Influence of the polishing process on the near-surface zone of hardened and unhardened steel

Interface phenomena on polishing are still not completely understood. On this account, ground hardened and unhardened workpieces of CrMo-steel were polished with diamond suspension in order to analyze the process. Using the synchro-speed kinematic for spherical lenses, a step-by-step polishing process was executed. After each polishing step, the surface topography of the workpieces was analyzed by both a light-microscope and a white light interferometer to determine the roughness. At the end of the process, transmission electron microscopy (TEM) analyses were made to visualize changes in the near-surface zone. The microstructures of the boundary layer and of the subsurface have been characterized and effects such as plastic deformation, flow of material and nanostructure formation, have been discussed. The results obtained for the hardened material were compared with those obtained for the unhardened. Based on the analyses made, it was possible to conclude that plastic deformation of the near-surface zone takes place in a higher degree when the unhardened steel is polished. It has been stated that material removal and surface quality improvement are both determined by the mechanical properties of the near-surface zone, which differ from those of the bulk material.