Corrosion Behavior of 304, 316 Stainless Steels and Inconel 617 Ni-based Alloy in Molten Nitrate Salt

Long-time immersion corrosion experiments were conducted on 304, 316 stainless steels and Inconel 617 Ni-based alloy in molten nitrate salt (60wt%NaNO₃+40wt%KNO₃) at 565℃. The corrosion kinetic curves and corrosion morphology, phase composition and microcomposition on surface of the three materials were studied and compared. The results show that oxidation corrosion occurred on the three materials. In addition, 304 and 316 stainless steels had parabolic corrosion kinetic characteristcs, while Inconel 617 Ni-based alloy exhibited significant corrosion mass loss after a brief mass increase. The corrosion resistance of Inconel 617 alloy was the best and that of 304 stainless steel was the worst. In the initial stage of corrosion, acicular and flaky corrosion products were formed on surfaces of 304 and 316 stainless steels; with increasing corrosion time, the corrosion products changed into spinel structure. The corrosion products on surface of Inconel 617 Ni-based alloy were granular, and some particles became larger with increasing corrosion time. The corrosion product layers on surfaces of 304 and 316 stainless steels were mainly composed of Fe₂O₃ and (Fe,Cr)₃O₄, while that on surface of Inconel 617 Ni-based alloy was mainly composed of NiO and CoO.