Transformation

A change from one phase to another as the temperature increases or reduces.

Some metals have different crystal structures (also known as phases) at different temperatures, even though they remain solid at these temperatures. The change from one structure to another is called a transformation. The temperature at which the transformation takes place is called the transformation temperature.

It is this property of iron, with its ferrite and austenite phases, which allows steel to be heat treated so readily. At high temperatures, the steel is transformed to its austenite phase. When austenite is quenched rapidly, it forms very hard martensite.

Certain transformations occur at a single temperature and composition and give a particular transformation product. These have specific names such as eutectoid transformation.