Article ID: ISIJINT-2019-449
In dephosphorization process in steelmaking, phosphorus in molten iron is distributed into molten slag after oxidized, and it forms 3CaO·P2O5. It has been known that dicalcium silicate (2CaO·SiO2) formed in molten slag and 3CaO·P2O5 make a solid solution, which could promote dephosphorization efficiency from molten iron. It has been reported that 2CaO·SiO2–3CaO·P2O5 solid solution (α phase) is formed for entire composition range at higher temperatures than 1673 K, and many previous studies on dephosphorization behavior assumed that the α phase would be precipitated from molten slag. However, we found that the α phase cannot be obtained at low phosphorus concentrations when the pellet of 2CaO·SiO2 and 3CaO·P2O5 powders mixture is annealed and quenched to room temperature. In this study, we conduct high temperature in-situ X-ray diffraction analysis to the aerodynamically levitated sphere of the 2CaO·SiO2–3CaO·P2O5 liquid to identify primary crystallized phase. It has been verified that the α phase is precipitated from the liquid for wide phosphorus concentrations. In addition, a rapid phase transition of the 2CaO·SiO2–3CaO·P2O5 solid solution has been detected by the time-division X-ray diffraction with high resolutions when the levitated sample containing the α phase is quenched from the precipitated temperature.