| Traditional Cr-Ni austenitic stainless steel has low strength and poor performance in extreme environments or special fields,and the existence of nitrogen porosity reduces the mechanical properties of high nitrogen steel additive.316L austenitic stainless steel wire is used as the base metal,and the melting electrode pulse MIG arc is used as the heat source to melt316L welding wire.Manganese nitride powder was added to 316L molten metal through a by-pass powder feeding device.The process stability test of high nitrogen austenitic steel augmented、effect of process parameters on surface morphology and macroscopic size process test by fusion electrode wire-powder composite additive manufacturing was carried out,The regression model between the process parameters and the macroscopic size of the high-nitrogen austenitic steel was established.The variation rules of microstructure,nitrogen content,micro-hardness,tensile properties and impact properties of the high-nitrogen austenitic steel were studied under different process parameters.It provides theoretical basis and engineering application reference for wire powder composite arc additive high strength and hard austenitic steel.Firstly,the influence of by-pass powder feeding parameters on the stability of wire-powder composite additive process was analyzed,The stability of melting electrode arc additive droplet transition has a great influence on the forming of the additive.The continuous blowing force of the powder feeding air will change the droplet force.The influence of different gas flow rate and position on droplet transition stability was studied.It is found that the powder flow deflects the droplet towards the direction of additive,drop transition mode transition from shoot drops into a short circuit transition,also increase with the distance between feeding tube and wire,the size of the drop decreased gradually,the drop is affected by the air flow is reduced,in a single feeding tube 9 mm away from the welding wire and double feeding tube 3 mm away from the wire can drop a stable transition.The effects of current,deposition speed,powder feeding amount,gas flow rate and powder feeding position on the surface morphology and macroscopic size of the wire-powder composite additive were further studied.The well-formed process parameters are obtained.Too much electricity or sedimentary speed too slow will wrinkle the deposited metal surface;Feeding position on the back can make the deposited metal surface uneven,feeding gas flow is too small will cause the double send powder tube feeding out unevenly,deposited metal tilt to one side;Multi-layer stacking,single powder feeding tube will make the metal surface bulge,large holes and other defects.When the distance between the double powder feeding tube and the welding wire is 3mm,the deposited metal is well formed;The regression model between the process parameters and the macroscopic size of the wire-powder composite additive was established through the well-formed process test,which can well predict the change of the size of the deposited metal by the wire-powder composite additive.On the basis of the above process tests,the forming part of high nitrogen austenitic stainless steel was tested by wire-powder composite arc additive.It was found that the pure austenite structure appeared in Cr-Ni stainless steel by adding manganese nitride powder in the process of wire powder composite additive.The central area of the additive is composed of fine austenitic equiaxed crystals,cellular crystals and dendrites.The maximum nitrogen content of the additive can reach 0.31%,the hardness of Cr-Ni stainless steel is increased from 165-180HV to 190-230HV,the tensile strength of Cr-Ni stainless steel is increased from 560-580MPa to 650-685MPa.The elongation after fracture did not decrease,and the impact toughness increased from 154-163J/cm~2 to 188-219 J/cm~2.The test results show that the wire-powder composite arc additive can produce high strength and impact resistance additive. |
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