Carburising is a case hardening process that introduces carbon into a solid ferrous alloy. This is accomplished by heating the metal in a carbonaceous atmosphere above transformation temperature for a pre-determined time. Subsequent to carburising, parts are quenched to harden the surface carburising layer. The core remains unaffected.
It is a widely used surface hardening process for low carbon steel. The industrial importance of carburising is expressed in its market share, as one third of all hardening heat treatment is covered by carburising and hardening.
Carburising and quench produce hard surfaces which are resistant to wear. Moreover, failure from impact loading is avoided due to a softer core. Unlike case hardening processes, this process is usually used for deep case depths.
Application & materials
Typical applications include transmission gears and shafts for automotive, wind turbine and pump components and all applications where components are required to operate for long periods and under high impact loads. A wide variety of steels can be carburised. The unique combination of a hard wear resistant surface and a tough core can be controlled by the choice of alloy elements and process parameters.
Carburising is a thermochemical diffusion process which adds carbon to the surface of a low carbon steel (typically 0.25% carbon) with other alloying elements. The carbon diffusion depth and the related effective case hardening depth (ECD) can vary from shallow, often less than 2mm, to deeper depths of 4 to 6mm. The total process is applied in three phases: