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 loading to the thermomechanical fatigue loading on the crack propagation behavior of the naturally initiated short crack in Low-carbon nitrogen-controlled 316 stainless steel was investigated. The experimental results indicated that the crack propagation path depends on the loading condition; the cracks appear to be initiated and propagated at grain boundary perpendicular to the loading axis which might be a relatively week region at elevated temperature under the in-phase type TMF loading and the LCF loading at high temperature, on the other hand, the cracks initiated and propagated by the transgranular mode under the out-of-phase type TMF loading and the LCF loading at middle temperature. The short crack growth rate has also affected the microstructure, i.e., the intergranular crack exhibits higher growth rate compared with the transgranular crack. In addition, the crack growth rate was accelerated by superimposing of the isothermal low cycle fatigue loading to the main thermo-mechanical fatigue loading. The short crack growth rate could be predicted according to summation law of crack growth behavior based on the J-integral approach considering with crack propagation path.