Corrosion behaviors of stainless steel 316 in NaCl-MgCl2 molten salt thermal convection loop (MSTCL)

초록

A long-term corrosion study on stainless steel 316 was conducted in a NaCl-MgCl2 thermal convection loop for 24 weeks to examine its corrosion behaviors across temperature gradients. Samples were placed at five positions with temperatures ranging from 500 degrees C to 570 degrees C. Samples were retrieved from the loop at a specific time interval to assess the time-dependent corrosion behaviors. Most samples exhibited weight loss, with surface and cross-sectional analyses revealing location-specific corrosion patterns. In the high-temperature region, the formation of MgO was absent, but Mo-rich carbides accumulated near the surface grain boundaries. Fe, Cr, and Ni dissolved at similar rates, with no selective Cr dissolution, and weight loss followed a diffusion-controlled process over time. Corrosion was initiated with surface grain boundary dissolution, followed by uniform corrosion. In the intermediate-temperature regions, selective Cr depletion and MgO penetration were observed. At lowtemperature regions, Ni- and Fe-rich deposits formed on the surface.

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