1 Material factors that affect bearing life In the early stage of rolling bearings, there are mainly failures such as wear, cracking, corrosion, plastic deformation and fatigue. Under normal operating conditions, it is mainly contact fatigue. In addition to being affected by operating conditions, bearing failure is also affected by the wear resistance, hardness, toughness, strength, corrosion resistance and internal stress state of the bearing steel. The main internal factors are as follows: 1.1 The martensitic high carbon in the quenched steel When the original structure of chromium steel is granular pearlite, the carbon content of quenched martensite in the state of quenching and tempering at low temperature significantly affects the mechanical properties of the steel. The strength and toughness are about 0.5%, the contact fatigue life is about 0.55%, and the crush resistance is about 0.42%. When the carbon content of the quenched martensite of GCr15 steel is 0.5% to 0.56%, the strongest resistance to failure can be obtained. comprehensive mechanical properties. The martensite obtained in this case is cryptocrystalline martensite and the measured carbon content is the average carbon content. In fact, the carbon content in the martensite is not uniform in the micro-region, the carbon concentration near the carbide is higher than that in the ferrite part far from the carbide, so they start to undergo martensitic transformation at different temperatures, Thus, the growth of martensite grains and the display of microscopic morphology are suppressed to become cryptocrystalline martensite. It can avoid micro-cracks that are prone to occur when high carbon steel is quenched, and its substructure is dislocation lath martensite with high strength and toughness. Therefore, only when the high carbon steel is quenched to obtain medium carbon cryptocrystalline martensite, it is possible for the bearing parts to obtain the matrix with the best resistance to failure. 1.2 The retained austenite high carbon chromium steel in the quenched steel can contain 8% to 20% Ar (retained austenite) after normal quenching. Ar in bearing parts has advantages and disadvantages. In order to eliminate disadvantages, the content of Ar should be appropriate. Since the amount of Ar is mainly related to the austenitizing conditions of quenching heating, its amount will affect the carbon content of the quenched martensite and the number of undissolved carbides, so it is difficult to correctly reflect the influence of the amount of Ar on the mechanical properties. To this end, the austenitic conditions were fixed, and the austenitizing thermal stabilization process was used to obtain different Ar contents. The effect of Ar content on the hardness and contact fatigue life of GCr15 steel after quenching and low-temperature tempering was studied. With the increase of austenite content, the hardness and contact fatigue life increase, and then decrease after reaching the peak value, but the peak Ar content is different, the hardness peak appears at about 17% Ar, while the contact fatigue life The peak occurs at around 9%. When the test load decreases, the influence of the increase of Ar content on the contact fatigue life decreases. This is because when the amount of Ar is small, the effect on the reduction of strength is small, while the effect of toughening is more significant. The reason is that when the load is small, a small amount of Ar deformation occurs, which not only reduces the stress peak, but also strengthens the deformed Ar processing and stress-strain-induced martensitic transformation. However, when the load is large, the large plastic deformation of Ar and the matrix will locally produce stress concentration and rupture, thereby reducing the service life. It should be pointed out that the beneficial effect of Ar must be in the stable state of Ar. If it spontaneously transforms into martensite, it will sharply reduce the toughness of the steel and cause embrittlement. 1.3 Undissolved carbides in quenched steel The quantity, morphology, size and distribution of undissolved carbides in quenched steel are not only affected by the chemical composition of the steel and the original structure before quenching, but also by the austenitizing conditions. There are few studies on the effect of undissolved carbides on bearing life. Carbide is a hard and brittle phase. In addition to being beneficial to wear resistance, it will cause cracks due to stress concentration with the matrix (especially the non-spherical carbide) during loading, which will reduce toughness and fatigue resistance. In addition to its own influence on the properties of steel, the quenched undissolved carbides also affect the carbon content and Ar content and distribution of quenched martensite, which have additional effects on the properties of the steel. In order to reveal the influence of undissolved carbides on properties, steels with different carbon contents were used. Since martensite has the same carbon content and high hardness, a small increase in undissolved carbide has little effect on the increase in hardness, but the crush load reflecting strength and toughness decreases, and the contact fatigue life sensitive to stress concentration is significantly reduced. Therefore, excessive quenched undissolved carbides are harmful to the comprehensive mechanical properties and failure resistance of steel. Properly reducing the carbon content of bearing steel is one of the ways to improve the service life of parts. In addition to the number of quenched undissolved carbides affecting the material properties, the size, morphology and distribution also affect the material properties. In order to avoid the harm of undissolved carbides in bearing steel, the undissolved carbides are required to be small (small number), small (small size), uniform (the size differs little from each other, and are evenly distributed), round (each carbide is spherical). It should be pointed out that it is necessary to have a small amount of undissolved carbides in the bearing steel after quenching, not only to maintain sufficient wear resistance,It is also a necessary condition for obtaining fine-grained cryptocrystalline martensite.