Corrosion behavior of 347 stainless steel in molten nitrate salts

The static corrosion behavior of 347 stainless steel (347SS) at 565 ℃ in molten nitrate salts (60%NaNO₃ + 40%KNO₃) was investigated via 2000 h immersion test. Corrosion kinetic curve of 347SS in molten salts at 565 °C were obtained through measuring the weight changes of the specimens at each time intervals. Moreover, XRD, SEM/EDS were used to characterize the morphology, composition and microstructure of the corrosion products on the surface and the cross section of corroded specimens, the corrosion mechanisms were also briefly described. Results showed that the corrosion behavior of 347 SS in molten nitrate salts at 565 °C was characterized by mass gain, its corrosion rate was very fast in the first period of 300 h, and then gradually slowed down after 300 h. As the corrosion time prolonged, the oxide scale of spinel gradually changed from needle-like and sheet-like to block-like, and it basically all tended to be block-like for corrosion up to 2000 h. After 2000 h corrosion, the outer portion of corrosion product, composed of Fe₂ O₃ and NaFeO₂, was uniform and loose with certain amount of cracks, while the inner portion of corrosion product, composed merely of (Fe,Cr)₃ O₄, was non-uniform and dense.