Viscosity-structure correlation in CaF2-free CaO-SiO2-Al2O3-MnO fluxes developed for submerged arc welding

Thermo-physical properties of selected CaO-SiO 2 -Al 2 O 3 -MnO formulations, developed as potential fluoride-free alternatives to conventional CaF 2 -containing submerged arc welding (SAW) fluxes, were characterised and compared with that of commercial prototypes of SAW fluxes. Structural features of the molten flux were characterized using Fourier Transform Infrared (FT--IR) and Raman spectroscopy techniques. At the same time, viscosity measurements were carried out over the temperature range of 1320 – 1480 °C, on the CaF 2 -free fluxes as well as the commercial prototypes. Viscosity of the proposed formulations was comparable to that of the commercial prototypes, confirming the potential use of the fluoride-free fluxes in submerged arc welding. The results indicate enhanced fluidity in the molten flux, arising from effective depolymerisation of the silicate and aluminate networks. Observations from Raman spectroscopy indicated that the simpler structural units like Q 0 Si were more prevalent in the melt, compared to the more complex Q 3 Si , Q 4 Al and Si-O-Al linkages, within the range of 15 – 20 mass% MnO. Further increase in MnO concentration led to an enhancement in viscosity, possibly caused by an increase in the relative fractions of Q 3 Si , Si-O-Al and Q 4 Al structural units.