敏化处理对316NG奥氏体不锈钢疲劳裂纹扩展行为的影响

Effects of Sensitization on Corrosion Fatigue Crack Growth Behavior of 316NG Austenitic Stainless Steel

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。

In order to investigate the fatigue crack growth behavior of 316NG austenitic stainless steel unsensitized and sensitized at 725℃, corrosion fatigue crack growth tests were conducted in simulated corrosion environments. SEM and OM were used to observe the microstructure and crack growth paths of the specimen. EDS was also applied to analyze the chemical components of the segregation. The fatigue crack growth rates of the unsensitized specimen decreased from 2.21 × 10.4 mm/cycle to 1.02 × 10^-4 mm/cycle for the specimen sensitized by 10 minutes, which means that the fatigue cracking in the corrosion environment has been remarkably restrained by the sensitization. Being sensitized, the amount of segregation particle and branch crack increase, which results in the reduction of the crack growth rates. However, the sensitizing heat treatment can increase the Cr element content in segregation particles, lead to chromium-depleted zone being formed in the vicinity of particles, electrochemical corrosion being intensified, and arack propagation being enhanced.