In-situ Measurement of Contact Electric Resistance of Oxide Films on Sensitised 304 Stainless Steel during Slow Strain Rate Test in High Temperature Water(EAC2)

Abstract

One possible way of explaining the environmentally assisted cracking of steel construction materials is to assume that the transport of atomic-scale species such as cation vacancies and metallic ions through the oxide film contribute to the growth rate of cracks in stainless steels. A similar approach can be followed to investigate the process that leads to the initiation of cracks on a smooth surface. At the moment, to our knowledge, there is no data available in the literature relating to the evaluation of the effect of stress on the electronic properties of oxide films. This is mainly due to the difficulties of carrying out reliable experiments in high temperature and high-pressure water environments. This paper describes a novel technique that can be used to measure in-situ the electronic properties of oxide films in different parts of a specimen during the slow strain rate test in high temperature aqueous solutions. By measuring the resistances of oxide films on sensitised 304 stainless steel in high purity water at 288℃, we found that during the straining process the oxide film resistance in the gauge part of the specimen increased significantly for up to 5% strain, and then gradually decreased again. The oxide film resistance on the unstressed part of the test sample behaved in a similar way, except the gradual decrease in film resistance at higher strain conditions was not observed. Ex-situ analysis of the oxide film thickness in different parts of the SSRT specimen indicated that the oxide film thickness was highest in the stressed part, thus supporting the idea of increased ion movement through the film.