Microstructure evolution and sensitization of additively manufactured duplex stainless steel during aging heat treatments

Duplex stainless steels (DSS) combine excellent mechanical and corrosion resistance properties. They are now increasingly fabricated by laser powder bed fusion (LPBF). A significant concern with DSS is sensitization, which is caused by the formation of deleterious precipitates during exposure to elevated temperatures. Yet, this behavior has never been systematically studied in additively manufactured DSS. Here, we investigate how the unique microstructure of LPBF-manufactured DSS affects the sensitization behavior by comparing hot-rolled, as-built, and solution-annealed LPBF specimens subjected to isothermal aging at 825 °C for 30 to 600 mins. Light optical and scanning electron microscopy, along with electron backscatter diffraction, reveal differences in the microstructural evolution, showing initially slower σ and χ precipitation in LPBF samples due to a more coherent ferrite/austenite boundary structure. Nevertheless, double-loop electrochemical potentiokinetic reactivation testing reveals that the sensitized, as-printed LPBF microstructure exhibits a comparatively faster deterioration of its corrosion resistance. This is attributed to the formation of low-Cr containing austenite during aging at 825 °C. Atom probe tomography corroborates this finding and reveals additional Cr-depletion adjacent to intermetallic phases. The annealed LPBF microstructure, by comparison, combines a favorable solute partitioning with more coherent interfaces, which is deemed responsible for an increased sensitization resistance when benchmarked against the as-built and hot-rolled conditions. This demonstrates that LPBF components, when appropriately heat-treated, can offer advantages over conventionally processed DSS for use in demanding environments. • Sensitization of laser powder bed fusion (LPBF) duplex stainless steels revealed • Solution annealed LPBF condition more sensitization resistant than hot rolled one • Coherent interfaces formed during solution annealing delay intermetallics formation • Austenite with low Cr content forms during aging, reducing overall corrosion resistance • Atom probe reveals local Cr and Mo depletion near σ/χ precipitates after aging