Study On Microstructure And Properties Of Nanobainite In Surface Layer Of Carburized Bearing Steel

Nano-bainitic bearing steel has been widely concerned in the bearing industry due to its excellent strength,toughness and rolling contact fatigue performance,and has been used in the manufacturing of heavy-duty bearings such as spindle bearings for large wind turbine units and rolling mill bearings.Because the high carbon part of carburized carbon steel surface is relatively thin and difficult to study,a kind of high carbon steel was designed to simulate the high carbon component of the surface of G23Cr2Ni2SiMo carburized nano-bainitic bearing steel.The influence of austenitizing temperature and isothermal time on the surface structure and properties of carburized nano-bainitic bearing steel was revealed by testing the hardness,impact toughness and compression properties of the samples.The following results are obtained:The size of the bainitic ferrite strip was less than 100 nm at two different austenitizing temperatures.The size of undissolved cementite obtained by isothermal process at higher austenitizing temperature was small,and the content was about 50%of that obtained by lower austenitizing temperature process.With the extension of the isothermal time of bainite transformation,the content of nano-bainite ferrite gradually increased,the content of martensite gradually decreased,and the content of residual austenite first increased and then decreased.Under different bainite isothermal processes,the minimum hardness of the two austenitization processes is greater than 58 HRC,which meets the minimum requirement of bearing hardness.On the premise of the same austenitizing temperature,the hardness of samples with different bainite isothermal time first decreases and then increases with the time extension.The compressive strength decreases with the extension of isothermal time and the strain value increases.The impact toughness increases with the extension of isothermal time,but when the cementite size and content is large,the impact toughness shows a positive correlation with the residual austenite content.The fatigue and wear test results showed that,on the premise of the same austenitizing temperature,the wear resistance gradually decreased with the extension of isothermal time,and the friction coefficient of all isothermal samples fluctuated around1.0 during wear.Under the condition of the same structure,a higher content of residual austenitic can effectively improve the wear resistance of the samples.Nanobainite tissues had the best fatigue performance,with a characteristic life V_s reaches 3.7×10~7.