The transient stages of inclusion evolution during Al and/or Ti additions to molten iron

This study investigates the evolution of inclusions as a result of Al and Ti additions to molten Fe at 1 873 K with the objective of elucidating the transient stages of inclusion formation during ladle processing of IF steel melts. The effects of order of addition, time after addition, Al/Ti ratio and oxygen content are evaluated through an experimental approach that involves de-oxidation and sampling inside a vacuum induction furnace under conditions where the total oxygen concentration of the melt and samples are maintained constant. Each sample is analyzed for chemistry and resulting inclusion characteristics (size, morphology and chemistry). All experiments were carried out under the thermodynamic condition that Al2O3 was the only stable inclusion. The following results were found. Firstly, the equilibration time of Al was found to be faster than that of T under the present experimental conditions and as a result Al2O3 forms initially when Al and Ti were simultaneously added. The addition of Ti results in the formation of oxide inclusions containing Ti up to 20 mol% as a result of local Al depletion and Ti-supersaturation. This was enhanced in terms of the fraction of Ti containing inclusions as the T content was increased. Ultimately, in all samples, the thermodynamically stable inclusion Al2O3 was predominant within 5 min, but the morphology of these final inclusions were of polygonal shape rather than the spherical inclusions that formed immediately after Al de-oxidation. This modification in shape could have consequences on clogging, during post ladle teeming and pouring, in continuous casting as the tendency for agglomeration would be expected to increase.