Change of Microstructure and Properties of Surface of U75VG Rail Steel Phase Transition White Layer During Friction and Wear

The surface of U75VG rail steel sample was subjected to local laser quenching, and the banded white layer with martensite transformation was obtained on the surface of the sample. Before and after quenching, two kinds of rail steel samples were grand against the accompanying wheel steel ER8C, and the rolling wear test was carried out on GPM-40 rolling contact friction fatigue testing machine. The microstructure and properties of of the surface of phase transition white layer during friction wear were analyzed by means of hardness tester, precision electronic balance and scanning electron microscope. The results show that during the wear test of U75VG rail steel samples treated by laser quenching, cracks are easy to generate at the starting end, ending end and both sides of the laser quenching phase change white layer strip, and the cracks are easy to expand at the interface between the edge of phase change white layer and the matrix and inside the white layer. The wear morphology of the strip without phase change white layer is the same as that of the original specimen, and the damage is uniform. When the wear test is run at 700000 turns, according to the mass loss, the laser quenched sample of U75VG rail steel has better wear performance than that of the original sample of U75VG rail steel. However, the quenched sample of U75VG rail steel is prone to crack initiation, crack propagation and spalling at the interface between the edge of phase-change white layer and the matrix, which is locally vulnerable to damage.