Effects of Impurities and Electrode Potentials on Stress Corrosion Cracking of Domestic Low Alloy Steel SA-508III in High Temperature Water Environments

The effects of impurities including chloride and sulphate in water and electrode potentials on the stress corrosion cracking (SCC) behavior of Chinese homemade low alloy steel SA-508Ⅲ (S: 0.0025%) in simulated primary water environments of pressurized water reactor (PWR) at 290 ℃ was studied mainly by using slow strain rate testing (SSRT) technique. The tests were mainly performed in the water at various applied electrode potentials in the range from -720 mV to +400 mV (SHE) which simulated the electrochemical conditions of the steel in the water environments with different dissolved oxygen and hydrogen contents. The results showed that the effects of electrode potentials on the susceptibility to SCC of the steel were similar in the three kinds of water environments with or without impurity doping. No apparent SCC was found on the specimens tested at the potentials in the range from -720 mV to -200 mV (SHE). With the rise of electrode potential, some signs of SCC appearred and then significant SCC happened which caused brittle fracture. Doping 10 mg·L-1 chloride or 10 mg·L-1 sulfate into the water increased the SCC susceptibility by decreasing the minimum potential for significant SCC. The cracks nucleated at inclusions and propagated in fan-shaped quasi-cleavage trangranular mode. The results suggest that the cracking mechanism should be anodic dissolution type.