Abstract: In order to explore the formation and evolution mechanism of large-size Al₂O₃-SiO₂-MnO inclusions with the size of more than 10 〖WTBZ〗μ〖WTB4〗m in 37Mn5 steel refining process, the molten steel was systematically sampled during the whole refining process of EAF-LF-VD-calcium treatment-continuous casting for production of 37Mn5 steel. The composition of molte steel was detected, and the morphology and composition characteristics of large-size Al₂O₃-SiO₂-MnO inclusions in different smelting stages were analyzed. Based on actual production process and thermodynamic calculation, the evolution law of this kind of inclusion was revealed. The results show that, due to the low Al content and high O content in local molten steel during EAF tapping process, large-size Al₂O₃-SiO₂-MnO inclusions are formed. At the beginning of LF refining, the local Ca content increases to form Al₂O₃-SiO₂-MnO-CaO inclusions. After the middle stage of LF refining, the Ti content increases to modify the two kinds of inclusions formed at the early stage to form inclusions containing TiOx. With the progress of smelting, the distribution of Ti is gradually uniform in the inclusions. Insufficient calcium treatment after VD results in unsatisfactory modification of inclusions, and has little effect on the large-size inclusions. Reasonable deoxidation, alloying and slagging process can reduce the formation of Al₂O₃-SiO₂-MnO-CaO inclusions, so as to reduce the number of inclusions and improve the quality of steel.

Key words: 37Mn5 steel, steel refining, inclusion, cleanliness