Phase chemistry of Submerged Arc Welding (SAW) fluoride based slags

Abstract

Phase chemical analysis of post-weld slags from Submerged Arc Welding (SAW) is applied to explain the chemical function of flux constituent compounds in the welding process. FactSage 6.4 calculations were used to aid in the interpretation of the phase chemical analyses. Five commercial agglomerated fluxes from two suppliers were used. These fluxes cover three types of fluoride based flux classes: Fluoride Basic flux, Aluminate Basic flux and Aluminate Rulile flux. Basic fluxes are based in the SiO2–Al2O3–MgO CaF2 system. The slag liquidus lowering effect of CaF2 is 19 °C/%CaF2 in the Fluoride Basic fluxes, and 4 °C/%CaF2 in the Aluminate Basic fluxes. The Aluminate Rutile flux is based in the SiO2–Al2O3–MgO–TiO2–MnO–CaF2 system. Little CaF2 addition is used in this flux since TiO2 addition lowers its liquidus temperature sufficiently. The level of CaF2 addition sets the quantity and chemistry of fluoride gas compounds formed. The main gas fluoride gas species expected to form in welding with the five fluxes are CaF2, MgF2, NaF, KF, NaAlF4, and AlF3. In addition, TiF3 is expected to form in welding with the Aluminate Rutile flux, indicating the importance of titanium oxidation state in fluoride gas formation.

Keywords

• Welding
• Flux
• Slag
• Phase chemistry
• Gas
• SAW