The 17-4 precipitation-hardened (PH) stainless steel (SS) is widely used in aerospace, energy, and biomedical applications due to its high strength, corrosion resistance, and weldability. However, laser powder bed fusion (LPBF) fabricated 17-4 PH SS often exhibits process-induced defects (e.g. lack of fusion, keyhole, and gas-induced porosity) and heterogeneous phase composition, leading to inconsistent mechanical performance even after standard precipitation hardening. In this study, powder bed preheating was applied to 17-4 PH SS, effectively reducing lack-of-fusion porosity, expanding the process-induced defect-free processing window, and refining grain structure while lowering retained austenite content. X-ray diffraction (XRD) and transmission electron microscopy (TEM) revealed phase evolution, martensite formation, and nanoscale copper precipitate distribution, correlating directly with yield strength, ultimate tensile strength, and ductility. The as-built mechanical properties were strongly influenced by process-induced defect fraction and phase composition, with higher bed preheating enhancing strength, but reducing ductility. Subsequent heat treatment produced a fully martensitic microstructure with well-dispersed precipitates, yielding consistent ASTM-compliant strength and ductility. These results establish powder bed preheating as an effective strategy to stabilize LPBF processing, enable reproducible microstructures, and overcome the long-standing challenge of unpredictable post-heat-treatment performance, providing a clear route to high-performance, application-ready 17-4 PH SS. • Bed preheating reduces lack-of-fusion defects, improving both strength and ductility • Preheating promotes finer grains and lowers retained austenite in as-built LPBF 17-4 PH • Microstructural refinement improves as-built strength but reduces ductility • Heat treatment yields uniform martensite with nanoscale Cu precipitates • Resulting strength–ductility meets ASTM standards with high reproducibility
Malhotra et al. (Fri,) studied this question.