Molybdenum effect on oxidation resistance and electric conduction of ferritic stainless steel for SOFC interconnect

The effect of molybdenum addition on the oxidation, electric property and Cr evaporation of Fe–22Cr–0.5Mn ferritic stainless steel is investigated in terms of mass gain, area specific resistance and Cr evaporation rate. Addition of 0.1–2 wt% Mo reduces the oxidation rate and especially area specific resistance of Fe–22Cr–0.5Mn steel. Mo addition of these contents increases the activation energy and suppresses the inward diffusion of oxygen, which indicates the defect chemistry of oxide scale is altered. This results in the increase of oxidation resistance and electric conductivity. When more than 4 wt% Mo is added, the oxidation rate increases after 300 h of oxidation at 800 °C in ambient air. The evaporation of volatile Mo species reduces the stability of protective chromia, so that rapid growing Fe-rich spinel is formed after 300 h of oxidation. The evaporation rate of Cr is similar in all alloys.

► Mo addition less than 2 wt% was effective to enhance oxidation resistance.
► Inward diffusion of oxygen was reduced by Mo addition.
► Mo addition reduced electric resistance and increased activation energy.
► Alloying Mo more than 4 wt% was detrimental to oxidation resistance.