The High Temperature Corrosion of Some Fe-Al Alloys under Low SO₂ Partial Pressures

Abstract

The corrosion of some Fe-Al alloys containing up to 7 mass% Al at 1073K under SO₂ partial pressures below 10³Pa was studied by thermogravimetry, X-ray diffraction, SEM, and EPMA. The effect of pre-oxidation on the corrosion of the alloys was also clarified. The addition of aluminum yielded a significant improvement in the corrosion resistance of the alloys to SO₂ gas. The parabolic rate constants obtained at given SO₂ partial pressures were exponentially decreased with the aluminum content, which was due to the increasing depression of the sulfide formation in the external scale. The increased corrosion resistance was interconnected to the depressed formation of sulfide for the alloys with high aluminum content, because of the reduced transport rate of rations through the oxide scale. The pre-oxidation treatment for the alloys yielded the remarkable decrease of the corrosion rate and the sulfide in the scales was scarcely found during the subsequent corrosion in the SO₂ atmospheres.