Karburisoimalla

Karburisoimalla, often translated as carburizing or case hardening, is a heat treatment process used to increase the surface hardness of a metal, typically steel. This is achieved by diffusing carbon into the surface layer of the workpiece. The process involves heating the steel in a carbon-rich atmosphere or medium. Common carburizing mediums include solid compounds like charcoal and barium carbonate, liquid baths containing salts like cyanide or carbonates, or gaseous atmospheres composed of carbon monoxide and hydrocarbons.

During the carburizing process, the carbon atoms from the surrounding medium penetrate the surface of the steel and dissolve into the iron matrix. The depth and concentration of carbon in the surface layer are controlled by factors such as temperature, time, and the composition of the carburizing medium. Higher temperatures and longer durations generally lead to deeper and more concentrated carbon penetration.

Following the carburizing step, the workpiece is typically quenched and tempered. Quenching rapidly cools the steel, transforming the high-carbon surface layer into a very hard martensitic structure. Tempering then reduces some of the brittleness, providing a balance between hardness and toughness. The core of the material, which has not absorbed significant amounts of carbon, remains relatively softer and more ductile, providing good impact resistance. Karburisoimalla is widely used for components that require a hard, wear-resistant surface while maintaining a tough core, such as gears, shafts, and tools.