Definitions

DEFINITION OF SOME USEFUL PROCESS ON STEEL
HEAT TREATMENT

Heat Treatment

Heat treatment is an operation or combination of operations involving the heating and cooling of a metal or alloy when in solid form, to obtain certain desirable conditions or properties. Heating and cooling for the sole purpose of mechanical working are excluded from the meaning of the definition.

Annealing

The term annealing usually implies to relatively slow cooling.

The composition, shape and size of the steel that is being treated, affects the temperature, time, rate of heating & cooling for the annealing process.
The purpose of annealing is to remove stress to induce softness, to reduce hardness, to alter ductility, toughness, improve machinability, facilitate cold working, to produce a desired micro-structure, to change electric, magnetic or other physical and mechanical properties.

Distortion

The deviation from the desired size, shape or form, as occurring in heat treatment.

PROCESS FOR HARDNESS

Hardening

Any process of increasing the hardness of metal or alloy superior to that obtained when an alloy is not quenched by suitable treatment, usually heating above the critical temperature range and cooled by Quenching. The term is usually restricted to the formation of martensite.

Case Hardening

Hardening a ferrous alloy in order to change the outer surface or case, to a substantially harder than the inner surface or core, by inward diffusion from a gas or liquid, followed by appropriate thermal treatment. The term is usually applied to carburizing, cyaniding or nitriding treatment followed by quenching to produce a hard case and a core of suitable properties.

Tempering

A process of reheating of a quench hardened or normalized steel, below the transformation range, then slowly cooling it at a desired rate.
The objective of this process is to obtain a desired combination of mechanical properties such as release of stress, restore, some ductility, develop toughness though regulation or readjustment of the embrittled structural constituents of the metal.