Dilution and Slag–Metal Reactions Control the Titanium Concentration in Submerged-Arc Weld Metal

Controlling the titanium concentration in weld deposits plays an important role in establishing weld metal microstructure. This work tested the effect of the reaction between the steel melt pool and liquid slag (molten flux) on titanium control during submerged-arc welding. Laboratory equilibration experiments confirmed that welding conditions are oxidizing towards titanium, with an expected equilibrium distribution coefficient of titanium between slag and metal of around 1000. Analysis of multilayer weld deposits confirmed the low recovery of titanium, but also a change in oxide inclusion composition in response to the titanium recovery in the weld metal. Both an approximate analytical model and a transient model considering full equilibration at the steel–slag interface demonstrated that titanium recovery is poorer if the steel–slag reaction proceeds further towards equilibrium. The relative importances—for the titanium concentration in the weld metal—of the rate of the steel–slag reaction and dilution of the added wire by remelted material are quantified with kinetic weighting factors. Considering these relative weights leads to general guidelines for control of the weld deposit composition.