Study On Mineralogical Structure Formation Mechanism Of Continuous Casting Fluxes Film

Through the phase diagram of software simulation and the experiment of constant temperature crystallization of flux film, this thesis will analyze the ore phase’s formation mechanism of normal film and accident film respectively in different steel grades and the same steel grade, based on the features of the ore phase structure of flux film.Based on the studies of previous researches and ingredients of casting powder, the simulated slag scheme with component of quaternary slag system is enacted, according to CaO/SiO₂=1-1.4, Al₂O₃=7-15% and CaF₂=9-17%. The thesis uses phase diagram’s simulation software Fact Sage to simulate the rule of crystallization of the flux film for some kind of minerals. And the simulated result is the crystallization of Cuspidine has the highest temperature, followed by Melilite and Wollastonite. The crystallizing quantity of Cuspidine increases with the augment of basicity and CaF₂ while the crystallizing quantity of Wollastonite is declined. And with the increase of basicity and Al₂O₃, the crystallizing quantity of Melilite is increased. Besides, the content of CaF₂ has the less influence on the crystallizing quantity of Melilite. On the basis of this, the laboratory makes the film of mould flux and studies its phase structure, and the crystallization experiment about film is, within the scope of simulation, the rule of crystallization of those minerals is consistent with the simulated result.With the systematical study about the phase structure of film of mould flux of mild steel SPHC, medium carbon steel Q235 B and high-carbon steel 45#, it can be seen that the phase structure of low-carbon steel SPHC’s film is “crystallizing layer—glassy layer”,and the Cuspidine is sole precipitation mineral. And the phase structure of Q235 B and45# are “glassy layer—crystallizing layer”. Among them, Q235 B has high crystallization rate and in its interior, there is obvious the hierarchy of Cuspidine and Melilite. While45# has low crystallization rate and has a few Wollastonite and Melilite on one side of casting blank. In terms of the comprehensive analysis of Fact Sage and experimental results, it can be concluded that the film’s formation mechanisms of SPHC, Q235 B and45# are respectively low basicity of casting powder, low crystallization rate of film, well heat conduction and few Cuspidine is separated out on one side of crystallizer; and Q235 B has high basicity of casting powder and high crystallization rate of film, besides,after the precipitation of Cuspidine, Melilite is continue to separated out; 45# has low basicity of casting powder and low crystallization rate of film. On the condition of growing crystal, there are few precipitations of Wollastonite and Melilite. These corresponding phase structures about three kinds of steel can meet the request of casting powder and film, so there is no quality problem.After systematically study Q235B’s film phase structure under the longitudinal crack of the surface of casting blank and the situation of cementation and bleed-out, it can be seen that the change of chemical component in film can change the phase structure of film. Analyzing simulated phase diagram and experimental results, it can be concluded that the reason forming the slag film which has longitudinal crack on the surface of casting blank is the content of slag film SiO₂ is relatively higher, so that the slag film’s crystallization rate declines, appearing the precipitation of Cuspidine and forming the phase structure of “crystallizing layer—glassy layer—crystallizing layer”. The formation mechanism about the situation of cementation and bleed-out is the content of SiO₂ is relatively lower, so that the basicity of slag film increases, forming the phase structure of“glassy layer—crystallizing layer” which has plenty of the precipitation of Cuspidine.This research result has the high practical significance for deploying the casting powder to guarantee process smoothly.