Submerged arc welding (SAW) is one of the significant metal-joining processes for manufacturing
marine vessels, steel pipes, and offshore structures with high deposition rate and engineering
reliability. Welding flux serves several essential functions, including atmospheric shielding, arc
stabilisation, bead morphology control and weld metal (WM) refinement. Therefore, from a
thermodynamic point of view, the focus for flux design and WM compositional/microstructural
modification has been placed to elucidating the transfer pathways and mechanisms of major alloying
elements, such as Si, Mn, Ti and O during welding. To this end, a thermodynamic model has been
established to predict alloying element contents in the WM. Such functions are enabled by the
physicochemical properties of the fluxes, which are inherently rooted in the nature of the fluxes. A
unique yet systematical investigation, including physicochemical property changes and structural
evolution behaviours, has been conducted over the wide range of fluxes applied to actual welding of
EH36 shipbuilding steels. Combined with spectroscopic methods, structural behaviours of network
formers such as SiO2, Al2O3 and TiO2 and network modifiers such as MgO, MnO and CaO have
been illustrated. Viscosity and ionic conductivity have been found to be positively associated with
the degree of polymerisation.