Study of the wall thickness effect on the solidification and mechanical properties of thin-walled SS316L built via LPBF additive manufacturing

Abstract

This study examines the fabrication of 316 L stainless steel (SS316L) thin-walled structures using the laser powder bed fusion (LPBF) process, with a focus on the influence of wall thickness and post-processing heat treatment on microstructural evolution and mechanical properties. As-built samples exhibited consistent epitaxial growth of the columnar grain structures aligned with the build direction in narrow dimensions. Thinner samples (0.6 mm wall thickness) showed more significant heat accumulation and slower cooling rates than thicker samples (1.0 mm wall thickness), with the former exhibiting substantial longitudinal grain growth, reduced residual stress, and lower tensile strength. Additionally, the thinner samples developed a stronger < 111 > texture, aligning with the build direction, which contributed to a decrease in microhardness and dislocation density. The high-temperature homogenization treatments refined the microstructure, leading to oriented coarse-grain structures with distinct crystallographic orientations. The post-processing reduced the microhardness by 36.60 % for the thicker sample and 19.83 % for the thinner sample. Furthermore, mechanical properties such as strength, hardness, ductility, and microhardness were closely linked to the observed crystallographic and grain structures. These findings highlight the significant impact of sample thickness, thermal history, and post-processing on the structural and mechanical properties of SS316L components manufactured using LPBF.