Oxidation behaviors of Fe-25Cr-20Ni-χNb austenitic weld metals at 1100 °C in ambient air: Role of elemental niobium

The isothermal oxidation behaviors of the Fe-25Cr-20Ni-chi Nb (0-1.6 wt.%) weld metals have been investigated in air at 1100 degrees C. Results showed that niobium has a detrimental effect on the elevated temperature oxidation resistance of the chromia-forming weld metals. In the Nb content range studied, the Nb content of 1.6 wt.% showed the most deleterious effect on the chromia layer. Niobium promoted the chromium depletion underneath the oxide/matrix interface by impeding the chromium diffusion, which ruined the compactness of the chromia layer. The oxidation of niobium at the oxide layer/metal interface can further cause severe damage to the chromia layer, resulting in catastrophic oxide spallation.