During submerged arc welding, the high-temperature molten pool readily absorbs oxygen. Excess oxygen will form oxide inclusions inside the weld, reducing its plasticity and impact toughness, and raising the risk of porosity. Agglomerated flux can be formulated with different deoxidizing components. It reduces the oxygen content of the molten pool through metallurgical reactions between slag and molten metal, which is a core focus in flux formulation development.
Manganese and silicon form the basic deoxidation pair, and their combined deoxidation performance is far better than either used alone. Manganese oxidizes into MnO and silicon into SiO₂. The two combine to form low-melting silicates, which easily float up into the slag and are removed. Manganese also serves as a desulfurizer to lower the risk of hot cracking in the weld; silicon improves the fluidity of the molten pool for smoother weld bead appearance. However, their ratio must be carefully controlled. Excessive silicon tends to leave refractory inclusions and degrade toughness.
Aluminum and titanium are strong deoxidizers with high affinity for oxygen. They are commonly adopted in fluxes requiring excellent low-temperature toughness, effectively cutting the total oxygen level of the weld. Nevertheless, their oxidation products have high melting points, so they can't be added in large quantities. Otherwise, spot-shaped inclusions will form and compromise non-destructive testing results.
Besides, deoxidation efficiency is affected by flux basicity. Basic slag facilitates the separation and flotation of deoxidation products, while acidic slag mostly relies on the silicon-manganese system for deoxidation. The selection and proportioning of deoxidizing elements are the key reasons for performance differences among various flux grades.
