Effect of flux composition on metal transfer characteristics in rutile-type flux-cored arc welding

This study clarified the effects of flux composition on metal transfer characteristics in rutile-type Flux-Cored Arc Welding (FCAW). Seven prototype wires with varying TiO2, SiO2, and CaF2 contents in the flux were tested at three currents (220–280 A) under Ar-20%CO2 shielding. The Droplet Diameter (DD), which is important for arc stability, is proportional to the ratio of the Wire Feed Speed (WFS) and the Metal Transfer Frequency (MTF), which are primarily governed by the energy and force balances, respectively. The WFS depended on the iron content in the flux, was almost independent of the TiO2, SiO2, and CaF2 content, and increased linearly with current. Increasing the CaF2 content reduced the MTF sharply from 86.9 to 34.0 Hz at 220 A due to either the strong recoil pressure caused by vaporization from CaF2 or strong arc pressure by the high specific heat of CaF2 plasma. These pressures pushed the droplet upward, hindering droplet detachment. TiO2 showed a slight increase in MTF with TiO2 content (for example, 162.5 to 170.3 Hz at 280 A). SiO2 showed a significant increase in MTF with SiO2 content, especially at 280 A (170.3 to 222.9 Hz), probably due to slag-metal reactions increasing the oxygen concentration in the droplets, leading to a lower surface tension; the effect is stronger for SiO2 because its basicity lower than that of TiO2. Thus, the flux composition affected the MTF much more strongly than the WFS, so that the DD was inversely proportional to MTF. Consequently, it was found that the DD depended strongly on flux composition through variations in the physical properties.