Microstructure And Properties Of Fatigue And Wear Of High-performance Carburizing Bearing Steel

Carburizing bearing steel met the requirements of the rapid development of aerospace, metallurgy, high-speed railways well, due to its characteristics of high load-bearing capacity and large impact resistance. For this purpose, high cleanliness, high uniformity and fine grain size for the tested steel was tried to obtain to meet the requirements of the use as component. Therefore, firstly the forging process affecting the grain was simulated by hot deformation behavior in this paper. Also, the effect of subsequent heat treatment and carburizing on grain was analyzed. Secondly, the microstructure and mechanical properties of the central portion were analyzed to lay the foundation for the good microstructure of carburized case. Then the microstructure and properties of the carburized case was analyzed. Lastly, rotating bending fatigue tests and friction and wear tests were carried out. The effect of microstructure and properties of central portion and carburized case on properties of fatigue and wear was analyzed. During experiments, many testing methods like optical microscopy(OM), scanning electron microscopy(SEM), transmission electron microscopy(TEM), and X-ray diffraction(XRD) were used.Fully dynamic recrystallization occurred, when strain 0.6, the strain rate 0.01 s-1, and the deformation temperature was 1 000℃. Fine and uniform grain was obtained, when the deformation temperature was between 1 000℃ and 1 050℃.Good strength-toughness of the tested steel’s central portion was obtained for the tensile strength 1 413 MPa, and the impact toughness 162 J/cm2. The strength-toughness mechanism was fine grain strengthening caused by the fine grain size and fine martensite lath and the second phase strengthening caused by the fine dispersion of M3 C and VC. The fine and uniform microstructure made contribution to good microstructure and properties of carburized case.The microstructure of the carburized case after tempering consisted of needle type martensite and a small amount of retained austenite and fine dispersion of M3 C and VC. The grain size was still between 10 μm and 15 μm. The hardness of the surface was above 700 HV. Near the surface of the carburized case, solid solution strengthening played a major role. As more and more far away from the surface, second phase strengthening gradually played a major role.Rotating bending fatigue fracture mechanism of the surface was intergranular fracture, the transition zone intergranular fracture and ductile fracture, the central zone ductile fracture. Increasing the hardness of the surface of the carburized case could improve the rotating bending fatigue performance.Under the condition of dry sliding wear, the wear mechanism was adhesive wear and oxidation wear. Under the condition of lubricating sliding wear, the wear mechanism was contact fatigue wear, and the friction coefficient and the size of worn morphology was greatly reduced. Under the condition of dry sliding fretting wear, the wear mechanism was adhesive wear and flake. Compared with the increase of load, the increase of frequency affected the diameter of worn morphology and flake less.