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 hypocutectoid pearlite steel with composition and microstructure similar to BS11 was designed and twin disc 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 60 mu m below the contact surface of the samples after 120000 revolutions. The largest deformation was approximately 200 mu m below the contact surface. Under the rolling-sliding contact condition, the nodularization of pearlite within 100 mu m below the contact surface was obvious. The microstructure and stress-strain distribution of the area within 2 mm 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 200-100 mu m 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.