Microstructure Optimization of High Carbon Steels for Additive Manufacturing; Heat treatment and Interstitial Alloying

Additive manufacturing (AM) is becoming increasingly popular and undergoes rapid technological developments. Recently, there has been a drive towards the application of high carbon steels; such steels have hitherto been associated with significant difficulties due to, for example, extensive cracking during fabrication. Several specialized high carbon (and nitrogen) powders are now being offered commercially for AM. In the present contribution high carbon overspray powders from spray forming of steels are investigated. These powders are highly suitable for AM because of their spherical nature. The alloy (overspray) powders are produced from recycled scrap steel using green energy from a renewable energy source.

The alloy powders investigated are stainless steel 440C, hot-work H13, high speed tool steel T15 and D2 cold work steel. The work focuses on the heat treatment response of these generically different special materials. The thermal behavior (heat treatment) is systematically investigated in a thermal analyzer combining calorimetry and thermogravimetry. Moreover, interstitial “alloying” with nitrogen of the 440C and D2 is performed in-situ in the analyzer by high temperature gaseous nitriding to reveal the influence of the addition of nitrogen on the thermal behavior. Additionally, light optical microscopy and X-ray diffraction analysis are used for characterization.