Heat Treatment and Nitrogen Alloying of Tool Steel Powders for Additive Manufacturing

Abstract This study systematically investigates the effects of nitrogen alloying and heat treatment on the microstructure and hardness of high-carbon tool steel powders (D2, H13, and T15) for additive manufacturing (AM) applications. The research combines advanced thermal analysis techniques, including thermogravimetric analysis (TG) and differential scanning calorimetry (DSC), with microstructural characterization to elucidate the complex interactions between nitrogen absorption, phase transformations, and cooling rates. The nitrogen uptake behavior in powders exposed to a controlled nitrogen containing atmosphere up to 1200°C and the phase stability applying different cooling rates – slow (1°C/min) and rapid (50°C/min) – are assessed. Key findings demonstrate that nitrogen alloying significantly influences austenite stability. The study reveals composition-dependent variations in nitride formation, with T15 exhibiting high nitrogen uptake due to its high V and W content. Microstructural evolution is shown to be critically dependent on cooling conditions, where rapid cooling promotes martensitic transformation and retained austenite, while slow cooling favors ferritic and pearlitic structures. These insights can provide a scientific foundation for optimizing postprocessing heat treatments and microstructure design in AM-fabricated tool steels.