Early failure in the form of a rolling bearing, the main rupture, plastic deformation, wear, corrosion and fatigue, under normal conditions, mainly contact fatigue. Failure bearing parts except service conditions, mainly by the steel hardness, strength, toughness, wear resistance, corrosion resistance and stress state within the constraints. The main internal factors affecting these properties and states the following items.
A martensitic hardening steel
Carbon chromium steel granular pearlite original organization when, in the state quenching and tempering, quenching martensite carbon content, significantly affect the mechanical properties of steel. Strength, toughness about 0.5%, the contact fatigue life of about 0.55%, Compressive capacity of about 0.42%, when GCr15 steel quenched martensite carbon content of 0.5% to 0.56%, the strongest available anti-failure mechanical properties.
It should be noted in this case to obtain martensite is cryptocrystalline martensite, the carbon content is measured by the average carbon content. In fact, the carbon content of martensite in the micro-region is uneven, the carbon concentration near the far higher than the carbide around a carbide former ferrite portion, so they began martensitic transformation temperature difference, thereby inhibiting the grain growth and microstructure of martensite morphology show and become hidden martensite. It avoids prone to high-carbon steel quenching microcracks, and its sub-structure for the strength and toughness of high dislocation strip plate martensite. Therefore, to obtain bearing parts could obtain the best anti-failure capability matrix carbon hidden martensite only when the high-carbon steel quenching.
2 hardened steel residual austenite
Carbon chromium steel after normal hardening, may contain 8% ~ 20% Ar (residual austenite). Bearing parts of Ar advantages and disadvantages, in order to better bring, Ar content should be appropriate. Due to the amount of principal and quenching Ar austenitizing conditions, how much it will affect the number of the carbon content of quenched martensite and undissolved carbides, difficult to accurately reflect the amount of influence on the mechanical properties of Ar. For this purpose, fixed austenitic conditions, using body heat of austenite stabilization process, in order to obtain different amount of Ar in this study the effects of Ar content on GCr15 steel hardness and contact fatigue life after quenching and tempering. With the increase in the content of austenite, hardness and contact fatigue life are attendant increase and reach a peak and then subsequently decreases, but the peak of the Ar content of different hardness peak at about 17% Ar, and the contact fatigue life peaking at around 9%. When the test load is reduced, the amount of the increase due to the impact of Ar contact fatigue life is reduced. This is because when the small amount of strength when Ar much lower impact, and the toughening effect is more obvious. The reason is that when the load is small, Ar has a little distortion, both reduction of stress peaks, but also to strengthen Ar machining the deformed and the occurrence of stress and strain-induced martensitic transformation and strengthening. However, if the load is large, Ar large plastic deformation of the matrix of the local stress concentration broken, so that the life expectancy is reduced. It should be noted, the beneficial effect of Ar must be stable under Ar, if spontaneously into martensite, will drastically reduce the toughness of the steel and embrittlement.
