Carburization susceptibility of chromia-forming alloys in high-temperature CO2

It is generally believed that when a chromia scale forms in high-temperature CO2 environments, carbon uptake of alloys is nearly eliminated, thereby preventing carburization and associated degradation of properties. Herein we quantitively assess this notion through careful examination of several chromia-forming Ni-based and Fe-based commercial alloys after long-term (10,000-h) exposures to CO2 and air at 700 °C. Small but measurable carbon uptake ensued independent of alloy base metal (Ni/Fe), alloy crystal structure (FCC/BCC), and chromia growth rate. The rate for Ni-based alloys was strongly dependent on Si and Mn content, highlighting the need to understand possible long-term effects on mechanical properties. [Display omitted] •Several chromia-forming alloys exposed to CO2 and air at 700 °C for 10,000 h.•Chromia scale growth accompanied by small but measurable carburization.•Alloy carburization rate independent of base metal (Fe vs Ni).•Carburization rate strongly dependent on alloy Si and Mn content.•Testing needed for possible effects on mechanical properties of susceptible alloys.