The influence of tensile hold time on the low cycle fatigue life for AISI 316 stainless steel is investigated at 873K with a strain rate of $4\times10^{-3}/\sec$ in Ar atmosphere. And the test results are used to analyze a characterization of the model for life prediction which is based on the cavitational damage under creep-fatigue condition.
As a result of fatigue test, the introduction of tensile hold time during a low cycle fatigue test(i.e. creep-fatigue interaction condition) reduces fatigue life compared to that of continuous cycling, and it is observed that the fatigue life decreases with increasing tensile hold time. From the result of the observation of fractured surfaces after fatigue cycling with tensile hold time, it can be found that the major effect on the reduction of fatigue life is the cavitational damage on grain boundaries and the cavities are formed continuously with cycles.
Using the modified life prediction model, the predicted fatigue life is in good agreement with the experimentally observed one for AISI 316 stainless steel. Investigating the relationship between the new cavity nucleation factor, P', considered as a material constant in this model and the distribution of grain boundary carbides, it is found that the new cavity nucleation factor(P') is increased with increasing the number of grain boundary carbides. Therefore it can be suggested that the modified cavity nucleation factor is closely related to the distribution of grain boundary carbides.
This is very meaningful result because, using this result a new alloy which has good properties under creep-fatigue interaction condition can be designed controlling the distribution of grain boundary carbides.
