Oxide scales formed on Fe–Cr–Al-based model alloys exposed to oxygen containing molten lead

Based on the state of the art oxide maps concerning oxidation behavior of Fe–Cr–Al model alloys at 800 and 1000°C in oxygen atmosphere, ten compositions, belonging to this alloy system, were designed in order to tap the borders of the alumina stability domain, during their exposure to oxygen (10−6wt.%) containing lead, at 400, 500 and 600°C. Eight alloys, Fe-6Cr-6Al, Fe-8Cr-6Al, Fe-10Cr-5Al, Fe-14Cr-4Al, Fe-16Cr-4Al, Fe-6Cr-8Al, Fe-10Cr-7Al and Fe-12Cr-5Al, were found to be protected against corrosion in oxygen containing lead, either by a duplex layer (Fe3O4+(Fe1−x−yCrxAly)3O4) or by (Fe1−x−yCrxAly)3O4, depending on the temperature at which they were exposed. Two alloys namely Fe-12Cr-7Al and Fe-16Cr-6Al were found to form transient aluminas, κ-Al2O3 (at 400 and 500°C) and θ-Al2O3 (at 600°C), as protective oxide scale against corrosion in oxygen containing lead. An oxide map illustrating the stability domain of alumina, grown on Fe–Cr–Al alloys when exposed to molten, oxygen containing lead, was drawn. The map includes also additional points, extracted from literature and corresponding to alumina forming alloys, when exposed to HLMs, which fit very well with our findings. Chromium and aluminium contents of 12.5–17wt.% and 6–7.5wt.%, respectively, are high enough to obtain thin, stable and protective alumina scales on Fe–Cr–Al-based alloys exposed to oxygen containing lead at 400, 500 and 600°C. For the temperature range and exposure times used during the current evaluation, the growth rate of the alumina scale was low. No area with detached scale was observed and no trace of α-Al2O3 was detected.