Mold Simulator Study on the Initial Solidification of Molten Steel Near the Corner of Continuous Casting Mold
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sting has been widely used for the production of steel slabs; however, problems of slab quality often arise during the process.[1] Defects of continuous-casting slab include internal and surface defects, and it is of great importance to eliminate these defects, as the defects tend to lead to a loss of yield and productivity.[2] Therefore, better quality of slab is required for the development of hot direct rolling technique[3] and thin-strip casting technique.[4] Surface cracks show severe damage to the final product, as they are easily oxidized and can’t be re-welded during rolling.[5] Transverse surface cracks of slab occur frequently during the process of continuous casting,[6,7] and they are usually found at the slab corner, which is introduced by the concentrated thermo-stress around the corner,[8,9] and the third embrittlement temperature
PEISHENG LYU and HAIHUI ZHANG, Graduate Students, and WANLIN WANG, Lotus Professor and Director of National Center for International Research of Clean Metallurgy, are with the School of Metallurgy and Environment, Central South University, Changsha 410083, Hunan, China. Contact e-mail: [email protected] Manuscript submitted June 14, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS B
region[10] [973 K to 1173 K (700 °C to 900 °C)] that the corner lies during bending and straightening operation. Compared with other steel grades, transverse corner cracks occur more easily for peritectic steel and micro-alloyed steel as there is a larger shrinkage stress and a more uneven shell growth due to the peritectic reaction (L þ d ! c) and phase transition (d ! c).[11–13] For Al-, Nb-, Ti-, and V-containing micro-alloyed steels, carbon nitrides or nitrides of micro-alloyed elements precipitate along the austenite boundary of the slab surface in the region of 1073 K to 1173 K (800 °C to 900 °C) during the bending and straightening operation, which would largely weaken the hot ductility of steel.[14,15] Consequently, many practices have been proposed to minimize transverse surface cracks, including the practice to adjust the composition of liquid steel for a better hot ductility,[15–17] the controlling of microstructure of slab surface by changing the secondary cooling to improve its hot ductility,[18,19] the modification of the slab corner temperature during bending and straightening operation to avoid the third embrittlement temperature region,[20,21] the increase of mold oscillation frequency,[22,23] and the application of non-sinusoidal oscillation mode,[24,25] as well as the mild cooling of meniscus region.[26] The importance of initial solidification of molten steel near meniscus has been widely acknowledged, as many
surface defects originate from the initial solidification.[27,28] Therefore, a clear understanding of initial solidification of molten steel near meniscus around the mold corner is of great importance for the control of corner defects. The means to conduct a study on the initial solidification of molten steel can be generally divided into four categories: plant experiments
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