Microstructure evolution of rail steels under different dry sliding conditions: A comparison between pearlitic and bainitic microstructures

Abstract Railway transportation has constantly been moving towards high-speed and heavy-haul direction, and at the same time, the requirements of wheel-rail steels' properties have been increased. Especially, at curved tracks and railway forks, the transformation of wheel-rail wear mode from rolling/sliding wear into sliding wear, accelerating rail failure. Therefore, it is of great importance to conduct a comparison study on the changes of microstructures and properties of the newly developed bainitic steel and the conventional pearlitic steel under different dry sliding wear conditions. Through comparing the microstructure evolution and the property changes of the surface layer of pearlitic steel and bainitic steel during the process of sliding wear under different cooling conditions, it was discovered that compared with pearlitic steel, bainitic steel possessed better wear resistance under the same condition of sliding wear. The damage form on the surface of pearlitic steel was mainly fatigue wear (that displayed flake-like spalling), while the damage form on the surface of bainitic steel was chiefly adhesion wear. During the process of sliding wear, cooling conditions affected wear mass losses and the evolution of microstructures in the surface layer. Under forced convection condition, for both pearlitic steel and bainitic steel, the microstructures in the surface layer underwent plastic deformation and a nanocrystalline layer was formed at the outermost layer. Compared with forced convection condition, under static air condition, the temperature of the worn contact surface was relatively higher, not only easily giving rise to oxidation that enhanced wear resistance, but also bringing about the transformation of the microstructures at the outermost layer. Pearlitic steel was inclined to experience austenitic transformation, forming martensite white etching layers, while bainitic steel was recrystallized, forming recrystallized white etching layers.