Microstructure And Properties Of WC-Co And Steel Joints Using Ni-Fe-C Wire

WC-Co cemented carbide has a high hardness, wear resistance and can be used at elevated temperatures; it therefore is used widely in industry. But cemented carbide products have some drawbacks such as limited size, simple form, high cost, poor toughness, etc., which limit its application to some extent. Connecting cemented carbide to steel has already become a main method to solve these problems.The purpose of the present work was to investigate the tungsten inert gas arc welding technique (TIG) of WC-Co cemented carbide and a medium carbon steel (Fe-0.45C wt.%). Six kinds of filler wires with different contents of Ni-Fe-C were designed in this experiment. By means of hardness testing, bend strength testing, X-ray diffraction (XRD), scanning electron microscope (SEM), and transmission electron microscope(TEM), the microstructure, phase and bending strength of the welded joints was investigated. Great emphasis was paid on the type and forming mechanism of η phase as well as the influence of wire composition on the structure and properties. The result showed that the η phase distributed at the interface of WC-Co cemented carbide and weld bead was Fe3W3C, which belonged to the type of M6C with FCC type in crystal structure. The reason that η phase formed laid in the C element lacking in system Fe-W-C at the interface of WC-Co and weld bead. It was the existence of the η phase that lowered the bend strength of the welded joint seriously to 0.960GPa. By using Ni-Fe-C alloy with proper carbon content as welding wire, the formation of the η phase could be well restrained and the bend strength of the welded joint could be improved to 1.341GPa. Wire (0.61C-55.29W-39.47C wt.%) was the most optimized filler alloy.