Martensitens

Martensitens refers to the martensite phase and related microstructures that form in iron–carbon alloys when austenite is cooled rapidly, a process known as quenching. Martensite is a supersaturated, metastable phase with a body-centered tetragonal lattice that is much harder and more brittle than the original austenite. The plural term martensitens is used in some languages to refer to martensite; in English, the standard form is martensite (plural martensites).

Formation and microstructure: The transformation is diffusionless, meaning carbon atoms do not diffusively rearrange during the change. Instead, the crystal lattice distorts by a coordinated shear, producing a refined, needle-like or plate-like morphology. The transformation begins at a temperature Ms and completes at Mf, with the exact temperatures depending on carbon content and alloying elements. Two common morphologies are lath martensite and plate martensite. Higher carbon content or different alloying can shift the transformation and alter the microstructure. Tempering martensite at elevated temperatures reduces hardness but increases toughness by allowing carbon to precipitate as carbides.

Properties and applications: Martensitens are characterized by very high hardness and wear resistance, along with high strength and limited toughness unless tempered. Tempering improves toughness at the expense of some hardness. Martensitic stainless steels, such as grades 410, 420, and 431, are widely used for cutlery, surgical instruments, and certain springs. Tool steels also rely on martensitic structures to achieve their performance.

See also: martensite, heat treatment, tempering, lath martensite, plate martensite, martensitic stainless steel.