Probing Element Transfer Behavior during the Submerged Arc Welding Process for CaF2-SiO2-Na2O-Cr2O3 Agglomerated Fluxes: A Thermodynamic Approach

Abstract

Submerged arc welding joins metal by the heating of the electrode, base metal, and flux in the arc plasma, while the weld pool is protected under the granular flux and molten slag. Due to complex chemical reactions occurring between the arc plasma, weld pool, and molten slag (flux), flux essentially affects the weld metal composition, which, in turn, dictates the mechanical properties of the weldment. Therefore, fine-tuning the weld metal composition is essential to ensure a sound weld, and efforts worldwide have been focused on the control mechanism of flux on the weld metal composition. Recently, agglomerated fluxes have been widely applied due to low energy consumption during manufacture. The Cr2O3-bearing agglomerated flux is one of the most commonly used flux types in fields of heavy industrial applications. However, few works concern the element transfer behavior when Cr2O3-bearing agglomerated fluxes are used. Within this framework, typical agglomerated CaF2-SiO2-Na2O-Cr2O3 fluxes with varying Cr2O3 content from 10 to 50 wt.% are designed and applied to Q345A steel. The influence of Cr2O3 content upon the transfer behaviors of essential elements, including O, Cr, and Mn, is quantified and interpreted from the point of thermodynamics. By incorporating a gas-slag-metal equilibrium consideration, the assumptions made in previous studies are justified. Additionally, evidence regarding the loss of Cr and Mn to the arc plasma is provided, and a possible thermodynamic approach to predict element transfer levels is proposed. It is revealed that the gas-slag-metal equilibrium consideration is able to qualitatively analyze the transfer behaviors involved in the submerged arc welding system, even under high temperatures. Based on the quantitative data, the practical implications as well as limitations of the gas-slag-metal equilibrium model are proposed.