Impurity-driven corrosion and redox control of SS316H in molten NaCl–MgCl2 salts

Molten chloride salts are promising heat transfer and energy-storage media, but corrosion of structural alloys remains challenging. We investigated SS316H in commercial-grade NaCl–MgCl 2 at 700 °C using immersion tests, multiscale characterization, thermodynamic analysis, and multiphysics electrochemical modeling. The 120 and 500 h baseline tests yielded equivalent area-averaged mass-loss corrosion rates of 460 and 470 μm yr −1 , with maximum penetration depths of 67 and 82 μm. Surface and cross-sectional analyses indicate dissolution of both Fe and Cr, while thermodynamic calculations supported a greater tendency for Cr chlorination. Surface Cr enrichment and MgCr 2 O 4 identification were consistent with Cr dissolution followed by secondary formation of MgCr 2 O 4 near the alloy surface, accompanied by MgO accumulation. Fe-containing species were detected in the recovered salt, consistent with Fe dissolution from the alloy. Relative to baseline rates, H 2 /Ar reduced corrosion rates by 36–37% under 234 h sparging and 81% under 500 h cover-gas conditions. An electrochemical model calibrated against measured rates projected impurity-species and corrosion-rate evolution beyond 500 h under stated assumptions. Time-matched tests are needed to quantitatively rank the delivery modes. These results clarify impurity-driven corrosion mechanisms and demonstrate the potential of gas-phase redox control in molten chloride systems.