Fatigue damage and life prediction for AISI H13 steel under cyclic thermomechanical loading

Based on strain-controlled thermomechanical fatigue (TMF) experiments, this study conducts a comprehensive analysis of the TMF behavior of AISI H13 hot work die steel. Moreover, a life prediction model for the TMF behavior of AISI H13 steel has been developed and validated. The experimental results reveal that, under the in-phase (IP) and out-of-phase (OP) TMF conditions, the stress–strain response curves of AISI H13 steel under different mechanical strain amplitudes exhibits the similar evolution tendency. However, it is worth noting that in the stable TMF cycle, the hysteresis loop area is enlarged with the increase of the number of cycles, which can be attributed to the cyclic softening characteristics of the AISI H13 steel under cyclic thermomechanical loading. When examining different TMF conditions, it is found that at higher strain amplitudes and under OP TMF conditions, the hysteresis loop area significantly expands, leading to a substantial reduction in the TMF life of AISI H13 steel. From a microstructural perspective, the thermal–mechanical coupling effect makes the recovery of martensitic matrix and the coarsening of carbide precipitation, which substantiates the deterioration of mechanical properties of AISI H13 steel. Finally, a modified Ostergren model by integrating the hysteresis loop area has been developed to assess the TMF life of AISI H13 steel under complex thermomechanical loading conditions, and this refined model exhibits strong agreement with experimental data. An evaluation using scatter band shows that the predicted TMF life of AISI H13 steel are within 1.2 times the experimental values, which illustrates a high reliability and validity.