Microstructure Distribution And Property Analysis Of 2205 Duplex Stainless Steel Made By CMT Arc-fusing Additive Manufacturing

2205 duplex stainless steel is widely used in nuclear power,petroleum and chemical industry because of its excellent weldability,comprehensive mechanical properties and corrosion resistance.With the advantages of high forming efficiency,low cost and good flexibility,wire and arc additive manufacturing technology has been tried in the manufacture of some 2205 duplex stainless steel structures.However,in the manufacturing process of wire and arc additive,thermal cycle and unreasonable process parameters will have a negative impact on the microstructure of 2205 duplex stainless steel,and then affect the performance of the forming specimens.Therefore,in this thesis,based on the cold metal transfer welding arc as a heat source of additive manufacturing system,the manufacturing experiment of 2205 duplex stainless steel wire and arc addictive is carried out,and the microstructure distribution,microhardness,tensile properties and corrosion resistance of the forming part are studied,and the relationship between the forming parameters(wire feeding speed,stacking speed,interlayer waiting time,additive path)and the microstructure distribution,mechanical properties and corrosion resistance is discussed.Firstly,the influence of process parameters on the forming process of different kinds of samples(single-layer single-pass,multi-layer single-pass and single-layer multi-pass)is studied.The results show that the forming size of single-layer single-pass samples is proportional to the wire feeding speed and inversely proportional to the scanning speed,is also applicable to multi-layer single-pass samples.When the overlap ratio?=1/3,the surface flatness of the single-layer multi-pass samples is good.With the increase of heat input and the change of heat dissipation conditions,the surface quality of multi-layer single-pass forming parts gradually deteriorates,it is also found that the forming quality of the samples can be improved by using reciprocating addition and adding interlayer waiting time.The optimum processing parameters were obtained in the range of wire feeding speed=65-75mm/s,scanning speed=5-7mm/s and interlayer waiting time=30-90s.Secondly,the microstructure distribution and phase composition of multi-layer single-pass forming parts in BD(Building Direction)and ND(Normal Direction)direction are analyzed by various analysis methods.The results show that the remelted zone and the non-remelted zone are alternately arranged inside the sample in the BD direction,and the microstructure in the bottom area is acicular widmanstatten austenite and fine dendrite,the middle region is transformed into strip austenite and dendrite,and the top region is coarsely austenite and columnar dendrite,and the?-Fe content and average grain size increase gradually.In the ND direction,the core is columnar equiaxed crystal,the grain size is small,the?-Fe content is more,the outside is dendrite and widmanstatten structure,the size is bigger,the?-Fe content is more.The precipitation of non-?phase and Cr₂N phase in the samples is analyzed by SEM,XRD and EBSD,and there are many strong texture orientations in the forming part,which result in lower tensile strength and higher elongation in the BD direction,while the tensile properties in TD(Transformation Direction)direction are opposite,the tensile properties show obvious anisotropy,and the tensile test samples in different directions show ductile fracture.It is also found that with the increase of heat input,the grain size and the content of?-Fe increase,which decrease the microhardness and tensile strength,but increase the elongation.Although the interlayer waiting time can improve the mechanical properties of the material,its influence on the mechanical properties of the forming part is less than the wire feed speed and the scanning speed.Finally,the effects of the two optimized parts(x path and y path)on the microstructure distribution,alloy element distribution,phase composition,mechanical properties and corrosion resistance of the multi-layer multi-pass parts are investigated.The results show that the ferrite content of the X path sample decreased from 29.74%at the bottom to 17.42%at the top,and that of the Y path sample decreased from32.56%at the bottom to 22.16%at the top,the microstructure distribution and phase ratio of Y path are more uniform than that of X path,and the grain size of Y path is smaller.The average tensile strength of Y path specimen is 10-30MPa higher than that of X path specimen.The pitting potential of Y path is 0.1V higher than that of X path,and the self-corrosion potential is 10-30mV higher,showing better corrosion resistance.Finally,Y path is determined to be the optimal additive path.