Enhanced strength-ductility synergy in super duplex stainless steel matrix composites with bimodal austenite grains via laser powder bed fusion

The improvement in the strength-ductility synergy of metals is critically important to fabricate various lightweight parts. In this study, for super duplex stainless steels (SDSSs), multi-scale hybrid reinforcements and bimodal austenite grains were developed to enhance their strength-ductility synergy via laser powder bed fusion (LPBF) and post-heat treatment. The introduction of micron-sized TiC particles into SDSS powder produced substantial fine ferrite grains (∼85 vol %) in as-built SDSS matrix composites, and some in-situ TiC_xN_y nanoparticles and a few in-situ M₂₃C₆ nanoparticles were found. The addition of super austenitic stainless steel (SASS) powder (∼15 wt %) to SDSSs generated some bimodal austenite grains. For heat-treated SDSS matrix composites, a few coarse austenite grains were retained, and more fine austenite grains were formed in addition to previously formed fine ferrite grains. Multi-scale hybrid reinforcements were developed in heat-treated SDSS matrix composites, containing micron-sized TiC particles, sub-micron M₂₃C₆ particles, and TiC_xN_y nanoparticles. The pinning of dislocations around sub-micron M₂₃C₆ particles and TiC_xN_y nanoparticles was found. Compared to heat-treated LPBF-fabricated 2507 SDSSs, the ultimate tensile strength value of heat-treated SDSS matrix composites was increased by ∼16.5 %, and their uniform elongation value was enhanced from ∼20.8 % to ∼22.4 %. It is believed that the developed approach can be employed for other metals, achieving enhanced strength-ductility synergy.