On the microstructure evolution and nanocrystalline formation of pearlitic wheel material in a rolling-sliding contact

The objective of this study is to characterize the microstructural evolution of pearlitic wheel material in a rolling-sliding contact. Continuous observations were carried out from the top layer of a rolling-sliding contact surface to the undeformed substrate using scanning electron microscopy (SEM), electron back-scattered diffraction (EBSD) and transmission electron microscopy (TEM). The results indicate that the microstructure of the pearlitic wheel material after rolling-sliding contact exhibits an obvious gradient structure in the depth direction. The microstructure evolution process in the wheel material is as follows: during the initial stage of rolling-sliding contact, the pearlite undergoes plastic deformation, resulting in a decrease in the pearlitic lamellar spacing, a large amount of dislocations in the ferrite and a small amount of cementite fractures. The dislocations accumulate, tangle and form dense dislocation walls (DDWs) inside the ferrite as the deformation strain increases. The cementite begins to dissolve into particles and the dislocation tangles (DTs), and DDWs transform into subboundaries with small misorientations. The low-angle grain boundaries (LAGBs) transform into high-angle grain boundaries (HAGBs). The refined grains repeatedly undergo deformation, the dislocation cells form and the LAGBs transform to HAGBs, forming a nanocrystalline grain structure.