THE EFFECT OF POTENTIAL ON INITIATION AND PROPAGATION OF STRESS-CORROSION CRACKS FOR TYPE 304L STAINLESS-STEEL IN A CHLORIDE SOLUTION CONTAINING THIOSULFATE

The effect of applied potential on the stress corrosion cracking (SCC) of Type 304L stainless steel in a chloride solution containing thiosu lfate ions (S2O32-) has been investigated by using a slow strain rate testing apparatus with a dynamic observation system. It was found from the SCC test that the material suffered SCC in the potential region f rom -360 to -410 mV(Ag/AgCl), and that maximum stress decreased with i ncrease in the potential. At any potential in that potential region, m oreover, polarity of the current changed from negative to positive dur ing the test, and strain where the current was zero decreased with inc rease in the potential. According to the detailed analysis of the crac ks from the observed images, the following findings were obtained: The number of pits and cracks increased with increase in the potential; S train where either a pit or a crack was detected first were decreased with increase in the potential, and was almost the same value as the s train where the current was zero; Apparent critical stress intensity f actor for SCC decreased with increasing potential; crack propagation r ate slightly increased with increasing potential. These findings sugge st that the potential accelerates the initiation process of pits and c racks more than the propagation process of the crack. (C) 1997 Elsevie r Science Ltd.