Stress Corrosion Cracking and Mechanical Behaviors of Domestic Low Alloy Steel SA-508III in Simulated PWR Primary Water Environment

The stress corrosion cracking (SCC) and mechanical behaviors of homemade low alloy steel SA-508Ⅲ (S: 0.0025%) in simulated pressurized water reactor (PWR) primary water environment at 290 ℃ were studied by slow strain rate test (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 environment with different dissolved oxygen and hydrogen contents. A test was also performed in pure nitrogen gas for comparison. Results showed that the susceptibility to SCC of the steel increased with increasing electrode potential. No apparent SCC was found on the specimens tested at the potentials in the range from -720 mV to -200 mV (SHE). Some signs like tiny SCC were observed on the specimens tested at -50 mV and +200 mV (SHE). Significant SCC happened when the potential was raised to +300 mV and +400 mV (SHE). The cracks were nucleated at inclusions and propagated in fan-shaped quasi-cleavage transgranular mode. Results suggest that the steel has excellent resistance to SCC. All the tensile curves of the tests exhibited the character of dynamic strain ageing (DSA). The SCC mechanism and its relation to DSA are discussed.