A cold metal transfer (CMT)-wire-arc additive manufacturing technology is used to fabricate high nitrogen steel walls at the interlayer temperatures of 50℃,150℃ and 250℃,and the relationships among the interlayer temperatures,the resulting microstructures and the material properties are studied.The results show that the interlayer temperature has significant effect on the forming quality,and the optimal results can be obtained at 50℃.The additive manufactured parts are primarily comprised of austenite and ferrite,where the ferrite is distributed within the austenite matrix in a skeletal and worm-like manner.The interlayer temperature can be reduced to enhance the cooling rate of the molten pool,reduce the spacing between secondary dendrite arms,and inhibit the growth of nitrogen bubbles,thus diminishing the size and number of micrometer-sized nitrogen pores and minimizing nitrogen loss.However,the hardness and tensile strength decrease as the interlayer temperature increases.Lower interlayer temperature promotes the formation of fine grains,enhancing hardness.Higher interlayer temperature lead to grain coarsening,reducing hardness.Regarding the tensile properties,the lower interlayer temperature strengthens the tensile strength,whereas the high temperature improves the ductility through the precipitation of a second phase.The material exhibits anisotropy,and the transverse specimens have superior tensile strength.The fracture morphology reveals a micro-void coalescence fracture mode,where the presence of manganese oxides and nitrogen pores adversely affects the tensile performance of additive manufactured workpiece.Moreover,the defects such as gas pores can act as initiation sites for corrosion,while the chloride ions facilitate the formation of primary cells on the surface of high-nitrogen steel,leading to chloride ion erosion.Nitrogen in solid solution can prevent a decrease in the pH value of solution in high-nitrogen steel,facilitate the rapid repassivation of sample surface,and prolong the maintenance of passivation state.However,an increase in interlayer temperature results in a decrease in the nitrogen content,which leads to reduced corrosion resistance of the additive manufactured parts.
