In order to optimize the material factors that affect the bearing life, it is necessary to control the original structure of the steel before quenching. Technical measures that can be taken include: high-temperature (1050 ℃) austenitization, rapid cooling to 630 ℃, isothermal normalizing to obtain pseudo eutectoid fine pearlite structure, or cooling to 420 ℃, isothermal treatment to obtain bainite structure. It is also possible to use forging and rolling waste heat for rapid annealing to obtain a fine-grained pearlite structure, in order to ensure that the carbides in the steel are fine and evenly distributed. The original structure in this state will aggregate into fine particles during quenching and austenitization, except for carbides dissolved in austenite.

When the original structure in steel is constant, the carbon content of quenched martensite (i.e. the carbon content of austenite after quenching heating), the amount of residual austenite, and the amount of undissolved carbides mainly depend on the quenching heating temperature and holding time. As the quenching heating temperature increases (time is constant), the amount of undissolved carbides in steel decreases (the carbon content of quenched martensite increases), the amount of residual austenite increases, and the hardness first increases with the increase of quenching temperature, reaches its peak, and then decreases with the increase of temperature. When the quenching heating temperature is constant, with the extension of austenitization time, the amount of undissolved carbides decreases, the amount of residual austenite increases, and the hardness increases. When the time is long, this trend slows down. When the carbides in the original structure are small, the hardness peak after quenching shifts to lower temperatures and appears in a shorter austenitization time due to the easy dissolution of carbides into austenite.

In summary, the optimal microstructure composition for GCr15 steel after quenching is approximately 7% undissolved carbides and 9% residual austenite (with an average carbon content of approximately 0.55% for hidden martensite). Moreover, when the carbides in the original structure are small and evenly distributed, it is beneficial to obtain high comprehensive mechanical properties and thus have a long service life by reliably controlling the microstructure composition at the above level. It should be pointed out that the original structure with small dispersed carbides will aggregate and grow undissolved small carbides during quenching, heating, and insulation, resulting in coarsening. Therefore, for bearing parts with this original structure, the quenching and heating time should not be too long. Adopting a rapid heating austenitization quenching process can achieve higher comprehensive mechanical properties.

In order to leave a large residual compressive stress on the surface of bearing parts after quenching and tempering, a carburizing or nitriding atmosphere can be introduced during quenching heating for a short period of time. Due to the low actual carbon content of austenite during quenching and heating of this steel, which is much lower than the equilibrium concentration shown on the phase diagram, it can absorb carbon (or nitrogen). When austenite contains a high amount of carbon or nitrogen, its Ms decreases, and during quenching, martensitic transformation occurs in the surface layer, inner layer, and core, resulting in significant residual compressive stress.

After heating and quenching GCrl5 steel in both carburizing and non carburizing atmospheres (both subjected to low-temperature tempering), contact fatigue tests showed that the service life of surface carburizing was 1.5 times longer than that of non carburizing. The reason is that the surface of carburized parts has a large residual compressive stress.

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

(1) The carbides in the original structure of steel before quenching are required to be small and dispersed. High temperature austenitization at 630 ℃ or 420 ℃ can be used, or the forging and rolling waste heat rapid annealing process can be utilized to achieve this.

(2) For GCr15 steel after quenching, it is required to obtain a microstructure with an average carbon content of about 0.55% of hidden martensite, about 9% of Ar, and about 7% of uniform and circular undissolved carbides. This microstructure can be controlled by using quenching heating temperature and time.

(3) After quenching and low-temperature tempering of parts, it is required to have a large residual compressive stress on the surface, which helps to improve fatigue resistance. The surface can be treated with short-term carburizing or nitriding during quenching heating, resulting in significant residual compressive stress on the surface.

(4) The steel used for manufacturing bearing parts requires high purity, mainly to reduce the content of O2, N2, P, oxides, and phosphides. It is advisable to use techniques such as electric slag remelting and vacuum smelting to achieve an oxygen content of less than 15PPM in the material.