【作者】 杨波；

【导师】 唐萍；

【作者基本信息】 重庆大学 ， 冶金工程， 2011， 硕士

【摘要】 保护渣是连铸过程中使用的一种关键性的功能材料,其对铸坯向结晶器的传热具有很重要的控制作用。通过调整保护渣的化学成分来改变保护渣的传热特性,从而减少裂纹敏感性钢种的纵裂纹被证实十分有效。但是由于目前对保护渣传热性能的测试方法不完善,导致了对保护渣传热性能的研究不够系统。结晶器渣膜热流模拟仪综合考虑了液渣的传热、固态渣膜的传热、以及固态渣膜与模拟铜结晶器之间的界面传热这一综合传热现象,同时具有方便、可靠、测试费用低的优点,具有被广泛应用的前景,然而其结晶器保护渣渣膜传热的表征方法没有实现完善的建立。本文利用现场获取渣膜与热流模拟仪获得的渣膜进行对比研究得出:模拟仪45s获得渣膜与实际结晶器弯月面附近45s的渣膜结构相近,而且45s时刻以后的热流密度变化缓慢,从而确定了模拟仪的渣膜热流测试结束的时间及取渣膜时间为45s。通过分析热流密度随时间变化的特征曲线,建立了基于模拟仪的表征方法,表征参数分别为:①最大热流密度表征液态保护渣的传热;②稳定气隙形成时间表征保护渣在弯月面传热热流降低的速度;③t1-t2之间的平均热流密度反映保护渣在弯月面区域的传热能力;④t2-45s表征气隙稳定形成后渣膜的传热能力;⑤t1-45s表征保护渣总的传热能力,这对应于生产实际现场反映的传热热流数据。并通过对比分析同一机型生产实际应用的中碳钢（MC）和低碳钢（LC）保护渣的测试参数,验证了表征方法的合理性。在建立了基于模拟仪的保护渣渣膜传热表征方法的基础上,研究了保护渣化学成分（R、CaF₂、Na₂O、Al₂O₃、MgO、Li₂O、MnO、以及用NaF代替CaF₂提供F-,并代替Na₂O提供Na⁺）对保护渣渣膜结构和传热性能的影响,获得了本渣系条件下的碱度及化学成分对保护渣稳定气隙形成时间、各类热流密度的影响规律。也由此得出:稳定气隙形成时间与渣膜厚度和结晶率相关,渣膜厚度越厚或者结晶率越高越有利于在弯月面区域形成稳定气隙,即有利于在弯月面传热热流降低速度的提高,渣膜厚度的影响高于结晶率的影响;影响各类热流密度最主要因素为渣膜厚度和结晶率,其中渣膜厚度的影响高于结晶率的影响;影响渣膜厚度的主要因素为熔点和粘度,其次为结晶能力,熔点越低、粘度越低越倾向于形成薄的渣膜,结晶能力提高促进渣膜厚度的增加。本文还研究保护渣物理性能（熔点和粘度）对其渣膜结构以及传热性能的影响,研究表明:①增加保护渣的熔点和粘度都有利于减小保护渣的传热能力,这是由于熔点和粘度的增加会导致渣膜厚度增加,②熔点对结晶率没有明显的影响规律,增加粘度有降低结晶率的趋势。更多还原

【Abstract】 Mold flux is a key functional material used in the continuous casting process, which has a very important function of controlling the heat transfer from strand to mould. It has been confirmed that change the heat-transfer character of mold flux through changing its chemical composition is very effective, and that will reduce the longitudinal crack of cracking sensitivity steel. But it is a difficulty to study the heat transfer properties of mold flux because of that the test methods of heat-transfer character are not perfect at present. The heat flux simulator of mold slag film comprehensively considered the comprehensive heat-transfer phenomenon of the heat-transfer of molten slag and solid slag, as well as the interface heat-transfer between solid slag film and simulate copper mould, it also has many advantages, such as conveniency, dependable, low test cost, and it has a widely application prospect. However, the parameters that can be used to characterize the mold flux’s heat-transfer properties have not been built perfectly.This paper take advantage of the heat flux simulator of mold slag film, put the plant acquisition slag flim and the slag film which acquired by simulator contrast, the research shows that structure of the slag film which acquired by simulator at 45s is near with the one which nearby the practical mould meniscus at 45s, and the heat flux density changes slowly after 45 second, so the 45s is determined as the time of heat flux mearurement and solid slag film acquisition of simulator. And through analyzing the characteristic curve of heat-flux density change with time, setting up the characteristic methods which based on the simulator.Characterization parameters are:①the maximum heat-flux characterize the heat-transfer of liquid slag;②the time of air gap formation steadily characterize the velocity of slag reduce heat transfer at meniscus;③the average heat-flux density between t1 and t2 reflects the heat-transfer capability of slag at meniscus;④the average heat-flux density between t2 and 45s characterize the heat-transfer capability of slag after air gap formed stably;⑤t1-45s characterize the total heat-transfer capability of slag, which is corresponding to actual heat flux data obtained from practical production. And proving the rationality of characteristic method through comparison analyze test parameters of slags employed for casting medium carbon steel （MC） and low carbon steel （LC） under the same caster type.Based on setting up the heat-transfer characteristic method of slag which on account of simulator, the effect of the chemical composition of mould slag （R, CaF₂, Na₂O, Al₂O₃, MgO, Li₂O, MnO, and use NaF replace CaF₂ offer F- and replace Na2O offer Na⁺） on slag film structure and heat-transfer property has been studied. Effect of basicity and chemical composition of mold fluxes on the formation time of stable air gap and all kinds of heat flux density has been obtained under the current slag system conditions.And the study shows that: Thickness and crystallization ration of slag film is related to the formation time of stable air gap. Thicker slag film or higher crystallization ration is beneficial to form stable air gap at the area of meniscus. It is to say heat flux can be reduced rapidly at meniscus. And the effect of thickness is greater than crystallization ration of slag film. Similarly, thickness and crystallization ration of slag film are key factors that could affect each kind of heat flux density. It is also that the effect of thickness is greater than crystallization ration of slag film. The main factors that could influence thickness of slag film are melting point, viscosity and crystallization capacity of the slag. Mold slag with lower melting point and viscosity is more likely to form thinner slag film, on the contrary, the crystallization capacity promoted.The effect of physical properties of mold slag （melting point and viscosity） on heat-transfer property and slag film structure has also been researched in the paper. The results indicate that①Increase both melting point and viscosity of slag would be beneficial to reduce the heat-transfer capability of slag. It is because that thickness of slag film increased with increasing melting point and viscosity.②The influence on crystallization ratio by melting point is not obviously, but the crystallization tendency reduced by increasing the viscosity of slag.更多还原