High-Temperature Corrosion of Aluminized Diffusion-Coating for Fe-Base Alloy in N2/H2O/H2S-Mixed Gas

Abstract

The pack-cementation is one of economical, efficient coating processes for Fe-base alloys. It can provide good protection against high-temperature oxidation and corrosion. In this study, the high-temperature corrosion behavior of the aluminized diffusion-coating on low-carbon T20 steel (Fe-2.0Cr-0.5Mo-0.8Mn-0.3S in at.%) was studied at 800 °C in N2/H2O/H2S-mixed gas. The aluminized coating consisted of Fe3Al. The aluminized T20 steel after corrosion at 800 °C for 10~100h in N2/H2O/H2S-mixed gases, the scale formed on the Fe3Al coating consisted primarily of α-Al2O3, Al2S3, FeAl2O4 and FeO, with relatively slow scaling rates. The Fe3Al intermetallics has reasonable corrosion-and oxidation-resistance, because it can form a protective alumina scale. Without the aluminized diffusion-coating, T20 steel corroded fast with serious scale failure. At the surface, coarse FeS grains with cracks formed. Since FeS has a very high concentration of cation vacancies, it grew fast through the outward diffusion of Fe2+ ions.