Synergistic effects of heat treatments and severe shot peening on residual stresses and microstructure in 316L stainless steel produced by laser powder bed fusion

Abstract

This study investigated the post-processing of laser powder bed fusion (LPBF) built 316L stainless steel components to address quality-related issues such as dangerous residual stresses and poor surface finish. Two different heat treatments (HT) at 600 °C and 900 °C, followed by severe shot peening (SSP), were employed to mitigate these concerns. The impact on roughness, residual stresses, microhardness, and microstructure in both as-printed and post-processed states was examined. Results indicate that the 600 °C HT fails to relieve residual stresses, while the 900 °C HT significantly reduces them by 90%. Furthermore, the SSP effectively reduced surface roughness by more than half of the initial values. The initial microstructures and residual stresses of the as-printed, 600 °C HT, and 900 °C HT samples differ, leading to distinct responses to identical SSP treatments. Notably, the 900 °C HT sample exhibited the deepest grain refinement after SSP and experienced the most substantial increase in surface hardness compared to the other samples. This research addressed critical quality issues in LPBF-built components by combining specific heat treatments and SSP. The 900°HT combined with SSP stood out as an effective method for relieving residual stresses and enhancing material properties. The distinct responses of the samples to post-processing highlight the importance of tailored treatments for LPBF components. These findings have significant implications for improving the quality and performance of LPBF components, with potential applications demanding improved fatigue and stress corrosion cracking performance.