Short-Term Solution Treatment of LPBF Fe–Cr–Mn–Mo–N High-Nitrogen Duplex Stainless Steel: Microstructure and Tensile Response of Two Initial States

Insufficient ductility and processing-dependent mechanical properties limit laser powder bed-fused (LPBF) high-nitrogen stainless steels. This study investigated short-term solution treatment of an Fe–Cr–Mn–Mo–N duplex stainless steel using two as-built samples with distinct microstructures and elongations. Samples were treated at 1050 and 1100 °C for 10 min and water quenched. Microstructure and deformation behavior were characterized by electron backscatter diffraction, tensile testing, loading–unloading–reloading experiments, and transmission electron microscopy. Treatment increased the austenite fraction from 16.0 and 21.1% to 70.8–77.0%, producing an austenite-dominated duplex microstructure with residual ferrite as short strips or isolated islands. Differences in tensile properties between the initial states decreased substantially, with ultimate tensile strengths of 1030.9–1049.9 MPa and elongations of 29.45–33.82%. A representative sample treated at 1100 °C achieved 1030.9 MPa and 33.82% elongation. Its back stress showed an overall increase during plastic deformation, indicating a contribution of long-range internal stresses to strain hardening. Early deformation involved planar slip and localized stacking faults in austenite. Further deformation produced denser planar defects and local 9R structures in austenite, with pronounced dislocation tangles in ferrite. Short-term solution treatment thus enhanced ductility while retaining approximately 1 GPa strength and reducing property discrepancies between initial LPBF-built states.