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 (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 optical and scanning electron microscopy, X-ray diffraction, microindentation tests and contact profilometry. Corrosion tests were carried out, using 3.5% NaCl aqueous solution as corrosive medium. The results obtained indicated that the electropolishing process on AISI 316L greatly reduces the values of the roughness parameters of the samples when proper parameters are used. However, the waviness exhibits a more irregular behavior. 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 of surface hardness. The corrosion resistance of AISI 316L increases after the electropolishing process. In the case of revolution specimens, greater homogeneity is obtained in the values of roughness parameters by using a cylindrical cathode concentric with the specimen, instead of flat cathodes.