Martenzitesedés

Martenzitesedés is a metallurgical term referring to the process of martensitic transformation. This is a diffusionless transformation that occurs in certain steels and other alloys when they are rapidly cooled from a high temperature. During this rapid cooling, the parent phase, typically austenite, transforms into martensite, a metastable, body-centered tetragonal (BCT) structure. This transformation is characterized by a shear mechanism rather than atomic diffusion, meaning atoms move in a coordinated manner. The speed of cooling is critical; if it is too slow, the austenite will transform into more stable phases like pearlite or bainite, and martensite will not form.

The resulting martensite structure is very hard and brittle due to its supersaturated solid solution of carbon and its distorted crystal lattice. This hardness is a desirable property for many applications, such as cutting tools and structural components, but the brittleness necessitates further heat treatments like tempering to reduce internal stresses and improve toughness. Tempering involves reheating the martensitic steel to a lower temperature, allowing some carbon to precipitate as carbides and reducing the lattice distortion. The specific properties of martensite and the resulting tempered martensite depend heavily on the alloy composition and the heat treatment parameters.