Tempering is a process of improving the characteristics of a metal by the heat treatment that is used to increase the toughness of iron-based alloys and to make it more resistant to stress.

Reference Definition by NACE: Tempering is a heat treatment by heating to a temperature below the lower critical temperature for the purpose of decreasing the hardness and increasing the toughness of hardened steel, hardened cast iron, and sometimes normalized steel.

Related Definitions in the Project: The Metallurgy (Corrosion and Cracking)