Martensite

The structure of steel after quenching (or hardening).

Martensite is an acicular (needle-like) type of ferrite. It is formed when austenite is cooled too rapidly for ferrite to form normally, in accordance with the equilibrium diagram. Since martensite is not an equilibrium phase, it is never shown on phase diagrams.

Martensite is very hard and brittle but can be made tougher (and softer) by tempering. Upon tempering, martensite breaks down into ferrite containing a fine precipitate of cementite. The structure obtained after tempering is today simply called tempered martensite. However, in the past the structures obtained from tempering martensite at different temperatures were called troostite (low temperature tempering) and sorbite (high temperature tempering).

Martensite was named after the German engineer, Adolf Martens (1850-1914).

See also martensitic.