What is Bainite Microstructure?

Bainite is a mixed microstructure in steel that forms at intermediate temperatures between high-temperature pearlite and low-temperature martensite.

It's mainly made up of supersaturated ferrite and carbides or carbon-rich retained austenite.

Traditional metallography divides it into upper and lower bainite, but as microscopic characterization techniques have improved, the features of granular bainite and lath bainite have been clearly defined, refining the classification system of bainite.

Bainite is an acicular microstructure (not a phase) that forms in steels at temperatures from approximately 250-550°C (depending on alloy content). First described by E. S. Davenport and Edgar Bain,

it is one of the decomposition products that may form when austenite (the face centered cubic crystal structure of iron) is cooled past a critical temperature of 727 °C (about 1340 °F).

Davenport and Bain originally described the microstructure as being similar in appearance to tempered martensite.