Detection of Non-metallic Inclusions in Steel Continuous Casting Billets
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CHARACTERIZING non-metallic inclusions is one of the most important aspects to assuring clean steel. Inclusions remaining in the final product can damage steel properties and degrade its quality.[1,2] To produce high-performance steel, non-metallic inclusions must be controlled. Generally, non-metallic inclusions can be classified as either indigenous or exogenous. Indigenous inclusions are a result of alloying elements within the steel reacting with dissolved gas (generally oxygen) to form solid inclusions in the cast steel. The inclusion could be formed during deoxidation, reoxidation, or solidification from reduced gas species solubility in the solid state. Exogenous inclusions come from sources outside the liquid steel, such as slag entrainment or refractory damage. The evaluation of non-metallic inclusions in steel is of great interest to metallurgists and materials scientists and includes exploring the total YING REN, Ph.D. Student, and LIFENG ZHANG, Professor, are Beijing Key Laboratory of Green Recycling and Extraction of Metals (GREM) and School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, No. 30, Xueyuan Road, Haidian District, Beijing 100083, P.R. China. Contact e-mail: [email protected] YUFENG WANG, Engineer, is with the R&D Group, SSAB, Muscatine, IA. SHUSEN LI, Assistant General Manager, Qian’an Steelmaking Co. Ltd., Shougang Group, Qian’an 064404, Hebei, P.R. China. XIANGJUN ZUO, Engineer, is with the Continuous Casting Department, CISDI Engineering Co. Ltd., Chongqing, P.R. China. SIMON N. LEKAKH, Research Professor, and KENT PEASLEE, Professor, are with the Department of Materials Science & Engineering, Missouri University of Science and Technology (Missouri S&T), Rolla, MO. Manuscript submitted June 28, 2011. Article published online March 11, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS B
amount, morphology, size distribution, and spatial distribution of inclusions; and identifying their chemical composition. The research group of the current author has extensively investigated the different aspects of inclusions, including the experimental investigation, industrial trials, modeling, and literature review.[1,3–12] Zhang and Thomas[1] reviewed more than twenty methods of evaluating impurities and inclusions in steel. Among these methods, a metallographic microscope[13] is widely applied to explore the two-dimensional morphology and size of inclusions in steel. However, it cannot identify the chemical composition of inclusions. Scanning electron microscopy[14] permits exploration of morphology of inclusions in the microscale. Further, by coupling with energy-dispersive spectroscopy, scanning electron microscopy permits identification of the elemental composition of inclusions and their relative proportions. Counting a large number of inclusions with this method, however, is too time-intensive to be practical. Acid extraction method can obtain the stereoscopic morphology of inclusions, but destroy sulfide inclusions.[15–18] For the extraction
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