Corrosion behavior of carburized 316 stainless steel in molten chloride salts

The corrosion has been investigated for carburized 316 stainless steel (SS) and 316SS in ternary molten NaCl-KCl-MgCl2 salt at 700 °C under argon atmosphere when adding Mg metal (1 wt%). Carburized 316SS has more severe intergranular corrosion than 316SS. Residual water and oxygen in the salts greatly oxidize Fe, Cr and Ni at the alloy surface in the initial stage of the corrosion process. Later, Fe and Cr at the alloy surface dissolve into salts through the redox reaction with metallic ion impurities such as Ni2+,Fe2+ and Fe3+ in the salts. Cr-rich carbides at grain boundaries in carburized 316SS are vulnerable to attack by molten chloride salts because Cr atoms in the carbides preferentially escape from the carbides and dissolve into salts, causing the decomposition of Cr-rich carbides and reducing the hardness of carburized 316SS.