Assessment of Weld Metal Compositional Prediction Models Geared Towards Submerged Arc Welding: Case Studies Involving CaF2-SiO2-MnO and CaO-SiO2-MnO Fluxes

Submerged arc welding has been performed by utilizing CaF2-SiO2-MnO and CaO-SiO2-MnO fluxes over a wide range of compositions and basicity index values. Contents of essential elements, including O, Si, and Mn, in the weld metal, are predicted by employing the basicity index model, slag–metal equilibrium model, and gas–slag–metal equilibrium model. Capabilities of each model to predict weld metal compositions have been evaluated from thermodynamic perspectives. The results show that the basicity index model is capable of predicting the variation trend of O content with MnO addition, but fails to differentiate O levels when fluxes with same basicity index are applied. The slag–metal model overestimates the contents of Si and Mn due to underestimated O level or overestimated oxide activity. The gas–slag–metal equilibrium model, on the other hand, offers better prediction accuracy for O content than the basicity index model, and is able to differentiate the O content of the weld metals produced by fluxes with varying formulas but same basicity index. Furthermore, when the gas–slag–metal equilibrium model is applied, the prediction error for Si and Mn contents is significantly reduced as compared to the slag–metal equilibrium model. Thermodynamic calculation data indicates that the consideration of gas formation, which essentially controls the predicted flux O potential and oxide activity, is necessary to improve the overall prediction accuracy.