Infiltration of Slag Film into the Grooves on a Continuous Casting Mold
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heat transfer is one of the most important factors for both the quality and productivity of continuous casting of steel. In particular, mold heat flux density should be maintained under a threshold value[1] at the vicinity of the meniscus to avoid the longitudinal surface cracks on cast slab. Generally, the mold slag film between the casting mold and solidifying steel shell shows the largest effect on mold heat transfer. It is well known that mold heat flux density decreases when one applies mold flux of a larger basicity or higher solidification temperature. Many previous reports[2–7] showed that crystalline phase in the slag film can reduce mold heat flux density. Though the mechanism has not been clarified yet, there were a few suggestions about why the crystalline phase increases thermal resistance—increase of interfacial thermal resistance due to volumetric contraction,[2–4] increase of radiative thermal resistance due to larger absorption coefficient,[7–10] and increase of conductive thermal resistance due to voids.[11] However, there is a limit to reduce the mold heat transfer by accelerating crystallization because the crystalline phase deteriorates JUNG-WOOK CHO, formerly Principal Researcher, with the Technical Research Laboratories, POSCO, Pohang, South Korea, is now Research Professor with the Graduate Institute of Ferrous Technology, Pohang University of Science and Technology, San 31, Hyoja-Dong, Nam-Gu, Pohang 790-784, South Korea. Contact e-mail: [email protected] HEE-TAE JEONG, Student, is with the Graduate Institute of Ferrous Technology, Pohang University of Science and Technology. Manuscript submitted May 11, 2012. Article published online October 12, 2012. 146—VOLUME 44B, FEBRUARY 2013
the lubrication of mold slag film, which may cause sticking type breakouts especially at the high speed thin slab casters. There have been several trials of mechanical texturing such as shot blast[12] or groove[13] on continuous casting molds to reduce mold heat flux density without worsening mold lubrication. It is believed that the surface texturing such as groove enhances the soundness of the cast slab by controlling nucleation, dispersion of thermal and transformation strain, and reduction of irregularity in solidifying steel shell due to the increase of the thermal resistance in the immediate vicinity of the textured surface. However, there has been no systematic model for understanding the thermal resistance determined by the infiltration behavior of mold slag into the grooves. Therefore, in this study, the authors aim to elucidate the slag film infiltration mechanism into the grooves to get the basis for a comprehensive understanding of mold heat transfer and solidification in the mold.
II.
EXPERIMENTAL
A grooved-type casting mold was applied. There are three factors to characterize the groove’s shape: pitch, width, and depth, as shown in Figure 1. In this study, the grooves were machined to have 0.8 mm of pitch, 0.7 mm of width, and 0.6 mm of depth on the wide face copper mold of overall 1200-mm height, which is di
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