The process of heat treatment in which a metal or alloy is heated to an appropriate temperature, held for a certain period of time, and then slowly cooled (usually as the furnace cools) is called annealing.
The essence of annealing is to heat steel to austenitize for pearlite transformation, and the annealed tissue is the nearly balanced one.
Purpose of annealing:
(1) Reduce the hardness of steel, improve the plasticity, and facilitate machining and cold deformation processing;
(2) Uniform steel chemical composition and structure, refine grain, improve steel performance or prepare for quenching structure;
(3) Eliminate internal stress and work hardening to prevent deformation and cracking.