Simultaneous enhancements of strength and ductility of wire arc additive manufactured 17-4PH steel via intrinsic heat treatment

During wire arc additive manufacturing (WAAM), the previous deposited pass inherently experiences the intrinsic heat treatment, i.e., rapid reheating from subsequent passes. This study exploited this intrinsic heat treatment to improve the mechanical properties of as-WAAMed 17–4PH steel. By controlling the interpass temperature after each pass, we initiated martensitic transformation within the deposited layer. Subsequently, the intrinsic heat treatment induced austenite reversion and precipitation of copper-rich clusters within the formed martensitic matrix, resulting in a combination of high ultimate tensile strength (1128 ± 32 MPa) and elongation (18.5 ± 3.1%) for the as-WAAMed part. In comparison, when the austenite was kept in the previous layer during subsequent passes, the intrinsic heat treatment had minimal impact on the formed microstructure. Consequently, a coarse martensitic structure was obtained after cooling without the reversed austenite and copper-rich precipitates, leading to lower ultimate tensile strength (1036 ± 18 MPa) and elongation (13.2 ± 2.7%). The findings of this study indicate that exploiting the intrinsic heat treatment is an effective strategy for simultaneously enhancing strength and ductility of 17–4PH steels during WAAM.