Effect of Li2O on the morphology of mold flux and slab surface quality for continuous casting of high strength steel

Abstract

In the steel industry, in case of slab surface cracks occur, additional treatment processes are required to eliminate the defect. This leads to increased productivity and cost, which lowers process efficiency, so many steel companies are continuously developing technology to prevent cracking of slab surfaces. Factors that affect the crack of the slab surface are complicated by various factors such as steel type characteristics, equipment conditions, cooling conditions, and mold flux, so efficient improvement activities are required. In this paper, we dealt with the current operation level of the POSCO Gwangyang Works No.3 Casting plant - No.2 machine and the test application results of mold flux with Li2O added with an increased basicity. In particular, this paper presents the effects of Li2O on structural aspects of Cuspidine (Ca4Si2F2O7) crystallization behavior of CaO-SiO2-CaF2 Mold Flux (basicity 1.7). In laboratory preliminary experiments, the crystallization temperature was measured using a differential scanning calorimeter (DSC), and the delay in relative crystallinity was also confirmed. The change in crystal morphology was confirmed by scanning electron microscopy (SEM) and optical microscopy (OM). These results for CaO-SiO2-CaF2-based Mold Flux lubricants can be utilized to optimize essential properties such as viscosity and crystallization temperature in continuous casting processes. The effect of retard Cuspidine crystalization in the early stages of melt crystallization was also observed in actual continuous casting plant and the technical possibility for improving the slab surface quality was also confirmed. In case of the high-basicity mold flux added with Li2O was applied, the temperature deviation of the widthwise thermocouple in the mold was reduced, and uneven temperature fluctuations over time were also alleviated. As a result of checking the slab structure by easy etching test, it was confirmed that the chill zone decreased, and initial solidification occurred relatively alleviated. In order to be finally commercialized, it was necessary to take a careful approach in consideration of operating conditions such as increased slag bear due to low viscosity and cost efficiency due to increased consumption.