一、Strict chemical composition requirements

General bearing steel is mainly high-carbon chromium bearing steel, that is, the carbon content of about 1%, adding about 1.5% chromium, and containing a small amount of manganese, silicon elements of hypereutectoid steel. Chromium can improve the heat treatment performance, improve the hardenability, microstructure uniformity, tempering stability, but also can improve the steel rust resistance and grinding performance. However, when the chromium content exceeds 1.65%, the quenching will increase the residual austenite in the steel, reduce the hardness and dimensional stability, increase the inhomogeneity of the carbide, and reduce the impact toughness and fatigue strength of the steel. For this reason, the chromium content in high-carbon chromium bearing steel is generally controlled below 1.65%. Only by strictly controlling the chemical composition of the bearing steel can the organization and hardness of the bearing properties be obtained through the heat treatment process.

二、High precision size requirements

Rolling bearing steel requires high dimensional accuracy, because most bearing parts are pressure-formed. In order to save materials and improve labor productivity, most of the bearing rings are forged, the steel ball is formed by cold heading or hot rolling, and the small-size roller is also formed by cold heading. If the dimensional accuracy of the steel is not high, it is impossible to accurately calculate the size and weight of the material, and can not ensure the product quality of the bearing parts, and it is easy to cause damage to the equipment and mold.

三、Very strict purity requirements

The purity of steel refers to the amount of non-metallic inclusions contained in steel, the higher the purity, the less non-metallic inclusions in steel. The harmful inclusions such as oxides and silicates in bearing steel are the main reasons that lead to early fatigue spalling and significantly reduce bearing life. In particular, the brittle inclusion is the most harmful, because it is easy to peel off the metal matrix during processing, which seriously affects the surface quality of the bearing parts after finishing. Therefore, in order to improve the service life and reliability of bearings, the content of inclusions in bearing steel must be reduced.

四、Strict low power and microscopic (high power) structure requirements

The low-power structure of bearing steel refers to the general loose, center loose and flat out, and the microscopic (high-power) structure includes the annealing structure of steel, carbide network, ribbon and liquid out. Carbide solution is hard and brittle, and its harm is the same as that of brittle inclusions. The network carbide reduces the impact toughness of the steel and makes the structure uneven, which is easy to deform and crack during quenching. Banded carbides affect annealed and quenched tempering structures and contact fatigue strength. The advantages and disadvantages of low and high structure have a great impact on the performance and service life of rolling bearings, so there are strict requirements for low and high structure in the bearing material standards.

五、Particularly stringent surface and internal defect requirements

For bearing steel, surface defects include cracks, slag inclusion, burrs, scars, 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, and these defects are clearly not allowed in the bearing material standards.

六、Particularly stringent carbide inhomogeneity requirements

In the bearing steel, if there is a serious uneven carbide distribution, it is easy to cause the uneven structure and hardness during the heat treatment process, and the uneven structure of the steel has a greater impact on the contact fatigue strength. In addition, serious carbide non-uniformity is also easy to crack bearing parts during quenching and cooling, and carbide non-uniformity will also lead to reduced bearing life. Therefore, in the bearing material standard, there are clear special requirements for different specifications of steel.

七、Particularly stringent surface decarburization layer requirements

In the bearing material standard for the steel surface decarburization layer has strict provisions, if the surface decarburization layer beyond the standard scope, and in the process of processing before heat treatment and not all of it removed, it is easy to produce quenching cracks in the process of heat treatment quenching, resulting in the scrap of parts.

八、Other requirements

In the bearing steel material standard, there are also strict requirements for the smelting method, oxygen content, annealing hardness, fracture, residual elements, spark inspection, delivery status, marking and so on.