Casehardening

Casehardening, treatment of mild steel to give it an extremely hard surface. The steel is heated for several hours in carbon-containing material, such as powdered charcoal. During this process carbon is slowly absorbed to a shallow depth, converting this part to high-carbon steel. On quenching with cold water this “case” becomes hard. An even harder case is produced by “nitriding,” in which the steel is heated in gaseous ammonia, from which the surface absorbs nitrogen. Casehardening is commonly used on gears, roller bearings, and crankshafts to produce a wear-resistant surface.

See also: Steel.