| In this paper,316 L austenitic stainless steel and 2209 dual phase steel were used as experimental materials,and CMT + P-MIG and CMT low heat input,double side auxiliary compensation gas protection and other process modes were used to carry out arc deposition additive manufacturing process experiments,focusing on the influence of different heat input on the microstructure evolution and related properties of stainless steel components along the deposition direction.A method of analyzing the appearance of the parts by using the continuous width and eccentricity curves is proposed.The concepts of effective deposition rate and effective deposition rate per unit work are used to compare and analyze the deposition efficiency of the parts under various process conditions;In this paper,the double wire process is used to explore the process of manufacturing functionally graded materials with dual phase steel arc additive.The main contents of this paper are as follows(1)Cold metal transfer + pulse MIG welding(CMT + P)process was used to carry out single pass multi-layer deposition experiments of 316 L stainless steel wire with different line energy and optimization experiments of interlayer residence time with different low line energy.The microstructure evolution mechanism and property change rule of 316 L stainless steel additive made by CMT + P process were analyzed.The results show that with the increase of linear energy,the strength of the deposited parts decreases,and the tendency of material peeling and crack initiation in the micro region of the sample increases obviously,which worsens the microstructure and increases the risk of brittle fracture.The microhardness of the bottom,middle and top regions of the sample on the center line of the cross section fluctuates along the direction of deposition and construction,and first decreases and then increases.The content of Cr and Mo in ferrite is higher than that in austenite,while the content of Ni is lower than that in austenite.Cr and Mo can promote the formation of ferrite,while Ni is on the contrary.During solidification,Mo,Cr and other alloying elements segregate to liquidus and Ni to solidus.The continuous deposition with too low linear energy will cause bad deposition defects and seriously affect the appearance of the molded parts.The application of intermediate residence time process can reduce the overall heat accumulation and interlayer temperature of the deposited parts,weaken the interaction between layers,and improve the size consistency and mechanical properties of the cross-section edge.(2)316L straight wall components were prepared by cold metal transition(CMT)process under the conditions of single pass continuous deposition and different interlayer residence time,respectively.The microstructure,element distribution and evolution mechanism of different areas of the deposited samples were studied by SEM and EDS.the forming properties of arc deposition parts were studied by continuous eccentricity method.The corrosion resistance of the deposited parts in different regions along the construction direction was analyzed by electrochemical experiments.The results show that the alloy in different regions solidified in the form of austenite ferrite(AF).The SEM morphology of solute atoms varies with the diffusion degree in different regions.The austenite dendrites in the top region are etched deeper than those in the bottom and middle regions,while the ferrite at the grain boundary becomes thicker and higher than that of austenite grains.The high temperature in the continuous deposition process can promote the formation of oxides.There are a lot of intermetallic compounds precipitates in the upper part of the deposition,which leads to the decrease of tensile strength and microhardness along the direction of construction and then increase.The relatively low dislocation density and the number of grain boundaries can form stable passivation film,and the corrosion resistance of the middle part of the arc deposition wall is the best.The high consumption of chromium atoms and the peeling of materials in the top region lead to the weakest integrity and the lowest corrosion resistance of passivation film in this region.The continuous eccentricity fluctuation of the cross section of the deposited parts is smaller than that of the 60 s interval residence time,while the deformation of the workpiece increases the cumulative deviation of the transverse dimension during the longer stay time.(3)A new method of bilateral auxiliary gas compensation is proposed and designed.The action mechanism of gas compensation jet in the deposition process and its influence on the microstructure and properties of the deposited parts were studied by comparative experiments.The forming experiments of dual phase steel(2209-DSS)under low,medium and high current conditions and different residence time between layers were carried out.The results show that the effect of gas flow strengthening on the stirring and rapid supercooling of molten pool is compensated to refine the grains.The strong cooling effect of protective air flow inhibits the precipitation of Cr,Ni,Mo and other corrosion resistant elements in the solidified alloy,and improves the pitting resistance,corrosion resistance and room temperature tensile strength of the deposited parts.Due to the great undercooling in the bottom area of DSS deposition parts,the high solid solubility of alloy elements is retained,and a large number of adherents and precipitates are produced in the friction and wear process to improve the wear resistance;The wear resistance in the middle area is the lowest,and the material peels off a lot;The disappearance of arc heat source and gas convection heat transfer promote the wear resistance of the top layer to rise.The results show that the higher the heat input is,the smaller the eccentricity of the sample is,and the better the verticality of the wall is,which indicates the shape correction ability of the auxiliary gas compensation.DSS deposition should avoid a long inter layer residence time of more than 60 s,while the inter layer waiting time of 20 s can obtain better comprehensive performance of tensile strength and elongation.(4)The influence mechanism of CMT and CMT + P processes on 2209 duplex stainless steel formability and product performance was studied.Through the comparison experiment of316 L single and double wire in CMT mode,the advantages of double wire deposition process are proved from many aspects such as deposition efficiency.The optimized process parameters were used to shape the stainless steel parts with a certain outline size.The fabrication experiments of 316 L stainless steel and 2209 dual phase steel were completed.The high frequency and high stability of droplet transfer ensure the deposition process of CMT mode with low heat and no spatter,and obtain better quality and deposition efficiency than the process with pulse current.The impact and stirring of double arc on the molten pool can break up the columnar and dendrite in the molten pool,inhibit their growth and promote non-uniform nucleation.The difference of tensile strength between horizontal h-direction and vertical vdirection in the middle of double wire deposition is smaller than that of single wire deposition.The double arc with lower electric heating concentration reduces the segregation of low melting point impurities in the grain boundary region,which makes the corrosion resistance of the parts better than that of the single wire and single arc deposition parts.Because the dynamic viscosity of 2209 dual phase steel is lower than that of 316 L austenitic stainless steel before 1457 ?,the former has better spreading and fluidity at high temperature,which makes its deposition formability better than the latter.The results show that the chemical composition and microstructure of the alloy can be directly controlled by changing the ratio of wire feeding,and the microstructure evolution,mechanical properties and electrochemical corrosion characteristics of the alloy can be changed. |
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