Study On High-carbon Hardfacing Welding Twin Electrode

Twin electrode arc welding is an innovative welding technology. During welding, twin core welding-wires link different power poles respectively, which means that it is unnecessary for the workpiece to connect power. In this case, electric arc can be formed between the two parallel insulated ends of core wires, and the parent material is melt by fused drops. This new welding method has many obvious advantages including high cladding efficiency, low dilution rates energy saving and smaller deformation to the workpiece. Based on aforementioned advantages of twin electrode arc welding, it is of great practical significance to apply it on hardfacing welding. In this paper, it is the first time to synthesize TiC-VC hardfacing coating on Q235 steel through metallurgy interaction in innovative twin electrode welding arc. Insulativity of twin electrode had been investigated and the microstructures of hardfacing coating was also characterized in order to study the application of twin electrode on the hardfacing welding.The insulativity of high-carbon hardfacing welding twin electrode related to the application of twin electrodes on the hardfacing welding. The results showed that the major factors which affected the insulativity of high-carbon hardfacing welding twin electrode were the sizes of conducting particles, the space between the two wire cores, the types and mass of water glass, and the good insulating parameters were that the sizes of electrode graphite and other conducting particles were 60～80 mesh, the space between the two wire cores was 1.6 mm, the right mass ratio of electrode covering and sodium silicate.When the contents of graphite, ferrovanadium and ferrotitanium were 10%-15%,15%～25%and 18%～20%in twin electrode coating under 45～ 50% gravity coefficient of coating, the welding current and arc voltage were 180～200A and 41～45V, the welding line exhibited good appearance.The microstructures and abrasion resistances of hardfacing coating were also analyzed. The results showed that due to the unique structure of the twin electrodes, the ferrotitanium in coatings tended to oxidation, which impacted seriously on the transition of Ti element to hardfacing coating. Because the coating between the two welding core wire generated gas which decreased the transfer coefficient of some active element such as Ti due to its strong oxidation activity. As a result, more titanium oxide could be found in the slag. In addition, the amount of TiC increased, when the coefficient of coatings inclined.Some VC particles were formed with the addition of ferrovanadium, and there bulk and rodlike VC particles distributed along the grain boundaries. The quantity or size of carbides changed in different layers. Gravity coefficient of coating affected the formation of cabides, transfer efficiency of ferroalloy and quantity of carbides increased in high gravity coefficient of coating of twin electrode. The microstructure of matix was low carbon martensite and residualaustenite, and the hardness of layer was over HRC55. Moreover, welding technological properties went bad in too much high gravity coefficient of coating of twin electrode. The result showed that 70% was the proper gravity coefficient of coating for twin electrode.When ferroniobium was added in the electrode coating, the hardfacing coating consisted of carbides, and the center of carbide particles mainly contained Nb, Ti and C elements while most of V element exited on the edge of carbide particles.