Understanding and detecting early stages of SCC initiation in sensitized stainless steel by means of electrochemical potential transients

Series of slow strain rate tests (SSRT) were conducted on moderately sensitized austenitic stainless steel in diluted aqueous solution of sodium thiosulfate at ambient temperature and pressure. Only a small area of the test piece was exposed to test solution and electrochemical potential transients obtained during the straining was used to detect an initiation or a precursor event of stress corrosion crack (SCC). Tests were stopped intermittently after getting potential transients, so as not to allow crack to propagate and to observe the morphology of very initial stage of SCC initiation site. Visual observation by scanning electron microscope (SEM) before and after the test shows direct correlation between electrochemical transient of certain characteristic to the crack initiation. SEM observation shows δ- ferrite in the alloy as one of the preferential SCC initiation site for typical electrochemical transient. Attempt was made to calculate the charge associated with crack initiation event from potential transient using dummy anode test.