Evaluation of SCC susceptibility of supermartensitic stainless steel using slow strain rate tests

The susceptibility to chloride stress corrosion cracking (Cl-SCC) of supermartensitic stainless steel (SMSS) was evaluated at different temperatures through slow strain rate tests. In order to evaluate the Cl-SCC susceptibility the reduction in area and the time to failure ratio were considered. It is clear that all specimens tested in the chloride solution exhibited a generally high resistance to chloride SCC. However, according to the slow strain rate tests results, at lower temperature (5°C) the susceptibility to Cl-SCC increases compared to the other temperatures studied; also an increase in the corrosion rate was observed as the temperature decreased according to electrochemical impedance spectroscopy measurement. The corrosion mechanism observed on the material under dynamic stress was a combination of high activation resistivity with a diffusive process on the metallic interface given by a thin film from a protector layer of chromium oxides. This mechanism generates a high corrosion resistance and therefore good performance to chloride induced SCC.