Research On The Welding Operation Performance Of Basic Mixture Gas-shielded Flux Cored Wire

Flux cored wires are the most attractive new welding materials with the fastest developing speed in recent years. In order to improve the welding operation performance of basic flux cored wire, the paper has modified the present slag system and developed a new slag system for mixture gas-shielded flux cored wire, i.e. MgO-fluoride-SiO₂-TiO₂ slag system. The paper has carried on systematic research and discussion around slag system composition influences on droplet transfer formations, welding arc stability, slag covering ability and detachability of the flux cored wire.The effects of slag system composition on droplet transfer formations of flux cored wire and welding spatter were investigated by high-speed photography, by collecting droplets in a water through and test of spatter. The results showed that when MgO was less than 25%, the droplet transfer was steady with relatively small molten droplets and welding spatter was smaller too. Replacing a part of CaF2 with Na2SiF6 could reduce welding spatter with thinning molten drops. But when the Na2SiF6 was more than 12%, it would increase the welding spatter.The arc voltage and welding current was recorded synchronous with the software Lookout Weldoffice2000 which matched with the welding machine, and then the arc voltage and welding electric current oscillogram were produced according these data. At the same time, the electric arc shape could be observed through the high-speed photography. The effects of slag system composition on welding arc stability of the flux cored wire were therefore studied. The results showed that when MgO was about 22%, CaF2 was 6% and Na2SiF6 was 9%, the welding arc stability was well.The paper has investigated the slag system composition influences on slag covering ability and slag detachability by slag covering ability evaluating and slag detachability testing, and established slag detachability mathematical model. The results showed that when the contents of MgO was 22%²5%, SiO₂ was5%⁷%, fluoride was about 15% and TiO₂ was 13%¹5%, the slag was covered well and it was easy to take off. In addition, the paper has analyzed the microstructures of slag, the inner surface structure of slag and the characteristic of slag fracture. The results showed that it was benefit for the slag detachability when the microstructure of slag was coarse, the second phase of microstructure presented strip-shaped distribution, and the slag structure was compact, and, contrariwise, the slag detachability became worse.Finally, the paper has acquired the slag system composition for the flux cored wire with favorable welding operation performance, i.e. MgO was 22%²5%, CaF₂ and Na₂SiF₆ were15%, SiO₂ was 5%⁷% and TiO₂ was about 15%.