电磁搅拌连铸中液态金属流动与传热特性及其对凝固过程的影响

Electromagnetic stirring continuous casting process is a very complex metallurgical process involving fluid flow, heat transfer, mass transfer, phase change, and many other physical and mechanical problems. The electromagnetic field, flow field and temperature field are coupled with each other. It is significant to clarify the fluid flow and heat transfer characteristics of steel liquid for the reasonable control of the magnetic field strength, the degree of superheat and other operating parameters in electromagnetic stirring continuous casting. Taking a combination of physical modeling, numerical simulation and experimental study in this project, the multi-physics model to describe the coupling of the magnetic field, flow field, and temperature field is improved; the turbulence model which can accurately describe the flow characteristics of steel liquid in complex geometry is proposed; the heat transfer model which can accurately describe thermal characteristics is also proposed. Using the simulation results, the reasonable regulation of the flow field and temperature field in the tundish and mold is achieved. The effect of regulation is ultimately reflected in the microstructure organization formed by the solidification, by carrying solidification experiments of steel liquid, and then combined with numerical simulation results and experimental results, the mechanism of grain refinement which considers the fluid flow and heat transfer macroscopic properties of steel liquid is explored. The result can provide a basis for the manufacture of homogenization and the fine grain of slab.

电磁搅拌连铸过程涉及流体流动、传热、传质及相变等诸多物理和力学问题，是一个非常复杂的冶金过程，其中电磁场、流场和温度场相互耦合。弄清电磁搅拌作用下钢液的流动和传热特性，对于合理控制磁场强度和过热度等操作参数具有重要意义。本项目采取物理建模、数值模拟及实验研究相结合的方法，完善描述磁场、流场与温度场相互耦合的多物理场计算模型，建立能准确描述复杂几何形状中钢液流动特征的大涡模拟湍流模型和描述传热特性的传热模型，从而实现对中间包和结晶器内的流场与温度场的合理调控。对流场与温度场调控的效果最终反映在所形成的凝固组织的微观结构上，开展钢液的凝固实验，与数值模拟结果结合，探讨钢液流动与传热的宏观特性对凝固过程中的晶粒细化的影响，为制造均质化与细晶化的连铸坯提供理论成果。

电磁搅拌技术可以扩大铸坯的等轴晶区，减轻铸坯的中心疏松、中心偏析和中心缩孔，目前已在连铸生产中广泛应用。为了确定电磁搅拌中的最佳工艺参数，本项目针对直接影响铸坏质量的结晶器内钢液的流动行为，从多物理场耦合算法、结晶器内钢液界面波动、非金属夹杂物动力学特性等方面展开研究。研究结果表明：1) 电磁搅拌作用下钢液液面呈旋转抛物面，与无电磁搅拌作用下的液面截然不同；液面波动会随着电磁搅拌强度的增大而增强，达到一定程度时会出现卷渣现象；2) 电磁搅拌能促进夹杂物的上浮，但夹杂物的上浮率并不与搅拌强度正相关，在其他操作条件相同下的情况下，存在一个最佳的搅拌强度可使夹杂物上浮率最高；3) 通过本项目的研究，得到了确定电磁搅拌器安装位置及搅拌强度等参数的方案。本项目研究过程中所提出的模拟多物理场作用下颗粒的运动特性及界面波动的方法，不仅可以作为夹杂物迁移行为的模拟手段，还能为正确认识工业过程中和自然界中微粒在多物理场相流体中的运动特性及荷电现象并加以控制利用提供理论借鉴。在项目执行期间发表SCI论文2篇，其中1篇发表在国际权威期刊《Physics Reports》(2015年影响因子：16.24)，受Springer出版社邀约合作撰写英文专著1部(目前已预售)。