Efficient utilization of remelt strategy for improving relative density and surface integrity to eliminate necessity of performing post-processing of additively manufactured 316L stainless steel

Selective Laser Melting (SLM) is an advanced additive manufacturing method for producing complex metal components. However, post-processing steps are often needed due to the nature of the process. These steps include sandblasting to address high surface roughness and heat treatment to address unintended porosity, microstructural heterogeneity, and hardness fluctuations. These post-processing steps increase costs and production time. Remelting is an alternative method that involves scanning layers without powder recoating, presenting its challenges. In this study, we investigate the effects of remelting parameters and scanning strategies on the surface roughness, relative density, and microstructure of SS316L steel parts manufactured using SLM. The goal is to design an optimal scanning strategy to eliminate the need for post-processing, saving time and reducing costs. The process parameters include the remelting of layers, scan line spacing, and relative rotation angle between two layers. Based on the experimental design using a full factorial approach, 27 samples were printed, with each parameter examined at three levels. The samples were then measured for surface roughness using laser profilometry and relative density using Micro-CT technology. The results were compared with samples subjected to post-processing steps such as sandblasting and heat treatment. The remelting strategy achieved a relative density of 99.12%; moreover, Micro-computed tomography analysis further revealed that the remelting process not only reduced porosity but also led to a notable enhancement in pore geometry, transitioning from crack-like and lack of fusion defects to smaller spherical pores. In terms of microstructure, a more uniform structure and higher hardness between 202 and 207 Vickers were achieved. The remelting strategy was able to reduce the surface roughness within the range of 7 µm. Some challenges posed by remelting, such as compatibility with other parameters, the significantly longer time required for remelting of all layers, and overmelt, were examined and addressed in the discussion.