采用慢应变速率试验(SSRT)和电化学控制结合的方法, 研究了水中杂质(氯离子和硫酸根离子)和电极电位对国产核电压力容器用SA-508Ⅲ(含S 0.0025%)低合金钢在模拟压水堆(PWR)一回路290 ℃高温高压水质环境中应力腐蚀破裂(SCC)性能的影响。电位范围从-720~+400 mV(SHE), 模拟从低氧含氢的理想状态到溶解氧显著超标状态的一系列服役环境。试验结果表明, 在无杂质掺杂、掺杂10 mg·L-1的氯离子和掺杂10 mg·L-1硫酸根离子的三种水环境中, 电极电位对该材料SCC的影响相似, 当电位处于-720~-200 mV(SHE)范围时, 试样上未发现SCC, 随着电位逐渐升高, 试样出现SCC迹象直至发生显著的SCC而脆断。水中掺杂10 mg·L-1的氯离子或硫酸根离子后, 发生显著SCC而脆断的电位下降, 即SCC敏感性提高。扫描电镜断口观察表明, SCC裂纹通常在试样表面的夹杂物处萌生, 并以准解理穿晶模式呈扇形扩展。分析表明, 该钢SCC破裂机理应该属于阳极溶解机制。

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.