Mechanical Properties Anisotropy Of High Nitrogen Steel Fabricated By Plasma Arc Additive Manufacturing

High-nitrogen steel materials have high strength and corrosion resistance,and are widely used in military equipment,marine engineering,chemical industry and other fields.Plasma arc additive manufacturing technology can be used to customize high-nitrogen steel parts with complex structures,but the mechanical properties of samples in different sampling directions are anisotropic,and the anisotropy of mechanical properties greatly limits the application of additive high-nitrogen steel parts.In this paper,plasma arc additive manufacturing technology is used to prepare a high nitrogen steel block with a nitrogen content of 0.8%,and the mechanical properties of the obtained block are studied in depth.Through experiments,the process parameters for arc additive manufacturing of high nitrogen steel are determined: current 130 A,arc travel speed 2.5m/min,wire feed speed0.6m/min,overlap rate 60%,and additive path is layer by layer orthogonal.According to this parameter,the accumulation of Cr-Mn high nitrogen steel additive block is carried out.Tensile,impact and fatigue tests were performed on the samples in three directions: arc scanning direction SD(scanning direction),45° of scanning direction 45°(45° of scanning direction),and additive stacking direction BD(building direction).Study the anisotropy of the mechanical properties of the additive block,and explain the anisotropy in combination with the tissue analysis test.The tensile strength of SD and 45° samples are 1048 MPa and 1029 MPa,respectively,which are not much different.The tensile strength of BD samples is 956 MPa,which is significantly lower than SD and 45° samples.The impact toughness of the SD sample is 36.5J/cm2,which is better than that of the BD sample,and the impact toughness of the BD sample is 27.5 J/cm2.Through EBSD analysis,it is found that the grains of the additive block are coarse columnar crystals that grow through the fusion line,and there is an obvious(100)preferred orientation.The analysis shows that the preferred orientation of the grains(100)leads to the good tensile properties and impact toughness of the additive in the SD direction.At the same time,the void defects inside the sample also reduced the tensile properties and impact toughness of the BD sample to a certain extent.Both the high-cycle stress fatigue life and the low-cycle strain fatigue life of the 45°sample are better than those of the SD sample,and the fatigue ultimate strength of the 45°sample is 200 MPa,and the fatigue ultimate strength of the SD sample is 175 MPa.Microstructure analysis found that the slip bands formed on the surface of the 45° sample during the fatigue process are denser,more fatigue cracks are induced,and the crack propagation path is more tortuous.A large number of cracks and the tortuous growth of cracks will absorb more energy,thereby increasing 45° The fatigue life of the sample.At the same time,there are many defects such as unfused holes and inclusions in the SD sample,which will reduce its fatigue performance.