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.
The capture rate of solid oxide-inclusion particles from molten steel by molten slag depends on the rate of steel film drainage (which occurs at certain particle velocities), interfacial separation, and dissolution into the slag. In this study the capture of common oxide inclusions of sizes 2.5-200 mm and with velocities ranging from their terminal velocities to 0.3 m · s Ϫ1 approaching the interface between molten iron and slags with chemistries corresponding to ladle, tundish and mold slags are investigated. Calculations, based on a model available in literature, show that film drainage (when applicable) is rapid enough to be ignored. A sensitivity analysis based on the slag properties show that the interfacial energy between slag and inclusion is the most pertinent property that could hinder interfacial separation. However, the interfacial tension needed to achieve this has to be a minimum of 0.41 N/m which is unreasonable for the case of common oxide inclusions such as Al 2 O 3 , MgO, ZrO 2 and MgAl 2 O 4 . The final step of dissolution was found based on studies with Confocal Scanning Laser Microscope experiments, to be significantly slower than the other steps. For a 100 mm particle, in the slags/inclusions investigated a correlation between slag viscosity, h
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 ...
The dissolution of Al2O3 and MgO inclusions in synthetic CaO‐Al2O3‐MgO slags have been investigated in situ with a confocal scanning laser microscope (CSLM). The dissolution mechanisms were elucidated by using analytical‐rate expressions. A set of parameters is introduced to distinguish between reaction control and diffusion control of the dissolution process. It was found that whereas Al2O3 inclusion dissolution rates are limited by diffusion, MgO dissolution appears to be limited by surface reaction. For both Al2O3 and MgO, the dissolution rate and the apparent activation energy increased when the slag composition was slightly shifted away from the saturation limit of the dissolving species in the phase diagrams.
Non-metallic inclusions composed of ZrO 2 , Al 2 O 3 , MgO and MgAl 2 O 4 are associated with problems during the continuous casting of steels and so it is desirable that such particles dissolve completely if they appear in the slag. The dissolution behaviour of particles of these oxides in a fluorine-free slag containing 1.5 wt% B 2 O 3 , was studied in situ using Confocal Scanning Laser Microscopy (CSLM). The effects of particle type, initial size, and slag temperature were investigated. Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM-EDS) was performed to chemically analyze quenched samples, in order to identify any surface reaction or diffusion layers formed. Analytical prediction models were compared to the experimental data to relate the kinetics to possible rate-limiting steps. Thermodynamic solubility limits for use in the model were determined using commercial CALPHAD based software. The dissolution rates of Al 2 O 3 , MgO and MgAl 2 O 4 were found to be comparable to one another whereas the dissolution rate of ZrO 2 , is four times slower. The surface reaction appears to be controlling the rate of dissolution, with the activation energy for ZrO 2 being 128.8 kJ/mol and for MgAl 2 O 4 being 77.8 kJ/mol. This implies that the removal of ZrO 2 particles by dissolution in this type of slag is not feasible for the typical residence times expected, and strategies that prevent the incorporation of these particles should be used.
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