Excellent isotropic mechanical properties of electron beam melted H13 tool steel: Process optimization and microstructural control

Additive manufacturing (AM) has revolutionized the fabrication of intricate steel components. However, anisotropic mechanical behaviors in AM-fabricated components remains a critical challenge, particularly for tool steels like H13, where repeated thermal cycling and complex solidification induce strong texture and microstructural heterogeneity. This study introduces a tailored electron beam melting (EBM) process to achieve isotropic mechanical properties by optimizing the volumetric energy density (VED) parameters. Systematic experiments are conducted to investigate the effects of varying VEDs on the defect formation, phase fraction, and grain morphology in H13 steel. Controlled energy input suppresses columnar grain development by modulating the solidification conditions, promoting the formation of a refined interwoven martensite-bainite matrix with minimal porosity. A predictive model correlating martensite/bainite fraction and grain scale to mechanical strength was established and experimentally validated. An optimal VED range (39.2 – 40.8 J/mm³) is identified, which weakens the crystallographic texture while enhancing the microstructural homogeneity. The optimized EBM- fabricated H13 steel exhibits isotropic tensile properties, including a yield strength of 1350 MPa, ultimate tensile strength of 1800 MPa, and elongation of 10 %, making it ideal for demanding engineering applications. The remarkable mechanical properties are attributed to the synergistic effects of high-density dislocations, precipitation strengthening, and grain refinement. This work not only provides an intrinsic process pathway to overcome anisotropy in AM-fabricated H13 steel, but also offers a transferable framework for microstructural control and performance prediction in other multi-phase alloys fabricated via AM.