Upgrading the prediction model for Mn content in submerged arc welded metal via CALPHAD technology: Case study into typical acidic and basic fluxes

Abstract

Fluxes (the granular materials containing oxides and CaF2) serve vital functions with respect to atmospheric shielding, arc stabilization, and weld metal composition control during the submerged arc welding process. Mn content must be carefully controlled since it dictates the toughness of the weldment. The slag-metal equilibrium model has been applied for decades to predict the Mn content in submerged arc welded metal, although there are several limitations regarding its application. With the aim of compensating for the limitations of the slag-metal equilibrium model, this study has been undertaken to upgrade the slag-metal equilibrium model to the gas-slag-metal equilibrium model via CALPHAD technology. Then, the Mn content in the weld metal is predicted by using both slag-metal and gas-slag-metal equilibrium models for typical acidic and basic fluxes. The capabilities of the models to predict Mn content is evaluated from the perspective of thermodynamics. It is concluded that the gas-slag-metal equilibrium model, which is independent of the basicity index model, possesses higher prediction accuracy than the slag-metal equilibrium model. Furthermore, the transfer direction of Mn, as well as Mn content are predictable even when no MnO is contained in the initial flux. Based on the measured and thermodynamic data, the mechanisms pertinent to Mn transfer in the welding process have been interpreted, and the limitations of the gas-slag-metal equilibrium model have been summarized.