Kovettumiskäsittelyt

Kovettumiskäsittelyt refer to a group of heat treatment processes used in metallurgy to increase the hardness and wear resistance of metal surfaces, particularly steels. These treatments achieve hardening by forming hard phases, such as martensite, within the material's microstructure. The most common kovettumiskäsittelyt are normalisointi, karkaisu, and pintakovetuskäsittelyt.

Normalisointi involves heating the steel to a temperature above its critical point and then cooling it in still air. This process refines the grain structure and improves machinability, but its primary hardening effect is less pronounced than other methods. Karkaisu, on the other hand, is a more aggressive hardening process where steel is heated to its austenitizing temperature and then rapidly quenched in a medium like water, oil, or air. This rapid cooling traps carbon atoms in the iron lattice, creating a hard and brittle martensitic structure. Tempering, a subsequent low-temperature heat treatment, is often performed after karkaisu to reduce brittleness and improve toughness.

Pintakovetuskäsittelyt, or surface hardening treatments, aim to harden only the surface layer of a component while leaving the core relatively soft and tough. This is achieved through various methods, including induction hardening, flame hardening, carburizing, and nitriding. These processes introduce carbon or nitrogen into the surface, which are then heat-treated to form hard compounds. The choice of kovettumiskäsittely depends on the specific material, the desired properties, and the intended application of the metal component.