Formation mechanism of zig-zag crack region on the shattered rim of railway wheel

Abstract

Shattered rim is a century-old problem that restricts the reliability of railway wheels in service. In this paper, the formation mechanisms of the zig-zag crack region on the shattered rim of railway wheel were investigated. First, the zig-zag crack region was observed using both scanning electron microscopy (SEM) and transmission electron microscopy (TEM) and was identified as a typical region for crack propagation in giga-cycle rolling contact fatigue behavior. The zig-zag crack bands have a height range of 3–30 μm, with an average of 13.4 μm, and a width range of 0–500 μm, with an average of 184.6 μm. The size values of band height and width are close to the values of the pearlite and protoaustenitic grain size. The formation of the zig-zag morphology in the zig-zag crack region is due to the periodic deflection of the propagation path relative to the initial propagation plane, which is a result of the limited plastic deformation zone at the crack tip that extends only a few grain diameters. The grain refinement and secondary cracks in the zig-zag crack region are attributed to the large compressive and shear stresses induced by the applied rolling contact loading.