Key metallurgical terms

Annealing – a treatment consisting of heating uniformly to a temperature, within or above the critical range, and cooling at a controlled rate to a temperature under the critical range. This treatment is used to produce a definite microstructure, usually one designed for best machinability and/or to remove stresses, induce softness and alter ductility, toughness or other mechanical properties.

Billet – a solid semi-finished round that has been hot worked. Also a general term for wrought starting stock for forgings or extrusions.

Elongation – the increase in gauge length, measured after the fracture of a specimen within the gauge length, usually expressed as a percentage of the original gauge length.

Forging – the process of converting a metal bar into another shape or form by heating before shaping in a press or between hammers.

Grinding – the process of improving the surface finish of a bar to almost a polish.

Hardness – the resistance of a metal to plastic deformation, usually by indentation.

Impact test – a test to determine the behaviour of materials when subjected to high rates of loading, usually in bending, tension or torsion. The quantity measured is the energy absorbed in breaking the specimen by a single blow, such as a Charpy or Izod test.

Machinability – the ability of a material to be machined determined by such factors as tool wear, tool life, swarf, surface finish and integrity.

Quenching – a treatment that consists of heating uniformly to a predetermined temperature and cooling rapidly in air or a liquid medium to produce a desired crystalline structure.

Reduction of area – the difference, expressed as a percentage of the original area, between the original cross-sectional area of a tensile test specimen and the minimum cross-sectional area measured after complete separation.

Specification – an explicit set of requirements to be satisfied by a material, including chemical composition and mechanical properties.

Tensile strength – the ratio of maximum load on a material experienced during a tensile test to the original cross-sectional area of the test sample.

Trepanning – the process of machining out the centre of a solid bar to produce a hollow shape.

Ultrasonic testing – a non-destructive testing method in which a high frequency sound wave is sent through a test sample to detect internal flaws.

Yield point – the first stress in a material at which an increase in strain occurs without an increase in stress.

Yield strength – the stress at which a material exhibits a specified deviation from proportionality of stress and strain. An offset of 0.2% is commonly used.