What is the result of rapidly quenching austenite?

Rapidly quenching austenite primarily leads to the formation of martensite, which is a key phase in steel and other iron alloys. When austenite, which is a face-centered cubic structure stable at high temperatures, is rapidly cooled (quenched), the diffusion of carbon atoms is effectively suppressed. This rapid cooling prevents the austenite from transforming into its more stable forms, such as ferrite or pearlite, which require time and lower temperatures for diffusion processes to occur.

As a result of this rapid cooling, a new structure is formed: martensite, characterized by a body-centered tetragonal structure. Martensite is typically harder and stronger compared to other microstructures, making this phase very desirable in many engineering applications where high strength is required.

Other phase transformations, such as the formation of pearlite or ferrite, occur at slower cooling rates, allowing ample time for atomic movements and transformations. However, quenching does not facilitate these transformations effectively due to the speed of the cooling process, thus further reinforcing martensite's formation as the primary product of rapid quenching.