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

Fatigue is the key parameter of nuclear power plant (NPP) primary coolant pipe design life assessment. In this paper, the fatigue of domestic 316LN 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 316LN decreases from 10⁵ to 10², as the strain amplitude increases from 0.2% to 1.2%. The fatigue crack initiates at the specimen 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.