Effects of calcium treatment on non-metallic inclusions in Al-deoxidized steel

How to control Al₂O₃ oxide inclusions in Al-deoxidized steel has long been a challenging issue in metallurgical production. Calcium treatment can modify high-melting-point Al₂O₃ oxide inclusions into low-melting-point calcium aluminate（12CaO·7Al₂O₃）, which effectively inhibits nozzle clogging and improves the hydrogen-induced cracking resistance of steel. However, parameters such as the timing and method of calcium addition directly affect the calcium yield and the degree of inclusion modification. Improper control may, on the contrary, exacerbate the nozzle clogging phenomenon. Therefore, the modification effect of calcium treatment on non-metallic inclusions in Al-deoxidized steel is reviewed. From the perspectives of kinetics and thermodynamics, the mechanism of action and key influencing factors are elaborated, including the effects of molten steel temperature, calcium addition method and timing, CaO/Al₂O₃ ratio of refining slag, as well as the contents of O, S and Al in molten steel on the compositional evolution and liquid phase fraction of inclusions. In addition, the technological optimization directions of calcium treatment is discussed, aiming to improve calcium utilization efficiency and inclusion control level, involving innovative approaches such as secondary calcium treatment, application of calcium-silicon iron, and calcium-magnesium alloy synergism.