Plastic Deformation and Softening of the Surface Layer of Railway Wheel

In this study scanning electron microscope (SEM) and optical micrograph observations were used to investigate the plastic deformation near the surface of the worn railway wheel following service. Microstructure, plastic deformation and micro-hardness of the material in the outermost tread layer of used passenger railway wheel were characterised. It was found that the material in the contact surface of wheel undergoes severe plastic deformation. Vickers micro-hardness measurements in the highly deformed layer could be correlated with softening of the outer wheel rim and the spheroidisation of the cementite phase. Examination of worn, railway wheel taken out of service, has indicated that cracks are predominantly initiated at the wheel surface down the edges of highly strained, pro-eutectoid ferrite zones (situated along prior austenite grain boundaries) and that such pro-eutectoid ferrite zones also facilitate crack propagation.