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SynopsisA method of mathematically analyzing interdendritic microsegregation was established using finite difference method and taking into consideration the diffusion of the solute in the solid and liquid phases. The cross-sectional shape of dendrites and the fact that the enrichment of the solute in the liquid phase at the solid-liquid interface restrains the advancement speed of the solid-liquid interface were considered. Directional solidification tests to examine interdendritic segregation were made to verify the mathematical analysis method established. The advantages of the new method over other methods were discussed. Then, spot-like segregation were mathematically analyzed applying the same method, and the results were in good agreement with the observations in continuously-cast slabs.

Alumina graphite rods were immersed in liquid iron to clarify the mechanismwherebycontinuous caster immersion nozzles made of alumina graphite were clogged, Even whenaluminum was not contained in the iron melt, alumina formed and deposited on the surface of the alumina graphite rod in contact with the iron meit. This experimental result suggests that alumina in the alumina graphite nozzle is reduced by graphite to suboxide gas, and the suboxide gas diffuses to the contact interface with molten steel and is reoxidized into alumina at the interface. This reaction is accelerated by silica in the alumina graphite nozz!e.KEYWORDS: continuous caster immersion nozzle; nozzle clogging; alumina graphite; suboxide gas; steelmaking. 32 (1992) As shown in Fig. 2(a), the alumina graphite rodThickness of alumina buildup and silicon and aluminumpickups in different immersion experimental runs.RunNo. External appearance of alumina graphite rods after immersion experiment. Fig. 4(a).In Fig. 2(b), the alumina graphite rod immersed in the 0.20/0 C iron melt in Run2 was covered with a white buildup, although no aluminum was added in the iron melt at the beginning of the immersion experiment. The white buildup was network particles and was found to be pure alumina from the results of EPMA analysis shown in Fig. 5. From a morphology point of view, this alumina buildup was clearly distinguishable from rectangular alumina particles originally contained in the alumina graphite rod. As shown in Fig. 4(b), the 0.2 olo C iron melt steeply increased in the silicon content at the start of the graphite rod immersion. After the silicon content leveled off, the dissolved aluminum content

The control of oxide dispersion is one of the most important factors in the newly explored field of study "oxides metallurgy in steels," utilizing fine oxide particles as heterogeneous nucleation sites for various precipitates. The distribution of oxides in the solidification structure is greatly influenced by interactions between the oxides and the advancing solid/Iiquid interface as solidification progresses. In order to clarify the behavior of oxides in steels during solidification, unidirectional sol idification experiments was conducted. The distribution of oxides was quantitatively analyzed by CMA, and the experimental results were discussed in comparison with a mathematical calculation taking account of microsegregation and precipitation during solidification. In Ti-deoxidized steel. Ti.O. segregated in the interdendritic region considerably more than calculated. The discrepancy means, that considerable numbers of oxides were rejected to the interdendritic region by advancing solid/liquid interface during solidification. In Zr-deoxidized steel, on the other hand, ZrO. distributed relatively uniformly, as expected from calculation. The difference between both species of oxides regarding the rejection/entrapment phenomena is most likely due to interfacial energy between the liquid steel and oxide particles.

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.