Hot Corrosion Behavior of JIS SS400 and JIS SUS304 steels in BaO₂-BaO

Abstract

The hot corrosion behavior of JIS SS400 and JIS SUS304 steels in BaO₂ salt has been examined by measuring the corrosion mass loss, observing the corrosion morphology and analyzing corrosion product. Because solid BaO₂ melts at 723 K and the molten BaO₂ dissociates into oxygen gas and solid BaO in the temperature region higher than 1073 K, particular attention was given to the change in the corrosion behavior with such an environmental change. In the molten BaO₂ at a temperature lower than 973 K, the SS400 steel formed an oxide scale consisting of FeO and Fe₃O₄ as the inner scale. In the same environment, on the other hand, the SUS304 steel formed a thick scale mainly consisting of BaFe₂O₄. In the molten BaO₂, the SUS304 steel showed a maximum corrosion mass loss at 773 K. The corrosion mass loss for SUS304 steel at this temperature was about 9 times as large as that for the SS400 steel. In the solid BaO in the temperature range higher than 1073 K, the corrosion rate for the SS400 steel remarkably increased with an increase in the temperature. In this case, the SS400 steel formed an inner scale consisting of FeO and Fe₃O₄, and an outer scale consisting of BaO and BaFe₂O₄. On the other hand, the corrosion rate for the SUS304 steel in the same environment was far lower than that for the SS400 steel. In this case, the SUS304 steel formed a thin scale which contained an inner scale consisting of Cr₂O₃･FeO.