austenit

Austenit, or austenite, is the face-centered cubic (FCC) phase of iron and its alloys in which carbon and other alloying elements are dissolved. It is the gamma-iron phase and is stable at high temperatures. In steel chemistry, austenite serves as the parent phase for many heat-treatment transformations.

The austenitic lattice can dissolve a relatively large amount of carbon compared with ferrite—up to about 2 weight percent carbon at high temperatures. The FCC structure gives austenite high ductility and, in many stainless steels, a non-magnetic or weakly magnetic character at room temperature.

In pure iron, austenite exists above roughly 912°C and remains stable to melting; in steels, the stability range is influenced by alloying elements. Nickel is a common austenite-stabilizer, allowing austenite to persist to room temperature and enabling austenitic stainless steels. Elements such as chromium, manganese, and nitrogen also affect its stability and properties.

During cooling from the austenitic region, austenite can transform to other microstructures. Rapid quenching can produce martensite, a hard phase; slower cooling yields bainite or pearlite depending on carbon content and cooling rate. The exact pathway determines strength, hardness, and toughness.

Austenite is a foundational concept in steel metallurgy and phase diagrams. It underpins the design of heat-treatment schedules and stainless steel alloys, where its stability and transformations are exploited to achieve desired performance.