Cracking Mechanism And Control Of K418 Superalloy Electron Beam Welding

In this paper,for the problem of poor weldability in the casting superalloy welding process,K418 superalloy is selected as the research material,GH4169 is the filler material,and the formation mechanism of welding cracks of the K418 superalloy welded by electron beam is studied.The K418 alloy welding cracks were controlled by changing the process parameters,using a narrow wire-filled butt joint,and then depositing GH4169,butt joints,and observed the microstructure of the joint,and tested the mechanical properties of the joint.The test found that K418 high-temperature alloy electron beam welding has a high crack sensitivity.During the welding process,there are crystalline cracks in the weld seam and liquefied cracks in the heat affected zone.The test reduces the welding internal stress by changing the process parameters,which can effectively reduce the welding cracks.The optimal parameters obtained were welding speed 600mm/min,electron beam current24 m A,O-scan.Weld cracks are caused by a large amount of carbides and low melting point eutectic between the dendrite axes.The liquefaction cracks in the heat-affected zone are due to the liquefaction of the low-melting eutectic grain boundaries and are generated under cooling shrinkage tensile stress.Precipitation phase ?? exists in the weld of K418 alloy,chromium element is concentrated around the precipitation phase ??,and there are fine carbides at the grain boundaries.The welding speed of 600mm/min,the wire feeding speed of 20mm/s,and the welding seam of the welding seam without welding cracks when the narrow gap of the wire filling is used.Liquefaction cracks in the heat-affected zone still exist,which is due to the greater stress in the welding.The main component phase in the weld is the ?'precipitated phase,the size is only 10 nm,and it is distributed in an oval shape on the matrix.The density is higher.The comparison of the diffraction spot and the PDF card shows that the matrix is ?-Fe0.64Ni0.36.The comparison of the mechanical properties of the joints found that the welds were strengthened due to the small size of the grains and precipitates,the welds had the highest microhardness and tensile strength,followed by the heat affected zone,and the lowest base metal.Compared with the liquefaction cracks in the heat-affected zone,the internal defects of the base metal have a more obvious effect on the material properties.The tensile results show that the weld strength is above1000 MPa,and the base material is only around 800 MPa.The fracture of the base material is mainly brittle fracture,and the elongation of the alloy is only ?=4%.There are a few tough sockets in the fracture of the base material.The cause of fracture is due to internal defects.Depositing GH4169 alloy with K418 alloy as the substrate shows that the alloy is dense and crack-free.The crack sensitivity of the K418 alloy is high,and even with low heat input,micro-cracks may be generated in the heat affected zone.The hardness of GH4169 alloy is the lowest,the hardness of the heat affected zone is the highest,and the hardness of the transition layer is in the middle.The K418 alloy deposited with GH4169 alloy was subjected to electron beam welding to obtain a joint without welding cracks,and the surface was well formed.Analysis of the mechanical properties of the joint revealed that the microhardness of the weld was only 260 HV,and the microhardness of the heat-affected zone of K418 alloy reached 440 HV.In the tensile test,the fracture position is the fusion line position of the GH4169 alloy weld,the tensile strength is about800 MPa,there are a large number of tough sockets in the fracture,and the tensile fracture is mainly ductile fracture.