Heat Treatment Optimization and Microstructural Characterization of HIP Diffusion-Bonded H13-Alloy 939 Dissimilar Material

H13-Alloy 939 dissimilar material was fabricated by hot isostatic pressing (HIP) diffusion bonding, in which Alloy 939 powder was consolidated and simultaneously bonded to an H13 substrate. Since H13 hot-work tool steel and Alloy 939 Ni-based superalloy are strengthened by different mechanisms, namely martensitic transformation and γ′ precipitation hardening, respectively, an appropriate post-HIP heat treatment is required to obtain balanced properties in both materials. In this study, several heat treatment conditions were investigated to establish an optimum heat treatment process for the HIP diffusion-bonded H13-Alloy 939 material. The heat treatment conditions were evaluated based on hardness, microstructural characteristics, and tensile properties at room temperature, 450 and 550 °C. Microstructural observations showed that the selected heat treatment produced a tempered martensitic structure in H13 and a γ′-strengthened microstructure with carbide precipitates in Alloy 939. EDS analysis revealed that coarse precipitates in Alloy 939 were mainly Ta- and Ti-rich MC-type carbides. The HIP-bonded interface remained sound after heat treatment without significant interfacial defects or debonding. Based on the combined evaluation of mechanical properties and microstructural stability, an appropriate heat treatment condition was selected for the H13-Alloy 939 dissimilar material.