Na2O对超高碱度连铸保护渣性能的影响

 在包晶钢连铸过程中,裂纹类缺陷频繁出现。生产实践表明,采用结晶性能较强的保护渣可以有效减少纵裂纹的发生,但会恶化保护渣的润滑功能。近年来,超高碱度保护渣由于兼具开始结晶温度低、结晶速率快的特点,可以成功协调包晶钢连铸过程中润滑与传热的矛盾。但在超高碱度条件下,有关组分对保护渣结晶性能的影响研究不多,且相应的熔渣结构特征也鲜有报道。Na₂O作为保护渣中一种常见的组元,对调节保护渣性能具有重要作用。论文采用半球点熔化温度测试仪、旋转黏度计以及高温原位结晶性能测试仪分析了超高碱度下(综合碱度R=1.75)Na₂O对连铸保护渣熔化流动特性以及凝固结晶性能的影响规律和作用机制。研究结果发现,随着Na₂O含量增加,保护渣的黏度(1 300 ℃)、熔化温度、转折温度和结晶温度都呈下降趋势,结晶速率呈现先减小后增大的趋势,当Na₂O质量分数为6%时结晶速率最低。此外,研究还发现超高碱度保护渣中主要析出相为枪晶石(Ca₄Si₂F₂O₇),随着Na₂O含量进一步增加,渣中出现新的结晶相CaF₂和Na₂CaSiO₄F。

Effect of Na2O on properties of ultra-high basicity continuous casting mold fluxes

During the continuous casting of peritectic steel, defects of longitudinal cracks of casting strands frequently appear. Production practice shows that mold fluxes with strong crystallinity can effectively reduce the occurrence of longitudinal cracks, but it will deteriorate the lubrication function of mold fluxes. In recent years, the ultra-high basicity continuous casting mold fluxes have the characteristics of low initial crystallization temperature and fast crystallization rate, which can successfully balance the contradiction between lubrication and heat transfer in the continuous casting of peritectic steel. However, there are few studies on the effects of related components on the crystallization properties of the ultrahigh basicity mold slag, and the corresponding structural characteristics are also rarely reported. Na₂O is a common component element in mold fluxes and plays an important role in adjusting the properties of mold fluxes. The effect and mechanism of Na₂O content on the melting flow characteristics and solidification and crystallization properties of continuous casting mold fluxes at ultra-high basicity(R=1.75) was analyzed by hemispherical point melting temperature tester, rotational viscometer and high temperature in-situ crystallization performance tester. The results showed that the viscosity (1 300 ℃) of mold fluxes,melting temperature,break temperature and crystallization temperature all decreased with the increase of Na₂O content,while the crystallization rate first decreased and then increased,and the crystallization rate was the lowest when mass percent of Na₂O was 6%. In addition,it is found that the main precipitates in the ultra-high basicity mold flux were gun spar(Ca₄Si₂F₂O₇). With the further increase of Na₂O content,the new crystalline phases CaF₂ and Na₂CaSiO₄F appeared in the mold flux.