Oxide Evolution During the Solidification of 316L Stainless Steel from Additive Manufacturing Powders with Different Oxygen Contents

The oxide evolution during the solidification of 316L stainless steel from additive manufacturing powders with different oxygen contents is studied by in situ observation of the melting and solidification of the powder materials, advanced characterization of the solidified materials, and non-equilibrium thermodynamic analysis. An oxide evolution map is established for the 316L powders with different oxygen contents. It reveals the relationship between the surface oxidation in the reused powder and its expected oxide species and morphology in the as-solidified component. For the 316L powder with oxygen content higher than ~ 0.039 pct, the liquid oxide formed first from the steel melt and then crystallized to certain oxide phases during solidification, while for the powder with lower oxygen, oxide phases are suggested to directly form from the steel melt. The oxide species in the as-solidified sample was predicted by the Scheil–Gulliver cooling calculation and verified by the TEM-based phase identification. The oxides formed in the melt of low O 316L alloy (0.0355 pct O) are predicted to be (Mn, Cr)Cr2O4 spinel and SiO2 oxide. In the high O (0.4814 pct O) 316L melt solidification, the final oxides formed are (Mn, Cr)Cr2O4 spinel, SiO2 oxide, and Cr2O3 corundum. As an important characteristic of powder materials, the oxygen pick-up due to the powder surface oxidation significantly influences the inclusion evolution in the powder fusion process.