HARDENING
Hardening is a process of heating followed by cooling generally fast for increase hardness .
To this end, the steel is heated to a temperature slightly higher than the upper critical (850-900ºC) and then cooled quickly in a medium such as, water, water mixed with soluble polymers, etc.
The steels that are normally used in induction hardening contain from 0.3% to 0.7% carbon.