Hybrid additive manufactured tool steels: Microstructural modifications and mechanical enhancements through heat treatments

This study investigates the microstructural and mechanical evolution of hybrid steel components produced via laser powder bed fusion (LPBF), wherein maraging steel (MS1) was deposited onto an S7 tool steel substrate. Two heat treatment schedules—heat treatment 1 (HT1: austenitizing at 880 °C for 1 h, air cooling), to enhance elemental diffusion and promote partial recrystallization, and heat treatment 2 (HT2: HT1 followed by aging at 500 °C for 2 h), to induce precipitation hardening in MS1—were performed. Comprehensive microstructural characterization was conducted on the as-built and heat-treated samples using optical microscopy, scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and energy dispersive x-ray spectroscopy (EDS). Vickers microhardness measurements and uniaxial tensile testing evaluated the effects of heat treatments. In the as-built condition, a narrow transition zone (∼300 μm) near the interface exhibited steep hardness gradients (from ∼250 HV in S7 to ∼650 HV in MS1); high dislocation density was observed. HT1 shifted the fracture location from the S7 substrate to the MS1 deposit. HT2 further refined the microstructure and resulted in an ultimate tensile strength (UTS) of ∼1730 MPa and a uniform hardness distribution across the interface. Fracture consistently occurred away from the interface, confirming a sound metallurgical bond. These findings demonstrate the effectiveness of tailored heat treatments in tuning the mechanical performance of hybrid additively manufactured components, offering a promising route for structural repair in tooling applications. Finally, this research highlights the potential of hybrid additive manufacturing for advanced tool inserts with improved cooling capabilities and durability.