Annealing and normalizing of bearing production process
Annealing is also called simmering, and the code is Th. It is to heat the steel to Ac1 or Ac3 above (30~50℃), keep it for a period of time, and then slowly cool it (usually with furnace cooling).
Normalizing, also known as open flame, code Z, is to heat steel parts above Ac3 or Acm (30~50℃), keep it for a period of time, and then cool it in air, the cooling rate is slightly faster than annealing.
The main difference between bearing annealing and normalizing is: normalizing is a metamorphosis or special case of complete annealing. The two are only different in cooling speed. Usually annealing is cooled with the furnace and normalizing is cooling in the air. Normalizing is suitable for Hypoeutectoid steel is also suitable for hypereutectic plate steel. For eutectoid steel, normalizing is generally used to eliminate network carbides; for hypoeutectoid steel, the purpose of normalizing is basically the same as that of annealing, mainly to refine grains. Eliminate defects in the structure, but the pearlite sheets in the normalized structure are thinner than the annealed ones, and the amount of pearlite in the hypoeutectoid steel is more and the amount of ferrite is less. Therefore, the hardness and strength of the normalized steel are higher than the annealed ones. Therefore, it can be seen that, in production practice, materials with net cementite in steel need to be normalized and eliminated before other processes can be used. For materials with performance requirements after heat treatment, according to different requirements and steel types Different annealing processes are selected. For example, if a certain strength and hardness are required after heat treatment, the normalizing process can be selected; if a certain degree of plasticity is required, the annealing process should be selected to reduce the strength and hardness as much 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 grains, 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.
