Characteristics of Nozzle Clogging and Evolution of Oxide Inclusion for Al-Killed Ti-Stabilized 18Cr Stainless Steel
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INTRODUCTION
THE addition of titanium in stainless steel can bind the interstitial elements C and N in steel and improve the corrosion resistance of stainless steel. Titanium-stabilized stainless steels usually use aluminum as a final deoxidizer to increase the yield of titanium alloys and reduce the formation of titanium-containing oxides. However, nonmetallic inclusions formed during Al-killed Ti-bearing stainless steelmaking process generally cause severe clogging of submerged entry nozzle (SEN) during continuous casting process.[1–3] The deposits on the inner layer of SEN would reduce casting throughput and even cause the shutdown of the continuous casting process. In addition, the dislodged clogs, mold-level fluctuations, and slag entrainment can lead to the surface defects of the final stainless steel
JINGYU LI and GUOGUANG CHENG are with the State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing, Beijing, 100083, P.R. China. contact e-mail: [email protected]. QIANG RUAN, JIXIANG PAN, and XINGRUN CHEN are with the Hongxing Iron & Steel Jiuquan Iron and Steel Co., Ltd., Jiayuguan, Gansu, 735100, P.R. China. Manuscript submitted May 6, 2019. Article published online October 4, 2019. METALLURGICAL AND MATERIALS TRANSACTIONS B
product.[1,4] After continuous casting of Al-killed steels, the alumina inclusions are usually found in the deposition of SEN, which is believed as the primary source in the buildup of the nozzle clogging.[1,5–8] Calcium treatment is commonly taken as an efficient way to reduce clogging of SEN.[9–13] However, sometimes clogging of SEN still occurs after calcium treatment. Calcium treatment can modify aluminum inclusions to liquid oxides, but the oxide inclusions that are not effectively modified can still be a source of clogging.[14,15] The clogging tendency in Al-killed Ti-bearing steel generally increases significantly.[1,2,16] The clogging deposits of Al-killed Ti-stabilized steel are found to be mainly coarse Al2O3 and spinel clusters and at least traces of Ti-oxide.[1,17] The wettability between steel and alumina inclusions is usually increased after the addition of titanium, which could lead to a decrease of removal rates of inclusions from molten steel.[18–20] As a consequence, more inclusions are likely to be present in Ti-stabilized molten steel, which increases the probability of clogging of SEN. The evolution mechanism of inclusions during Al-killed Ti-bearing steelmaking process has been widely investigated to control the formation of oxide inclusions and improve the molten steel cleanness before casting.[21–24] Oxide inclusions formed in molten steel
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with the decreasing temperature during continuous casting could also affect the formation of clogging.[25,26] The temperature drop would decrease the solubility of oxygen in molten steel. Subsequently, alumina would be precipitated in Al-killed molten steel, which could increase the clogging tendency.[25] During Ti-stabilized stainless steel continuous casting proce
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