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

Numerical simulation is developed on grain structure development during weld solidification of steel. Monte Carlo (MC) method is applied to the simulation of nucleation and growth of solid, being combined with finite difference calculation of heat conduction and solute diffusion. Based on the experimental result that titanium nitride (TiN) works as a nucleating agent of equiaxed grain formation, given number density of TiN is allocated to MC cells randomly and instantaneous nucleation is assumed to occur when the melt undercooling of the cell exceeds a given critical level. It is found that the simulation can reproduce the weld solidification by reflecting the effect of TiN as a nucleating agent and the effect of soluble titanium that increases melt undercooling. Those effects have been recognized only as combined effects in previous experimental studies, but through the present simulation, they are first investigated in a separate manner. The simulation results indicate that equiaxed grain formation is promoted not only by a nucleating agent, TiN, but also by melt undercooling increased by soluble titanium and that both are requisite to bring about the columnar-to-equiaxed transition (CET). The results are discussed in connection with theoretical models on CET and confirm the rationality of the models. q

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The dissolution of δ -ferrite in continuously cast slabs of SUS304 has been studied during heat treatment in the temperature range of 1 373 to 1 473 K. The dissolution behavior can be expressed by KolmogorovJohnson-Mehl-Avrami equation. The dissolution rate is affected by annealing temperature and secondary dendrite arm spacing. Moreover, the numerical methodology for multi-phase field method has been performed in Fe-Cr-Ni alloy. It is thought that dissolution behavior of δ -ferrite during heat treatment can be also predicted by this method.