Dry passivation of austenitic SUS 301L stainless steel against pitting corrosion in marine atmospheric environment

Being an exclusive construction material for lightweight rail vehicles, protection from pitting corrosion in harsh marine atmospheric environment in high humidity and Cl− ion concentration is critical for austenitic SUS 301L stainless steel (SS), especially when it inevitably suffers from mechanical damages during post disposals. Herein, an innovative dry passivation method for austenitic SUS 301L SS was established in a closed air atmosphere at low temperature and constant pressure. The process parameters were optimized, and the passivation mechanism was explained using polarization curve, electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS), and contact angle measurement. The pitting corrosion susceptibility of the passive film prepared in a closed air chamber under 1.0×105 Pa at 80 °C for 80 min was evaluated in 3.5% NaCl solution and exhibited higher pitting potential and corrosion resistance, lower passivity-maintaining current density, and wettability when compared with conventional nitric acid treatment. Besides, dry passivation facilitated the repairing of the surface structural defect itself and the post-processing damage, similar to the accelerated aging of film. The decrease in oxygen concentration and convection-diffusion strengthened the preferential chromium oxidation to form a compact chromium-rich passive film to resist the aggression of Cl− ion.