INITIATION AND PROPAGATION OF IGSCC FOR SENSITIZED TYPE-304 STAINLESS-STEEL IN DILUTE SULFATE-SOLUTIONS

Initiation and propagation of IGSCC for sensitized Type 304 stainless steel in dilute sulfate solutions have been investigated by the slow s train rate test (SSRT) with a CCD camera system. An increase in concen tration of sulfate ion was found to cause decrease in crack initiation strain and fracture strain, resulting in the increase in the IGSCC su sceptibility. Statistical analysis made it clear that the increase in concentration of sulfate ion had little effect on crack initiation fre quency, and crack initiation time obeyed the exponential probability d istribution, but the crack velocity obeyed the Weibull probability dis tribution. With increase in the concentration of sulfate ion, the crac k velocity increased, and the number of cracks decreased. On the contr ary, the mean crack velocity decreased and the number of cracks increa sed with time. The dependence of the crack velocity on the concentrati on of sulfate ion and the number of active cracks under potentiostatic SSRT conditions was successfully explained by a multiple cracks model combined with the mass transport model. (C) 1997 Elsevier Science Ltd .