Process: heat the steel to AC1 ~ AC3 (hypoeutectoid steel) or AC1 ~ ACCM (hypereutectoid steel) and cool it slowly after heat preservation to obtain a heat treatment process close to equilibrium structure.
It is mainly used to obtain spherical pearlite structure of hypereutectoid steel to eliminate internal stress, reduce hardness and improve machinability. Spheroidizing annealing is a kind of incomplete annealing.
A heat treatment process for spheroidizing carbides in steel to obtain granular pearlite.
Process: When heated to the temperature of 20~30℃ above AC1, the holding time should not be too long, generally 2~4H is appropriate. The cooling method is usually furnace cooling, or isothermal at about 20 ℃ below AR1 for a long time.
Objective: To reduce the hardness, homogenize the structure, improve the machinability and prepare the structure for quenching.