Marangoni convection driven by thermocapillary and solutocapillary forces in the Fe-O alloy pool during the solidificati
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I. INTRODUCTION
VARIOUS phenomena caused by the surface characteristics (particularly, surface tension) of liquid metals and their alloys have been encountered in material production processes and have been studied extensively.[1,2] Studies on Marangoni convection have been conducted from the viewpoint of controlling these phenomena. However, Marangoni convection is not yet sufficiently understood, owing to the experimental difficulty and the complexity of the associated phenomena. Furthermore, most previous studies focused on thermocapillary convection.[3–9] Among the other studies conducted, the experimental study of thermocapillary convection of liquid gallium by Priede et al.[9] revealed an anomalous pattern of the melt-surface velocity with the tracer particles moving from cold to hot regions. This implies the formation of solutocapillary force caused by contamination of the melt surface of gallium by a very small amount of lead. However, the solutocapillary effect was not sufficiently clarified, owing to the lack of surface-tension data on a gallium-lead system. In the present study, in order to elucidate the nature of Marangoni convection during the solidification or remelting process, both experimental and numerical approaches were taken, paying attention to the formation of solutocapillary force induced by the nonuniformity of solute concentration on the melt surface (in addition to thermocapillary force). Marangoni convection during the solidification or remelting process was investigated in a small pool of a liquid Fe-O alloy with a low Prandtl number but a high Schmidt number. This alloy is also characterized by a small equilibrium-distribution coefficient of oxygen.
KEIJI NAKAJIMA, Associate Professor, and SHOZO MIZOGUCHI, Professor, are with the Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai, 980-8577, Japan. Contact e-mail: [email protected] SHOICHI YASUHIRO, Research Associate, and NOBUYUKI IMAISHI, Professor, are with the Institute of Advanced Material Study, Kyushu University, Fukuoka, 816-8580, Japan. Manuscript submitted September 4, 2001. METALLURGICAL AND MATERIALS TRANSACTIONS B
II. EXPERIMENT A confocal scanning laser microscope[10] was used for the in-situ observation of Marangoni convection during the solidification or remelting process in a small melt pool in contact with a solid metal. An infrared-image furnace, as shown in Figure 1, was selected in order to exclude other factors related to the flow. Two materials were used: normal low-carbon aluminum-killed steel cut from a continuously cast slab, and a specially made low-carbon steel of high oxygen content. Chemical analyses were performed for each material before and after the in-situ observation, in order to confirm the oxygen content. The former and latter contain about 0.002 and 0.050 mass pct of oxygen, respectively. A small piece of each material was machined into a disc (4.3 mm in diameter and 2 mm in height), mirror polished, and set in an alumina crucible. The specimen in
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