The Main Differences And Types Of Operations Between Annealing And Normalizing In The Production Process Of Bearings

Normalization, also known as open flame, code Z, is the process of heating steel parts to Ac3 or Acm or higher (30-50 ℃), holding for a period of time, and then cooling them in air at a slightly faster cooling rate than annealing.

The main difference between bearing annealing and normalizing is that normalizing is a deformation situation of complete annealing, and their only difference is the cooling rate. Generally, annealing is cooled in the furnace, while normalizing is cooled in air. Normalization is suitable for hypoeutectoid steel and hypereutectoid steel plates. For eutectoid steel, normalizing is usually used to eliminate network carbides; For hypoeutectoid steel, the purpose of normalizing is basically the same as annealing, mainly to refine grains and eliminate structural defects. However, the pearlite flakes in the normalized structure are smaller than those in the annealed structure, and the pearlite content is higher and the ferrite content is lower in the hypoeutectoid steel. Therefore, the hardness and strength of normalized steel are higher than those of annealed steel. From this, it can be seen that in production practice, materials containing network carbides in steel need to undergo normalizing treatment to eliminate carbides before proceeding with other processing. For materials with performance requirements after heat treatment, annealing processes can be selected according to different requirements and steel types. For example, if a certain strength and hardness are required after heat treatment, the normalizing process can be chosen; If a certain degree of plasticity is required while minimizing strength and hardness, annealing process should be chosen.

Common types of annealing processes in bearing production

(1) Complete annealing (commonly known as annealing) is mainly used for castings, forgings, and hot-rolled profiles of eutectic bridge steel and alloy steel, and some are also used for welding structural components. Its purpose is to refine grain size, improve microstructure, eliminate residual stress, reduce hardness, enhance plasticity, and improve cutting performance. Complete annealing is a time-consuming annealing process. In order to shorten the annealing time, isothermal annealing process is usually used instead of complete annealing. Compared with complete annealing, isothermal annealing has the same purpose, but the annealing time is greatly shortened.

(2) Spheroidal annealing is mainly used for hypereutectoid steel and alloy tool steel (such as cutting tools, measuring tools, molds, and bearings). Its main purpose is to reduce hardness, improve cutting performance, and prepare for subsequent quenching.

(3) Stress relief annealing (also known as low-temperature annealing) is mainly used to eliminate internal stresses in castings, forgings, welded parts, hot-rolled parts, and other components.

(4) Recrystallization annealing is used to eliminate work hardening caused by cold working (cold drawing, cold stamping, cold rolling, etc.). Its purpose is to eliminate internal stress, improve plasticity, and enhance organizational structure.

(5) Diffusion annealing is mainly used for alloy steel, especially for alloy steel castings and ingots. The purpose is to utilize the high diffusion ability of atoms at high temperatures to alleviate or eliminate the phenomenon of uneven chemical composition in steel.