Annealing refers to heating the steel to a certain temperature, holding it for a certain time, and then slowly cooling it to room temperature.
The purpose is to
① Reduce the hardness of steel and improve the plasticity, so as to facilitate cutting and cold deformation processing
② Refine the grain, homogenize the structure of the steel, improve the properties of the steel and prepare for future heat treatment
③ Eliminate internal stress in steel. Prevent deformation and cracking of parts after processing
(1) Complete annealing: heat the steel parts to 30-50 º C above the critical temperature (the critical temperature of different steels is also different, generally 710-750 ℃, and the critical temperature of some alloy steels can reach 800-900 º C), hold for a certain time, and then slowly cool down with the furnace (or bury in the sand for cooling)
It can refine grains, uniform structure, reduce hardness, fully eliminate internal stress, and complete annealing is applicable to forgings or steel castings with carbon content (mass fraction) below 0.8%
(2) Spheroidizing annealing: heat the steel parts to 20 ~ 30 º C above the critical temperature, and then slowly cool them to below 500 ℃ after heat preservation, and then discharge them for air cooling.
It can reduce the hardness of steel, improve cutting performance, and prepare for future quenching to reduce deformation and cracking after quenching. Spheroidizing annealing is applicable to carbon steel and alloy tool steel with carbon content (mass fraction) greater than 0.8%
(3) Stress relief annealing: heat the steel parts to 500 ~ 650 º C, hold them for a certain time, and then slowly cool them (generally cooling with the furnace)
It can eliminate the internal stress generated during welding and cold straightening of steel parts, and eliminate the internal stress generated during cutting of precision parts, so as to prevent deformation in the process of later processing and use.
Stress relief annealing is applicable to all kinds of castings, forgings, weldments and cold extruded parts