Mn–Cr–O spinel often formed on austenitic alloys is an oxide phase that could be protective against high temperature carbonaceous attack. In this research, various Mn–Cr–O samples were tested in carburization environments with controlled oxygen partial pressures. The stoichiometric MnCr 2 O 4 shows better resistance to carburization and coke formation than the Mn-rich Mn–Cr–O and the Cr-rich Mn–Cr–O samples because of its highest thermodynamic stability as compared with MnO and Cr 2 O 3 . (Mn,Cr) 7 C 3 formed after carburization is catalytic to coke formation, and was found instable at higher levels of H 2 O/oxygen and may form volatile phases in the presence of H 2 O, leading to a continuous reduction in sample weight.