A new grain refinement route for duplex stainless steels: Micro-duplex stainless steel matrix composites processed by laser powder bed fusion

The employment of grain refinement approaches is regarded as a favorable strategy to increase mechanical properties of duplex stainless steels (DSSs). In this work, a new grain refinement route was successfully developed via laser powder bed fusion (LPBF) of micro-duplex stainless steel (SS) matrix composites along with a subsequent quenching process. For as-built composites, TiC_xN_y nanoparticles were first formed in-situ via the introduction of submicron/micron-sized TiC particles with low cost into 2205 DSSs, and fine equiaxed high-temperature ferrite (δ-ferrite) grains were formed due to the ultra-high cooling rate of LPBF and heterogeneous nucleation sites provided by in-situ formed TiC_xN_y nanoparticles. The formation of TiC_xN_y nanoparticles inhibited the epitaxial growth of δ-ferrite grains, and no obvious textures were found in as-built composites. Subsequently, fine austenite grains were produced at grain boundaries of fine unrecrystallized δ-ferrite during quenching treatment of as-built composites, which enabled heat-treated composites to achieve an ensemble of outstanding ultimate tensile strength and uniform elongation. The δ-ferrite recrystallization was mainly inhibited by the existence of TiC_xN_y nanoparticles. This study can provide a groundwork for designing grain refinement methods to produce high-performance DSS parts with complex geometry based on LPBF technique.