Kinetics of Scrap Melting in Liquid Steel: Multipiece Scrap Melting
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years, industrial melting of steel scrap in a liquid steel bath in an electric arc furnace (EAF) has become increasingly important as large flat baths become common. A ‘‘hot heel’’ operation utilizes the molten steel left in the bottom of the furnace from the prior heat to assist in the melting of fresh scrap entering the EAF. Some new processes such as CONSTEEL and ECOARC employ a permanent liquid bath to melt steel scrap.[2] Scrap melting in a liquid steel bath is a process involving multiple scrap pieces. The interaction between scrap pieces plays an important role in establishing the final scrap melting time. In particular, the formation of solidified shells around original scrap pieces, and agglomeration of these shells (termed as ‘‘steel icebergs’’), may dominate the melting process. The present work was undertaken with two aims. The first was to conduct a comprehensive experimental study on multipiece steel scrap melting kinetics. Following the single-bar melting experiments introduced in a previous article,[1] more complex melting experiments involving two and more bars were explored to investigate how parameters such as spacing between bars and initial steel JIANGHUA LI, formerly a Graduate Student with Materials Science and Engineering, McMaster University, is presently a Postdoctoral Fellow with Department of Materials Science and Engineering, University of Toronto, Toronto, ON, Canada M5S 3E4. Contact e-mail: [email protected] NIKOLAS PROVATAS, Associate Professor, is with Material Science and Engineering, McMaster University, Hamilton, ON, Canada L8S 4L7. Manuscript submitted May 8, 2007. Article published online March 20, 2008. 268—VOLUME 39B, APRIL 2008
sample temperature affect steel iceberg formation and the melting time. The details of this experimental investigation are presented in Section II. The second aim of this work was to extend a phenomenological phase-field model developed in a previous article,[1] which was shown to successfully capture the kinetics of single-bar melting, to the case of two-bar and randomly distributed steel scrap melting. After comparing model simulations against the two-bar melting experiments, two types of simulations involving multipiece randomly distributed scrap were performed. The first of these corresponded to the limiting case of scrap melting in a perfectly stirred bath, while the second corresponded to the case of conduction or lowlevel, natural-convection-dominated heat transfer in the liquid steel bath. The following specific issues associated with scrap melting practice were addressed: (1) the effect of scrap porosity on melting, (2) the effect of preheating scrap on melting, (3) the effect of liquid steel bath temperature on melting, (4) the effect of stirring on melting, and (5) the effects of scrap size on melting. In addition, for the case of conduction-dominated melting, a simple mean-field analytical model was developed and found to predict the kinetics of the melting front through the steel bath quite well. Details of the two-bar melting simulations are pres
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