Oxide scales on the surface of Fe-based alloys play an important role in prevention of metal dusting corrosion. Phase composition of oxide scales was studied by Raman spectroscopy, x-ray diffraction, and scanning microscopy. Chromium oxide (Cr2O3) and spinel phase were observed on the surface of alloys after exposure in metal dusting environments. Disordered chromium oxide may constitute a third constituent in some oxide scales. The metal dusting rate was low if the major phase of oxide scale was Cr2O3. The spinel phase could be reduced by carbon, thereby creating defects for metal dusting corrosion. High steam pressure stabilizes the spinel phase. In a gas with low PH2O, magnetite (Fe3O4) on surface of Alloy T22 (UNS K21590) was reduced to cementite (Fe3C) and increased metal loss rate. The phase composition of the oxide scales was determined as a function of alloy composition, oxygen partial pressure, and pretreating conditions. Selecting appropriate alloy composition to minimize spinel phase on the surface of alloys can reduce metal dusting corrosion.

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