Austenitization soaking time

Austenitizing time is the time the steel is held at hardening temperature. It must be long enough for the carbides to fully dissolve and the structure to become homogeneous. If the time is too short, carbides remain and the part can crack later. But if you leave the part in too long, the grain grows and the steel becomes tough. So you have to get a feel for how long your steel needs to "soak" – that depends on thickness and alloy.