Electropolishing of AISI 316L: effect on surface characteristics and corrosion behavior

The surface characteristics and corrosion behavior of electropolished AISI 316L stainless steel specimens were analyzed. The influence of the electropolishing process parameters, such as voltage, temperature, time, cathode material, cathode geometry, and cathode–anode distance, was also evaluated using an electrolyte composed of sulfuric acid, phosphoric acid, and water. The surface characteristics of the specimens were determined by means of scanning electron microscopy, X-ray diffraction, microindentation tests, and contact profilometry. Corrosion tests were carried out using 3.5% w/v NaCl aqueous solution as a corrosive medium. The results indicate that the electropolishing process on AISI 316L greatly reduces the roughness of the samples when proper parameters are used. However, the waviness exhibits a more irregular behavior. It is also demonstrated that the use of stainless steel cathodes instead of copper cathodes allows obtaining surfaces with less roughness. Electropolishing produces the elimination of the deformed surface layer and, if present, of the martensite phase. This results in a decrease in surface hardness. The corrosion resistance of AISI 316L increases after the electropolishing process. In the case of cylindrical specimens, greater homogeneity in roughness parameters is obtained by using a cylindrical cathode concentric with the specimen instead of flat cathodes.