High-Temperature Molten Salt Corrosion and Wear Resistance of a Novel Nb-Alloyed Austenitic Steel for MSR Structural Applications

摘要: The next-generation Molten Salt Reactor (MSR) utilizes a liquid-fuel system, in which fissile material is dissolved in high-temperature molten salts. This dual-purpose medium acts as both fuel and primary coolant, offering exceptional thermal stability and inherent safety features. However, MSR poses extreme thermo-chemical challenges to structural materials due to the corrosive and oxidative nature of the high-temperature molten chloride salts. Consequently, structural materials for MSR must exhibit outstanding corrosion and wear resistance to ensure long-term reliability. Therefore, in this study, the corrosion and wear resistance of a newly developed Nb-containing austenitic alloy ("New alloy") against conventional MSR-relevant materials (316SS, 304SS, and Hastelloy C-276) were evaluated and compared. Static corrosion tests were performed at 800 °C in a NaCl-MgCl₂-KCl (20-40-40 wt.%) salt mixture. Postcorrosion degradation was assessed via weight loss, surface roughness, cross-sectional SEM, and elemental analysis using EDS and XRD. Scratch and two-body wear tests were also conducted to evaluate mechanical performance. The New alloy exhibited the lowest weight loss (0.057 mg/mm³), minimal surface roughness increase, and no detectable leaching of Fe, Cr, or Ni into the molten salt. Post-corrosion hardness increased from 250 HV to 310 HV, attributed to the formation of Ni-Nb intermetallics and M₂₃C₆ carbide precipitates, which served as protective phases. Compared to 316SS, it showed over 90% lower wear and superior chemical stability. These findings establish the New alloy as a robust, cost-effective structural material for high-temperature MSR environments, capable of resisting both corrosive attack and mechanical degradation.