Corrosion of Fe-Ni-Cr alloys with various aluminum additions in a carburizing-oxidizing atmosphere at 900 °C

•All the Fe-19Ni-13/21Cr-xAl alloys exposed to a mixed CO gas underwent an internal carburization.•For the alloys Fe-19Ni-21Cr-xAl and Fe-19Ni-13Cr-6Al the carbon attack in the CO gas was lighter than in a purely carburizing atmosphere with a similar carbon activity.•The addition of aluminum reduced the carburization of Fe-19Ni-13Cr-6Al and Fe-19Ni-21Cr-xAl.•The surface area fraction covered by Cr2O3 increased at higher Cr and/or Al contents.•The critical Cr and Al contents needed for their external oxidation in the CO gas are larger than in a purely oxidizing gas. The corrosion behavior of Fe-19Ni-13/21Cr-xAl (x = 0, 2, 6 at.%) alloys in a carburizing-oxidizing atmosphere was compared with that in a purely carburizing atmosphere at 900 °C. The presence of oxygen did not improve the corrosion resistance of the two alloys Fe-19Ni-13Cr-xAl (x = 0, 2 at.%), while oxygen reduced the carbon attack significantly for the other alloys. The extent of the carbon attack decreased with the increase of the aluminum content, except for the addition of 2 at.% Al to Fe-19Ni-13Cr, which did not reduce the carbon attack. Addition of sufficient aluminum promoted the formation of external Cr2O3.