A challenge with microstructural control and refinement in laser powder bed fusion (LPBF) is maintaining high density when choosing parameters for desired microstructures. Rescanning during LPBF has been reported to improve densification and decrease surface roughness for many different alloys. However, little has been reported regarding the effects of locally rescanning with varying processing parameters on sub-grain cell size refinement for 316L stainless steel (SS). This study presents a novel solution to enable high densification with microstructural control in 316L SS by using a set of initial scanning parameters to achieve densification and a different set of rescanning parameters to refine the microstructure. Results showed that rescanning resulted in heterogeneous microstructure with coarse cell size of 0.84 μm and locally refined cell size of 0.35 μm, while maintaining a high level of densification (99.96 %), therefore enabling potential variations in component strength and hardness. The spatial distribution of local microstructure refinement was dictated by the melt pool dimensions of initial scanning and rescanning relative to the powder layer thickness. To better understand the link between LPBF process parameters and microstructure, the Wilson-Rosenthal equation was used to predict cooling rate (G × R) and correlate with sub-grain cell size. Such variation in properties may be useful for applications requiring parts with hardened surfaces, or localized strengthening at stress concentrations and sites of expected failure.

激光粉末床熔合 (LPBF) 中微观结构控制和细化的挑战是在为所需微观结构选择参数时保持高密度。据报道，LPBF 期间的重新扫描可以提高许多不同合金的致密化并降低表面粗糙度。然而，关于使用不同加工参数进行局部重新扫描对 316L 不锈钢 (SS) 亚晶胞尺寸细化的影响的报道很少。本研究提出了一种新的解决方案，通过使用一组初始扫描参数来实现致密化和一组不同的重新扫描参数来细化微观结构，从而在 316L SS 中通过微观结构控制实现高致密化。结果表明，重新扫描会导致异质微观结构，粗细胞尺寸为 0。84 μm 和 0.35 μm 的局部细化单元尺寸，同时保持高水平的致密化 (99.96 %)，因此可以实现组件强度和硬度的潜在变化。局部微观结构细化的空间分布由初始扫描和重新扫描的熔池尺寸相对于粉末层厚度决定。为了更好地理解 LPBF 工艺参数和微观结构之间的联系，Wilson-Rosenthal 方程被用来预测冷却速率（G × R）并与亚粒细胞大小相关。这种性质的变化对于需要具有硬化表面的零件或在应力集中和预期失效部位进行局部强化的应用可能是有用的。