Strict low power and microscopic (high power) tissue requirements. The low magnification microstructure of bearing steel refers to general loose, center loose and segregation, and the microscopic (high magnification) microstructure includes the annealing microstructure of steel, carbide network, strip and liquid evolution, etc. The carbide solution is hard and brittle, and its harmfulness is the same as that of brittle inclusion. The network carbide reduces the impact toughness of steel and makes the structure uneven, which is easy to deform and crack during quenching. Banded carbides affect annealed and quenched tempering microstructure and contact fatigue strength. The quality of low and high power structure has a great impact on the performance and service life of rolling bearings, so there are strict requirements for low and high power structure in bearing material standards.
Extremely strict requirements for surface defects and internal defects. For bearing steel, surface defects include cracks, slag inclusion, burrs, scarring, oxide skin, etc., and internal defects include shrinkage holes, bubbles, white spots, serious porosity and segregation. These defects have a great impact on the processing of bearings, bearing performance and life. It is clearly stipulated in the bearing material standards that these defects are not allowed.
Strict carbide inhomogeneity requirements. In bearing steel, if there is serious uneven carbide distribution, it is easy to cause uneven microstructure and hardness in the process of heat treatment. The uneven microstructure of steel has a great influence on the contact fatigue strength. In addition, serious carbide non-uniformity is also easy to crack bearing parts during quenching cooling, and carbide non-uniformity will also lead to the reduction of bearing life. Therefore, in bearing material standards, there are specific requirements for different specifications of steel.
Strict surface decarburization layer depth requirements. There are strict regulations on the surface decarburization layer of steel in the bearing material standards. If the surface decarburization layer exceeds the prescribed scope of the standard, and it is not completely removed in the processing process before heat treatment, it is easy to produce quenching cracks in the process of heat treatment quenching, resulting in the scrap of parts.
In the bearing steel material standard, there are also strict requirements on the smelting method, oxygen content, annealing hardness, fracture, residual elements, spark test, delivery status, marking and so on.
Post time: Apr-12-2023