Effect of HCO3- on passivation and pitting behavior of super 13Cr martensitic stainless steel

The work aims to investigate the influence of HCO3- on the passivation and pitting behavior of super 13Cr martensitic stainless steel in 0.1 mol/L NaCl containing borate acid buffer solution. Potentiodynamic and potentiostatic polarization tests, Mott-Schottky analysis and electrochemical impedance spectroscopy measurements were adopted to observe the pitting morphology and study the electrochemical corrosion behavior of super 13Cr martensitic stainless steel in combination with 3D ultra-depth-of-field microscope. The passive region of super 13Cr was enlarged with the increase of HCO3- concentration, thus contributing to more positive pitting potential and decreasing the sensitivity of stable pitting. HCO3- reduced the metastable pitting of super 13Cr and reduced the average value of peak current density of metastable pitting. With the increase of HCO3- concentration, the passivation film resistance Rf and the charge transfer resistance Rct of super 13Cr increased, but the passivation film capacitance Cf decreased. The presence of HCO3- changed the semiconductivity of the passive film from n-type to n+p type and the donor density ND and acceptor density NA in passivation film decreased with the increase of HCO3- concentration. The addition of HCO3- effectively thickens the passive film of super 13Cr stainless steel and lowers the density of point defects in the passive film, which thereby enhances the protective effect of the passive film on the steel matrix and inhibits the occurrence of metastable and stable pitting corrosion of super 13Cr. © 2019, Chongqing Wujiu Periodicals Press. All rights reserved.