Development of creep-fatigue evaluation method for 316FR stainless steel

316FR鋼のクリープ疲労評価法の開発

永江 勇二 ; 高屋 茂  ; 浅山 泰 

Nagae, Yuji; Takaya, Shigeru; Asayama, Tai

In the design of fast reactor plants, the most important failure mode to be prevented is creep-fatigue damage at elevated temperatures. 316FR stainless steel is a candidate material for the reactor vessel and internal structures of such plants. The development of a procedure for evaluating creep-fatigue life is essential. The method for evaluating creep-fatigue life implemented in the Japan Society of Mechanical Engineers code is based on the time fraction rule for evaluating creep damage. Equations such as the fatigue curve, dynamic stress-strain curve, creep rupture curve, and creep strain curve are necessary for calculating creep-fatigue life. These equations are provided in this paper, and the predicted creep-fatigue life for 316FR stainless steel is compared with experimental data. For the evaluation of creep-fatigue life, the longest time to failure is about 100,000h. The creep-fatigue life is predicted to an accuracy that is within a factor of 2 even in the case with the longest time to failure. Furthermore, the proposed method is compared with the ductility exhaustion method to investigate whether the proposed method gives conservative predictions. Finally, a procedure based on the time fraction rule for the evaluation of creep-fatigue life is proposed for 316FR stainless steel.