Severe shot peening: A promising solution for mitigating stress corrosion cracking in solution-annealed LPBF 316 l stainless steel

Laser powder bed fusion (LPBF) effectively fabricates intricate 316L stainless steel components but often results in significant tensile residual stresses and anisotropic microstructures, compromising mechanical performance. Solution annealing at 1050–1100 °C reduces anisotropy along with mitigating these stresses but may reduce stress corrosion cracking resistance (SCC). Therefore, this study combined solution annealing with severe shot peening (SSP) to enhance the surface properties and the SCC performance.

Despite these benefits, recent studies have raised concerns regarding the impact of high-temperature solution annealing on the stress corrosion cracking (SCC) resistance of 316L stainless steel. SCC is a critical failure mode where the combined action of tensile stress and a corrosive environment leads to crack formation and growth, particularly problematic in chloride-rich environments common in marine and chemical processing applications. While solution annealing reduces residual stresses and homogenizes the microstructure, it may also reduce SCC resistance due to changes in microstructural features that influence crack initiation and propagation.

To enhance mechanical performance and SCC resistance, this study explores the combined use of solution annealing and severe shot peening (SSP) as post-processing techniques. SSP is an intensified form of traditional shot peening, characterised by increased exposure time and higher intensity of shot impacts. This mechanical surface treatment introduces a layer of compressive residual stress on the material's surface and subsurface regions, counteracting the tensile stresses that drive crack propagation and enhancing SCC resistance. In this study, as-printed LPBF 316L samples were subjected to solution annealing at 1100 °C, followed by air blast SSP. The findings from this study aim to provide a comprehensive understanding of how combined thermal and mechanical treatments can synergistically improve the performance of LPBF 316L stainless steel.

Conclusions 

Heat treatment at 1100 °C reduced tensile stresses significantly, while subsequent SSP treatment induced beneficial compressive stresses exceeding −750 MPa, crucial for improving material integrity and delaying crack propagation.

SSP increased surface microhardness to 473 HV0.05 from 171 HV0.05 of the HT1100 sample, enhancing material strength near the surface.

SSP after HT1100 reduced surface roughness from 11.8 µm to 5.1 µm, thereby reducing the crack initiation sites.

SSP induced the grain refinement on the surface and subsurface, crucial for delaying crack initiation.

These modifications not only strengthen the material against mechanical failures but also mitigate the vulnerabilities that lead to stress corrosion cracking, thereby extending the service life and reliability of components subjected to harsh operating conditions.