Observation on Physical Growth of Nonmetallic Inclusion in Liquid Steel During Ladle Treatment
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INTRODUCTION
NONMETALLIC inclusions, in most cases, detrimentally affect the quality of the final steel product. In the last decades, great efforts have been made to reduce the number of inclusions in the steel. Bigger nonmetallic inclusions would have a better probability of being removed to the slag phase by buoyancy force. However, inclusions that have larger sizes are more harmful when they remain in the final product. To optimize the steelmaking processes, knowledge of physical growth of the inclusions resulting from agglomeration is essential. In line with this direction, several studies[1–8] have been carried out to study and model the agglomeration of inclusions. However, understanding of the physical growth of inclusions in liquid steel is still limited. In a pioneer work, Emi introduced a confocal scanning laser microscope (CSLM) in steel research.[9–12] The device detects blur-free signals only from the focal plane. The combination of a microscope with a laser enables YOUNGJO KANG, formerly with the Institute of Industrial Science, The University of Tokyo, Tokyo 153-8505, Japan, is now Senior Researcher with Technical Research Laboratories, POSCO, Pohang, Korea. BAHMAN SAHEBKAR, Former Senior Engineer, and PIOTR R. SCHELLER, Professor, are with the Institute of Iron and Steel Technology, Freiberg University of Mining and Technology, Freiberg 09596, Germany. KAZUKI MORITA, Professor, is with the Institute of Industrial Science, The University of Tokyo, Tokyo 153-8505, Japan. DU SICHEN, Professor, is with the Department of Materials Science and Engineering, Royal Institute of Technology, Stockholm 100 44, Sweden. Contact e-mail: [email protected] Manuscript submitted September 15, 2010. Article published online March 4, 2011. 522—VOLUME 42B, JUNE 2011
high-resolution images at high temperature. Since then, many phenomena of nonmetallic inclusions in iron- and steelmaking, such as dissolution,[13–16] precipitation, and crystal growth,[17–20] have been examined in situ. Although observations have been made of the behavior of the inclusions in liquid steel,[21,22] most studies have been focused on the slag–metal interface. Yin et al.[23,24] employed this technique to study the agglomeration and growth of inclusions on the surface of liquid steel. Despite these valuable investigations, little has been done to compare the observation in the confocal microscope with the findings in industrial practice. It is noted that the behaviors of inclusions observed in the confocal microscope is related to their movement on the steel surface. Whether they would behave similarly in the bulk of liquid steel has been an important but unclear issue for researchers and industrial engineers. The present research aims at the industrial investigation of the inclusions in ladle treatment as well as a laboratory study of the behavior of the inclusions using a confocal microscope. It is expected that a comparison of the results of these two types of studies would provide a clear idea regarding the physical behavior of different types of incl
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