Effect of Cerium Content on Inclusions in an Ultra-Low-Carbon Aluminum-Killed Steel
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UCTION
SINCE the demand for higher performance steels increases yearly, increasingly strict requirements on the quality of steels are proposed. Non-metallic inclusions have a significant detrimental effect on the properties of steels.[1–3] Thus, many efforts have been devoted to control the composition, size and amount of inclusions.[4–8] Since rare earth elements have a high affinity with oxygen and sulfur in the steel, they have been widely used to modify inclusions and promote properties of steel products such as the impact toughness,[9–12] magnetic properties[13–15] and corrosion resistance.[16–19] Cerium has the highest abundance among rare earth elements so that much attention has been devoted to it. Many studies have investigated the formation and modification of inclusions in the steel after adding cerium. Katsumata[20] found that inclusions were Al2O3-Ce2O3 when both aluminum and cerium were added, and the fraction of Ce2O3 increased with the increasing cerium content. Wang[21] studied the QIANG REN is with the School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing (USTB), Beijing 100083, China. LIFENG ZHANG is with the State Key Lab of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004, China. Contact e-mail: [email protected] Manuscript submitted June 6, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS B
modification of MgOÆAl2O3 inclusions by adding cerium to spring steel and reported that MgOÆAl2O3 inclusions were wrapped by rare earth inclusions to form a ring-like shaped Ce-rich band around the inclusion, so that the diffusion of cerium, aluminum and magnesium in the core of the inclusion and in the intermediate layer was the dominant step for the modification process. Li[22] investigated the effect of the cerium treatment on Al2O3 inclusions in a low-carbon high-manganese steel and reported that inclusions were modified into rare earth ones along the route of Al2O3 fi Ce2O2SAl2O3 fi Ce2O2S when the cerium in the steel increased from to 0.034 wt pct. Huang[23] investigated the modification mechanism of the cerium on oxides in a H13 steel, and found that the evolutionary process was MgOÆAl2O3 fi CeAlO3 fi Ce-O and Ce-O-S when the cerium content increased from 0 to 0.03 wt pct. Although most of the published efforts were devoted to thermodynamic study or experimental analysis,[24–29] little combination work of an experimental study with thermodynamic analysis was done, especially for the formation of Ce2O2S inclusions in the steel. Also, the relationship between the steel composition and inclusions has been little studied. The current study is to investigate the effect of cerium content on the modification of Al2O3 inclusions in an ultra-low-carbon Al-killed steel. Thermodynamic calculation was performed to analyze the stable phase of
inclusions, and a model was developed to predict the composition of inclusions according to the composition of the steel.
II.
composition, size, position, amount and morphology of inclusions automatically. Th
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