Basic requirements for metallurgical quality of bearing steel

2018-06-23 The service life and reliability of rolling bearings are closely related to the metallurgical quality of bearing steel. Because of the characteristics of bearing steel, the requirements for metallurgical quality are much stricter than those of general industrial steel.
The strict chemical composition requirements of 1
The main rolling bearing steel is mainly high carbon chromium bearing steel, that is, the carbon content is about 1%, adding about 1.5% of chromium, and containing a small amount of manganese and silicon elements. Only by strictly controlling the chemical composition in the bearing steel can the heat treatment process wait until the microstructure and hardness of the bearing are satisfied.
Higher dimensional precision of 2
For the rolling bearing steel, the requirement of steel dimension accuracy is high, because most bearing parts are molded by pressure. In order to save material and improve labor productivity, most bearing rings are forged by forging, steel ball is cold heading or hot forging, and the small size roller is also formed by cold heading. If the size of steel is not high, the size and weight of the material can not be calculated accurately, and the quality of the bearing parts can not be guaranteed. Quantity is easy to create
Damage of preparation and mold.
3 specially strict requirements for purity
The purity of steel is the amount of non-metallic inclusions in steel, the higher the purity, the lower the content of non-metallic inclusions in steel. Harmful inclusions, such as oxide, silicate and non - deformation inclusions in bearing steel, are the main reasons for the early fatigue peeling of bearing and significantly reducing the life span of bearing. Moreover, the brittle inclusions are easily spalling off the metal matrix during the grinding process, which seriously affects the surface quality of the bearing parts after finishing. In order to improve the service life and reliability of bearings, the content of non-metallic inclusions in bearing steel must be reduced.
4 strict tissue and microscopic (high power) tissue requirements.
The low fold structure of the bearing steel refers to the general porosity, central porosity and segregation, and the microstructure (high times) of the microstructure includes the annealed structure of bearing steel, carbide mesh, strip and liquid analysis. The advantages and disadvantages of low and high power structures have a great influence on the performance and service life of rolling bearings. Therefore, in the bearing steel material standards, there are strict requirements for low and high power organizations.
5 strict surface defects and internal defect requirements
For bearing steel, surface defects include surface cracks, surface slags, burrs, folds, scars, oxide skins and so on. Internal defects include shrinkage, bubbles, white spots, overheating, serious porosity and segregation, micropores and so on. These defects have a great influence on the processing of bearing, the performance of bearing and the service life, and these defects are not allowed in the material standard of bearing steel.
6 specially strict carbide inhomogeneity requirements
In the bearing steel, if the carbide distribution is uneven, it is easy to cause uneven microstructure and hardness during the heat treatment process. The martensite needle like structure is formed in the areas with less carbide distribution, and the hardness is low. Because of the strict requirements for the microstructure, hardness and hardness uniformity after heat treatment in the heat treatment technical conditions for rolling bearing parts, the non uniformity of carbides also makes the bearing parts crack during the quenching and cooling, and the non uniformity of carbides also leads to the reduction of the bearing life.
7 specially strict surface decarburization requirements
There are strict rules for the surface decarburization of steel material in the material standard of bearing steel. If the surface decarburization layer is beyond the standard range, it is not completely removed during the process of heat treatment, so it is easy to produce quenching cracks in the process of heat treatment and quenching, resulting in the scrap of the parts.