This is generally performed at temperatures around 700 o C . This results in increased strength but less ductility in the metal. It also produces a higher yield strength with greater tensile strength, and in most instances, a higher impact resistance. This method provides greater strength and hardness than slow cooling, but it is accompanied by brittleness . Tempering reduces the brittleness and relieves internal stresses.
Tempering is actually a re-heating and slow cooling process.
The cooling is accurately controlled to impart certain characteristics to the base metal. The purpose is to reduce internal stresses, caused by welding, quench hardening or by cold working. It also has an advantageous effect on the elasticity, ductility and strength of the metal. It is the application of heat to the base metal prior to a welding or cutting operation. It does not change the properties of the steel, but it is advisable under certain conditions to drive off moisture and helps to ensure even expansion to eliminate undesirable stresses.