The effect of different tempering treatments on the mechanical properties of H13 steel

In this thesis, the mechanical performance of AISI H13 hot-work tool steel subjected to cryogenic treatment followed by different tempering strategies was systematically investigated. Owing to its excellent high-temperature strength, toughness, and wear resistance, H13 steel is widely used in demanding tooling applications; however, its service life and operational efficiency are highly dependent on the applied heat treatment route. Within this context, conventional heat treatment—comprising austenitizing, oil quenching at 1040 °C, and subsequent single or double tempering—was employed as the baseline procedure. In addition, a shallow cryogenic treatment (SCT) at –120 °C for 4 hours was integrated into the process flow to assess its influence relative to traditional protocols. Unlike the extensively studied deep cryogenic treatment (DCT), SCT offers lower cost, shorter processing times, and greater industrial feasibility, representing the novel aspect of this study. Three groups of specimens were prepared: (i) quenched + SCT, (ii) quenched + SCT + single tempering, and (iii) quenched + SCT + double tempering. Mechanical characterization was conducted through hardness and tensile testing. The results demonstrated that the specimen subjected only to cryogenic treatment exhibited the highest tensile strength, albeit with a significant loss in ductility. Single tempering provided a notable improvement in ductility while maintaining strength, whereas double tempering resulted in the most balanced mechanical behavior in terms of both strength and ductility. Vickers hardness measurements confirmed that SCT refined the martensitic microstructure, enhancing hardness, and that subsequent tempering stages moderated this hardness to achieve an optimized state. These findings affirm that shallow cryogenic treatment can induce microstructural improvements comparable to those obtained through deep cryogenic treatment. When combined with proper tempering protocols, SCT emerges as a viable and efficient heat treatment alternative for H13 tool steel. Particularly, the application of double tempering following SCT is shown to significantly improve the strength-ductility balance, thus extending the potential service life of tooling components under harsh conditions. This study provides valuable insight for the development of advanced thermal treatment strategies in high-performance tool steels.