Dissolutive Wetting and Spreading Phenomena Between Al 2 O 3 Substrate and CaO-Al 2 O 3 Liquid Slags
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INTRODUCTION
NON-METALLIC inclusions such as Al2O3 are formed by de-oxidation or by the reaction between molten steel and alumina-containing refractory. They usually deteriorate mechanical and surface properties of steel products (ductility, toughness, anisotropy) because the inclusions act as potential sites of stress concentration. Also the inclusions can cause nozzle clogging. The non-metallic inclusions must be removed to achieve better product quality.[1–3] In general, the inclusions float up toward the interface between the molten metal and slag due to the different densities between the inclusion and the molten steel. Magnetic stirring and argon gas injection improve the flotation of the inclusions. The floating inclusions have to be separated from the molten steel to the slag. In order to effectively remove the inclusions, a good wetting property, high spreading rate, and a high dissolution rate between the inclusion and the slag are necessary. If the inclusions do not firmly attach and absorb to the slag, the inclusions that are floated at the interface are re-entrapped into the molten steel by fluid steel.[4]
SEONJIN KIM, Graduate Student, and YONGSUG CHUNG, Professor, are with the Department of Advanced Materials Engineering, Korea Polytechnic University, Siheung 429-793, Korea. Contact e-mail: [email protected] KYUYOUNG LEE, Professor, is with the Department of Consilience, Korea Polytechnic University. Manuscript submitted November 10, 2015. Article published online February 1, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS B
Several studies on dissolution of Al2O3 inclusions into the slag have been carried out using a CSLM (confocal scanning laser microscope) and RCM (rotating cylinder method).[5–14] In comparison with research on dissolution, there have been few studies on the wetting property and spreading rate. Choi and Lee[4] observed apparent wetting behavior of various components of CaO-Al2O3-SiO2 slag and sintered Al2O3. They explained that a smaller contact angle that is related to the interfacial tension, not the viscosity. In addition, they applied a new model that considers chemical interactions (dissolution) because wetting and spreading rate are influenced by the dissolution reaction at the interface between the slag and the Al2O3 substrate. However, they did not evaluate the phenomenon of the dissolution on the spreading rate as time progresses. Park et al. studied the initial wetting angle and spreading kinetics between CaO-SiO2 slag and MgO substrate. They found that the slag wetted on MgO in less than a 1 second and the spreading behavior fitted a non-reactive viscous model, which meant that dissolution did not significantly affect the spreading behavior in the early stage of wetting.[15] In this study, the effect of dissolution of Al2O3 into a slag is discussed in relation to the spreading rate and the wetting behavior. The slag compositions used in this study are non-saturated slag and saturated by Al2O3 at 1823 K (1550 C). For non-saturated slag, the Al2O3 substrate will be dissolved into slag
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