Influence of aging treatments on 17-4 PH stainless steel parts realized using material extrusion additive manufacturing technologies

The most relevant criticalities of parts produced by material extrusion additive manufacturing technologies are lower mechanical properties than standard material performances, the presence of pores caused by the manufacturing method, and issues related to the interface between layers and rods. In this context, heat treatments can be considered an effective solution for tailoring the material behavior to different application fields, especially when using precipitation hardening stainless steels. In this work, aging treatments were conducted on parts realized using three different extrusion-based processes: Atomic Diffusion Additive Manufacturing, bound metal deposition, and fused filament fabrication. Two conditions of direct aging (H900 and H1150) were considered with the aim of comparing the response of properties in the opposite conditions of peak-aged and overaged. The hardness tests revealed that H900 aging significantly influenced hardness (max increase of 52%), and porosity (- 34.3% with respect to the as-sintered condition). On the other hand, the H1150 aging decreased the hardness (- 18% max) and porosity (- 32.2% max). Substantial differences among the microstructures due to grain size and delta-ferrite were illustrated. A statistical test was included to better highlight the influence of the heat treatment on the investigated properties.