Investigation on enhanced impact toughness and deformation mechanisms of an additively manufactured 17-4 PH stainless steel

Abstract

International audienceThis study investigated the effect of solution treatment temperature on the microstructure and mechanical (hardness, tensile and impact toughness) properties of 17-4 PH stainless steel produced by laser powder bed fusion (PBF-LB). We applied three solution treatments (900 °C, 1040 °C, and 1125 °C) to the as-built material, followed by a standardized ageing treatment (620 °C/4 h). Microstructural characterization revealed that the lowest temperature (900 °C) failed to fully homogenize the initial structure, leading to elemental segregation (Cr, Ni, Cu). In contrast, the highest temperature (1125 °C) produced a fully homogenized and recrystallized microstructure but also caused significant coarsening of SiO2 oxide particles, which became concentrated along grain boundaries. From a mechanical perspective, the 900 °C treatment produced the lowest yield and ultimate tensile strengths; however, it provided high ductility, strong strain-hardening capacity, and excellent impact toughness, comparable to that of conventionally processed 17-4 PH. This behaviour is attributed to the formation of a duplex-matrix microstructure composed of δ-ferrite and martensite, combined with controlled SiO2 particle size and distribution. In contrast, the 1125 °C treatment, despite yielding a more homogeneous microstructure, significantly reduced toughness due to the formation of coarse oxide particles and distribution along grain boundaries. This work demonstrates that the use of a low (non-standard) solution treatment temperature offers additional opportunities for tailoring the mechanical properties of PBF-LB components