is described by
C 28 911 standard.
designations of different
steel grades according to these standards reflect the maximum power
watts for one kilogram of the metal concerned and an induction of
these losses depend on the thickness, the designation includes the
thicknesses (0.5 and 0.65 mm for the semi and fully processed produces.
0.35 mm for fully processed materials). For example, the FeV 660 50
corresponds to a material with a thickness of 50 hundredths of a
for which the guaranteed total losses must not exceed 6.6 W/kg measured
standard Epstein frame. The difference between the two semi processed
standards NF C 28 925 and 28 926 concerns the amounts of alloying
first applying to unalloyed steels (0.5 wt. % Si) and the second to
grenades (according to the NF EN 10 020 standard). The designations are
differentiated by two letters. HD for unalloyed semi processed grades,
alloyed semi processed materials and HA for the fully processed sheets.
C 28 900 standard mentions certain requirements concerning magnetic
packing factor (volume increase on stacking) and magnetic anisotropy.
not really electrical
steels, these XC grades are used for the manufacture of small motors
infrequent utilization (e.g. kitchen mixers, electric automobile window
etc.), for which the efficiency is of little importance. Although their
magnetic properties are never guaranteed, their mechanical
severely controlled. Their blanking capacity must be excellent and
Semi processed grades
grades are presently
available, in different thicknesses. They cover all the requirements of
domestic appliance and small industrial motor markets. The differences
the guaranteed maximum power losses, and are essentially related to the
of alloying additions in the steel. The latter include the four main
which increase the resistively, i.e., silicon, aluminum, phosphorus and
manganese. Table 1 gives the guaranteed magnetic properties of these
compared to those required by the standards, together with their
The trend in semi processed
steels is towards more
efficient decarburization during melting. This improves their intrinsic
quality, but most of all, simplifies the process for the end user, by
eliminating the need for decarburizing, increasing the productivity of
grain coarsening furnace. Moreover, modern stacking techniques, such as
Fastec process, become accessible to the semi processed grades. Since
is performed immediately after blanking, decarburizing is not possible.
However, in these applications, varnishing of the coils becomes
development enables the steelmaker to differentiate between semi and
grades at a much later stage in the manufacturing cycle, significantly
simplifying internal product management.
Fully Processed Grades
large number of fully processed
grades are available on the market. For a given thickness, it is
choose from a wide range of different power loss levels. Various types
varnish can be applied to the sheets. Table 2. illustrates the extreme
in terms of guaranteed maximum power losses for three standard
together with their typical mechanical characteristics.
choice of power loss level
depends on the application concerned, varying greatly from a washing
motor to a nuclear power station turbine. Metallurgically speaking, the
variations are due mainly to differences in the silicon and aluminium
and in the annealing cyles employed.
Preparing and heating the initial materials
Preparations for rolling
initial materials (ingots and
billets) are prepared to be rolled by removing various surface flaws.
called surface conditioning and is an important operation, especially
rolling quality carbon and alloy steels intended for the manufacture of
components in various fields of industry. The cost of preparing the
materials will be justified in this case by the possibility of
product of the specified quality and by the decrease in the amount of
a rule, hot ingots are charged
into the soaking pits and, therefore, surface conditioning operations
performed on the billets (however, flaws may also be removed from the
of the hot ingots).
are made to the surface of alloy and high alloy steel ingots.
cast ingots may be completely cooled, surface conditioned and then
subsequent rolling (a softening heat treatment may be employed before
the flaws). In this case, surface flaws are removed both from the
from the billets.
defects, subject to
removal, include scabs, hair lines, cracks, rolling laps, nonmetallic
inclusions, scratches, etc. All of these flaws are revealed by
all surface defects are to be removed, the billet is first pickled.
enclosed by scale and therefore hidden from ordinary inspection, may be
detected by acid pickling.
Chipping operations to remove
performed by means of pneumatic hammers usually operating under an air
of 5 to 5.5 atm, are still in wide use. This method has a low
capacity, especially for alloy steels, and is a health hazard as far as
operations are concerned.
requires the highest
labour input of all rolling operations and is therefore little suited
rates of production. It is chiefly employed in the surface conditioning
billets and sometimes as a supplementary operation for removing certain
flaws on ingots. These are flaws such as may remain, for example, after
the whole surface of the ingot or after performing some other allover
are usually chipped in a
direction along the length of the billet or ingot since transverse
caulk such defects as cracks. The sides of the chipped groove should
gently and its width to depth ratio must be such that no new cracks or
defects will be produced on the surface of the finished product in
frame grinders are also
used for surface conditioning operations. They are mounted on a special
suspension device allowing them to be easily swiveled about a vertical
titled from the vertical position. Due to the high grinding speeds, the
abrasive wheels used are of aluminum oxide with a resinoid (bakelite)
contradiction to chipping with
pneumatic hammers, conditioning with a grinder is carried out in the
direction (on the billet) since it is difficult to detect hair lines or
cracks, usually running along the billet, in longitudinal grinding.
have a low production
capacity in surface conditioning operations and the cost is higher than
chipping. Consequently grinding finds application in removing a large
slight defects and chiefly for conditioning high alloy steel billets.
of the latter with pneumatic hammers is extremely difficult or even
In removing flaws by grinding from hard steel billets, the intensive
the metal and subsequent cooling may lead to the formation of grinding
This can be avoided by taking lighter cuts and by selecting the grain
grade and peripheral speed of the grinding wheel to suit the steel
processed. Grinding cracks are more liable to appear in conditioning
steels. That were rapidly cooled after rolling, producing high
stresses. Air hardening
steels should be conditioned in the as annealed state to prevent the
new surface conditioning
method, called flame scarifing, has come into use in the last years. It
consists in burning out the flaws in the surface by means of a torch
Flame scarfing is performed
either by hand or in
a rule, hand (torch) scarfing
is a localised operation in which certain definite defects are removed
surfaces of ingots and billets. Here the tip of the torch is directed
end of the defect and the metal is preheated to a temperature of 950°
This takes several seconds. The torch is held at a angle of 75° 80° to
billet surface. When the metal is heated to the burning point, the
oxygen supplied to the torch is increased.
oxygen removes a layer of
metal by oxidizing or burning the metal. As soon as the metal begins to
the torch is titled to an angle of 25° 30° to the surface. Then the jet
oxygen not only burns the metal but also blows the slag and liquid
the surface being scarfed.
present, almost all types of
steel are torch scarfed. All carbon and low alloy steels may be torch
without difficulty. Stainless, heat resistant and other steels, with
chromium content, require the application of special fluxes and
facilitate burning and form slag with a low melting point. Frequently a
torch is used to scarf these steels. It differs from the ordinary torch
having a supplementary injector, supplied through one hose with an
mixture, and with additional cutting oxygen through a second hose.
the beginning of the cut
is heated, then the oxygen and flux delivery are turned on. When a
amount of molten slag has formed, the supplementary oxygen injector is
on and torch is moved along the line of scarfing.
which may be formed in
flame scarfing, are due to the thermal stresses resulting from large
temperature differences along the cross section of the billet and also
associated with the formation of a martensite or troosto martensite
from the austenite. The lower the thermal conductivity and initial
of the billet being scarfed, the higher its coefficient of thermal
and the lower the ambient temperature, the higher the thermal stresses
The higher the austenite stability and carbon content of the steel and
higher the cooling rate after scarfing, the more susceptible the steel
to crack formation. Stresses due to scarfing may be reduced by
billet or by surface conditioning directly after rolling when the
scarfing is performed in a
direction along the billet. The scarfed groove should have sloping
should be of a width at least five times its depth and of a length at
three times the width.
production capacity of hand
torch scarfing is several times higher than chipping with pneumatic
Highest output is achieved, however, in flame scarfing machines where
defects are removed by an allover burning of the surface layer with an
scarfing machines are
usually installed beyond the mill, for example, in the roller table
between the blooming mill and the shear. Here hot blooms and slabs are
directly after they leave the mill. Here, the surface layer of metal is
simultaneously from all four sides of the bloom.
same type of mechanized
allover surface conditioning is also practiced in the billet storage
billets are treated either cold or preheated. In these installations,
head is mounted on a truck traveling on rails along which the billets
Other surface conditioning
methods, used for billets
and ingots, are 1) milling, 2) planning and 3) turning.
Of these, turning is the most
operation for roughing ingots and billets.
is applied in roughing
round ingots and billets of heat resistant, stainless and other special
steels for the production of high quality seamless tubing. Special
available at present for roughing such round ingots. These lathes are
with special fixtures for rapidly setting up and centre drilling the
The use of several tools clamped on a single carriage effectively
and high alloy steel
ingots, intended for producing sections, sheet or plate, are also
special cases. Such ingots have a square or rectangular cross section
machined on special tracer controlled lathes. These machine tools,
multiple cornered lathes, can accommodate ingots and billets of any
multiple cornered lathes
came into use, square and rectangular ingots were roughed all over on
and special planers. The low output and high cost have almost excluded
method from general practice.
The surfaces of ingots and
billets are milled both
for allover surface roughing and for removing separate defects. This
is performed on special milling machines.
surface defects, of a width
up to 50 mm and a depth up to 15 mm, difficult to cut out by pneumatic
chipping, are usually removed by a local milling operation.
and billets of mild and
medium hard steels are machined without being previously annealed. Hard
are annealed before machining.
Bolt and NuT Manufacturing Technology
The metal working industry
employs a range of
different technologies. These include the casting of molten metal into
fusion by welding, cold and hot mechanical working, cutting and
machining, technologies consist of a variety of distinct techniques for
example, metal cutting technology includes amongst many other
turning, milling and drilling. The manufacture of nearly all threaded
requires the employment of methods or techniques from more than one
In later chapters, bolts and
nuts are described as
being manufactured using a particular technology. It does not
follow that only one technology is employed in the full sequence of
manufacturing operations. Rather, the characterization refers only to
important technology that is used in the complete manufacturing
The next section of this
chapter provides an
introduction to the principles involved in the manufacturing of
fasteners. It is followed by more detailed discussion of alternative,
technologies, the ranges of alternative techniques within each
the types of tools and machines that are used. The descriptions of the
principles and technologies are not comprehensive the purpose of this
is to give a reasonable idea about the nature of choice currently
to provide sufficient information to enable the reader unfamiliar with
manufacturing to follow the discussion in later chapters of the study.
The three main metal working
technologies used in
the manufacture of threaded fasteners are cold mechanical working or
forming, hot mechanical working or hot forging and metal cutting. In
working, the processes used to shape metal include rolling, drawing,
upsetting open die forging, closed die forging, and presswork. Although
mechanical working changes the shape of work pieces it does not change
substantially. The processes involve the plastic re shaping or
either cold or heated work pieces by the external action of special
Mechanical working strengthens components by drawing impurities and
bands along the direction of working and closing minute cavities.
Fundamentals of Mechanically working and cutting metals
When metals are subjected to
loads they first deform elastically. If the load is increased beyond a
point the metal becomes plastic. Curve A on the load extension diagram
figure 1 shows how the rate and degree of deformation can vary with the
magnitude of the applied load. Stress, which is the load per unit area,
plotted on the vertical axis of the diagram while deformation,
terms of strain is shown on the horizontal axis. Beyond the transition
curve A between elastic and plastic deformation some deformation
the load is removed. If the load continues to be raised the metal
Cold forming metal within its
decreases its plasticity and this phenomenon is called strain or work
hardening. Curves A and B in Figure provide a comparison of how mild
behaves before and after cold working. Work hardening is not only
with an appreciable decrease in plasticity but also with an increase in
strength. Advantage is sometimes taken of this to deliberately increase
strength of a piece of metal by cold working it, but since plasticity
with cold working there is a maximum limit to the amount of cold
may be undertaken. Advantages of cold forming over hot forging are that
are free of surface scale, may require less raw material since they can
formed closer to final size, do not need to be pre heated and require
cool downtime after working.
For each metal there is a
range of temperatures in
which the plasticity and resistance to work hardening is greatly
forging temperature range varies from metal to metal. For mild steel it
around 1,200°C while for lead it is room temperature. The forgability
metal is its ability to flow into the required shape without cracking
low resistance to the forces shaping it. Forging a metal to a given
requires considerably less power than cold working it, but the accuracy
finish of the work piece are generally inferior.
There are several ways of
cutting metal sawing,
abrasive cutting off (grinding), shearing or cropping, and machining.
methods have much in common both with each other and with the
working technologies all involve working metal in the zone beyond the
In this section each of the
main bolt and nut manufacturing
technologies employing the principles described in Section 2 is
Cold Forming of Bolts
Four widely used methods of
cold forming are shown
in the top row of Figure 2. These are upsetting etc. which involves a
in length and increase in cross sectional area of work pieces, forward
backward extrusion which both have the effect of reducing the area and
increasing the length of work pieces and thread rolling. In thread
dies penetrate the surface of the blank to form the thread root, the
material flowing outwards and upwards to form the crest of the thread.
or shearing, trimming and piercing are often carried out in association
cold forming but they employ cutting rather than forming techniques,
in the lower half of Figure 2. Most work pieces or blanks to be cold
first cut off by cropping them from wire stock. Hexagonal bolt heads
usually formed by trimming the periphery of cylindrical upset heads
hollow hexagonal punch. Trimming removes any cracks on the edge of the
caused by upsetting. Piercing involves the removal of a slug from the
piece to form a hole and is used in the cold forming of nuts.
One sequence of operations
which can be used to
produce a bolt to its final shape together with an outline of the
tooling is shown in the left hand side of Figure 3. In this case the
machine cuts off and upsets the blanks in two blows. The additional
operations required to finish the blanks are carried out on a single
trimming machine and thread rolling machine.
In heading machines, the end
of a coil of cold drawn
wire that has been precoated with a lubricant passes through
feed rollers which push the wire through the cut off quill until it
against a stop. The blank is sheared from the end of the wire and
to the heading position by the cut off mechanism. During the firsts
the heading station the punch pushes the blank into the die until it
against the ejector pin and then commences the shaping of the head by
a cone. Between the first and second blow the first punch is moved
the second punch takes its place. The second punch forms the head into
cylindrical cheese and usually also embosses the top of the head of the
with symbols to permit identification of the manufacture, tensile
sometimes of the tread forms. Once the second punch has withdrawn, the
forced from the die by the ejector pin and falls clear of the die
next blank is inserted.
Two blows are needed to form
the cheese head because
there is a limit to the amount of metal that can be upset in a single
without buckling the portion of the blank that is not supported within
In a single blow, the maximum amount that can be cold upset under
two and a quarter diameters but most single blow heading is within the
one to one and a half diameters. In two blow heading four and a half
can be upset.
There are other limitations
to the lengths of
material that can be headed using the methods shown in Figure 3.
buckle if they are unsupported over a length of more than eight times
diameter which limits the length diameter ratio of formed b1they anks
within a die. One way round this problem is to provide support to the
pins by using a telescopic ejector mechanism. This makes it possible to
formed blanks with lengths contained within the dies up to twelve times
as their diameters. For even longer parts which are upset (but not
split dies are used which are made in two halves. The two halves are
together during the upsetting operation and act in a similar way to
dies but are forced apart before ejection. With this arrangement blanks
inserted from the back as opposed to the front of the dies and are cut
the back of the split dies before they close for the upsetting
length of the wire for the next blank to be upset ejects the previous
the die. The head of very long bolts can be cold formed by holding pre
blanko in split dies during upsetting. The heads of most cold formed
fasteners are upset using the closed rather than the split die
reason is that when bolts are made from wire the split die
requires a different set of dies for each blank length whereas only the
pin requires replacement when, blank lengths are altered using closed
After heading, the blanks are
collected from under
the heading machine and transported to the trimming machine. The
machine performs two distinct functions first it gives the head a
shape by trimming off material and second, it straightens the body and
extrudes the end of the body in preparation for thread rolling. The
blanks are usually deposited into the hopper of a trimming machine
are first automatically orientated correctly for delivery into a chute
lower end of which they are picked up and transferred to a point over
trimming die centre by a pair of fingers. The punch pushes the blank
the extrusion die as depicted in the left hand column of Figure3.
end of its forward stroke the punch forces the head of the blank
hexagonal trimming die. Once the punch is on the return stroke the
ejected from the die by means of a spring behind the ejector pin.
There are limitations to the
amount of forward
extrusion that can be carried out with a single blow. If buckling of
portion of the blank that is not supported in the die is to be avoided
extrusion, the reduction in cross sectional area resulting from a
operation must not exceed 30 per cent.
The diameter to be thread
rolled could be reduced by
machining rather than extrusion, but this would waste material. Another
of producing threads is to cut them but this also wastes material.
rolling has other advantages, however, over thread cutting. Firstly,
working action during rolling increases the strength of the threads
grain of the material follows the thread contours and secondly,
stresses are imparted to the thread roots during rolling which offset
stresses produced by tightening nuts into bolts. In flat die thread
parts are threaded between a pair of flat dies, one reciprocating and
stationary. The thread shaped ridges on the working faces of the dies
inclined at the angle necessary to produce a continuous thread on the
thread is rolled on one blank at a time while it rotates about its own
axis, during the forward stroke of the reciprocating die. Thread
take other forms. In planetary thread rolling, blanks are rolled
centrally located rotating die and a stationary concave die segment.
circular die in the middle rotates continuously with the result that
three parts can be passing between the dies simultaneously. Such
machines can only
roll relatively small diameter blanks. In another arrangement the blank
squeezed between two cylindrical rotating dies, which have, thread form
round their circumferences.
Thread rolling machines, like
trimming machines, are
usually arranged so that the blanks are automatically fed down a chute
hopper although, in the case of very long blanks, it is necessary to
both trimming and rolling machines. Some fastener manufacturers link
heading, trimming and rolling machines by providing conveyors, which
the blanks from under one machine and deliver them to the hopper feed
next machine in the line. Although conveyors can reduce the amount of
handling required between the operations they have two disadvantages.
all the machines in a line linked by conveyor must be working on the
of blank (when the machines are not linked up this is unnecessary) and
overall machine utilization in a linked system can be low because when
machine stops running for more than a short period the other machines
it must also halt.
The heading, trimming,
extrusion and rolling
operations can be combined in a single specialized machine. The
illustrated diagrammatically on the right hand side of Figure3. The
shows a machine having a bank of five stations, with a cut off, four
four punches. Transfer fingers move each blank along the row of dies
position at a time between blows. Each blank receives a single blow
punch. In the case shown in Figure 3, wire with a diameter greater than
finished shank diameter is used. By extruding the body if the bolt down
finished shank diameter in the first dies the head can be upset in only
blow by the second punch without buckling occurring. This is possible
the section of the blank forming the head is less than two and a
the diameter of the original wire compared to two blow heading there is
deformation in the head for a given bolt size. The result is a better
of properties between head and shank with the result that normalizing
finished bolts may be necessary. The portion of the shank that is to be
rolled is extruded in the third die and the head is trimmed in the
In some machines, the trimmed blanks pass through the centre of the
die and enter a tube through which they are delivered to either a
then a thread rolling station or directly to a thread rolling station.
pointing operation cuts a chamfer round the tip of the body so that the
of the rolled thread is even. In other machines, a trimming punch is
parts are allowed to drop into a collecting belt after ejection from
There are several types of
cold forming machines,
which represent intermediate stages between two blow heading machines
integrated machines. Often when parts with large diameter heads and
shanks are required, two dies, three blow headers are used. Machines
with four or
five stations in line but without pointing or thread rolling stations
called either progressive or transfer headers. These machines are most
used for cylindrical parts other than bolts which would otherwise have
machined from solid bar.
In addition to the precoated
solid lubricants on the
wire small quantity of oil is usually applied to the material stock to
lubricate forming operations. An oily rag is often tied round the wire
the feed rolls but oil can be sprayed into the tool zone where there is
of large quantities of oil entering the die and causing work pieces to
partially filled. The important characteristics of these oils are
high pressure and temperature and the minimum emission of smoke and
Most cold forming wires are precoated with thin dry coatings.
Cold Forming of Nuts
4. shows a cold nut
forming sequence and an outline of the tooling. Cold nut forming
quite similar to short stroke progressive headers. The wire stock is
through feed rollers, the cut off quill and the cut off bush up against
length stop. A cylindrical blank is cut off and inserted into a
gripper which presents it to the first forming station. After forming
first die the blank is ejected and received by a second gripper for
the next forming station. This sequence is repeated until the blank
last die position finished formed. During two of the transfers in the
shown in Figure 4 the blank is turned end on end through 180 degrees to
the punches to work on both ends of the blank. Because of the work
that occurs during forming, the slug is punched out cleanly at the last
Nuts can also be formed in
four stations cold nut
forming machines which accept wire with a hexagonal cross section or
alternatively by cutting off and performing cylindrical blanks on one
heat treating the blanks to remove the effect of the work hardening
during the initial forming and then finish forming the blanks on a
forming, nut blanks have
their thread cut on tapping machines.
Hot Forging of Bolts
Figure 5. shows two
alternative operation sequences
for the production of hot forged bolts together with outlines of the
tooling. Bolts are forged from hot rolled round bar of a diameter equal
of the finished bolt shanks.
In the first process in
Figure 5, a blank, or pin,
of sufficient length to form one bolt is cut off. Sawing is rarely used
this operation since it takes longer than cropping. Equipment used for
ranges from manually operated shears intended for cutting reinforcing
building sites to fully automatic high speed cropping machines.
controlled purpose made semi automatic cropping machines are available
simple reciprocating mechanical presses can be equipped with cropping
do the job in the same way. In such machines the bar stock is supported
lower shear knife and the head carrying the upper knife reciprocates
continuously while an operator pushes the bar in by hand against a stop
the interval between strokes. Sometimes two pins can be cut per stroke
loading bars in parallel. There is usually provision for stopping the
the raised position between strokes to allow time for the manipulation
bars. Automatic cropping machines are fed from stocks of bars held in
magazines, which can be replenished without interrupting production.
Most hot forged bolts are
thread cut because steel in
the hot rolled state tends to have an uneven and scaly finish, which is
unsuitable for extrusion and thread rolling. Slight chamfers are
usually cut on
the ends of the shanks these serve to remove metal distorted during
which might prevent the shank entering the forging die, provide lead
thread cutting tools and also help start threads when bolts and nuts
assembled. This pointing operation is similar to that carried out on
formed bolts. A variety of purpose built pointing machines are
ranging from magazine fed automatics to simple manually loaded
Sometimes old lathes can be modified to do the job.
Before forging, the end of
the pin, which is to form
the bolt head, is heated. Simple pin heaters consist of open hearths
solid fuel with ledges round the top edges on which pins rest. The tips
pins are introduced through holes in the refectory bricks. More
furnaces using oil, gas or electric induction heating are available
deliver heated pins at a predetermined rate. Induction heating
expensive to purchase but results in less surface scale and allows
control over temperature. Three unsupported diameters of bar can be hot
in a single blow if the end of the bar is square to its longitudinal
However, because the ends of most cropped pins are not flat and may be
deflected sideways it is usual to employ two blows even for heads
less than three diameters of material. The two blow hot heading method
the left hand column of Figure 5 is similar to two blow cold heading in
cone and cheese are upset using two punches and a closed die which
shank of the blank. On most two blow headers the die is mounted on a
that it can be moved clear of the punches for the insertion of long
operator can push the saddle back and forward but more often this is
automatically. The operator uses tongs to load the heated pins into the
After heading, the ejector pin pushes the blank out so that its shank
grasped by tongs for complete removal. Due to the uneven surface of hot
bar more clearance is provided between the bores of hot heading dies
pieces than in cold heading dies. Because of this clearance and because
ejector pin does not have to push the bolt right out of the die, the
blank that can be hot headed in a closed die is not restricted as in
forming and this is a major advantage of hot over cold solid die
is usually used to cool the hot heading tools.
After hot heading a separate
machine is used to hot
trim or strip the cheese to form a hexagonal head. The layout consists
oil fired pin heater, a hot heading machine and a hot stripping
layout enables a furnace man and one operator on each machine to head
bolts in one heat. The rate of output of such teams of three men is
governed by the work pace of the heading machine operator.
The sequence of operations on
the right hand side of
Figure 5 can be used to forge bolt heads without trimming waste. This
is called hot upsetting and is carried out on forging machines. Forging
machines squeeze rather than hammer the work into the required shape.
and surface defects are set cut away from round the head by stripping
operation, this method is usually employed for heading large bolts with
absolute tolerances than those on small bolts. The length of bar
form the head is measured by the operator pushing the heated end of the
against the first outside die. The gripper dies are closed to hold the
before the heading stroke of the outside die commences. If the finish
head is unsatisfactory, the bar can be rotated one sixth of a turn and
operation repeated. The head is finish formed at the second station.
Forging machines can be
equipped so that the work
piece is manipulated mechanically, but on the smaller machines required
most sizes of bolt, the operator usually inserts and removes the work
tongs. Since the shanks of bolts protrude from the forging machine
upsetting the process does not restrict the length of bolt that can be
Screw cutting which is the
final operation required
to finish hot forged bolts is usually carried out on special purpose
using rotating tangential cutting dies arranged as shown at the bottom
Figure 5. One advantage of this particular type of thread cutting is
dies can be resharpened many times. The dies cut the thread in one pass
spring open before the return stroke.
Hot Forging of Nuts
The material stock for hot
forged steel nuts is
normally hot rolled bar. Figure 6 shows alternative ways of hot forging
blanks. In the sequence on the left of the figure the rectangular bar
progressively fed into the semi automatic nut press by an operator.
bar has cooled below the forging temperature it is returned by the
the furnace. Forging is accomplished by first forging vees into the top
bottom faces of the bar to produce two sides of the hexagon of the
and two sides of the second nut and then shearing the blank of the
off from the parent bar. During shearing the cut off tool pushes the
horizontally into an enclosed die where the hole is then pierced before
finished blank is ejected. Since forging in a hot nut press takes place
enclosed die an automatic adjustment is provided to compensate for
scale and variations in bar section. After hot pressing it is common
end face of a nut to be lightly machined to remove punch burrs. This
called frazing, is most simply carried out using an end milling cutter
centrally in a vertical rotating spindle above a nut clamping fixture.
The automatic hot nut forging
sequence on the right
hand side of Figure 6 has more in common with the cold nut forming
Figure 4 than with the hot nut pressing method. The bar heated can be
fed from an automatic magazine or manually and the heat source can be a
oil or gas fired furnace or an electric induction coil. From the heater
pass straight into the hot nut forging machine. Due to the ductility of
steel only three forming stations are required.
A third method of upsetting a
hexagon from round bar
in a forging machine is not shown in Figure 6 since it is similar to
for hot upsetting bolt heads shown on the right hand side of Figure 5.
upsetting a hexagonal nut blank on the end of a round bar, a hole is
through the upset hexagon, by pushing the bar back, this leaves the
in the die. The metal pierced out of the nut remains attached to the
end of the
bar and is incorporated into the next nut. Several nuts can be made
length of bar in one heat. Although this upsetting process wastes
little or no
metal, it is relatively slow with the result and it is usually only
large nuts for which there is a relatively small demand.
Machining of Bolts and Nuts
from Hexagon Bar
The bar stock for turned
bolts and nuts is usually
cold drawn to a hexagonal section and machining is usually on automatic
or operator controlled capstan or turret lathes. Both capstan and
grip one end of the work piece in a chuck or collet leaving the space
the other end of the work piece unrestricted so that a series of tools
positioned there in an indexible turret. This arrangement is convenient
drilling and boring through the centre of a part and for facing its
end. Turret and capstan lathes can have additional tools mounted on
slides between the chuck and the turret.
Figure 7 shows sequences of
operations for turning
bolts and nut blanks from hexagonal bar. The chuck which rotates the
opened when it is necessary to feed a new length of bar. The bar stock
against a job stop mounted in the first turret station. The second
station holds a roller steady tool holder for turning the shank of the
Roller steady tool holders are designed so that the cutting thrust,
to deflect the work piece away from the tool is balanced by rollers
the opposite side of the work piece. During the roller supported
operation the turret is driven along the bed. The tool in the third
station is a screw cutting die head, which springs open automatically
end of the screw cutting run prior to a rapid return stroke. The back
cross slide carries a parting off tool which is also used for cutting
annular groove prior to the head chamfering operation. A form cutter
chamfering is amounted on the front of the cross slide. This
based on the use of three turret stations, but the turrets could be
kitted by loading an identical set of tools into the remaining stations
halve the turret indexing time per piece.
Nuts are turned using a
similar tool set up to that
just described for bolts. The place of the roller box tool holder is
taken by a
drill and a tool to chamfer the lip of the hole as the drill completes
On manually operated lathes,
the operator starts and
stops the spindle, changes gear to alter the spindle speeds and tool
between cuts, indexes the turret and feeds the bar stock. It may
be possible to take two cuts simultaneously by, for example, cutting
chamfer on the corners of a nut while the hole is being drilled. But
automatic lathes can take more than one cut at a time, which can result
considerable savings in the time required to manufacture each piece.
advantage of the automatic lathe is its reduced dependence on operator
this in turn reduces waste and inspection requirements. Multi spindle
automatics are available which can work on several parts simultaneously
passing each part to a succession of tools. The tool motions and feed
most automatics are controlled by rotating cams but increasingly
sequence controlled single spindle automatics are used which can be set
quickly than can automatics and require less attention from operators
The internal threads on
standard nuts are usually
not cut before the nut is parted from the material stock because of the
reverse the direction of spindle rotation to remove the thread cutting
the blind hole.
The threads on most nuts are
cut by specialized bent
tap machines. Blanks are gravity fed down a channel from a magazine
nose of a continuously rotating tap. The cutting flutes of the tap are
positioned in the middle of a stationary hollow hexagonal guide way,
prevents the nuts from rotating as they move along the tap. The shank
tap beyond the threaded portion is bent so that it can be driven and
are thrown off radially. Another type of nut tapper has a number of
spindles carrying straight taps. Nuts are placed by hand in a trough of
lubricant under each spindle and foot pedals lower the spinning taps
nuts. Threaded nuts collect on the taps and are periodically removed by
Casting of Steel for Flat Products
Type of Cast Products
products utilized for flat
rolling can be produced in the following forms
1. Ingots These
are castings of simple shape. Slab
ingots range in weight from 9 to 36 metric tons (10 to 40 net tons). In
to roll strip from the ingots, the latter are usually first rolled down
size of a slab with thickness range from 150 to 350 mm (6 to 14 in.).
are further reduced in thickness at the roughing stands of hot strip
to 25 65 mm (1.0 2.5 in.) with subsequent reduction to the desired hot
thickness at the finishing mill. Final reduction in thickness may be
rolling at the cold mill.
Thick cast slabs These
castings are usually from 150 to 350 mm (6 to 14 in.) in thickness.
of the thick cast slabs allows one to eliminate reduction at the
Thin cast slabs These
castings may be from 25 to 64 mm (1 to 2.5 in.) thick. Utilization of
slabs allows the elimination of both the slabbing mill and the roughing
Cast strip The
thickness of the cast strip can be as thin as 1.3 mm (0.05 in.). It
to eliminate entirely the hot rolling process.
Casting of Ingot
After the steel making
operation is completed, the
liquid steel is poured into a steel ladle. Additional alloying
deoxidizers may be added during the tapping of heat. The steel is then
or teemed into a series of molds of the designed dimensions.
The ingot molds are tall box
like containers made of
cast iron with the internal cavity that is usually tapered from the top
bottom of the mold. There are two principal types of molds
end down molds.
end up molds.
The inner wells of the molds
may be plain sided,
cambered, corrugated, or fluted. The last two shapes of the wall
cooling and therefore minimize surface cracking during solidification.
There are two methods of teeming the
The use of the bottom pouring
method is found
especially beneficial for high quality steels.
Types of Ingots
Molten steel solidifies first
at the regions close
to the mold walls, so the gases, chiefly oxygen, evolved from still
portions may be trapped to produce blowholes.
amount of gases released during solidification, the following types of
Fully killed ingot It
is fully deoxidized and therefore it evolves no gas, its top is
concave, and below the top there is a shrinkage cavity that is commonly
Semi killed ingot This
ingot is deoxidized less than fully killed. As a result, a small amount
carbon monoxide evolves producing a domed top. The blowhole formation
lower half of the ingot is prevented due to ferrostatic pressure.
3. Capped ingot It
is produced by pouring steel
into big end down bottle top molds in which the constructed top or
mouth of the
mold facilitates the capping operation. The rimming action is allowed
normally but is then terminated at the end by sealing the mold with a
cap. In capped ingot, the gas bubbles in upper half are swept away due
strong rimming action. An ingot of this type does not have the
interiors of its
blowholes exposed to oxidation during heating and soaking.
Rimmed ingot This type
of ingots is usually tapped without addition of deoxidizers to the
steel in the
furnace, and with only small additions to the molten steel in the
evolution of gas produces a boiling action that is commonly known as
Ingot No. 7 in Fig. 3 is a typical rimmed ingot in which gas evolution
strong that the formation of blowholes was confined to only lower part
There are two types of design for the
Non hot topped
The big end up; hot topped
killed steel ingots are
used in order to provide a complete freedom from pipe.
Methods of Continuous Casting of Thick Slabs
A number of methods have been
continuous casting of steel. Below are some of the methods that have
or stick casting In
this method, a straight mold, a vertical cooling chamber and a flame
are used. A tilting receiving mechanism transfers the continuously cast
onto horizontal run out table.
plus bending casting In
this method the casting direction is smoothly changed from vertical to
horizontal as soon as the cast steel emerges from vertical cooling
Semi horizontal or curved
mold casting This method
allows one to simplify design and to substantially reduce dimensions of
continuous casting machines.
representation of a typical horizontal casting machine is shown in Fig.
horizontal casting machines provide continuous movement of strand with
oscillation of either both tundish and mold or mold only. However, the
reliable operation was achieved by providing an intermittent strand
shown Figs. 6c 6e.
Continuous Casting of Thick Slabs
The most common method for
continuous casting of
thick slabs is vertical plus bending casting. Below is a brief
the casting process that utilizes this method.
In order to start the casting
process, the dummy bar
is inserted in the mold so that its top closes the bottom of the mold.
insertion of the dummy bar is made either from the top of the machine
through entire machine in the bottom of the mold. Liquid steel is then
at a controlled rate from ladle into the tundish and then the metal
through nozzles in the bottom of tundish and fills the mold.
There are two methods of
pouring the steel from
ladle to tundish and from tundish to mold
Open stream casting
Close stream or shrouded casting.
In an open stream casting the
liquid metal flows
through the air and therefore it picks up oxygen and some nitrogen from
air. It results in formation of undesired inclusion in the liquid
Shrouded casting allows to avoid this problem. In this method, steel is
protected from contact with the air either by refractory tubes or by
shrouding as shown in Fig. 9.
After the mold is filled,
withdrawal of the dummy
bar is initiated. The gradually solidifying metal would follow the
head. At certain position, the dummy bar head is mechanically
from solidified metal being cast and then the dummy bar is removed.
Liquid steel starts to
solidify in the water cooled
mold and the solidification of steel continues progressively along its
The rate of solidification is controlled by secondary cooling water
distance from the meniscus level in the mold to the point of complete
solidification is called metallurgical length. The point of complete
solidification is usually ahead of straightener. Electromagnetic
liquid steel during solidification may be implemented in order to
quality and increase casting rate.
The mold is oscillated in a
vertical direction in
order to prevent sticking of the solidified shell to the mold. Also,
such as oils or fluxes are used to reduce friction. Support rolls are
to guide the metal and to prevent bulging of the solidifying shell from
internal ferrostatic pressure. Cutting of the cast section is done
straightening either by shears or by torches.
1 shows main characteristics
of one of the continuous casting machines installed at the Indiana
for casting of thick slabs.
Slab Width Control
Desired slab width is usually
achieved by using one
of the following three methods.
Slab slitting This
method allows one to cast a small number of master slab sizes with the
product being slit longitudinally in a separate operation using either
gas torches or rolling machines.
Adjustable mold width This
method allows one to minimize the time required to replace a mold.
design for changing the mold widths is utilized. In the continuous
machines of earlier designs, the mold width adjustment can be made
previously cast slab is being removed from the machine. In the latest
the mold taper can be changed during the actual casting operation.
Divided molds According
to this method a divider installed in the mold permits the casting of
narrow slabs simultaneously in a single strand machine.
The Rolling of Rails, Wheels and Rings
By definition, the standard
rail is a section
symmetrical about its vertical axis, which consists of three areas
and base. The term tee is used to designate the general class of rail
which resemble an inverted letter T, and to distinguish those rails,
generally used in open track construction, from girder and girder guard
which are usually embedded in pavements. Crane rails differ from
in that they feature shorter, thicker webs, larger heads and thicker
withstand heavy, concentrated loads. For railroad applications rails
to sections up to 155 pounds per yard although most rails made today
pounds per yard or less and are of the standard length of 39 feet.
Normally, the rail section is
rectangular blooms by a series of 10 passes. Roll passes must be
designed and the rolling operation properly supervised in order to meet
stringent dimensional and quality specifications. After rolling, the
with their complete identification hot stamped or rolled into them, are
sawn so that they cool to within 3/8 inch of the desired cold length.
then cambered (with the head on the convex side) so that they will be
essentially straight at ambient temperature.
Many rails are controlled
cooled, being cooled
normally on hot beds until their temperature falls to within the range
1000ºF. The rails are then charged into large insulated metal
containers for a
minimum of 10 hours.
After cooling, rails are
subjected to various
finishing operations (straightening and drilling for joint bolts),
the rail head chamfered in a grinding operations and the ends of the
Many rails are now heat
treated by a full oil quench
and temper, which hardens the entire rail section, or subjected to an
heating operation, which provides a surface hardening of the wearing
the head. However, with the use of chromium and molybdenum as alloying
elements, rails are being conventionally produced with yield strength
200,000 psi and with a wear resistance equivalent to that of heat
This chapter reviews the
early types of rails and
their production, examines the evolution of rail mills, describes some
rail making facilities and discusses rail joints and their manufacture.
addition, the production of railroad wheels and the hot rolling of
Early Types of Rails and Their Production
The earliest type of metal
rail used in the eighteenth
century consisted of a wooden base with flat strips of cast metal about
inches wide, 1¼ inches thick and 5 feet long nailed to wooden
illustrated in Figure 1 A. The cast metal straps were replaced by
straps about 1820 but this simple design soon proved to be inadequate.
consequence, many improvements were soon developed, one of which is
Figure 1 B. This particular type of rail was rolled for the Amboy
the Pennsylvania Railroad as late as 1831.
John Birkenshaw of the
Bedligton Iron Works in
England produced in 1820 rails consisting of a head and a web but no
Rails such as these, laid on the ties in cast chairs, were used on the
Stocketon Darlington Railway in 1825. They were produced with rolls
as illustrated in Figure 1 D. A more advanced design, shown in Figure 1
used on the Boston and Lowell Railroad in 1830 as well as in England.
Although the preference in
England was for the
bullhead rail shown in Figure 1 F, in the U.S.A., the tee rail soon
popular. R. L. Stevens of the Camden and Amboy Railroad designed the
rail in 1830, which was rolled in Great Britain in 1831.
Another popular type of rail
was the U rail shown in
Figure 1 H, rolled by the Mount Savage Rolling Mill Company of
County, Maryland, in 1844 and said to be the first shaped rail produced
U.S.A. Roll passes used for a similar type of rail made in England
are shown in Figure 2.
Of the many different rails
produced during the last
two hundred years, one interesting type was the hollow iron or closed U
rolled at the Camkbria Iron Works. However, the demand for more metal
head of the rail for better wear resistance forced a final return in
1858 to 1868 to the tee shape with wide thin flanges.
With respect to the early
rolling of rails, it is
probable that existing mills designed to roll bars were utilized with
alterations as were necessary. Credit for rolling the first steel rail
is given to the Dowlais Plant in Wales while credit for the first steel
the U.S.A. goes to Captain Wards North Chicago Rolling Mills, where the
50 pound Bessemer steel rails were rolled experimentally in 1865 from
made of hammered ingots at Wyandotte, Michigan.
Rail production was initiated
on two high mills with
the bar pulled back over the top roll. To eliminate idle passes,
of unique design were tried. These included mills with oscillatory
provided rails of limited length, and the Double Duo mill featuring two
of work rolls in the same mill stand, such as was used at the Dowlais
Another mill, credited to Cabrols Colamineur, was developed about 1850.
consisted of two trains of rolls set almost side by side with each set
in opposite directions. After a bar had emerged from one pair of rolls,
transferred laterally by a hand buggy for entry into the other pair.
In 1866, a two high mill
utilizing, for the first
time, a reversing steam engine was developed by the Ransbottom Crewe
the London and Northwestern Railway. About the same period,
engines were used with gearing and clutches being employed to reverse
The Evolution for the Rail Mill
The successful development of
the three high mill in
1857 by John Fritz of the Cambria Iron Company of Johnstown,
to its general use in rail mills. In fact, by 1866, many of the two
used for rolling rails had been converted to three high units, commonly
The three high mill produced
rails from blooms or
piles of bars in 7 passes with the stand using hanging guides on the
Such guides were necessary for the back pass and their construction is
illustrated in the top drawing of Figure 3. However, in 1857, an
English 3 high
rail mill was designed to roll rails in 5 passes and used resting
throughout, as shown in the bottom drawing of Figure 3. To avoid the
hanging guides and alternate live and dead holes in the mill, it was
to turn the bar over between passes.
Because of the considerable
demand for rails, a
large number of mills were built in the U.S.A. primarily for rolling
products. Sixty nine mills were reported to have been rolling rails of
weights in 1874, one being as far west as Laramie, Wyoming. Of these
rolled Bessemer rails exclusively, seven rolled iron and Bessemer, two
steel headed rails only, two rolled steel headed and iron rails and one
produced cast steel and also rolled iron rails. Of the sixty nine
five made heavy (65 to 140 IL/yd) and thirty four made light rails (60
The layout of a rail mill
built in 1881 at South
Chicago is illustrated in Figure 4. Considered an excellent mill for
it consisted of a 40 inch three high blooming mill rolling 14½ inch
ingots and a 26 inch two high reversing finishing mill with a table
with beveled collars on the table rollers for turning the bars when
ingots were heated in four flat hearth furnaces, each holding 12
ingots were charged and discharged from the furnaces by a hydraulic
were delivered to the blooming train by a hand operated buggy. The
15 passes (eleven box and four roughing passes).
After blooming and roughing,
the workpiece was
conveyed on driven spools to the finishing rolls 120 feet ahead of the
the lifting table. Sixty feet ahead of the finishing mill was a shear
workpiece was cropped after one pass in the finishing mill. After
piece was returned to the finishing mill where the rolling was
a total of two roughing and five finishing passes.
The finished rail was then
conveyed to a single hot
saw equipped with movable gages. After sawing, the rail passed through
cambering machine and then to the cooling beds, with the straightening
rails being accomplished by gag presses.
In 1902, the mill was
completely rebuilt on a more
elaborate basis as shown in Figure 5. In 1927, the three high blooming
replaced with a two high reversing mill. The finishing mill, as it was
reconstructed, consisted for four three high stands. The roughing and
stands were driven by one engine and the second roughing and dummy were
by another. The blooming mill produced a bloom approximately 8 inches
and the finishing mill converted the bloom to a rail in 9 passes direct
the ingot (three in the roughing, one in the second roughing, one in
the dummy stand
and four in the finishing stand). Using the three high blooming mill
pass arrangement, a record tonnage of 1730 gross tons of 90 1b rails
in a 12 hour turn with approximately one hour delay.
Prior to 1865, the stock used
for rolling the larger
rails in the U.S.A. consisted of wrought iron piles or hammered or
blooms of puddled iron. In rolling tee rails from piles, considerable
difficulty was experienced in the flange passes because of
welding between the layers of the piles. As mentioned in the preceding
a few small Bessemer steel ingots were experimentally rolled into light
at the works of the North Chicago Rolling Mill Company in 1865. Two
later, the first Bessemer steel rails made to order for a railroad were
produced on the 21 inch three high mill of the Cambria Iron Company of
Johnstown, Pennsylvania. Although iron rails were not completely
until much later, steel rails were in great demand and several new
built to roll them. Yet, as the demand for rails subsequently
of the rail mills went out of existence or were converted to roll other
Modern Rail Mills
By the mid 1900s, only eleven
mills on the North
American continent were rolling large tee rails and, of these, only
classified strictly as rail mills. Some of these had been built much
and had been modified in the intervening years. Only three mills in the
rolled rails directly from the ingot without any reheating operation.
In the 1950s the largest rail
mill in the U.S.A. was
that of the U.S. Steel Corporation in Gary, Indiana, the layout and
design for which are shown in Figure 6. This mill began operation in
1909 and rolled more than 880,000 tons of rails and other products
This mill includes for 40 inch two high stands in tandem (one 2000 hp,
6600 v a c motor driving stands 1 and 2 through gear drives and a
motor driving stands 3 and 4) in which 24 inch square fluted ingots of
ranging from 74½ inches to 89 inches are given one pass per stand and
turned after each pass. The first four blooming passes are of the
diamond square and box pass design. The bloom then enters a three high
blooming mill stand with five box passes, the final pass being slightly
tapered. Following this stand is the 10 inch by 10 inch electrically
bloom shear and the cross country arrangement of seven stands in two
three stands and one separate stand. These seven 28 inch stands are as
a three high rougher (with three passes) equipped with vertical lifting
a two high former stand, a dummy stand, a first edger stand, a second
stand, a leader stand (containing a head wheel when rolling rails) and
finishing stand (using a base wheel for rail rolling). The rougher,
edger and leader stands are in a train powered by a 6000 hp, 83.3 rpm,
6600 v a
c motor through pinion gears. The former stand is a 28 inch single, two
powered by one 2000 hp, 58 rpm motor. The dummy, first edger and
stands constitute the finishing train which is driven by a 6000 hp, 88
6600 v a c motor. Transfer beds are located after the dummy stand for
conveyance of the workpieces to the second mill line and after the
stand for their transfer to the third mill line.
Data pertaining to the
various passes used in
rolling rail section 11525 are presented in Table 1 and sketches
the passes of the leader and finisher stands are shown in Figure 7.
At the end of 1969, only five
mills in the U.S.A.
were producing railroad rails. These mills were far from standardized
layout. Some had a large number of stands others only a few. Some used
stands throughout while others used three high units.
Rails are formed by two
general methods know as the
tongue and groove (or flat or slab and edging) and the diagonal (or
methods. Some rail mills combine these two methods. The tongue and
method is illustrated by a roughing stand shown in Figure 8 and it is
noted that the axis of symmetry of the rail coincides with the pitch
is parallel to the train line of the rolls. The diagonal or angular
rolling is exemplified by the roughing stand shown in Figure 9. It
the slabbing method in that the shaping of the rail is begun in the
in the roughers and, instead of first compressing the bloom to a
and then forming the section partly through compression and partly by
spreading, the process is one of compression from beginning to end.
One of the more recently
installed large section
mills that is used for the rolling of heavy rails has been described by
and Gocho. A layout of this mill is shown in Figure 10. The facility
uses 13 ton
ingots (that have been bloomed, hot scarfed, sheared, cooled, spot
reheated) to roll rails as long as 50 meters. The pass sequence
the rolling of rails is shown in Figure 11 and it is seen that four
used, these being a breakdown mill, two roughers and a finisher.
To produce rails of the
desired quality, the mill
stands feature high moduli (22 ton/mm), mill motors of adequate power
excellent control characteristics, a high pressure descaling system and
lubrication (consumption about 2 litres/ton). Grain rolls are used in
second rougher and finishing stands to minimize spalling, these being
manufactured to provide a barrel hardness of 50±3 shore, a barrel
strength of 7
to 8 kg/mm2 and a wobbler strength of 20 kg/mm2.
Following the rolling
operation, ordinary rails are
identified on the web by the use of a marking wheel (carrying type on
periphery), end finished and shipped. Rails to be head hardened are
by crane on to the quenching furnace approach table without
as prebending. Charging into the furnace is continuous at 360 mm/min,
aid of pinch rolls. The 2390 mm long quenching furnace has a
1150ºC which heats the rails to about 820ºC. The rails are then water
and tempered in a 3460º mm long furnace held at 820ºC which reheats the
to about 570ºC.
The sizes of the sections
rolled on the above mill
and the corresponding production rates are presented in Table 2.
Another Japanese rail mill,
built at the Yawata
Works of Nippon Steel Corporation was commissioned in 1970. It utilizes
reversing break down and universal mill stands.
The U.S.S.R. claims to be the
world leader in rail
production rolling some 3.2 million tonnes in 1975. Open train
built in post World War II years roll heavy rails (up to 75 kg/m) from
blooms at speeds up to 2.5 m/sec.
The latest rail mill planned
for the U.S.A. is that
to be built by U.S. Steel Corporation at Chicago. This facility will be
a continuous caster.
Mill automation for the rolling of flat products
Automation of flying shear operation in a continuous hot
Upon leaving the last stand,
the strip speed is
usually 2 to 5 per cent higher than the peripheral speed of the rolls
forward slip which is a function of many variable values (temperature,
coefficient of friction, strip thickness, etc.) that change during the
of even a single strip.
To obtain higher accuracy in
cutting the strip into
measured lengths, the speed of the flying shear must coincide with the
travelling speed of the strip on the table and not with the peripheral
the rolls. For this purpose, a special measuring roller is held against
strip from which it is rotated without slipping. A tachogenerator TGR
mounted on the roller shaft (Fig. 1.). Before rolling begins, the speed
shear drums conforms to the stand roll speed by mean of tachogenerator
whose voltage is compared to the voltage of the shear generator G. As
runs out of the rolls, the excitation of this generator is switched
over to the
tachogenerator TGR of the measuring roller. After this, the speed of
will exactly coincide with that of strip travel (by comparison of the
of TGR and TGS which excite the rotary amplifier RA in the circuit of
exciter GE of generator G).
Still higher accuracy may be
achieved with an
electronic counting circuit (Fig. 2). Here, the speed of the driven
rollers MR corresponds to that of the driven feed rolls FR. A
relay PR is mounted before the feed rolls at a definite distance from
shear. This relay switches on shear SH upon the approach of a strip.
speed and the distance from the photoelectric relay to the shear
length of strip cut. The speed of the measuring rollers equals the
the pulse generator PG on the roller shaft (a wheel with teeth and a
transmit pulses to the electronic counting circuit ECC. Rotation of the
pulse generator through one division (one tooth) corresponds to a strip
50 mm. Provision is made for obtaining 200 pulses when strip is cut
maximum lengths of 10 m. The pulses are counted by the counting circuit
definite number of pulses, the counting circuit sends a command to
shear. This number of pulses after which a cut is made is set up
Automation of coiler operation for hot strip
When the strip leaves the
last stand of a continuous
strip mill it is traveling at a speed from 6 to 10 m per sec along
driven pinch rolls 2 and guide rolls 3 direct the strip to coiler drum
strip is held against the drum by wrapping rollers 5. After 3 or 4
turns of the
strip on the drum, the wrapping rollers are withdrawn. The tightness of
first turns is due to the fact that the peripheral speed of the drum is
slightly higher than that of the pinch rolls. Speeds are made to
the following manner.
The reference winding RW is
connected to the
armature of tachogenerator TG on the last stand of the mill while the
winding VW is connected to the armature of generator GPR which supplies
pinch roll drive motor MPR. The characteristics of the drive windings
adjusted so that upon idle rotation of the coiler drum its speed
of the pinch rolls. Therefore, the strip is tensioned when it begins to
the coiler to obtain several tight turns of the strip on the drum. This
the pinch roll motor MPR. Strip tension is regulated by the current
and also in the circuit of the coiling drums motor MCD.
Automation of strip measuring gauges for hot rolling
Measuring the strip width. It
is desirable that the
slab width correspond to the given strip width at a definite thickness.
reduces the amount of scrap trimmed from the side edges of the strip.
strip obtained from the slab is wider than required for subsequent
the finished sheet, it will be necessary to roll a narrower slab in the
A photoelectric width gauge
is mounted beyond the
finishing stand of the mill, above the roll table, to continuously
The edges of the hot strip
are projected through
optical lenses to the photoelectric heads PH. Upon changes in strip
intensity of the light illuminating the photoelectric heads is changed
correspondingly. As a result, the indicating or registering instrument
control desk will show the variation (in mm) of strip width.
Measuring strip thickness.
One system of continuous
measurement of the thickness of moving hot rolled strip is based on the
principle of X ray absorption by the strip.
The X ray tube XT emits two
perpendicular beams, one
upwards through wedge WI on the strip and the other, to the right on
wedge W2. The tube is supplied with alternating current and, therefore,
beams pulsate, Head H2 is arranged behind wedge W2 and has a
screen. The head contains a gas discharge tube which also pulsates and
as a standard. If the brightness of the fluorescent screen upon
the right hand beam from the X ray tube is equal to the standard
the gas discharge tube, then the luminous flux incident to a
element in head H2 does not have variable component and the potential
amplifier EA2 equals zero. If there is a difference in luminescence,
voltage of amplifier EA2 acts upon the sensitive electronic regulating
RD which reduces the voltage on the high voltage transformer TIIV as
required to equalize the brightness of the screen and of the tube.
tube serves as a standard, the regulating device RD maintains constant
capacity of the X ray tube XT. Head HI is similar to H2 if the strip
equals the thickness of wedge W1, the potential at the electronic
equals zero. If potential appears at EAI, the reversible motor RM is
on. This motor will advance wedge W1 and thus equalize the brightness
luminescence on the screen and tube in head HI. The total thickness of
strip and wedge WI will be equal to this thickness of wedge W2.
Thus, the strip thickness
equals the difference in
thicknesses of W2 and W1. The position of wedge W1 is transmitted by
ST to synchrorepeater, SR which has a scale graduated into units
deviation of the strip thickness from the specified value. The same
transmission is provided in the actuating mechanism of wedge W2 on the
STI, the operator sets the graduation beforehand corresponding to the
thickness of the strip. If the hand on the other scale OI points to
the strip thickness equals the specified value.
Deviation of hand OI from its
corresponds to deviation of strip thickness from the present value. A
device can be connected to the synchrorepeater. SR for registering
in strip thickness during the rolling process. The readings of the
are stabilized by supplying the whole installation from a constant
regulator CVR. The X ray tube is mounted above the roll table in a
rigid water cooled
Automation of continuous pickle line operation
Strip is pickled in a
continuous line at a speed of
2 3 m per sec. To provide continuous operation, the tail end of each
welded to the leading end to the next strip. This operation is done in
where the ends of the strip are set by hand under the clamps of the
obtain an even weld. The strips are welded without stopping the
movement of the
strip through the baths. Looping pits are provided in the line to
continuous strip travel. Several loops of the strip with a total length
to 200 m are made available beforehand in the pit. During welding of
the line is supplied from the slack in the pit. After making the weld,
entry speed of the strip into the looping pit increases and the
In new mills, the size of the
loops in looping pits
2 is checked automatically by means of photocells and light sources.
number of loops of strip is reduced in the pit, the photocells are
after another by the lamps. Pulses transmitted by the photocells reduce
strip speed through pickling tanks I and increase the strip uncoiling
The strip speed through the tanks is
controlled by a dancer
roll the lever of this roll is linked to the slide of a rheostat which
the exciting current of motor M1 powering the pinch rolls PR.
Automation of strip thickness gauges for cold reduction
The strip thickness is
measured in cold reduction in
a continuous (or reversing) mill with the same type of X ray gauge used
rolling (this gauge was first applied to cold reduction and only
Essential disadvantages of X
ray gauges are their
high cost and the necessity for having a complete outfit to generate
Radiation thickness measuring
gauges that have come
into use in the last years, since they are more economical, employ
(for thick strip) or beta rays (for thin strip), i.e., they employ
isotopes that emit these rays.
Beta ray gauges are
substantially cheaper than X ray
types while their accuracy is sufficient for this purpose (1 percent
up to 0.5 mm thick).
The principle of the
radiation gauges is similar to
that of the X ray gauge. An artificial radioactive emitter E of beta
located under the strip S. Part of the rays passing through the strip
ionizing chamber IC, arranged above the strip and produce an ionizing
This current is very small, however, and cannot be directly measured by
instrument. Therefore, a high ohmic measuring resistance MR is
the current circuit. The voltage drop over this resistance is
the chamber current and, therefore, to the strip thickness. This
is not directly measured but is compared to a preset value, i.e., the
determined value is the difference in voltages appearing when the strip
thickness deviates from that specified. The recording instrument RI is
connected in parallel with the indicating device ID, as well as the
device SD. The latter is operated when the strip thickness variation
the permissible value and it signals the operator. If the isotope
is employed, steel strip up to 0.15 mm thick can be measured while
is suitable for strip up to 0.9 mm thick. The half – life of this
isotope is such that it can be used for up to 40 years and, therefore,
practically require replacement.
In passing through the strip,
the beam of beta rays
is weakened not only by the metal but by oil and water as well.
rolling it is necessary to see that the strip surfaces are clean at the
of measurement (by wiping, etc.).
General Steelmaking Processes
Welding Material for Super Low Temperature Steels
U.S. Patent 3,966,424 June
29, 1976 assigned to Kobe
Steel Ltd., Japan describe a nickel base alloy welding material which
excellent strength and impact value characteristics to the weld zone in
of super low temperature steels. These and other objects as will
become more readily apparent, have been attained by this welding
comprising not more than 0.2% carbon, 5 to 12% manganese, not more than
chromium, 4 to 8% niobium, not more than 22% iron and not more than
silicon, the balance being substantially nickel. The welding material
by integrally combining a metal forming material having the above
with a flux of the lime or lime titania type.
The welding material can be
used with any known
welding method, such as manual welding, TIG welding or submerged arc
The term Welding material formed by integrally combining a metal
material with a flux includes a coated electrode for arc welding,
composed of a
core wire covered with a flux. A composite wire composed of a metal
packed with alloy powder optionally together with a flux or the like.
The flux comprises, on the
weight basis, 10 to 50%
calcium carbonate, 16 to 50% fluorspar, 2 to 20% magnesia clinker and
up to 10%
rutile. An especially preferable flux is one containing magnesia
having a ratio of fluorspar to calcium carbonate of 1 to 1.5. Not more
of ingredients of such flux may be substituted by a deoxidizing agent,
constituting element or the like.
The process of preparing a
welding material is described
briefly by reference to a welding rod. The components of the lime or
coating material and the above alloy components are blended together
glass (an aqueous solution of a mixture of sodium silicate and
silicate)—10 to 2% based on the total weight of the welding rod. The
is dried at 200º to 250ºC. Thus, the process is not different from the
conventional process of preparing welding rods.
composition (1)—The chemical composition of the core wire (%) is
C, 0.05 Mn, 10.2 Si, 0.42 P,
0.005 S, 0.006 Cr, 18.5
Nb, 6.0 Fe, 11.5 and Ni, the balance.
The blending ratios of the
ingredients of the
coating material are calcium carbonate, 40% fluorspar, 53% rutile, 5%
ferrosilicon, 2% (silicon content equals 50%). The binder is an aqueous
solution of the mixture of sodium silicate and potassium silicate of SG
The covering ratio of the coating material is 25% based on the total
the welding rod.
Welding Material Composition
composition of the core wire (%) is
C, 0.06 Mn, 1.2 Si, 0.55 P,
0.4 S, 0.006 Cr, 14.0
Nb, 1.5 Fe, 7.3 and Ni, the balance.
The blending ratios of the
ingredients of the
coating material are calcium carbonate, 28% fluorspar, 31% rutile, 2%
clinker, 4% metallic mangahjese, 15% and ferroniobium, 20% (niobium
equals 70%). The binder is an aqueous solution of the mixture of sodium
silicate and potassium silicate of SG 1.40. The covering ratio of the
material is 40% based on the total weight of the welding rod.
Welding Material Composition
(3)—The filler rod
composition (%) is
C, 0,10 Mn, 7.0 Si, 0.7 P, 0.05 S,
0.04 Cr, 14.0 Nb, 6.0 Fe,
10 and Ni, the balance.
The above three welding
materials [welding materials
of the compositions (1) and (2) are for arc welding using a coated
and the welding material of the filler rod composition (3) is for MIG
and a commercially available nickel base alloy welding rod were
tensile test, impact test and chemical analysis with respect to the as
deposited metal. Further the tensile test and impact test were
conducted on the
weld metal in the weld zone of 9% nickel steel.
The welding was conducted and
tensile test specimens
and impact test specimens were taken. The tensile test was conducted at
temperature and the impact test at –196ºC. As is apparent from the test
on welding rods shown in the following table, the deposited metal
tensile strength and ductility comparable to those of 9% nickel steel
together with a sufficient low temperature toughness.
9% Ni steel was subjected to
groove welding, and
mechanical properties of the weld metal diluted with the base metal
examined. Two sheets of 20 mm (thickness) × 250 mm (length) × 200 mm
were welded in a butt joint to form a test specimen. The groove
as follows a groove angle of 60º, a root face of 0.5 mm, and a root gap
mm. The surface side was metal welded, and then the back chipping was
followed by one layer welding on the back.
Tensile test specimens were
taken in a direction
parallel to the welding direction. Impact test specimens were taken.
tensile test was conducted at room temperature and the impact test was
at –196ºC. As is apparent from the test results shown in the table
welding rods the weld metal exhibited a tensile strength comparable to
the base metal and a sufficient low temperature toughness.
Refining Steel by Blowing Oxygen Beneath the Surface
U.S. Patent 3.960,547 June 1,
1976 assigned to
Youngstown Sheet and Tube Company describe a process for melting iron
material adding the melt to another molten composition to modify the
content of the composition and further refining the resultant mix with
The method includes oxy fuel
melting a charge of
solid material, bearing iron, which melting produces a relatively low
composition. The low carbon composition is added to another molten
of relatively higher carbon content, such as that produced by
blast furnace practice, to provide a molten mix. Unmolten iron bearing
is added to the molten mix in a refining vessel having means for
essentially pure oxygen beneath the surface of the melt of the refining
Suitably, the high carbon
melt may be blast furnace
iron at 2400º to 2500ºF comprising, by weight 0.5 to 2.0% silicon, at
carbon, 0.40 to 1.5% manganese, and the balance being essentially iron.
Preferably, the high carbon molten composition comprises 1% silicon, 4%
0.5 to 1.0% manganese, and the balance essentially iron. Also
composite molten mix is provided which is comprised of 40 to 75% low
composition and 60 to 25% of the high carbon composition. The mix will
result in a composition being at a temperature of 2600ºF and comprising
0.6% silicon, 1.8 to 2.0% carbon, 0.3 to 0.4% manganese, and the
In a typical and preferred
molten mix metal is provided to the vessel, where refining is to take
without the addition of more heat, to constitute 85 to 95% of the total
anticipated work charge. The remaining 5 to 15% of the charge may be
advantageously comprised of cold unmolten scarp, and/or iron ore
and/or other iron bearing materials in solid form. After the charge is
completed, refining is conducted by introducing substantially pure
beneath the surface and blowing through the molten charge. Of course,
additional heat is provided, such as by burners in the refining vessel,
the amount of unmolten scrap may be increased.
It will be noted that the
total hot metal
(relatively high carbon content composition) input to the refining
vessel is 22
to 54%, i.e., 25 to 60% total charge to mixing vessel × 90% total
refining vessel. In contrast, conventional open hearth and BOF
utilize 55 to 60% and 70% hot metal, respectively. It is also
higher yields of usable steel are attainable through the use of the
medium below the surface of the molten bath, as opposed to blowing unto
surface. One of the contributing factors is better utilization of the
medium attained by virtue of the more intimate contact with the bath.
factor is that there is less iron oxide emission loss than that
with the use of oxygen lances and the resultant fuming.
Cold Reduced Aluminum Stabilized Steel having High Drawability
U.S. Patent 3.959,020 May 25,
1976 assigned to
Nippon Kokan KK, Japan described a steel which is suitable for severe
forming. Al stabilized steel is subjected, after a first cold working
decarburizing annealing as an intermediate heat treatment. The steel is
successively passed through a second cold reducing step and then a
softening annealing step. The resulting steel is capable of
press forming operation.
Al stabilized steel which may
be used consists of
0.03 to 0.15% C, 0.02 to 0.07% SolAl, and other elements, e.g., Fe, Mn,
N, present in ordinary quantities as in other Al stabilized steels.
continuous hot rolling is used, the finishing temperature should be
the Ar3 point, and the coiling should be carried out at less than
that precipitation of AlN does not occur. In this case, thickness of
3.2 mm will be desired as the finishing thickness of a hot rolled
because the next two stages of cold reducing may be more readily
depending upon the thickness.
The first cold reducing is
carried out at a
reduction rate of more than 30% and successively the steel is subjected
intermediate decarburizing annealing wherein the C content in the steel
reduced to less than 0.01%, preferably to 0.002%. The reduction rate of
second cold reducing stage is more than 30%, and preferably more than
final annealing process is carried out to produce a steel having an r
(Lankford value) or 2.2 to 2.3. Such a Lankford value shows that the
capable of sustaining any severe press forming.
Sulfide Modification of Steel
U.S. Patent 3,955,967 May 11,
1976 assigned to The
Algoma Steel Corporation, Limited, Canada describes sulfide
molten steel in the ladle suitably during transportation of the molten
from the steel making furnace for casting. This treatment is effected
addition of agents, which usually have a high affinity for oxygen,
rare earth metal silicides.
The process comprises
enclosing the addition agent
in a metal container, and fixedly suspending the container in the ladle
submerge at least that portion of the container containing the addition
so as to melt the container and release the addition agent beneath the
of the molten steel in the ladle. The container has walls of selected
to provide the required time delay in releasing the addition agent into
molten steel to allow for the desired amount of deoxidation of the
have taken place. While rare earth metal silicides are particularly
to completely deoxidize molten steel for sulfide modification, other
particularly boron compounds, calcium metal, and alloys, e.g., calcium
and deoxidizers may be used.
The process also provides a
device for use in the
treatment of molten steel in a ladle during transportation of the
from a steelmaking furnace for casting by the addition of agents which
normally strong deoxidizing agents. The device comprises a yoke adapted
extend across the open top of the ladle and at least one hollow tube
one end for containing the addition agent.
The tube is fixedly mounted
in the yoke such that
when the yoke is in position on the ladle each tube is suspended
the ladle with at least that portion of the tube adjacent the closed
containing the addition agent submerged in molten steel contained in
Each tube is of preselected wall thickness to provide a selected time
releasing the addition agents into the molten steel in the ladle after
contact of each tube with molten metal to allow for the desired amount
deoxidation to take place.
It is a critical feature that
containing the additive be fixedly suspended in the ladle with that
containing the additive disposed beneath the surface of the steel bath.
ensures that the additive is released beneath the surface of the bath
on the surface of the bath and further that the distribution pattern of
additive in the molten steel can be selected to best advantage.
A heat was produced in a
basic oxygen furnace of
nominal 100 ton capacity. It was desired to produce plate to meet a
yield strength of 65,000 psi and notch toughness of minimum Charpy
energy (heat average based on 2/3 size transverse specimen at 0ºF) of
30 ft lb.
To attain these minimum requirements it is necessary to desulfurize the
to a level of 0.012% sulfur and to modify the sulfide inclusion
treatment with rare earth elements. Prior to tapping the furnace into
ladle, a yoke was assembled suspending two 10 foot long, 11 inch
pipes each having a wall thickness of one half inch. Before assembling,
pipe had been filled with 65 lb of rare earth silicide which contained
contained rare earth elements. The space in the pipes above the top
the rare earth silicide was filled with lime. The wall thickness of the
had been so designed that the steel pipes at their lower extremity will
whereby the rare earth silicides are released well below the level of
steel in the ladle during the pour from the furnace. Furthermore, the
regions of the pipes do not melt until a discrete time interval after
completion of the tap from the furnace and after the artificial slag
At the time of tapping the furnace
into the ladle, the
following ladle additions were made 340 lb aluminum, 3,800 lb
330 lb ferrocolumbium, and 250 lb lime. In addition, 700 lb of fly ash
added to the ladle at the end of the tap to provide the artificial slag
The temperature of the steel after all additions were made was 2855ºF.
teeming the melt into ingot molds, the steel in the ladle was stirred
argon gas injector for 7 minutes to achieve a uniform distribution of
additions made and to equalize the temperature for teeming at 2840ºF.
From the analysis and
properties attained it would
be obvious that good sulfide modification was effected and full value
from the rare earth silicide addition. In an alternative process, the
tipped into the ladle from the steel making furnace together with the
deoxidizing agent and the device is subsequently lowered into the ladle
to submerge the tubes. The melting of the walls of the tubes releases
earth metal silicides into the steel beneath the surface of the slag
for a distribution of the rare earth metal silicides in the steel. Good
distribution of the rare earth metal silicides and other additives
strong affinity for oxygen is assisted by argon stirring the ladle
prior to teeming the steel into the ingot molds.
Steel Sheets having Excellent Enamelability
U.S. Patent 3,950,191 April
13, 1976 assigned to
Kawasaki Steel Corporation, Japan describe a method for producing cold
steel sheets having an excellent enamelability. The process comprises
a molten steel containing not more than 0.020% of carbon, not more than
of silicon, not more than 0.50% of manganese, not more than 0.01% of
not more than 0.050% of oxygen, and having a nitrogen content of less
0.01%, boron with a range of 0.005 to 0.020% in such amounts that B(%)
is more than 1 × 10–5, hot rolling the resulting steel, cold rolling,
recrystallization annealing under a decarburization atmosphere.
Example The steels having the
components as shown in
Table 1 were melted and slabbed and then hot rolled into a sheet having
thickness of 2.8 mm at a finishing temperature of 860ºC and a coiling
temperature of 550ºC. The hot rolled sheet was pickled and then cold
a tandem roll into a sheet having a thickness of 0.8 mm, after which
sheet was annealed in a bell type annealing furnace at a uniform
760ºC or subjected to decarburization annealing in an open annealing
a uniform temperature of 700ºC and then to a tempering rolling of 1%.
resulting steel sheets are subjected to the enameling treatment to
results as shown in Table 2.
As the conditions for the
enameling treatment, such
pretreatment steps that fish scales and the other defects are liable to
caused were selected and the immersion in Ni bath which is practically
inevitable was omitted and the frit for the high temperature firing was
In Table 2, the adherence PEI
(%) was determined by
means of Porcelain Enamel Institute adherence tester as follows. The
subjected to a compression deformation and the glaze was forcedly
measure electrically the exposed area of the base metal and calculate
applied with the glaze on the deformed portion and the total area of
deformed portion to read as PEI (%) no exfoliation is expressed by 100%
entirely exfoliated area is expressed by 0%. The method for measuring
index is described in ASTM C 313. From the results of this test, it can
that even if the steel is enameled under the conditions which are apt
the defects, very stable results can be obtained.
Liquid Sintering with Titanium Alloys
Sintering ferrous materials
have found wide
application as structural components in machines. The failure to use
materials as main structural components stems from the porous character
components, which are inferior in mechanical properties to casting, or
materials having the same composition. To promote the use of sintered
in such components, various efforts have been made to increase the
the sintered material up to a value close to the theoretical density.
Accordingly, U.S. Patent
3.950,165 April 13, 1976
assigned to Mitsubishi Jukogyo KK, Japan describe a method of sintering
materials which comprises mixing an iron powder with an alloy of iron
and forming a liquid phase during the sintering. The alloy is prepared
mixing selected amounts of iron and titanium powders to form an iron
alloy powder consisting of 14 to 46% by weight of tatanium and the
iron, and preferably 14 to 30% by weight of titanium. The sintering
carried out as a temperature at which the powdered mixture is always in
liquid phase during sintering. Under these conditions oxidation of
suppressed during melting and the alloy is not too soft nor too
pulverize and use for manufacturing machine components such as piston
which have surprisingly good properties.
Liquid Solid Alloys for Casting
Patent 3.948,650 Apr. 6,
1976 assigned to Massachusetts Institute of Technology describe a metal
composition characterized by degenerate dendritic or nodular primary
solid particles suspended in a secondary phase having a lower melting
than the primary particles and which secondary phase can be solid or
This composition may be prepared by raising the temperature of a metal
a value at which the alloy is largely or completely in the molten state.
melt then is subjected to
vigorous agitation and the temperature is reduced to increase the
the mixture in solid degenerate dendrite or nodular form up to 65%, but
up to 50%, while continuing the agitation. At this juncture the
the liquid solid composition can be stored and later it can be brought
the liquid solid mixture state and then recast.
The compositions can be
formed form any metal alloy
system or pure metal regardless of its chemical composition. Even
metals and eutectics melt at a single temperature, they can be employed
the composition since they can exist in liquid solid equilibrium at the
point by controlling the net heat input or output to the melt so that,
melting point, the pure metal of eutectic contains sufficient heat to
a portion of the metal or eutectic liquid. This occurs since complete
of heat of fusion in a slurry employed in the casting process cannot be
obtained instantaneously due to the size of the casting normally used
and the desired
composition is obtained by equating the thermal energy supplied, for
vigorous agitation and that removed by a cooler surrounding environment.
Varnishing and Printing of Packaging Steels
The success of metal
packaging in tinplate or
chromium plated steel is due to a large extent to the varnishing and
printing operations which complete the corrosion protection already
the electrolytic coatings. For this reason, varnishing is always used
chromium plated sheet and is also employed in the majority of tinplate
applications. In the sheet by sheet varnishing process, most frequently
for packaging materials, one coat of varnish or ink is applied at a
followed by baking in a convectively heated horizontal oven. It is a
discontinuous operation, in which the sheets are unstacked at the start
line and restacked at the end, as many times as there are coats of
one or other of the two faces. Continuous coil varnishing processes
capable of high speed coating of either one or both faces.
General Aspects of Organic Coatings Used for Varnishing and
The organic coatings
(varnishes, pigmented coatings
or inks) are used for the internal protection and external decoration
packaging whenever justified by the technical or commercial
requirements of the
intended application. In fact, these coatings serve three purposes
They protect the metal against
chemical corrosion by the
contents of the packaging and against various external aggressions,
atmospheric corrosion, scratching, shock, forming, etc.
decorate the outside of the
They facilitate forming, for
example by acting as a
lubricant during drawing.
Varnishes are liquid
preparations which, when
applied as a thin film on a substrate, are transformed by evaporation
volatile constituents and reaction of their binder resins to a solid
film which adheres to the metal surface.
Types of Organic Coating
Varnishes are clear
transparent substances, which
may sometimes be colored. Apart from a few special cases, such as
finishing varnishes (blue, green, etc.), the color of varnishes is due
to their base resin. For example, the golden tint of epoxy phenolic
is due to the color of the phenolic resin. When varnishes are colored
titanium oxide, they are called white pigmented lacquers. This is the
frequently encountered in food packaging, but other colors, such as
black, etc., are often used for decorative purposes on the outside. The
coatings are classified according to their applications
inks are used only for printing the outside of the packages.
coats are applied directly to the metal (usually tinplate) and serve as
layer for the inks, films or varnish topcoats. They are used in small
quantities (3 6 g/m2).
coats or topcoats are applied in similar thicknesses (4 6 g/m2).
varnishes are specifically designed to resist mechanical forming
chemical attack. The thickness applied (5 8 g/m2) depends on the degree
more rarely, colored coatings are generally applied to the outside, but
occasionally used on the inside. Their thicknesses vary from 15 to 20
average, depending on the degree of protection desired on the inside or
opacity required on the outside.
Organic Coating Constituents
The formulation of varnishes
pigments, solvents and additives, such as surfactants, lubricants,
and filler materials.
The resins or binders
The binders are composed of a
non crystalline solid
(natural or synthetic resin), which, after drying and hardening, forms
essential component of the film. The resins belong to a limited number
chemical families (the phenolic, epoxy, vinyl, polyester, acrylic and
resins), but can be modified to a greater or lesser extent with other
depending on the properties required. These different families and
principal characteristic properties are described in Table 1.
The pigments are present in
the form of very fine
crushed solid particles, of the order of a micron in size, dispersed in
the binder, in which they are insoluble. They are usually inorganic
such as titanium and iron oxides or aluminum. The printing inks use
pigments, which may be either inorganic or organic, in order to cover a
wider range of colors.
The solvents are volatile
liquids, which transform
the binder to a solution sufficiently fluid to facilitate application.
the resin must be soluble, the solvents employed vary with the type of
the most common ones being alcohols, esters, ketones, aliphatic and
hydrocarbons and water. In fact, mixtures of two or more solvents are
employed, since more than one resin must generally be dissolved. After
application, the solvents are allowed to evaporate from the varnish
leading to uniform spreading and better wetting of the metal, and
formation of a porous coating. The solvents also serve to adjust the
of the varnishes or lacquers, in order to compensate for evaporation
recycling of the unused product.
Although the additives
represent minor constituents
of varnishes and films, they are by no means of secondary importance.
particular, the surfactants lower the surface tension of the paint,
wetting and facilitating spreading.
The lubricants are added to
facilitate handling and
forming of the varnished sheets, particularly drawing operations.
The catalysts enhance
chemical reactions between the
different constituents of the varnish and accelerate cross linking.
usually acids, amines or metal salts.
Application and curing of organic Coatings
Application with Roller Varnishing Machines
The liquid mixture mentioned
above, consisting of
macro molecules and solvents, is generally applied on a flat surface.
be done on separate sheets or coiled strip with the aid of a roller
machine. The latter has a number of rollers, which transfer an
quantity of varnish from a tray and apply it in a uniform controlled
onto the surface of the metal as it passes through the machine. The
pumped from a container E into the tray in which the feed roller A
taking up a small amount of varnish, which is distributed over the
roller B. The varnish is then passed from the transfer roller to the
application roller C which coats the surface of the metal sheet. The
between the different rollers and their relative velocities can be
deposit a precise quantity of varnish on the metal. The application
made of steel and is coated either with hardened gelatine or
elastomer. The varnish can either be applied to the whole surface or
edges can be left, as is necessary, for example for welded cans. The
application roller then has an appropriate profile so as to leave part
In coil coating operations,
both faces can be coated
simultaneously, by means of a second application roller, which replaces
counter roller D, additional rollers being added to drive the strip. In
sheet varnishing, the tangential speed of the application roll is
equal to the sheet displacement velocity, whereas in coil coating, the
application rollers can move in the opposite direction to the strip,
improved coating quality.
After application, the
organic coatings are baked to
obtain a dry film. The solvents are evaporated and the constituents
produce cross linking of the polymer chains, forming a solid film
attached to the metal. Baking or curing is generally performed in a
tunnel oven. Conveyor ovens consist of a series of individual metal
wickets mounted on a chain which is drawn slowly through the heating
The chain speed being synchronized with the varnishing machine, so that
wickets receives a sheet after passing through the machine. The
generally gas fired, with either direct or indirect heating. The baking
(temperature and time) depends on the type of varnish, and
usually given by the manufacturers. Higher temperatures allow the use
shorter baking times, so that various combinations are possible.
varnishes can be cured in extremely short times, of the order of a few
Another curing technique is
based on induction
heating, the heat being generated directly within the metal substrate.
treatments can be extremely rapid (a few seconds) and are well suited
varnishing speeds (>100 m/mn), such as those prevailing in coil
such cases, flash curing is essential to maintain reasonable oven
Other Application Techniques
Varnishes can also be applied
with spray guns, for
applications such as
Local side stripe lacquering of
weld zones to protect the
regions left uncoated before the welding operation
For the internal protection of DWI
(drawn and wall ironed)
beverage cans and certain aerosol containers, where varnishing cannot
performed before forming
For repair varnishing of the inside
of DRD (draw and
redraw) cans after drawing.
include electrostatic powder deposition, which is used for side stripe
lacquering and is being introduced in other areas, due to process
Several heating methods are employed for baking side stripe lacquers,
hot air, induction, direct flame impingement, and infrared radiation.
times vary from 2 to 30 seconds.
The protective action of the
varnish is related to
three essential factors, namely adherence to the metal substrate,
inertia and the absence of porosity. The film/substrate interface is
loaded during forming of the varnished tinplate to can components, and
varnish must be able to follow the metal without delamination or
adhesion is obtained when surface bonding of the two mating components
complete, but there are sometimes incompatibilities between the two
Chemical inertia is generally assured if the varnish has been
since complete cross linking eliminates the active groups capable of
with ions from the can contents. The presence of porosity can
impair the protective quality of the film, and must be carefully
Increasing film thickness decreases the tendency for porosity.
Phase Transformation in Steel
phase diagram is a graphical
representation of the temperature, pressure and composition limits of
fields in an alloy system as they exist under conditions of complete
equilibrium. It is also known as equilibrium or constitutional diagram.
a phase diagram, temperature
is plotted vertically and composition is plotted horizontally. Any
point on the
diagram represents a definite composition of a constituent and its
each value being found by projecting to the proper reference axes. For
illustration, let us consider the changes that take place during
cooling of an
alloy containing 50 percent element A and 50 percent element B. The
remains homogeneous liquid solution until temperature drops to a value
by the intersection of the liquidus line at c0. The crystals which form
50 liquid consist of a solid solution, the composition of which is
found on the
solidus line at c1, 80 percent element B and 20 percent element A.
As the mass cools, the
composition of the growing
crystals changes along the solidus line from c1 to c5, while the
liquid alloy varies in composition along the liquidus line from c0 to
Figure 2 illustrates the iron
diagram, which is also known as iron carbon phase diagram.
Constituents in Steels
Plain carbon steels are
generally defined as the
alloys of iron and carbon which contain up to 2.0% carbon. For the
will neglect the effects of such elements as manganese which may be
most ordinary steels and regard steels as being simple iron carbon
Constituents in steels exist
mainly as phases. They
include molten alloy, delta ferrite, austenite (gamma phase), ferrite
phase), cementite and graphite. Another constituent in steels is
is not a phase but an aggregate.
In iron carbon alloys
austenite is the solid
solution formed when carbon dissolves in face centered cubic (gamma)
amounts up to 2%. Its microstructure is usually large grained.
Austenite is a difficult
structure to retain at room
temperature unless a steel contains a large percentage of alloy, such
manganese or nickel. Austenitic steel is characterized by high tensile
and unusually great ductility. The tensile strength is often around
pounds per square inch with elongation in two inches of 35 to 40
In iron carbon alloys ferrite
is a very dilute solid
solution of carbon in a body centered cubic (alpha) iron and containing
most only 0.02% carbon. Its microstructure appears as polyhedral grains.
Ferrite is very ductile and
soft and has a low
tensile strength but high elongation. Its tensile strength is about
pounds per square inch and an elongation in 2 inches of about 40%.
or graphitic carbon, is a
free carbon in steel or cast iron. The carbon is amorphous, having no
The metallographic appearance
of graphite in a low carbon
steel which has been subjected to a prolonged heating at a temperature
at which austenite is formed.
Cementite, or iron carbide,
is an interstitial
compound of iron and carbon containing 6.69% carbon. Its approximate
formula is Fe3C. When it occurs as a phase in steel, the chemical
will be altered by the presence of manganese and other carbide forming
In case of a slow cooled,
relatively high carbon
steel, microstructure of cementite appears as a brilliant white network
the pearlite colonies or as some needles interspersed with the
metallographic appearance of spheroidized cementite in a steel, which
heated to a temperature just below that at which austenite first forms.
Cementite is a very hard
compound. Its tensile
strength is about 5,000 pounds per square inch and an elongation in 2
equal to zero. Cementite is an unstable phase. Given sufficient time,
decomposes into two complete equilibrium constituents, iron and
The term eutectoid is
usually defined as
An isothermal reversible reaction
in which a solid
solution is converted into two or more intimately mixed solids on
number of solids formed being the same as the number of components in
An alloy having the composition
indicated by the eutectoid
point on an equilibrium reaction.
An alloy structure of intermixed
solid constituents formed
by a eutectoid.
Pearlite is a lamellar
aggregate of ferrite and
cementite. It is a result of the eutectoid reaction which takes place
plain carbon steel of approximately 0.08% carbon is cooled slowly from
temperature range at which austenite is stable.
Pearlite has lamellar
micrographic structure known
as the eutectoid structure. It exerts maximum hardening power of any
constituent. It has a tensile strength of around 125,000 pounds per
and an elongation in 2 inches of 10 percent.
The term eutectic is usually
An isothermal reversible reaction
in which a liquid
solution is converted into two or more intimately mixed solids on
number of solids formed being the same as the number of components in
An alloy having the composition
indicated by the eutectic
point on an equilibrium diagram.
An alloy structure of intermixed
solid constituents formed
by an eutectic reaction.
is a eutectic of the
iron carbon system, the constituents being an austenite and a
eutectic contains 4.3% carbon.
This eutectic is a constituent of iron carbon alloys containing more
carbon and for this reason the dividing line between steels and cast
set at 2.0% carbon.
Phases in Hypoeutectoid Steel
Hypoeutectoid steels are
those containing less than
the eutectoid percentage of carbon, which is about 0.80% in plain
At some temperature above
Ae3, steel containing
0.40% carbon is completely austenitic. On slow cooling below Ae3 the
first rejects ferrite, which concentrates at grain boundaries. As the
temperature falls down to Ae1, the crystals of austenite shrink and
carbon content increases to 0.80%. On cooling below Ae1, the austenite
to pearlite so that the final constituents in steels below Ae1 are
pearlite as illustrated in Fig. 3.
Phases in Eutectoid Steel
Eutectoid steel is a steel
containing the eutectoid
percentage of carbon which is about 0.80% in plain carbon steels.
The eutectoid steel will not
begin to transform from
austenite on cooling until the critical temperature Ae1 3 is reached.
transformation will begin and end at the same temperature (723ºC or
The final structure will be entirely pearlite as shown in Fig. 4.
Phases in Hypereutectoid Steel
Hypereutectoid steels are
those containing more than
the eutectoid percentage of carbon, which is about 0.80% in plain
At some temperature above
Aecm, a steel containing
1.2% carbon is completely austenitic. On slow cooling below Aecm the
will precipitate as needle shaped crystals of cementite around the
grain boundaries. As a result the carbon content in an austenite will
gradually reduced down to 0.80% at the temperature Ae1 3. Below this
remaining austenite will then transform to pearlite as shown in Fig. 5.
Phase Transformation Hysteresis
The phase transformations do
not occur at the same
temperature in heating as in cooling. The metal is rather reluctant to
its physical state so that on heating, the Ac temperatures are somewhat
than equilibrium temperature Ae. Likewise, the Ar temperatures on
lower than equilibrium temperatures Ae. The difference in temperature
the Ac and the Ar varies. In some cases it is as great as 24ºC, or 75ºF.
Supercooling or Austenite
As it has been shown in this
chapter that austenite transforms
to pearlite when it is cooled slowly below the Ar critical temperature.
more rapidly cooled, however, this transformation is retarded. The
cooling rate, the lower the temperature at which transformation occurs
resulting in a formation of the micro constituents shown in Table 1.
Martensite is a metastable
phase of steel formed by
a transformation of austenite below Ms temperature. It is an
supersaturated solid solution of carbon in iron having a body centered
Transformation to martensite
occurs almost instantly
during cooling and the percentage of transformation is dependent only
temperature to which it is cooled. It is the hardest of the
products of austenite. The microstructure of martensite is acicular, or
This structure is formed when
martensite is reheated
to a subcritical temperature after quenching.
Optimization and Modernization of Hot Strip Mills
Main Strategy in Optimization of Rolling Process
In the process of rolling a
uniformly preheated slab
in hot strip mill, its temperature changes due to the various types of
transfer have been described earlier. The following three temperature
are usually used for evaluating the temperature rundown of the
well as a degree of uniformity of the temperature along its length and
Temperature rundown of a selected
portion (for example, a
head end, tail end, or a middle portion of the workpiece expressed) in
to each rolling pass.
Temperature variation along the
workpiece length after the
same rolling pass.
Temperature variation across the
temperature rundown in hot
strip mill is shown in general form in Fig. 1. The main parameters of
The temperature variation
across the workpiece
length can be defined as a difference between the temperatures measured
middle and near the edge of the workpiece DTW.
controlling the workpiece temperature during hot rolling is twofold.
it is necessary to maintain the optimum temperature of the rolled
allows one to obtain the desired properties of the rolled product with
energy consumption, required production rate, and maximum yield.
is desirable to achieve a uniform workpiece temperature in both
and transverse direction during each rolling pass which helps to
quality of the rolled product.
The boundary conditions for
during the rolling deformation process are defined by metallurgical
homogeneity of the rolled product, all deformations in conventional hot
process are usually made in the austenitic phase. For low carbon steel,
implies that the last deformation must occur at a strip temperature TE
the phase transformation point between austenite and ferrite for low
steel the optimum range for TE is 1550 to 1650ºF.
metallurgical requirement is that the slab temperature T0 be high
ensure dissolution of intermetallic phases or compounds resulting from
addition of alloying elements. From this point of view, the minimum
value of T0
for low carbon steel is approximately 2000ºF.
The maximum value of T0 is
usually limited because
of another metallurgical phenomenon related to excessive grain
which can have a detrimental effect on the final product. The maximum
T0 for low carbon steel is approximately 2400ºF.
More detailed description of
requirements for rolling of different types of steels is given in the
Energy Consumption Requirements
Energy consumption directly related
to the hot rolling
process can be divided into three components
required for heating the slab in the reheat furnace.
required for maintaining heat during transfer of the workpiece between
required for hot rolling of the workpiece.
Product Quality Requirements
Temperature variation of the
rolled material in both
the longitudinal and the transverse direction is a major obstacle in
maintaining the required strip gage, profile and shape tolerance.
The most drastic variation in
direction occurs when the transfer bar enters the first finishing
Because the head end of the bar is usually transferred from the last
stand to the first finishing stand in less time than the tail end of
the tail end is subjected to heat radiation loss for a longer time than
head end. The resulting temperature rundown increases with increasing
weight. As will be shown later, if no preventive measures are taken to
this rundown, the temperature differential between head and tail end of
at the entry of the finishing train DTF can be as much as 300ºF for a
The adverse effect of this
on strip shape is inversely proportional to the rolled material
Rolled material temperature
variation in the
transverse direction is mainly due to excessive radiation near the
the surface to volume ratio increases substantially. If no measures are
to reduce edge cooling, the transverse temperature variation DTF can be
Analysis of Temperature Conditions in Hot Strip Mill
Review of the foregoing
requirements shows that
there is no universal definition of optimum temperature conditions for
strip mills. For example, a possible reduction in reheat furnace
due to heat conservation on the transfer table might not be fully
because of power limitations of the roughing train or, in another case,
of poor surface quality of the slabs loaded into the furnace, which
maintaining the higher reheat furnace temperature needed to enhance the
process that helps to improve the slab surface.
facts suggest that the
optimum temperature conditions must be found for each hot strip mill on
individual basis. However, the following common criteria can be applied
objective evaluation of different solutions
mean temperature differential, MTD
primary scale, m
fuel energy, Ef
electrical energy consumption, Ee
cost savings due to reheating and rolling optimization, St
additional capital cost, Ct
Low Carbon Constructional Alloy Steels
Low Temperature High Strength Tough Steel
U.S. Patent 3,960,612 June 1,
1976 assigned to
Nippon Steel Corporation, Japan describe the preparation of steel for
use as a
pressure container to be used at temperature below the ice point, or as
structural material such as a pipeline in a cold environment capable of
standing high pressure and low temperature.
The method comprises (1)
providing a steel material
as hot rolled comprising 0.03 to 0.15% C, 0.05 to 0.40% Si, 0.2 to 2.0%
to 4.5% Ni, 0.1 to 0.5% Mo, 0.005 to 0.050% Nb, not more than 0.02% N,
0.070% Al, and if necessary, one or more than one member of the group
consisting of V, Ti, Cr, Ca and Ce, the rest being iron and unavoidable
impurities (2) quenching the material after heating at 660º to 750ºC
(3) tempering after heating at 650ºC or less.
The steel material in the
form of plates, rods, etc.
having the above composition can be manufactured as follows. The molten
obtained by the use of a converter, electric furnace or other smelting
furnaces, and if necessary, a vacuum degassing apparatus is formed into
through the steps of ingoting, blooming or continuous casting, and then
to the steel material. The steel material as hot rolled can be any
type, but it
is preferable that the crystal grain is larger than the crystal grain
5 of JIS and that the space factor is below 80%, and the smaller, the
In order to make the structure of the steel finer as hot rolled, the
material used may be that which has been heated at 840º to 930ºC and
The steel material which can
thus be manufactured by
hot rolling with or without the subsequent heat treatment is subjected
quench treatment of heating at 660º to 750ºC), followed by rapid
whereby extremely fine structure can be obtained, which results in the
enhancement of the low temperature toughness. This steel material is
subjected to a temper treatment at 650ºC or less (preferably at least
whereby the strength and the toughness are enhanced and the cold
and the brittleness due to strain aging can be improved.
In the heat treatment
normalizing the steel material
after it has been hot rolled but before temper treatment may be
quenching treatment of this process, however, produces a material of
structure and is thus of advantage.
Alloy Steel for Arctic Service
The development of oil and
gas fields in the Arctic
had encouraged a search for structural steels having good low
properties for such applications as line pipe, line pipe fittings and
bridge members. The low cost carbon and high strength, low alloy steels
currently used for these applications in warmer environments do not
desired toughness at low temperatures in section thicknesses of about 1
inches. For such Arctic applications, it will be necessary that the
steel have a minimum yield strength of at least 60 ksi, and good impact
toughness down to temperatures as low as –80ºF.
Patent 3,955,971 May 11,
1976 assigned to United States Steel Corporation describes a low alloy
ideally suited for Arctic applications. This weldable, low alloy steel
characterized in the quenched condition by a ferritic pearlitic
microstructure which in the tempered condition has a minimum yield
65 ksi in plate thicknesses to at least 2 inches, and a Charpy V notch
shear transition temperature below –80ºF and a Charpy V notch energy
of at least 50 ft/lb in both the longitudinal and transverse
Iron and conventional impurities
In the quenched and tempered
condition, at least in
thicker sections (i.e., 5/8 inch and greater) the above composition
a ferritic pearlitic bainitic micro structure. Unlike the quenched and
low carbon constructional alloy steels, the above steel is not
high hardenability and is not martensitic in the quenched condition.
lower yield strengths are achieved but low temperature toughness is
The quenched and tempered low carbon ultra service steels can be
distinguished in addition to containing considerably more carbon and
Example An 80 ton commercial
heat was produced in an
electric furnace, aiming for a content of 1% each of nickel and
0.30% molybdenum. The product composition was 0.09% C, 0.58% Mn, 0.007%
0.010% S, 0.31% Si, 1.05% Ni, 0.98% Cr, 0.30% Mo and 0.03% Al. Ingots
heat were processed to 5/8 , 1 and 2 inch thick plates and to 24 inch
0.969 inch wall seamless pipe (610 by 24.6 mm). The table 1 gives the
results. It is significant to note that all products exceed a 65 ksi
strength and a transverse Charpy V notch energy absorption of 50 ft/lb
shear fracture appearance at –80ºF.
High Strength Cold Rolled Steel with High Press Formability
Demands have been
increasingly made for development
of a cold rolled steel sheet having still higher strength without
lowering press formability as compared with the conventional cold
sheet for use in inside sheets and outside skins of a safety
Particularly, for parts such as member sides which are subjected to
stretching and bending and whose increased strength has a large effect
safety, demands are increasingly made for a cold rolled steel sheet
high tensile strength such as 45 to 90 kg/mm2, 35 to 75 kg/mm2 yield
as well as excellent ductility such as stretchability and yet shows a
value of drawability in certain applications.
U.S. Patent 3,951,696 April
20, 1976 assigned to
Nippon Steel Corporation, Japan describe a method for producing a high
cold rolled steel sheet having the above strength properties and yet
good press formability, particularly stretchability. The method
rolling and cold rolling a low Si Mn killed steel, heating the cold
steel sheet with an average heating rate not lower than 3ºC per second,
annealing the steel sheet for 1 to 15 minutes at a temperature between
and the A3 transformation point and cooling of the steel sheet at an
cooling rate between 0.5 and 30ºC per second down to 500ºC.
The steel comprises 0.03 to
0.30% C, less than 0.7%
Si, 0.6 to 2.5% Mn, 0.01 to 0.20% sol Al, not more than 0.015% O with
balance being Fe and unavoidable impurities.
Example Steel slabs were
produced by melting in a
converter, by ordinary ingot making and partly by a continuous casting
A2 and B2), and these slabs were subjected to hot rolling, cold
annealing and averaging to obtain cold rolled steel sheets of 1.0 mm
All of the products were subjected to skin pass rolling of 1.0%. The
compositions, production conditions, mechanical properties. F values
secondary workability are shown in the table 2 and 3.
As for the secondary
workability test, the following
impact secondary workability test was conducted. A steel sheet disc of
160 mm diameter was drawn into a cup like form with an appropriate
ratio (primary working drawing ratio), and this cup like test piece was
immersed in a vessel containing water and ice to lower the temperature
test piece fully.
Then a conical punch was
inserted into the cup like
test piece on the thick steel plate and a steel lump of 20 kg weight
dropped from a height of 3 m to the punch, to see if an embrittlement
(longitudinal crack) was caused in the test piece. In this test, the
primary working drawing ratio (limit drawing ratio), which does not
embrittlement crack, represents better impact secondary workability.
secondary workability tends to lower in a steel sheet having higher
In case of an ordinary mild rimmed steel the limit drawing ratio is 3.0
As understood from the table, when the steel composition is worked into
rolled steel sheet by the production steps including the continuous
according to this process, it is possible to produce a high strength
rolled steel sheet having a high yield ratio of 0.75 and yet excellent
secondary workability or drawability.
Meanwhile, if the steel
composition is subjected to
a box annealing at 700ºC, a high yield point cannot be obtained
satisfactory drawability is obtained so that the utility of this
directed to the inside sheets and outside sheets of safety automobiles
In case of a box annealing,
the grain growth is
suppressed when the annealing is done at a low temperature (600ºC) and
possible to obtain a somewhat high yield point property, but remarkable
as obtained by the rapid heating and the short time annealing cannot be
Production of High Strength Cold Rolled Steel Sheet
U.S. Patent 3,947,293 March
30, 1976 assigned to
Nippon Steel Corporation, Japan describe a method for producing a high
cold rolled steel or strip. Steel comprising 0.05 to 0.15% of C 0.02 to
of Si 0.10 to 1.5% of Mn 0.02 to 0.07% of Al and a total of 0.02 to
art least one of Nb, V, Ti and Zr with the remainder being iron and
impurities, is hot rolled whereafter the hot rolled steel sheet or
coiled below 750ºC. The coiled sheet or strip is then cold rolled where
the cold rolled steel sheet or strip is subjected to annealing at 670º
for 20 seconds to 10 minutes.
The increase of strength by
the continuous annealing
is considered to be due to the fact that the solid dissolved elements,
Nb, V, Ti and Zr, which have not completely precipitated during the hot
rolling, remain as partial precipitates during the continuous
annealing. If the
holding time of the continuous annealing is excessively long, the
of the above elements become coarse above the A1 transformation
thus lowering the strength as in case of box annealing and causing
Then the cold rolled steel
sheet or strip which has
been subjected to the short time continuous annealing as above is
cooled so that much carbon in solid solution remains in the steel,
when the coiling temperature is relatively low, to wit, not higher than
commonly called quench
aging, and lowering ductility is thus caused. In order to avoid this
it is desirable that an over aging treatment for one or ten minutes,
two to five minutes at between 300º to 400ºC, preferably 300º to 350ºC,
conducted during the cooling step after the continuous annealing to
the carbide precipitation, thereby avoiding the hardening effects
continuously annealed materials.
In this context it should be
observed that the
carbides and nitrides of Nb, V, Ti, etc. do not precipitate completely
low temperature coiling at 550ºC or lower so that it is necessary to
precipitate them completely by over aging in the continuous annealing
contrast, in case of a high temperature coiling between 550º and 750ºC,
carbides and nitrides of Nb, V, Ti, etc. are precipitated completely so
the over aging treatment is not necessary in the continuous annealing
The material properties,
particularly the balance
between yield point and total elongation of the high strength cold
sheet produced in the above manner are found to be better than those
by box annealing. Also it is possible to control very strictly the
temperature along the whole length of the coil so that nonuniformity of
strength and ductility due to the temperature difference encountered in
annealing can be avoided.
Example A steel heat
comprised of 0.12% C, 0.25% Si,
1.33% Mn, 0.0113% P, 0.007% S, 0.05% Nb, 0.03% V, 0.026% Al, and
0.0042% N was
tapped and continuously hot rolled. In the hot rolling step, the steel
rolled to a thickness of 3.2 mm and coiled at 490ºC. The thus obtained
rolled steel strip was cold rolled to a thickness of 0.8 mm by an
method, and thereafter subjected to a continuous annealing at 700ºC for
minute and 750ºC for one minute and successively subjected to an over
treatment at 350ºC for five minutes. The results are shown below in
with those of the box annealing.
Full Continuous Annealing Process
U.S. Patent 3,936,324
February, 3, 1976 and K.
Uchida, K. Araki, H. Narita, S. Fukunaka and T. Kurihara U.S. Patent
September 9, 1975 both assigned to Nippon Kokan KK, Japan described a
making a high strength cold reduced steel having the most suitable
properties required as a safe countermeasure for an automobile, and
particularly being easily pressable into a required shape and stepping
strength by a coating baking treatment after the above presswork.
A steel comprising 0.04 to
0.12% C, 0.50 to 2.00%
Si, and 0.10 to 1.60% Mn is passed through ordinary hot and cold
processes and is subjected to a full continuous annealing process. The
continuous annealing process is selected from the following processes
upon the intended use and the required strength level.
High Strength Killed Wire Rods and Bars
U.S. Patent 3,926687 December
16, 1975 assigned to
Nippon Steel Corporation, Japan describe a method for producing a high
steel wire rod having a structure of good workability by controlling
temperature of the rolled steel material and also controlling the
after the finish rolling. The steel material obtained is useful for
bolts, PC wire, metal networks, Umbrella ribs, spring washers and
A wire rod as hot rolled is
subjected only to slight
skin pass drawing into a required size, and then to heading and
works, to obtain a bolt having 80 to 100 kg/mm2 of tensile strength
defect. Heat treatments such as spheroidizing annealing, quenching and
tempering can be omitted and thus a high level of economy is assured.
Further, when applied to
production of PC wires
(prestressed concrete wires) it is sufficient that the wire rod is
only to slight skin pass drawing and shape working including indent
application in prestressed concrete products. Thus the patenting heat
which is conventionally done can be omitted. Yet a wire having high
strength and very excellent spot weld ability can be obtained.
The wire contains 0.02 to
0.20% C, 0.03 to 0.90% Si
and 1.00 to 1.85% Mn together with one or more of not more than 0.05%
more than 0.08% V, not more than 0.25% Ti, not more than 0.30% Zr, not
than 0.005% B and not more than 0.40% Cr, and contains Al in an amount
contained in an ordinary killed steel with the balance being iron and
The process is carried out by
heating a steel having
the above composition to at least 1150ºC, conducting intermediate
and/or finish rolling at 700º to 1150ºC, controlling the cooling rate
finish of the hot rolling to a coiling to 40º to 350ºC/sec, and
cooling rate from the coiling to gathering to 1º to 15ºC/sec. Hot
wire rods and bars are obtained having excellent workability and spot
weldability and having a tensile strength not lower than 50 kg/mm2 and
reduction of area not lower than 50%.
High Formability High Strength Steel
There is an ever present and
increasing demand for
high strength steels having good formability properties particularly
biaxial stretching and uniaxial bending properties required, for
the automotive industry for auto mobile bumper systems.
U.S. Patent 3,926,686
December 16, 1975 assigned to
The Algoma Steel Corporation, Limited, Canada describe a high strength
alloy steel strip having a minimum yield strength of 50,000 psi and
formability properties. The steel consists, by weight, of 0.10% maximum
0.30 to 0.80% manganese, 0.01% maximum sulfur, 0.02 to 0.06% aluminum,
0.12% columbium, 0.06% maximum cerium, the balance being iron and
impurities. Depending upon the composition of the steel, lower yield
of 50,000 to 80,000 psi are attained. This composition when hot rolled
at 1620º to 1700ºF and coiled or collected at 1150º to 1375ºF, exhibits
unique relationship of strength and maximum formability at each of the
levels in the range.
At each strength level, from
50,000 to 80,000 psi,
the final structure of the steel is composed principally of ferrite
limited amounts of pearlite. In conjunction with this and essential to
improved formability properties is the controlled dispersion of the
as columbium carbides of columbium carbonitrides. While pearlite is in
boundaries and as cementite (Fe3C) in the form of skeletal carbides,
columbium has been found to have a dual form, of row precipitates in
200 Angstrom units from which the initial ferrite grains have formed
secondly, within the ferrite grain itself, as a finely dispersed
of 30 to 120 Angstrom units.
It may be noted in the steel
composition that the
level of both C and Mn is considerably lower than in known steels in
strength range, which provides several major factors contributing to
improved formability properties. The low content of the steel
course, reduces the pearlite content directly. However, more important,
carbon content and low manganese values act to increase the austenite
ferrite transformation temperature.
It has been found that this
increase or higher
austenite to ferrite transformation temperature controls the proportion
columbium that precipitates into coarse and fine dispersion in the
and distributes the available columbium into its dual form for the
grain refinement and precipitation strengthening. The coarse
columbium occurs during the hot deformation or actual rolling of the
to and including the final deformation, the collecting. This coarse
precipitation acts to retard the recrystallization of austenite,
after the final deformation, until transformation to ferrite is
Transformation from the highly deformed austenite guarantees
a fixed and constant ferrite grain size. The ferrite grain size will
according to the amount of columbium present and the temperature at
finishing rolling is carried out.