应变速率对304L焊接件应力腐蚀开裂行为的影响

Influence of strain rates on stress corrosion cracking behaviors of welded 304L stainless steel

采用慢应变速率拉伸试验方法（SSRT）,研究了在氯离子和充氧环境下不同应变速率对304L焊接件在模拟一回路高温高压硼锂水介质中应力腐蚀开裂的影响。结果表明：当应变速率较高时（1~4.17×10-5s-1）,主要表现为材料的机械拉伸性能。当应变速率较低时（4.17×10-6~8.33×10-8s-1）,主要为脆性断裂。304L焊接件的应力腐蚀敏感性随着应变速率的降低而逐步增加,当应变速率为4.17×10-7s-1时,304L焊接件的应力腐蚀敏感指数达到最大值37.4%,进一步降低应变速率为8.33×10-8s-1时,应力腐蚀敏感指数几乎不变,但是至断时间却从116.7 h增加到584 h。当应变速率为4.17×10-6s-1时,对材料的应力腐蚀敏感性区分度较高,且试验时间长短合理。大部分断口位于焊缝和热影响区,在拉伸试验过程中,焊缝和热影响区发生了巨大形变,能观察到大量滑移带,焊缝和热影响区是整个焊接件的薄弱环节。

In this study,we performed slow strain rate testing（ SSRT） to investigate the stress corrosion cracking（ SCC） of simulated reactor components of welded 304 L stainless steel in a chloride ion and oxygenation atmosphere at different strain rates. The basic water chemistry was simulated in a pressure water reactor（ PWR） primary loop,in high-temperature and high-pressure water containing boric and lithium ions. The results mainly reflected the mechanical properties of the welded 304 L stainless steel when the strain rate was high（ 1 ~ 4.17×10-5s-1）. At lower strain rates（ 4.17×10-6~ 8.33 × 10-8s-1）,brittle fractures mainly occurred. The SCC susceptibility of the welded304 L stainless steel increased with a decreasing strain rate. When the strain rate was 4.17×10-7s-1,the SCC susceptibility reached a maximum of 37.4%. When the strain rate declined to 8.33×10-8s-1,the susceptibility was almost the same,while the time-to-fracture increased from 116.7 h to 584 h. When the stain rate was 4.17×10-6s-1,the distinction between the SCC susceptibility of materials was higher,and the test time was reasonable. Most of the fractures were located in the welded joint and heat-affected zones. During the tensile test,a huge deformation occurred in the welded joint and heat-affected zones during the SSRT experiments. A large number of slip bands were also observed. The welded joint and heat-affected zones are the weak links in the entire weldment.