Researchers at Wroclaw University of Science and Technology have published a comparative study evaluating five metal additive manufacturing methods for producing H13 tool steel, identifying significant differences in density, microstructure, and heat-treatment response across the technologies. Published in Materials, the research compares filament-based extrusion, binder jetting, laser powder bed fusion, and directed energy deposition to assess their suitability for industrial tooling applications.
H13 is a widely used hot-work tool steel for forging, die casting, and extrusion tools, where resistance to thermal fatigue, wear, and high temperatures is critical. While metal 3D printing has enabled new tooling designs such as conformal cooling channels, the authors note that a systematic comparison of multiple additive manufacturing routes for H13 under comparable evaluation criteria has been lacking.
Density and porosity distinguish melt-based and sinter-based processes
The study examined Fused Deposition Modeling and Sintering (FDMS) using two commercial systems, Binder Jetting, Laser Powder Bed Fusion (LPBF), and wire-based Directed Energy Deposition (DED). Microstructural analysis revealed a clear divide between sinter-based and melt-based processes.
FDMS samples exhibited the highest porosity, ranging from approximately 6% to over 9%, with pores and cracks concentrated along layer boundaries and grain junctions. Binder jetting achieved significantly higher density, with porosity around 0.7%, while LPBF and DED produced near fully dense parts with porosity below 0.1%.
Due to their high internal defect content, FDMS samples were excluded from further heat-treatment evaluation. The researchers concluded that porosity at this level would compromise hardness measurements and increase the risk of cracking during quenching.
Heat treatment response depends on printing process
Heat-treatment trials were conducted on binder jetting, LPBF, and DED samples, including tempering, quenching, and quenching followed by tempering at temperatures aligned with industrial H13 standards.
Binder jetting samples showed low hardness in the as-printed condition but responded strongly to post-processing, reaching hardness values comparable to conventionally treated H13. The authors attribute this behavior to chemical segregation introduced during sintering, which promotes secondary carbide precipitation during tempering.
LPBF samples exhibited high hardness directly after printing, reflecting rapid solidification and repeated thermal cycling during the build process. Additional tempering further increased hardness, suggesting incomplete in-process tempering during fabrication.
DED samples also showed high as-printed hardness but responded differently to post-processing. The larger melt pools and slower cooling rates associated with DED resulted in extensive in-process tempering, limiting the benefits of additional heat treatment and, in some cases, leading to over-tempering.
Selecting the right process for H13 tooling
Based on microstructure, hardness development, deposition rate, and practical considerations such as accuracy and equipment cost, the authors conclude that no single additive manufacturing method is universally optimal for H13 tooling.
LPBF was identified as the most suitable option for high-precision tooling requiring near-theoretical density and stable mechanical properties. DED was highlighted as a strong candidate for large tools, repairs, and applications where high deposition rates outweigh surface finish requirements. Binder jetting was positioned as a viable route for high-accuracy, small-series production, provided production volumes justify the higher system costs.
FDMS, while the most accessible and lowest-cost option, was found to be suitable only for applications where lower density and reduced mechanical performance can be tolerated.
Melt-based metal AM and the limits of accessibility
Metal additive manufacturing has already been adopted for production tooling in applications where thermal fatigue, durability, and dimensional stability are critical. In automotive die casting, metal AM has enabled the manufacture of tooling with conformal cooling channels that cannot be produced through conventional machining, improving thermal management under demanding operating conditions. These deployments demonstrate that melt-based metal AM tooling can meet the performance and reliability requirements of high-volume industrial production, where fully dense material and controlled microstructure are essential.
For high-performance tool steels such as H13, the study shows that additive manufacturing outcomes depend as much on process thermal history as on material chemistry. While sinter-based methods improve accessibility, melt-based processes such as LPBF and DED are required to achieve the density and mechanical integrity expected of functional tooling. The results offer manufacturers a practical reference for application-driven process selection.
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Featured image shows Microstructure of H13 steel etched with Nital after various heat treatment processes for samples printed using the Binder Jetting, LPBF, and DED methods. Image via Widomski et al., Materials (2025).
