Influence of shielding gas nitrogen content on the microstructure and mechanical properties of Cu-reinforced maraging steel fabricated by wire arc additive manufacturing

This study investigated the effects of using shielding gases with different nitrogen concentrations on the microstructures and mechanical properties of SHER-120G maraging steel fabricated by wire arc additive manufacturing (WAAM). With increases in the nitrogen concentration, the contents of nitrogen and austenite in the bulk specimens increased significantly, while δ-ferrite formation was inhibited. In addition, nitrogen was absorbed by the molten pool and decomposed into N atoms during WAAM. Some N atoms formed a solid solution with the matrix and the rest reacted with Cr to form Cr2N, which plays an important role in the process of martensite lath refinement. The optimal shielding gas composition was 94% Ar + 2% O2 + 4% N2, which resulted in a tensile strength and micro-hardness of 1324 MPa and 441 HV, respectively. These values are 12.3% and 12.5% higher, respectively, than those of samples fabricated without nitrogen in the shielding gas.