This paper focuses on the microstructural evolution of 304 L austenitic stainless steel (SS) manufactured by laser powder bed fusion (LPBF) after stress-relieving annealing (650 °C) and solution annealing (1050 °C). Multiple advanced characterizations were adopted to disclose the microstructural characteristics and investigate the annealing-driven dislocation migration process. At 650 °C, the dislocation density of cellular walls decreased slightly, associated with a slight decrease of strength. At 1050 °C, the dislocations of cellular walls migrated to more energetically favorable regions, forming subgrain boundaries with higher dislocation density and resulting in a strength-ductility trade-off. The temperature of 1050 °C could slightly increase the recrystallization volume fraction and induce the coalescence of multi-oriented fine-grained tribes into single-oriented grains. The nano-scale characterization indicated that the as-built samples and annealed samples at 650 °C contained the square lattice distortion networks composed of orthogonal strain ripples. However, after annealing at 1050 °C, only unidirectional strain ripples in square lattice distortion networks were retained due to unidirectional dislocation migration. Direct experimental results were provided that the local misorientation ranges of cellular interior, cellular walls, and newly formed subgrain boundaries were <0.2°, 0.2°-0.5°, and 0.5°-2°, respectively. After tensile deformation, interacting deformation twins occurred in <111> and 〈101〉 oriented grains of as-built and annealed specimens at 650 °C, while the twins occurred in all oriented grains of annealed specimens at 1050 °C due to the disappearance of cellular substructure and the increase of tensile elongation. This work yields new insights into misorientation across the cellular walls, dislocation migration process during annealing, strengthening mechanisms, and work hardening behaviors, which can be used to design and optimize future annealing routines for LPBF materials.

本文重点研究了激光粉末床熔合 (LPBF) 制造的 304 L 奥氏体不锈钢 (SS) 在去应力退火 (650 °C) 和固溶退火 (1050 °C) 后的显微组织演变。采用多种先进的表征来揭示微观结构特征并研究退火驱动的位错迁移过程。在 650 °C 时，细胞壁的位错密度略有下降，强度略有下降。在 1050°C 时，细胞壁的位错迁移到能量更有利的区域，形成具有更高位错密度的亚晶界，并导致强度-延展性权衡。1050 ℃的温度可以略微增加再结晶体积分数，并诱导多取向细晶部落聚结成单取向晶粒。纳米级表征表明，在 650 °C 下完成的样品和退火样品包含由正交应变波纹组成的方形晶格畸变网络。然而，在 1050 °C 退火后，由于单向位错迁移，方格畸变网络中仅保留了单向应变波纹。直接实验结果表明，细胞内部、细胞壁和新形成的亚晶界的局部错误取向范围分别为<0.2°、0.2°-0.5°和0.5°-2°。拉伸变形后，<111>中出现相互作用的变形孪晶 和<101>在650 ℃退火试样的取向晶粒，而在1050 ℃退火试样的所有取向晶粒中都出现了孪晶，这是由于蜂窝亚结构的消失和拉伸伸长率的增加。这项工作对跨细胞壁的取向错误、退火过程中的位错迁移过程、强化机制和加工硬化行为产生了新的见解，可用于设计和优化 LPBF 材料的未来退火程序。