Annealing is a metal heat treatment process. According to the purpose of annealing the workpiece, there are many kinds of annealing specifications. Commonly used are complete
annealing, spheroidizing annealing, and stress relief annealing.
Annealing is mainly for
1) Reduce the hardness of metal materials, which is conducive to cutting and cold deformation processing
2) reduce residual stress, stabilize size, reduce deformation and crack tendency;
3) Refine the grain, uniform the structure of the steel, and eliminate the internal stress in the steel
4) Uniform material organization and composition to improve material properties or subsequent heat treatment processes
(1) Complete annealing
Also called recrystallization annealing, only used for annealing steel, heating the steel to critical temperature (the critical temperature of different steels is also different,
generally 710-750 ° C, the critical temperature of individual alloy steel can reach 800-900 ° C) 30 - 50oC,
Keep warm for a certain period of time, then slowly cool with the furnace (or buried in the sand to cool), fully annealed for carbon content (mass fraction) at O. Forgings
or cast steel parts below 8%. Complete annealing is mainly to refine the grains, uniform structure, reduce the hardness, and completely eliminate the internal stress of the steel.
(2) Spheroidizing annealing
The steel is heated to a critical temperature of 20 to 30 ° C. After the heat preservation, it is slowly cooled to below 500 ° C and then air-cooled.
Spheroidizing annealing is suitable for carbon content (mass fraction) greater than O. 8% carbon steel and alloy tool steel
Spheroidizing annealing mainly reduces the hardness of medium carbon steel and high carbon steel, improves cutting performance, and has large
cold deformation ability, and prepares for later quenching of tool steel to reduce deformation and cracking after quenching.
(3) Stress relief annealing
The steel is heated to 500-650oC for a certain period of time. Then it is generally cooled slowly with the furnace. The de-stress heating temperature is low,
and there is no tissue transformation during the annealing process. It is mainly suitable for blanks and machined parts.
Castings, forgings, welded parts and cold extrusions. In order to eliminate the residual stress in the blank and the part, the size and shape of the workpiece
are stabilized, and the deformation and crack tendency of the part during cutting and use are reduced.