Effect of LPBF build efficiency on oxide inclusions and toughness of maraging stainless steel

In LPBF maraging steel, processing efficiency is strongly correlated with microstructure and oxide inclusions, which in turn affect mechanical properties. This study doubled the processing efficiency to examine how it alters oxide characteristics and properties. High‑efficiency samples had coarser and more abundant micron‑scale oxides (2.24 μm, 41.7 /mm²) than low‑efficiency ones (2.17 μm, 27 /mm²), but fewer and larger nano‑scale oxides (6.17 × 10¹⁹ /m³, 31 nm vs. 1.35 × 10²⁰/m³, 27 nm). Heat treatment did not change oxides, eliminated cellular substructures, and produced similar retained austenite. Despite comparable tensile strengths, low‑efficiency samples exhibited much higher toughness (195 vs. 160 J at 25 °C; 106 vs. 88 J at −196 °C), primarily due to oxide differences. Modelling suggests slower cooling in high‑efficiency processing suppresses nucleation but enhances growth, while stronger convection drives oxides to the surface, leaving more micron‑sized oxides internally after track overlaps. Hence, build efficiency must be carefully balanced to optimize oxide behavior and toughness.