Synergistic effect of Cl− and F− on the corrosion behavior and mechanism of 316 stainless steel in NaNO3-based molten salts and vapor

Abstract

The corrosion behaviors of 316 stainless steel (316 SS) in NaNO3-NaCl-NaF molten salt and vapor were investigated at 450 °C for 130 h under argon gas and air conditions, respectively. 316 SS suffered from weight gain under the argon gas condition yet experienced weight loss under the air condition. Fe-O enriched layer with different crystal forms (i.e., whisker-like, flake, and grain shapes) was detected by XRD. The crystal forms were relatively homogeneously distributed after the NaNO3-NaCl-NaF molten salt corrosion but were not uniform after the NaNO3-NaCl-NaF vapor corrosion. 316 SS experienced a more serious corrosion attack in salts vapor than that in NaNO3-NaCl-NaF molten salt regardless of the experimental condition. The corresponding corrosion mechanisms were also investigated, and results show that the oxides helped mitigate further corrosion attacks. These findings provide direct guidelines for choosing the appropriate molten salts and alloys for CSP.