Abstract

ZHAO, S. et al. Effect of different refining slag systems on the cleanliness of molten steel for carbon structural steel. J. S. Afr. Inst. Min. Metall. [online]. 2017, vol.117, n.4, pp.343-350. ISSN 2411-9717.  http://dx.doi.org/10.17159/2411-9717/2017/v117n4a5.

The effect of two refining slags (A: 1.0-1.8 CaO/Al₂O₃ ratio, 11-20 wt% SiO₂; and B: 1.0-1.2 CaO/SiO₂ ratio, 25-35 wt% Al₂O₃) on the inclusion morphology of a carbon structural steel (Q235B) was studied by controlling the balance between the steel and the refining slag at 1600°C in a Si-Mo resistance laboratory furnace. The results showed that most of the inclusions in the molten steel balanced with slag A were formed by a low-melting CaO-MgO-Al₂O₃-SiO₂ system with a total oxygen content (T[O]) being fixed at 6-13 ppm. The inclusions in liquid steel balanced with the slag B were mostly formed by the CaO-MnO-Al₂O₃-SiO₂ system, with T[O] controlled to 19-26 ppm. The overall size of the inclusions under balance conditions was higher in the steel reacted with the slag B than that reacted with slag A, with the latter showing more inclusions smaller than 3 μΐη. In order to generate a large number of spherical CaO-MgO-Al₂O₃-SiO₂ inclusions smaller than 3 μηι while decreasing the T[O] in the resulting steel, the composition of slag A should be used. This composition allowed improving the cleanliness of the slab, and is also advantageous for the castability of the molten steel.

Keywords : carbon structural steel; cleanliness; refining slag; inclusions.

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