Abstract
316L stainless steel has emerged as the material of choice in aerospace and marine engineering applications due to its exceptional corrosion resistance and weldability. In these applications, intricate and near-net-shaped geometries are often required. While Laser Powder Bed Fusion (LPBF) enables the fabrication of these complex forms, the process introduces unique microstructural heterogeneities and defects that complicate fracture predictability. This study investigates the fracture behaviour of LPBF-fabricated 316L by integrating multiscale microstructural characterization with mechanical performance testing. Melt pool morphology, grain orientation, phase distribution, and defects, specifically porosity and lack of fusion, were analyzed and correlated with tensile properties. The findings reveal that microstructural heterogeneity, particularly the distribution of melt pool boundaries and localized defects, acts as the primary driver for crack initiation and propagation. Specifically, the results indicate that the morphology and distribution of porosity and microstructure dictate the mechanical response under the varying loading scenarios. These insights establish a clearer link between additive manufacturing parameters and structural integrity, providing a foundation for more robust qualification strategies for 316L in demanding environments.