Study On Electron Beam Welding Of GH3625/9Cr18Mo Dissimilar Alloys Closed Structure

The GH3625/9Cr18 Mo dissimilar alloys closed structure in the fuel spray nozzle welding component was weld by electron beam.The influence of welding parameters on macro morphology of weld was investigated.The process window was constructed,according to the technical requirements for macro morphology of weld.The phase constitution,microstructure characteristics and composition of various regions in the joint were analyzed with the aid of X-ray diffraction,metallographic microscope,scanning electron microscope and energy dispersive spectrometer,the hardness distribution of the joint was measured by the vickers microhardness and the relationship between microstructure characteristics and hardness was studied.The results show that when parameters used in welding the component are in the process window,a joint satisfied the technical requirements can be obtained by electron beam welding without defects such as undercuts and cracks.With the increase of electron current,the weld penetration increase,while the change of weld width is not significant.With increase of welding speed,the weld penetration and weld width decrease.With the increase of heat input,the melting quantity of both base materials increase.The grain size is not change obviously compared to its base material in the heataffected zone(HAZ)of GH3625,but the number of precipitates decrease.The number of carbides decrease in the HAZ of 9Cr18 Mo under the influence of the welding thermal cycle.The microstructure of weld is austenite and NbC,Cr23C6 particles precipitate discontinuously at the boundaries.The macrosegregation,which leads to the form of element enrichment regions is found in the weld.The transition zones of composition are found in the both side fusion zone.In the fusion zone of 9Cr18 Mo,the microstructure transforms from austenite to martensite.The hardness of weld is 270 HV,which is higher than that of both base materials.The hardness increase along the direction of weld in the HAZ of 9Cr18 Mo,and the highest hardness can reach to 483 HV,but the hardness reduce to 383 HV suddenly in the fusion zone of 9Cr18 Mo.