连铸保护渣润滑与传热行为协调控制新途径及其作用机理研究

In the continuous casting of peritectic steels, controlling of the heat flux at meniscus plays a key role in preventing the formation of longitudinal surface cracks on slabs. Owing to the existing difficulties of the coordination control between the heat flux and lubrication functions for conventional high-basicity mold fluxes, ultrahigh-basicity mold fluxes, which prevents longitudinal cracks obviously with more stable performances, were developed by the applicants. However, the coordination mechanism between heat flux control and lubrication functions for these types of mold fluxes is still unclear.Therefore, the influencing factors and kinetics mechanism of the crystallization process of ultrahigh-basicity mold fluxes will be studied using an improved confocal laser scanning microscope (CSLM). The structure evolution of solidified slag film, especially the roughness of film surfaces contacted with the copper probe, and the closed porosity of films will be examed using an improved water-cooled copper probe to reveal their corresponding possible control methods. Besides, the micro-structure of ultrahigh-basicity and conventional high-basicity fluxes at high temperatures and upon cooling will be investigated by means of molecular dynamics simulation and Raman spectroscopy. The physical behaviors of fluxes and its causes at macro-scale will be analyzed based on their micro-structures. Finally, the action mechanism of ultrahigh-basicity mold fluxes in coordinating control between the heat flux and lubrication functions could be revealed. The results of this study will promote the development of basic theories of mold fluxes, and also will enhance the slab quality and casting efficiency.

在包晶钢连铸生产中，弱化结晶器内弯月面区域传热是控制铸坯表面纵裂纹的关键。针对传统的高碱度保护渣在控制传热和润滑铸坯之间矛盾愈加难以协调的问题，申请人前期已开发的超高碱度保护渣能在生产安全顺行的情况下较传统保护渣大幅消除铸坯表面纵裂，然而其协调传热和润滑的机制尚未明确。为此，以超高碱度连铸保护渣为研究对象，利用改进的高温共聚焦显微镜技术探究保护渣析晶行为的影响因素和动力学机理；采用优化的水冷铜探头浸入法等手段分析固渣膜生长过程中结构特征及其演变规律，重点探讨对传热有重要影响的铜/渣界面渣膜粗糙度和固渣膜闭孔率等控制途径；通过分子动力学模拟和拉曼光谱仪等光谱学方法对比研究超高碱度和高碱度保护渣熔渣结构特性及其冷凝过程中变迁，阐述熔体宏观行为变化的微结构机制。综合上述研究，最终揭示超高碱度保护渣协调润滑与控制传热的机理。研究结果对丰富保护渣基本理论、促进连铸坯质量和生产效率有效提升有积极意义。

在包晶钢连铸生产中，弱化结晶器弯月面区域传热是控制铸坯表面纵裂纹的关键。针对传统的高碱度保护渣在控制传热和润滑铸坯之间矛盾愈加难以协调的难题，以超高碱度连铸保护渣为研究对象，利用改进的高温共聚焦显微镜技术探究了保护渣析晶性能；采用优化的水冷铜探头浸入法等手段分析了固渣膜生长过程中结构特征及其演变规律，重点探讨了对传热有重要影响的铜/渣界面渣膜粗糙度和固渣膜闭孔率等因素；通过分子动力学模拟和拉曼光谱仪等对比研究了超高碱度和高碱度保护渣熔渣结构特性。研究结果表明CaF2对熔渣结构的解聚作用不明显，但提高碱度能够明显使硅酸盐熔体结构简单化，有利于熔体快速析晶。在超高碱度保护渣中典型组元对微观结构作用特性方面，随Na2O、Li2O增加，Q0增加，Q1、Q2、Q3减小，熔渣整体聚合度下降；而Al2O3增加，Q0减少，Q1、Q2、Q3先增加后减少，渣中Al-O-Al结构增加，熔渣整体聚合度增大；随着碱度增加，保护渣凝固温度和结晶温度先增加后降低，但析晶速率总体呈现增加的趋势。而且保护渣碱度越高，凝固渣膜偏析程度越高，剩余液渣的液相线温度大幅度降低，枪晶石的最大结晶比例也有所降低；相对于传统高碱度和低碱度保护渣，超高碱度保护渣固渣膜生长速率和厚度较稳定，有利于保证液渣膜均匀性，而渣膜表面粗糙度较高且渣膜总体闭孔率在渣膜生长过程中保持在较高水平，有利于固态渣膜有效控制传热。研究揭示了超高碱度保护渣在润滑和传热方面协调控制的方法和机理，即相对较低的凝固温度和结晶温度以持续维持对运动铸坯的润滑，而相对较高的结晶速度、结晶体比例以及高气孔率和高表面接触粗糙度能有效控制弯月面区域的传热以防止纵裂纹的产生。项目完善了基于选分结晶的保护渣润滑与传热协同控制理论，为包晶钢连铸顺行及良好的铸坯表面质量提供了新的技术思路和途径。