Influence of Grain Size and Composition on Creep Performance of Additively Manufactured and Wrought Type 316 Stainless Steels

Abstract Gas metal arc-directed energy deposition (GMA-DED) is being investigated as a manufacturing method for producing large pressure retaining components in power generation applications, with the aim of reducing costs and lead times. This work evaluated the creep performance of GMA-DED and wrought 316H and 316L at 650 °C over a range of stress conditions to enhance understanding of the long-term microstructure stability of GMA-DED stainless steels. To understand the effect of grain size on creep performance, the wrought plate was annealed to grow the grain size to better match the linear average grain length of the GMA-DED material. The wrought conditions exhibited longer creep lives and lower minimum creep rates compared to the GMA-DED conditions. Creep damage and boundary precipitation were evaluated to understand differences in creep life. A creep rupture time model was evaluated and shown to match well with experimental data. The results from the model indicate that differences in minimum creep rate are the dominating factor dictating creep life within the dislocation climb creep regime rather than grain size. The model correlates with experimental results where the creep behavior of the heat treated wrought 316H condition is extremely similar to the as-received wrought 316H condition, indicating the minimal impact of grain size on creep performance for the conditions evaluated. Differences in creep strength (minimum creep rate) between the wrought and GMA-DED conditions may be related to microsegregation due to remnant δ-ferrite in the GMA-DED microstructure which could increase the stacking fault energy and suppress M23C6 precipitation, both of which decreases creep strength, compared to the wrought conditions. Overall, 316L exhibited longer creep life than 316H, within the respective wrought and GMA-DED conditions, with no clear compositional or microstructural explanation, indicating 316L or 316H can likely be used interchangeably for creep limited applications.