Initiation of stress corrosion cracking of sensitized type 304 stainless steel

Abstract

The corrosion potential of stressed sensitized Type 304 stainless steels were studied in oxygen-containing solutions to determine the relation between potential fluctuations and the initiation of stress-corrosion cracking. An in situ scanning vibrating electrode technique was shown to detect currents coming from growing stress corrosion cracks in dilute thiosulfate solutions at temperatures below 90/sup 0/C. The onset of the cracking was clearly indicted by rapid decreases in the potential. It was observed that small cracks, which had grown for a limited period, were not susceptible to reinitiation of the cracking process. The onset of cracking was clearly observable by marked decreases in the potential which continued to decrease if cracking remained active and increased when cracking stopped. At and above 200/sup 0/C there were no potential fluctuation indicative of the onset of stress-corrosion cracking. Small potential differences between platinum and stainless steel were observed demonstrating the presence of a single electrochemically reversible reaction determined the potential of all metals within the stainless steel autoclave, and thus masking the onset of cracking. The presence of only an iron-containing deposit on the platinum suggested that a sufficiently reversible redox couple was set up between deposited iron oxide and a soluble iron species in solution which dominated the potential of the stainless steel and the platinum