Design of a novel Si-Fe-Ca alloy with enhanced Ca yield for silicon steel refining: Tailoring phase composition and thermodynamic stability

To enhance the calcium yield during calcium treatment of non-oriented silicon steel, a novel Si-Fe-Ca alloy is designed and prepared using commercial FeSi, Si-Ca alloy, and silicon steel scrap. The influence of Fe content on elemental yield, phase characteristics, physicochemical properties, and calcium-treatment efficiency is systematically investigated. The obtained results show that the yields of Si and Ca elements exceeding 85% in the prepared Si-Fe-Ca alloy. Low-Fe alloys (S1, S2) primarily consist of Si, FeSi 2 , and CaSi 2 phases. With increasing Fe content (S3–S6), the dominant phase changes from Si to FeSi, accompanied by refined Si phase, coarsened FeSi and finely dispersed CaSi 2 in the matrix. Thermodynamic calculations indicate that although higher Fe content raises Ca activity, it remains below 0.0008 (<50 wt.% Fe), and the resulting vapor pressure is much lower than that of pure Ca, effectively suppressing Ca volatilization. The activity and vapor pressure of Si in the alloy also decrease with Fe. Alloy density increases as the Fe content increases, dynamic viscosity decreases, and the liquidus temperature exhibits a non-monotonic trend, first decreasing and then increasing. Calcium treatment experiments in silicon steel demonstrate that alloys with higher Fe content promote the modification of Al 2 O 3 inclusions into low-melting-point Al-Ca-O and Al-Ca-O-S complex inclusions because increased alloy density prolongs residence time in steel, and refined CaSi 2 phase lowers Ca release rate, and reduced local Ca activity suppresses violent vaporization of Ca. This study provides theoretical and technical insights for designing high-Ca-yield alloys and optimizing calcium treatment in non-oriented silicon steel production.