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

It is generally believed that when a chromia scale forms in high-temperature CO 2 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 CO 2 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. • Several chromia-forming alloys exposed to CO 2 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.