The influence of niobium content (0.5-2.0 wt.%) on the
oxidation behaviour of Fe-15% Cr-15% Ni austenitic stainless
steels has been studied by cyclic oxidation tests in air at different
temperatures in the range 800-1200 ºC. The isothermal oxidation
rate, the scaling index and the cumulative oxide loss decreased with
increasing niobium content. X-ray diffraction and fluorescence
analysis of detached oxide scales revealed that the niobium in the
alloy matrix facilitated the formation of chromium rich (Fe,Cr)203
and niobium containing mixed oxide near the metaumetal oxide
boundary, which decreased further oxidation. SEM/EDX investigations
revealed that the external oxide changed from being
predominantly iron rich iron-chromium oxide to being chromium
rich iron-chromium oxide.