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利用U弯样品研究了国产压水堆核电站主管道用锻造态316L不锈钢在330℃Na OH溶液中的应力腐蚀开裂行为。结果表明,浸泡720 h后在样品表面观察到明显的应力腐蚀裂纹,裂纹扩展完全穿透样品厚度。样品表面生长的氧化膜内层富Fe,中间层富Ni,外层是富含Ni和Fe的分散的颗粒状氧化物,氧化膜缺乏保护性。EBSD和断口观察发现样品主要是沿晶型开裂,断口主要体现冰糖状花样,局部还分布有河流花样和准解理台阶。在应力的作用下,晶界富含Fe和Ni的氧化物的脆性断裂导致应力腐蚀裂纹的扩展。316L不锈钢的脆性断裂机制属于阳极溶解型-应力使晶界氧化膜破裂机制。
U-bend samples were used to study the stress corrosion cracking behavior of forged 316L stainless steel in 330 ℃ NaOH solution at the main pipe of domestic PWR nuclear power plant. The results showed that obvious stress corrosion cracking was observed on the sample surface after soaking for 720 h, and the crack propagation completely penetrated the sample thickness. The oxide film grown on the sample surface is rich in Fe, the middle layer is Ni-rich, the outer layer is dispersed granular oxide rich in Ni and Fe, and the oxide film lacks protection. The observation of EBSD and fracture shows that the samples are mainly cracked along the crystal form, and the fractures mainly show the shape of rock candy, and the local patterns of rivers and quasi-cleavage steps are also distributed. Under the action of stress, the brittle fracture of oxide rich in Fe and Ni in the grain boundary leads to the expansion of stress corrosion cracking. The brittle fracture mechanism of 316L stainless steel belongs to anodic dissolution type - the stress makes the grain boundary oxide film rupture mechanism.