Nickel-Free Austenitic Stainless Steel Manufactured by Laser Powder-Bed Fusion from Martensitic Powder Mixed with Interstitial Compounds

Using laser powder bed fusion (L-PBF), nickel-free austenitic stainless steel was manufactured from mixing AISI 420S martensitic stainless-steel powder with austenite-stabilizing components. Chromium nitride (Cr2N), chromium carbide (Cr3C2), chromium (Cr) and graphite (C) powder were admixed in different quantities. The resulting microstructures were investigated using light- and electron microscopy, X-ray diffraction, and hardness indentations. Nitrogen, carbon, and chromium from the admixed powders were dissolved in solid solution; no remnants of nitrides/carbides were identified. The as-built specimens had a lower nitrogen content than the mixed powders. Insufficient additions of austenite-stabilizing elements resulted in a dual-phase microstructure of austenite and martensite, which experienced in-situ tempering of martensite during fusion of consecutive layer(s) in the L-PBF process. Relatively high contents of austenite-stabilizing elements resulted in a fully austenitic microstructure with a hardness of 380–500 HV5, depending on Cr and interstitial content. The tendency for forming hot cracks was found to correlate with the solidification interval as calculated using a modified version of the Scheil-Gulliver model.