Sulfur Effect on Corrosion Behavior of Fe-20Cr-(Mn, Si) and Fe-20Ni-20Cr-(Mn, Si) in CO2-H2O at 650°C

Model alloys, Fe-20Cr and Fe-20Cr-20Ni (wt%), and these alloys doped with 0.5% Si or 2% Mn, were exposed to Ar-20%CO2-20%-H2O-(0%, 0.1%, 0.5%, 1.0%)SO2 gas mixtures at 650 degrees C. The reaction kinetics were analyzed gravimetrically and the reaction products were characterized using X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. In sulfurfree gases, thick iron-rich oxide scales and internal carbides formed on alloys of Fe-20Cr-(2Mn) and Fe-20Cr-20Ni-(0.5Si). Additions of SO2 promoted the maintenance of protective chromia scale on these alloys, but had no benefit for the already highly corrosion resistant Fe-20Cr-0.5Si and Fe-20Cr-20Ni-2Mn alloys. The role of sulfur in retarding carburization is discussed with reference to its strong adsorption on oxide-metal interfaces and oxide grain boundaries. (C) The Author(s) 2015. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. All rights reserved.