Iushi zhongguo effect of nano/ultrafine grain on passive film properties of metastable austenitic stainless steels with and without loading

The passive behaviors of coarse and nano/ultrafine grain austenitic stainless steels processed by cold rolling and reversion annealing were investigated. The average grain about 200 nm was obtained by cold rolling down to 94% reduction in thickness and reversion annealing at 800 °C for 250 s. Passive films formed in borate buffer solution (pH 9.2) have been characterized by electrochemical impedance spectroscopy and Mott–Schottky plots. The impedance results indicated a distinct inflection was observed with the increasing of potential, however, the Mott–Schottky analysis did not show such inflection point in the same potential range. There were not evident differences in passive properties between coarse and nano/ultrafine grain samples. This was attributed to synergistic effect of grain refinement and orientation. However, the corrosion resistance of the passive film in nano/ultrafine grain sample was higher than that in coarse grain sample after immersion test by the three-point-bend loading.