THE EFFECT OF NIOBIUM ON THE OXIDATION BEHAVIOR OF FULLY AUSTENITIC FE-15-PERCENT-CR-15-PERCENT-NI STAINLESS-STEELS

The influence of niobium content (0.5-2.0 wt.%) on the oxidation behav iour of Fe-15% Cr-15% Ni austenitic stainless steels has been studied by cyclic oxidation tests in air at different temperatures in the rang e 800-1200-degrees-C. The isothermal oxidation rate, the scaling index and the cumulative oxide loss decreased with increasing niobium conte nt. X-ray diffraction and fluorescence analysis of detached oxide scal es revealed that the niobium in the alloy matrix facilitated the forma tion of chromium rich (Fe, Cr)2O3 and niobium containing mixed oxide n ear the metal/metal 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 ri ch iron-chromium oxide.