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

This study explores the heat treatment response and microstructure evolution of (high)-carbon steels for additive manufacturing, focusing on the impact of nitrogen as an alloying element. Nitrogen alloying can i) stabilize austenite or ii) lead to formation of alloy element nitrides, which can change the behavior in additive manufacturing processes. Overspray powders of cold-work D2, hot-work H13, and high-speed T15 tool steel, produced through spray forming, are investigated. Their thermal behavior is assessed using a thermal analyzer that combines calorimetry (DTA) and thermogravimetry (TG). In-situ nitrogen alloying is conducted to investigate the effect on transformation behavior. The equilibrium nitrogen solubility in the alloys is assessed in reactive N₂ gas atmosphere across temperatures ranging from 800 to 1250°C. Microstructural analysis of the steel powders is carried out using light optical microscopy and X-ray diffraction.

The study highlights the potential of preventing thermal cracking with nitrogen alloying and underscores the significance of optimized heat treatment protocols for enhancing the performance of high-carbon steels in additive manufacturing applications.