Annealing, also known as annealing, code-named Th, is to heat the steel piece above Ac1 or Ac3 (30~50°C), keep it warm for a period of time, and then slowly cool it (generally use furnace cooling).
Normalizing, also known as open flame, code-named Z, is to heat the steel piece to above Ac3 or Acm (30~50°C), keep it warm for a period of time, and then cool it in the air. The cooling speed 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 cooled in air, normalizing is suitable for both Hypoeutectoid steel is also suitable for hypereutectoid steel. For eutectoid steel, normalizing is generally used to eliminate reticular carbides; for hypoeutectoid steel, the purpose of normalizing is basically the same as annealing, mainly to refine grains. Eliminate defects in the structure, but the pearlite sheets in the normalized structure are thinner than those in the annealed one, and the amount of pearlite in the hypoeutectoid steel is more than that of the ferrite, so the hardness and strength of the steel after normalizing are higher than those in the annealed one , it can be seen that in production practice, materials with reticulated cementite in steel need to be eliminated by normalizing before other processes can be used, and for materials with performance requirements after heat treatment, according to different requirements and steel types Different selection of annealing process, such as: if a certain strength and hardness are required after heat treatment, the normalizing process can be selected; if a certain plasticity is required, and the strength and hardness should be reduced as much as possible, the annealing process should be selected.
Types of annealing operations commonly used in bearing production\
(1) Complete annealing (commonly known as annealing) is mainly used for castings, forgings and hot-rolled profiles of subeutectic 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 residual stress, reduce hardness, improve plasticity, and improve cutting performance. Complete annealing is a long-time annealing process. In order to shorten the annealing time, isothermal annealing is often used to replace the complete annealing process. Compared with complete annealing, isothermal The purpose of fire is the same as full annealing, but it greatly shortens the annealing time.
(2) Spheroidizing annealing is mainly used for hypereutectoid steel and alloy tool steel (such as all steel types such as knives, measuring tools, molds and bearings). Its purpose is mainly to reduce hardness, improve machinability, and prepare for subsequent quenching.
(3) Stress-relieving annealing (also known as low-temperature annealing) is mainly used to eliminate internal stress 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 stamping, cold rolling, etc.). The purpose is to eliminate internal stress, improve plasticity and improve organization.
(5) Diffusion annealing is mainly used for alloy steel, especially castings and ingots of alloy steel. The purpose is to reduce or eliminate the phenomenon of uneven chemical composition in steel by using the large diffusion ability of atoms at high temperature.
