保护渣渣膜结构演变对结晶器传热和钢液初始凝固行为的影响机理

The shell surface defects originate from continuous casting mold during the early stage of liquid steel solidification that could be eliminated by adjusting the heat transfer between mold and shell with a proper structure of mold/shell slag film. The structure of the slag film has significant effect on its heat transfer behavior. However, the relationship between the slag film structure evolution and the initial shell solidification cannot be observed and studied directly due to the harsh environment in the mold. In this project, mold simulator will be used to mimic initial shell solidification and lubrication of mold flux infiltrates into mold/shell gap such that the slag film and the initial shell would be obtained. Then the structure evolution of the slag film along casting direction will be studied by analyzing the change of crystals morphology. Secondly, the changes of the conduction and radiative heat transfer as well as thermal resistances of the liquid and solid slag film along the casting direction during one cycle of mold oscillation will be analyzed by using inverse problem that could determine the thermal field from limited experiment measured data. Next, the structure evolution mechanism of slag film along the casing direction would be studied, and also its effects on mold/shell heat transfer will be investigated. Finally, the relationships between slag film structure, mold/shell heat transfer, shell surface quality and solidification structure would be studied. Those results could provide the theory basis for optimizing the continuous casting technology and improving the shell quality.

铸坯表面缺陷起源于钢液在结晶器内初始凝固过程，合理控制结晶器与坯壳间隙内保护渣渣膜的传热行为是提高铸坯表面质量的关键。渣膜的传热行为与其结构有密切的关系。然而结晶器内环境恶劣，无法直接观察研究渣膜结构的变化和钢水凝固行为。基于此，项目拟采用连铸结晶器高温钢液凝固模拟装置（mold simulator）对结晶器钢液初始凝固行为进行有效模拟，以此制备渣膜和初始凝固坯壳；通过分析渣膜中晶体的形貌和分布，获得拉坯方向渣膜结构的演变特征；其次，根据反问题理论集成数学模型和实验数据，研究结晶器振动周期内，渣膜中液、固渣膜的传导和辐射传热及其热阻（包括结晶器-渣膜界面热阻）沿着拉坯方向的变化规律；进而阐明沿着拉坯方向渣膜结构的演变机理，及其行为对结晶器/坯壳间传热的影响规律；从而建立渣膜结构演变与结晶器/坯壳间传热，坯壳表面质量和凝固组织之间的相互关系模型，为优化连铸工艺及提高铸坯质量提供理论基础。

连铸是现代钢铁产业的关键技术，其中结晶器是钢液初始凝固的地方，决定最终铸坯质量和连铸生产效率。本项目结合数学模型耦合热力学和动力学理论计算、实验技术开发以及使用结晶器钢液初始凝固热模拟技术等在实验室进行了连铸实验，生产了初始坯壳和结晶器与坯壳之间的保护渣渣膜，以此研究了结晶器内钢液初始凝固、保护渣渗透、结晶、润滑、传热等行为；揭示了结晶器内钢液初始凝固行为、结晶器与铸坯之间渣膜的传热和润滑性能与坯壳表面质量和凝固组织之间的关系。阐明了结晶器振动、结晶器角部形状，拉速、渣钢反应等对结晶器热流变化，保护渣传热、结晶和润滑性能，以及坯壳表面形貌，厚度、凝固组织等的影响机理。提出了保护渣传热、结晶和润滑性能的综合性能评价方法，从而为保护渣的优化与设计提供实验室规模的连铸试验方法。研究成果可为保护渣的优化和设计，连铸工艺参数的优化提供理论基础或者新方法。