Casehardening

Casehardening is a surface hardening process for ferrous alloys, most commonly steel. It involves diffusing carbon into the surface of a low-carbon steel part to create a hard, wear-resistant outer layer, while the core remains tough and ductile. This differential hardening is achieved by heating the steel in a carbon-rich environment.

There are several methods of casehardening. Pack carburizing involves heating steel packed in a carbonaceous material, such as charcoal or bone, in a sealed container. Gas carburizing utilizes a carbon-rich gas, like propane or methane, in a furnace. Cyaniding involves immersing the steel in a molten salt bath containing cyanide salts, which both carburize and nitride the surface. Induction hardening and flame hardening are surface hardening methods that heat the surface rapidly using electrical induction or a flame, followed by quenching, but they do not add carbon and are thus distinct from true casehardening processes.

The depth of the hardened case depends on the temperature, time, and type of carburizing medium. After carburizing, the part is typically quenched in oil or water to achieve its desired hardness. Tempering may follow to reduce brittleness and improve toughness. Casehardening is widely used for components subjected to wear, such as gears, camshafts, and cutting tools, as it provides a hard bearing surface without compromising the structural integrity of the core.