The annealing and normalizing of bearing production
Annealing, also known as simmering, code th, is to heat the steel parts above AC1 or AC3 (30 ~ 50 ℃), hold them for a period of time, and then slowly cool them (usually furnace cooling).
Normalizing, also known as open fire, code Z, is to heat the steel parts above AC3 or ACM (30 ~ 50 ℃), keep them warm for a period of time, and then cool them in air. The cooling speed is slightly faster than annealing.
The main differences between bearing annealing and normalizing are as follows: normalizing is a kind of abnormal or special case of complete annealing, and the two are only different in cooling speed. Generally, annealing is cooled with furnace, while normalizing is cooled in air. Normalizing is applicable to hypoeutectoid steel and hypereutectoid steel.
For eutectoid steel, normalizing is generally used to eliminate network carbide; For hypoeutectoid steel, the purpose of normalizing is basically the same as that of annealing, which is mainly to refine grains and eliminate defects in the structure. However, the pearlite sheet in the normalized structure is thinner than that in annealing, 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 steel after normalizing are higher than those in annealing. It can be seen that in production practice, For materials with network cementite in steel, other processes can be used only after normalizing. For materials with performance requirements after heat treatment, the annealing process can be selected according to different requirements and steel types. For example, normalizing process can be selected if it is required to have certain strength and hardness after heat treatment; If a certain plasticity is required and the strength and hardness are reduced as much as possible, the annealing process shall 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 sections of sub common bridge steel and alloy steel, and some are also used as welded structural parts. Its purpose is to refine grains, improve microstructure, eliminate residual stress, reduce hardness, improve plasticity and improve machinability. Complete annealing is an annealing process with a long time. In order to shorten its annealing time, At present, isothermal fire process is often used to replace complete annealing process. Compared with complete annealing, the purpose of isothermal fire is the same as complete annealing, but it greatly shortens the annealing time.
2. Spheroidizing annealing is mainly used for hypereutectoid steel and alloy tool steel (such as all kinds of steel such as cutting tools, measuring tools, molds and bearings). Its main purpose is to reduce hardness, improve machinability and prepare for future quenching.
3. Stress relief annealing (also known as low temperature annealing) is mainly used to eliminate the internal stress of castings, forgings, weldments 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 microstructure.
5.Diffusion annealing is mainly used for alloy steel, especially alloy steel castings and ingots. The purpose is to reduce or eliminate the non-uniformity of chemical composition in steel by using the large diffusion ability of atoms at high temperature.
