Formation and Evolution of Non-metallic Inclusions in Ti-Bearing Al-Killed Steel During Secondary Refining Process
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UE to the strong affinity to oxygen, aluminum and titanium are used as the main deoxidizers in steelmaking process. Meanwhile, titanium is also an important alloying element in steel, which can improve the strength, ductility, formability, and welding properties of steel.[1–3] To achieve good performance, titanium is added in many steel grades, e.g., IF steel, gearing steel, and stainless steel. On the other hand, the addition of titanium may affect the castability of liquid steel, leading to clogging problem of submerged entry nozzle (SEN) during continuous casting process.[4–7] Many publications[4–8] pointed out that the inclusions in steel are one of the main reasons to cause clogging.
ZHIYIN DENG is with the Key Laboratory for Ecological Metallurgy of Multimetallic Minerals (Ministry of Education), Northeastern University, Shenyang 110819, P.R. China, and with the School of Metallurgy, Northeastern University, and with Shandong Iron & Steel Cop. Ltd. Laiwu Branch, Jinan 271104, P.R. China. Contact e-mail: [email protected] LEI CHEN, GUODONG SONG, and MIAOYONG ZHU are with the with Key Laboratory for Ecological Metallurgy of Multimetallic Minerals (Ministry of Education), Northeastern University, and also with the School of Metallurgy, Northeastern University. Manuscript submitted July 28, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS B
A lot of researchers studied the behaviors of inclusions during the deoxidation process using titanium.[3,9–13] It was found that the content of titanium has an evident influence on the phase and the composition of inclusions in steel. These studies mainly focused on low carbon and ultra-low carbon steel grades. Because deoxidation needs to be carried out after decarburization during vacuum treatment, the slag generally contains a very high FeO content.[4] As a result, the effect of top slag on the modification of inclusions in steel would be very weak. In these cases, the reported inclusions were mainly Al2O3 and Al2O3TiOx system inclusions.[3,4,10–13] In contrast to ultra-low carbon steel grades, the refining process of middle and high carbon steel grades usually has a longer refining time, and the control of their slags is much stricter. Due to the longer impact time and the much lower oxygen in slag, the inclusions in steel would transform into different types of inclusions during refining process.[14–21] Generally, these inclusions are different from the initial products of deoxidation. Many investigators[14–21] spent a lot of efforts to study the evolution of inclusions in steel. Their study results showed that refining slag and refractory have an important influence on the evolution of inclusions in steel. The interaction between steel and slag/ refractory would generate a trace of dissolved Mg and Ca in liquid steel, leading to the transformation of inclusions along the evolution route of ‘‘Al2O3 fi
MgOÆAl2O3 spinel fi CaO-Al2O3(-MgO) system’’. Note that the steel grades in these studies were Ti-free steel grades. In fact, some researchers[22–27] investigated the formation of som
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