Low-carbon steels with easily machining properties are subjected to a hardening process by impregnating their surfaces with carbon for their intended use after processing. This process increases the wear resistance of the surface of the part and ensures that the core area remains soft and the whole part displays tough properties and has a high impact resistance. Carburising can take place in solid, liquid or gas phase media. The easiest and most economical method to control is carburising in gas environment. Hydrocarbons such as CO or methane gas are used as carbon donors. Salts of carbon donors such as sodium cyanide and potassium cyanide are commonly used in liquid media carburising. Liquid medium carburising is more suitable for hardening of small parts. More charcoal is used in solid media carburising. It is a method that is difficult to control and requires experience and is not preferred much. In the carburising process, it is tried to increase the surface carbon ratio to 0.7-0.8%. The carbon impregnated above this causes carbide precipitation, creating a brittle surface. The main criterion for carburising is the effective carburising depth.

After the carbon impregnation process, the wall is hardened by quenching. Quenching is carried out by quenching at the carbon impregnation temperature (direct quenching), cooling to room temperature and improving (single quenching), or by quenching at the carbon impregnation temperature at low temperature. Tempering (Blueing) must be done after quenching processes. The highest abrasion resistance to be achieved after the carburising process is obtained not at the highest hardness, but after Tempering (Blueing) at approximately 300˚C.

Usage Areas

Common applications include long-running and heavy-impact parts such as transmission gears and automobile shafts, wind turbine and pump parts. Carburising can be done on many different types of steel. The choice of alloying elements and process parameters provides a unique combination of hard wear resistant surface and tough core.