超高速方坯连铸结晶器区钢液凝固行为的科学原理

For achieving endless rolling of steel billets to make the matching between continuous casting and hot rolling process proper, or purely improving casting speed to lower production costs, ultra-high speed casting is essential for steel billets. It may be a new generation of frontier technology after high-efficiency of continuous casting has achieved, therefor, the basic research of ultra-high speed continuous casting of billets is significant..The cooling control of molten steel in mold zone is the key to achieve ultra-high speed continuous casting, therefore, research methods, including theoretical research, mathematical modeling, mathematical analysis and physical simulation considering solidification phenomenon (solidified shell and fluid flow imbalance characters) will be applied in this project, which is to reveal scientific principle of fluid flow behavior and level fluctuation of molten metal in mold during ultra-high speed continuous casting of billets; also, clearly define the principle of high efficient heat transfer and criterion of heat transfer limitation in mold, for further obtaining the mothed and realizing the approach of efficient solidification heat transfer during ultra-high speed continuous casting of billets; based on the theoretical analysis of billet solidification shrinkage and mold deformation at high temperature, the method for mold taper design to ensure efficient heat transfer and billet quality should be established; the rubbing behavior and the mechanism affecting that behavior should be revealed during ultra-high speed continuous casting of billets. Finally, the scientific principle of molten steel solidification behavior in mold zone could be established, which will lay a theoretical and technical foundation for industrial application of ultra-high speed continuous casting of billets.

基于实现方坯无头轧制促使连铸与轧制工序产能良好匹配之目的，或者纯粹地提高拉速降低成本，方坯连铸都需要实现超高速。超高速方坯连铸应是连铸高效化技术后的新一代前沿技术，开展其基础研究具有重要意义。.结晶器区钢液的凝固冷却控制是实现超高拉速的关键。对此，为实现超高速，项目应用理论研究、数学模型构建、数学解析和考虑凝固现象(凝固壳厚度和流体流量不平衡特征)的物理模拟等研究方法，揭示超高速高通钢量下结晶器内钢液的流动行为及表面波动的科学原理；明确结晶器区域高效传热原理及传热极限准则，获取超高速方坯连铸高效凝固传热的实现方法与实现途径；基于铸坯凝固收缩与结晶器高温变形的理论与数学分析，确立高效传热和保证铸坯质量的超高速方坯连铸结晶器锥度的确定方法；揭示超高速连铸铸坯与结晶器间的摩擦行为及其影响机理。最终确立超高速方坯连铸结晶器区钢液凝固行为的科学原理，为超高速方坯连铸工艺的工业应用奠定理论和技术基础。

方坯连铸的高速化对铸坯无头轧制和连铸的高效化及绿色化有重要意义。目前，方坯超高速连铸技术理论基础薄弱，限制了该技术工业应用的发展进程。鉴于此，本项目通过建立的方坯连铸结晶器钢液流动传热数学模型，明确了超高速下结晶器内钢液的流动特征与合适的浸入式水口参数；并额外开展了耦合不同计算域的结晶器钢液流动传热仿真计算方法和液渣特性对钢液流动行为影响的研究。此外，还进行了考虑凝固现象的方坯结晶器流体流动的水模拟实验，明晰了凝固现象对超高速下结晶器内钢液流动行为的定量影响并对数学解析的结果进行了验证。为了实现超高速连铸结晶器区的高效传热，采用构建的方坯连铸结晶器内钢液、保护渣膜、铜管和冷却水于一体的流动与传热数学模型，揭示了铜管长度、圆角半径等参数对超高速化结晶器区高效传热的影响规律，并在结晶器出口坯壳厚度与安全厚度的基础上获得了超高拉速连铸结晶器的最高拉速；另外，还分析了超高速下五种基于冷却水强制流动的水冷结构下结晶器区的传热行为，提出了超高速下采用高效传热与冷却两段式结晶器(水套式结晶器+喷淋式结晶器)的思路。在传热研究的基础上，构建铸坯和结晶器铜管的高温应力应变模型，利用测得的包晶钢和非包晶钢高温力学性能参数，明确了没有气隙状态下拉速、过热度对典型钢种铸坯高温应力应变及收缩的影响规律和铜管的热变形规律；综合铸坯收缩和铜管热变形，获得了不同拉速等工艺参数下、不产生气隙时两类钢种连铸结晶器周向边界上特征点处沿拉坯方向锥度的变化规律。基于传热模拟结果，建立了方坯结晶器表面保护渣的流动模型和保护渣液渣层速度分布模型，并揭示了结晶器振动状态和保护渣特性对超高拉速下结晶器与铸坯间摩擦力的影响规律。基于上述研究，明确了超高速下结晶器区钢液的流动特征与高效传热行为，确定了超高速化结晶器的内腔锥度和结晶器与铸坯间摩擦力的变化规律，为实现方坯连铸的超高速化奠定了必要的理论和技术基础。

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