A Novel Heat Treatment Strategy Based on Quenching and Carbides Preprecipitation and Subsequent Critical Quenching to Improve the Thermal Fatigue Performance of AISI H13 Tool Steel

The effects of conventional quenching and based on quenching and carbides preprecipitation and subsequent critical quenching (QPQ) processes on the microstructure evolution, thermal stability and thermal fatigue are studied for H13 tool steel. The results show that the QPQ treatment is beneficial to precipitate smaller and more uniformly distributed carbides during the tempering. According to the analysis of microstructure and mechanical properties, it is found that the tempering after QPQ treatment can refine the grain size of the steel by about 60% and can increase the impact toughness by 34.8%. Moreover, it is also found that the activation energy required by the QPQ treatment is higher than that of the conventional quenched samples for long-time tempering, which is mainly related to the coarsening and accumulation of carbides. According to the statistical analysis results of average thermal fatigue crack length, crack density, and surface hardness, the improvement of thermal fatigue performance of the QPQ treatment after tempering is mainly attributed to the uniform fine carbide and grain refinement, which passivates the crack tip and improves the service life to a certain extent.