Attachment of Alumina on the Wall of Submerged Entry Nozzle During Continuous Casting of Al-Killed Steel
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INTRODUCTION
DUE to its strong impact on steel cleanliness and steelmaking process control, the attachment of inclusions on the submerged entry nozzle (SEN) is one of the most important problems during continuous casting. Substantial attachment of inclusions would lead to clogging of the nozzle. The clogging behavior has been studied by many researchers, and classified into four types: deoxidation products, solidified steel, complex oxides, and reaction products.[1] Even without clogging, the attachment of inclusions on SEN is also harmful, as it results in macro non-metallic inclusions in the final product. Alumina phase is usually found in the attachments on the SEN after the casting of aluminum-killed steels. Some researchers concluded that the attached alumina was the deoxidation product,[2,3] and some suggested that it was formed by the reaction between the steel and nozzle refractory.[4,5] Besides, reoxidation was also considered as a possible source.[6] However, the solid alumina inclusions already presented in the steel before casting were believed as the primary source.[1,7]
Calcium treatment is commonly used as an efficient way to reduce clogging. Actually, sometimes clogging still occurs after calcium treatment in industrial practice. Different complex oxides, e.g., calcium aluminates,[8] were found in the attachment. The researchers usually believed that the solid inclusions caused by the non-suitable calcium treatment were the main reason of clogging.[8] In fact, liquid calcium aluminate inclusions also have the possibility to attach on the SEN wall.[9] On the other hand, alumina inclusions are not stable, when there is trace of dissolved Mg or dissolved Ca in liquid steel.[10,11] In some steel plants, alumina attachment appears sometime on the outer wall of the SEN for calcium-treated steel, although the steelworkers try to adjust the calcium content to modify them. The present work is to study the different mechanisms of alumina attachment on the wall of SEN during the continuous casting of Al-killed steels. It focuses on two different morphologies of alumina attachment found in different steelmaking processes. Based on the mechanism study, suggestions for process control and reducing the alumina attachment are given.
II. ZHIYIN DENG, Ph.D Student, is with the School of Metallurgy, Northeastern University, Shenyang 110819, China, and also with the Department of Materials Science and Engineering, KTH Royal Institute of Technology, SE-100 44 Stockholm, Sweden. MIAOYONG ZHU, Professor, and YELIAN ZHOU, Ph.D Student, are with the School of Metallurgy, Northeastern University, China. Contact e-mail: [email protected]. DU SICHEN, Professor, is with the Department of Materials Science and Engineering, KTH Royal Institute of Technology. Manuscript submitted August 10, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS B
INDUSTRIAL INVESTIGATION
A. Main Features of the Processes Two different Al-killed steel grades were considered in this study, namely high-strength low-alloyed steel (HSLA) and ultra-low carbon st
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