The heat treatment process of heating the metal or alloy to an appropriate temperature, holding it for a certain period of time, and then slowly cooling (usually cooling with the furnace) is called annealing.
The essence of annealing is to heat the steel to austenitization and then carry out pearlite transformation, and the structure after annealing is close to the equilibrium structure.
Purpose of annealing:
(1) Reduce the hardness of steel, improve plasticity, and facilitate machining and cold deformation processing.
(2) Uniform the chemical composition and structure of the steel, refine the grains, improve the performance of the steel or prepare the structure for quenching.
(3) Eliminate internal stress and work hardening to prevent deformation and cracking.
Annealing and normalizing are mainly used for preliminary heat treatment. For parts with low stress and low performance requirements, annealing and normalizing can also be used as final heat treatment.