结晶器角部几何特征对连铸坯角裂的影响机理

Transverse corner crack of continuous casting slab is one of the most typical and difficultly eliminated defects in micro-alloy continuous casting steel. In the project, one of the tasks is to establish a three-dimensional coupled mathematical model to simulate heat transfer between molten steel, mould copper plate and cooling water under different mould corner geometrical characteristics (vertical corner, round corner, big chamfer corner and polyline corner); the orther is to establish the corner slag flow field, friction distribution and slab corner stress model under under different mould corner geometrical characteristics and mould oscillation. Based on mould corner geometrical characteristics, the accurate research method of heat transfer, flow field and stress model of solidifying shell in mould and secondary cooling should be obtained. Clearly defining the dynamic influences of mould corner and mould socillation change on temperature field, stress field; the dynamic regular influences on variation of corner slag behaviours and friction as well as inherited effects of mould corner geometrical characteristics on slab corner temperature and stress in secondary cooling. The project will construct the relationship between mould corner geometrical characteristics and Transverse conrner cracks and obtain formation and growth mechanism of Transverse conrner crack; establish right process and equipment parameters, such as water seam, mould oscillation parameters and the slab corner cooling type in secodary cooling zone to provide a theoretical and technological foundation for transverse conrner crack elimination or relievation.

板坯连铸角部横裂纹是连铸微合金钢等的典型缺陷，消除难度较大。本项目拟建立结晶器角部不同几何特征下（直角、圆角、大倒角、多折线倒角等）钢液、铜板和冷却水的三维耦合传热数学模型；建立基于结晶器角部不同几何特征和结晶器振动状态下的角部区域保护渣运动、摩擦力分布及角部铸坯应力模型。获得基于结晶器角部几何特征的精确的结晶器和二冷区铸坯凝固传热、流动、应力模型的研究方法；明确结晶器几何特征、结晶器振动状态对铸坯角部温度场、应力场的变化特征，对铸坯角部区域保护渣运动行为及摩擦力变化的影响规律，结晶器几何特征对二次冷却铸坯角部温度应力的遗传规律；构建结晶器角部几何特征与铸坯角部横裂纹的对应关系，明确角部横裂生成和扩展的机理；确立合适的结晶器角部几何特征下合理的水缝结构、结晶器振动参数及二冷铸坯角部冷却模式等工艺与装备参数，为最大程度减轻或消除铸坯角部横裂纹奠定理论和技术基础。

角部横裂纹是板坯微合金钢连铸生产中的典型缺陷，消除比较困难。而结晶器角部几何特征直接影响了铸坯角部的传热行为，控制了应力分布，从而决定了角部横裂纹产生的可能性。本项目通过构建结晶器角部不同几何特征下（直角、大倒角、多倒角和圆角）考虑铸坯收缩的耦合钢液、铜板和冷却水的三维板坯结晶器流动传热模型，深入研究了结晶器角部几何特征对结晶器内流动、传热和凝固行为的影响机理。并额外进行了板坯倒角结晶器物理模拟研究，与数学模拟互相验证。根据传热模型结果，计算获得了结晶器内保护渣的分布，同时通过引入保护渣断裂强度测试，补充修正了液渣运动模型和固渣受力模型，揭示了结晶器角部不同几何特征下铸坯角部摩擦力的变化规律。并研究了不同结晶器振动方式和参数下铸坯角部区域摩擦力的变化规律。基于结晶器传热和摩擦模型结果，建立了三维板坯结晶器应力应变模型和振痕微元模型，分析了结晶器角部几何特征对铸坯应力分布及横裂纹的影响规律。另外，测试了连铸过程三种微合金钢的高温物理性能和两种微合金钢的高温力学性能，为铸坯角部温度及应力分析研究提供依据。根据结晶器出口铸坯温度场，建立了二冷区铸坯二维切片传热模型，明确了结晶器角部几何特征对二冷区铸坯角部温度的遗传影响。继而构建了弯曲和矫直段耦合铸坯和辊子的应力模型，分析了弯曲和矫直过程中铸坯角部应力的变化特征，从而明确了结晶器角部几何特征对二冷区角部横裂纹生成可能性的遗传规律。基于上述研究，构建了结晶器角部几何特征与铸坯角部横裂纹的对应关系，确立了多倒角和圆角结晶器的水缝结构、结晶器非正弦振动参数及二冷铸坯冷却模式，为最大程度减轻或消除铸坯角部横裂纹奠定了一定的理论和技术基础。