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 SteelSometimes 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.

   

AllotropyThe 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 SteelA 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 IronThe body centered cubic form of iron which, in pure iron,

  exists up to 910 deg C.

   

AnnealingHeating 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 FurnaceA 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.

   

AustemperingQuenching 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.

   

AusteniteThe 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.

   

BainiteAn 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 MetalA 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 TestBending 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.

   

BilletA 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.

   

BrazingBrazing 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 AnnealingAn 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 DrawingThe 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 DrawingThe 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.

  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

  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 FractureA 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

Drawingtemperatures (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

Latticeatomic 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.

   

FerriteThe solid solution of carbon in body-centered cubic

  iron, a constituent of carbon steels.

   

Ferritic SteelA 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.

   

FinIn 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.

   

FractureFractures 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 IronAlso 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 CracksCracks 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 FacingA 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.

   

HardeningIncreasing 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).

   

HeatIn 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 SteelThe 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.

   

HydrogenAn 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-EutectoidA steel that contains more than 0.83% carbon which

  with appropriate heat treatment consists of

pearlite

  and cementite.

   

Hypo-Eutectoid Steel A steel that contains less than 0.83% carbon and

 which in annealed condition has a structure of ferrite

  and pearlite.

   

I Chemical symbol for Iodine.

   

Impact Test A test designed to give information on how a

  specimen of a known material will respond to a

  suddenly applied stress, e.g. shock. The test

  ascertains whether the material is tough or

  brittle. A notched test piece is normally

  employed and the two methods in general use

  are either the Izod or Charpy test. The result is

  usually reported as the energy in ft.lbs. or KJ.

  required to fracture the test piece.

   

In Chemical symbol for Indium.

   

Inclusion Count A method of assessing the number and size of

  non-metallic inclusions present in metal.

   

Inclusions Usually non-metallic particles contained in

  metal. In steel they may consist of simple or

  complex oxides, sulphides, silicates and

  sometimes nitrides of iron, manganese, silicon,

  aluminium and other elements. In general they

  are detrimental to mechanical properties but

  much depends on the number, their size,

  shape and distribution.

   

Induction Hardening A widely used process for the surface

  hardening of steel. The components are

  heated by means of an alternating magnetic

  field to a temperature within or above the

  transformation range followed by immediate

  quenching. The core of the component remains

  unaffected by the treatment and its physical

  properties are those of the bar from which it

  was machined, while the hardness of the case

  can be within the range 37/58 Rc. Carbon and

  alloy steels with a carbon content in the range

  0.40/0.45% are most suitable for this process.

   

Ingot The mass of metal that results from casting

  molten steel into a mold. An ingot is usually

  rectangular in shape and is subsequently rolled

  into blooms and billets for rods, bars and

  sections and slabs for plates, sheet and strip.

  With the increasing use of the continuous

  casting process the ingot route is less used as

  the molten steel is now directly cast into a

  bloom or billet.

   

Ingot Mold The receptacle into which molten steel is

  poured to form an ingot. After solidification the

  steel is suitable for subsequent working, i.e.

  rolling or forging.

   

Intercrystalline Corrosion Chromium-nickel austenitic stainless steels are

  prone to this form of corrosion when they are

  welded and subsequently in contact with

  certain types of corrosive media. When heated

  within a temperature range of 450-800 deg C

  precipitation of the chromium carbides takes

  place at the grain boundaries in the area of the

  weld and these areas no longer have the

  protection of the chromium on the peripheries

  of the grains. This type of corrosion is also

  known as Weld Decay and Intergranular

  Corrosion. The most common way to avoid the

  problem is to select a grade of steel that is

  very low in carbon i.e. 0.03% or less, or one

  that is stabilised with niobium or titanium.

   

Interrupted Quenching Rapid cooling to a selected temperature by

  quenching in a suitable medium, usually molten

  salt, holding at the temperature for an

  appropriate time and then cooling to room

  temperature. This process is used to minimise

  the risk of distortion.

   

Iron The term iron, as used in the chemical or

  scientific sense of the word, refers to the

  chemical element iron or pure iron and is the

  chief constituent of all commercial iron and

  steel.

   

Isothermal Annealing Heating to and holding at a temperature above

  the transformation range, then cooling to and

  holding at a suitable temperature until the

  austenite to pearlite change is complete.

   

Isothermal Transformation Also known as the Time Temperature

Curve Transformation Curve. If a small piece of steel

  is heated sufficiently slowly for it to become

  austenitic and then plunged into a salt bath

  and held at a constant temperature below the

  upper critical point for a definite time followed

  by rapid quenching, it is possible by

  examination to determine the extent to which

  the transformation of the austenite has

  occurred. By taking a number of specimens of

  the same steel and treating them in the same

  way, but varying the holding temperature and

  time the behavior of the steel with time and

  temperature can be studied. The information

  obtained can be plotted as time-temperature

  transformation curves which is useful in heat

  treatment practice, particularly for

  martempering and austempering.

   

Izod Impact Test A test specimen, usually of square crossed

  section is notched and held between a pair of

  jaws, to be broken by a swinging or falling

  weight. When the pendulum of the Izod testing

  machine is released it swings with a downward

  movement and when it reaches the vertical the

  hammer makes contact with the specimen

  which is broken by the force of the blow. The

  hammer continues its upward motion but the

  energy absorbed in breaking the test piece

  reduces its momentum. A graduated scale

  enables a reading to be taken of the energy

  used to fracture the test piece. To obtain a

  representative result the average of three tests

  is used and to ensure that the results conform

  to those of the steel specification the test

  specimens should meet the standard

  dimensions laid down in BS 131.

   

Jominy TestA 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.

   

JouleA unit of energy. One joule is equal to the energy expended in

 one second by one ampere against the resistance of one ohm.

 In the mechanical testing of steel it is the unit used in the

  Charpy V notch impact test.

   

K Chemical symbol for potassium.

   

 A method of producing steel from molten iron, using

Kaldo Process an inclined rotating converter and a water cooled

 oxygen lance inserted through the converter mouth.

 Originating in Sweden, this process is no longer in use

  in the UK.

   

Killed SteelThe 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.

   

LapA defect appearing as a seam on a rolled bar. Laps

 are rolled over pieces of material that arise when a

  bar is given a pass through the rolls after a sharp

  overfill or fin has been formed, causing the

  protrusion to be rolled into the surface of the

  product. The presence of oxides usually prevents

  the lap welding to the original bar surface, so that

  in subsequent cold working it is carried through as

  a longitudinal crack.

   

L-D Process An oxygen steel making process named after the

  towns in Austria, Linz and Donawitz, where it was

  first developed. It is a modified Bessemer process,

  steel is produced in a solid bottom converter by

 injection of oxygen into the molten iron bath from a

  water cooled lance inserted through the converter

  mouth. Present day BOS (basic oxygen

  steelmaking) plants are developments of the L-D

  Process.

   

Leaded Steels When added to steel, lead does not go into

  solution but exists in a very finely divided state

  along the grain boundaries. It greatly assists

  machinability as it acts as a lubricant between the

  steel and the tool face. Lead is normally added in

 amounts between 0.15-0.35% and when combined

  with similar amounts of sulphur, optimum

 machinability is attained as in such steel as BS 970

  230M07 Pb.

   

Li Chemical symbol for Lithium.

   

Limiting Range of The greatest range of stress that a metal can

Stresswithstand for an indefinite number of cycles without

  failure. If exceeded, the metal fractures after a

  certain number of cycles, which decrease as the

  range of stress increases.

   

Limiting Ruling SectionThe maximum diameter of cross section of a bar or

  component in which certain specified mechanical

  properties are achieved after heat treatment.

   

Limits A term used to determine a minimum and

  maximum. In a mechanism, it should denote the

  minimum and maximum sizes for each part,

  between which the parts will function properly in

  conjunction with each other and outside of which

  they will not. The words "limits" and "tolerances"

  are often interchanged, "tolerance" represents the

  difference between the minimum and maximum

  limits.

   

Limits of Proportionality The stress (load divided by original area of cross

  section of the test piece) at which the strain

  (elongation per unit of gauge length) ceases to be

  proportional to the corresponding stress. It is

 usually determined from a load-elongation diagram,

  obtained by plotting extensometer readings and is

  the stress at which the load-elongation line ceases

  to be straight.

   

Liquid CarburisingA widely used method of case-hardening steel that

  eliminates scaling and the tendency to

  decarburisation and results in clean components.

  Sodium cyanide is the common media for this

  process, usually heated within the range of

  900-930 deg C. It is advisable to pre-heat the

 components in neutral salts to avoid a temperature

 drop resulting from immersing cold components into

 the cyanide. After carburising, either single quench

 hardening or refining and hardening and tempering

  is carried out.

   

Machinability Simply defined as a measure of the ease with

  which a metal can be machined satisfactorily.

   

Macrostructure The general crystalline structure of a metal and

  the distribution of impurities seen on a polished

  or etched surface by either the naked eye or

  under low magnification of less than x10.

   

Magnetic Crack Detection The bar or component to be tested is

  magnetised by passing a heavy current through

  it or by making it the core of a coil through

  which a heavy current is passed. Cracks or

  inclusions cause the magnetic flux to break the

  surface forming free magnetic poles. When the

  component is sprayed with a suspension of

  finely divided magnetic particles they collect at

  the free poles to visibly show the presence of

  defects.

   

Malleability It can be defined as the property of a metal to

  be deformed by compression without cracking or

  rupturing. The load may be applied slowly or

  suddenly and will determine whether the

  material will be suitable for forging or rolling into

  thin sheet.

   

Manganese One of the most important constituents of steel

  in which it fulfils a number of functions. It acts

  as a mild de-oxidising agent. It combines with

  the sulphur present to form globular inclusions

  of Manganese Sulphide which are beneficial to

  machining. It increases tensile strength and the

  hardenability of steel.

   

Martempering A heat treatment involving austenitisation

  followed by step quenching, at a rate fast

  enough to avoid the formation of ferrite, pearlite

  or bainite to a temperature slightly above the Ms

  point. Soaking must be long enough to avoid

  the formation of bainite. The advantage of

  martempering is the reduction of thermal

  stresses compared to normal quenching. This

  prevents cracking and minimises distortion.

   

Martensite The hard constituent produced when steel is

  cooled from the hardening temperature at a

  speed greater than its critical cooling rate.

  Martensite is an acicular phase when seen in

  the microstructure of steel.

   

Mass Effect A term used to signify the effect of size and

  shape during heat treatment, since it is the rate

  of cooling of a piece of steel which determines

  the properties resulting from the hardening and

  quenching process.

   

Matrix The mass or principal constituent (e.g. iron in

  the case of steel) in which other constituents

  are embedded.

   

Maximum Stress In the testing of the strength of steel a sample

  is machined into a standard test piece and is

  stretched in a tensile testing machine until it

  breaks. The results are expressed in N/mm2 and

  is the value of the maximum load reached in the

  test divided by the original cross sectional area

  of the specimen.

   

McQuaid EHN Grain Size A method of assessing grain size. It consists of

Test a test piece at 927 deg C for 8 hours by slow

  cooling and subsequent microscopical

  examination. The grain size is measured at x100

  magnification and compared to standard charts,

  the figures range from No. 1 -very coarse, to

  No. 8 - very fine.

   

Meehanite A trade name applied to a certain type of cast

  iron.

   

Melting Point The temperature at which a solid begins to

  liquefy.

   

Mg Chemical symbol for Magnesium.

   

Micron A unit of length equal to one millionth of a

  metre (0.001mm).

   

Microstructure The structure that is observed when a polished

  and etched specimen of metal is viewed in an

  optical microscope at magnifications in range of

  approximately x25 to x1500.

   

Mn Chemical symbol for Manganese.

   

Mo Chemical symbol for Molybdenum.

   

Modulus of Elasticity When a material is subjected to an external load

  it becomes distorted or strained. With metals,

  provided the loading is not too great, they return

  to their original dimensions when the load is

  removed, i.e. they are elastic. Within the limits

  of elasticity, the ratio of the linear stress to the

  linear strain is termed the modulus of elasticity

  or more commonly known as Young's Modulus.

   

Molybdenum Its use as an alloying element in steel increases

  hardenability and in low alloy steels reduces the

  risk of temper brittleness. When added to

  stainless steels it increases their resistance to

  corrosion. It is also used in high speed steels.

   

N Chemical symbol for Nitrogen.

   

Na Chemical symbol for Sodium.

   

Nb Chemical symbol for Niobium.

   

Ni Chemical symbol for Nickel.

   

Nickel One of the most widely used alloying elements in

  steel. In amounts 0.50% to 5.00% its use in alloy

 steels increases the toughness and tensile strength

  without detrimental effect on the ductility. Nickel

 also increases the hardenability, thus permitting the

 steel to be oil-hardened instead of water quenched.

  In larger quantities, 8.00% and upwards, nickel is

  the constituent, together with chromium, of many

  corrosion resistant and stainless austenitic steels.

   

Niobium Also known as columbium. Niobium is a strong

  carbide forming element which is added to certain

  18/8% chromium-nickel stainless steels as a

 stabiliser to prevent inter-granular corrosion arising

  from welding.

   

Nitriding A case hardening process that depends on the

 absorption of nitrogen into the steel. All machining,

 stress relieving, as well as hardening and tempering

  are normally carried out before nitriding. The parts

  are heated in a special container through which

 ammonia gas is allowed to pass. The ammonia splits

  into hydrogen and nitrogen and the nitrogen

reacts

  with the steel penetrating the surface to form

  nitrides. Nitriding steels offer many advantages: a

  much higher surface hardness is obtainable when

  compared with case-hardening steels; they are

  extremely resistant to abrasion and have a high

  fatigue strength.

   

Nitrogen Nitrogen is a gas that forms approximately 79% by

 volume or 77% by weight of the atmosphere. It can

  combine with many metals to form nitrides and is

  thus applied to the case-hardening of steel, the

  usual source for this purpose being ammonia.

   

Noble Metals Metals such as gold, silver and platinum which are

  resistant to corrosion by all but the most powerful

  acids.

   

Non Destructive Those forms of testing that do not result in

Testingpermanent damage or deformation to the part being

  tested. Typical examples are magnetic crack

  detection, ultrasonic inspection, X-Ray inspection

  and gamma radiography.

   

Non Magnetic SteelsAustenitic 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 TestA test to determine the resistance of a material to a

  suddenly applied stress, i.e. shock. A notched test

 piece is employed in an Izod or Charpy machine and

  the results are recorded in ft.lbs. or Joules.

   

O Chemical symbol for Oxygen.

   

Occlusion A term applied, in the case of metals, to the

  absorption or entrapment of gases.

   

Oil Hardening Steel Used to describe tool or alloy steels where oil is

  used as the quenching medium in the hardening

  process.

   

Open Hearth Furnace Developed in the middle of the last century, the

  open hearth or Siemens-Martins process, as it is

 known, accounted for a major proportion of UK steel

 production until the early 1970's. For economic and

 quality reasons it has been replaced by the Electric

  Arc Furnace and the Basic Oxygen Steelmaking

 process. There are no open hearth furnaces in use

 in Britain today but they are still in use in Russia and

  Eastern Europe.

   

Orange Peel Effect An effect that arises on the surface of steel sheets

  when they are stretched beyond their elastic limit.

   

Ore An ore is a material that contains a metal in such

  quantities that it can be mined and worked

  commercially to extract that metal. The metal is

 usually contained in chemical combination with some

  other element in addition to various impurities.

   

Os Chemical symbol for Osmium.

   

Overheating Failure of tools and components in heat treatment

 can arise through overheating. This may be caused

  due to quenching from a temperature too high for

 the type of steel involved. Overheating is evidenced

  by cracking, grain-coarseness, erratic surface

  hardness and pitting.

   

Oxidation A common form of chemical reaction which is the

  combining of oxygen with various elements and

  compounds. The corrosion of metals is a form of

  oxidation, rust on iron for example is iron oxide.

   

Oxy-Acetylene Welding A process for joining two pieces of metal in which

  the required high temperature is obtained by the

 combustion of acetylene gas and oxygen. The gases

  are thoroughly mixed in the nozzle or tip of the

  welding torch to ensure perfect combustion. The

 weld may be formed directly between two adjoining

  surfaces, but usually metal from a welding rod is

  fused in between the surfaces of the joint.

   

Oxygen Oxygen is one of the chief constituents of the

  atmosphere of which it forms approximately one

  fifth. It is odorless and invisible. Although oxygen

  itself does not burn it is extremely efficient in

  supporting combustion, nearly all other chemical

 elements combine with it under evolution of heat. It

  has many uses in industry and is essential to the

  BOS (Basic Oxygen Steelmaking Process).

   

P Chemical symbol for Phosphorus.

   

Parkerising A chemical treatment applied to ferrous metals to

 improve their corrosion resistance. The process is based

 on a manganese phosphate solution which produces a

 fairly thick coating. This can subsequently be painted or

 impregnated with oil. Patenting A heat treatment process

 often applied to high carbon wire. The steel is heated to

 a suitable temperature well above the transformation

 range, followed by cooling in air or a bath of molten lead

 or salt. A structure is produced suitable for subsequent

 cold drawing and which will give the desired mechanical

  properties in the finished state.

   

Pd Chemical symbol for Palladium.

   

PearliteA lamellar constituent of steel consisting of alternate

 layers of ferrite (alpha-iron) and cementite (iron Carbide

 Fe3C) and is formed on cooling austenite at 723 deg C. This

 produces a tough structure and is responsible for the

  mechanical properties of unhardened steel.

   

Ph Chemical symbol for Lead.

   

pH ValueA 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.

   

PhosphorusAn element that forms 0.12% of the earth's crust, chiefly

 in the form of phosphates. Its presence in steel is usually

 regarded as an undesirable impurity due to its embrittling

 effect, for this reason its content in most steels is limited

  to a maximum of 0.050%.

   

PicklingA process to chemically remove scale or oxide from steel

 to obtain a clean surface. When applied to bars or coils

 prior to bright drawing, the steel is immersed in a bath of

 dilute sulphuric acid heated to a temperature of around

 80 deg C. An inhibitor is added to prevent attack and pitting

 of the cleaned metal. After pickling, a washing process

 takes place followed by immersion in a lime-water bath to

 neutralise any remaining acid. For environmental reasons

  shot blasting has largely replaced pickling.

   

Pig IronThe product of the blast furnace. The term was derived

 from the method of casting the bars of the pig iron in

 depressions or molds formed in the sand floor adjacent

  to the furnace. These were connected to a runner

 (known as a sow) and when filled with metal the runner

 and the numerous smaller molds were supposed to

 resemble a litter of suckling pigs, hence the term pig

  iron.

   

Pinch PassA term applied when, after annealing, sheet or strip is

 lightly rolled with the object of preventing stretcher lines

  or kinks on subsequent cold working.

   

PipeA 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 RatioIf a square bar is stressed in a testing machine in the

 direction of its length so that the length increases, there

  is a contraction in each opposite direction, which

 produces a decrease in the thickness of the bar. The

 ratio between the contraction at right angles to a stress

 and the direct extension is called the Poisson's ratio. Its

  value in steel is in the order of 0.28.

   

Pot QuenchingQuenching 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-HeatingUsed in the hardening process. Tools are pre-heated

  before heating to the final temperature, this is

  particularly important in tools of complex shape to

 prevent distortion or cracking. Pre-heating reduces the

 time of exposure to the hardening temperature and helps

  to minimise scaling and decarburisation.

   

Projection WeldingA 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 StressThe 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.

   

QuenchingRapid cooling from a high temperature by immersion in a

 liquid bath of oil or water. Molten salts may also be used.

   

Quenching CrackA fracture, often termed a hardening crack, which arises

 from thermal stresses induced during rapid cooling.

   

Ra Chemical symbol for Radium.

   

Radiography A method of non-destructive testing. Internal

  examination of a metallic structure or component

  is carried out by exposing it to a beam of X-Ray

  or gamma radiation. Internal defects can be

  seen on a screen or recorded on film.

   

Rb Chemical symbol for Rubidium.

   

Re Chemical symbol for Rhenium.

   

Re-crystallisation The re-arrangement of crystals in cold worked

  metal brought about by heating so that the

  deformed crystals are absorbed by newly-formed

  crystals and the effects of work hardening are

  removed. Also occurs when steel is heated

  through the transformation range and when steel

  is hot worked.

   

Red Hardness A term sometimes associated with high speed

  steel because it has the property of retaining

  sufficient hardness for cutting metals even when

  heated to a temperature high enough to cause a

  dull redness. The tungsten content has a

  significant influence on this property.

   

Reduction of area The percentage decrease in the cross-sectional

  area of a tensile test piece caused by wasting or

  necking of the specimen. It is expressed as a

  percentage of the original area of the test piece

  and is a measure of ductility.

   

Refining (a) The removal of impurities and metallic oxides

  from the molten bath by the reaction of the slag

  and other additions. (b) A heat treatment

  process with the object of refining or making the

  grain size of the steel uniform.

   

Residual Stress The stress which exists in an elastic solid body

  in the absence of, or in addition to, the stresses

  caused by an external load. Such stresses can

  arise from deformation during cold working such

  as cold drawing or stamping, in welding from

  weld metal shrinkage, and in changes in volume

  due to thermal expansion.

   

Rh Chemical symbol for Rhodium.

   

Rockwell Hardness Testing A method for testing the hardness of metals by

  determining the depth of penetration of a steel

  ball or a diamond sphero-conical indentor. The

  value is read from a dial and is an arbitrary

  number related to the depth of penetration. For

  testing hard steels, a sphero-conical diamond is

  used with a 150 kg load, the result is read from

  the black scale on the dial and is prefixed with

  the letter C. A hardened tool steel would

  typically give a reading of 62Rc. For softer

  metals Scale B is used with a 1/16" diameter

  steel ball and a standard load of 100 kgs.

   

Rolling The process of shaping metal by passing it

  between rolls revolving at the same peripheral

  speed and in opposite directions. In steel there

  are a number of different types of rolling mill for

  processing the ingot to its finished shape. These

  are variously known as Cogging mills, Slabbing

  mills, Billet mills, Bar mills and Strip mills, which

  produce plate, sections, bars, sheet and strip.

  Cold rolling of previously hot rolled strip is

  carried out to produce strip that is accurate to

  size and with a smooth bright polished surface.

   

Rolling Lap A fault arising from the overfilling or mis-

  alignment of rolls, the result is a bulge on the

  bar which is rolled into the metal and is lapped

  over. It remains throughout subsequent working

  and appears as a longitudinal crack.

   

Ru Chemical symbol for Ruthenium.

   

Ruling Section More accurately termed limiting ruling section.

  One of the most important factors associated

  with the choice of steel for a given purpose is to

  ensure that the desired mechanical properties

  are obtained throughout the section when the

  material has been heat treated. The limiting

  ruling section determines the maximum diameter

  or cross-section of a bar or component in which

  the specified properties can be achieved by a

  given heat treatment. The analysis of the steel

  also has an important bearing on this.

   

S Chemical symbol for Sulphur.

   

Salt BathA method of heating steel using a bath of molten salts.

 Salt baths give uniform heating and prevent oxidation,

 they are used for hardening, tempering or quenching. The

 type of salt used depends on the temperature range

  required. For hardening, sodium cyanide, sodium

 carbonate and sodium chloride are in common use.

   

Sb Chemical symbol for Antimony.

   

ScaleThe oxidised surface of steel produced during hot working,

 as in rolling, and by exposure to air or steam at elevated

  temperature.

   

ScarfingAlso 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.

   

ScrapIt 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.

   

SeChemical 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  

HardnessAn increase in hardness which sometimes occurs when

 hardened steel is re-heated. It can be caused by the

 transformation of retained austenite to martensite or by

  the precipitation of alloy carbides.

   

SegregationA 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.

   

SeleniumAn 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 IronAn abbreviation for Spheroidal Graphite Cast Iron. As the

 name implies, graphite is present in spheroidal form

 instead of flakes and compared with Grey Cast Iron it has

 higher mechanical strength, ductility and increased shock

  resistance.

   

Shearing TestThe 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.

   

ShoreAn instrument that measures the hardness of a sample in

Scleroscopearbitrary 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.

   

SpinningThe 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 WeldingA 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.

   

StabilisationA term applied to a number of processes: a) A type of heat

 treatment to relieve internal stresses: b) The retarding or

 prevention of a particular reaction by the addition of a

 stabilising element; c) A thermal and/or mechanical

 treatment given to magnetic material in order to increase

 the permanency of its magnetic properties or condition.

   

Stainless SteelCan 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.

   

SteelGenerally defined as a metallic product whose principal

  element is iron and where the carbon content is

not more

 than 2%. (The presence of large quantities of carbide

 forming elements may modify the upper limit of the carbon

  content.)

   

Strain Ageing The gradual changes in physical and mechanical

 properties, in particular hardness and tensile strength,

 which takes place following cold rolling or deformation. At

 atmospheric temperatures, this may take place over a

 number of weeks but can be accelerated by heating.

   

Strain HardeningThe loss of ductility and gain in hardness resulting from

  strain ageing.

   

Stress RelievingA 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 StrainA graph in which stress (load divided by the original cross

Curvesectional area of the test piece) is plotted against strain

 (the extension divided by the length over which it is

  measured).

   

Sub-CriticalHeating to, and holding at, some point below the critical

Annealingtemperature. 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-zeroA low temperature treatment carried out after quenching

Treatmenton 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.

   

SulphurGenerally regarded as an impurity in steel as it can have

 detrimental effects on strength, ductility and weldability as

 well as producing hot and cold shortness. Its content in

  most steels is limited to a maximum of 0.050%.

Sulphur is

 beneficial to machining and is added to freecutting steels

 in amounts up to 0.35% with the manganese content

  increased to overcome any detrimental effects.

   

SurfaceA method of hardening the surface of steel to increase its

Hardeningwear resistance. Depending on the analysis of the steel,

  the following treatments can be employed:

 Case-hardening, Nitriding, induction hardening, Flame

  hardening.

   

SwagingA method of forming or reducing steel or other metals to a

 desired shape by a series of blows rapidly applied by dies

 or hammers. The process is applied to wires, rods and

 tubes and can be used for a variety of pointing, tapering,

  sizing and reducing operations.

   

SwarfThe particles of metal arising from machining or grinding

 operations, much of it finds its way to the steel maker for

  remelting.

   

Ta Chemical symbol for Tantalum.

   

Tantalum A rare metal of silver white color having

  excellent corrosion resistance and a high

  melting point. It is widely used for chemical

  process equipment and specialised

  aero-space and nuclear applications.

   

Te Chemical symbol for Tellurium.

   

Tellurium Its main use in the steel industry is as an

  additive in leadbearing freecutting steels to

  further improve their machinability. Its

  presence in the steel is either within the

  manganese sulphide particles, where it is

  partially soluble, or as particles combined

  with lead or manganese. For certain

  applications it offers significant improvements

  in machinability but the added cost is a factor

  that should be taken into account.

   

Temper A term to which a number of definitions can

  be applied. These include: a) The operation

  of tempering; b) The degree of hardness left

  in a steel bar after quenching and tempering;

  c) The grading of the hardness of low carbon

  cold rolled strip, e.g. Hard, Half Hard,

  Quarter Hard, Skin Passed, Soft; d) An

  indication of the amount of carbon present in

  a tool steel, e.g. razor temper, file temper,

  die temper, etc.

   

Temper Brittleness The loss in impact resistance that is present

  in some low and medium carbon alloy steels

  when tempered in the range of 350 deg C -

  600 deg C. It is revealed by the notched bar

  impact test but not the tensile test.

   

Temper Colors Before the use of instruments such as

  pyrometers, colors were used to judge

  temperatures when hardening and tempering.

  For example, on carbon tool steel where the

  tempering range may typically be from 200 deg C

  to 350 deg C, the colors change with the rise in

  temperature giving Light Straw at around

 210 deg C, Purple at 275 deg C, and Grey at 330 deg C.

  The practice still continues in workshops

  where controlled heat treatment facilities are

  not available.

   

Temper Rolling A light pass given to annealed cold rolled

  strip to prevent the formation of kinks and

  stretcher strain markings on subsequent cold

  working. Also termed Pinch pass and Skin

  pass.

   

Tempering A heat treatment applied to ferrous products

  after hardening. It consists of heating the

  steel to some temperature below the

  transformation range and holding for a

  suitable time at the temperature, followed by

  cooling at a suitable rate. The object of

  tempering is to decrease hardness and

  increase toughness to produce the desired

  combination of mechanical properties.

   

Tensile Strength The maximum load applied in breaking a

  tensile test piece divided by the original

  cross-sectional area of the test piece.

  Originally quoted as tons/sq.in. it is now

  measured as Newtons/sq.mm. Also termed

  Maximum Stress and Ultimate Tensile Stress.

   

Tensile Test A standard test piece is gripped at either end

  by suitable apparatus in a testing machine

  which slowly exerts an axial pull so that the

  steel is stretched until it breaks. The test

  provides information on proof stress, yield

  point, tensile strength, elongation and

  reduction of area.

   

Thomas Process The Continental name for the basic Bessemer

  steel making process, now superseded by

  modern day BOS plants.

   

Ti Chemical symbol for Titanium.

   

Time Temperature An isothermal transformation diagram

Transformation Curve showing the relationship between

  temperature and the time taken for the

  decomposition of austenite when the

  transformation occurs at constant

  temperature.

   

Tin When present in steel it is an undesirable

  impurity which gives rise to temper

  brittleness. When used as a coating on steel,

  it has a good resistance to corrosion for many

  applications.

   

Titanium Small amounts added to steel contribute to

  its soundness and give a finer grain size. In

  austenitic stainless steels it acts as a carbide

  stabiliser and is used to prevent

  intercrystalline corrosion, commonly termed

  "weld decay". Titanium carbide is also used

  with tungsten carbide in the manufacture of

  hard metal tools.

   

Tolerances The amount of variation permitted on

  dimensions or surfaces. The tolerance is

  equal to the difference between the maximum

  and minimum limits of any specified

  dimension.

   

Tool Steel A generic term applied to a wide range of

  steels, both plain carbon and alloy. It

  includes steels suitable for various types of

  cutting tools, press tools, hot and cold

  heading dies, molds for plastics and die-

  casting, extrusion tools, hand tools, etc.

   

Torsional Strength The resistance of a bar to twisting. Closely

  related to its shear strength.

   

Toughness The ability of a metal to rapidly distribute

  within itself both the stress and strain caused

  by a suddenly applied load, or more simply

  expressed, the ability of a material to

  withstand shock loading. It is the exact

  opposite of "brittleness" which carries the

  implication of sudden failure. A brittle

  material has little resistance to failure once

  the elastic limit has been reached.

   

Transformation Range The temperature range within which austenite

  forms and ferrite or carbide progressively

  dissolves while ferrous alloys are being

  heated. Also the temperature range within

  which austenite decomposes to form ferrite

  and carbide on cooling.

   

Transformation Temperature The temperature at which a change in phase

  occurs or the limiting temperature of a

  transformation range. These critical points

  are denoted by symbols, e.g. Ac1; the

  temperature at which austenite begins to

  form on heating. There are 12 principal

  temperatures to which symbols are applied.

   

Transition Temperature The temperature at which a transition from

  ductile to brittle fracture takes place in steel.

  It is usually determined by making a series of

  Charpy impact tests at various temperatures,

  the transition temperature is usually taken as

  the point where 50% of the fracture is brittle.

   

Transverse Strength A measurement of strength when the load is

  applied across the longitudinal flow of the

  grain of a metal. Certain impurities such as

  sulphur have a detrimental effect on the

  transverse strength. This can be minimised by

  the inclusion modification process.

   

Transverse Test A test taken at right angles to the principal

  direction of rolling or forging.

   

TTT Curve An abbreviation of Time Temperature

  Transformation Curve.

   

Tufftriding A form of surface hardening, the process

  involves nitrogen but does not achieve the

  hardness of conventional nitriding.

   

Tungsten When used as an alloying element it

  increases the strength of steel at normal and

  elevated temperatures. Its "red hardness"

  value makes it suitable for cutting tools as it

  enables the tool edge to be maintained at

  high temperatures. In conjunction with other

  alloying elements it finds applications in heat

  resisting and other severe service conditions.

   

U Chemical symbol for Uranium.

   

Ultimate AnalysisIn 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 InspectionA means of locating defects in steel. When acoustic

  energy in the ultrasonic range is passed through

  steel, the sound waves tend to travel in straight

  lines, rather than diffusing in all directions as they

  do in the audible range. If there is a defect in the

  path of the beam it will cause a reflection of some

  of the energy, depleting the energy transmitted.

  This casts an acoustic shadow which can be

  monitored by a detector placed opposite the

 transducer or energy source. If the acoustic energy

  is introduced as a very short burst, then the

  reflected energy coming back to the originating

  transducer can also be used to show the size and

  depth of the defect. Ultrasonic techniques can be

  used to detect deeply located defects or those

 contained in the surface layer. Skill and experience

 are required in interpreting the results portrayed on

  the cathode ray tube.

   

Unkilled Steel Steel which has been insufficiently deoxidised and

  evolves gas during solidification with the formation

  of blow-holes.

   

Upsetting Working a piece of steel so that its length is

 shortened and its cross-sectional area is increased.

  Its effect is to increase ductility in the radial and

  tangential directions.

   

Uranium A white malleable metal which is softer than steel.

 Its specific gravity is 18.7, it melts at a temperature

  of 2400 deg C.

   

V Chemical symbol for Vanadium.

Vacuum Arc  

RemeltingA process used for producing advanced steels to the

  most demanding and critical specifications,

 particularly in such areas as aerospace applications.

  The steel is first produced to a very close analysis

  and the resulting ingot is slowly remelted in a

  Vacuum Arc Remelting furnace for up to 14 hours.

  Such steels are, by necessity, expensive to

  manufacture.

   

Vacuum Degassing A ladle of molten metal is placed within a chamber

  which is then evacuated. This reduces the gas

  content, particularly hydrogen, as well as reducing

  non-metallic inclusions. Modern secondary steel

 making processes using Vacuum Arc Degassing units

  that include automated stirring and control of

  temperature and chemical analysis, ensure a

  consistent and high quality product.

   

VanadiumSteels containing vanadium have a much finer grain

  structure than steels of similar composition without

  vanadium. It raises the temperature at which grain

 coarsening sets in and increases hardenability where

 it is in solution in the austenite prior to quenching. It

  also lessens softening on tempering and confers

 secondary hardness on high speed steels. Vanadium

  is used in nitriding, heat resisting, tool and spring

  steels in conjunction with other alloying elements.

   

Vickers Hardness Test A method of determining the hardness of steel

  whereby a diamond pyramid is pressed into the

 polished surface of the specimen and the diagonals

  of the impression are measured with a microscope

  fitted with a micrometer eye piece. The rate of

 application and duration are automatically controlled

  and the load can be varied.

   

W Chemical symbol for Tungsten, from wolfram.

   

WeldingThe process of joining together two pieces of metal

  so that bonding accompanied by appreciable

  interatomic penetration takes place at their original

  boundary surfaces. The boundaries more or less

  disappear at the weld, and integrating crystals

 develop across them. Welding is carried out by the

  use of heat or pressure or both and with or without

  added metal. There are many types of welding

 including Metal Arc, Atomic Hydrogen, Submerged

  Arc, Resistance Butt, Flash, Spot, Stitch, Stud and

  Projection.

   

Whiskers Thin hair-like growths on metal that are barely

 visible to the naked eye, they are stronger than the

  metals from which they are formed, probably

  because they are free from defects.

   

White Annealing A heat treatment process carried out on pickled

  steel with the objective of eliminating the hydrogen

  that has entered the steel during the pickling

  operation and thus removing any tendency to

  hydrogen embrittlement.

   

Widmanstatten Structure A microstructure resulting when steels are cooled

  at a critical rate from extremely high temperatures.

  It consists of ferrite and pearlite and has a

 cross-hatched appearance due to the ferrite having

  formed along certain crystallographic planes.

   

Wolfram The alternative name for tungsten.

   

Woody Fracture A fracture that is fibrous or woody in appearance

  due to the elongation of the individual grains. This

  may be accentuated by the presence of slag or by

  a banded structure. It is grey and dull and is

  characteristic of ductile but non-homogeneous

  material such as wrought iron.

   

Work HardeningThe increase in hardness and strength produced by

  cold plastic deformation or mechanical working.

   

Wrought Iron A commercial iron that has little use today and has

  been replaced by mild steel. It was commonly

  produced by the puddling process. The

  temperatures employed in its production are too

  low to render it fluid, it is heated until it forms a

  pasty mass then it is squeezed or forged. The

  process does not lend itself to removal of

  impurities so it contains an appreciable quantity of

  slag. It will not respond to any heat treatment

  designed to increase the hardness or strength.

   

X-Ray CrystallographyX-ray photographs of metals are a means of providing

 information which in many cases cannot be obtained

 by microscopic methods. The lines produced by each

  element, or phase are characteristic, and their

 general pattern enables the crystalline structure to be

  identified. The scale of the pattern can be used to

  determine accurately the size of the unit cell and,

 therefore, the distance apart of the individual atoms.

 From the relative intensity of the lines it is possible to

 deduce the distribution throughout the unit cell, the

  various types of atoms in an alloy or the degree of

  preferred orientation in the material.

   

Yield PointCan be defined as the point where a tensile test piece

 begins to extend permanently. If the load is reduced to

 zero, the test piece will not return to its original length.

   

Yield StrengthThe stress at which general plastic elongation of the test

 piece takes place. This point is well defined in hardened

 and tempered or annealed structures but can be ill defined

  in "as drawn" structures.

   

Young's ModulusWithin the limits of elasticity, the ratio of the linear stress

 to the linear strain is termed the modulus of elasticity or

 Young's Modulus and may be written Young's Modulus, or

 E =(Stress/Strain) It is this property that determines how

 much a bar will sag under its own weight or under a

  loading when used as a beam within its limit of

 proportionality. For steel, Young's Modulus is of the order

  of 205000 N/mm2.

   

ZincZinc is a metallic chemical element, it has a white color with a

 bluish tinge. It has a high resistance to atmospheric corrosion and

 a major use is as a protective coating for iron and steel sheet and

 wire. Galvanised sheets are a prime example. The melting point

  of zinc is 419 deg C.

   

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

   

Zn Chemical symbol for Zinc.

   

Zr Chemical symbol for Zirconium.