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Design of bearing steel ball treatment process
Factors affecting the quality of bearing steel balls
1. Material influence: Steel balls, cast iron balls, alloy steel balls, etc. have varying densities depending on the material. Steel has a higher density than cast iron, while alloy steel varies depending on the density and content of the main alloying elements.
2. The influence of manufacturing methods for bearing steel balls: the microstructure of cast steel balls, cast iron balls, or cast alloy balls is dense, while that of rolled and forged steel balls is dense, with high density and low relative density.
3. The influence of metallographic structure on bearing steel balls: The density of different crystal structures such as martensite, austenite, bainite, and ferrite varies, which can also affect the fineness of the crystals.
Design basis for bearing steel balls
In order to ensure a high service life and reliability of the lower bearing steel ball during operation, the heat treatment method and process of the steel ball are basically the same as that of the ring heat treatment, generally including annealing, quenching, tempering, surface heat treatment, etc. It is necessary to heat treat the steel ball to improve its hardness, rigidity, and other mechanical properties. There are also advanced heat treatment methods such as atmosphere quenching and vacuum quenching.
1. After hot heading and sintering, the steel ball blank is subjected to spheroidization annealing to obtain a fine-grained pearlite structure, which improves the mechanical processing performance.
2. Quenching is carried out to obtain comprehensive mechanical properties such as good elasticity, toughness, and dimensional stability through tempering, in order to improve the hardness, strength, wear resistance, and contact fatigue performance of steel balls.
3. Tempering treatment can greatly improve toughness and achieve good comprehensive mechanical properties while reducing internal stress, stabilizing structure and size, and slightly reducing hardness
4. Surface treatment can make the surface of parts have high strength, hardness, and wear resistance, while the core has a certain degree of strength, sufficient forming, and toughness.
Main text of bearing steel ball design
1. Design process
Bearing steel spheroidization annealing (heated to 750C) and holding for 3 hours. Cool the furnace to 600C and cool the furnace air to room temperature. Quench the steel ball to 320C and hold it in a potassium nitrate bath for a period of time. Remove the air cooling and heat the steel ball to 150c-170. Temper for 3 hours
2. Spheroidization annealing
Annealing of bearing steel balls is an annealing process that involves spheroidizing carbides in the steel balls. Obtain a uniformly distributed spherical or granular carbide structure on the ferrite matrix. The microstructure obtained by air cooling of steel balls consists of layered pearlite and mesh like cementite, which are hard and brittle. Not only is cutting difficult, but the steel balls are heated to 750 degrees Celsius and cooled slowly after a period of insulation. Moreover, they are prone to deformation and cracking during subsequent quenching processes. On the other hand, after spheroidization annealing, a spherical pearlite structure is obtained. Compared with plate-like pearlite, it not only has lower hardness and is easier to cut, but also the cementite is spherical particles dispersed on the ferrite matrix. Moreover, it is difficult for austenite particles to grow during quenching and heating
The annealing and heating temperature of the bearing steel ball is above 727 degrees, and it can be isothermal cooled or directly annealed after insulation. Therefore, it is impossible to remove the network carbides. When there are network carbides in hypereutectoid steel, it is necessary to normalize before spheroidizing annealing. During spheroidizing annealing, austenitization is "incomplete", but plate-like pearlite transforms into austenite, and a small amount of excess carbides dissolve.