Motions of alloying additions during furnace tapping in steelmaking processing operations

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INTRODUCTION

THE addition of alloying elements to liquid steel baths for adjusting steel chemistry to required specifications is a common steelmaking practice. In today's steelworks, these addition making operations are mostly carried out during the tapping of liquid steel from a furnace into a teeming ladle. It is therefore an integral feature in the production and refining of liquid steel. Consequently, where large tonnages of many grades of steel are made, there is considerable interest in developing, or at least identifying, efficient methods for introducing deoxidizers and alloying additions into liquid steel baths. A specific problem faced by steelmakers in this particular area for many years has been the low and erratic recoveries of light metal additions, particularly aluminum. Slag carryover from the steelmaking furnace, entrained air in the tapping stream, air oxidation of the dissolved solute elements, and residual slag from a previous heat are now recognized as some of the principal causes for poor and erratic recoveries of buoyant additions. Furthermore, it is well known that such buoyant additions under normal circumstances rise back to the (steel/slag)-air surface. Liquid aluminum, etc. is therefore likely to be released from an encasing steel shell at the upper free surface M. TANAKA, formerly Doctoral Candidate, Department of Mining and Metallurgical Engineering, McGill University, is Manager, Steelmaking Technical Section, Kashima Steel Works, Sumitomo Metal Industries Ltd., Japan. D. MAZUMDAR, formerly Assistant Professor, Department of Metallurgical Engineering, Indian Institute of Technology, Kanpur, 208016, India, is Visiting Professor, Department of Mining and Metallurgical Engineering, McGill University. R.I.L. GUTHRIE, Macdonald Professor of Metallurgy, is with the Department of Mining and Metallurgical Engineering, McGill University, Montreal, Canada H3A 2A7. Manuscript submitted July 29, 1986.

METALLURGICAL TRANSACTIONS B

rather than in the bulk liquid, leading to poor recovery rates, t~,2,31 Such poor and erratic recovery rates of deoxidizer and alloying elements can introduce unacceptable variabilities into the final product chemistry. From a technical as well as economic point of view, therefore, the addition of alloying materials during tapping procedures from BOF or electric furnaces are among the most important operations in steelmaking. However, little fundamental research work has been carried out in this area. The purpose of the present work was to analyze the behavior of additions in teeming ladles during furnace tapping operations so as to obtain a clearer understanding of the phenomena involved and to identify means to effect improvements. Consequently, this article reports on the results of a comprehensive investigation carried out to describe the hydrodynamic features of alloy addition making operations using a 0.15 scale model of a 250 ton ladle. In an earlier study, Henein and coworkers t~,31 used full scale conditions to drop spheres of 1- to 4-cm diameter in free-