Fundamentals of hydrogen dissolution in novel calcium-Aluminate welding fluxes containing FeO_t and NaF for advanced high strength steels

The effect of NaF, CaO/Al₂O₃, and FeO_t on the hydrogen solubility in the CaO-Al₂O₃-FeO_t-NaF welding flux system that could be utilized for high Al containing steels has been investigated. Halide components such as NaF added for increased fluidity and electrical conductivity had relatively minimal effect on the hydrogen dissolution at various CaO/Al₂O₃ ratio and FeO_t concentrations. Using wet analytical titration, results showed Fe³⁺ to be dominant in the present flux compositions and moisture atmosphere. Higher Fe³⁺ or Fe₂O₃ affected hydrogen dissolution depending upon the dominant mechanism apparent in the compositional range of interest. At acidic compositions of CaO/Al₂O₃ of 0.8, the dominant hydrogen dissolution mechanism was found to be incorporated hydroxyl, where higher Fe₂O₃ content increased the hydrogen solubility in the flux. At basic compositions of CaO/Al₂O₃ above unity, the dominant hydrogen dissolution mechanism was found to be free hydroxyl, where higher Fe₂O₃ content decreased the hydrogen solubility in the flux. Corresponding to the hydrogen analysis, structural analyses using FTIR and Raman spectroscopy showed higher NaF was ineffective in modifying the structure of the flux, but changes with the Fe₂O₃ and CaO/Al₂O₃ provided unit structural changes that coincided to the hydrogen dissolution behavior observed for the present flux.