Reactions of Fe-Cr and Ni-Cr alloys in CO/CO2 gases at 850 and 950 °C

Abstract

A series of Fe-Cr and Ni-Cr solid solution alloys was reacted at 850 and 950 °C in CO/CO2 gas mixtures in which FeO and NiO were unstable. The compctitive tendencies toward the carburization and oxidation of the chromium solute, as compared to a graphical thermodynamic "metastability" criterion, were tested experimentally. Relatively good agreement was found between predictions and experiments for the occurrence of Cr carburization beneath Cr2O3 internal oxides or external scales. The chromium contents required for the transition from internal oxidation of Cr to the formation of Cr2O3 external scales in CO/CO2 gas mixtures were established for Fe-Cr and Ni-Cr alloys. The Cr2O3 external scales formed on Fe-Cr alloys were found to be relatively impervious to carbon penetration for short (12-hour) experiments. No carburization was observed in the Ni-Cr alloys, but the only alloys that were predicted to carburize were the ones that formed external scales.