Evolution of Nonmetallic Inclusions During Spring Steel Treatment

Abstract

Features of nonmetallic inclusion formation and evolution in the course of treating spring steel of 54SiCr6 (60S2KhA) grade are studied. It is established that the majority of nonmetallic inclusions (NI) present within steel are complex oxides of the composition SiO₂–MnO–Al₂O₃–CaO–MgO, at whose surface during steel crystallization and cooling as a rule there is a deposit of MnS. NI composition changes in the course of metal treatment. At the start of treatment, their base is MnO–SiO₂–Al₂O₃, and subsequently there is an increase in content of CaO and MgO as a result of molten metal reaction with slag and lining. The average NI size and overall oxygen content decrease in the course of steel treatment, and this points to effective refining. The composition of NI present is close to that of the slag cover assimilating layer used in the intermediate ladle. A more significant increase is noted in MgO and Al₂O₃ content within it, and this points to effective assimilation of NI of the most unfavorable types.