Integrated materials–processing design strategy for metastable-austenite-enabled strength–ductility synergy in laser powder bed fusion 17-4 PH stainless steel

Laser powder bed fusion (LPBF) and heat-treatment strategies offer substantial potential due to their distinct microstructures and resulting properties. However, their complex material–processing interactions can induce poor qualities and degrade properties. Therefore, integrated materials–processing design should be systematically established to minimize defects and achieve strength–ductility synergy. Here, we establish an integrated materials–processing framework for transformation-induced plasticity (TRIP)-assisted 17-4 PH stainless steel (SS) fabricated by LPBF. A lack-of-fusion index (LFI), calculated from melt-pool sizes, was found to remain below a critical value of 0.953 to enable densification and prevent degradation of hardness and tensile properties. For the TRIP-assisted alloy, an N 2 atmosphere was employed during powder atomization and LPBF processing to promote metastable FCC/austenite retention. The resulting FCC/BCC microstructures produced a favorable strength–ductility balance, reaching a tensile strength of 1223.68 MPa and an elongation of 13.92% through TRIP-assisted strain hardening. Hot isostatic pressing (HIP) followed by aging treatment (AT), denoted as HAT, further improved the yield strength by 95.68% through retained-FCC-containing hierarchical microstructures. Direction-dependent microstructural differences clarified that anisotropic tensile behavior was governed by the inherited as-built microstructure and was partially alleviated after AT through reverted austenite formation and stress relaxation. Finally, the TRIP-assisted 17-4 PH SS demonstrated buckling tolerance in Schwarz structures, with a 240.60% improvement in energy absorption compared with the HAT condition. This study provides guidance for designing energy-absorbing alloys through metastable-austenite-enabled TRIP mechanisms.