Introduction to the operation types of NSK bearing annealing and normalizing
Normalizing is a kind of metamorphosis or special case of complete annealing. The two are only different in cooling rate. Usually annealing is cooled with the furnace and normalizing is cooling in air. Normalizing is suitable for both hypoeutectoid steels and super-eutectoid steels. For steel, for eutectoid steel, normalizing is generally used to eliminate network carbides; for hypoeutectoid steel, the purpose of normalizing is basically the same as annealing, mainly to refine grains and eliminate defects in the structure, but the normalizing structure The medium pearlite sheet is thinner than the annealed one, and the amount of pearlite in the hypoeutectoid steel is more than that of the ferrite. Therefore, the hardness and strength of the normalized steel are higher than that of the annealed. It can be seen that in production practice, The material with net cementite in the steel needs to be normalized and eliminated before other processes can be used. For materials with performance requirements after heat treatment, the annealing process should be selected according to different requirements and different steel types, such as: after heat treatment is required If there is a certain strength and hardness, the normalizing process can be selected; if a certain degree of plasticity is required, the annealing process should be selected if the strength and hardness are as low as possible.
Common types of annealing operations in bearing production
(1) Complete annealing (commonly known as annealing) is mainly used for castings, forgings and hot-rolled sections of Asian bridge steel and alloy steel, and some are also used as welded structural parts. The purpose is to refine the grain, improve the structure, and eliminate residuals. Stress, reduce hardness, increase plasticity, and improve cutting performance. Complete annealing is a long annealing process. In order to shorten the annealing time, isothermal fire technology is often used to replace the complete annealing process. Compared with complete annealing, isothermal The purpose of fire is the same as complete annealing, but it greatly shortens the annealing time.
(2) Spheroidizing annealing is mainly used for hypereutectoid steels and alloy tool steels (such as cutting tools, measuring tools, molds, bearings and other steel grades). The main purpose is to reduce the hardness, improve the machinability, and prepare for later quenching.
(3) Stress relief annealing (also called low temperature annealing) is mainly used to eliminate internal stresses in castings, forgings, welded parts, and hot-rolled parts.
(4) Recrystallization annealing is used to eliminate work hardening caused by cold working (cold drawing, cold punching, cold rolling, etc.). The purpose is to eliminate internal stress, increase plasticity, and improve organization.
(5) Diffusion annealing is mainly used for alloy steel, especially alloy steel castings and ingots. The purpose is to use the greater diffusion ability of atoms at high temperatures to reduce or eliminate the phenomenon of uneven chemical composition in steel.