In order to establish a molten salt blanket, the microscopic corrosion of JLF-1 steel (Fe-9Cr-2W) was investigated by comparing with its alloying elements (pure Fe, Cr, and W) and pure Ni. Impedance measurements in LiF-NaF-KF at 500°C and scanning electron microscope and transmission electron microscope observations were performed. The charge transfer resistance of JLF-1 steel was similar to that of pure Fe, three times higher than that of pure Cr, and ten times lower than that of pure W and Ni. The concentration of W in JLF-1 steel was higher near the surface than at the bulk, which also indicated the higher corrosion resistance of W than Fe and Cr. For corrosion resistance of JLF-1 steel, the degradation by 9 mass % Cr was more effective than the improvement by 2 mass % W. The dominant corrosion was the intergranular corrosion at lath boundaries, leading to lath dropout for JLF-1 steel, the intergranular corrosion along grain boundaries for pure Fe, pitting corrosion for pure Cr, and entire surface corrosion for pure W and Ni.