国产316LN不锈钢在模拟AP1000一回路水环境中的疲劳行为

Fatigue Behavior of Domestic 316LN Stainless Steel under Simulated AP1000 Primary Coolant Environment

一回路水环境下的疲劳性能是核电站主管道设计寿命评估的重要参数。针对国产主管道材料316LN开展了模拟AP1000一回路水环境的低周疲劳试验,分析了疲劳行为和失效机理。研究结果表明:国产316LN峰值应力随应变幅的增大而增大,大应变幅试样在疲劳过程中先后发生了循环硬化、循环软化和失稳,而小应变幅试样在失稳前未发生明显的循环硬化和循环软化;在应变幅由0.2%逐渐增加至1.2%的过程中,疲劳周次从105逐渐降低至102;疲劳断口具有典型的疲劳断口特征,裂纹萌生于试样表面,以穿晶方式垂直于主应力方向扩展,裂纹扩展区具有典型的疲劳辉纹,辉纹上有菱形颗粒状腐蚀产物,环境辅助开裂机制倾向于氢致开裂。

Fatigue is the key parameter of nuclear power plant（NPP）primary coolant pipe design life assessment.In this paper,the fatigue of domestic 316 LN stainless steel,which is used for AP1000 NPP main pipe,was test under simulated primary coolant environment,then the fatigue behavior and the fracture mechanism were analyzed.The results show that the peak stress increases with the strain amplitude;the large strain amplitude specimens exhibit cyclic hardening,cyclic softening and instability behavior,while the low strain amplitude specimens show neither hardening nor softening behavior before instability;the fatigue life of domestic 316 LN decreases from 105 to 102,as the strain amplitude increases from 0.2%to 1.2%.The fatigue crack initiates at the speci-men surface,propagates on the direction perpendicular to the principal stress through transgranular manner,and leaves typical fatigue striations.A lot of rhombus corrosion products are found on the striation,and the environment assist crack mechanism is apt to hydrogen-induced cracking mechanism.