Research On The Influence Of Heat Treatment Process On The Microstructure And Mechanical Properties Of Steel Used In Urban Rail Bearings

In recent years, along with the development of high-speed railway and urban railway, many kinds of bearings are needed in these industries. Thus the requirements to the performance of rolling bearing have been stricter. However, many key parts of rolling bearing still rely on import. So it is necessary to develop bearings that have independent intellectual property rights as well as high-performance. First, this article selected isothermal quenching process which is commonly used in factory to deal with a set of bearing. Comprehensive tests were made to GCr15roller and GCrl8Mo rings, including the composition, hardness, organization and distribution of the residual stress. Also the influence of heat treatment process on the microstructure and properties were analyzed. Besides, based on the analysis of finished products, we made preheat treatment and final heat treatment on the two kinds of steel materials which were used. After that, we discussed the influence of different heat treatment processes on materials’microstructure and mechanical properties to provide important experimental data in improving the service life of bearing used inurban rail vehicles. Research findings show that microstructure and hardness of the three specimens from the surface to the core are uniform. The average hardness of the roller, the inner ring and the outer ring is56.2HRC,60.8HRC and60.8HRC. Main structures of the three components are Lower Bainite and Carbide. But in rings, the size of Lower Bainite and Carbide are smaller than those in roller. The length-width ratio of Lower Bainite needle in roller is about7.5, which is about10in two rings. The average diameter of Carbide in roller, inner ring and outer ring are0.55μm,0.39μm and0.42μm, within which the ratios from0.2μm to0.8μm are86.5%,88.2%and93.2%. Residual stress states in the outside surface of the three components are compressive stress and axial compressive stress is greater than the hoop. After heat treatment, the axial compressive stress and the hoop compressive stress in roller is about-480MPa and-90MPa, which is about-588MPa and-390MPa in the inner ring. After heat treatment and polishing, the axial compressive stress and the compressive stress is about-398MPa and-61.5MPa, which is about-483MPa and-231MPa in inner ring. The spheroidizing effect after three cycles of spheroidizing annealing in GCr18Mo steel is ideal. After analysis on microstructure and hardness of the two kinds of steel which has been made quenching tempering, we can find that structures of the two samples are made up by Martensite, Carbide and retained Austenite. The hardness peaks of GCrl5and GCr18Mo bearing steels are heating in840℃tempering in160℃and heating in860℃tempering in180℃.