Study On Twin-wire Indirect Arc Welding Surfacing Technology And Corrosion Resistance Of Surfacing Layers

Twin-wire indirect arc gas shielded welding(TWIA)is a new welding technology,in which twin wires connect negative and positive electrodes of a direct current power source and a work piece is used as an independent unit.The arc burning between twin wires,the heat generated by the arc is mainly used to melt the wires and only a little used to melt the workpiece.This new welding method has the advantages of high efficiency,energy saving and small fusion ratio,has the good prospects for engineering application.In this paper,the austenitic stainless steel was surfaced on the Q235 by twin-wire indirect arc welding,with applying the external magnetic field or TIG hybrid heat source.The arc shape and droplet transfer were captured by high speed camera.The microstructure and morphology of the surfacing layers were analyzed by means of optical microscope(OM),scanning electron microscopy(SEM)and energy dispersive spectroscopy(EDS).The effect of welding parameters,external magnetic field and TIG hybrid heat source on the welding process,intergranular corrosion resistance and pitting corrosion resistance were studied by potentiodynamic testing.Twin-wire indirect arc shape was captured by high speed camera is similar to a basket.The droplets are composed of two strings of anode and cathode droplets.The welding current is greater,the angle between two strings of droplets is smaller.The applied magnetic field can change the arc shape,the contractive arc with X positive direction magnetic field,the elongated arc with X negative direction magnetic field.The elongated arc can increase the workpiece heat input.The arc is deflected on the YOZ plane with Y direction magnetic field and on the XOZ plane with Z direction magnetic field.The appearance of surfacing layers obtained by twin-wire indirect arc welding was observed.It is found that the larger the welding current is or the larger the angle between the wires is,the better the surfacing layer formation is.When the angle is 30°and the welding current is more than 160A,the appearance of surfacing layers is good.X negative direction magnetic field and TIG hybrid heat source could improve the surfacing layer shape.The TIG hybrid heat can increase the penetration of the surfacing layers.The microstructure and ferrite content of the surfacing layers prepared by twin-wire indirect arc welding were analyzed.The surfacing layer solidification mode with ER308 wire by twin-wire indirect arc welding is FA.And the ferrite content also increases with the smaller angle,X negative direction magnetic field or TIG hybrid heat source.The shape of ferrite in the surfacing layers is mainly the spot and worm with 30° angle between the twin wires and it exists as skeleton and strip with 70°angle.The intergranular corrosion testing results by electrochemical potentiodynamic reactivation show that the surfacing layers prepared by twin-wire indirect arc welding are very good.When the angle between the twin wires is 30°,the reactivation rate Ra decreases firstly and then increases with the increasing of welding current.The applied X negative direction magnetic field and the TIG hybrid heat source have some influence on the intergranular corrosion resistance of the surfacing layers,but still keeping good intergranular corrosion resistance.When the angle between the twin wires is 70°,the Ra values increase slightly with the welding current increasing or the welding speed decreasing.The intergranular corrosion resistance of the surfacing layers by twin-wire indirect arc welding is better than that of MIG welding,it is slightly less than 304 stainless steel base metal,but far better than 304 stainless steel surfacing layer.The pitting corrosion test results show that the pitting potential decreases with the angle increasing,the welding speed decreasing,the welding current increasing,the applied magnetic field or the TIG hybrid heat source,which is related to Chromium depleted zone and the welding residual stress affected by cooling rate of deposited metal.The pitting corrosion resistance of the surfacing layers by twin-wire indirect arc welding is better than MIG welding.The metastable pits emerge on the surfacing layers prepared by twin-wire indirect arc welding before pitting.Some metastable pits are passivated due to insufficient conditions,and some are converted to steady-state pits.There are hole covers above the steady state corrosion pits,which is similar to the shape of lace.