High Temperature Oxidation of Fe-Cr-(Al) and Fe-Cr-Ni Alloys under Tensile Stress

Abstract

In order to examine the influence of tensile stress on the high temperature oxidation, wire specimens of heat resistant Fe base alloys were oxidized under a constant load in O2 or in air at 1173 K. It was anticipated that the oxidation of loaded specimen is accelerated because of the breakdown of protective scale due to elongation of the alloy substrate. In the case of ferritic alloys (Fe-20Cr and Fe-18Cr), however, no accelerated oxidation was observed in comparison with the oxidation without load. The absence of acceleration is attributed to rapid healing of scale on the ferritic alloys by virtue of a large diffusion rate of Cr in the alloys. On the other hand, the oxidation of an austenitic alloy Fe-20Cr-12Ni was somewhat accelerated under an average strain rate of 2.8×10−6 s−1 and the oxidation of an Fe-17Cr-6Ni alloy was very severely accelerated under the same strain rate. This acceleration is attributed to smaller diffusion rates of Cr in the austenitic alloys. A threshold of average strain rate to acceleration was observed to be of the order of 2×10−6 s−1.