| Aluminum is one of the most common alloying elements in the production of modern steel.It is widely used in the production of TRIP steel,non-oriented electrical steel,austenitic non-magnetic steel,iron-chromium-aluminum stainless steel,and other series of high-aluminum steels.However,due to the high content of Al in high-aluminum steel,there is a serious slag-steel interface reaction in the mold during the continuous casting process,which changes the composition of the mold flux,deteriorates the metallurgical function seriously,and leads to defects in the quality of the cast slab.Therefore,the traditional CaO-SiO2 based mold flux is not suitable for continuous casting high-aluminum steel.It is urgent to develop special mold fluxes for continuous casting high-aluminum steel.This paper took the calcium-aluminum-based mold flux used by a domestic steel plant as the research object.In order to solve the problems of easy slagging circle and frequent bonding steel breakout alarms during the continuous casting process,a new type of low-reactivity CaO-Al2O3 based mold flux was first designed.On the basis of focusing on the macroscopic properties of the mold flux,such as the microstructure,melting temperature,viscosity and crystallization properties,and their changing laws,the new type of mold flux was designed with suitable properties.Under the conditions of this paper,the main conclusions are summarized as follows:(1)With the increase of w(CaO)/w(Al2O3),the melting temperature and the degree of polymerization of the mold flux decreased gradually.The crystallization performance weakened first and then increased gradually.After analyzing the crystalline phases,the change law of the crystalline phases was LiAlO2+Ca2Al2SiO7→Ca2Al2SiO7→LiAlO2+Ca12Al14O32F2+Ca3B2O6.(2)With the increase of w(B2O3)instead of CaF2,the melting temperature of the mold flux decreased gradually,the degree of network polymerization increased,and the viscosity gradually increased at 1300℃.The crystallization performance of the mold flux was obviously inhibited,and the crystallizing phase of the mold flux changed.The law was Ca12Al14O32F2→Ca2Al2SiO7→single liquid phase.(3)With the increase of w(Li2O),the melting temperature of the mold flux showed the trend of decreasing first and then increasing,the depolymerization of network structure was obvious,the viscosity at 1300℃ gradually decreased,and the crystallization ability gradually increased.The change rule of the crystalline phases was Ca2Al2SiO7→LiAlO2+Ca12Al14O32F2+Ca3B2O6.(4)The physical and chemical properties of the new mold flux CaO-Al2O3-SiO2-CaF2-Li2O-B2O3-Na2O was designed in this paper were effectively improved compared with the industrial slag.The melting temperature was 1043℃,the viscosity was 0.102 Pa·s at 1300℃ and the main crystalline phase was single Ca2Al2SiO7.The research work of this paper can provide theoretical basis for the design,development and performance control of special mold fluxes for continuous casting high Al steels. |
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