铸坯中心缺陷轧除的力学机理与综合判据研究

Central defect in casting slab is main reason of the fault of internal quality in rolled products. How to eliminate the defect is always the important task for the subsequent rough rolling technology. Traditional slab method, limit analysis and finite element methods are all isolated to research defect closing or healing with different characteristic, so are failure to present a comprehensive criterion for closing and syncronously healing the central defect. . Based on mathematical solution to continuum forming force, the present project is about to integrate a priori and differentiate a posteriori in calculus of variation. In particular, using strain rate vector inner product or substituting specific plastic power of linear yield criterion for nonlinear integrand of the functional to get a linear expression of rolling power first, and then partial differentiating with respect to defect size, reduction in pass, neutral angle, etc. in order to get the extreme rolling power and the rate of change of rolling power to those undetermined parameters. At the same time, the temperature rises across heat lines, namely velocity discontinuity lines in deformation zone, are also calculated as the bond to establish evolution relationships among local temperature rise with atom diffusion coefficient and vacancy mobility, among the lattice distortion energy with specific free energy change as well as healing inner variable for the closed microcrack. Finally, the mechanical mechanism for eliminating central defect of casting slab will be clarified and a comprehensive criterion for closing and simultaneously healing a central defect will be obtained for a single rolling pass. The proposed criterion provides theory support for the design of process parameters and the quality improvement of rolled plate.

铸坯中心缺陷是影响轧材内部质量的主要根源，在粗轧中消除铸坯缺陷是轧制工艺的重要任务。传统工程法、极限分析法、有限元法从各自不同特点孤立地研究粗轧坯的缺陷压合或愈合，因此无法同时给出缺陷压合与愈合自发过程的综合判据。项目拟从连续体成形力的数学解法入手，基于变分法先积分与后微分的依赖关系，以应变速率矢量内积法或线性屈服准则比塑性功率取代泛函被积函数的方法，经先积分获得轧制功率的线性化解析表达式；再以复合变分法对缺陷尺寸、压下率、中性角等待定参量后微分，确定轧制功率极值以及轧制功率对这些参量的变化率；同时以变形区热线温升为纽带建立裂纹体积元局部温升与原子扩散系数及空位迁移率、轧制储存的晶格畸变能与体元比自由能及愈合内变量间的相互关系，最终阐明铸坯中心缺陷轧除的力学机理并获得同时发生压合与愈合自发过程的综合判据，从而为轧制工艺设计以及板材质量提高提供理论支撑。

铸坯中心缺陷是降低轧材内部质量的主要根源，消除这类缺陷是粗轧工序的重要任务。项目利用塑性成形能量原理系统研究了这类缺陷的轧除力学机理与综合判据，发现缺陷与坯料尺寸间的协调关系，构建了含缺陷三角形速度场和连续速度场，以比塑性功率取代法和共线矢量内积法解决了非线性轧制能率泛函积分困难的关键问题，进而利用逐次求极法获得了控轧条件下的缺陷压合判据，开展了实验验证与参数分析，揭示了板坯尺寸、压下量、温度以及温升等参数对缺陷压合与愈合的影响规律，并开发了厚板质量控制技术，在企业生产试验中取得应用，显著提升了成材率与生产效率。. 项目运行3年以来，发表基金资助一作学术论文10篇、通讯论文1篇，其中在本领域权威期刊Applied Mathematical Modelling、Meccanica、Acta Mechanica、Journal of Manufacturing Processes上发表高水平SCI论文7篇（包括I区Top期刊1篇），并得到多篇发表于Scientific Reports、International Journal of Mechanical Sciences、Meccanica等高水平期刊论文的引用和肯定；出版基金资助的教材、专著各1部；申请国家发明专利7项（已授权2项）；获得江苏省教育科学研究成果奖1项；所开发的厚板质量控制技术得到初步应用；在培硕士生2名，并且课题组2名教师晋升为副教授。. 项目严格按照计划，超额完成立项SCI/EI论文4-6篇、申请专利1-2项的预期目标。已取得的主要创新成果及其科学意义如下：. （1）在对非线性Mises屈服准则线性化的研究上取得突破，开发了加权平均屈服准则、平均边心距屈服准则，并导出了它们的比塑性功率表达式，实现了对拟求解变形力学方程的简化，提出了比塑性功率取代法获得轧制能率泛函解析解的新方法。. （2）准确描述了轧件的流动变形规律，提出了缺陷尺寸与健全速度场相耦合的位移协调法，构建了含缺陷三角形速度场和连续速度场，继而以逐次求极法获得了缺陷压合判据，并阐明了缺陷消除的工艺条件。. （3）提出综合应用理论解析、数值模拟以及实验研究分析轧制过程并建立精确参量表达式的新思路，获得的力学参数更加符合实测数据，促进了研究成果的转化与应用。