Carburising
Carburising is also called Case Hardening. Case hardening, properly known as carbon case hardening, is used to give a hard, wear and indentation resisting surface to mild and low alloy steels, up to depths of 4-5 mm. This is achieved by diffusion of carbon into the surface of the steel. At the same time the core of the steel is usually strengthened, but left tough. Being one of the most common heat treatment processes used in the world, case hardening is commonly applied to gears, machinery, automotive and aerospace applications and many others.
Carburising is carried out in the temperature range 800 - 960ºC where carbon is diffused into the steel surface. The core of the steel is strengthened by rapidly quenching from these temperatures and the resulting hardness is dependant on the quench rate and also the steel. It is recommended that Carburised parts are tempered at low temperatures for optimum toughness.
Changes in size or shape can occur to components, however certain components can be Press Quenched to minimize this.
Steels
Carburising is an excellent process to provide a hard, wear resistant surface to inexpensive steels such as low or medium carbon steels. Mild steels can also be treated but will not generate good core strength.
CarboNitriding
Under the heading of Case Hardening is also included carbonitriding, which is used to give a hard case onto the cheapest steels which are often not capable of being case hardened because of their chemical composition. The carbonitriding process is applied to low carbon and mild steels and results in less distortion than traditional carburising techniques.