Mold behavior and its influence on quality in the continuous casting of steel slabs: Part i. Industrial trials, mold tem
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I.
BACKGROUND
OVER three decades, the continuous-casting process has largely replaced conventional ingot casting/rolling for the production of semifinished steel shapes like slabs. The advantages of continuous casting--higher yield, enhanced productivity, improved quality, and reduced cost--are numerous, but the process is not without its problems. Depending on its design, operation, and maintenance, a continuous-casting machine may produce slabs exhibiting surface defects, such as longitudinal or transverse cracks, star cracks, longitudinal off-corner depressions, and deep oscillation marks. The presence of defects assumes greater importance if the slabs are hot charged to the reheat furnace, or direct rolled, without surface inspection and conditioning. In addition to having an adverse impact on the quality of the rolled product, such defects may contribute to operating problems like breakouts. Thus, the influence of casting machine design and operation on slab quality assumes critical importance. This is the subject of the present investigation which focuses primarily on the meniscus region where, to a large extent, surface quality is made.
R.B. MAHAPATRA, formerly Graduate Student, Centre for Metallurgical Process Engineering, The University of British Columbia, is with BHP Research and New Technology, Clayton, Victoria, Australia 3168. J.K. BRIMACOMBE, Stelco/NSERC Professor and Director, I.V. SAMARASEKERA, Professor, and N. WALKER, Senior Technician, are with the Centre for Metallurgical Process Engineering, The University of British Columbia, Vancouver, BC, Canada V6T 1Z4. E.A. PATERSON is with Research and Development, Stelco Inc., Hamilton, ON, and J.D. YOUNG, formerly with Research and Development, Stelco Inc., is now with Hoogovens Canada. Manuscript submitted September 17, 1990. METALLURGICAL TRANSACTIONS B
A major factor affecting slab surface quality is the behavior of the mold flux in the vicinity of the meniscus shown in Figure 1. Beyond its primary function of providing lubrication in the liquid state between the oscillating mold and descending solid shell, the mold flux must also transfer heat, absorb inclusions, and insulate the top surface of the liquid pool. These processes are complicated by the sintering and melting behavior of the mold flux which, based on the CaO-SiOz-AIzO3 system with additions of alkali oxides, fluorides, and carbon, is adjusted in practice to control these events at the meniscus.
II.
PREVIOUS WORK
Unfortunately relationships among mold flux composition, heat transfer, and slab surface quality have not been established quantitatively, owing to the complexity of the mold flux behavior at the meniscus. Thus, the selection of mold flux composition is frequently by trial and error, guided by experience. One of the problems has been a paucity of knowledge on the extraction of heat by the mold above and below the meniscus in direct response to mold flux behavior. Below the meniscus, the heat flux is governed by the flux-filled gap separating the solidifying shell from th
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