| In the field of physics and nuclear technology, welding of dissimilar-metals onniobium alloy and stainless steel have always been a difficult and hot problem，highlyconcerned. In this paper, based on the theory of electron beam welding and forging,electron beam welding and canned forging technology are applied to achieve acomposite bonding technology of stainless steel and high-purity niobium. Takeadvantages of high vacuum in the electron beam welding process and high-qualitywelding with high purity, preparing for the subsequent canned forging process Thisspecial joint of stainless steel and high-purity niobium has been rarely reported，whichis welded by electron beam welding and canned forging technology.The results of thermal effect are simulated by MARC finite element analysissoftware during the electronic beam welding90mm×80mm3-dimensional finiteelement model is used for this study. The Gaussian surface heat source and a rotationalparaboloidal heat source have been established so as to simulate the results of thermaleffect and stress field during electron beam welding process. Weld has obvious meltingdepth and nail tip morphology, and the characteristic of distribution of temperature fieldis the same with the molten pool in vacuum electron beam welding process. Comparingthe simulating bead geometry with The actual one，both of them are very similar, anderrors of width and depth of molten pool are shown extremely small; direct couplingmethod is employed to analyze distribution of stress state and residual stress state,simulation results show that residual stresses near the weld area is mainly the tensilestress in the welding process, which can cause deformation and cracking of welding,residual stress distribution after welding does not cause cracking。it is mainly residualcompressive stress, essentially unchanged in high-purity niobium and stainless steelconnection interface。residual stress exists in the axial direction, the axial shrinkageoccurred after welding，Providing pre-tightening force for subsequent trials，in favour oftight junctions of high-purity niobium and stainless steel.The jointing mechanism is investigated between316L stainless steel andhigh-purity niobium during canned forging technology, and the result shows that threelayers exist at the interface; as the holding time increases, the diffusion layers increasegradually at the interface, the Fe, Cr and Ni elements in the stainless steel near the Nbside diffuse into the high-purity niobium, and the Cr element whose content is morediffusions to diffusion layers, but the content of Ni is not obvious; at the reaction layernear the stainless steel, the Nb element diffuse into the stainless steel easily and the diffusion layer is connected in good quality.Different positions of the inhomogeneous deformation and microstructure incoincidence with the basic law of the forging process. However, cracking took place atthe welding joint during the forging process. Analysis indicates that the diffusion layerendures large strain rate when the compression and the rate of strain is very large, thusthe sample have no time to deform. And violent collision occurred between the two basemetals, stress concentration was induced due to the obstructing effect of the phaseboundaries on the grain boundary slips, and thus cracking occurred.This experiment and experience has shown that welding of high-purity niobiumand316L stainless steel is theoretically feasible in the process of electron beam weldingand canned forging. There are many factors that affect the joint performance, thus afurther investigation should be conducted to explore this new manufacturing technologyand study the effect of various process parameters on the microstructure performance,and the results of the experiment will provide instructions to the academic investigationof this technology. |
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