Building orientation dependency of recrystallization kinetics in 316L stainless steel produced via laser powder bed fusion

Abstract

316L stainless steel produced by laser powder bed fusion (LPBF) exhibits distinct microstructural features such as columnar grains, cellular substructures, anisotropy, and secondary phases. This study investigates the influence of building orientation on the recrystallization kinetics of the LPBF 316L stainless steel samples fabricated in vertical and horizontal orientations. Heat treatments were performed at 900 °C, 1000 °C, and 1100 °C for up to 240 min. After annealing at 1100 °C for 240 min, the hardness values of the vertical and horizontal samples decreased by 27 % and 36 % respectively. Avrami values revealed sluggish recrystallization in both orientations compared to conventional 316L stainless steel, mainly due to non-random nucleation and strong Zener pinning from carbide and oxide particles. Despite this, the vertical sample exhibited higher recrystallization rates and coarser grains after annealing, attributed to shorter laser scan lengths and a lower volume fraction of carbide particles, which enhanced grain boundary mobility compared to the horizontal sample. At 1000 °C and 1100 °C, the Avrami exponents for vertical samples (0.7 and 0.79) were higher than those for horizontal samples (0.5 and 0.6). Both orientations also showed low apparent activation energy (∼20 kJ/mol), reflecting high stored energy and restrained grain growth.