Softening Behavior and Hardness Prediction of H13 Hot-Work Die Steel during Isothermal Tempering

In this study, the microstructural evolution of H13 hot-work die steel during isothermal tempering at 500 approximate to 650 degrees C is evaluated, and kinetic equations and a neural network are constructed to describe the softening behavior. The results show that the softening behavior appears as a loss of hardness with increasing isothermal tempering temperature and time. The softening mechanism is ascribed to the decomposition of martensitic laths, annihilation and rearrangement of dislocations, formation of sub-grains, and precipitation and coarsening of secondary carbides. The evolution of secondary carbides includes the coarsening of V-rich MC nanoprecipitates, and the precipitation and coarsening of secondary phases (Cr-rich M23C6 and Mo-rich M6C carbides) during long-term isothermal tempering. Regarding the applicability of the model in precipitation evolution and hardness prediction, the Johnson-Mehl-Avrami model is considered to be more suitable than the Hollomon-Jaffe, Lifshitz-Slyozov-Wagner, and back-propagation neural network models. In this work, the mechanism of microstructural evolution during long-term isothermal tempering is elucidated, and the Hollomon-Jaffe, Lifshitz-Slyozov-Wagner, Johnson-Mehl-Avrami, and back-propagation neural network models are innovatively constructed and evaluated to describe the softening behavior of H13 steel.image (c) 2023 WILEY-VCH GmbH