Multiscale study of additively manufactured 316 L microstructure sensitivity to heat treatment over a wide temperature range

Abstract

The main subject of this study is to investigate the correlations between the evolution of mechanical behavior and the multiscale microstructure of 316 L stainless steel obtained by laser powder bed fusion process (LPBF) after various post-manufacturing heat treatments across a wide temperature range. The microstructure of 316 L LPBF parts exhibits a hierarchical microstructure based on unique grain structures, chemical segregations, dislocation arrangements at the microscopic scale and fine nano-oxides at the nanoscopic scale. These microstructural elements play a crucial role in determining the material's mechanical and corrosion properties. To understand how different microstructural features contribute to the material's behavior, the researchers conduct post-manufacturing heat treatments to isolate and study these components. The results show that dislocation and/or micro-segregation networks significantly influence the high tensile properties of 316 L LPBF steel in its as-built state and after heat treatments above 900∘C. Despite their disappearance during heat treatments, the material maintains high tensile strength due to an increase in strain-hardening capabilities. The study also examines the impact of nano-oxides and the σ phase on the material's properties. The contribution of nano-oxides to yield strength diminishes with increasing temperature. Interestingly, the σ phase does not necessarily lead to a detrimental effect on failure elongation for 316 L LPBF steel. Overall, this research provides insights into the relationship between microstructure and mechanical properties for additively manufactured stainless steel. By understanding these relationships, it becomes possible to tailor the microstructure to achieve desired mechanical properties for specific applications and extend the use of 316 L LPBF to higher temperatures compared to conventional methods.