high: temperature corrosion RESISTANCE OF Fe-Cr-Ni ALLOYS IN CO2-H2O

摘要

Recent developments aiming at reducing CO2 emissions from coal combustion for power generation will lead to changes in service conditions affecting the requirements for high temperature structural materials. In particular, in the oxyfuel process, materials will be exposed to gas mixtures of CO2 and HiO at high temperatures. Accordingly, the corrosion behaviour of Fe-Cr-Ni alloys in these atmospheres has been investigated in the present study. Binary Fe-9Cr and Fe-25Cr alloys, as well as ternary alloys containing 10 and 20 wt. % Ni were exposed to dry and wet CO2 at 800 °C. Additions of Ni caused a significant slowing in the metal consumption rate for the low Cr alloys, whereas the opposite effect was observed for the high Cr alloys. The alloys containing 9 wt. % Cr formed Fe-rich oxide scales, which suffered mechanical damage, and underwent internal oxidation and carburization. Addition of H2O caused an increase of the reaction rates, proved detrimental in terms of scale adherence to the substrate, and promoted carburization of the Fe-9Cr alloy. In contrast, 25Cr alloys were readily covered by a protective chromia layer in both atmospheres. Good resistance to corrosion was maintained up to 100 h, except for ternary alloys which failed during long exposures. The presence of H2O resulted in improved scale mechanical properties and in the suppression of carburization for the Fe-25Cr alloy. The role of CO2 and H2O on the corrosion process of the different alloys is discussed in terms of the chemical composition of the oxide scales.