Research progress on process, microstructure and property regulation of additive manufacturing tool steels

Additive manufacturing (AM) provides a novel technological route for the complex shaping and damage repair of high-performance tool steels. However, the inherently high carbon and alloying contents of tool steels, coupled with their pronounced hot cracking susceptibility, impose stringent demands on precise process control. This review systematically summarizes the research progress of two representative AM technologies-powder bed fusion (PBF) and directed energy deposition (DED)-in the fabrication and repair of tool steels, with emphasis on the influence of key process parameters (e.g., power, scanning speed) on melt-pool thermodynamics, solidification microstructure evolution, and residual stress distribution. The formation mechanisms of typical defects, including porosity, lack-of-fusion (LOF), hot cracks, and cold cracks, are systematically elucidated, and the as-built microstructures of medium-carbon H13 steel and high-carbon high-speed steel are comparatively analyzed under rapid non-equilibrium solidification conditions. Furthermore, the effects of various post-processing routes-such as preheating, direct tempering, quenching and tempering, hot isostatic pressing (HIP), surface treatment, and nanoparticle reinforcement-on residual stress relief, microstructural homogenisation, and carbide evolution are comprehensively reviewed. Finally, the service reliability of additively manufactured tool steels is assessed in terms of mechanical properties, fatigue behavior, and wear resistance. This review aims to provide a systematic theoretical foundation for process optimization, microstructural control, and engineering applications of high-performance additively manufactured tool steels.