Technical Information

Understanding The Heat Treatment Of Steels

Many changes occur when steel is subjected to heat. There are different heat treatment processes which are listed below:

Normalising

Heating to a suitable temperature, between 800-900 Deg C, according to analysis, holding at temperature followed by cooling in still air. Relieves internal stresses, refines the grain size and improves mechanical properties.

Annealing

Heating and holding at a suitable temperature and cooling slowly in the furnace with the object of softening the steel, improving machinability and cold working properties.

Spheroidising

A form of annealing often used in high carbon steels with the object of obtaining the softest possible state to assist machinability.

Stress Relieving

Frequently carried out after rough machining or cold work to remove stresses. It is usually carried out at a temperature of 600-650 Deg C.

Hardening

Heating to a temperature slightly above the critical range, soaking for sufficient time at that temperature followed by quenching in a suitable media such as air, oil or water.

Tempering

Carried out immediately after hardening to relieve stresses, remove brittleness and reduce hardness to the required range. Usually carried out between 150-650 Deg C. Cool in still air or quench.

Nitriding

A process for producing a very hard case by the absorption of nitrogen into the surface of the steel. depending on the specification of the steel, hardness figures up to 1100 VPN can be attained.

Carburising

The diffusion of carbon into the surface of a steel that is low in carbon by heating in a solid, liquid or gaseous medium, containing carbon at a temperature around 900 Deg C.

Induction Hardening

A surface hardening process where a component is heated by high frequency induction followed by immediate quenching.The surface hardness will depend on the carbon content of the steel. For ideal results this is usually in the range 0.40% - 0.45% C.