| Abstract Scope |
Additive manufacturing (AM) processes such as gas metal arc directed energy disposition (GMA-DED) and laser powder bed fusion (L-PBF) provide a fabrication pathway that can significantly reduce costs and production time within the power generation sector. Implementation of AM components will require welding AM components to other non-AM components, highlighting the need to understand the weldability of these AM alloys. Austenitic stainless steels, which are conventionally considered ductile, are reported to experience a drop in ductility at elevated temperatures due to a solid-state cracking mechanism known as ductility dip cracking (DDC). In this work, the DDC susceptibility of GMA-DED, L-PBF, and wrought austenitic stainless steel was investigated through hot ductility testing. A Gleeble thermal-mechanical simulator was used to conduct on-cooling tests from the nil ductility temperature, and the reduction in area was measured to assess ductility response. The impact of post-build heat treatment was also investigated by comparing the performance of the as-built and solution annealed GMA-DED and L-PBF conditions. Differences in ductility response were associated with differences in stacking fault energy (SFE) between the conditions due to variations in composition, microsegregation, and secondary phase formation. A higher relative SFE between the conditions promoted dynamic recrystallization, leading to increased ductility. The formation of delta-ferrite appears to reduce DDC susceptibility by raising the SFE of the austenite and creating tortuous boundaries that reduced grain boundary sliding. In addition to evaluating ductility response, the impact of Gleeble joule heating and freezing range variations on hot ductility test development will be discussed in relation to test reliability and repeatability. |