双相钢中再结晶与相变相互作用的实验研究和模拟计算

In this study, ferrite recrystallization and austenite transformation as well as their interactions which occur for various intercritically annealed Dual-Phase (DP) steels on materials that had been initially cold rolled are to be investigated both by experiments and by numerical modeling. Different from previous studies mostly related with the processing techniques, this study places particular interests on an investigation into the associated transformation mechanisms. On the bases of the fine characterizations of the DP microstructure by Optical Microscopy, SEM, TEM, EBSD ect., mechanisms of the interaction between recrystallization and phase transformation as well as the associated controlling factors are to be analyzed at a individual grain level. Meanwhile, a modified Cellular Automaton (CA) model is to be developed to depict the discrete microstructural constituents either in recrystallization or phase transformation by coupling a crystal plasticity finite element model (CPFEM) designed for the deformation simulation on duplex-phase materials and the thermodynamic calculations by the Thermo-Calc software. This model enables us to obtain a detailed microstructural insight into the mutual interactions between these various metallurgical processes. The proposed study is intended to achieve the fundamentals of tailoring the microstructure in DP steels products which can be implemented to design ideal microstructures and optimize the processing techiques. Therefore, the present study can not only enhance the theoretical understandings of the interaction mechanism between recrystallization and phase transformation, but also improve the simulation techniques at the mesoscale. Moreover, this study is also of significant interest for developing proper processing technology to produce ideal microstructures for DP steels with an excellent performance.

通过实验研究与模拟计算结合，对冷轧双相钢中的再结晶和相变及它们之间的相互作用进行深入研究。与以往以双相钢生产工艺为主导的研究思路不同，本研究以物理转变机理为首要研究对象，结合金相、扫描电镜（SEM）、透射电镜（TEM）、EBSD等对双相钢再结晶/相变精细组织的表征，探索单晶粒层次上再结晶与相变之间的相互作用机理及控制因素。同时，结合基于晶体塑性理论的双相结构变形模拟和Thermo-Calc热力学计算，开发介观尺度模拟双相钢再结晶/相变的元胞自动机耦合模型，从转变过程出发分析这两个物理转变之间的相互作用机理。本研究旨在为双相钢生产中的微观组织控制问题提供理论依据，在此基础上提出双相钢热处理工艺的优化方案，设计双相钢理想组织。本项研究不仅会加深对再结晶和相变相互作用机理的理解，而且对促进介观尺度模拟技术的发展、 设计/优化双相钢理想组织和生产工艺都具有重要意义。

铁素体再结晶和奥氏体相变是影响双相钢微观组织状态最重要的两个物理过程，研究它们的转变机理及其相互作用对设计/优化双相钢理想组织和生产工艺具有重要意义。本项目从实验表征、建模与计算等方面对冷轧双相钢中的再结晶与相变的微观组织行为和机理开展了研究，阐述了再结晶与相变的相互作用机理。1）基于物理冶金基本原理，对冷轧双相钢连续退火过程中的再结晶与相变复合过程进行了介观尺度元胞自动机建模，从转变过程与转变动力学的角度阐述铁素体再结晶与奥氏体相变的微观组织行为以及它们之间的相互作用机理。 2）基于相界面处的吉布斯自由能守恒原则，从热力学角度考虑了相界面迁移中因替换型溶质原子拖曳所引起的局部自由能耗散，对多组元合金等温相变及临界区循环相变过程的微观组织转变行为和相变动力学进行了元胞自动机建模，定量描述溶质拖曳对相界面迁移动力学的影响。 3）发展了冷轧双相钢双相组织变形与再结晶的晶体塑性有限元-元胞自动机耦合模型，在晶粒尺度上描述双相基体组织的塑性变形的各向异性行为，通过与CA模型耦合准确模拟双相钢变形后的再结晶微观组织演变的非均匀行为。4）在单晶粒层次对珠光体片层溶解过程中的奥氏体相界面的演化过程进行了元胞自动机建模，模型中引入Gibbs-Thomson效应，综合考虑了相界面曲率、形貌演化以及局部区域溶质分布之间的相互作用，从细观上定量描述奥氏体相在珠光体内部的界面迁移运动学。5）发展了双相钢临界区奥氏体-铁素体相变的多相场模型，基于模拟分析了扩散控制生长模式与界面控制生长模式之间的动力学转化现象；进一步从界面迁移动力学的角度对Fe-C-Mn三元合金中因替换性元素在相界面配分所导致的相变停滞和相变不完全现象进行阐述；并描述了奥氏体-铁素体相变过程中铁素体晶粒生长形貌的多样性。6）基于热模拟及微观组织表征析了冷轧双相钢再结晶与相变过程的微观组织行为，研究了两转变过程强相互作用与弱相互作用下的组织特征与机理。