Steam oxidation of Super 304H and shot-peened Super 304H

Oxidation of Super 304H and shot-peened Super 304H austenitic stainless steel was conducted over a temperature range of 600-700 degrees C in steam at atmospheric pressure and compared with oxidation in laboratory air. It was observed that the mass gain was higher in steam compared with air. It should be noted that the shot-peening treatment improved the oxidation resistance in both air and steam considerably. Furthermore, spallation was only observed on the pickled Super 304H specimens and only in steam after exposures at 650 degrees C and 700 degrees C. The protective films found at the base of the duplex oxide grown on pickled Super 304H in air and steam were found to differ in that after exposure to air, a chromium rich film was present whereas after exposure to steam, a less protective Cr-Mn spinel was present. The oxidation kinetics were assumed to be parabolic for purposes of comparison and parabolic rate constants, K-p, were calculated for oxide growth under the different oxidation conditions. The K-p value for the oxidation of shot-peened Super 304H in air at 700 degrees C compared well with known K-p values for chromia formation but less-protective oxides were formed in steam and in both air and steam for the pickled surfaces.