What Are The Material Factors That Affect Bearing Life?

1. Material factors affecting bearing life

The early failure forms of rolling bearings mainly include rupture, plastic deformation, wear, corrosion and fatigue, and the main failure forms are contact fatigue under normal conditions. In addition to service conditions, the failure of bearing parts is mainly restricted by the hardness, strength, toughness, wear resistance, corrosion resistance and internal stress state of steel. The main intrinsic factors that affect these performance and states are the following.

2. Control of material factors affecting bearing life

In order to make the above material factors affecting the bearing life in the best state, first of all, it is necessary to control the original structure of the steel before quenching, the technical measures can be taken are: high temperature (1050℃) austenitizing fast cooling to 630℃ isothermal normalizing to obtain pseudo-eutectoid fine pearlite structure, or cold to 420℃ isothermal treatment, obtain bainite structure. In order to ensure the fine and uniform distribution of carbides in steel, fine pearlite structure can also be obtained by fast annealing of waste heat from forging and rolling. During quenching and heating austenitizing, the undissolved carbides will aggregate into fine particles except the carbides dissolved in austenitizing.

When the original organization must be in the steel, the carbon content of quenched martensite (that is, the austenite after quenching heating carbon content), the residual austenite and the body not dissolve carbide mainly depends on the amount of quenching heating temperature and holding time, with higher quenching heating temperature (a), not dissolve the decrease in the number of carbide in steel (quenching martensite increased carbon content), the number of retained austenite increase, The hardness first increases with the increase of quenching temperature and then decreases with the increase of quenching temperature. When the quenching temperature is constant, the amount of undissolved carbide decreases and the amount of residual austenite increases with the extension of austenitizing time, and this trend slows down when the time is longer. When the carbides in the original structure are small, the hardness peak after quenching shifts to a lower temperature and appears in a shorter austenitizing time because the carbides are easy to dissolve into austenite.

In conclusion, the optimum microstructure composition of GCrl5 steel after quenching is about 7% undissolved carbide and 9% residual austenite (the average carbon content of cryptocrystalline martensite is about 0.55%). Moreover, when the carbides in the original tissue are fine and evenly distributed, it is beneficial to obtain high comprehensive mechanical properties and thus have a long service life when the microstructure composition at the above level is controlled reliably. It should be noted that in the original tissue with fine dispersed carbides, the undissolved fine carbides will aggregate and grow up to coarsening during quenching. Therefore, for bearing parts with such original structure, the quenching heating time should not be too long, and the rapid heating austenitizing quenching process can obtain higher comprehensive mechanical properties.

In order to make the bearing parts after quenching and tempering surface residual large compressive stress, can be in the quenching heating through carburizing or nitriding atmosphere, for a short time of surface carburizing or nitriding. Carbon (or nitrogen) can be absorbed because the actual carbon content of austenite during quenching and heating is not very high, well below the equilibrium concentration shown on the phase diagram. When the austenite contains higher carbon or nitrogen, its Ms decreases, and martensite transformation occurs in the surface layer compared with the inner layer and the core during quenching, resulting in larger residual compressive stress. GCrl5 steel was heated and quenched in both carburizing atmosphere and non-carburizing atmosphere (both were tempered at low temperature). The contact fatigue test showed that the life of surface carburized steel was 1.5 times higher than that of non-carburized steel. The reason is that the surface of carburized parts has a large residual compressive stress.

3 conclusion

The main material factors and control degree that affect the service life of high carbon chromium steel rolling bearing parts are as follows:

(1) The carbide in the original structure of steel before quenching should be fine and diffuse. It can be achieved by high temperature austenitizing at 630℃ or 420℃, or by forging and rolling waste heat rapid annealing process.

(2) For GCr15 steel after quenching, it is required to obtain the microstructure of cryptocrystalline martensite with an average carbon content of about 0.55%, about 9% Ar and about 7% undissolved carbides in uniform and round state. The microstructure can be controlled by quenching heating temperature and time.

(3) After quenching and tempering parts at low temperature, large compressive stress remains on the surface, which contributes to the improvement of fatigue resistance. The surface can be carburized or nitriding for a short time during quenching and heating, resulting in a large compressive stress residual on the surface.

(4) Manufacturing steel for bearing parts requires a high purity, mainly to reduce the content of O2, N2, P, oxide and phosphide. Electroslag remelting, vacuum smelting and other technical measures can be used to make the oxygen content of the material ≤15PPM.