Comparing the corrosion of SS310 stainless steel in NaCl-KCl-CaCl ₂ and NaCl-KCl-MgCl ₂ molten salt vapors

Replacing MgCl 2 with CaCl 2 may serve as an effective strategy to reduce the corrosivity of chloride molten salt vapor, which is considered more critical than the molten salt itself. In this study, we comparatively investigated the corrosion behaviors of SS310 stainless steel in the NaCl-KCl-MgCl 2 (NKM) and NaCl-KCl-CaCl 2 (NKC) molten salt vapors. The volatility and hygroscopicity of MgCl 2 are significantly higher than those of CaCl 2 , leading to a remarkably higher HCl concentration and consequently more severe corrosion in the NKM molten salt vapor. A compact corrosion product layer is formed on SS310 in the NKC molten salt vapor, providing effective protection to the substrate. The corrosion in this environment progresses at an extremely slow rate through the depletion and oxidation of Fe and Cr. In contrast, a loose and porous corrosion product layer is formed on SS310 in the NKM molten salt vapor, resulting from the reactions involving HCl and MgO. The crevices and voids within this layer facilitate the rapid inward diffusion of corrosive substances and outward depletion of Cr into the vapor, thereby accelerating the corrosion rate.