The improvement of the corrosion resistance of 309 stainless steel in the transpassive region by nano-crystallization

Abstract

The effect of nano-crystallization on the corrosion behavior of 309 stainless steel in the transpassive region was investigated in 0.5 M Na 2SO 4 (pH 2) solution. Three parts defined as transpassive dissolution, secondary passivity and oxygen evolution can be observed in the transpassive potential region of the anodic polarization curves. In the whole transpassive region the nano-crystalline coating has a smaller corrosion current density than the bulk steel, which indicates the transpassive dissolution rate is decreased by nano-crystallization. In addition, there is an obvious difference in the surface micrographs of the two materials at transpassive potentials, as scanning electron microscopy (SEM) shows. The electron probe microanalysis (EPMA) reveals that nano-crystallization improves the homogeneity of Cr on the surface. Mott–Schottky plots displays that the carrier density of the oxide film in the transpassive region is decreased by nano-crystallization. Thus, the interfacial reactions are decelerated and the corrosion resistance of the stainless steel in the transpassive region has been greatly improved by nano-crystallization.