Effects of grain refinement on the passivation and film composition of low alloy steels in NaHCO3 solution

In this study, the passivation of coarse-grained and ultrafine-grained steels was investigated through electrochemical measurements and potentiostatic polarization at 0 VSCE, 0.3 VSCE, 0.5 VSCE, and 0.8 VSCE in 0.1 M NaHCO3 solutions. Then Mott-Schottky, Raman spectra, X-ray photoelectron spectroscopy, and atomic force microscopy were adopted to characterize the compositions, topographic structure and semiconductor performance of the passive film. The findings indicate a positive correlation between grain refinement and enhanced corrosion resistance of the passive films. Specifically, grain refinement leads to an increase in the ratio of Fe3+/ Fe2+ and average surface roughness, while the trends of donor concentration and the content of Fe0 demonstrate a decrease. These findings elucidate the impact of grain refinement on the enhanced corrosion resistance of the passive film. Moreover, it is observed that the corrosion resistance of the passive films initially increases and subsequently diminishes with rising passive potentials.