Isothermal and thermomechanical fatigue interaction in fatigue crack propagation behavior of a low-carbon nitrogen-controlled 316 stainless steel

In this work, the effect of superimposing of isothermal Low Cycle Fatigue (LCF) loading to the thermomechanical (TMF) fatigue loading on the short crack propagation behavior of low-carbon nitrogen-controlled 316 stainless steel is investigated. The experimental results indicate that the crack propagation path depends on the loading condition; cracks initiate and propagate at grain boundary perpendicular to the loading axis (intergranular mode), which is a relatively weak region, under the in-phase TMF loading and the LCF loading at high temperature. On the other hand, cracks initiate by the transgranular mode under the out-of-phase TMF loading and the LCF loading at middle temperature. The crack growth rate is also affected by the microstructure, i.e., the intergranular crack exhibits higher crack growth rate compared with the transgranular crack. In addition, the crack growth rate is accelerated by the superimposing of the isothermal LCF loading to the TMF loading. The crack growth rate can be predicted according to the summation law of crack growth behavior based on the fatigue J-integral approach taking into account the crack propagation path