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在模拟压水堆腐蚀环境条件下,进行了未敏化与725℃敏化处理的316NG奥氏体不锈钢腐蚀疲劳实验。采用扫描电镜(SEM)、能谱分析仪(EDS)、金相显微镜(OM)分析了试样微观结构、偏析相化学成分及裂纹扩展状况,研究了材料疲劳裂纹扩展行为。研究结果表明:敏化处理可显著抑制316NG奥氏体不锈钢在腐蚀环境中的疲劳裂纹扩展;裂纹扩展速率由未经敏化处理的2.21×10~(-4) mm/次减小到敏化处理10min的1.02×10~(-4) mm/次。敏化处理试样的偏析相颗粒数量增多,萌生的支裂纹也增多,导致裂纹扩展速率减小。但是,敏化处理会导致偏析相颗粒中Cr元素含量增加,颗粒附近的基体成为贫铬区,电化学腐蚀加剧,促进裂纹的扩展。
The corrosion fatigue test of 316NG austenitic stainless steel, which is not sensitized and sensitized at 725 ℃, was carried out under simulated environmental conditions of PWR. The microstructure, chemical composition of segregation phase and crack propagation were analyzed by scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and optical microscope (OM). The fatigue crack growth behavior was studied. The results show that sensitization treatment can significantly reduce the fatigue crack growth of 316NG austenitic stainless steel in corrosive environment. The crack propagation rate decreases from 2.21 × 10 -4 mm / min without sensitization to sensitization 1.02 × 10 ~ (-4) mm / time for 10min. The number of segregation phase particles in the sensitized samples increased, and the number of branch cracks increased, resulting in the decrease of crack propagation rate. However, the sensitization treatment results in the increase of Cr content in the segregation phase particles, the matrix near the particles becomes a chromium-depleted zone, and the electrochemical corrosion is aggravated and the crack growth is accelerated.