The process of hardening the surface of steel whilst 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.

A process in which the surface (case) of the steel is hardened and the interior (core) of the steel is left unchanged. A number of different techniques are available for achieving this objective.

Adding carbon to the surface of iron-base alloys by absorption through heating the metal at a temperature below its melting point in contact with carbon material. The oldest method of surface hardening wrought iron and other low-carbon steels by packing it in charcoal or some other carbon-based material, then heating it for several hours above 1650.

The process of hardening the outer surface of the steel only. Requires only a low carbon content (usually less than 0.2%) to perform on alloy or carbon steel. Leaves the steel with a very hard and highly wear-resistant case.

A method for surface hardening wrought iron by packing it in charcoal or other organic material and heating it for hours above 900*c.