Impact of hard-turning parameters on the surface integrity of hybrid 60 steel

Abstract

This master thesis investigates the surface integrity of hard-turned Hybrid 60, focusing on the effects of machining parameters on the material's microstructure and mechanical properties. Seven samples were machined: samples A, B, C, and D with varying cutting speeds and feed rates, and samples E1, E2, and E3 under identical conditions. To analyze the surface integrity, techniques such as X-ray diffraction (XRD), optical microscopy (OM), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) were employed alongside surface roughness measurements. The XRD and topography analyses revealed a characteristic hook-shaped residual stress profile across all samples, with the highest compressive stresses occurring at the subsurface. Notably, samples machined at high feed rates and low cutting speeds exhibited the highest subsurface compressive stresses, while high cutting speeds induced more thermal stresses, resulting in lower surface roughness. SEM analyses identified a thin, notable layer on the machined surfaces of samples B, C, D, and E1, significantly thinner than the typical white layers observed in hard-turned bearing steels. Interestingly, this thin layer was absent in sample A, which instead showed severe plastic deformation. This variation underscores the influence of different cutting parameters on the material's surface integrity. These findings offer valuable insights into optimizing hard turning processes for Hybrid 60, demonstrating the critical role of machining parameters in influencing the material's microstructural and mechanical behavior.