Formation of Si Diffusion Layer on Fe and Fe-Cr Alloy and High-Temperature Corrosion Resistance in a Molten Salt

A thick silicon-enriched layer was formed on the surface of Fe and Fe-15 mass% Cr alloys by Si electrodeposition using a molten salt as the medium. This surface-treated sample was embedded in the molten salt and the high-temperature corrosion behavior was investigated. For comparison, the high-temperature corrosion behavior of untreated samples was also investigated. The effect of the surface Si conversion by the molten salt electrodeposition treatment on the high-temperature corrosion resistance of the Fe and Fe-15 mass% Cr alloys was then evaluated. As a result, the surface Si electrodeposition-treated Fe did not improve the corrosion resistance as compared to the untreated sample. However, for the Fe-15 mass% Cr alloy, the untreated corrosion weight loss sharply increased and the corrosion rate increased. On the other hand, the corrosion rate was lower on the surface of the Si-treated sample. After the high-temperature corrosion test, a cross section of the sample to which the molten salt was attached was observed and analyzed by SEM and EPMA. As a result, in the untreated sample of Fe, the elemental metal dissolved in the molten salt. In the Si electrodeposition-treated Fe, cracks were generated at the Fe interface between the electrodeposition layer and the substrate, and corrosion proceeded from there. On the other hand, for the Fe-15 mass% Cr alloy, it was confirmed that the surface Si-treated sample formed a continuous SiO2 layer on the surface. It is considered that this SiO2 improved the corrosion resistance.