Surface integrity and corrosion performances of hardened bearing steel after hard turning

The primary role of hard turning is to realize surfaces with high dimensional accuracy and high surface integrity to improve functional performances of the manufactured product. To this aim, the turning process parameters have to be carefully chosen. The present work deals with the correlation between hard turning parameters, surface and sub-surface characteristics, and corrosion behavior of the AISI 52100 bearing steel. Different cutting speeds and cooling conditions, specifically conventional flood and cryogenic cooling, were used for hard turning. Microstructural observations, residual stresses, nano-hardness, and surface finish measurements were carried out to assess the surface integrity modifications induced by machining. Then, potentiodynamic polarization curves were carried out, and the corroded surfaces were inspected. The obtained results showed that a remarkably improved corrosion resistance was obtained by using the lowest adopted cutting speed coupled with cryogenic cooling. Specifically, the former contributed to generate a wider nanostructure layer close to the machined surface, while the latter induced compressive residual stress state in correspondence of it.