Study On The Effect Of Transition Layer On Laser Welding Of Cemented Carbide And 45 Steel

Cemented carbide often needs to be connected with steel in practicalapplication.Thefusion welding of cemented carbide and steel has always been a thorny problem of cemented carbide connection.The most important problem is the formation of harmful phases by metallurgical reaction during welding and the cracking caused by large residual stress due to the difference of linear expansion coefficient.In recent years,with the development of precision and advanced industry,laser welding has become a widely used welding method.More and more scholars try to use laser welding to realize the connection between cemented carbide and steel,but most scholars use electroplating or preset intermediate layer,which has some drawbacks.In this paper,ENi102 electrode,Z408 electrode and Fe55NiC wire are selected to pre-surfacing the transition layer on 45 steel surface by arc welding,and then laser welding with YG20.Scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),hardness test and bending mechanical properties test are carried out on the laser welded joint.The effects of transition layer on laser welding of cemented carbide and steel are systematically studied,and the results are obtained.The optimum laser welding process for the optimum transition layer was obtained.The main results are as follows:harmful brittleη_phase and fishbone eutectic carbides were formed at the interface between YG20 cemented carbide and 45 steel without transition layer during direct laser welding,and the loss zone of Co with a width of about 15 um was formed on the side of cemented carbide,resulting in weaker joint performance;after surfacing transition layer on 45 steel surface,the formation of brittleη phase_was inhibited,and the carbide dispersed in a dot shape.There is no obvious Co loss zone on the cemented carbide side,and the hardness of the weld metal is obviously lower than that of the weld without transition layer.In the transition layer of the same welding material,the content of Ni in the two layers is higher than that in the one layer,and the carbide content is less than that in the one layer.There will be a small number of Co loss holes near the interface of the one layer transition layer cemented carbide,while there are almost no Co loss holes on the side of the two layers transition layer cemented carbide.The bending strength of the two layers of Ni102 transition layer joints is lower than that of the joints without transition layer,because the linear expansion coefficient of the two layers of Nil 02 transition layer is the Large,so it can not play the role of relieving welding residual stress,but make the residual stress larger and lead to low mechanical properties.The bending properties of the other transition layer joints are greatly improved compared with those without transition layer,because the linear expansion coefficients of other transition layers are between YG20 cemented carbide and 45 steel,and the closer the linear expansion coefficients of transition layer are to cemented carbide,the better the stress relief effect and the higher the bending strength of the joints;the mechanical properties of the two-layer Fe55NiC transition layer joints are the best,because the two-layer Fe55NiC transition layer joints have the best mechanical properties.The coefficient of expansion is closest to that of YG20 cemented carbide,which can relieve the residual stress to the greatest extent.The optimum laser welding parameters of the joint with two layers of Fe55NiC transition layer were obtained by orthogonal test:laser power 3.7 kW,defocus+4 mm,welding speed 1.5 m/min and laser defocusing side 0.25 mm.