The Mechanical Performance of Additively Manufactured 316L Austenitic Stainless Steel

Abstract

Additive manufacturing (AM) offers the potential for significantly reducing the time and cost of new nuclear components. This process may also permit unique design features, for example internal geometries. However, the limitations of the technology need to be better understood to enable implementation and accreditation. Here a “blown powder” and laser melting process, within a helium shielded environment, was used to fabricate austenitic stainless steel 316L walls of ∼2.4 mm thickness, with the deposition parameters minimizing the surface roughness. A key aim was to evaluate the effect of the as-deposited surface finish and the bulk material on the tensile and fatigue properties. In addition, the effect of material orientation was also considered to be important. Microstructural characterization demonstrated the complex nature of the grain morphology arising from the as-manufactured AM process, including elongated grains following the thermal gradients. However, areas of equiaxed grains were also observed at the sample surfaces. Si-Mn-O particles, up to ∼20 μm in diameter, were noted throughout the samples produced. Residual strains have also been measured and correlated with microstructural features. The tensile performance was generally similar to wrought 316L material but exhibited some anisotropy. The fatigue endurance of as-deposited AM 316L was significantly lower than wrought material. However, surface grinding of the AM 316L was shown to be beneficial. It was noted that in all cases examined, fatigue crack initiation was found to occur at the Si-Mn-O particles, in both surface finishes — clearly a performance limitation.