Tailoring microstructure and mechanical properties of 17-4PH steel fabricated by wire-arc directed energy deposition via a combination of intrinsic and post-processing heat treatments

Abstract

This paper examines the effect of intrinsic heat treatment, i.e., multiple transient heating from subsequent passes, and post-processing heat treatment on the microstructure and mechanical properties of 17–4PH stainless steel fabricated by wire-arc directed energy deposition. By carefully controlling the interpass temperature to remain below the martensite start (Ms) temperature, intrinsic heat treatment effectively triggers the formation of Cu-rich clusters and the reversion of austenite. This approach results in a concurrent enhancement in the ultimate tensile strength, increasing from 1036 MPa to 1128 MPa, and elongation, increasing from 13.2% to 18.5%, for the as-built part. During post-processing heat treatment, the microstructural response to direct aging treatment hinges on the initial microstructure induced by intrinsic heat treatment. Notably, direct aging treatment significantly enhances the hardness and ultimate tensile strength of the as-built part created at an interpass temperature surpassing the Ms temperature. Conversely, its influence on the mechanical properties of the as-built component, fabricated at an interpass temperature lower than the Ms temperature, remains minimal. Additionally, the application of a solution treatment effectively eradicates the inherent microstructural characteristics, regardless of the initial fabrication conditions. Nonetheless, the grain size of the solution-treated specimen is markedly influenced by the as-built microstructure. Ultimately, a judicious amalgamation of intrinsic and post-processing heat treatments yields an exceptional combination of properties, including high hardness (465 HV), ultimate tensile strength (1437 MPa), and elongation (14.5%). These results underscore the significance of a comprehensive consideration of intrinsic and post-processing heat treatments to tailor the microstructure and mechanical properties of 17–4PH steel fabricated by wire-arc directed energy deposition.