Abstract

ZHAO, S. et al. Control of complex inclusions in high-strength ship plate steel by reducing calcium treatment. J. S. Afr. Inst. Min. Metall. [online]. 2019, vol.119, n.1, pp.41-48. ISSN 2411-9717.  http://dx.doi.org/10.17159/2411-9717/2019/v119n1a5.

To eliminate nozzle clogging during continuous casting of ship plate steel and reduce the calcium addition required, the composition of CaO-MgO-Al₂O₃ inclusions in the liquid phase region must be controlled. Thermodynamic calculations using FactSage show that when the balanced Al content is 0.03 mass %, a_Cain the liquid steel is 1-10 ppm, and a_Mgis 0.01-0.3 ppm; and when the balanced Al content is 0.06 mass %, a_Ca in the liquid steel is 1-30 ppm, and a_Mgis 0.05-0.9 ppm. The CaO-Al₂O₃-CaS inclusions can be controlled in the liquid region below 1600°C at a_Cavalues of 5 ppm, 15 ppm, and 30 ppm, and the balanced Al content should be controlled in the range of 0.001-0.050, 0.005-0.250, and 0.010-0.50 mass %, respectively. Based on theoretical analysis, the refining slag composition should be controlled to 45-53 mass % CaO, 30-37 mass % Al₂O₃, 6-12 mass % SiO₂, and 6-8 mass % MgO. Optimization of the slag system and steel composition can reduce, or even eliminate, the requirement for calcium treatment. The total oxygen content in the slab can be controlled to 15-21 ppm, with typical micro-inclusions < 10 μm in size, with compositions in the CaO-Al₂O₃-MgO and CaO-Al₂O₃-CaS systems.

Keywords : alcium treatment; refining slag; inclusions; ship plate steel; melting point.

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