Formation Mechanism of Large-size CaO–Al₂O₃–MgO–SiO₂ Inclusions in High Carbon Chromium Bearing Steel

摘要

Industrial experiments and thermodynamic analyses were carried out to investigate the formation mechanism of large-size (>30 μ m) CaO–Al_(2)O_(3)–MgO–SiO_(2) (CAMS) inclusions in high carbon chromium bearing steel. It was found that the large-size CAMS inclusions existed during the whole refining process, most of which compositions were located in the liquid region. The average content of SiO_(2) in CAMS inclusions decreased from 27.5 mass% at argon-blowing station to 3.0 mass% in the hot-rolled bars. The results calculated by Factsage 7.3 indicated that the CAMS inclusions were originated from slag entrapment. During BOF tapping, the low basicity slag with 60 mass% SiO_(2) was entrapped into steel and combined with the deoxidation product Al_(2)O_(3), forming a large amount of liquid CAMS inclusions. During LF refining process, [Al], [Ca] and [Mg] in molten steel were affected by the activities of corresponding slag components. The reaction between these three elements and SiO_(2) in CAMS inclusions originating from slag lead to the decrease of SiO_(2) in the inclusions. Due to the low interfacial energy between liquid CAMS inclusions and steel, a few large-size inclusions may be inherited to hot-rolled bars. In light of this, several optimization steps were conducted during BOF tapping and argon-blowing station. After the optimization, large-size CAMS originated form BOF tapping were effectively removed.