austeniittien

Austeniitti is a high-temperature phase of iron and steel. It is a solid solution of carbon in gamma-iron (γ-Fe), which has a face-centered cubic (FCC) crystal structure. Unlike ferrite, which has a body-centered cubic (BCC) structure, the FCC structure of austenite allows for a much higher solubility of carbon. The name "austenite" honors the British metallurgist Sir William Chandler Roberts-Austen.

Austenite is typically stable above a specific temperature, which varies depending on the carbon content and other alloying elements. For pure iron, this transition temperature is around 912°C. In steels, the presence of carbon and other alloying elements like nickel and manganese can significantly lower the temperature at which austenite becomes stable, or even stabilize it at room temperature in certain stainless steels.

The properties of austenite differ significantly from those of ferrite. Austenite is generally non-magnetic, has higher ductility, and is readily worked and formed. However, it is also softer than hardened martensite. The transformation of austenite during cooling is a critical process in heat treatment of steels, as it dictates the final microstructure and mechanical properties. For example, rapid cooling (quenching) of austenite can lead to the formation of martensite, a very hard phase. Slower cooling allows for the formation of pearlite or bainite, which have different combinations of strength and toughness.