Study On Process And Performance Of Nickel-Based Alloy Low-heat Input Arc Surfacing Welding

Nickel-based alloys have excellent high temperature performance and excellent corrosion resistance,and have been widely used in aerospace,nuclear power,petrochemical and other fields.By means of surfacing welding technology,a layer of nickel-based alloy on the surface of steel components can greatly improve the high temperature and corrosion resistance of the components and expand its application fields and occasions.However,it is very important to study the low-heat input arc surfacing welding process and properties of nickel-based alloy because the high heat input can easily lead to large stress deformation and crack defects.In this paper,cold metal transition?CMT?and Plasma arc with low heat input were used as heat sources for surfacing of Inconel625alloy on 304 stainless steel surface.The influence of process parameters on the forming characteristics of the surfacing layer was studied,and the microstructure characteristics,hardness distribution and bonding properties of the surfacing layer with low heat input were analyzed.Both the CMT and Plasma Inconel625 alloys provide a beautifully formed and well developed surfacing layer.Using stem elongation is 15 mm,heat input is 4.5 kJ/cm to 60°CMT welding forming,welding Angle is better,and Plasma welding using heat input is12.3 kJ/cm,wire feeding speed is 3.5 m/min when access to forming good surfacing layer.The CMT surfacing layer is only able to obtain better spallation at higher heat input,but its dilution rate does not change much.However,Plasma surfacing has better spallation and significantly higher dilution rate with the increase of heat input.The multivariate linear regression equations for the establishment of CMT and Plasma surfacing process parameters and dilution rate were:Y_CMT=-1.10328-6.6187X₁+1.6387X₂-0.04748X₃,Y_Plasma=6.22935+0.00108X₂-9.0366X₄.The structure of Inconel625 nickel base alloy CMT and Plasma surfacing layer is composed of columnar crystal and columnar dendrite.The microstructure of the surfacing layer is all composed of?-Ni substrate phase and NbC,in which NbC is distributed as fine particles or strips along columnar grain boundaries,and its size is about 0.6?m under low heat input.The distribution of Ni,Cr and Mo elements in the CMT and Plasma surfacing layers was relatively uniform,while the C,Nb and Fe elements presented obvious grain boundary segregation.In addition,the fusion zone of the three elements Fe,Ni and Mo from the substrate to the surfacing layer fluctuated greatly.The mean hardness values of the CMT and Plasma surfacing layers are 266 HV and265 HV,respectively,and both of them are greater than the hardness values of the matrix.The highest hardness value is at the fusion zone,which is about 280HV.The CMT surfacing layer and 304 matrix bond interface have a tensile shear strength of 602 MPa,and Plasma surfacing has a tensile shear strength of 705 MPa.The tensile and shear specimens of CMT and Plasma surfacing show mixed fracture characteristics of toughness and brittleness.Under different thermal inputs,the CMT surfacing layers are all fractured from the bonding interface,while Plasma surfacing has two forms of fracture from the bonding interface and the bonding layer.To sum up,the Inconel625 nickel-based alloy with good spreading,high dilution rate and high interfacial bonding strength can be obtained by using collateral wire Plasma.