Research On Nickel-based Pulsed MIG Surfacing Weld Seam Forming Law And Microstructure And Properties Of Surfacing Layer

The garbage combustion boiler will release a lot of corrosive gases such as HCl,HF,S0₂ and so on.These corrosive gases corrode the boiler water-cooled wall tube row seriously,thus bringing great threats and losses to normal production operations.A layer of corrosion-resistant nickel-based surfacing layer is prepared on the surface of carbon steel by surfacing technology,which can significantly improve the corrosion resistance of the surface of the water-cooled wall pipe row,ensure the safe and stable operation of the pipe row,and effectively reduce the waste incinerator rework.Probability,bring huge economic benefits to production.In this paper,direct current pulsed MIG welding and alternating current pulsed MIG welding are respectively used to overlay Incone1625 alloy on Q235 carbon steel surface.The forming rules of overlaying layer welds under different process parameters are studied.The microstructure and interface changes of overlaying layer are observed by metallographic microscope.The element distribution of overlaying layer is studied by EDS and XRD.The relationship between element distribution and overlaying layer properties is established.The corrosion resistance of overlaying layer under the two methods is compared and analyzed according to electrochemical polarization curves.The results show that when DC pulsed MIG welding is used,when the welding current is 240A,the welding speed is 1.2m/min and the welding torch swing width is2mm,the surfacing layer with metallic luster and no spatter can be formed.Under this condition,the dilution rate of surfacing layer is 17.2%.Using AC pulsed MIG surfacing,under the same welding current and welding speed,when the EN ratio is 0,a well-formed surfacing layer can be obtained,and the dilution rate of the surfacing layer is9.3%.The microstructure of Inconel625 surfacing layer is composed of planar crystal,cellular dendritic crystal,cellular dendritic crystal and fine equiaxed crystal.The grain size will increase with the increase of heat input during welding.MC and Laves phases are distributed in the intercrystalline of the surfacing layer.The content of each element in the overlaying layer has obvious mutation at the part of the fusion line,while the content of Fe element in the overlaying layer is relatively low and increases abruptly after passing through the fusion line.The Fe content of the surfacing layer near the surface area using DC pulsed MIG welding is about 10.9%,while the Fe content of the surfacing layer near the surface area using AC pulsed MIG welding is about 3.6%.The comparison shows that the dilution ratio of the surfacing layer obtained by AC pulsed MIG welding is lower.The hardness of the surfacing layer is higher than that of the substrate.Hardness of the surfacing layer is between 220HV and 280HV,and hardness of the substrate material is between 140HV and 180HV.The hardness value at the bottom of the overlaying layer is the largest.When the welding torch swing width decreases,the welding speed decreases,and the welding current increases,the hardness of the overlaying layer increases.Under the same welding current and welding speed,the corrosion current of AC pulsed MIG welding is-210m V and that of DC pulsed MIG welding is-502m V.The comparison shows that the corrosion resistance of AC pulsed MIG welding is better than that of DC pulsed MIG welding.