Comparison of Electrochemical and Mechanical Measurements during SCC Processes on Austenitic Stainless Steel in Sodium Thiocyanate Solution

摘要

Electrochemical voltage and current noise (EN) were measured during Slow-Rate-Load-Tensile (SRLT) tests on specimens made from two qualities of austenitic stainless steel of type 304: sensitized and non-sensitized. A highly aggressive medium, a diluted aqueous solution of sodium thiocyanate, was used as a electrolyte. During the experiments, characteristic simultaneous electrochemical and mechanical transients were observed after the yield point had been reached. Two different types of electrochemical transients were observed: (1) sharp transients of short duration, and (2) smooth transients that lasted over a longer period. A comparison of the current transient amplitudes with the corresponding displacement rates indicated a good linear relationship in both of the experimentally investigated systems. A comparison was also made between the current transient amplitudes and the corresponding charges. In this case, too, a linear relationship was found for all investigated corrosion systems. However, during the test on the sensitized stainless steel in the sodium thiocyanate solution two different linear relationships, characteristic for the first and second types of electrochemical noise transients, were observed. Although certain parameters suitable for the description of the different types of cracking were obtained in this study, additional research is needed in order to distinguish reliably between them, on the basis of measured EN and mechanical transients.