Coupling of CFD and PBE Calculations to Simulate the Behavior of an Inclusion Population in a Gas-Stirring Ladle
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THE reduction of the weight of high performance materials together with the improvement of mechanical properties and the increase of the recycling of used metal are new challenges which emphasize the importance of metal cleanliness. Ladle treatment of specialty steels has long been described as the secondary metallurgical process is mainly responsible for the non-metallic inclusion derived from the deoxidation process. As shown in Figure 1, the ladle is positioned in a sealed vessel and a primary pumping device allows the pressure to reach about 1 mbar. The main purpose of the degassing operation concerns the elimination or reduction of the dissolved gaseous components (nitrogen, oxygen, hydrogen) and the removal of sulfur from the liquid steel. Elements such as aluminum or calcium are introduced in the form of cored wires (Figure 1) with the aim of deoxidating the bath. Finally, an injection of argon through one or more porous plugs at the bottom of the ladle provides both mixing of the liquid metal to achieve thermal and chemical homogeneity and the entrapment of the inclusions by the bubbles well known as the flotation mechanism. The physical processes involved in gas-stirred ladles are numerous and complex owing to the 3-D and multiphase (metal-gas and inclusions) nature of the reactor. A precise JEAN-PIERRE BELLOT, Professor, VALERIO DE FELICE, BERNARD DUSSOUBS, and ALAIN JARDY, Scientists, are with the Institut Jean Lamour, UMR 7198, CNRS (‘LabEx DAMAS’)/ Universite´ de Lorraine, 54011 Nancy, France Contact e-mail: [email protected] STE´PHANE HANS, Scientist, is with the Aubert & Duval, Les Ancizes Steel Plant BP1, 63770 Les Ancizes, France. Manuscript submitted August 29, 2012. Article published online September 13, 2013. METALLURGICAL AND MATERIALS TRANSACTIONS B
description of the large number of interactions is necessary in order to obtain a good representation of the evolution of the inclusion population during the treatment. The mechanisms involved are: (a) the collisions between inclusions, which can lead to aggregation and even to agglomeration if reconstruction of the aggregate occurs, (b) the collisions with bubbles, which lead to the mechanism of floatation, (c) the entrapment at the interface between the liquid bath and slag coverage, (d) the separation induced by gravity, (e) the entrapment at the ladle walls. The modeling of the liquid steel ladle has already been the subject of many studies. Until the late ’80s, research on inclusion cleanness has been divided between thermodynamic studies aimed to determine the experimental equilibrium slag-metal-inclusion[1] and the first calculations on secondary metallurgical reactors.[2] Since the ’90s, the knowledge of thermo-chemical equilibrium has been capitalized on and has given birth to computing software, now widely used in the steel industry to predict the composition of stable phase inclusions.[3] Furthermore, the simulations of liquid metal processing were developed with an increasing level of sophistication. This type of wo
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