Detection and Differentiation of SCC Processes

Abstract Electrochemical voltage and current noise were measured during Slow-Rate-Load-Tensile (SRLT) tests on specimens made from two qualities of austenitic stainless steel of type 304: non-sensitized and sensitized. A highly aggressive medium (a diluted aqueous solution of sodium thiocyanate), and a non-aggressive medium (de-ionised water) were used as electrolytes. 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 between them in all four of the experimentally investigated systems. Another comparison, between the current transient amplitudes and the charges, indicated a linear relationship between these parameters in all of the investigated systems. However, two different linear relationships, characteristic for the first and second type of electrochemical noise transients, were observed. Although certain parameters were obtained by this study, additional research is needed in order to correlate the different types of cracking with the characteristic electrochemical noise signal in order to distinguish between the different types of cracking modes.