Microstructural Evolution of a Hypoeutectoid Pearlite Steel under Rolling-sliding Contact Loading

To study the microstructural evolution of pearlite steel subjected to pure rolling and rolling-sliding contact loading,a hypoeutectoid pearlite steel with composition and microstructure similar to BS11 was designed and twindisc tests of this pearlite steel were performed to simulate the wheel/rail system.After a series of twin-disc tests,optical microscope(OM)observation,scanning electron microscope(SEM)observation,X-ray diffraction(XRD),and micro-hardness tests were conducted to characterize the microstructure.Under the pure rolling contact condition,a large amount of reticular cracks emerged within 60μm below the contact surface of the samples after 120 000 revolutions.The largest deformation was approximately 200μm below the contact surface.Under the rolling-sliding contact condition,the nodularization of pearlite within 100μm below the contact surface was obvious.The microstructure and stress-strain distribution of the area within 2mm below the contact surface were investigated.The distribution of micro-hardness under the contact surface varied with contact conditions.Finite element method(FEM)was used to simulate the stress-strain distribution.The results of SEM,FEM,and micro-hardness tests indicated that under the pure rolling contact condition,the maximum plastic strain was approximately 200-400μm below the contact surface.Conversely,under the rolling-sliding contact condition,the maximum plastic strain emerged on the contact surface.Under the pure rolling contact condition,the distribution of micro-hardness was almost identical to that of the equivalent plastic strain.Under the rolling-sliding contact condition,the distribution of micro-hardness was affected by the equivalent plastic strain and tangential stress.