martenzit

Martensite is a hard, brittle phase that forms in steel and other alloys upon rapid cooling from the austenite phase. This process is known as quenching. The formation of martensite is a diffusionless transformation, meaning that the atoms do not move significantly from their original positions within the crystal lattice. Instead, the transformation occurs through a shear mechanism, distorting the austenite lattice into a body-centered tetragonal structure. This unique crystal structure is responsible for the hardness of martensite.

The amount and properties of martensite formed depend on the cooling rate, the carbon content of the steel, and the presence of alloying elements. Higher carbon content generally leads to higher hardness but also increased brittleness. If the cooling rate is too slow, other less hard phases like pearlite or bainite can form instead of or alongside martensite. Martensite is typically metastable, meaning it will decompose into more stable phases at higher temperatures, a process often achieved through tempering. Tempering reduces hardness and improves toughness by allowing carbon atoms to diffuse and form carbides, while the remaining iron matrix transforms to ferrite.