Powder Metallurgy and Additive Manufacturing of High-Nitrogen Alloyed FeCr(Si)N Stainless Steel

Nitrogen, as an alloying element in stainless steels, is valued for its ability to enhance strength, corrosion resistance, and its strong austenite-stabilizing effect. Compared to other elements like nickel and manganese, nitrogen is more accessible, biocompatible, and cost-effective, making it ideal for sustainable and economical austenitic stainless steel production. This study explores a powder metallurgical approach to produce an austenitic stainless steel based on the FeCr(Si)N alloy system. A powder mixture of Fe20Cr and Si3N4 is hot isostatically pressed (HIP), dissolving Si3N4 and enriching the matrix with nitrogen. While a primarily austenitic microstructure is formed, small martensitic regions appear due to localized silicon segregation (lower austenite stability). The same powder mixture was used in the laser powder bed fusion (PBF-LB/M) process to manufacture shell-core samples. In this method, a partially powdered core is encased by a dense shell, with subsequent HIP ensuring full compaction and dissolution of the remaining Si3N4 particles in the powdered regions. However, an Si3N4 decomposition reaction during PBF-LB/M results in nitrogen loss, leading to a martensitic-ferritic microstructure instead of an austenitic one. Optimization strategies to achieve an austenitic FeCr(Si)N microstructure also in the PBF-LB/M process, which is particularly relevant for medical technology, are presented.