Effect of CaO/Al2O3 ratio on desulphurization and non-metallic inclusions in low-density steel

To determine the effect of the CaO/Al2O3 ratio on desulphurization and inclusion evolution in low-density steel, a series of laboratory-scale experiments are performed. The results show that violent reaction occurs at the interface between refining slag and molten steel. As the slag-steel reaction progresses, (CaO) and (MgO) are reduced to [Ca] and [Mg] by dissolved [Al]. The deoxidation product Al2O3 dissolves into the slag and accumulates at the slag-steel interface. The evolution process of the sulphide inclusions is CaS -> MgS -> MnS. The sulphide outer layer wraps AlN and spinel inclusions, floats up and is absorbed by the top slag. During refining process, the accumulated Al2O3 at the slag-steel interface easily forms MgO center dot Al2O3. Finally, a dense spinel layer can be formed at the slag-steel interface, which inhibits the desulphurization reaction. Reducing the C/A ratio can reduce the formation of MgO center dot Al2O3 and has a positive effect on the desulphurization in low-density steel. The influence of the C/A ratio on desulphurization kinetics should be considered in the design of slag composition.