Alumina clusters extracted from molten steel and from a cast slab at our plant were analyzed by SEM and TEM. It was found that a small amount of liquid FeO could accelerate the clustering of alumina inclusions in aluminum-killed steel because of the strong liquid-capillary negative pressure of liquid FeO. The sources of the FeO are most likely oxygen contamination from ferroalloy additives, residual steel adhering to the refractory surfaces of ladles and vessels, and air entrainment.

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The effects of the agitation field and the crystal morphology on the primary and secondary crystallization temperatures of CaO-SiO 2 -CaF 2 supercooled melts were systematically investigated by measuring the electrical capacitance.Two-stage decreases in electrical capacitance were observed for most samples investigated. These stages correspond to the primary crystallization and the eutectic reaction resulting from the compositional change in the supercooled melts associated with the primary crystallization, respectively.The primary crystallization of dendritic CaO·SiO 2 was affected by the agitation in the same manner as reported previously, but the crystallization of faceted 3CaO·2SiO 2 ·CaF 2 revealed little dependence on the agitation. This indicates that the effects of the agitation are different for different morphologies of the primary crystalline phase because of shifts in the rate-determining step of crystallization.

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