引張保持を伴う熱機械疲労下におけるSUS316鋼の疲労寿命評価

抄録

The fatigue lives of austenitic stainless steel SUS316 were evaluated under thermomechanical fatigue (TMF) loading condition with and without tension hold. When correlating the fatigue lives with the mechanical strain range, the fatigue lives under the in-phase condition were shorter than those under isothermal low cycle fatigue (LCF) condition at the maximum temperature of TMF tests, on the other hand, those under the out-of-phase condition was longer. The introduction of the hold dwell at the maximum tension strain extended the fatigue lives under the in-phase condition because of the decrease in the stress range due to cyclic softening augmented by the tension hold. The prediction method for TMF lives from the LCF data was proposed based on the small crack propagation law taking into consideration the temperature dependence of the tensile strength and the crack propagation path, with some assumptions; such as, the m values in Paris’s law are comparable in the intergranular and the transgranular crack propagation modes, the fatigue life is proportional to the crack propagation life, and the fatigue crack propagation morphology of the tested material is similar to that of the 316FR steel, etc. The TMF lives of austenitic stainless steel SUS316 could be predicted with higher accuracy by the proposed method.