The effect of basicity (weight ratio of CaO/SiO 2) and B 2 O 3 on the viscosity and structure of Fluorine-free mold flux for the casting of medium carbon steels was conducted in this article, through the rotating cylinder method combined with the Fourier transform infrared (FTIR) spectroscopy. The results showed that, with the increase of basicity, the viscosity of mold flux was attenuated dramatically, and then kept constant or slight increased in the low temperature region. The reason could be explained as the degree of polymerization (DOP) of the network structure was first reduced significantly with the addition of basicity, and then the further depolymerization is less pronounced with the further increase of basicity. Beside the formation of high melting point substance leads to the slight increase of viscosity. Moreover, it suggested that the viscosity of mold flux is decreased with the addition of B 2 O 3 content, due to the fact that B 2 O 3 is a low melting point oxide which could substantially lower the break temperature of mold flux. The result of FTIR indicated B 2 O 3 acts as network former, and tends to form [BO 3 ]-trihedral and [BO 4 ]-tetrahedral structural units, which would connect with each other to form some simple network structure such as diborate or pentaborate. With the addition of B 2 O 3 , the free oxygen ions (O 2-) would depolymerize the diborate structural unit, and the depolymerized diborate would link again with free [BO 3 ]-trihedral to form complex pentaborate groups. Moreover, the effect of above addition on the apparent activation energy for viscous flow and break temperature of mold flux also were discussed. The results obtained in this paper provide the detailed study of the structure evolution of Fluorine-free mold flux when B2O3 is added.
With the development of multiphase slag system for hot-metal treatment to achieve better dephosphorization efficiency, it is very important to improve the distribution ratio of P2O5 between the solid solution (2CaO·SiO2-3CaO·P2O5) and liquid phase slag. This study was carried out to investigate the effects of Na2O and B2O3 on P2O5 distribution ratio and morphologies of corresponding solid solutions in CaO-SiO2-Fe2O3-P2O5 slag system. The results indicated that the distribution ratio of P2O5 would be improved with the increase of Na2O content due to the formation of (2CaO·SiO2-Na2O·2CaO·P2O5) solid solution with a similar morphology as that of reference solid solution (2CaO·SiO2-3CaO·P2O5) in the reference slag. While B2O3 plays an opposite role, it would not only reduce the phosphorus distribution ratio, but also change the morphology of its corresponding solid solution due to the formation of complex solid solution (2CaO·SiO2-Ca9.93(P5.84B0.16O24) (B0.67O1.79)). Besides, the effect of cooling rate on the size of the solid solution was also studied. It would provide an instructive way for the design of multiphase slag for hot metal treatment.
An investigation was carried out to study the influences of basicity and Li 2 O on the melting, crystallization, and heat transfer behavior of Fluorine-free mold flux designed for the casting of medium carbon steels using double hot thermocouple technology and infrared emitter technique. The results showed that with the addition of basicity, the melting and crystallization temperatures of the mold fluxes were increased, and the final heat transfer rate was reduced, as the basicity tends to promote the crystallization behavior of the designed mold fluxes. Besides, with the increase of Li 2 O content in the mold flux, the melting and crystallization temperature decreased, as the Li 2 O tends to inhibit the formation of high melting temperature crystal and lower the system melting temperature zone; meanwhile the crystallization capability of the mold flux was enhanced in the low-temperature region. Moreover, the results of EDS and XRD were confirmed that the main crystal phase in the Fluorine-free mold fluxes is calcium borate silicate (Ca 11 Si 4 B 2 O 22 ). Those results obtained can provide guidelines for the design of new Fluorine-free mold flux for the casting medium carbon steels.
Recently, a new refining method of using a solid/liquid coexistence multiphase slag for dephosphorization of hot metal was proposed, with the aim to improve the utilization efficiency of CaO and the degree of dephosphorization. Based on this method, an ion and molecule coexistence theory (IMCT) based the thermodynamic model has been developed to clarify the behavior of solid CaO dissolution and the phosphorus-enrichment capability of calcium silicates in the multi-phase slag in this article. According to the calculated mass action concentration of the related structural units, the reaction mechanism between solid CaO and the liquid slag in the multiphase slag is explained. Meanwhile, the phosphorus-enrichment capability of calcium silicates is probed. The results show that the dissolution of solid CaO into the multi-phase slag will be enhanced with the addition of the temperature or the increase of the FeO content, the mass percent ratio of FeO to Fe 2 O 3 (m(FeO)/m(Fe 2 O 3 )), and the P 2 O 5 content, while the high basicity (CaO/SiO 2 ) will restrict the dissolution of solid CaO. Besides with the increase of basicity and m(FeO)/m(Fe 2 O 3 ), the phosphorus-enrichment contribution ratio of 2CaO Á SiO 2 displays an exponential growth tendency, while it exhibits an asymmetric parabolic relationship with the increase of FeO, and it slightly decreases with the increase of P 2 O 5 and unchanged with the temperature. Those results obtained can provide a fundamental guidance for the dephosphorization by using the CaO-based solid/liquid coexistence multiphase slag for hot metal treatment.
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