Influence of non-uniform microstructure on rolling contact fatigue behavior of high-speed wheel steels

Rolling contact fatigue (RCF) failure is an important concern for wheel and rail system of railway transportation. In this work, the effect of non-uniform microstructure of the pearlite- ferrite wheel steel on RCF was investigated. Some bainite regions dispersedly distributed in the matrix of ferrite and pearlite. The hardness and chemical composition of different regions of wheel steel were determined by Vickers hardness tester and electron probe microanalysis (EPMA) respectively. As the hardness was different in these two regions, the initiation and propagation of cracks occurred at the boundary of abnormal microstructure mainly. EPMA results showed that the contents of Mn and Si were higher in positive segregation region than those of the matrix. In addition, the thermodynamic model was used to calculate the evolution of time-temperature-transformation (TTT) diagram of steel with element segregation. Result showed that the increase of Mn and Si in positive segregation region changed the shape of the TTT curves and caused the formation of abnormal microstructure.