The thermodynamic effect of SiO2 on the composition of the weld metal in submerged arc welding is analyzed by employing the basicity index model, the slag–metal model, and a multi-zone thermodynamic framework. A CaF2-SiO2 binary flux system is employed to isolate the intrinsic effect of SiO2. The results show that the basicity index model captures the overall decrease in weld metal O content with increasing flux basicity index but fails to resolve variations in the high-basicity region. The slag–metal equilibrium model provides a thermodynamic description of interfacial reactions yet remains limited to the weld pool zone. In contrast, the multi-zone model incorporates reactions in the droplet and weld pool zones, revealing pronounced O enrichment in the droplet due to flux decomposition and arc–plasma interactions, followed by redistribution under gas–slag–metal equilibrium. By accounting for droplet-stage evaporation and cross-zone interactions, the multi-zone model improves the predictive accuracy of Si and Mn contents and explicitly captures their cross-zone transfer behavior compared with conventional prediction approaches.
Zhang et al. (Sun,) studied this question.