It is used to reduce the risk of cracking and breaking of martensite formation during rapid cooling processes. It is also known as gradual quenching. The material is cooled from the austenite zone to a temperature just above the martensite initial temperature, then left for a while before it reaches the limit of bainite formation and is completed to room temperature. With holding, the surface and core temperatures of the workpiece with cross-sectional differences are equalized.
It is used in many applications where less deformation is desired in aviation landing gear, automotive parts and defense industry.
Salt baths are often used as a cooling medium.