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4/17/13 Maryland Metrics: Metals Glossary

mdmetric.com/tech/metalsglossary.htm

Maryland Metrics: Metals Glossary

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 above910 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.


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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 transformationrange 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 areaustenitic 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


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urnaces use as c n ngs.

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 therolling 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.


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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 thendetermined 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 alloysteels 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 elevatedtemperatures.

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


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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 andphosphorus 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 pouringmolten 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 thechemical 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


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n s coun ry. o are quo e n e curren

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 iscarried 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


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,

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.

ate

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


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.

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. thetemperature 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.


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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 duringsolidification 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


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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. Thesurface 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 shapeand 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


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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 electrodeis 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 expressedas 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


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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 toflow 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 waythat 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 scratchesor 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


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ron, a cons uen o car on s ee s.

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 tr im 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 causesconsiderable 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.


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,

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 asGamma 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, r ich 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 thecomposition 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


15/41



, , , ,

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 graphitedistributed 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 coatin .


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.

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 thecomposition 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

for in is excluded from this definition.


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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 formany 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 issubstantially 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.


18/41



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 butmuch 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 itwas 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 continuouscasting 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


19/41



orros on. e mos common way o avo e

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 andholding 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 whichthe 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


20/41



energy a sor e n rea ng e es p ece

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, usingKaldo 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


21/41


22/41



usua y e erm ne rom a oa -e onga on agram,

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 thecomponent 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


23/41



,

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).


24/41



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


25/41



.

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.


26/41



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 andcompounds. 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).


27/41



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 themechanical 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, chieflyin 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 processtakes 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


28/41



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 stressand 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-heatedbefore 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


29/41



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 steelis 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 ornecking 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 bodyin 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


30/41



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 agiven 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


31/41



.

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 thetransformation 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


32/41



,

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 mechanicaltreatment 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.


33/41



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 anumber 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 isbeneficial 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.


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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.


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,

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 rolledstrip 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 bycooling 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

tem erature.


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.

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. Inaustenitic 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 maximumand 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. Closelyrelated 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


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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 ofCharpy 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


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steel, the sound waves tend to travel in straight

lines, rather than dif

maryland metrics_ metals glossary.pdf

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