Laser-Directed Energy Deposition of Dissimilar Maraging Steels with a Defect-Free Interface: Design for Improved Surface Hardness and Fracture Toughness

다국어 초록 (Multilingual Abstract)

Maraging steels are a class of low-carbon ultra-high-strength martensitic steels. Due to their excellent weldability, these steels have been widely applied for laser-based additive manufacturing (AM). MAR-60HRC is a newly developed maraging grade for AM with a nominal chemical composition of 13.0Ni-15.0Co-10.0Mo-0.2Ti, Fe bal. (wt%), capable of achieving hardness levels of ~ 740 HV. Alternatively, 18Ni300 is a commercialized maraging steel with an excellent combination of strength and toughness at the peak aged hardness (i.e., ~ 590 HV). This work aims to investigate the properties and microstructure of MAR-60HRC fabricated by Laser Directed Energy Deposition (L-DED). Further, the manufacturability of bimetallic parts comprising a tough 18Ni300 core and a hard MAR-60HRC on the surface was evaluated. After proper aging, the multi-layered material showed a surface hardness of ~ 720 HV1 and apparent fracture toughness of 71 MPa m1/2, higher than that of MAR-60HRC (i.e., 60 MPa m1/2), and lower than 18Ni300 (i.e., 90 MPa m1/2). The excellent combination of surface hardness and fracture toughness was discussed, considering the crack arrest at the interface and the flawless interface between the two steels.