本文概述了硬质合金的性能特点及其在工业领域中的主要焊接问题，即强度不高，焊接残余应力过大，抗磨耗腐蚀能力差，接头使用寿命偏低等。同时阐述了目前应用于硬质合金焊接的主要方法、工艺要素及相关研究现状，其中包括火焰钎焊、激光钎焊、感应钎焊、微波钎焊、电子束钎焊、真空钎焊、扩散焊等，提出了有待进一步研究的相关问题。结合扩散焊结合致密，强度高，焊接温度低和真空钎焊变形小残余应力小，润湿及化学冶金结合良好的优点，开发出真空复合焊接工艺。本课题研究了YG8与42CrMo的复合焊接工艺（镀层、钎焊工艺、扩散工艺等）对接头力学性能（剪切强度、显微硬度等）的影响。利用扫描电镜、润湿性试验、显微硬度计、万能拉伸试验机、X射线衍射仪、能谱分析仪等测试手段，对复合接头微观组织结构、显微硬度、接头剪切强度、断口形貌特征及接头区的物相成份等进行了较为系统的研究，探讨接头中产生宏观缺陷和微观缺陷的原因。 研究结果表明：当其他参数不变的情况下，纯Ni层厚度为60μm，钎焊温度1045℃，保温时间15min，扩散温度750℃、焊接压力8MPa下保温40min的条件下获得的接头平整美观，没有明显变形，钎缝区过渡均匀，界面结合良好，没有气孔和缺陷，其剪切强度为364MPa，接头区最小显微硬度为HV187。硬质合金中的W元素基本未向焊缝区扩散，Ni、Co、Cu、Zn元素在一定范围内形成固溶体组织，焊后分布在钎缝中。接头剪切断裂多出现在YG8一侧，断裂机制为韧-脆混合型。Ni层能有效地缓解残余应力，但不能完全消除。该工艺将对截齿、钻头和其他切削刀具焊接部件性能的提高具有重要意义。

The characteristics and major welding problems such as low joint strength, large residual stress, low anti-abrasive corrosion ability and short service life in industrial applications of hardalloy were summarized in this paper. Some welding methods that may be used on hardalloy, including flame brazing, laser brazing, induction brazing, vacuum brazing, microwave brazing, electron beam brazing, diffusion welding and so on were reviewed, and the forwarding problems were also pointed out. A new type of composite welding for YG8/42CrMo was developed by combining the advantages that lower welding temperature, higher joint strength of diffusion and lower residual stress, and perfect chemical and metallurgical bond of vacuum brazing using a vacuum furnace. The effect of welding processing parameters such as coating thickness, brazing and diffusion parameters on microstructure and mechanical properties such as the share strength and the minimum microhardness of the joint area were studied in this paper. And the cross-section morphology, fracture characteristic, microstructure, chemical components, elements diffusion, microhardness, share strength, wettability and coating binding ability were studied by metalloscope, X-ray diffraction (XRD), scanning electron microscope (SEM) with energy dispersive spectrometer (EDS), microhardness tester and the universal mechanical testing machine, grid-based method and so on. The defects both in macro and micro formed in the joint were also studied. The study shows that, the best joint was obtained when the thickness of pure Ni layer is 60μm, the brazing temperature maintain at 1045℃ for 15min, the diffusion temperature maintain at 750℃ for 40min under the pressure of 8 MPa. The obtained joint is smooth and good, without obvious deformation and defects such gas holes, inclusions and cracks. The shear strength is 364 MPa, the minimum microhardness of the joint is HV187. The shearing fracture of the joints usually occurs within the hardalloy, which shows that the Ni layer cannot eliminate the joint stress exhaustively. And the fracture mechanism is ductile and brittle type judged by fracture morphology. The composite welding method will improve the joint properties of boring or cutting tools greatly.