| Underground space will be fully exploited in the 21st century.To be mentionable,the shield machine plays an irreplaceable position as a significant tool of underground engineering.The connection between the Co-based WC blade and the steel knife in the cutter tooth is evolved to the key to the tunneling capability of cutter tooth of the shield machine as an important component of the shield machine.In China,the silver-based brazing filler metal induction brazed joint is mostly used for the shield machine.In this way,the cost is quite high.Furthermore,its property cannot be easily ensured due to the occurrence of leakage and opening during welding.In this paper,interface structure,hardness distribution and shear property of the brazed joint is studied according to the vacuum brazing made for Co-based WC/40Cr steel and the influence of brazing layer structure on mechanical property and deformational behavior of the brazed joint is discussed in a bid to provide theoretical basis for welding structure design of the shield machine's cutter and extending its service life.According to the result,it could be found that the shear strength of its joint is stronger than that of induction brazed joint when CuMnNi+CuMnNi brazing layer is used for Co-based WC/40Cr steel conventional vacuum brazing.225.5 MPa shear strength could be obtained within 20 min under thermal insulation at the brazing temperature of 925?.However,if compared to the imported joint,the plasticity of conventional vacuum brazed joint is not desirable.Since the Ni net added to the imported brazed joint can effectively increase the weld width,and the Ni net can better relieve the residual stress,the imported joint has better plastic property.The property of the brazed joint is obviously improved by using the vacuum brazed Co-based WC/40Cr with CuMnNi+304B+CuMnNi brazing layer structure.The property of the joint is mainly under the control of welding temperature.When brazed at the temperature of 925?,unexceptionable property of the welded joint could be obtained.Its shearing curve can be divided into three stages such as elastic&plastic deformation and fracture.Its shear strength can reach 250 MPa.With the rising brazing temperature(975?),the element diffusion of the welded joint interface is more sufficient.Meanwhile,the shear strength of the brazed joint will be arrive at 375 MPa.However,due the occurring of dissolution at the interface of 304 stainless steel and brazing,the structural property of the compensated net is reduced.Meanwhile,the ability to mitigate the residual stress of the joint is also reduced.Therefore,the plastic property of the brazed joint is reduced by the joint brazed at the temperature of 925?.Along with the further increase in brazing temperature(1000?),the element diffusion of the joint interface is more drastic.A lot of WC particles are resolved.Elements Fe and Co are collected at interface of Co-based WC and brazing,and the phase content of fragile ? is increased.However,the property of the joint is deteriorated.The fracture position of the vacuum brazed joint of Co-based WC/40Cr steel with CuMnNi+304B+CuMnNi brazing layer structure is consistent with the lower position of joint interface hardness.When the brazing temperature was 925?,the joint was broken on the 40Cr side.At higher brazing temperatures(975?,1000?),the joints all fractured on the Co-based WC side.Exceptionable plasticity of welded joint could be obtained by using vacuum brazed Co-based WC/40Cr steel with CuMnNi+304B+CuMnCoZn brazing layer structure.Along with increasing shear deformation,joint will be fractured when the shear strength reaches 285 MPa.after elastic deformation.The shear stress is reduced until the joint is completed fractured along with slight reduction of shear deformation. |
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