Effect of surface graphitization on the corrosion behavior and interfacial mechanism of 316L stainless steel in KNO2–KNO3–K2CO3 molten salt

This study combined high-temperature corrosion experiments with molecular dynamics simulations to investigate the long-term corrosion behavior of surface-graphitized 316L stainless steel in a molten salt mixture of 0.259KNO 2 –0.687KNO 3 –0.054K 2 CO 3 at 500 °C. Over exposure periods ranging from 480 to 1000 h, the graphitized specimens exhibited lower mass loss and corrosion rates than the untreated specimens. After 1000 h exposure, the corrosion rate of the graphitized specimens remained at 0.0052 mm y −1 , compared with 0.0064 mm y −1 for untreated 316L. At the same exposure duration, the corrosion-scale thickness was approximately 1.49 μm for the graphitized specimen and 1.99 μm for untreated 316L. The corrosion products formed on untreated 316L stainless steel consisted primarily of Fe 2 O 3 and Fe 3 O 4 , whereas FeCr 2 O 4 was additionally identified on the graphitized specimens, indicating that surface graphitization altered the composition and evolution of the corrosion scale. The molecular dynamics simulations revealed that the graphite layer suppressed the local accumulation of NO 3 − and other ionic species near the alloy surface, reduced the mobility of major ions, and shifted the interfacial interaction energy from −4.085 to 0.630 eV. The experimental and simulation results indicate that the corrosion mitigation effect of surface graphitization is associated with changes in both corrosion product evolution and the interfacial behavior of KNC.