Multi-scale characterisation of microstructure and texture of 316L stainless steel manufactured by laser powder bed fusion

Abstract

316L stainless steel produced by additive manufacturing (AM) offers superior mechanical and corrosion properties compared to parts of the same steel processed by conventional methods. However, thorough understanding of the detailed microstructural evolution during various additive manufacturing techniques is lacking when compared to conventionally produced counterparts. As such, the present work contributes to filling this gap in knowledge by using advanced microscopy techniques to analyse the microstructure of 316L stainless steel builds produced by laser powder bed fusion. The results show that changes in processing parameters lead to variations in grain structures, texture, and hardness. For instance, the dominant texture and grain structure is heavily influenced by changes to the laser scanning rotation between individual layers, while increasing laser power reduces hardness. The current study also provides additional insights into how grains in AM 316L steel accommodate strain. Due to the complex strain fields in austenite grains, they are usually split into complex-shaped regions separated by dislocation boundaries with characters similar to deformation- and micro-band boundaries in conventionally deformed austenite. Through electron probe micro-analysis over a large area, the current study reveals the tendency of Mo and Si concentrations to fluctuate around the cell and melt pool boundaries.