Acid Steel

Steel produced in a furnace with an acid lining, i.e.
consisting of a siliceous refractory and under a siliceous
slag. With an acid slag, carbon, silicon and manganese
only are removed so that the pig iron must not contain
sulphur and phosphorus in percentages exceeding those
permissible for the specification being made. Most steel
manufactured today is in furnaces with basic linings.

Air-Hardening Steel

Sometimes referred to as self-hardening steel. A steel
that becomes fully hardened when cooled in air from
above its critical point and does not require rapid
quenching by oil or water. The risk of distortion is
greatly reduced by air hardening. High Speed Steel was
one of the earliest examples of this type of steel.

Allotropy

The property possessed by certain elements to exist in
two or more distinct forms that are chemically identical
but have different physical properties. In the case of iron
the crystal structure has one form at room temperature
and another at high temperature. When heated above
910 deg C the atomic structure changes from body centered
cubic to face centered cubic but reverts again when
cooled. The allotropy of iron modifies the solubility of
carbon, and it is because of this that steel can be
hardened.

Alloy Steel

A steel to which one or more alloying elements other
than carbon have been deliberately added (e.g.
chromium, nickel, molybdenum) to achieve a particular
physical property.

Alpha Iron

The body centered cubic form of iron which, in pure iron,
exists up to 910 deg C.

Annealing

Heating steel to, and holding at a suitable temperature,
followed by relatively slow cooling. The purpose of
annealing may be to remove stresses, to soften the
steel, to improve machinability, to improve cold working
properties, to obtain a desired structure. The annealing
process usually involves allowing the steel to cool slowly
in the furnace.

Arc Furnace

A steel melting furnace in which heat is generated by an
arc between graphite electrodes and the metal. Both
carbon and alloy steels are produced in electric arc
furnaces and scrap rather than molten metal is used as
the base material. Furnaces with capacities up to 200
tons are now in use.

Austempering

Quenching from a temperature above the transformation
range to a temperature above the upper limit of
martensite formation, and holding at this temperature
until the austenite is completely transformed to the
desired intermediate structure, for the purpose of
conferring certain mechanical properties.

Austenite The solid solution of carbon in gamma (face centered
cubic) iron.

Austenitic Steels

Steels containing high percentages of certain alloying
elements such as manganese and nickel which are
austenitic at room temperature and cannot be hardened
by normal heat-treatment but do work harden. They are
also non-magnetic. Typical examples of austenitic steels
include the 18/8 stainless steels and 14% manganese
steel.

B

Chemical symbol for Boron.

Bainite

An acicular aggregate of ferrite and carbide particles
formed when austenite is transformed on cooling at
temperatures in the intermediate (200-450 deg C) range,
i.e. above the martensite and below the pearlite
range.

Balanced Steel

Steels in which the deoxidisation is controlled to
produce an intermediate structure between a rimmed
and killed steel. Sometimes referred to as semi-killed
steels, they possess uniform properties throughout the
ingot and amongst their applications are boiler plate
and structural sections.

Base Metal

A metal which oxidises when heated in air, e.g. lead,
copper, tin, zinc, as opposed to noble metals such as
gold and platinum.

Basic Steel

Steel produced in a furnace in which the hearth
consists of a basic refractory such as dolomite or
magnesite, as opposed to steel melted in a furnace
with an acid lining. The basic process permits the
removal of sulphur and phosphorous and in this
respect is superior. Present day BOS and electric arc
furnaces use basic linings.

Be

Chemical symbol for Beryllium.

Bend Test

Bending tests are carried out to ensure that a metal
has sufficient ductility to stand bending without
fracturing. A standard specimen is bent through a
specified arc and in the case of strip, the direction of
grain flow is noted and whether the bend is with or
across the grain.

Bessemer Process

A method of producing steel, first introduced in the
last century, where air is blown under pressure
through molten iron to remove the impurities by
oxidation. The development of the process has led to
the present day Basic Oxygen Steel making plants
that account for bulk production of commercial quality
steels in the UK.

Bi

Chemical symbol for Bismuth.

Billet

A section of steel used for rolling into bars, rods and
sections. It can be a product of the ingot route, or
increasingly today produced directly by continuous
casting.

Blast Furnace

A tall, cylindrical, refractory lined furnace for the
production of pig iron or hot metal for direct
conversion into steel.

Bloom

A large square section of steel intermediate in the
rolling process between an ingot and a billet. Blooms
are now also being produced by the continuous
casting process eliminating the necessity of first
producing an ingot.

Boron Steels

The addition of boron in the range 0.0005-0.005% to
certain steels increases the hardenability. A range of
boron steels is now listed in the current BS 970 and
are widely used for the production of cold headed
fastenings.

Brazing

Brazing is a method of joining metal parts together by
fusing a layer of brass between the adjoining surfaces.
A red heat is necessary and a flux is used to protect
the metal from oxidation.

Bright

Annealing An annealing process that is carried out in a controlled
atmosphere furnace or vacuum in order that oxidation
is reduced to a minimum and the surface remains
relatively bright.

Bright Drawing

The process of drawing hot rolled steel through a die
to impart close dimensional tolerances, a bright, scale
free surface, and improved mechanical properties. The
product is termed bright steel.

Brinell Hardness Test

The Brinell hardness test for steel, involves impressing
a ball 10 mm diameter, of hard steel or tungsten
carbide, with a loading of 3000 kilograms into the
steel surface. The hardness of the steel is then
determined by measurement of the indentation. For
steels with a hardness over 500 BHN the Vickers test
is more reliable.

C

Chemical symbol for Carbon.

Ca

Chemical symbol for Calcium.

Calcium

In the form of calcium silicide acts as a deoxidizer
and degasifier when added to steel. Recent
developments have found that carbon and alloy
steels modified with small amounts of calcium show
improved machinability and longer tool life.
Transverse ductility and toughness are also
enhanced.

Carbon

Carbon is an essential element in steel, it is added
in specific amounts to control the hardness and
strength of the material. In general, increased
carbon content reduces ductility but increases
tensile strength and the ability of the steel to
harden when cooled rapidly from elevated
temperatures.

Carbon Steel

A steel whose properties are determined primarily
by the amount of carbon present. Apart from iron
and carbon, manganese up to 1.5% may be
present as well as residual amounts of alloying
elements such as nickel, chromium, molybdenum,
etc. It is when one or more alloying elements are
added in sufficient amount that it is classed as an
alloy steel.

Carbo-Nitriding

A case-hardening process in which steel
components are heated in an atmosphere
containing both carbon and nitrogen.

Carburising

The introduction of carbon into the surface layer of
a steel that has a low carbon content. The process
is carried out by heating the components in a solid
liquid, or gaseous carbon containing medium. The
depth of penetration of carbon into the surface is
controlled by the time and temperature of the
treatment. After carburising it is necessary to
harden the components by heating to a suitable
temperature and quenching.

Case-Hardening

The process of hardening the surface of steel
while leaving the interior unchanged. Both carbon
and alloy steels are suitable for case-hardening
providing their carbon content is low, usually up to
a maximum of 0.2%. Components subject to this
process, particularly in the case of alloy steels,
have a hard, wear-resistant surface with a tough
core.

Cast Iron

A definition can be applied that Cast Iron is an
alloy of iron and carbon in which the carbon is in
excess of the amount that can be retained in solid
solution in austenite at the eutectic temperature.
Carbon is usually present in the range of 1.8% to
4.5%, in addition, silicon, manganese, sulphur and
phosphorus are contained in varying amounts.
Various types of cast iron are covered by a British
Standard classification and includes grey, malleable
and white irons. Elements such as nickel,
chromium, molybdenum, vanadium can be added to
produce alloy cast irons.

Cast Steel

A term originally applied to crucible steel and
sometimes today used to describe tool steels. The
term is misleading and is falling into misuse. It can
also be applied to steel castings made by pouring
molten steel into a mold but which are not subject
to further forging or rolling.

Cb

Chemical symbol for Columbium.

Ce

Chemical symbol for Cerium.

Cementite

An iron carbide (Fe3C) constituent of steel. It is
hard, brittle and crystalline. Steel which has cooled
slowly from a high temperature contains ferrite and
pearlite in relative proportions varying with the
chemical composition of the steel. Pearlite is a
lamellar structure of ferrite and cementite.

Charpy Test

A test to measure the impact properties of steel. A
prepared test piece, usually notched, is broken by a
swinging pendulum. The energy consumed in
breaking the test piece is measured in Joules. The
more brittle the steel the lower the impact strength.
Izod is a similar and more widely used impact test
in this country. Both are quoted in the current
edition of BS 970.

Chromium

When used as an alloying element, chromium
increases the hardenability of steel and in
association with high carbon gives resistance to
wear and abrasion. Chromium has an important
effect on corrosion resistance and is present in
stainless steels in amounts of 12% to 20%. It is
also used in heat-resisting steels and high duty
cast irons.

Co

Chemical symbol for Cobalt.

Cobalt

An alloying element used in tool, magnet and heat
resisting steels. Together with tungsten and
molybdenum, cobalt is used to form the super high
speed steels. It improves the red hardness value of
the steel, that is, it enables the steel to resist
softening at a high temperature or in the case of a
cutting tool to hold its edge under severe
conditions.

Coefficient of Expansion

The ratio of change in length, area, or volume per
degree to the corresponding value at a standard
temperature.

Cogging

An intermediate rolling process when a hot ingot is
reduced to a bloom or slab in a cogging mill.

Cold Drawing

The process of reducing the cross sectional area of
wire, bar or tube by drawing the material through a
die without any pre-heating. Cold drawing is used
for the production of bright steel bar in round
square, hexagonal and flat section. The process
changes the mechanical properties of the steel and
the finished product is accurate to size, free from
scale with a bright surface finish.

Cold Working

Altering the shape or size of a metal by plastic
deformation. Processes include rolling, drawing,
pressing, spinning, extruding and heading, it is
carried out below the recrystallisation point usually
at room temperature. Hardness and tensile strength
are increased with the degree of cold work while
ductility and impact values are lowered. The cold
rolling and cold drawing of steel significantly
improves surface finish.

Contact Corrosion

When two dissimiliar metals are in contact without
a protective barrier between them and they are in
the presence of liquid, an electrolytic cell is
created. The degree of corrosion is dependent on
the area in contact and the electro-potential
voltage of the metals concerned. The less noble of
the metals is liable to be attacked, i.e. zinc will act
as a protector of steel in sea water whereas copper
or brass will attack the steel in the same
environment.

Continuous Casting

A method of producing blooms, billets and slabs in
long lengths using water cooled molds. The
castings are continuously withdrawn through the
bottom of the caster while the teeming of the
metal is proceeding. The need for primary and
intermediate mills and the storage and use of large
numbers of ingot molds is eliminated. The
continuous casting process is also used in the
production of cast iron, aluminium and copper
alloys.

Controlled Atmosphere

A gas or mixture of gases in which steel is heated
to produce or maintain a specific surface condition.
Controlled atmosphere furnaces are widely used in
the heat treatment of steel as scaling and
decarburisation of components is minimised by this
process.

Core

In the case of steel this refers to a component that
has been case-hardened where the centre is softer
than the hard surface layer or case. It can also be
applied to the central part of a rolled rimming steel.

Corrosion

Fatigue Fatigue that arises when alternating or repeated
stress combines with corrosion. The severity of the
action depends on the range and frequency of the
stress, the nature of the corroding condition and
the time under stress.

Cr

Chemical symbol for Chromium.

Creep

The form of plastic deformation that takes place in
steel held for long periods at high temperature.
Methods of creep testing involve the determination
of strain/time curves under constant tensile load
and at constant temperature.

Critical Cooling R

The slowest rate of cooling from the hardening
temperature which will produce the fully hardened
martensitic condition.

Critical Point

This generally refers to a temperature at which
some chemical or physical change takes place.
These transformations cause evolution of heat on
cooling or absorption of heat on heating and
appear as discontinuities or arrest points in the
heating and cooling curves. The temperatures vary
with the carbon content of the steel and the rate of
cooling.

Critical Temperature

The temperature at which some phase change
occurs in a metal during heating or cooling, i.e. the
temperature at which an arrest or critical point is
shown on heating or cooling curves.

Crystalline Fracture

A type of fracture that appears bright and glittering,
it having formed along the cleavage planes of the
individual crystals. Normally an indication that
brittle fracture has occurred.

Cu

Chemical symbol for Copper.

Cyanide Hardening

A process of introducing carbon and nitrogen into
the surface of steel by heating it to a suitable
temperature in a molten bath of sodium cyanide, or
a mixture of sodium and potassium cyanide, diluted
with sodium carbonate and quenching in oil or
water. This process is used where a thin case and
high hardness are required.

Decalescence

A term used in reference to the absorption of
heat without a corresponding increase in
temperature, when steel is heated through the
critical points (phase changes).

Decarburisation

The loss of carbon from the surface of steel as
a result of heating in a carbon weak
atmosphere. During the rolling of steel hot
surfaces are exposed to the decarburising
effects of oxygen in the atmosphere and as a
result the surface is depleted of carbon. In
steels where the components are to be
subsequently heat treated it is necessary to
remove the decarburised surface by machining.

Delta Iron

When pure or practically carbon-free iron is
cooled from above its melting point it solidifies
at about 1535 deg C as delta iron having a
body-centred cubic lattice structure, which
persists down to about 1400 deg C. On further
cooling it undergoes an allotropic change to
gamma iron which has a face-centred cubic
lattice and is non-magnetic.

Deoxidation

Elements such as silicon and aluminium when
added to molten steel react to form stable
oxides and reduce the amount of dissolved
oxygen. The solubility of oxygen in steel is
reduced as temperature is lowered during
solidification and the excess oxygen combines
to form carbon monoxide. If the molten metal
is not deoxidised the effervescence produced
by the evolution of carbon monoxide during
solidification would result in blow holes and
porosity. Steel treated in this way is termed,
"Killed Steel".

Descaling

It is necessary to remove the scale from hot
rolled bars or coil before bright drawing. This is
normally carried out by shot blasting or pickling
in acid. Other methods of descaling steel
products include sand blasting, flame
descaling and tumbling.

Deseaming

A process of burning out defective areas on
the surface of ingots, blooms or billets. The
condition of the surface is such that it can then
be rolled or forged into a satisfactory product.

Diamond Pyramid Hardness

This test, more commonly known as the
Test Vickers test, finds greater use in the laboratory
than the workshop. It employs a pyramid
shaped diamond with an included angle of
136o which is impressed into the specimen
using loads of 5 to 120 kg making a small
square impression. This test is used for
finished or polished components because the
impression can be very small. The diamond
pyramid hardness number is obtained from a
calculation based on measuring the diagonals
of the impressions in the steel.

Die

The term die is most commonly used in
tooling, i.e. press tools "punch and die" but
there are many other types of die, e.g. thread
cutting dies, forming dies, forging dies,
die-casting dies, etc. The term when applied to
steel often refers to drawing dies through
which hot rolled wire and bar are drawn to
produce the finish and dimensional accuracy
that is required for bright steel.

Dislocation

A discontinuity in the crystal lattice of a metal.
The movement of dislocations under stress
may be used to explain slip, creep, plastic
yielding, etc.

Dolomite

A natural carbonate of calcium and magnesium
generally used as a flux in blast furnaces.

Drawing

The process of pulling metal wire, rods, or bars
through a die with the effect of altering the
size, finish and mechanical properties. In the
USA, it is a term used for tempering.

Drop Forging

An operation in which a metal shape is formed
by forcing hot metal into impressions formed in
solid blocks of hardened alloy steel, the
forging dies. The dies are made in halves, one
attached to the rising and falling block of the
drop forge and the other to the stationary
anvil. Drop forgings are widely used in the
automotive industry for crankshafts, stub-axles,
gears, etc.

Ductility

The property of metal which permits it to be
reduced in cross sectional area without
fracture. In a tensile test, ductile metals show
considerable elongation eventually failing by
necking, with consequent rapid increase in
local stresses.

Dye

Penetrant Inspection A method for detecting surface porosity or
cracks in metal. The part to be inspected is
cleaned and coated with a dye which
penetrates any flaws that may be present. The
surface is wiped clean and coated with a white
powder. The powder absorbs the dye held in
the defects indicating their location.

Elastic Limit

The maximum stress that can be applied to a
metal without producing permanent deformation.
When external forces act upon a material they
tend to form internal stresses within it which
cause deformation. If the stresses are not too
great the material will return to its original shape
and dimension when the external stress is
removed.

Elasticity

The property which enables a material to return
to its original shape and dimension.

Electrical Steels

Steels which are characterised by their magnetic
properties and are intended for the manufacture
of electrical circuits. They are supplied in the
form of cold rolled sheet or strip, generally less
than 2mm thick and up to 1500mm wide. Grain
orientated steels have preferential magnetic
properties in the direction of rolling and non-
grain orientated steels have similar magnetic
properties both transversely and in the direction
of rolling.

Electroslag

Refining A specialised steel making process in which a
rolled or a cast ingot in the form of an electrode
is remelted in a water cooled copper mold. The
melting is activated by resistive heat generated
in a conductive slag. The resulting product has a
similar basic chemical composition to the original
ingot, but is characterised by high purity and low
inclusion content. Typical applications include
high integrity components for the aerospace
industry.

Elevated

Temperature A process of drawing steel bars at elevated
Drawing temperatures (normally 250-300 deg C) which under
optimum conditions produce steels that have
higher tensile and yield strengths than those cold
drawn with the same degree of reduction. The
process is little used in the United Kingdom.

Elongation

A test to measure the ductility of steel. When a
material is tested for tensile strength it elongates
a certain amount before fracture takes place.
The two pieces are placed together and the
amount of extension is measured against marks
made before starting the test and is expressed
as a percentage of the original gauge length.

End

Quench Test More commonly referred to as Jominy Test it is
used to determine the hardening ability of steel.

Equiaxed

Crystals Crystals, each of which has axes approximately
equal in length. These are normally present in
the centre of a steel ingot.

Equilibrium

A diagram constructed from thermal and other
data showing the limits of composition and
temperature within which the various
constituents or phases of alloys are stable.

Etching

Treatment of a prepared metal surface with acid
or other chemical reagent which, by differential
attack, reveals the structure.

Eutectic

A mixture of two or more constituents which
solidify simultaneously out of the liquid at a
minimum freezing point.

Eutectoid

A mixture of two or more constituents which
forms on cooling from a solid solution and
transforms on heating at a constant minimum
temperature. A eutectoid steel contains
approximately 0.83% carbon.

Extrusion

The production of a section by forcing a billet to
flow through a die. Often used for producing
complex sections, the process is used with both
hot and cold metal. Seamless tubes are
produced by forcing a hot billet to flow through a
die over a mandrel positioned centrally in the
die.

F

Chemical symbol for Fluorine.

Face Centred Cubic

An arrangement of atoms in crystals in which the
Lattice atomic centres are disposed in space in such a way
that one atom is located at each of the corners of
the cube and one at the centre of each face. Steel
in the face-centred cubic arrangement is termed
austenite.

Fatigue

The effect on metal of repeated cycles of stress.
The insidious feature of fatigue failure is that there
is no obvious warning, a crack forms without
appreciable deformation of structure making it
difficult to detect the presence of growing cracks.
Fractures usually start from small nicks or scratches
or fillets which cause a localised concentration of
stress. Failure can be influenced by a number of
factors including size, shape and design of the
component, condition of the surface or operating
environment.

Fatigue Limit

The maximum value of the applied alternating
stress which a test piece can stand indefinitely.

Fatigue Testing

Fatigue tests are made with the object of
determining the relationship between the stress
range and the number of times it can be applied
before causing failure. Testing machines are used
for applying cyclically varying stresses and cover
tension, compression, torsion and bending or a
combination of these stresses.

Fe

Chemical symbol for Iron.

Ferrite

The solid solution of carbon in body-centered cubic
iron, a constituent of carbon steels.

Ferritic Steel

A term usually applied to a group of stainless steels
with a chromium content in the range of 12-18o
and whose structure consists largely of ferrite. Such
steels possess good ductility and are easily worked
but do not respond to any hardening or tempering
processes. Types of applications include
automotive trim and architectural cladding.

Ferro Alloys

Alloys of iron with chromium, manganese, silicon,
tungsten, molybdenum or vanadium. Used in
steelmaking as a means of introducing these
alloying elements into the cast or as deoxidisers.

Fettling

The removal of sand adhering to castings by
hammering, tumbling or shot blasting.

Fin In rolling mill practice a fin is a projection extending
from the side of rolled sections. It causes
considerable trouble and is the result of overfill.
The fin, formed when the bar or shape is fed
through one pass, is likely to be rolled back into the
bar at the next pass. It is rarely encountered in
modern rolling mills.

Flame Hardening

A surface hardening process in which heat is
applied by a high temperature flame followed by
quenching jets of water. It is usually applied to
medium to large size components such as large
gears, sprockets, slide ways of machine tools,
bearing surfaces of shafts and axles, etc. Steels
most suited have a carbon content within the range
0.40-0.55%.

Flash

A fin that arises from metal in excess of that
required to fill the final impression in a forging die
and is exuded from the parting line between the
dies; similarly it can arise at the mold joint in a
casting.

Forging

A process of working metal to a finished shape by
hammering or pressing and is primarily a "hot"
operation. It is applied to the production of shapes
either impossible or too costly to make by other
methods or needing properties not obtainable by
casting. Categories of forgings include Hammer,
Press, Drop or Stamping.

Fracture

Fractures are often described by the appearance of
the surface of the break in a piece of steel.
Crystalline is bright and glittering, failure having
developed along the cleavage planes of individual
crystals and can be typical of brittle material. A
silky fracture has a smooth dull grain indicative of
ductile material such as a mild steel. In tensile
testing fractures are described by shape, e.g. cup
and cone.

Freecutting Steels

Steels which have had additions made to improve
machinability. The most common additives are
sulphur and lead, other elements used include
tellurium, selenium and bismuth.

Ga

Chemical symbol for Gallium.

Galvanic Action

When iron and steel are subject to conditions of
aqueous corrosion the incidence and rate at which
the corrosion takes place will alter if the steel is
coupled with other metals or alloys that are also
exposed to the electrolyte. Copper, brass, bronze,
lead and nickel are more "noble" and act as
auxiliary cathodes to the steel and accelerate its
anodic dissolution, that is, its corrosion.
Magnesium, zinc and zinc-base alloy are nearly
always less noble and tend to divert the attack
from the steel to themselves. The galvanic
relationship of various metals is an important factor
affecting corrosion.

Gamma Iron

The allotropic form of iron existing between the
temperature 910 deg C and 1400 deg C is known as
Gamma Iron. It has a face centred cubic lattice and
is non-magnetic. Gamma iron containing carbon or
other elements in solution is known as austenite.

Gas Carburising

A heat treatment method used in the case-
hardening of steel. Carbon is absorbed into the
outer layers of the components by heating in a
current of gas, rich in carbon compounds. The
process is more versatile than some other methods
as the depth of the case and the limiting carbon
content of the case can be controlled by the
composition of the atmosphere, the dew point and
the temperature.

Gauge Length

Used in the mechanical testing of steel, it is the
length marked on the parallel portion of a tensile
test piece from which the elongation is measured.

Gauge Plate

An alloy tool steel supplied in flat and square
section with the surfaces ground to close limits. It
is also known as Ground Flat Stock and is used for
the manufacturing of gauges, punches, dies, jigs,
templates etc.

Ge

Chemical symbol for Germanium.

Grain Size

Control When a steel is austenitised by heating to above
the critical range, time is required for the
production of a homogeneous structure during
which there is a tendency towards grain growth.
Although subsequent hot and cold working affect
the grain size, it is originally controlled at the steel
making stage by the addition ofaluminium.

Grain Size Measurement

Grain size is normally quantified by a numbering
system. Coarse 1-5 and fine 5-8. The number is
derived from the formula N=2n-1 where n is the
number of grains per square inch at a magnification
of 100 diameters. Grain size has an important
effect on physical properties. For service at
ordinary temperatures it is generally considered
that fine grained steels give a bettercombination of
strength and toughness, whereas coarse grained
steels have better machinability.

Graphitising

An annealing process applied to cast iron and
steels with a high carbon and high silicon content
by which the combined carbon is wholly or in part
transformed to graphitic or free carbon.

Grey Iron

Also known as flake iron on account of all or part of
the carbon content being in the form of graphite
distributed through the metal as flakes.

Grinding

A machining process:- (a) to shape components
that are too hard to be machined by conventional
methods such as hardened tool steels and case or
induction hardened components. (b) to obtain a
high degree of dimensional accuracy and surface
finish on a component.

Grinding Cracks

Cracks can arise from incorrect grinding and appear
in the form of a network. They are caused by the
generation of high heat and rapid cooling in the
area of contact and they mostly occur when
grinding fully hardened material such as tool steel.

H

Chemical symbol for Hydrogen.

Hard Metal Facing

A method of increasing the wear resistance of a metal
by the deposition of a hard protective coating. Alloys
such as Stellite or a metallic carbide are most often
used for the coating.

Hard Metals

A group of materials more commonly known as
cemented carbides. They consist of mixtures of one or
more of the finely divided carbides of tungsten,
titanium, tantalum and vanadium embedded in a
matrix of cobalt or nickel by sintering. Widely used for
cutting tools where for many applications they have
replaced conventional high speed steels.

Hardenability

The property that determines the depth and
distribution of hardness when steel is heated to a
given temperature and then quenched (more precisely
it may be defined as an inverse measure of the
severity of cooling conditions necessary to produce on
continuous cooling a martensitic structure in a
previously austenitized steel i.e. to avoid
transformations in the pearlitic and bainitic ranges).
The lower the cooling rate to avoid these
transformations, the greater the hardenability. The
critical cooling rate is largely a function of the
composition of the steel. In general the higher the
carbon content, the greater the hardenability, while
alloying elements such as nickel, chromium,
manganese and molybdenum increase the depth of
hardening for a given ruling section.

Hardening

Increasing the hardness of steel by heat treatment.
This normally implies heating the steel to a required
temperature and quenching in a suitable medium, e.g.
oil or water.

Hardness

The hardness of steel is generally determined by
testing its resistance to deformation. A number of
methods are employed including Brinell, Vickers and
Rockwell. The steel to be tested is indented by a
hardened steel ball or diamond under a given load
and the size of the impression is then measured. For
steel there is an empirical relationship between
hardness and tensile strength and the hardness
number is often used as a guide to the tensile
strength, e.g. 229 Brinell = 772N/mm2 (50 tons/sq.in).

Heat

In steel making terms this is often used to define the
batch or cast produced from a single melting
operation.

Heat Treatment

A process where solid steel or components
manufactured from steel are subject to treatment by
heating to obtain required properties, e.g. softening,
normalising, stress relieving, hardening. Heating for
the purpose of hot-working as in the case of rolling or
forging is excluded from this definition.

High Speed Steel

The term `high speed steel' was derived from the fact
that it is capable of cutting metal at a much higher
rate than carbon tool steel and continues to cut and
retain its hardness even when the point of the tool is
heated to a low red temperature. Tungsten is the
major alloying element but it is also combined with
molybdenum, vanadium and cobalt in varying
amounts. Although replaced by cemented carbides for
many applications it is still widely used for the
manufacture of taps, dies, twist drills, reamers, saw
blades and other cutting tools.

Hooke's Law

This states that "within the limits of elasticity the
strain produced by a stress of any one kind is
proportional to the stress". The stress at which a
material ceases to obey Hooke's Law is known as the
limit of proportionality.

Hot Quenching

Cooling in a medium, the temperature of which is
substantially higher than room temperature.

Hot Work

The rolling, forging or extruding of a metal at a
temperature above its recrystallisation point.

Hydrogen

An undesirable impurity if present in steel and a cause
of fine hairline cracks especially in alloy steels.
Modern vacuum treatment eliminates this problem.
Steel
Hyper-Eutectoid A steel that contains more than 0.83% carbon which
with appropriate heat treatment consists of pearlite
and cementite.

Hypo-Eutectoid Steel

A steel that contains less than 0.83% carbon and
which in annealed condition has a structure of ferrite
and pearlite.

I

Chemical symbol for Iodine.

Impact Test

A test designed to give information on how a
specimen of a known material will respond to a
suddenly applied stress, e.g. shock. The test
ascertains whether the material is tough or
brittle. A notched test piece is normally
employed and the two methods in general use
are either the Izod or Charpy test. The result is
usually reported as the energy in ft.lbs. or KJ.
required to fracture the test piece.

In

Chemical symbol for Indium.

Inclusion Count A method of assessing the number and size of
non-metallic inclusions present in metal.

Inclusions

Usually non-metallic particles contained in
metal. In steel they may consist of simple or
complex oxides, sulphides, silicates and
sometimes nitrides of iron, manganese, silicon,
aluminium and other elements. In general they
are detrimental to mechanical properties but
much depends on the number, their size,
shape and distribution.

Induction Hardening

A widely used process for the surface
hardening of steel. The components are
heated by means of an alternating magnetic
field to a temperature within or above the
transformation range followed by immediate
quenching. The core of the component remains
unaffected by the treatment and its physical
properties are those of the bar from which it
was machined, while the hardness of the case
can be within the range 37/58 Rc. Carbon and
alloy steels with a carbon content in the range
0.40/0.45% are most suitable for this process.

Ingot

The mass of metal that results from casting
molten steel into a mold. An ingot is usually
rectangular in shape and is subsequently rolled
into blooms and billets for rods, bars and
sections and slabs for plates, sheet and strip.
With the increasing use of the continuous
casting process the ingot route is less used as
the molten steel is now directly cast into a
bloom or billet.

Ingot Mold

The receptacle into which molten steel is
poured to form an ingot. After solidification the
steel is suitable for subsequent working, i.e.
rolling or forging.

Intercrystalline Corrosion

Chromium-nickel austenitic stainless steels are
prone to this form of corrosion when they are
welded and subsequently in contact with
certain types of corrosive media. When heated
within a temperature range of 450-800 deg C
precipitation of the chromium carbides takes
place at the grain boundaries in the area of the
weld and these areas no longer have the
protection of the chromium on the peripheries
of the grains. This type of corrosion is also
known as Weld Decay and Intergranular
Corrosion. The most common way to avoid the
problem is to select a grade of steel that is
very low in carbon i.e. 0.03% or less, or one
that is stabilised with niobium or titanium.

Interrupted Quenching

Rapid cooling to a selected temperature by
quenching in a suitable medium, usually molten
salt, holding at the temperature for an
appropriate time and then cooling to room
temperature. This process is used to minimise
the risk of distortion.

Iron

The term iron, as used in the chemical or
scientific sense of the word, refers to the
chemical element iron or pure iron and is the
chief constituent of all commercial iron and
steel.

Isothermal Annealing

Heating to and holding at a temperature above
the transformation range, then cooling to and
holding at a suitable temperature until the
austenite to pearlite change is complete.

Isothermal Transformation

Also known as the Time Temperature
Curve Transformation Curve. If a small piece of steel
is heated sufficiently slowly for it to become
austenitic and then plunged into a salt bath
and held at a constant temperature below the
upper critical point for a definite time followed
by rapid quenching, it is possible by
examination to determine the extent to which
the transformation of the austenite has
occurred. By taking a number of specimens of
the same steel and treating them in the same
way, but varying the holding temperature and
time the behavior of the steel with time and
temperature can be studied. The information
obtained can be plotted as time-temperature
transformation curves which is useful in heat
treatment practice, particularly for
martempering and austempering.

Izod

Impact Test A test specimen, usually of square crossed
section is notched and held between a pair of
jaws, to be broken by a swinging or falling
weight. When the pendulum of the Izod testing
machine is released it swings with a downward
movement and when it reaches the vertical the
hammer makes contact with the specimen
which is broken by the force of the blow. The
hammer continues its upward motion but the
energy absorbed in breaking the test piece
reduces its momentum. A graduated scale
enables a reading to be taken of the energy
used to fracture the test piece. To obtain a
representative result the average of three tests
is used and to ensure that the results conform
to those of the steel specification the test
specimens should meet the standard
dimensions laid down in BS 131.

Jominy Test

A method for determining the hardenability of steel. The Jominy
test is covered by BS 4437:1987. A standard test piece 25mm x
100mm is heated to a pre-determined temperature and
quenched by a jet of water sprayed onto one end. When the
specimen is cold, hardness measurements are made at intervals
along the test piece from the quenched end and the results are
plotted on a standard chart from which is derived the
hardenability curve. BS 970 contains hardenability curves for
many of the steels in the Standard. Properly carried out, this
test will illustrate the effect of mass upon a chosen steel when
heat treated and indicate if the steel is of a shallow, medium or
deep hardening type.

Joule

A unit of energy. One joule is equal to the energy expended in
one second by one ampere against the resistance of one ohm.
In the mechanical testing of steel it is the unit used in the
Charpy V notch impact test.

K

Chemical symbol for potassium.

A method of producing steel from molten iron, using
Kaldo Process an inclined rotating converter and a water cooled
oxygen lance inserted through the converter mouth.
Originating in Sweden, this process is no longer in use
in the UK.

Killed Steel

The term indicates that the steel has been completely
deoxidised by the addition of an agent such as silicon
or aluminium, before casting, so that there is
practically no evolution of gas during solidification.
Killed steels are characterised by a high degree of
chemical homogeneity and freedom from porosity.

Knoop Hardness Test

A micro hardness test in which an elongated
pyramidical diamond is pressed into the surface.

La

Chemical symbol for Lanthanum.

Lap

A defect appearing as a seam on a rolled bar. Laps
are rolled over pieces of material that arise when a
bar is given a pass through the rolls after a sharp
overfill or fin has been formed, causing the
protrusion to be rolled into the surface of the
product. The presence of oxides usually prevents
the lap welding to the original bar surface, so that
in subsequent cold working it is carried through as
a longitudinal crack.

L-D Process

An oxygen steel making process named after the
towns in Austria, Linz and Donawitz, where it was
first developed. It is a modified Bessemer process,
steel is produced in a solid bottom converter by
injection of oxygen into the molten iron bath from a
water cooled lance inserted through the converter
mouth. Present day BOS (basic oxygen
steelmaking) plants are developments of the L-D
Process.

Leaded Steels

When added to steel, lead does not go into
solution but exists in a very finely divided state
along the grain boundaries. It greatly assists
machinability as it acts as a lubricant between the
steel and the tool face. Lead is normally added in
amounts between 0.15-0.35% and when combined
with similar amounts of sulphur, optimum
machinability is attained as in such steel as BS 970
230M07 Pb.

Li

Chemical symbol for Lithium.

Limiting

Range of The greatest range of stress that a metal can
Stress withstand for an indefinite number of cycles without
failure. If exceeded, the metal fractures after a
certain number of cycles, which decrease as the
range of stress increases.

Limiting Ruling Section

The maximum diameter of cross section of a bar or
component in which certain specified mechanical
properties are achieved after heat treatment.

Limits

A term used to determine a minimum and
maximum. In a mechanism, it should denote the
minimum and maximum sizes for each part,
between which the parts will function properly in
conjunction with each other and outside of which
they will not. The words "limits" and "tolerances"
are often interchanged, "tolerance" represents the
difference between the minimum and maximum
limits.

Limits of Proportionality

The stress (load divided by original area of cross
section of the test piece) at which the strain
(elongation per unit of gauge length) ceases to be
proportional to the corresponding stress. It is
usually determined from a load-elongation diagram,
obtained by plotting extensometer readings and is
the stress at which the load-elongation line ceases
to be straight.

Liquid Carburising

A widely used method of case-hardening steel that
eliminates scaling and the tendency to
decarburisation and results in clean components.
Sodium cyanide is the common media for this
process, usually heated within the range of
900-930 deg C. It is advisable to pre-heat the
components in neutral salts to avoid a temperature
drop resulting from immersing cold components into
the cyanide. After carburising, either single quench
hardening or refining and hardening and tempering
is carried out.

Machinability

Simply defined as a measure of the ease with
which a metal can be machined satisfactorily.

Macrostructure

The general crystalline structure of a metal and
the distribution of impurities seen on a polished
or etched surface by either the naked eye or
under low magnification of less than x10.

Magnetic Crack Detection

The bar or component to be tested is
magnetised by passing a heavy current through
it or by making it the core of a coil through
which a heavy current is passed. Cracks or
inclusions cause the magnetic flux to break the
surface forming free magnetic poles. When the
component is sprayed with a suspension of
finely divided magnetic particles they collect at
the free poles to visibly show the presence of
defects.

Malleability

It can be defined as the property of a metal to
be deformed by compression without cracking or
rupturing. The load may be applied slowly or
suddenly and will determine whether the
material will be suitable for forging or rolling into
thin sheet.

Manganese

One of the most important constituents of steel
in which it fulfils a number of functions. It acts
as a mild de-oxidising agent. It combines with
the sulphur present to form globular inclusions
of Manganese Sulphide which are beneficial to
machining. It increases tensile strength and the
hardenability of steel.

Martempering

A heat treatment involving austenitisation
followed by step quenching, at a rate fast
enough to avoid the formation of ferrite, pearlite
or bainite to a temperature slightly above the Ms
point. Soaking must be long enough to avoid
the formation of bainite. The advantage of
martempering is the reduction of thermal
stresses compared to normal quenching. This
prevents cracking and minimises distortion.

Martensite

The hard constituent produced when steel is
cooled from the hardening temperature at a
speed greater than its critical cooling rate.
Martensite is an acicular phase when seen in
the microstructure of steel.

Mass

Effect A term used to signify the effect of size and
shape during heat treatment, since it is the rate
of cooling of a piece of steel which determines
the properties resulting from the hardening and
quenching process.

Matrix

The mass or principal constituent (e.g. iron in
the case of steel) in which other constituents
are embedded.

Maximum Stress

In the testing of the strength of steel a sample
is machined into a standard test piece and is
stretched in a tensile testing machine until it
breaks. The results are expressed in N/mm2 and
is the value of the maximum load reached in the
test divided by the original cross sectional area
of the specimen.

McQuaid EHN Grain Size

A method of assessing grain size. It consists of
Test a test piece at 927 deg C for 8 hours by slow
cooling and subsequent microscopical
examination. The grain size is measured at x100
magnification and compared to standard charts,
the figures range from No. 1 -very coarse, to
No. 8 - very fine.

Meehanite

A trade name applied to a certain type of cast
iron.

Melting Point The temperature at which a solid begins to
liquefy.

Mg

Chemical symbol for Magnesium.

Micron

A unit of length equal to one millionth of a
metre (0.001mm).

Microstructure

The structure that is observed when a polished
and etched specimen of metal is viewed in an
optical microscope at magnifications in range of
approximately x25 to x1500.

Mn

Chemical symbol for Manganese.

Mo

Chemical symbol for Molybdenum.

Modulus of Elasticity

When a material is subjected to an external load
it becomes distorted or strained. With metals,
provided the loading is not too great, they return
to their original dimensions when the load is
removed, i.e. they are elastic. Within the limits
of elasticity, the ratio of the linear stress to the
linear strain is termed the modulus of elasticity
or more commonly known as Young's Modulus.

Molybdenum

Its use as an alloying element in steel increases
hardenability and in low alloy steels reduces the
risk of temper brittleness. When added to
stainless steels it increases their resistance to
corrosion. It is also used in high speed steels.

N

Chemical symbol for Nitrogen.

Na

Chemical symbol for Sodium.

Nb

Chemical symbol for Niobium.

Ni

Chemical symbol for Nickel.

Nickel

One of the most widely used alloying elements in
steel. In amounts 0.50% to 5.00% its use in alloy
steels increases the toughness and tensile strength
without detrimental effect on the ductility. Nickel
also increases the hardenability, thus permitting the
steel to be oil-hardened instead of water quenched.
In larger quantities, 8.00% and upwards, nickel is
the constituent, together with chromium, of many
corrosion resistant and stainless austenitic steels.

Niobium

Also known as columbium. Niobium is a strong
carbide forming element which is added to certain
18/8% chromium-nickel stainless steels as a
stabiliser to prevent inter-granular corrosion arising
from welding.

Nitriding

A case hardening process that depends on the
absorption of nitrogen into the steel. All machining,
stress relieving, as well as hardening and tempering
are normally carried out before nitriding. The parts
are heated in a special container through which
ammonia gas is allowed to pass. The ammonia splits
into hydrogen and nitrogen and the nitrogen reacts
with the steel penetrating the surface to form
nitrides. Nitriding steels offer many advantages: a
much higher surface hardness is obtainable when
compared with case-hardening steels; they are
extremely resistant to abrasion and have a high
fatigue strength.

Nitrogen

Nitrogen is a gas that forms approximately 79% by
volume or 77% by weight of the atmosphere. It can
combine with many metals to form nitrides and is
thus applied to the case-hardening of steel, the
usual source for this purpose being ammonia.

Noble Metals

Metals such as gold, silver and platinum which are
resistant to corrosion by all but the most powerful
acids.

Non Destructive

Those forms of testing that do not result in
Testing permanent damage or deformation to the part being
tested. Typical examples are magnetic crack
detection, ultrasonic inspection, X-Ray inspection
and gamma radiography.

Non Magnetic Steels

Austenitic steels such as the 14% manganese steels
and the 303 type 18/8% chromium-nickel stainless
steels.

Normalising

A heat treatment process that has the object of
relieving internal stresses, refining the grain size and
improving the mechanical properties. The steel is
heated to 800-900 deg C according to analysis, held at
temperature to allow a full soak and cooled in still
air.

Notched Bar Test

A test to determine the resistance of a material to a
suddenly applied stress, i.e. shock. A notched test
piece is employed in an Izod or Charpy machine and
the results are recorded in ft.lbs. or Joules.

O

Chemical symbol for Oxygen.

Occlusion

A term applied, in the case of metals, to the
absorption or entrapment of gases.

Oil Hardening Steel

Used to describe tool or alloy steels where oil is
used as the quenching medium in the hardening
process.

Open Hearth Furnace

Developed in the middle of the last century, the
open hearth or Siemens-Martins process, as it is
known, accounted for a major proportion of UK steel
production until the early 1970's. For economic and
quality reasons it has been replaced by the Electric
Arc Furnace and the Basic Oxygen Steelmaking
process. There are no open hearth furnaces in use
in Britain today but they are still in use in Russia and
Eastern Europe.

Orange Peel Effect

An effect that arises on the surface of steel sheets
when they are stretched beyond their elastic limit.

Ore An ore is a material that contains a metal in such
quantities that it can be mined and worked
commercially to extract that metal. The metal is
usually contained in chemical combination with some
other element in addition to various impurities.

Os

Chemical symbol for Osmium.

Overheating

Failure of tools and components in heat treatment
can arise through overheating. This may be caused
due to quenching from a temperature too high for
the type of steel involved. Overheating is evidenced
by cracking, grain-coarseness, erratic surface
hardness and pitting.

Oxidation

A common form of chemical reaction which is the
combining of oxygen with various elements and
compounds. The corrosion of metals is a form of
oxidation, rust on iron for example is iron oxide.

Oxy-Acetylene Welding

A process for joining two pieces of metal in which
the required high temperature is obtained by the
combustion of acetylene gas and oxygen. The gases
are thoroughly mixed in the nozzle or tip of the
welding torch to ensure perfect combustion. The
weld may be formed directly between two adjoining
surfaces, but usually metal from a welding rod is
fused in between the surfaces of the joint.

Oxygen

Oxygen is one of the chief constituents of the
atmosphere of which it forms approximately one
fifth. It is odorless and invisible. Although oxygen
itself does not burn it is extremely efficient in
supporting combustion, nearly all other chemical
elements combine with it under evolution of heat. It
has many uses in industry and is essential to the
BOS (Basic Oxygen Steelmaking Process).

P

Chemical symbol for Phosphorus.

Parkerising

A chemical treatment applied to ferrous metals to
improve their corrosion resistance. The process is based
on a manganese phosphate solution which produces a
fairly thick coating. This can subsequently be painted or
impregnated with oil. Patenting A heat treatment process
often applied to high carbon wire. The steel is heated to
a suitable temperature well above the transformation
range, followed by cooling in air or a bath of molten lead
or salt. A structure is produced suitable for subsequent
cold drawing and which will give the desired mechanical
properties in the finished state.

Pd

Chemical symbol for Palladium.

Pearlite

A lamellar constituent of steel consisting of alternate
layers of ferrite (alpha-iron) and cementite (iron Carbide
Fe3C) and is formed on cooling austenite at 723 deg C. This
produces a tough structure and is responsible for the
mechanical properties of unhardened steel.

Ph

Chemical symbol for Lead.

pH Value

A method of expressing differences in the acidity or
alkalinity of a solution. A figure of 7 is regarded as
neutral, figures below this indicate the decree of acidity
and above alkalinity.

Phosphorus

An element that forms 0.12% of the earth's crust, chiefly
in the form of phosphates. Its presence in steel is usually
regarded as an undesirable impurity due to its embrittling
effect, for this reason its content in most steels is limited
to a maximum of 0.050%.

Pickling

A process to chemically remove scale or oxide from steel
to obtain a clean surface. When applied to bars or coils
prior to bright drawing, the steel is immersed in a bath of
dilute sulphuric acid heated to a temperature of around
80 deg C. An inhibitor is added to prevent attack and pitting
of the cleaned metal. After pickling, a washing process
takes place followed by immersion in a lime-water bath to
neutralise any remaining acid. For environmental reasons
shot blasting has largely replaced pickling.

Pig Iron

The product of the blast furnace. The term was derived
from the method of casting the bars of the pig iron in
depressions or molds formed in the sand floor adjacent
to the furnace. These were connected to a runner
(known as a sow) and when filled with metal the runner
and the numerous smaller molds were supposed to
resemble a litter of suckling pigs, hence the term pig
iron.

Pinch Pass

A term applied when, after annealing, sheet or strip is
lightly rolled with the object of preventing stretcher lines
or kinks on subsequent cold working.

Pipe

A defect that arises during the solidification of steel in
the ingot mold. As steel contracts on solidification a
central cavity forms in the upper portion of the ingot, if
this is not completely removed before rolling into bars a
central defect known as "pipe" results. The risk of piping
is considerably reduced on continuously cast steel due to
molten steel being available to fill any shrinkage cavity.

Poisson's Ratio

If a square bar is stressed in a testing machine in the
direction of its length so that the length increases, there
is a contraction in each opposite direction, which
produces a decrease in the thickness of the bar. The
ratio between the contraction at right angles to a stress
and the direct extension is called the Poisson's ratio. Its
value in steel is in the order of 0.28.

Pot Quenching

Quenching carburised parts directly from the carburising
pot or box.

Powder Metallurgy

A method of producing components by pressing or
molding metal powders which may be simultaneously or
subsequently heated to produce a coherent mass.

Pre-Heating

Used in the hardening process. Tools are pre-heated
before heating to the final temperature, this is
particularly important in tools of complex shape to
prevent distortion or cracking. Pre-heating reduces the
time of exposure to the hardening temperature and helps
to minimise scaling and decarburisation.

Projection Welding

A welding process that uses small projections on one or
both components of the weld to localise the heat and
pressure, the projections collapse when the weld is
made.

Proof Stress

The stress that will cause a specified small, permanent
extension of a tensile test piece. Commonly the stress to
produce 0.2% extension is quoted in N/mm2 for steel.
This value approximates to the yield stress in materials
not exhibiting a definite yield point.

Quenching

Rapid cooling from a high temperature by immersion in a
liquid bath of oil or water. Molten salts may also be used.

Quenching Crack

A fracture, often termed a hardening crack, which arises
from thermal stresses induced during rapid cooling.

Ra

Chemical symbol for Radium.

Radiography

A method of non-destructive testing. Internal
examination of a metallic structure or component
is carried out by exposing it to a beam of X-Ray
or gamma radiation. Internal defects can be
seen on a screen or recorded on film.

Rb

Chemical symbol for Rubidium.

Re

Chemical symbol for Rhenium.

Re-crystallisation

The re-arrangement of crystals in cold worked
metal brought about by heating so that the
deformed crystals are absorbed by newly-formed
crystals and the effects of work hardening are
removed. Also occurs when steel is heated
through the transformation range and when steel
is hot worked.

Red Hardness

A term sometimes associated with high speed
steel because it has the property of retaining
sufficient hardness for cutting metals even when
heated to a temperature high enough to cause a
dull redness. The tungsten content has a
significant influence on this property.

Reduction of area The percentage decrease in the cross-sectional
area of a tensile test piece caused by wasting or
necking of the specimen. It is expressed as a
percentage of the original area of the test piece
and is a measure of ductility.

Refining (a)

The removal of impurities and metallic oxides
from the molten bath by the reaction of the slag
and other additions. (b) A heat treatment
process with the object of refining or making the
grain size of the steel uniform.

Residual Stress

The stress which exists in an elastic solid body
in the absence of, or in addition to, the stresses
caused by an external load. Such stresses can
arise from deformation during cold working such
as cold drawing or stamping, in welding from
weld metal shrinkage, and in changes in volume
due to thermal expansion.

Rh

Chemical symbol for Rhodium.

Rockwell Hardness Testing

A method for testing the hardness of metals by
determining the depth of penetration of a steel
ball or a diamond sphero-conical indentor. The
value is read from a dial and is an arbitrary
number related to the depth of penetration. For
testing hard steels, a sphero-conical diamond is
used with a 150 kg load, the result is read from
the black scale on the dial and is prefixed with
the letter C. A hardened tool steel would
typically give a reading of 62Rc. For softer
metals Scale B is used with a 1/16" diameter
steel ball and a standard load of 100 kgs.

Rolling

The process of shaping metal by passing it
between rolls revolving at the same peripheral
speed and in opposite directions. In steel there
are a number of different types of rolling mill for
processing the ingot to its finished shape. These
are variously known as Cogging mills, Slabbing
mills, Billet mills, Bar mills and Strip mills, which
produce plate, sections, bars, sheet and strip.
Cold rolling of previously hot rolled strip is
carried out to produce strip that is accurate to
size and with a smooth bright polished surface.

Rolling Lap

A fault arising from the overfilling or mis-
alignment of rolls, the result is a bulge on the
bar which is rolled into the metal and is lapped
over. It remains throughout subsequent working
and appears as a longitudinal crack.

Ru

Chemical symbol for Ruthenium.

Ruling Section

More accurately termed limiting ruling section.
One of the most important factors associated
with the choice of steel for a given purpose is to
ensure that the desired mechanical properties
are obtained throughout the section when the
material has been heat treated. The limiting
ruling section determines the maximum diameter
or cross-section of a bar or component in which
the specified properties can be achieved by a
given heat treatment. The analysis of the steel
also has an important bearing on this.

S

Chemical symbol for Sulphur.

Salt Bath

A method of heating steel using a bath of molten salts.
Salt baths give uniform heating and prevent oxidation,
they are used for hardening, tempering or quenching. The
type of salt used depends on the temperature range
required. For hardening, sodium cyanide, sodium
carbonate and sodium chloride are in common use.

Sb

Chemical symbol for Antimony.

Scale

The oxidised surface of steel produced during hot working,
as in rolling, and by exposure to air or steam at elevated
temperature.

Scarfing

Also termed deseaming. It is a process for burning out
defective areas on the surface of ingots or semi-finished
products such as billets so that the product is suitable for
subsequent rolling or forging.

Scrap

It forms the basic raw material for making steel by the
electric arc process. Steel offers ecological advantages as
it can be recycled enabling the discarded car of today to
appear as part of a new model tomorrow. Scrap is sorted
and graded before use and the necessary elements are
added during the steel making process to achieve the
desired specifications.

Se

Chemical symbol for Selenium.

Seams

A surface defect caused during the steel making process. Seams are
generally formed from blow holes in the ingot, non metallic
inclusions, or stresses arising during the solidification
stage. They appear as longitudinal discontinuities in the
bar.
Secondary Hardness

An increase in hardness which sometimes occurs when
hardened steel is re-heated. It can be caused by the
transformation of retained austenite to martensite or by
the precipitation of alloy carbides.

Segregation

A term applied to the concentration and partial separation
of one or more elements from solution during solidification
of liquid steel in an ingot mold. Sulphur and phosphorus
tend to segregate to a greater extent than other elements
which can have a particular adverse effect on machinability
in high sulphur free-cutting steels. Modern steel making
and continuous casting have largely overcome this
problem.

Selenium

An element that closely resembles sulphur in its properties.
The main use in steel is as a freecutting additive but due
to high cost its use is limited to stainless steel. One of the
benefits being the ability to obtain a very good surface
finish on machined components.

SG Iron

An abbreviation for Spheroidal Graphite Cast Iron. As the
name implies, graphite is present in spheroidal form
instead of flakes and compared with Grey Cast Iron it has
higher mechanical strength, ductility and increased shock
resistance.

Shearing

Test The test applied to metal to determine the stress required
to fracture it across its section.

Sherardizing

A process developed in Britain in 1904 by Sherard
Cowper-Coles. It is a method of producing a protective
zinc coating on iron and steel products.

Shore

An instrument that measures the hardness of a sample in
Scleroscope arbitrary terms of elasticity. A diamond tipped hammer is
allowed to fall freely down a graduated glass tube on to
the sample under test. The hardness is measured by the
height of the rebound. In another form the rebounding
hammer actuates the pointer of a scale so that the height
of the rebound is recorded.

Spinning

The formation of sheet metal blanks into hollow circular
shapes. This is carried out on a lathe with forming tools
which service to press and shape the metal. Annealing
may be needed during and/or after the operation to
remove the effects of work hardening.

Spot Welding

A process for joining steel sheets. The two parts are held
between electrodes and the heat generated at the
interface between the sheets causes local welding when
pressure is applied.

Spring Steel

The steels used for spring making depend on the
application and type of spring. They range from plain
carbon grades in the range 0.5% to 1.00% C. to
Chromium, Chromium-Vanadium,
Nickel-Chromium-Molybdenum, Silico-Manganese and
Silicon-Manganese-Chromium-Molybdenum types. Full
details can be found in BS5770.

Stabilisation

A term applied to a number of processes: a) A type of heat
treatment to relieve internal stresses: b) The retarding or
prevention of a particular reaction by the addition of a
stabilising element; c) A thermal and/or mechanical
treatment given to magnetic material in order to increase
the permanency of its magnetic properties or condition.

Stainless Steel Can be defined as a group of corrosion resisting steels
containing a minimum 10% chromium and in which varying
amounts of nickel, molybdenum, titanium, niobium as well
as other elements may be present. An Englishman, Harry
Brearley, is generally acknowledged to be the pioneer who
developed stainless steels for commercial use.

Steel

Generally defined as a metallic product whose principal
element is iron and where the carbon content is not more
than 2%. (The presence of large quantities of carbide
forming elements may modify the upper limit of the carbon
content.)

Strain Ageing

The gradual changes in physical and mechanical
properties, in particular hardness and tensile strength,
which takes place following cold rolling or deformation. At
atmospheric temperatures, this may take place over a
number of weeks but can be accelerated by heating.

Strain Hardening

The loss of ductility and gain in hardness resulting from
strain ageing.

Stress

Relieving A heat treatment including heating and soaking at a
suitable temperature (e.g. 600-650 deg C) followed by cooling
at an appropriate rate in order to reduce internal stresses
without substantially modifying the steel's structure. This
treatment may be used to relieve stresses induced by
machining, quenching, welding or cold working.

Stress Strain

A graph in which stress (load divided by the original cross
Curve sectional area of the test piece) is plotted against strain
(the extension divided by the length over which it is
measured).

Sub-Critical Heating to, and holding at, some point below the critical
Annealing temperature. Subsequent cooling may be in air. This form
of heat treatment has a variety of uses depending on the
temperature and specification of the steel, its purpose is
often to soften the material.

Sub-zero

A low temperature treatment carried out after quenching
Treatment on hardened steel to transform the retained austenite into
martensite. It involves immersing the component in a bath
of solid carbon dioxide at a temperature of minus 70-80 deg C.

Sulphur

Generally regarded as an impurity in steel as it can have
detrimental effects on strength, ductility and weldability as
well as producing hot and cold shortness. Its content in
most steels is limited to a maximum of 0.050%. Sulphur is
beneficial to machining and is added to freecutting steels
in amounts up to 0.35% with the manganese content
increased to overcome any detrimental effects.

Surface

A method of hardening the surface of steel to increase its
Hardening wear resistance. Depending on the analysis of the steel,
the following treatments can be employed:
Case-hardening, Nitriding, induction hardening, Flame
hardening.

Swaging

A method of forming or reducing steel or other metals to a
desired shape by a series of blows rapidly applied by dies
or hammers. The process is applied to wires, rods and
tubes and can be used for a variety of pointing, tapering,
sizing and reducing operations.

Swarf

The particles of metal arising from machining or grinding
operations, much of it finds its way to the steel maker for
remelting.

Ta

Chemical symbol for Tantalum.

Tantalum

A rare metal of silver white color having
excellent corrosion resistance and a high
melting point. It is widely used for chemical
process equipment and specialised
aero-space and nuclear applications.

Te

Chemical symbol for Tellurium.

Tellurium Its main use in the steel industry is as an
additive in leadbearing freecutting steels to
further improve their machinability. Its
presence in the steel is either within the
manganese sulphide particles, where it is
partially soluble, or as particles combined
with lead or manganese. For certain
applications it offers significant improvements
in machinability but the added cost is a factor
that should be taken into account.

Temper

A term to which a number of definitions can
be applied. These include: a) The operation
of tempering; b) The degree of hardness left
in a steel bar after quenching and tempering;
c) The grading of the hardness of low carbon
cold rolled strip, e.g. Hard, Half Hard,
Quarter Hard, Skin Passed, Soft; d) An
indication of the amount of carbon present in
a tool steel, e.g. razor temper, file temper,
die temper, etc.

Temper Brittleness

The loss in impact resistance that is present
in some low and medium carbon alloy steels
when tempered in the range of 350 deg C -
600 deg C. It is revealed by the notched bar
impact test but not the tensile test.

Temper Colors

Before the use of instruments such as
pyrometers, colors were used to judge
temperatures when hardening and tempering.
For example, on carbon tool steel where the
tempering range may typically be from 200 deg C
to 350 deg C, the colors change with the rise in
temperature giving Light Straw at around
210 deg C, Purple at 275 deg C, and Grey at 330 deg C.
The practice still continues in workshops
where controlled heat treatment facilities are
not available.

Temper Rolling

A light pass given to annealed cold rolled
strip to prevent the formation of kinks and
stretcher strain markings on subsequent cold
working. Also termed Pinch pass and Skin
pass.

Tempering

A heat treatment applied to ferrous products
after hardening. It consists of heating the
steel to some temperature below the
transformation range and holding for a
suitable time at the temperature, followed by
cooling at a suitable rate. The object of
tempering is to decrease hardness and
increase toughness to produce the desired
combination of mechanical properties.

Tensile Strength

The maximum load applied in breaking a
tensile test piece divided by the original
cross-sectional area of the test piece.
Originally quoted as tons/sq.in. it is now
measured as Newtons/sq.mm. Also termed
Maximum Stress and Ultimate Tensile Stress.

Tensile Test

A standard test piece is gripped at either end
by suitable apparatus in a testing machine
which slowly exerts an axial pull so that the
steel is stretched until it breaks. The test
provides information on proof stress, yield
point, tensile strength, elongation and
reduction of area.

Thomas Process

The Continental name for the basic Bessemer
steel making process, now superseded by
modern day BOS plants.

Ti

Chemical symbol for Titanium.

Time Temperature An isothermal transformation diagram
Transformation Curve showing the relationship between
temperature and the time taken for the
decomposition of austenite when the
transformation occurs at constant
temperature.

Tin

When present in steel it is an undesirable
impurity which gives rise to temper
brittleness. When used as a coating on steel,
it has a good resistance to corrosion for many
applications.

Titanium

Small amounts added to steel contribute to
its soundness and give a finer grain size. In
austenitic stainless steels it acts as a carbide
stabiliser and is used to prevent
intercrystalline corrosion, commonly termed
"weld decay". Titanium carbide is also used
with tungsten carbide in the manufacture of
hard metal tools.

Tolerances

The amount of variation permitted on
dimensions or surfaces. The tolerance is
equal to the difference between the maximum
and minimum limits of any specified
dimension.

Tool Steel

A generic term applied to a wide range of
steels, both plain carbon and alloy. It
includes steels suitable for various types of
cutting tools, press tools, hot and cold
heading dies, molds for plastics and die-
casting, extrusion tools, hand tools, etc.

Torsional Strength

The resistance of a bar to twisting. Closely
related to its shear strength.

Toughness

The ability of a metal to rapidly distribute
within itself both the stress and strain caused
by a suddenly applied load, or more simply
expressed, the ability of a material to
withstand shock loading. It is the exact
opposite of "brittleness" which carries the
implication of sudden failure. A brittle
material has little resistance to failure once
the elastic limit has been reached.

Transformation Range

The temperature range within which austenite
forms and ferrite or carbide progressively
dissolves while ferrous alloys are being
heated. Also the temperature range within
which austenite decomposes to form ferrite
and carbide on cooling.

Transformation Temperature

The temperature at which a change in phase
occurs or the limiting temperature of a
transformation range. These critical points
are denoted by symbols, e.g. Ac1; the
temperature at which austenite begins to
form on heating. There are 12 principal
temperatures to which symbols are applied.

Transition Temperature

The temperature at which a transition from
ductile to brittle fracture takes place in steel.
It is usually determined by making a series of
Charpy impact tests at various temperatures,
the transition temperature is usually taken as
the point where 50% of the fracture is brittle.

Transverse Strength

A measurement of strength when the load is
applied across the longitudinal flow of the
grain of a metal. Certain impurities such as
sulphur have a detrimental effect on the
transverse strength. This can be minimised by
the inclusion modification process.

Transverse Test

A test taken at right angles to the principal
direction of rolling or forging.

TTT Curve

An abbreviation of Time Temperature
Transformation Curve.

Tufftriding

A form of surface hardening, the process
involves nitrogen but does not achieve the
hardness of conventional nitriding.

Tungsten

When used as an alloying element it
increases the strength of steel at normal and
elevated temperatures. Its "red hardness"
value makes it suitable for cutting tools as it
enables the tool edge to be maintained at
high temperatures. In conjunction with other
alloying elements it finds applications in heat
resisting and other severe service conditions.

U

Chemical symbol for Uranium.

Ultimate Analysis In chemistry, this is a quantitative analysis in which
percentages of all elements in the substance are
determined.
Ultimate Tensile
Strength The highest load applied in breaking a tensile test
piece divided by the original cross-sectional area of
the test piece.

Ultrasonic Inspection

A means of locating defects in steel. When acoustic
energy in the ultrasonic range is passed through
steel, the sound waves tend to travel in straight
lines, rather than diffusing in all directions as they
do in the audible range. If there is a defect in the
path of the beam it will cause a reflection of some
of the energy, depleting the energy transmitted.
This casts an acoustic shadow which can be
monitored by a detector placed opposite the
transducer or energy source. If the acoustic energy
is introduced as a very short burst, then the
reflected energy coming back to the originating
transducer can also be used to show the size and
depth of the defect. Ultrasonic techniques can be
used to detect deeply located defects or those
contained in the surface layer. Skill and experience
are required in interpreting the results portrayed on
the cathode ray tube.

Unkilled Steel

Steel which has been insufficiently deoxidised and
evolves gas during solidification with the formation
of blow-holes.

Upsetting

Working a piece of steel so that its length is
shortened and its cross-sectional area is increased.
Its effect is to increase ductility in the radial and
tangential directions.

Uranium

A white malleable metal which is softer than steel.
Its specific gravity is 18.7, it melts at a temperature
of 2400 deg C.

V

Chemical symbol for Vanadium.
 

Vacuum Arc

Remelting A process used for producing advanced steels to the
most demanding and critical specifications,
particularly in such areas as aerospace applications.
The steel is first produced to a very close analysis
and the resulting ingot is slowly remelted in a
Vacuum Arc Remelting furnace for up to 14 hours.
Such steels are, by necessity, expensive to
manufacture.

Vacuum Degassing

A ladle of molten metal is placed within a chamber
which is then evacuated. This reduces the gas
content, particularly hydrogen, as well as reducing
non-metallic inclusions. Modern secondary steel
making processes using Vacuum Arc Degassing units
that include automated stirring and control of
temperature and chemical analysis, ensure a
consistent and high quality product.

Vanadium

Steels containing vanadium have a much finer grain
structure than steels of similar composition without
vanadium. It raises the temperature at which grain
coarsening sets in and increases hardenability where
it is in solution in the austenite prior to quenching. It
also lessens softening on tempering and confers
secondary hardness on high speed steels. Vanadium
is used in nitriding, heat resisting, tool and spring
steels in conjunction with other alloying elements.

Vickers Hardness Test

A method of determining the hardness of steel
whereby a diamond pyramid is pressed into the
polished surface of the specimen and the diagonals
of the impression are measured with a microscope
fitted with a micrometer eye piece. The rate of
application and duration are automatically controlled
and the load can be varied.

W

Chemical symbol for Tungsten, from wolfram.

Welding

The process of joining together two pieces of metal
so that bonding accompanied by appreciable
interatomic penetration takes place at their original
boundary surfaces. The boundaries more or less
disappear at the weld, and integrating crystals
develop across them. Welding is carried out by the
use of heat or pressure or both and with or without
added metal. There are many types of welding
including Metal Arc, Atomic Hydrogen, Submerged
Arc, Resistance Butt, Flash, Spot, Stitch, Stud and
Projection.

Whiskers

Thin hair-like growths on metal that are barely
visible to the naked eye, they are stronger than the
metals from which they are formed, probably
because they are free from defects.

White Annealing

A heat treatment process carried out on pickled
steel with the objective of eliminating the hydrogen
that has entered the steel during the pickling
operation and thus removing any tendency to
hydrogen embrittlement.

Widmanstatten Structure

A microstructure resulting when steels are cooled
at a critical rate from extremely high temperatures.
It consists of ferrite and pearlite and has a
cross-hatched appearance due to the ferrite having
formed along certain crystallographic planes.

Wolfram

The alternative name for tungsten.

Woody

Fracture A fracture that is fibrous or woody in appearance
due to the elongation of the individual grains. This
may be accentuated by the presence of slag or by
a banded structure. It is grey and dull and is
characteristic of ductile but non-homogeneous
material such as wrought iron.

Work Hardening

The increase in hardness and strength produced by
cold plastic deformation or mechanical working.

Wrought Iron

A commercial iron that has little use today and has
been replaced by mild steel. It was commonly
produced by the puddling process. The
temperatures employed in its production are too
low to render it fluid, it is heated until it forms a
pasty mass then it is squeezed or forged. The
process does not lend itself to removal of
impurities so it contains an appreciable quantity of
slag. It will not respond to any heat treatment
designed to increase the hardness or strength.

X-Ray Crystallography

X-ray photographs of metals are a means of providing
information which in many cases cannot be obtained
by microscopic methods. The lines produced by each
element, or phase are characteristic, and their
general pattern enables the crystalline structure to be
identified. The scale of the pattern can be used to
determine accurately the size of the unit cell and,
therefore, the distance apart of the individual atoms.
From the relative intensity of the lines it is possible to
deduce the distribution throughout the unit cell, the
various types of atoms in an alloy or the degree of
preferred orientation in the material.

Yield Point

Can be defined as the point where a tensile test piece
begins to extend permanently. If the load is reduced to
zero, the test piece will not return to its original length.

Yield Strength

The stress at which general plastic elongation of the test
piece takes place. This point is well defined in hardened
and tempered or annealed structures but can be ill defined
in "as drawn" structures.

Young's Modulus

Within the limits of elasticity, the ratio of the linear stress
to the linear strain is termed the modulus of elasticity or
Young's Modulus and may be written Young's Modulus, or
E =(Stress/Strain) It is this property that determines how
much a bar will sag under its own weight or under a
loading when used as a beam within its limit of
proportionality. For steel, Young's Modulus is of the order
of 205000 N/mm2.

Zinc

Zinc is a metallic chemical element, it has a white color with a
bluish tinge. It has a high resistance to atmospheric corrosion and
a major use is as a protective coating for iron and steel sheet and
wire. Galvanised sheets are a prime example. The melting point
of zinc is 419 deg C.

Zirconium

Acts as a deoxidising element in steel and combines with sulphur.

Zn

Chemical symbol for Zinc.

Zr

Chemical symbol for Zirconium.