Carburizing of Steel

a type of thermochemical treatment in which the surface layer (case) of objects made of low-carbon steel (0.1–0.2 percent C) is impregnated with carbon by means of diffusion as the steel is heated in an appropriate medium.

The purpose of carburizing is to increase the hardness and wear resistance of the surface by enriching the case with carbon (up to 0.8–1.2 percent) with subsequent quench hardening; the core of the object, which has not been impregnated with carbon, remains very ductile. The depth of the hardened case ranges from 0.5 to 1.5 mm (rarely more); the carbon concentration in the case decreases from the surface to the core. Carburizing and subsequent heat treatment improve the endurance limit of the metal and make the metal less sensitive to stress concentrators. The carbonaceous material used may be a solid (pack carburizing) or a gas (gas carburizing). Gas carburizing is usually used in mass-production plants because it is easier to regulate the carbon concentration in the case, the length of the process is shorter, the process may be completely mechanized or automated, and the subsequent heat treatment is simplified.