In the process of heat treatment, a different range of properties can be obtained by controlling the rate of cooling. Parts may be quenched in oil, water, soluble oil solutions, aqueous polymer solutions, inert or nitrocarburizing atmospheres or air. Quenching and Tempering shall be in accordance and the heating atmosphere shall be neutral to the surface of the steel being treated to prevent decarburization or carburization of the steel surface. Quenching may be direct quenched (cooled to austenitizing temperature prior to quenching) rather than being slow cooled to room temperature and hardened.
Tempering shall occur within 4 hours of quench. Soaking time shall not be less than 2 hours plus one hour additional for each inch of thickness or fraction thereof greater than 1 inch. Parts may be snap tempered for 2 hours at a temperature that is lower than the tempering temperature.
This process is usually a low temperature heat treatment which removes stress and fragile through quenching and develop the essential mechanical properties.