The high-temperature corrosion of Fe–28Al base alloys containing Cr and Y additions in H2/H2S/H2O mixed gases

The high-temperature corrosion behavior of three Fe-28Al-xCr (where x = 2, 5, and 10 at. pct) ternary and Fe-28Al-5Cr-0.5Y quaternary alloys was studied over the temperature range of 700-900 C in H2/H2S/H2O mixed gases. The results showed that the corrosion kinetics followed the parabolic rate law in all cases. The parabolic rate constants decreased with decreasing temperature, but fluctuated with increasing Cr-content. It was found that Fe-28Al-5Cr revealed the best performance to improve the corrosion resistance compared with Fe-28Al in the ternary alloys studied. The Fe-28Al-10Cr alloy showed poor corrosion resistance, and whose corrosion rates were only slightly lower than those of Fe-28Al and much higher than those of low-Cr alloys. The addition of Y did not provide any significant reduction in the corrosion rates as compared with those of Fe-28Al-5Cr at T < 800 C. The scales formed on Fe-28Al-xCr were strongly dependent on temperature and Cr-content, consisting of most Al2O3, some FeS, and minor Cr2S3/Cr3S4 (for 2Cr- and 5Cr-content alloys) and of most FeS, minor amounts of Cr2S3/Cr3S4 and Al2O3 (for Fe-28Al-10Cr). The scales formed on the Y-containing alloy were nearly identical to those of Fe-28Al-5Cr.