Mechanical properties of lamellar-structured 18Ni300 maraging steel manufactured via directed energy deposition

Abstract

The combination of repetitive melting–solidification cycles, directional laser scanning, and microstructure design using additive manufacturing (AM) is effective for enhancing the mechanical properties of metallic alloys. Because the ultrafine metastable phases in as-built metallic alloys are beneficial to their mechanical properties, there is a design window to enhance the strength–ductility combination by controlling the metastable phase distribution with AM. In this study, ultrafine lamellar-structured maraging steel consisting of martensite and austenite was manufactured using directed energy deposition. The stripe laser scan strategy induced linear (Mo, Ti, Ni)-rich segregations that formed lamellar-structured austenite by reducing the martensitic transformation starting temperature in the high-Ni-content maraging steel. The deformation-induced martensitic transformation and back-stress hardening near the austenite–martensite interfacial region enhanced the plasticity capability of the AM-processed maraging steel and achieved a better strength–ductility combination compared with conventional and recently developed AM-processed maraging steels. This result indicates that artificial microstructural design via AM is important for enhancing the performance of metallic alloys, which can also be achieved with conventional metallic alloys by distributing the metastable phase with processing variable control.