Effect of Stress-Relief Heat Treatment on Residual Stress in 316L Stainless Steel Fabricated by Selective Laser Melting Process

Abstract Additive manufacturing (AM) is an emerging technology for producing industrial objects and components in a controlled, layer-by-layer fashion based on a digital model. Selective laser melting (SLM), as an AM technique, offers advantages such as design freedom and reduced material waste compared to traditional manufacturing technologies. However, residual stress is induced during the printing process due to steep thermal gradients and possible mechanical impacts of the particles. The main focus of this study was to investigate the effect of stress-relief heat treatment on the microstructure and residual stress in SLM samples. For comparison, the same study was conducted on conventionally manufactured hot-rolled (HR) 316L stainless-steel samples. The x -ray diffraction method was used to measure the residual stress built up in each sample, and transmission electron microscopy (TEM) images were used to study dislocation densities before and after heat treatment. Stress-relief heat treatment at 450 °C was applied for 1.5 h to all 316L samples. The residual stress was reduced by around 30% in the heat-treated SLM samples, while it did not have a significant effect on the HR 316L samples. The built-up residual stress in SLM 316L was found to be tensile in nature, whereas HR 316L samples exhibited more compressive residual stress. This study also applied one of the well-known developed models for calculating residual stresses in AM-processed metallic materials. The results were in acceptable agreement with the experimental ones only for the SLM-processed sample. TEM observations revealed that the dislocation density of the SLM structure was reduced by around 50% after the stress-relief heat treatment, which could be the main reason for the residual stress reduction after heat treatment.