The effect of heat input on the microstructure and mechanical properties of 18Ni 300 maraging steel fabricated by arc directed energy deposition

The effect of heat input on the microstructure and mechanical properties of 18Ni 300 maraging steel fabricated by arc directed energy deposition is investigated, and a thermodynamic simulation model is designed for the investigation. Cold metal transition welding (CMT), pulse-gas metal arc welding (P-MIG), and the combination of CMT and P-MIG (CMT + P-MIG) technologies are designed to control the heat input. The additive mode is changed every two layers for the CMT + P-MIG mode. The results show that the CMT sample has the lowest fraction of ferrite in the middle region; meanwhile, the P-MIG sample has the highest fraction of ferrite. The CMT + P-MIG sample shows alternate variations in microstructure morphology along the building direction, especially in the middle region, leading to soft and hard variations in the microhardness. The EBSD results show that the low heat input is beneficial for obtaining {110} < 001 > Goss texture. As the heat input increases, the {110} < 001 > Goss texture gradually disappears and the {100} < 001 > Cube texture gradually forms. The low heat input is beneficial for obtaining better mechanical properties, the CMT sample has the best UTS and EL in the horizontal direction (1271 ± 28 MPa and 19.7 ± 0.6%, respectively). The results of the study reveal the successful application of WAAM technology in manufacturing 18Ni 300 martensite aging steel components, and verify the feasibility of controlling the heat input to achieve hierarchical changes in the microstructure.