A thermochemical process in which steel is heated into the austenitic region in a carbon-rich atmosphere, so causing carbon to diffuse into the steel surface. The carburised steel product is then quenched.

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 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.

Diffusion of carbon at about 900oC (by pack, gas, salt bath or plasma process) into low carbon steel, followed by quenching and tempering to produce martensitic case (typically 1mm thick).