Effect of Oxide Scale Compositions on Metal Dusting Corrosion of Fe-Based Alloys Available to Purchase

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.