Effect of C-Mn-Cu on microstructure and properties of wire arc additive manufacturing of high-manganese steels

High-manganese steels, due to their unique combination of strength and elongation, have been widely used in aerospace, petrochemical and rail transportation. However, a prevalent challenge in advancing the utilization of high-manganese steel is the need for corresponding welding consumables. The deformation mechanism of high-manganese steel encompasses three primary mechanisms: martensitic phase transformation, twinning and dislocation movement. The stacking fault energy (SFE) is a critical factor in determining the dominant deformation mechanism in high-manganese austenitic steels. Furthermore, the magnitude of the SFE is principally influenced by the alloying elements present and the temperature at which deformation occurs. Alloying elements can significantly influence the microstructure and mechanical properties of wire arc additive manufacturing (WAAM) of high-manganese steels. The metal powder-cored wire of high-manganese steel with full austenitic microstructure was designed in this paper. The effects of C, Mn and Cu on the microstructure, solute segregation and properties of WAAM of high-manganese steels were systematically investigated by optical microscopy, electron microscopy and mechanical testing. The influence of SFE on the microstructure characteristics and work hardening behaviour were also studied. The results showed that as an increase of the C content, the tensile strength and elongation of deposited metals were improved. The corresponding low-temperature impact toughness increased at first and then decreased. The highest value of impact toughness was 68.5 J with 0.79%C. As the Mn increased, the strength decreased, the elongation increased and the low-temperature impact toughness value displayed an initial increase followed by a subsequent decrease. With the increase of Cu, the yield strength and elongation improved significantly. The tensile strength exhibited a marginal initial increase followed by a decrease, whereas the change was not substantial. In contrast, the low-temperature impact toughness value showed a substantial increase followed by a decrease. The developed M3 wire containing 1.10%C-21%Mn-0.3%Cu possessed the optimum performance (yield strength of 551 MPa, tensile strength of 909 MPa, elongation at break of 30.2%, impact toughness value of 57.5J), with the good mechanical stability and low solidification cracking sensitivity.