Low cycle fatigue characteristics and life prediction of 316LN austenitic stainless steel

An investigation was conducted on the low cycle fatigue behavior, fatigue life, and fatigue fracture mechanism of forged 316LN stainless steel at 330 ​°C, under varying strain amplitudes. The results indicate that the cyclic softening degree of 316LN austenitic stainless steel increases proportionally with the strain amplitude. This increase can be attributed to variations in the arrangement and development process of the dislocation structure. Additionally, it was observed that both back stress and friction stress augment as the total strain amplitude increases. This phenomenon is primarily caused by enhanced interactions between dislocations and precipitated phases, as well as dislocations themselves. The hysteresis loop area exhibits an increase in direct correlation with the total strain amplitude. Moreover, a smaller strain amplitude corresponds to reduced plastic strain energy and increased fatigue life. In engineering applications, the simplicity and universality of a model, along with easily obtainable parameters, are crucial considerations. To evaluate the fatigue life of 316LN austenitic stainless steel, four models were employed: Coffin-Manson fatigue life model, energy life model, three-parameter power model, and three-parameter power life correction model. The predicted data from the three-parameter power life correction model fell within the acceptable error range of 1.2, demonstrating a strong alignment with the experimental values. Consequently, it can be concluded that the three-parameter power life correction model exhibits remarkable accuracy in predicting low cycle fatigue (LCF) behavior, thereby facilitating the safety assessment of component lifespan. The fatigue fracture surface exhibits distinct features of fatigue striations, with a noticeable decrease in the interval between these striations as the total strain amplitude increases.