What is the purpose of tempering?

The main purpose of tempering is to reduce or eliminate internal stress in quenched steel parts, or to reduce their hardness and strength, in order to improve their ductility or toughness.

Tempering is a metal heat treatment process that involves reheating a quenched workpiece to an appropriate temperature below the lower critical temperature, holding it for a period of time, and then cooling it in a medium such as air, water, or oil.

Alternatively, the quenched alloy workpiece can be heated to an appropriate temperature, held for a certain period of time, and then slowly or rapidly cooled. Generally used to reduce or eliminate internal stress in quenched steel parts, or to reduce their hardness and strength, in order to improve their ductility or toughness.