Effect of initial hardness on the thermal fatigue behavior of AISI H13 steel by experimental sand numerical investigations

Based on the Uddeholm thermal fatigue test, the mechanism of thermal fatigue crack initiation and propagation and the influence of initial hardness on the thermal fatigue behavior of AISI H13 steel were investigated. Furthermore, an electromagnetic-thermo-mechanical coupled finite element model was established to analyze the temperature evolution and stress accumulation in specimen during thermal cycles. The experimental results demonstrate that, after 3000 thermal cycles, the surface hardness of specimen markedly decreases, and the lath martensite structure seems to completely evolve into a mixture of ferrite and irregularly sphere-like and bar-like M23C6 and M6C carbides. According to the numerical results, the effective stress of specimen will increase slightly after every thermal cycle. It presents a distinct stress accumulation phenomenon with increasing number of thermal cycles. Especially at the corner of specimen, it is more significant. The thermal fatigue test results also prove that it is a major site where the initiation and propagation of thermal fatigue primary cracks occur. Both the numerical and experimental results suggest that specimen with initial hardness of 46HRC has the slowest stress accumulation rate, the lowest thermal fatigue damage factor, and the longest thermal fatigue life.