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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 above
  910 deg C the atomic structure changes from body centered
  cubic to face centered cubic but reverts again when
  cooled. The allotropy of iron modifies the solubility of
  carbon, and it is because of this that steel can be
  hardened.
   
Alloy Steel A steel to which one or more alloying elements other
  than carbon have been deliberately added (e.g.
  chromium, nickel, molybdenum) to achieve a particular
  physical property.
   
Alpha Iron The body centered cubic form of iron which, in pure iron,
  exists up to 910 deg C.
   
Annealing Heating steel to, and holding at a suitable temperature,
  followed by relatively slow cooling. The purpose of
  annealing may be to remove stresses, to soften the
  steel, to improve machinability, to improve cold working
  properties, to obtain a desired structure. The annealing
  process usually involves allowing the steel to cool slowly
  in the furnace.
   
Arc Furnace A steel melting furnace in which heat is generated by an
  arc between graphite electrodes and the metal. Both
  carbon and alloy steels are produced in electric arc
  furnaces and scrap rather than molten metal is used as
  the base material. Furnaces with capacities up to 200
  tons are now in use.
   
Austempering Quenching from a temperature above the transformation
  range to a temperature above the upper limit of
  martensite formation, and holding at this temperature
  until the austenite is completely transformed to the
  desired intermediate structure, for the purpose of
  conferring certain mechanical properties.
   
Austenite The solid solution of carbon in gamma (face centered
  cubic) iron.
   
Austenitic Steels Steels containing high percentages of certain alloying
  elements such as manganese and nickel which are
  austenitic at room temperature and cannot be hardened
  by normal heat-treatment but do work harden. They are
  also non-magnetic. Typical examples of austenitic steels
  include the 18/8 stainless steels and 14% manganese
  steel.
   
B Chemical symbol for Boron.
   
Bainite An acicular aggregate of ferrite and carbide particles
  formed when austenite is transformed on cooling at
  temperatures in the intermediate (200-450 deg C) range,
  i.e. above the martensite and below the pearlite
  range.
   
Balanced Steel Steels in which the deoxidisation is controlled to
  produce an intermediate structure between a rimmed
  and killed steel. Sometimes referred to as semi-killed
  steels, they possess uniform properties throughout the
  ingot and amongst their applications are boiler plate
  and structural sections.
   
Base Metal A metal which oxidises when heated in air, e.g. lead,
  copper, tin, zinc, as opposed to noble metals such as
  gold and platinum.
   
Basic Steel Steel produced in a furnace in which the hearth
  consists of a basic refractory such as dolomite or
  magnesite, as opposed to steel melted in a furnace
  with an acid lining. The basic process permits the
  removal of sulphur and phosphorous and in this
  respect is superior. Present day BOS and electric arc
  furnaces use basic linings.
   
Be Chemical symbol for Beryllium.
   
Bend Test Bending tests are carried out to ensure that a metal
  has sufficient ductility to stand bending without
  fracturing. A standard specimen is bent through a
  specified arc and in the case of strip, the direction of
  grain flow is noted and whether the bend is with or
  across the grain.
   
Bessemer Process A method of producing steel, first introduced in the
  last century, where air is blown under pressure
  through molten iron to remove the impurities by
  oxidation. The development of the process has led to
  the present day Basic Oxygen Steel making plants
  that account for bulk production of commercial quality
  steels in the UK.
   
Bi Chemical symbol for Bismuth.
   
Billet A section of steel used for rolling into bars, rods and
  sections. It can be a product of the ingot route, or
  increasingly today produced directly by continuous
  casting.
   
Blast Furnace A tall, cylindrical, refractory lined furnace for the
  production of pig iron or hot metal for direct
  conversion into steel.
   
Bloom A large square section of steel intermediate in the
  rolling process between an ingot and a billet. Blooms
  are now also being produced by the continuous
  casting process eliminating the necessity of first
  producing an ingot.
   
Boron Steels The addition of boron in the range 0.0005-0.005% to
  certain steels increases the hardenability. A range of
  boron steels is now listed in the current BS 970 and
  are widely used for the production of cold headed
  fastenings.
   
Brazing Brazing is a method of joining metal parts together by
  fusing a layer of brass between the adjoining surfaces.
  A red heat is necessary and a flux is used to protect
  the metal from oxidation.
   
Bright Annealing An annealing process that is carried out in a controlled
  atmosphere furnace or vacuum in order that oxidation
  is reduced to a minimum and the surface remains
  relatively bright.
   
Bright Drawing The process of drawing hot rolled steel through a die
  to impart close dimensional tolerances, a bright, scale
  free surface, and improved mechanical properties. The
  product is termed bright steel.
   
Brinell Hardness Test The Brinell hardness test for steel, involves impressing
  a ball 10 mm diameter, of hard steel or tungsten
  carbide, with a loading of 3000 kilograms into the
  steel surface. The hardness of the steel is then
  determined by measurement of the indentation. For
  steels with a hardness over 500 BHN the Vickers test
  is more reliable.
   
C Chemical symbol for Carbon.
   
Ca Chemical symbol for Calcium.
   
Calcium In the form of calcium silicide acts as a deoxidizer
  and degasifier when added to steel. Recent
  developments have found that carbon and alloy
  steels modified with small amounts of calcium show
  improved machinability and longer tool life.
  Transverse ductility and toughness are also
  enhanced.
   
Carbon Carbon is an essential element in steel, it is added
  in specific amounts to control the hardness and
  strength of the material. In general, increased
  carbon content reduces ductility but increases
  tensile strength and the ability of the steel to
  harden when cooled rapidly from elevated
  temperatures.
   
Carbon Steel A steel whose properties are determined primarily
  by the amount of carbon present. Apart from iron
  and carbon, manganese up to 1.5% may be
  present as well as residual amounts of alloying
  elements such as nickel, chromium, molybdenum,
  etc. It is when one or more alloying elements are
  added in sufficient amount that it is classed as an
  alloy steel.
   
Carbo-Nitriding A case-hardening process in which steel
  components are heated in an atmosphere
  containing both carbon and nitrogen.
   
Carburising The introduction of carbon into the surface layer of
  a steel that has a low carbon content. The process
  is carried out by heating the components in a solid
  liquid, or gaseous carbon containing medium. The
  depth of penetration of carbon into the surface is
  controlled by the time and temperature of the
  treatment. After carburising it is necessary to
  harden the components by heating to a suitable
  temperature and quenching.
   
Case-Hardening The process of hardening the surface of steel
  while leaving the interior unchanged. Both carbon
  and alloy steels are suitable for case-hardening
  providing their carbon content is low, usually up to
  a maximum of 0.2%. Components subject to this
  process, particularly in the case of alloy steels,
  have a hard, wear-resistant surface with a tough
  core.
   
Cast Iron A definition can be applied that Cast Iron is an
  alloy of iron and carbon in which the carbon is in
  excess of the amount that can be retained in solid
  solution in austenite at the eutectic temperature.
  Carbon is usually present in the range of 1.8% to
  4.5%, in addition, silicon, manganese, sulphur and
  phosphorus are contained in varying amounts.
  Various types of cast iron are covered by a British
  Standard classification and includes grey, malleable
  and white irons. Elements such as nickel,
  chromium, molybdenum, vanadium can be added to
  produce alloy cast irons.
   
Cast Steel A term originally applied to crucible steel and
  sometimes today used to describe tool steels. The
  term is misleading and is falling into misuse. It can
  also be applied to steel castings made by pouring
  molten steel into a mold but which are not subject
  to further forging or rolling.
   
Cb Chemical symbol for Columbium.
   
Ce Chemical symbol for Cerium.
   
Cementite An iron carbide (Fe3C) constituent of steel. It is
  hard, brittle and crystalline. Steel which has cooled
  slowly from a high temperature contains ferrite and
  pearlite in relative proportions varying with the
  chemical composition of the steel. Pearlite is a
  lamellar structure of ferrite and cementite.
   
Charpy Test A test to measure the impact properties of steel. A
  prepared test piece, usually notched, is broken by a
  swinging pendulum. The energy consumed in
  breaking the test piece is measured in Joules. The
  more brittle the steel the lower the impact strength.
  Izod is a similar and more widely used impact test
  in this country. Both are quoted in the current
  edition of BS 970.
   
Chromium When used as an alloying element, chromium
  increases the hardenability of steel and in
  association with high carbon gives resistance to
  wear and abrasion. Chromium has an important
  effect on corrosion resistance and is present in
  stainless steels in amounts of 12% to 20%. It is
  also used in heat-resisting steels and high duty
  cast irons.
   
Co Chemical symbol for Cobalt.
   
Cobalt An alloying element used in tool, magnet and heat
  resisting steels. Together with tungsten and
  molybdenum, cobalt is used to form the super high
  speed steels. It improves the red hardness value of
  the steel, that is, it enables the steel to resist
  softening at a high temperature or in the case of a
  cutting tool to hold its edge under severe
  conditions.
   
Coefficient of Expansion The ratio of change in length, area, or volume per
  degree to the corresponding value at a standard
  temperature.
   
Cogging An intermediate rolling process when a hot ingot is
  reduced to a bloom or slab in a cogging mill.
   
Cold Drawing The process of reducing the cross sectional area of
  wire, bar or tube by drawing the material through a
  die without any pre-heating. Cold drawing is used
  for the production of bright steel bar in round
  square, hexagonal and flat section. The process
  changes the mechanical properties of the steel and
  the finished product is accurate to size, free from
  scale with a bright surface finish.
   
Cold Working Altering the shape or size of a metal by plastic
  deformation. Processes include rolling, drawing,
  pressing, spinning, extruding and heading, it is
  carried out below the recrystallisation point usually
  at room temperature. Hardness and tensile strength
  are increased with the degree of cold work while
  ductility and impact values are lowered. The cold
  rolling and cold drawing of steel significantly
  improves surface finish.
   
Contact Corrosion When two dissimiliar metals are in contact without
  a protective barrier between them and they are in
  the presence of liquid, an electrolytic cell is
  created. The degree of corrosion is dependent on
  the area in contact and the electro-potential
  voltage of the metals concerned. The less noble of
  the metals is liable to be attacked, i.e. zinc will act
  as a protector of steel in sea water whereas copper
  or brass will attack the steel in the same
  environment.
   
Continuous Casting A method of producing blooms, billets and slabs in
  long lengths using water cooled molds. The
  castings are continuously withdrawn through the
  bottom of the caster while the teeming of the
  metal is proceeding. The need for primary and
  intermediate mills and the storage and use of large
  numbers of ingot molds is eliminated. The
  continuous casting process is also used in the
  production of cast iron, aluminium and copper
  alloys.
   
Controlled Atmosphere A gas or mixture of gases in which steel is heated
  to produce or maintain a specific surface condition.
  Controlled atmosphere furnaces are widely used in
  the heat treatment of steel as scaling and
  decarburisation of components is minimised by this
  process.
   
Core In the case of steel this refers to a component that
  has been case-hardened where the centre is softer
  than the hard surface layer or case. It can also be
  applied to the central part of a rolled rimming steel.
   
Corrosion Fatigue Fatigue that arises when alternating or repeated
  stress combines with corrosion. The severity of the
  action depends on the range and frequency of the
  stress, the nature of the corroding condition and
  the time under stress.
   
Cr Chemical symbol for Chromium.
   
Creep The form of plastic deformation that takes place in
  steel held for long periods at high temperature.
  Methods of creep testing involve the determination
  of strain/time curves under constant tensile load
  and at constant temperature.
  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 Fracture A type of fracture that appears bright and glittering,
  it having formed along the cleavage planes of the
  individual crystals. Normally an indication that
  brittle fracture has occurred.
   
Cu Chemical symbol for Copper.
   
Cyanide Hardening A process of introducing carbon and nitrogen into
  the surface of steel by heating it to a suitable
  temperature in a molten bath of sodium cyanide, or
  a mixture of sodium and potassium cyanide, diluted
  with sodium carbonate and quenching in oil or
  water. This process is used where a thin case and
  high hardness are required.
   
Decalescence A term used in reference to the absorption of
  heat without a corresponding increase in
  temperature, when steel is heated through the
  critical points (phase changes).
   
Decarburisation The loss of carbon from the surface of steel as
  a result of heating in a carbon weak
  atmosphere. During the rolling of steel hot
  surfaces are exposed to the decarburising
  effects of oxygen in the atmosphere and as a
  result the surface is depleted of carbon. In
  steels where the components are to be
  subsequently heat treated it is necessary to
  remove the decarburised surface by machining.
   
Delta Iron When pure or practically carbon-free iron is
  cooled from above its melting point it solidifies
  at about 1535 deg C as delta iron having a
  body-centred cubic lattice structure, which
  persists down to about 1400 deg C. On further
  cooling it undergoes an allotropic change to
  gamma iron which has a face-centred cubic
  lattice and is non-magnetic.
   
Deoxidation Elements such as silicon and aluminium when
  added to molten steel react to form stable
  oxides and reduce the amount of dissolved
  oxygen. The solubility of oxygen in steel is
  reduced as temperature is lowered during
  solidification and the excess oxygen combines
  to form carbon monoxide. If the molten metal
  is not deoxidised the effervescence produced
  by the evolution of carbon monoxide during
  solidification would result in blow holes and
  porosity. Steel treated in this way is termed,
  "Killed Steel".
   
Descaling It is necessary to remove the scale from hot
  rolled bars or coil before bright drawing. This is
  normally carried out by shot blasting or pickling
  in acid. Other methods of descaling steel
  products include sand blasting, flame
  descaling and tumbling.
   
Deseaming A process of burning out defective areas on
  the surface of ingots, blooms or billets. The
  condition of the surface is such that it can then
  be rolled or forged into a satisfactory product.
   
Diamond Pyramid Hardness This test, more commonly known as the
Test Vickers test, finds greater use in the laboratory
  than the workshop. It employs a pyramid
  shaped diamond with an included angle of
  136o which is impressed into the specimen
  using loads of 5 to 120 kg making a small
  square impression. This test is used for
  finished or polished components because the
  impression can be very small. The diamond
  pyramid hardness number is obtained from a
  calculation based on measuring the diagonals
  of the impressions in the steel.
   
Die The term die is most commonly used in
  tooling, i.e. press tools "punch and die" but
  there are many other types of die, e.g. thread
  cutting dies, forming dies, forging dies,
  die-casting dies, etc. The term when applied to
  steel often refers to drawing dies through
  which hot rolled wire and bar are drawn to
  produce the finish and dimensional accuracy
  that is required for bright steel.
   
Dislocation A discontinuity in the crystal lattice of a metal.
  The movement of dislocations under stress
  may be used to explain slip, creep, plastic
  yielding, etc.
   
Dolomite A natural carbonate of calcium and magnesium
  generally used as a flux in blast furnaces.
   
Drawing The process of pulling metal wire, rods, or bars
  through a die with the effect of altering the
  size, finish and mechanical properties. In the
  USA, it is a term used for tempering.
   
Drop Forging An operation in which a metal shape is formed
  by forcing hot metal into impressions formed in
  solid blocks of hardened alloy steel, the
  forging dies. The dies are made in halves, one
  attached to the rising and falling block of the
  drop forge and the other to the stationary
  anvil. Drop forgings are widely used in the
  automotive industry for crankshafts, stub-axles,
  gears, etc.
   
Ductility The property of metal which permits it to be
  reduced in cross sectional area without
  fracture. In a tensile test, ductile metals show
  considerable elongation eventually failing by
  necking, with consequent rapid increase in
  local stresses.
   
Dye Penetrant Inspection A method for detecting surface porosity or
  cracks in metal. The part to be inspected is
  cleaned and coated with a dye which
  penetrates any flaws that may be present. The
  surface is wiped clean and coated with a white
  powder. The powder absorbs the dye held in
  the defects indicating their location.
   
Elastic Limit The maximum stress that can be applied to a
  metal without producing permanent deformation.
  When external forces act upon a material they
  tend to form internal stresses within it which
  cause deformation. If the stresses are not too
  great the material will return to its original shape
  and dimension when the external stress is
  removed.
   
Elasticity The property which enables a material to return
  to its original shape and dimension.
   
Electrical Steels Steels which are characterised by their magnetic
  properties and are intended for the manufacture
  of electrical circuits. They are supplied in the
  form of cold rolled sheet or strip, generally less
  than 2mm thick and up to 1500mm wide. Grain
  orientated steels have preferential magnetic
  properties in the direction of rolling and non-
  grain orientated steels have similar magnetic
  properties both transversely and in the direction
  of rolling.
   
Electroslag Refining A specialised steel making process in which a
  rolled or a cast ingot in the form of an electrode
  is remelted in a water cooled copper mold. The
  melting is activated by resistive heat generated
  in a conductive slag. The resulting product has a
  similar basic chemical composition to the original
  ingot, but is characterised by high purity and low
  inclusion content. Typical applications include
  high integrity components for the aerospace
  industry.
   
Elevated Temperature A process of drawing steel bars at elevated
Drawing temperatures (normally 250-300 deg C) which under
  optimum conditions produce steels that have
  higher tensile and yield strengths than those cold
  drawn with the same degree of reduction. The
  process is little used in the United Kingdom.
   
Elongation A test to measure the ductility of steel. When a
  material is tested for tensile strength it elongates
  a certain amount before fracture takes place.
  The two pieces are placed together and the
  amount of extension is measured against marks
  made before starting the test and is expressed
  as a percentage of the original gauge length.
   
End Quench Test More commonly referred to as Jominy Test it is
  used to determine the hardening ability of steel.
   
Equiaxed Crystals Crystals, each of which has axes approximately
  equal in length. These are normally present in
  the centre of a steel ingot.
   
Equilibrium A diagram constructed from thermal and other
  data showing the limits of composition and
  temperature within which the various
  constituents or phases of alloys are stable.
   
Etching Treatment of a prepared metal surface with acid
  or other chemical reagent which, by differential
  attack, reveals the structure.
   
Eutectic A mixture of two or more constituents which
  solidify simultaneously out of the liquid at a
  minimum freezing point.
   
Eutectoid A mixture of two or more constituents which
  forms on cooling from a solid solution and
  transforms on heating at a constant minimum
  temperature. A eutectoid steel contains
  approximately 0.83% carbon.
   
Extrusion The production of a section by forcing a billet to
  flow through a die. Often used for producing
  complex sections, the process is used with both
  hot and cold metal. Seamless tubes are
  produced by forcing a hot billet to flow through a
  die over a mandrel positioned centrally in the
  die.
   
F Chemical symbol for Fluorine.
   
Face Centred Cubic An arrangement of atoms in crystals in which the
Lattice atomic centres are disposed in space in such a way
  that one atom is located at each of the corners of
  the cube and one at the centre of each face. Steel
  in the face-centred cubic arrangement is termed
  austenite.
   
Fatigue The effect on metal of repeated cycles of stress.
  The insidious feature of fatigue failure is that there
  is no obvious warning, a crack forms without
  appreciable deformation of structure making it
  difficult to detect the presence of growing cracks.
  Fractures usually start from small nicks or scratches
  or fillets which cause a localised concentration of
  stress. Failure can be influenced by a number of
  factors including size, shape and design of the
  component, condition of the surface or operating
  environment.
   
Fatigue Limit The maximum value of the applied alternating
  stress which a test piece can stand indefinitely.
   
Fatigue Testing Fatigue tests are made with the object of
  determining the relationship between the stress
  range and the number of times it can be applied
  before causing failure. Testing machines are used
  for applying cyclically varying stresses and cover
  tension, compression, torsion and bending or a
  combination of these stresses.
   
Fe Chemical symbol for Iron.
   
Ferrite The solid solution of carbon in body-centered cubic
  iron, a constituent of carbon steels.
   
Ferritic Steel A term usually applied to a group of stainless steels
  with a chromium content in the range of 12-18o
  and whose structure consists largely of ferrite. Such
  steels possess good ductility and are easily worked
  but do not respond to any hardening or tempering
  processes. Types of applications include
  automotive trim and architectural cladding.
   
Ferro Alloys Alloys of iron with chromium, manganese, silicon,
  tungsten, molybdenum or vanadium. Used in
  steelmaking as a means of introducing these
  alloying elements into the cast or as deoxidisers.
   
Fettling The removal of sand adhering to castings by
  hammering, tumbling or shot blasting.
   
Fin In rolling mill practice a fin is a projection extending
  from the side of rolled sections. It causes
  considerable trouble and is the result of overfill.
  The fin, formed when the bar or shape is fed
  through one pass, is likely to be rolled back into the
  bar at the next pass. It is rarely encountered in
  modern rolling mills.
   
Flame Hardening A surface hardening process in which heat is
  applied by a high temperature flame followed by
  quenching jets of water. It is usually applied to
  medium to large size components such as large
  gears, sprockets, slide ways of machine tools,
  bearing surfaces of shafts and axles, etc. Steels
  most suited have a carbon content within the range
  0.40-0.55%.
   
Flash A fin that arises from metal in excess of that
  required to fill the final impression in a forging die
  and is exuded from the parting line between the
  dies; similarly it can arise at the mold joint in a
  casting.
   
Forging A process of working metal to a finished shape by
  hammering or pressing and is primarily a "hot"
  operation. It is applied to the production of shapes
  either impossible or too costly to make by other
  methods or needing properties not obtainable by
  casting. Categories of forgings include Hammer,
  Press, Drop or Stamping.
   
Fracture Fractures are often described by the appearance of
  the surface of the break in a piece of steel.
  Crystalline is bright and glittering, failure having
  developed along the cleavage planes of individual
  crystals and can be typical of brittle material. A
  silky fracture has a smooth dull grain indicative of
  ductile material such as a mild steel. In tensile
  testing fractures are described by shape, e.g. cup
  and cone.
   
Freecutting Steels Steels which have had additions made to improve
  machinability. The most common additives are
  sulphur and lead, other elements used include
  tellurium, selenium and bismuth.
   
Ga Chemical symbol for Gallium.
   
Galvanic Action When iron and steel are subject to conditions of
  aqueous corrosion the incidence and rate at which
  the corrosion takes place will alter if the steel is
  coupled with other metals or alloys that are also
  exposed to the electrolyte. Copper, brass, bronze,
  lead and nickel are more "noble" and act as
  auxiliary cathodes to the steel and accelerate its
  anodic dissolution, that is, its corrosion.
  Magnesium, zinc and zinc-base alloy are nearly
  always less noble and tend to divert the attack
  from the steel to themselves. The galvanic
  relationship of various metals is an important factor
  affecting corrosion.
   
Gamma Iron The allotropic form of iron existing between the
  temperature 910 deg C and 1400 deg C is known as
  Gamma Iron. It has a face centred cubic lattice and
  is non-magnetic. Gamma iron containing carbon or
  other elements in solution is known as austenite.
   
Gas Carburising A heat treatment method used in the case-
  hardening of steel. Carbon is absorbed into the
  outer layers of the components by heating in a
  current of gas, rich in carbon compounds. The
  process is more versatile than some other methods
  as the depth of the case and the limiting carbon
  content of the case can be controlled by the
  composition of the atmosphere, the dew point and
  the temperature.
   
Gauge Length Used in the mechanical testing of steel, it is the
  length marked on the parallel portion of a tensile
  test piece from which the elongation is measured.
   
Gauge Plate An alloy tool steel supplied in flat and square
  section with the surfaces ground to close limits. It
  is also known as Ground Flat Stock and is used for
  the manufacturing of gauges, punches, dies, jigs,
  templates etc.
   
Ge Chemical symbol for Germanium.
   
Grain Size Control When a steel is austenitised by heating to above
  the critical range, time is required for the
  production of a homogeneous structure during
  which there is a tendency towards grain growth.
  Although subsequent hot and cold working affect
  the grain size, it is originally controlled at the steel
  making stage by the addition ofaluminium.
   
Grain Size Measurement Grain size is normally quantified by a numbering
  system. Coarse 1-5 and fine 5-8. The number is
  derived from the formula N=2n-1 where n is the
  number of grains per square inch at a magnification
  of 100 diameters. Grain size has an important
  effect on physical properties. For service at
  ordinary temperatures it is generally considered
  that fine grained steels give a bettercombination of
  strength and toughness, whereas coarse grained
  steels have better machinability.
   
Graphitising An annealing process applied to cast iron and
  steels with a high carbon and high silicon content
  by which the combined carbon is wholly or in part
  transformed to graphitic or free carbon.
   
Grey Iron Also known as flake iron on account of all or part of
  the carbon content being in the form of graphite
  distributed through the metal as flakes.
   
Grinding A machining process:- (a) to shape components
  that are too hard to be machined by conventional
  methods such as hardened tool steels and case or
  induction hardened components. (b) to obtain a
  high degree of dimensional accuracy and surface
  finish on a component.
   
Grinding Cracks Cracks can arise from incorrect grinding and appear
  in the form of a network. They are caused by the
  generation of high heat and rapid cooling in the
  area of contact and they mostly occur when
  grinding fully hardened material such as tool steel.
   
H Chemical symbol for Hydrogen.
   
Hard Metal Facing A method of increasing the wear resistance of a metal
  by the deposition of a hard protective coating. Alloys
  such as Stellite or a metallic carbide are most often
  used for the coating.
   
Hard Metals A group of materials more commonly known as
  cemented carbides. They consist of mixtures of one or
  more of the finely divided carbides of tungsten,
  titanium, tantalum and vanadium embedded in a
  matrix of cobalt or nickel by sintering. Widely used for
  cutting tools where for many applications they have
  replaced conventional high speed steels.
   
Hardenability The property that determines the depth and
  distribution of hardness when steel is heated to a
  given temperature and then quenched (more precisely
  it may be defined as an inverse measure of the
  severity of cooling conditions necessary to produce on
  continuous cooling a martensitic structure in a
  previously austenitized steel i.e. to avoid
  transformations in the pearlitic and bainitic ranges).
  The lower the cooling rate to avoid these
  transformations, the greater the hardenability. The
  critical cooling rate is largely a function of the
  composition of the steel. In general the higher the
  carbon content, the greater the hardenability, while
  alloying elements such as nickel, chromium,
  manganese and molybdenum increase the depth of
  hardening for a given ruling section.
   
Hardening Increasing the hardness of steel by heat treatment.
  This normally implies heating the steel to a required
  temperature and quenching in a suitable medium, e.g.
  oil or water.
   
Hardness The hardness of steel is generally determined by
  testing its resistance to deformation. A number of
  methods are employed including Brinell, Vickers and
  Rockwell. The steel to be tested is indented by a
  hardened steel ball or diamond under a given load
  and the size of the impression is then measured. For
  steel there is an empirical relationship between
  hardness and tensile strength and the hardness
  number is often used as a guide to the tensile
  strength, e.g. 229 Brinell = 772N/mm2 (50 tons/sq.in).
   
Heat In steel making terms this is often used to define the
  batch or cast produced from a single melting
  operation.
   
Heat Treatment A process where solid steel or components
  manufactured from steel are subject to treatment by
  heating to obtain required properties, e.g. softening,
  normalising, stress relieving, hardening. Heating for
  the purpose of hot-working as in the case of rolling or
  forging is excluded from this definition.
   
High Speed Steel The term `high speed steel' was derived from the fact
  that it is capable of cutting metal at a much higher
  rate than carbon tool steel and continues to cut and
  retain its hardness even when the point of the tool is
  heated to a low red temperature. Tungsten is the
  major alloying element but it is also combined with
  molybdenum, vanadium and cobalt in varying
  amounts. Although replaced by cemented carbides for
  many applications it is still widely used for the
  manufacture of taps, dies, twist drills, reamers, saw
  blades and other cutting tools.
   
Hooke's Law This states that "within the limits of elasticity the
  strain produced by a stress of any one kind is
  proportional to the stress". The stress at which a
  material ceases to obey Hooke's Law is known as the
  limit of proportionality.
   
Hot Quenching Cooling in a medium, the temperature of which is
  substantially higher than room temperature.
   
Hot Work The rolling, forging or extruding of a metal at a
  temperature above its recrystallisation point.
   
Hydrogen An undesirable impurity if present in steel and a cause
  of fine hairline cracks especially in alloy steels.
  Modern vacuum treatment eliminates this problem.
  Steel
Hyper-Eutectoid A steel that contains more than 0.83% carbon which
  with appropriate heat treatment consists of pearlite
  and cementite.
   
Hypo-Eutectoid Steel A steel that contains less than 0.83% carbon and
  which in annealed condition has a structure of ferrite
  and pearlite.
   
I Chemical symbol for Iodine.
   
Impact Test A test designed to give information on how a
  specimen of a known material will respond to a
  suddenly applied stress, e.g. shock. The test
  ascertains whether the material is tough or
  brittle. A notched test piece is normally
  employed and the two methods in general use
  are either the Izod or Charpy test. The result is
  usually reported as the energy in ft.lbs. or KJ.
  required to fracture the test piece.
   
In Chemical symbol for Indium.
   
Inclusion Count A method of assessing the number and size of
  non-metallic inclusions present in metal.
   
Inclusions Usually non-metallic particles contained in
  metal. In steel they may consist of simple or
  complex oxides, sulphides, silicates and
  sometimes nitrides of iron, manganese, silicon,
  aluminium and other elements. In general they
  are detrimental to mechanical properties but
  much depends on the number, their size,
  shape and distribution.
   
Induction Hardening A widely used process for the surface
  hardening of steel. The components are
  heated by means of an alternating magnetic
  field to a temperature within or above the
  transformation range followed by immediate
  quenching. The core of the component remains
  unaffected by the treatment and its physical
  properties are those of the bar from which it
  was machined, while the hardness of the case
  can be within the range 37/58 Rc. Carbon and
  alloy steels with a carbon content in the range
  0.40/0.45% are most suitable for this process.
   
Ingot The mass of metal that results from casting
  molten steel into a mold. An ingot is usually
  rectangular in shape and is subsequently rolled
  into blooms and billets for rods, bars and
  sections and slabs for plates, sheet and strip.
  With the increasing use of the continuous
  casting process the ingot route is less used as
  the molten steel is now directly cast into a
  bloom or billet.
   
Ingot Mold The receptacle into which molten steel is
  poured to form an ingot. After solidification the
  steel is suitable for subsequent working, i.e.
  rolling or forging.
   
Intercrystalline Corrosion Chromium-nickel austenitic stainless steels are
  prone to this form of corrosion when they are
  welded and subsequently in contact with
  certain types of corrosive media. When heated
  within a temperature range of 450-800 deg C
  precipitation of the chromium carbides takes
  place at the grain boundaries in the area of the
  weld and these areas no longer have the
  protection of the chromium on the peripheries
  of the grains. This type of corrosion is also
  known as Weld Decay and Intergranular
  Corrosion. The most common way to avoid the
  problem is to select a grade of steel that is
  very low in carbon i.e. 0.03% or less, or one
  that is stabilised with niobium or titanium.
   
Interrupted Quenching Rapid cooling to a selected temperature by
  quenching in a suitable medium, usually molten
  salt, holding at the temperature for an
  appropriate time and then cooling to room
  temperature. This process is used to minimise
  the risk of distortion.
   
Iron The term iron, as used in the chemical or
  scientific sense of the word, refers to the
  chemical element iron or pure iron and is the
  chief constituent of all commercial iron and
  steel.
   
Isothermal Annealing Heating to and holding at a temperature above
  the transformation range, then cooling to and
  holding at a suitable temperature until the
  austenite to pearlite change is complete.
   
Isothermal Transformation Also known as the Time Temperature
Curve Transformation Curve. If a small piece of steel
  is heated sufficiently slowly for it to become
  austenitic and then plunged into a salt bath
  and held at a constant temperature below the
  upper critical point for a definite time followed
  by rapid quenching, it is possible by
  examination to determine the extent to which
  the transformation of the austenite has
  occurred. By taking a number of specimens of
  the same steel and treating them in the same
  way, but varying the holding temperature and
  time the behavior of the steel with time and
  temperature can be studied. The information
  obtained can be plotted as time-temperature
  transformation curves which is useful in heat
  treatment practice, particularly for
  martempering and austempering.
   
Izod Impact Test A test specimen, usually of square crossed
  section is notched and held between a pair of
  jaws, to be broken by a swinging or falling
  weight. When the pendulum of the Izod testing
  machine is released it swings with a downward
  movement and when it reaches the vertical the
  hammer makes contact with the specimen
  which is broken by the force of the blow. The
  hammer continues its upward motion but the
  energy absorbed in breaking the test piece
  reduces its momentum. A graduated scale
  enables a reading to be taken of the energy
  used to fracture the test piece. To obtain a
  representative result the average of three tests
  is used and to ensure that the results conform
  to those of the steel specification the test
  specimens should meet the standard
  dimensions laid down in BS 131.
   
Jominy Test A method for determining the hardenability of steel. The Jominy
  test is covered by BS 4437:1987. A standard test piece 25mm x
  100mm is heated to a pre-determined temperature and
  quenched by a jet of water sprayed onto one end. When the
  specimen is cold, hardness measurements are made at intervals
  along the test piece from the quenched end and the results are
  plotted on a standard chart from which is derived the
  hardenability curve. BS 970 contains hardenability curves for
  many of the steels in the Standard. Properly carried out, this
  test will illustrate the effect of mass upon a chosen steel when
  heat treated and indicate if the steel is of a shallow, medium or
  deep hardening type.
   
Joule A unit of energy. One joule is equal to the energy expended in
  one second by one ampere against the resistance of one ohm.
  In the mechanical testing of steel it is the unit used in the
  Charpy V notch impact test.
   
K Chemical symbol for potassium.
   
  A method of producing steel from molten iron, using
Kaldo Process an inclined rotating converter and a water cooled
  oxygen lance inserted through the converter mouth.
  Originating in Sweden, this process is no longer in use
  in the UK.
   
Killed Steel The term indicates that the steel has been completely
  deoxidised by the addition of an agent such as silicon
  or aluminium, before casting, so that there is
  practically no evolution of gas during solidification.
  Killed steels are characterised by a high degree of
  chemical homogeneity and freedom from porosity.
   
Knoop Hardness Test A micro hardness test in which an elongated
  pyramidical diamond is pressed into the surface.
   
La Chemical symbol for Lanthanum.
   
Lap A defect appearing as a seam on a rolled bar. Laps
  are rolled over pieces of material that arise when a
  bar is given a pass through the rolls after a sharp
  overfill or fin has been formed, causing the
  protrusion to be rolled into the surface of the
  product. The presence of oxides usually prevents
  the lap welding to the original bar surface, so that
  in subsequent cold working it is carried through as
  a longitudinal crack.
   
L-D Process An oxygen steel making process named after the
  towns in Austria, Linz and Donawitz, where it was
  first developed. It is a modified Bessemer process,
  steel is produced in a solid bottom converter by
  injection of oxygen into the molten iron bath from a
  water cooled lance inserted through the converter
  mouth. Present day BOS (basic oxygen
  steelmaking) plants are developments of the L-D
  Process.
   
Leaded Steels When added to steel, lead does not go into
  solution but exists in a very finely divided state
  along the grain boundaries. It greatly assists
  machinability as it acts as a lubricant between the
  steel and the tool face. Lead is normally added in
  amounts between 0.15-0.35% and when combined
  with similar amounts of sulphur, optimum
  machinability is attained as in such steel as BS 970
  230M07 Pb.
   
Li Chemical symbol for Lithium.
   
Limiting Range of The greatest range of stress that a metal can
Stress withstand for an indefinite number of cycles without
  failure. If exceeded, the metal fractures after a
  certain number of cycles, which decrease as the
  range of stress increases.
   
Limiting Ruling Section The maximum diameter of cross section of a bar or
  component in which certain specified mechanical
  properties are achieved after heat treatment.
   
Limits A term used to determine a minimum and
  maximum. In a mechanism, it should denote the
  minimum and maximum sizes for each part,
  between which the parts will function properly in
  conjunction with each other and outside of which
  they will not. The words "limits" and "tolerances"
  are often interchanged, "tolerance" represents the
  difference between the minimum and maximum
  limits.
   
Limits of Proportionality The stress (load divided by original area of cross
  section of the test piece) at which the strain
  (elongation per unit of gauge length) ceases to be
  proportional to the corresponding stress. It is
  usually determined from a load-elongation diagram,
  obtained by plotting extensometer readings and is
  the stress at which the load-elongation line ceases
  to be straight.
   
Liquid Carburising A widely used method of case-hardening steel that
  eliminates scaling and the tendency to
  decarburisation and results in clean components.
  Sodium cyanide is the common media for this
  process, usually heated within the range of
  900-930 deg C. It is advisable to pre-heat the
  components in neutral salts to avoid a temperature
  drop resulting from immersing cold components into
  the cyanide. After carburising, either single quench
  hardening or refining and hardening and tempering
  is carried out.
   
Machinability Simply defined as a measure of the ease with
  which a metal can be machined satisfactorily.
   
Macrostructure The general crystalline structure of a metal and
  the distribution of impurities seen on a polished
  or etched surface by either the naked eye or
  under low magnification of less than x10.
   
Magnetic Crack Detection The bar or component to be tested is
  magnetised by passing a heavy current through
  it or by making it the core of a coil through
  which a heavy current is passed. Cracks or
  inclusions cause the magnetic flux to break the
  surface forming free magnetic poles. When the
  component is sprayed with a suspension of
  finely divided magnetic particles they collect at
  the free poles to visibly show the presence of
  defects.
   
Malleability It can be defined as the property of a metal to
  be deformed by compression without cracking or
  rupturing. The load may be applied slowly or
  suddenly and will determine whether the
  material will be suitable for forging or rolling into
  thin sheet.
   
Manganese One of the most important constituents of steel
  in which it fulfils a number of functions. It acts
  as a mild de-oxidising agent. It combines with
  the sulphur present to form globular inclusions
  of Manganese Sulphide which are beneficial to
  machining. It increases tensile strength and the
  hardenability of steel.
   
Martempering A heat treatment involving austenitisation
  followed by step quenching, at a rate fast
  enough to avoid the formation of ferrite, pearlite
  or bainite to a temperature slightly above the Ms
  point. Soaking must be long enough to avoid
  the formation of bainite. The advantage of
  martempering is the reduction of thermal
  stresses compared to normal quenching. This
  prevents cracking and minimises distortion.
   
Martensite The hard constituent produced when steel is
  cooled from the hardening temperature at a
  speed greater than its critical cooling rate.
  Martensite is an acicular phase when seen in
  the microstructure of steel.
   
Mass Effect A term used to signify the effect of size and
  shape during heat treatment, since it is the rate
  of cooling of a piece of steel which determines
  the properties resulting from the hardening and
  quenching process.
   
Matrix The mass or principal constituent (e.g. iron in
  the case of steel) in which other constituents
  are embedded.
   
Maximum Stress In the testing of the strength of steel a sample
  is machined into a standard test piece and is
  stretched in a tensile testing machine until it
  breaks. The results are expressed in N/mm2 and
  is the value of the maximum load reached in the
  test divided by the original cross sectional area
  of the specimen.
   
McQuaid EHN Grain Size A method of assessing grain size. It consists of
Test a test piece at 927 deg C for 8 hours by slow
  cooling and subsequent microscopical
  examination. The grain size is measured at x100
  magnification and compared to standard charts,
  the figures range from No. 1 -very coarse, to
  No. 8 - very fine.
   
Meehanite A trade name applied to a certain type of cast
  iron.
   
Melting Point The temperature at which a solid begins to
  liquefy.
   
Mg Chemical symbol for Magnesium.
   
Micron A unit of length equal to one millionth of a
  metre (0.001mm).
   
Microstructure The structure that is observed when a polished
  and etched specimen of metal is viewed in an
  optical microscope at magnifications in range of
  approximately x25 to x1500.
   
Mn Chemical symbol for Manganese.
   
Mo Chemical symbol for Molybdenum.
   
Modulus of Elasticity When a material is subjected to an external load
  it becomes distorted or strained. With metals,
  provided the loading is not too great, they return
  to their original dimensions when the load is
  removed, i.e. they are elastic. Within the limits
  of elasticity, the ratio of the linear stress to the
  linear strain is termed the modulus of elasticity
  or more commonly known as Young's Modulus.
   
Molybdenum Its use as an alloying element in steel increases
  hardenability and in low alloy steels reduces the
  risk of temper brittleness. When added to
  stainless steels it increases their resistance to
  corrosion. It is also used in high speed steels.
   
N Chemical symbol for Nitrogen.
   
Na Chemical symbol for Sodium.
   
Nb Chemical symbol for Niobium.
   
Ni Chemical symbol for Nickel.
   
Nickel One of the most widely used alloying elements in
  steel. In amounts 0.50% to 5.00% its use in alloy
  steels increases the toughness and tensile strength
  without detrimental effect on the ductility. Nickel
  also increases the hardenability, thus permitting the
  steel to be oil-hardened instead of water quenched.
  In larger quantities, 8.00% and upwards, nickel is
  the constituent, together with chromium, of many
  corrosion resistant and stainless austenitic steels.
   
Niobium Also known as columbium. Niobium is a strong
  carbide forming element which is added to certain
  18/8% chromium-nickel stainless steels as a
  stabiliser to prevent inter-granular corrosion arising
  from welding.
   
Nitriding A case hardening process that depends on the
  absorption of nitrogen into the steel. All machining,
  stress relieving, as well as hardening and tempering
  are normally carried out before nitriding. The parts
  are heated in a special container through which
  ammonia gas is allowed to pass. The ammonia splits
  into hydrogen and nitrogen and the nitrogen reacts
  with the steel penetrating the surface to form
  nitrides. Nitriding steels offer many advantages: a
  much higher surface hardness is obtainable when
  compared with case-hardening steels; they are
  extremely resistant to abrasion and have a high
  fatigue strength.
   
Nitrogen Nitrogen is a gas that forms approximately 79% by
  volume or 77% by weight of the atmosphere. It can
  combine with many metals to form nitrides and is
  thus applied to the case-hardening of steel, the
  usual source for this purpose being ammonia.
   
Noble Metals Metals such as gold, silver and platinum which are
  resistant to corrosion by all but the most powerful
  acids.
   
Non Destructive Those forms of testing that do not result in
Testing permanent damage or deformation to the part being
  tested. Typical examples are magnetic crack
  detection, ultrasonic inspection, X-Ray inspection
  and gamma radiography.
   
Non Magnetic Steels Austenitic steels such as the 14% manganese steels
  and the 303 type 18/8% chromium-nickel stainless
  steels.
   
Normalising A heat treatment process that has the object of
  relieving internal stresses, refining the grain size and
  improving the mechanical properties. The steel is
  heated to 800-900 deg C according to analysis, held at
  temperature to allow a full soak and cooled in still
  air.
   
Notched Bar Test A test to determine the resistance of a material to a
  suddenly applied stress, i.e. shock. A notched test
  piece is employed in an Izod or Charpy machine and
  the results are recorded in ft.lbs. or Joules.
   
O Chemical symbol for Oxygen.
   
Occlusion A term applied, in the case of metals, to the
  absorption or entrapment of gases.
   
Oil Hardening Steel Used to describe tool or alloy steels where oil is
  used as the quenching medium in the hardening
  process.
   
Open Hearth Furnace Developed in the middle of the last century, the
  open hearth or Siemens-Martins process, as it is
  known, accounted for a major proportion of UK steel
  production until the early 1970's. For economic and
  quality reasons it has been replaced by the Electric
  Arc Furnace and the Basic Oxygen Steelmaking
  process. There are no open hearth furnaces in use
  in Britain today but they are still in use in Russia and
  Eastern Europe.
   
Orange Peel Effect An effect that arises on the surface of steel sheets
  when they are stretched beyond their elastic limit.
   
Ore An ore is a material that contains a metal in such
  quantities that it can be mined and worked
  commercially to extract that metal. The metal is
  usually contained in chemical combination with some
  other element in addition to various impurities.
   
Os Chemical symbol for Osmium.
   
Overheating Failure of tools and components in heat treatment
  can arise through overheating. This may be caused
  due to quenching from a temperature too high for
  the type of steel involved. Overheating is evidenced
  by cracking, grain-coarseness, erratic surface
  hardness and pitting.
   
Oxidation A common form of chemical reaction which is the
  combining of oxygen with various elements and
  compounds. The corrosion of metals is a form of
  oxidation, rust on iron for example is iron oxide.
   
Oxy-Acetylene Welding A process for joining two pieces of metal in which
  the required high temperature is obtained by the
  combustion of acetylene gas and oxygen. The gases
  are thoroughly mixed in the nozzle or tip of the
  welding torch to ensure perfect combustion. The
  weld may be formed directly between two adjoining
  surfaces, but usually metal from a welding rod is
  fused in between the surfaces of the joint.
   
Oxygen Oxygen is one of the chief constituents of the
  atmosphere of which it forms approximately one
  fifth. It is odorless and invisible. Although oxygen
  itself does not burn it is extremely efficient in
  supporting combustion, nearly all other chemical
  elements combine with it under evolution of heat. It
  has many uses in industry and is essential to the
  BOS (Basic Oxygen Steelmaking Process).
   
P Chemical symbol for Phosphorus.
   
Parkerising A chemical treatment applied to ferrous metals to
  improve their corrosion resistance. The process is based
  on a manganese phosphate solution which produces a
  fairly thick coating. This can subsequently be painted or
  impregnated with oil. Patenting A heat treatment process
  often applied to high carbon wire. The steel is heated to
  a suitable temperature well above the transformation
  range, followed by cooling in air or a bath of molten lead
  or salt. A structure is produced suitable for subsequent
  cold drawing and which will give the desired mechanical
  properties in the finished state.
   
Pd Chemical symbol for Palladium.
   
Pearlite A lamellar constituent of steel consisting of alternate
  layers of ferrite (alpha-iron) and cementite (iron Carbide
  Fe3C) and is formed on cooling austenite at 723 deg C. This
  produces a tough structure and is responsible for the
  mechanical properties of unhardened steel.
   
Ph Chemical symbol for Lead.
   
pH Value A method of expressing differences in the acidity or
  alkalinity of a solution. A figure of 7 is regarded as
  neutral, figures below this indicate the decree of acidity
  and above alkalinity.
   
Phosphorus An element that forms 0.12% of the earth's crust, chiefly
  in the form of phosphates. Its presence in steel is usually
  regarded as an undesirable impurity due to its embrittling
  effect, for this reason its content in most steels is limited
  to a maximum of 0.050%.
   
Pickling A process to chemically remove scale or oxide from steel
  to obtain a clean surface. When applied to bars or coils
  prior to bright drawing, the steel is immersed in a bath of
  dilute sulphuric acid heated to a temperature of around
  80 deg C. An inhibitor is added to prevent attack and pitting
  of the cleaned metal. After pickling, a washing process
  takes place followed by immersion in a lime-water bath to
  neutralise any remaining acid. For environmental reasons
  shot blasting has largely replaced pickling.
   
Pig Iron The product of the blast furnace. The term was derived
  from the method of casting the bars of the pig iron in
  depressions or molds formed in the sand floor adjacent
  to the furnace. These were connected to a runner
  (known as a sow) and when filled with metal the runner
  and the numerous smaller molds were supposed to
  resemble a litter of suckling pigs, hence the term pig
  iron.
   
Pinch Pass A term applied when, after annealing, sheet or strip is
  lightly rolled with the object of preventing stretcher lines
  or kinks on subsequent cold working.
   
Pipe A defect that arises during the solidification of steel in
  the ingot mold. As steel contracts on solidification a
  central cavity forms in the upper portion of the ingot, if
  this is not completely removed before rolling into bars a
  central defect known as "pipe" results. The risk of piping
  is considerably reduced on continuously cast steel due to
  molten steel being available to fill any shrinkage cavity.
   
Poisson's Ratio If a square bar is stressed in a testing machine in the
  direction of its length so that the length increases, there
  is a contraction in each opposite direction, which
  produces a decrease in the thickness of the bar. The
  ratio between the contraction at right angles to a stress
  and the direct extension is called the Poisson's ratio. Its
  value in steel is in the order of 0.28.
   
Pot Quenching Quenching carburised parts directly from the carburising
  pot or box.
   
Powder Metallurgy A method of producing components by pressing or
  molding metal powders which may be simultaneously or
  subsequently heated to produce a coherent mass.
   
Pre-Heating Used in the hardening process. Tools are pre-heated
  before heating to the final temperature, this is
  particularly important in tools of complex shape to
  prevent distortion or cracking. Pre-heating reduces the
  time of exposure to the hardening temperature and helps
  to minimise scaling and decarburisation.
   
Projection Welding A welding process that uses small projections on one or
  both components of the weld to localise the heat and
  pressure, the projections collapse when the weld is
  made.
   
Proof Stress The stress that will cause a specified small, permanent
  extension of a tensile test piece. Commonly the stress to
  produce 0.2% extension is quoted in N/mm2 for steel.
  This value approximates to the yield stress in materials
  not exhibiting a definite yield point.
   
Quenching Rapid cooling from a high temperature by immersion in a
  liquid bath of oil or water. Molten salts may also be used.
   
Quenching Crack A fracture, often termed a hardening crack, which arises
  from thermal stresses induced during rapid cooling.
   
Ra Chemical symbol for Radium.
   
Radiography A method of non-destructive testing. Internal
  examination of a metallic structure or component
  is carried out by exposing it to a beam of X-Ray
  or gamma radiation. Internal defects can be
  seen on a screen or recorded on film.
   
Rb Chemical symbol for Rubidium.
   
Re Chemical symbol for Rhenium.
   
Re-crystallisation The re-arrangement of crystals in cold worked
  metal brought about by heating so that the
  deformed crystals are absorbed by newly-formed
  crystals and the effects of work hardening are
  removed. Also occurs when steel is heated
  through the transformation range and when steel
  is hot worked.
   
Red Hardness A term sometimes associated with high speed
  steel because it has the property of retaining
  sufficient hardness for cutting metals even when
  heated to a temperature high enough to cause a
  dull redness. The tungsten content has a
  significant influence on this property.
   
Reduction of area The percentage decrease in the cross-sectional
  area of a tensile test piece caused by wasting or
  necking of the specimen. It is expressed as a
  percentage of the original area of the test piece
  and is a measure of ductility.
   
Refining (a) The removal of impurities and metallic oxides
  from the molten bath by the reaction of the slag
  and other additions. (b) A heat treatment
  process with the object of refining or making the
  grain size of the steel uniform.
   
Residual Stress The stress which exists in an elastic solid body
  in the absence of, or in addition to, the stresses
  caused by an external load. Such stresses can
  arise from deformation during cold working such
  as cold drawing or stamping, in welding from
  weld metal shrinkage, and in changes in volume
  due to thermal expansion.
   
Rh Chemical symbol for Rhodium.
   
Rockwell Hardness Testing A method for testing the hardness of metals by
  determining the depth of penetration of a steel
  ball or a diamond sphero-conical indentor. The
  value is read from a dial and is an arbitrary
  number related to the depth of penetration. For
  testing hard steels, a sphero-conical diamond is
  used with a 150 kg load, the result is read from
  the black scale on the dial and is prefixed with
  the letter C. A hardened tool steel would
  typically give a reading of 62Rc. For softer
  metals Scale B is used with a 1/16" diameter
  steel ball and a standard load of 100 kgs.
   
Rolling The process of shaping metal by passing it
  between rolls revolving at the same peripheral
  speed and in opposite directions. In steel there
  are a number of different types of rolling mill for
  processing the ingot to its finished shape. These
  are variously known as Cogging mills, Slabbing
  mills, Billet mills, Bar mills and Strip mills, which
  produce plate, sections, bars, sheet and strip.
  Cold rolling of previously hot rolled strip is
  carried out to produce strip that is accurate to
  size and with a smooth bright polished surface.
   
Rolling Lap A fault arising from the overfilling or mis-
  alignment of rolls, the result is a bulge on the
  bar which is rolled into the metal and is lapped
  over. It remains throughout subsequent working
  and appears as a longitudinal crack.
   
Ru Chemical symbol for Ruthenium.
   
Ruling Section More accurately termed limiting ruling section.
  One of the most important factors associated
  with the choice of steel for a given purpose is to
  ensure that the desired mechanical properties
  are obtained throughout the section when the
  material has been heat treated. The limiting
  ruling section determines the maximum diameter
  or cross-section of a bar or component in which
  the specified properties can be achieved by a
  given heat treatment. The analysis of the steel
  also has an important bearing on this.
   
S Chemical symbol for Sulphur.
   
Salt Bath A method of heating steel using a bath of molten salts.
  Salt baths give uniform heating and prevent oxidation,
  they are used for hardening, tempering or quenching. The
  type of salt used depends on the temperature range
  required. For hardening, sodium cyanide, sodium
  carbonate and sodium chloride are in common use.
   
Sb Chemical symbol for Antimony.
   
Scale The oxidised surface of steel produced during hot working,
  as in rolling, and by exposure to air or steam at elevated
  temperature.
   
Scarfing Also termed deseaming. It is a process for burning out
  defective areas on the surface of ingots or semi-finished
  products such as billets so that the product is suitable for
  subsequent rolling or forging.
   
Scrap It forms the basic raw material for making steel by the
  electric arc process. Steel offers ecological advantages as
  it can be recycled enabling the discarded car of today to
  appear as part of a new model tomorrow. Scrap is sorted
  and graded before use and the necessary elements are
  added during the steel making process to achieve the
  desired specifications.
   
Se Chemical symbol for Selenium. Seams A surface defect
  caused during the steel making process. Seams are
  generally formed from blow holes in the ingot, non metallic
  inclusions, or stresses arising during the solidification
  stage. They appear as longitudinal discontinuities in the
  bar.
Secondary  
Hardness An increase in hardness which sometimes occurs when
  hardened steel is re-heated. It can be caused by the
  transformation of retained austenite to martensite or by
  the precipitation of alloy carbides.
   
Segregation A term applied to the concentration and partial separation
  of one or more elements from solution during solidification
  of liquid steel in an ingot mold. Sulphur and phosphorus
  tend to segregate to a greater extent than other elements
  which can have a particular adverse effect on machinability
  in high sulphur free-cutting steels. Modern steel making
  and continuous casting have largely overcome this
  problem.
   
Selenium An element that closely resembles sulphur in its properties.
  The main use in steel is as a freecutting additive but due
  to high cost its use is limited to stainless steel. One of the
  benefits being the ability to obtain a very good surface
  finish on machined components.
   
SG Iron An abbreviation for Spheroidal Graphite Cast Iron. As the
  name implies, graphite is present in spheroidal form
  instead of flakes and compared with Grey Cast Iron it has
  higher mechanical strength, ductility and increased shock
  resistance.
   
Shearing Test The test applied to metal to determine the stress required
  to fracture it across its section.
   
Sherardizing A process developed in Britain in 1904 by Sherard
  Cowper-Coles. It is a method of producing a protective
  zinc coating on iron and steel products.
   
Shore An instrument that measures the hardness of a sample in
Scleroscope arbitrary terms of elasticity. A diamond tipped hammer is
  allowed to fall freely down a graduated glass tube on to
  the sample under test. The hardness is measured by the
  height of the rebound. In another form the rebounding
  hammer actuates the pointer of a scale so that the height
  of the rebound is recorded.
   
Spinning The formation of sheet metal blanks into hollow circular
  shapes. This is carried out on a lathe with forming tools
  which service to press and shape the metal. Annealing
  may be needed during and/or after the operation to
  remove the effects of work hardening.
   
Spot Welding A process for joining steel sheets. The two parts are held
  between electrodes and the heat generated at the
  interface between the sheets causes local welding when
  pressure is applied.
   
Spring Steel The steels used for spring making depend on the
  application and type of spring. They range from plain
  carbon grades in the range 0.5% to 1.00% C. to
  Chromium, Chromium-Vanadium,
  Nickel-Chromium-Molybdenum, Silico-Manganese and
  Silicon-Manganese-Chromium-Molybdenum types. Full
  details can be found in BS5770.
   
Stabilisation A term applied to a number of processes: a) A type of heat
  treatment to relieve internal stresses: b) The retarding or
  prevention of a particular reaction by the addition of a
  stabilising element; c) A thermal and/or mechanical
  treatment given to magnetic material in order to increase
  the permanency of its magnetic properties or condition.
   
Stainless Steel Can be defined as a group of corrosion resisting steels
  containing a minimum 10% chromium and in which varying
  amounts of nickel, molybdenum, titanium, niobium as well
  as other elements may be present. An Englishman, Harry
  Brearley, is generally acknowledged to be the pioneer who
  developed stainless steels for commercial use.
   
Steel Generally defined as a metallic product whose principal
  element is iron and where the carbon content is not more
  than 2%. (The presence of large quantities of carbide
  forming elements may modify the upper limit of the carbon
  content.)
   
Strain Ageing The gradual changes in physical and mechanical
  properties, in particular hardness and tensile strength,
  which takes place following cold rolling or deformation. At
  atmospheric temperatures, this may take place over a
  number of weeks but can be accelerated by heating.
   
Strain Hardening The loss of ductility and gain in hardness resulting from
  strain ageing.
   
Stress Relieving A heat treatment including heating and soaking at a
  suitable temperature (e.g. 600-650 deg C) followed by cooling
  at an appropriate rate in order to reduce internal stresses
  without substantially modifying the steel's structure. This
  treatment may be used to relieve stresses induced by
  machining, quenching, welding or cold working.
   
Stress Strain A graph in which stress (load divided by the original cross
Curve sectional area of the test piece) is plotted against strain
  (the extension divided by the length over which it is
  measured).
   
Sub-Critical Heating to, and holding at, some point below the critical
Annealing temperature. Subsequent cooling may be in air. This form
  of heat treatment has a variety of uses depending on the
  temperature and specification of the steel, its purpose is
  often to soften the material.
   
Sub-zero A low temperature treatment carried out after quenching
Treatment on hardened steel to transform the retained austenite into
  martensite. It involves immersing the component in a bath
  of solid carbon dioxide at a temperature of minus 70-80 deg C.
   
Sulphur Generally regarded as an impurity in steel as it can have
  detrimental effects on strength, ductility and weldability as
  well as producing hot and cold shortness. Its content in
  most steels is limited to a maximum of 0.050%. Sulphur is
  beneficial to machining and is added to freecutting steels
  in amounts up to 0.35% with the manganese content
  increased to overcome any detrimental effects.
   
Surface A method of hardening the surface of steel to increase its
Hardening wear resistance. Depending on the analysis of the steel,
  the following treatments can be employed:
  Case-hardening, Nitriding, induction hardening, Flame
  hardening.
   
Swaging A method of forming or reducing steel or other metals to a
  desired shape by a series of blows rapidly applied by dies
  or hammers. The process is applied to wires, rods and
  tubes and can be used for a variety of pointing, tapering,
  sizing and reducing operations.
   
Swarf The particles of metal arising from machining or grinding
  operations, much of it finds its way to the steel maker for
  remelting.
   
Ta Chemical symbol for Tantalum.
   
Tantalum A rare metal of silver white color having
  excellent corrosion resistance and a high
  melting point. It is widely used for chemical
  process equipment and specialised
  aero-space and nuclear applications.
   
Te Chemical symbol for Tellurium.
   
Tellurium Its main use in the steel industry is as an
  additive in leadbearing freecutting steels to
  further improve their machinability. Its
  presence in the steel is either within the
  manganese sulphide particles, where it is
  partially soluble, or as particles combined
  with lead or manganese. For certain
  applications it offers significant improvements
  in machinability but the added cost is a factor
  that should be taken into account.
   
Temper A term to which a number of definitions can
  be applied. These include: a) The operation
  of tempering; b) The degree of hardness left
  in a steel bar after quenching and tempering;
  c) The grading of the hardness of low carbon
  cold rolled strip, e.g. Hard, Half Hard,
  Quarter Hard, Skin Passed, Soft; d) An
  indication of the amount of carbon present in
  a tool steel, e.g. razor temper, file temper,
  die temper, etc.
   
Temper Brittleness The loss in impact resistance that is present
  in some low and medium carbon alloy steels
  when tempered in the range of 350 deg C -
  600 deg C. It is revealed by the notched bar
  impact test but not the tensile test.
   
Temper Colors Before the use of instruments such as
  pyrometers, colors were used to judge
  temperatures when hardening and tempering.
  For example, on carbon tool steel where the
  tempering range may typically be from 200 deg C
  to 350 deg C, the colors change with the rise in
  temperature giving Light Straw at around
  210 deg C, Purple at 275 deg C, and Grey at 330 deg C.
  The practice still continues in workshops
  where controlled heat treatment facilities are
  not available.
   
Temper Rolling A light pass given to annealed cold rolled
  strip to prevent the formation of kinks and
  stretcher strain markings on subsequent cold
  working. Also termed Pinch pass and Skin
  pass.
   
Tempering A heat treatment applied to ferrous products
  after hardening. It consists of heating the
  steel to some temperature below the
  transformation range and holding for a
  suitable time at the temperature, followed by
  cooling at a suitable rate. The object of
  tempering is to decrease hardness and
  increase toughness to produce the desired
  combination of mechanical properties.
   
Tensile Strength The maximum load applied in breaking a
  tensile test piece divided by the original
  cross-sectional area of the test piece.
  Originally quoted as tons/sq.in. it is now
  measured as Newtons/sq.mm. Also termed
  Maximum Stress and Ultimate Tensile Stress.
   
Tensile Test A standard test piece is gripped at either end
  by suitable apparatus in a testing machine
  which slowly exerts an axial pull so that the
  steel is stretched until it breaks. The test
  provides information on proof stress, yield
  point, tensile strength, elongation and
  reduction of area.
   
Thomas Process The Continental name for the basic Bessemer
  steel making process, now superseded by
  modern day BOS plants.
   
Ti Chemical symbol for Titanium.
   
Time Temperature An isothermal transformation diagram
Transformation Curve showing the relationship between
  temperature and the time taken for the
  decomposition of austenite when the
  transformation occurs at constant
  temperature.
   
Tin When present in steel it is an undesirable
  impurity which gives rise to temper
  brittleness. When used as a coating on steel,
  it has a good resistance to corrosion for many
  applications.
   
Titanium Small amounts added to steel contribute to
  its soundness and give a finer grain size. In
  austenitic stainless steels it acts as a carbide
  stabiliser and is used to prevent
  intercrystalline corrosion, commonly termed
  "weld decay". Titanium carbide is also used
  with tungsten carbide in the manufacture of
  hard metal tools.
   
Tolerances The amount of variation permitted on
  dimensions or surfaces. The tolerance is
  equal to the difference between the maximum
  and minimum limits of any specified
  dimension.
   
Tool Steel A generic term applied to a wide range of
  steels, both plain carbon and alloy. It
  includes steels suitable for various types of
  cutting tools, press tools, hot and cold
  heading dies, molds for plastics and die-
  casting, extrusion tools, hand tools, etc.
   
Torsional Strength The resistance of a bar to twisting. Closely
  related to its shear strength.
   
Toughness The ability of a metal to rapidly distribute
  within itself both the stress and strain caused
  by a suddenly applied load, or more simply
  expressed, the ability of a material to
  withstand shock loading. It is the exact
  opposite of "brittleness" which carries the
  implication of sudden failure. A brittle
  material has little resistance to failure once
  the elastic limit has been reached.
   
Transformation Range The temperature range within which austenite
  forms and ferrite or carbide progressively
  dissolves while ferrous alloys are being
  heated. Also the temperature range within
  which austenite decomposes to form ferrite
  and carbide on cooling.
   
Transformation Temperature The temperature at which a change in phase
  occurs or the limiting temperature of a
  transformation range. These critical points
  are denoted by symbols, e.g. Ac1; the
  temperature at which austenite begins to
  form on heating. There are 12 principal
  temperatures to which symbols are applied.
   
Transition Temperature The temperature at which a transition from
  ductile to brittle fracture takes place in steel.
  It is usually determined by making a series of
  Charpy impact tests at various temperatures,
  the transition temperature is usually taken as
  the point where 50% of the fracture is brittle.
   
Transverse Strength A measurement of strength when the load is
  applied across the longitudinal flow of the
  grain of a metal. Certain impurities such as
  sulphur have a detrimental effect on the
  transverse strength. This can be minimised by
  the inclusion modification process.
   
Transverse Test A test taken at right angles to the principal
  direction of rolling or forging.
   
TTT Curve An abbreviation of Time Temperature
  Transformation Curve.
   
Tufftriding A form of surface hardening, the process
  involves nitrogen but does not achieve the
  hardness of conventional nitriding.
   
Tungsten When used as an alloying element it
  increases the strength of steel at normal and
  elevated temperatures. Its "red hardness"
  value makes it suitable for cutting tools as it
  enables the tool edge to be maintained at
  high temperatures. In conjunction with other
  alloying elements it finds applications in heat
  resisting and other severe service conditions.
   
U Chemical symbol for Uranium.
   
Ultimate Analysis In chemistry, this is a quantitative analysis in which
  percentages of all elements in the substance are
  determined.
Ultimate Tensile  
Strength The highest load applied in breaking a tensile test
  piece divided by the original cross-sectional area of
  the test piece.
   
Ultrasonic Inspection A means of locating defects in steel. When acoustic
  energy in the ultrasonic range is passed through
  steel, the sound waves tend to travel in straight
  lines, rather than diffusing in all directions as they
  do in the audible range. If there is a defect in the
  path of the beam it will cause a reflection of some
  of the energy, depleting the energy transmitted.
  This casts an acoustic shadow which can be
  monitored by a detector placed opposite the
  transducer or energy source. If the acoustic energy
  is introduced as a very short burst, then the
  reflected energy coming back to the originating
  transducer can also be used to show the size and
  depth of the defect. Ultrasonic techniques can be
  used to detect deeply located defects or those
  contained in the surface layer. Skill and experience
  are required in interpreting the results portrayed on
  the cathode ray tube.
   
Unkilled Steel Steel which has been insufficiently deoxidised and
  evolves gas during solidification with the formation
  of blow-holes.
   
Upsetting Working a piece of steel so that its length is
  shortened and its cross-sectional area is increased.
  Its effect is to increase ductility in the radial and
  tangential directions.
   
Uranium A white malleable metal which is softer than steel.
  Its specific gravity is 18.7, it melts at a temperature
  of 2400 deg C.
   
V Chemical symbol for Vanadium.
Vacuum Arc  
Remelting A process used for producing advanced steels to the
  most demanding and critical specifications,
  particularly in such areas as aerospace applications.
  The steel is first produced to a very close analysis
  and the resulting ingot is slowly remelted in a
  Vacuum Arc Remelting furnace for up to 14 hours.
  Such steels are, by necessity, expensive to
  manufacture.
   
Vacuum Degassing A ladle of molten metal is placed within a chamber
  which is then evacuated. This reduces the gas
  content, particularly hydrogen, as well as reducing
  non-metallic inclusions. Modern secondary steel
  making processes using Vacuum Arc Degassing units
  that include automated stirring and control of
  temperature and chemical analysis, ensure a
  consistent and high quality product.
   
Vanadium Steels containing vanadium have a much finer grain
  structure than steels of similar composition without
  vanadium. It raises the temperature at which grain
  coarsening sets in and increases hardenability where
  it is in solution in the austenite prior to quenching. It
  also lessens softening on tempering and confers
  secondary hardness on high speed steels. Vanadium
  is used in nitriding, heat resisting, tool and spring
  steels in conjunction with other alloying elements.
   
Vickers Hardness Test A method of determining the hardness of steel
  whereby a diamond pyramid is pressed into the
  polished surface of the specimen and the diagonals
  of the impression are measured with a microscope
  fitted with a micrometer eye piece. The rate of
  application and duration are automatically controlled
  and the load can be varied.
   
W Chemical symbol for Tungsten, from wolfram.
   
Welding The process of joining together two pieces of metal
  so that bonding accompanied by appreciable
  interatomic penetration takes place at their original
  boundary surfaces. The boundaries more or less
  disappear at the weld, and integrating crystals
  develop across them. Welding is carried out by the
  use of heat or pressure or both and with or without
  added metal. There are many types of welding
  including Metal Arc, Atomic Hydrogen, Submerged
  Arc, Resistance Butt, Flash, Spot, Stitch, Stud and
  Projection.
   
Whiskers Thin hair-like growths on metal that are barely
  visible to the naked eye, they are stronger than the
  metals from which they are formed, probably
  because they are free from defects.
   
White Annealing A heat treatment process carried out on pickled
  steel with the objective of eliminating the hydrogen
  that has entered the steel during the pickling
  operation and thus removing any tendency to
  hydrogen embrittlement.
   
Widmanstatten Structure A microstructure resulting when steels are cooled
  at a critical rate from extremely high temperatures.
  It consists of ferrite and pearlite and has a
  cross-hatched appearance due to the ferrite having
  formed along certain crystallographic planes.
   
Wolfram The alternative name for tungsten.
   
Woody Fracture A fracture that is fibrous or woody in appearance
  due to the elongation of the individual grains. This
  may be accentuated by the presence of slag or by
  a banded structure. It is grey and dull and is
  characteristic of ductile but non-homogeneous
  material such as wrought iron.
   
Work Hardening The increase in hardness and strength produced by
  cold plastic deformation or mechanical working.
   
Wrought Iron A commercial iron that has little use today and has
  been replaced by mild steel. It was commonly
  produced by the puddling process. The
  temperatures employed in its production are too
  low to render it fluid, it is heated until it forms a
  pasty mass then it is squeezed or forged. The
  process does not lend itself to removal of
  impurities so it contains an appreciable quantity of
  slag. It will not respond to any heat treatment
  designed to increase the hardness or strength.
   
X-Ray Crystallography X-ray photographs of metals are a means of providing
  information which in many cases cannot be obtained
  by microscopic methods. The lines produced by each
  element, or phase are characteristic, and their
  general pattern enables the crystalline structure to be
  identified. The scale of the pattern can be used to
  determine accurately the size of the unit cell and,
  therefore, the distance apart of the individual atoms.
  From the relative intensity of the lines it is possible to
  deduce the distribution throughout the unit cell, the
  various types of atoms in an alloy or the degree of
  preferred orientation in the material.
   
Yield Point Can be defined as the point where a tensile test piece
  begins to extend permanently. If the load is reduced to
  zero, the test piece will not return to its original length.
   
Yield Strength The stress at which general plastic elongation of the test
  piece takes place. This point is well defined in hardened
  and tempered or annealed structures but can be ill defined
  in "as drawn" structures.
   
Young's Modulus Within the limits of elasticity, the ratio of the linear stress
  to the linear strain is termed the modulus of elasticity or
  Young's Modulus and may be written Young's Modulus, or
  E =(Stress/Strain) It is this property that determines how
  much a bar will sag under its own weight or under a
  loading when used as a beam within its limit of
  proportionality. For steel, Young's Modulus is of the order
  of 205000 N/mm2.
   
Zinc Zinc is a metallic chemical element, it has a white color with a
  bluish tinge. It has a high resistance to atmospheric corrosion and
  a major use is as a protective coating for iron and steel sheet and
  wire. Galvanised sheets are a prime example. The melting point
  of zinc is 419 deg C.
   
Zirconium Acts as a deoxidising element in steel and combines with sulphur.
   
Zn Chemical symbol for Zinc.
   
Zr Chemical symbol for Zirconium.
 
 

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