A Review on Parallel Development of Flux Design and Thermodynamics Subject to Submerged Arc Welding

Submerged arc welding is a complex metallurgical process with a temperature of nearly 2000 degrees C (a temperature much higher than that in traditional steelmaking) and different phases, including flux (slag), metal, and plasma. Flux serves vital functions in order to produce the weld metal with desired qualities. It is well known that understandings of the thermodynamic properties regarding flux and slag are essential to aid in flux design and optimization. Actually, the developments of flux design and thermodynamics have been promoting each other. Within this review, the flux design stages have been documented and reviewed in detail from the perspective of thermodynamics. The thermodynamic design principles for fluxes have been evaluated systematically, the limitations of each flux have been elucidated, and the thermodynamic significance of the designed fluxes upon the development of welding thermodynamics has been analyzed. Based on the hypothesis that thermodynamic equilibrium is attained locally considering that the high temperatures and surface-to-volume ratio counteract the short time available for chemical reactions to be completed, both slag-metal and gas-slag-metal equilibrium models have been evaluated, which may provide technical assistance for flux design and matching. Then, recent applications of Calphad (Computer Coupling of Phase Diagrams and Thermochemistry) technology in the fields of flux design and matching have been introduced. The incumbent review demonstrates that thermodynamic consideration is essential to develop new fluxes or upgrade existing ones to meet the growing demands concerning submerged arc welding quality. Furthermore, it is revealed that the thermodynamic approach is capable of facilitating the flux design process geared toward submerged arc welding. Finally, further investigation into welding thermodynamics is proposed to better aid in flux design and matching.