Reaction between refractory and molten steel causes clogging in the immersion nozzle in continuous casting process. Reaction mechanismbetweenthe silica-containing alumina graphite nozzle and the molten steel was studied on the observation of the used immersion nozzle and the basic experiments. The results are summarized as follows.( 1) The used immersion nozzle refractory reveals a reacted zone where the SiO. and C contents are reduced and there are many pores.( 2) The overall reaction in the refractory can be arranged as Si02(s) +C(s) =SiO(g) +CO(g) With the Si02-C refractory containing no Al20.. 50"/. of Si02 is reduced by the C to the SiO gas, and the remaining 500/0 is reduced by the C to SiC. On the other hand, with the AI.O.-Si02-C refractory.all of SiO. is reduced to the SiO gas.

As a fundamental study to clarify the agglomeration and coalescence of alumina inclusions in molten steel from the viewpoint of interfacial chemical interactions, it has been experimentally verified for the first time that significant agglomeration force is exerted between alumina particles in aluminum deoxidized molten steel by using a newly established experimental method. In this method, the agglomeration force exerted between alumina particles in molten steel is directly measured separately from the effect of molten steel flow. In addition, it has been quantitatively demonstrated that the contact angles measured between aluminum deoxidized molten steel and an alumina plate are larger than those between the molten iron-oxygen alloy and the alumina plate, which have already been measured by other researchers. Moreover, it has also been indicated by analyzing the actual measurement values of agglomeration force with an interaction model taking contact angles and interfacial properties into consideration that the agglomeration force between the alumina particles in aluminum deoxidized molten steel derives not from the van der Waals force but from the cavity bridge force occurring due to molten steel, which is unlikely to wet the alumina particles. Meanwhile, it has been assumed that the agglomeration force on spherical alumina inclusions in aluminum deoxidized molten steel calculated on the basis of the interaction model according to the cavity bridge force is greater than the buoyant force and drag force, and the alumina inclusions once coming into contact are therefore not prone to be simply dissociated even under molten steel flow. Thus, they maintain the agglomeration state and are subsequently sintered and form comparatively solidly bonded alumina clusters.

Ja pan.Steel Institute of Japan, It is necessary to clarify the reoxidation factors and quahtitatively determine the contribution of each factor to the reoxidation of the molten steel to prevent the cOntamination in the tundish. In this study, the molten steel in tundish has beensampled in production scale experiment and from the composition changeof the molten steel the amount of reoxidation of the molten steel teemed from the first ladle into an actual tundish has been quantified by factor contents of the molten steel at the tundish inlet remained practically constant and approximately agreed with

Basic experiments were conducted on the adhesion of Al 2 O 3 in molten steel when molten FeO is present in the molten steel. It was found that the adhesion and coalescence of Al 2 O 3 particles are promoted when molten FeO is present in the molten steel, that FeO and FeAl 2 O 4 are observed in the bond between the Al 2 O 3 particles, and that this observed result agrees with the pattern of Al 2 O 3 adhesion to the continuous caster nozzle when the molten steel is reoxidized. Based on these experimental results, a study was made of the mechanism whereby Al 2 O 3 adheres to the continuous caster nozzle when the molten steel is reoxidized. When the oxygen concentration in the molten steel is locally raised by the reoxidation of the molten steel, the adhesion force of the Al 2 O 3 particles due to the liquid bridge force of the molten FeO is far greater than the adhesion force of the Al 2 O 3 particles due to the van der Waals force or the surface tension of the molten steel. The adhesion of Al 2 O 3 to the nozzle interface is thus considered to proceed mainly with the molten FeO serving as binder. Since the molten FeO binder changes into a solid bridge of FeAl 2 O 4 in a short time, the Al 2 O 3 particles adhering to the nozzle interface are considered to integrate to form a network of Al 2 O 3 particles faster than possible with solid-phase sintering.

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