Martemper & Marquench
Martempering (also known as "Marquenching").
This is the term used to describe the treatment of a through hardening steel in which the cooling is interrupted just above the Martensite transformation temperature, and held until the surface and the core of the component are at the same temperature, This is usually carried out in an elevated temperature quench bath of molten salt or oil. The cooling is then resumed at a controlled rate so that the surface and the core transform at the same time, the residual stress is lower as the entire component should have the same % transformation, which in turn minimises distortion and the risk of cracking. This process is limited to selected alloy-containing steels and suitable section sizes. It is a more expensive process than conventional quenching and may not be possible on many metals.