Study On The Mixed Interface And Mechanical Properties Of High Nitrogen Steel And Low Carbon Steel Fabricated By The Plasma Arc Additive Manufacturing

Based on the plasma arc additive manufacturing technology,high nitrogen steel and low carbon steel wire was used as the research object to study the additive manufacture process.The microstructure of mixed interface fabricated by these two wires and its influence on the mechanical properties of additive components has been studied in depth.First,the plasma arc single-pass process parameters for high nitrogen steel and low carbon steel was studied separately,and the influence of current,wire feed speed and deposition speed on the form dimensions was determined.The width of weld bead is mainly affected by current,and its thickness is mainly affected by the wire feed speed.Taking morphology,size,and defects as sieve directions,the optimal process parameters were obtained through experiment optimization,and the weld beads have a good forming as its thickness was 0.6mm.The torch lifting height between each layer and ion gas flow were reduced to ensure the forming of additive component’s side wall and avoid hole defects.With the detection and analysis of the nitrogen loss in high nitrogen steel additive procedure,the height from the tip of wire to the molten pool was determined preferably as 0.5mm.This paper focuses on the effects of the high nitrogen steel and low carbon steel differernt additive mixing methods on the structure and properties of the mixed interface.The deposition order combination of high-nitrogen steel(denoted as A)and low carbon steel(denoted as B)was considered and analyzed.The oder ―sequential deposition of high nitrogen steel,low carbon steel,and high nitrogen steel‖(denoted as ABA)and ―high nitrogen steel is deposited on both sides of the low carbon steel deposited first‖(denoted as BAA)were retained for study.The difference in the microstructure of the hybrid interface obtained by using different dissimilar material overlap rate with that two additive orders and its influence on the performance of additive component were analyzed.The model of hardness distribution law on mixed interface is established.Both of the mixed interfaces fabricated by ABA-type and BAA-type have the hardened area and weakened area,and the the peak value in hardened area reached 410 HV,which is 28% higher than the hardness level of high nitrogen steel.The valley value in the weakened area is about 260 HV.The microstructure characteristics and distribution of different mixed interfaces were observed.The mixed interface fabricated by ABA-type is mainly divided into four zones: high nitrogen steel zone,low carbon steel zone and two transition zones.The microstructure of high nitrogen steel zone appears as columnar austenite grains.The microstructure of low carbon steel zone mainly appears as bulk ferrite grains.One transition zone mainly have cellular austenite grains and bulk ferrite grains.Another transition zone is a two-phase zone composed by cellular austenite grains,equiaxed grains and nitride precipitation phase.And the first transition zone does not exist in the mixed interface of BAA-type.The microstructure characteristics and distribution of the mixed interface correspond to the hardness distribution law.The tensile and impact resistance of heterogeneous additive components with mixed interfaces were studied,both mechanical properties appears anisotropy.There are reinforced tensile specimens in the components,the tensile strength of which reaches 1050MPa,and the elongation after break can reach more than 30%.The impact toughness value of the specimen fluctuates up and down on the high-nitrogen steel additive state level,but not as high as the low carbon steel additive state.Finally,based on the optimized process parameters and additive path planning,vertical overlapping additive components formed by high nitrogen steel and low carbon steel were designed and fabricated.There is no obvious anisotropy for impact resistance of the components in the horizontal direction,due to the rotation of each additive layer by 90°.And the impact resistance change in the direction perpendicular to the horizontal plane is still large.As the proportion of mixed interface in the cross section of the impact specimen increases,the impact toughness value of the specimen increases,and the impact force direction has little effect on the impact toughness value of the specimen.The above research results show that the mixed interface can improve the mechanical properties of heterogeneous additive components,and the addition of low carbon steel plays a key role in the improvement of its toughness.And it is possible to control the local organization and mechanical properties of heterogeneous additive components by changing the mixing method of heterogeneous materials(deposition order and overlapping amount of heterogeneous materials),which has certain reference value and significance for the mechanical properties control study of heterogeneous additive components.