Effects of Electrode Potential and Strain Rate on Stress Corrosion Cracking Behavior of Dissimilar Metal Weld 16MND5/309L/308L in High Temperature Water Environments

Effects of electrode potential and strain rate on the stress corrosion cracking (SCC) behavior of dissimilar metal weld 16MND5/309L/308L in simulated primary water environment of pressurized water reactor (PWR) were investigated by means of slow strain rate testing (SSRT). Results showed that at strain rate of 5×10-7s-1, the SSRT specimens always failed in the bulk zone of stainless steel 308L weld metal with ductile appearance when tested in the potential range from -720 mV to +100 mV (vs. SHE). When electrode potential was raised to +200 mV, SCC happened in the 16MND5/309L interface area, with transgranular SCC in low alloy steel 16MND5 zone close to the interface, intergranular SCC in the 309L weld metal close to the interface. There was a critical cracking potential above which SCC occurred, within the range from +100 mV to +200 mV for the dissimilar metal weld when tested at the strain rate of 5×10-7s-1 in simulated primary water environment of PWR. When strain rate was decreased to 1×10-7s-1, the critical cracking potential was still within the range from +100 mV to +200 mV although the test time increased significantly. When strain rate was raised to 1×10-6s-1, SCC was not observed even at the potentials +200 mV and +300 mV.