Nano-strand formation in CaF2-SiO2-Al2O3-MgO flux reacted at 1350 °C with Al-Ti-Fe powder : SEM analyses and gas reaction thermochemistry

Abstract

Nano-strands form in fluoride-based slag during submerged arc welding (SAW) due to the re-condensation of gas species formed at high temperatures in the arc cavity. The SAW process is complex due to gas-slag-metal reactions occurring across several reaction zones and over a wide temperature range. This complicates research on specific process aspects, such as gas formation from the oxy-fluoride slag. The objective of this work is to demonstrate that oxy-fluoride nano-strands form in molten flux reacted with Al-Ti-Fe metal powder, even at the low temperature of 1350 °C, which is much lower than SAW process temperatures of 2000 °C–2500 °C. Energy dispersive X-ray spectroscopy (EDS) analyses and thermochemical calculations provide insights into formation reactions in nano-strand formation. Thermochemical analysis clarifies the role of Al in shifting the gas phase composition to limit Ti-fluoride loss to the gas phase. These results motivate the study of gas phase reactions at relatively lower reaction temperatures to gain insights into SAW flux behaviour.