In this paper, titanium-bearing blast furnace slags (CaO-SiO 2 -TiO 2 ) produced at Panzhihua Iron and Steel Company (P. R. China) is used as the base material to develop fluoride-free (F-free) mold powders to improve the heat transfer between the mold and the strand. Effects of the binary basicity (CaO/SiO 2 ), TiO 2 , Na 2 O, Li 2 O, MgO, MnO and B 2 O 3 on the melting temperature, viscosity and heat flux of F-free mold powders are investigated. The laboratory results indicate that 1) the melting temperature and the viscosity of the F-free powder decrease, as expected, with increasing the content of Li 2 O, B 2 O 3 and Na 2 O respectively, but the lowest viscosity is achieved with 6.0 mass% TiO 2 ; 2) the heat flux of the F-free slag film with 1.0-6.0 mass% TiO 2 is close to that of a conventional mold slag film with 2.0-10.0 mass% F; 3) the effect of basicity of the F-free powder on the heat flux is the same as the powder bearing fluoride; 4) the heat flux changes significantly with more than 8.0 mass% Na 2 O and about 4.0 mass% MnO, whereas the effects of Li 2 O and B 2 O 3 in the F-free powder on heat flux are not significant. The suitable range of main components of the F-free powder with TiO 2 is proposed for casting peritectic-grade-steel slabs. The industrial trials of peritectic steel casting, using the proposed F-free flux, reveals a good surface quality of the slab, and wellcontrolled heat transfer at the continuous casting mold by the F-free powder with the precipitated crystalline phase being perovskite (CaTiO 3 ) instead of cuspidine in the conventional mold slags that contain fluoride.

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 Al 2 O 3 was the only stable inclusion. The following results were found. Firstly, the equilibration time of Al was found to be faster than that of Ti under the present experimental conditions and as a result Al 2 O 3 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 Ti content was increased. Ultimately, in all samples, the thermodynamically stable inclusion Al 2 O 3 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.KEY WORDS: IF steel; nozzle clogging; de-oxidation; Al Ti inclusion morphology; inclusion formation mechanism.dation experiment at 1 873 K and observed the morphology of inclusions in melts with total oxygen contents between 300 and 500 ppm. In the cases of Al de-oxidation, they reported that spherical Al 2 O 3 and Al-(Mn)-O oxides were produced through the reduction of existing Fe-Mn-O oxide inclusions. The Al 2 O 3 were acicular at first, but gradually changed to become clusters of granular Al 2 O 3 spheres. Ti addition after Al de-oxidation did not have any significant effect and resulted in similar oxide and cluster formations. On the other hand, during Ti-deoxidation, spherical Ti-O oxides were formed but the addition of Al reduced these by forming Al 2 O 3 oxides which evolved to form Al 2 O 3 clusters. Kunisada and Iwai 12,13) also conducted similar experiments at 1 873 K and observed spherical oxides resulting from Ti de-oxidation and the reduction of Ti-oxides to form Al-oxides, while angular oxide products resulted from Al de-oxidation and Ti addition after Al de-oxidation. From these previous studies, it can be summarized that oxides clusters form during Al 2 O 3 formation as a result of either de-oxidation of the melt or reduction of Ti-oxides. The studies report the existence of both complex Al-Ti-O oxides and dual-phase oxides ...