Effect of rolling direction on microstructure evolution of CL60 wheel steel

The effect of rolling direction on the microstructure evolution of CL60 wheel steel was systematically studied using a rolling-sliding wear testing apparatus. The evolution of microstructures in depth and on the sub-surface was investigated using Electron Backscatter Diffraction (EBSD) and scanning electron microscopy (SEM). The results indicated that the microstructure in depth underwent a transition from the sub-boundaries introduced at low strain into grains with large-angle grain boundaries (LAGBs), leading to a full ultra-fine grain (UFG) microstructure at a large strain. Notably, an abnormal growth of the strain-induced UFGs near the surface occurred at the beginning of the rolling direction reversal (RDR). Meanwhile, the microstructure of the surface layer was changed from a fiber structure parallel to the surface under the unidirectional rolling of wheel materials to a wave structure. With the increase in the number of cycles after the RDR, the grain orientation on the sub-surface was changed from {111} to {101} and finally to a random orientation, resulting in a completely reversed plastic deformation layer. Additionally, the number of cycles per reversal and the total number of cycles also played an important role in microstructure evolution.