The Role of Extraneous Oxygen in the Formation of Oxide Inclusions in 316L Stainless Steel Manufactured by Laser Powder Bed Fusion

Oxide inclusions in stainless steel act as initiation sites for microvoids which result in significant effects on mechanical properties. In the case of additive manufacturing (AM) 316L stainless steel, oxide inclusions can nucleate during laser melting and remain in the solidified microstructure. This work is aimed at assessing whether extraneous oxygen in process environment contributes to inclusion formation. The stainless-steel alloy 316L was employed and fabricated under series of different oxygen content environments. The characterization of oxide inclusions in AM processed materiel were conducted using scanning electron microscopy (SEM) and they are found enriched in oxygen getters such as Si and Mn. Inert gas fusion (IGF) was used to measure oxygen content before and after AM processing. Results indicated that extraneous oxygen from the process environment played a role in oxide inclusion formation. Furthermore, the average inclusion size was found to increase with increasing oxygen content in process environment, suggesting a coarsening mechanism of oxides due to the interactions between them in the melt pool.