Term	Definition
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.
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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