Bearings are composed of inner and outer rings, rolling elements (balls, rollers or needle rollers) and cages. Except for the cages, the rest are made of bearing steel. When the bearing is working, the inner and outer rings of the bearing and the rolling elements of the bearing bear the action of high frequency and variable stress. The working conditions of bearings are very complicated. The load is concentrated on a small area of the rolling elements. Theoretically speaking, for the ball, it acts on one point; for the roller, it acts on a line, and the contact area between the rolling body and the ring is also small (point/line contact), so when the bearing parts are working, their The unit area of the surface of the rolling body and the ring is subject to a large pressure, generally as high as 1500-5000N/mm2; when the bearing rotates, it also bears the centrifugal force, and the force increases with the increase of the speed; the rolling body and the sleeve There is not only rolling but also sliding between the rings, so there is friction between the rolling elements and the rings. Under the combined action of the above forces, fatigue cracks are first generated on the surface of the ferrule or rolling element with low fatigue strength, and finally fatigue spalling is formed, causing the bearing to fail. The normal form of damage to bearings is contact fatigue damage, and plastic deformation, indentation, wear, and cracks are common.

Although the life and reliability of bearings are related to factors such as bearing design, manufacturing, lubrication conditions, installation, and maintenance, the high quality and reliability of bearing materials are the key. Rolling bearing parts must work at high speed and for a long time under complex stress states and high stress values such as tension, compression, bending, shearing, and alternating. Therefore, the requirements for rolling bearings are:

    1) High resistance to plastic deformation,

    2) High anti-friction and wear properties,

    3) High rotation accuracy and dimensional accuracy,

    4) Good dimensional stability,

    5) Long service life and high reliability.

For bearings working under special conditions, there are special requirements, such as high temperature resistance, low temperature resistance, corrosion resistance and antimagnetic properties, etc.