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The subject of the study was to determine the corrosion resistance of the bearing steel 67SiMnCr6-6-4 with a nanocrystalline structure compared to those with the conventional structure of tempered martensite. In order to obtain a nanocrystalline structure one set of steel samples was subjected to heat treatment consisting on quenching and austempering at 240°C. This treatment produced a homogenous nanobainitic structure composed of nanometric plates of carbide-free bainite separated by thin layers of retained austenite. The microstructures formed were investigated by use of transmission electron microscopy techniques. For comparison a conventional quenching and tempering at 350 °C for 1 h was applied to second set of steel samples. Time and temperature of tempering was chosen so that the hardness of both samples (nanostructured and quenching and tempered) was similar. The microstructure obtained was a tempered martensite. The corrosion resistance studies of both kinds of steels with different microstructures were carried out in Na2SO4 acidic and neutral environment using potentiodynamic and electrochemical impedance spectroscopy (EIS) methods. The obtained results indicate, that the nanobainitic structure produced in bearing steel 67SiMnCr6-6-4 does not affect the corrosion resistance of the steel as compared with conventional quenching and tempering treatment in both acidic and neutral environment.
Keywords: Bearing steel, austempering, nanocrystalline structure, corrosion resistance© This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.