Effect of tellurium on supersaturation in aluminum deoxidized liquid iron
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I.
INTRODUCTION
SUPERSATURATION phenomena in aluminum deoxidation have been reported in a number of laboratory scale experiments, t1-111 but there is little published work on the influence of surface active elements such as Te, Se, S, and O on supersaturation. It is well recognized that the interfacial energy between liquid iron and alumina is lowered to a considerable degree by the addition of these elements, t12,~31 and the deoxidation reaction is strongly influenced by these additives, t~3,14,15jThe effect of surface active element on deoxidation may be explained by the decrease in the value of critical supersaturation necessary for homogeneous nucleation and/or the increase in the rate of inclusion removal by flotation as well as absorption into top slag. In this work, the effect of tellurium addition on supersaturation in aluminum deoxidized liquid iron was studied at 1873 K as a function of Te and A1 contents and cooling rate.
II.
EXPERIMENTAL
A. Procedure Detailed descriptions of the experimental procedure are given in the previously cited articles. 16,9-1H In this study, the master slags prepared by premelting mixtures of reagent grade CaCO3 and A1203 in a Pt crucible and liquid iron were melted in a vertical resistance furnace with heating bars of LaCrO3. The temperature was measured by a Pt-6 mass pct Rh/Pt-30 mass pct Rh thermocouple. The following equilibrium and supersaturation experiments were carried out at 1873 K using an A1203 crucible. In equilibrium experiments, high-purity electrolytic iron (30 g, 99.99 mass pct) and CaO-A1203 slag (7 g) were melted in an A1203 crucible (~b30 • 4)22 • 55 mm) under a deoxidized Ar atmosphere. It was confirmed that the oxygen level was in the range of 300 to 1000 mass ppm. An appropriate amount of an Fe-2 (or 10) mass pct JUN TANABE, Research Associate, and HIDEAKI SUITO, Professor, are with the Institute for Advanced Materials Processing, Tohoku University, Sendai 980, Japan. Manuscript submitted November 29, 1993. METALLURGICAL AND MATERIALS TRANSACTIONS B
A1 alloy was added by dropping later. Alumina precipitates immediately after addition of A1, since the oxygen level at a given AI content is far above the critical supersaturation in which spontaneous nucleation occurs. Melts were stirred over a period of 3 hours by an A1203 rod for 2 minutes at 30-minute intervals. To eliminate oxide inclusions by flotation, melts were unstirred for at least 1 hour before quenching. After equilibration, the crucible containing a sample was pulled out of the furnace and quenched rapidly in a He gas stream, followed by water quenching in rapid cooling experiments. In slow cooling experiments, the sample was cooled from 1873 to 1723 K at the cooling rate of 2.7 K / m i n and quenched rapidly. Equilibrium experiments with Te addition were not carried out. In supersaturation experiments, the master alloy (Fe-0.02 to 0.1 mass pct A1 alloy or Fe-0.06 to 0.2 mass pct A1-0.008 to 0.2 mass pct Te alloy) was prepared by premelting in a deoxidized Ar atmosphere using an arc furnace
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