低合金钢微结构调控TMCP技术中相变热力学/动力学相关性研究

By combining controlled rolling and controlled cooling, Thermo-Mechanical Control Process (TMCP) technology is able to achieve a combined control of deformation and phase transformation so that the mechanical properties of steels can be optimized. However, the current TMCP technology dose not combine the overall effects of microstructure status, non-equilibrium effects, and deformation with the functions of thermodynamics and kinetics of phase transformations involved in TMCP. Therefore, the coordinative adjustments on the TMCP processing parameters (thermodynamics/kinetics) which are essentially important on achieving the desired microstructures and mechanical properties are not able to be carried out. ..This project aims to fill this gap. By combining theoretical modeling, multi-scale computer simulation, and experimental investigations, the correlation between thermodynamics and kinetics involved in TMCP processing of low-alloyed steels will be quantitatively described; a united micro-scale rate equation and a united kinetic model dealing with diffusively/displacively controlled transformation under local non-equilibrium condition will be developed. Accordingly, a quantitative relationship among the thermodynamic driving force, the kinetic barrier, and the microstructure evolution will be established, so that an integrative and quantitative research on processing conditions, phase transformation mechanisms, and microstructures/mechanical properties can be achieved. ..Based on the developed theory, aiming at several typically industrial low-alloyed steels, the microstructures resulted from any TMCP processes will be predicted quantitatively; then, the thermodynamic/kinetic parameters corresponding to the desired microstructures will be converted to the TMCP processing parameters and the most efficient TMCP route to achieve the desired microstructure will be obtained. On this basis, a novel concept for TMCP will be proposed based on the established theory.

制备热轧钢所需的控轧控冷技术（TMCP）旨在将控制变形和控制相变结合来调控钢材微结构及性能。当前，TMCP调控技术未能将微观组织状态、非平衡效应以及形变的综合影响同所涉及相变的热力学/动力学函数相耦合，因此无法开展面向目标组织、性能的加工条件（热力学/动力学）的协同性调控。..本项目拟通过理论建模、多尺度模拟及实验研究，定量描述低合金钢TMCP涉及相变中动力学通量与热力学驱动力间关系，建立扩散、切变统一型微观速率方程及相变动力学模型，获得热力学驱动力和动力学能垒间函数关系及热力学驱动力、动力学能垒与组织演化的定量关系，实现加工条件、相变机制与组织、性能的一体化、定量化研究。..针对典型工业用低合金钢，基于所建立的热力学/动力学相关性理论，实现TMCP工艺条件下微观组织的定量预测，获得面向目标组织的最佳热力学/动力学条件并将其转化为TMCP调控工艺参量，进而提出TMCP调控新理念。

本项目针对高强度低合金钢微结构调控涉及的重要相变，旨在探讨热力学驱动力和动力学能垒间固有规律；通过研究上述规律在组织调控涉及相变中的定量体现，建立热力学驱动力、动力学能垒同相变组织间定量关系，以指导和设计典型工业用低合金钢的组织调控。首先，从一阶相变，即凝固和固态相变(聚焦于低合金钢组织调控涉及的重要相变)中演绎出热-动力学相关性，其次，表征热-动力学相关性在晶界迁移和相界迁移中的模型化体现，最后，相关性模型应用于钢铁组织调控，实现组织预测和工艺确定。.本项目在热-动力学及其应用于材料设计方面得到四个标志性成果，可归纳为：（1）一普适思想：热-动力学相关性；（2）一通用模型：非平衡多尺度组织演化方程；（3）一先进材料：双相双峰高强塑纳米块体钢铁；（4）一协同判据：大驱动力-大能垒-大广义稳定性材料设计策略。从热-动力学理论和实验工作中总结出热-动力学相关性的学术思想，从而悟道组织演化模型以及驱动力-能垒-组织关联。进一步推导出基于热-动力学协同的非平衡多尺度组织演化模型，从而从数学解析上得知大驱动力大能垒相变对应优异组织。据此，设计纳米相变得到双相双峰组织。分析双相双峰组织形成和变形机理，推导出广义稳定性，进而推断出大驱动力-大能垒-大广义稳定性对应大强度大塑性。.该项目在金属材料重要刊物Acta Mater发表论文10篇。基于所建立的非平衡相变热-动力学协同理论，形成了面向目标组织的相变设计等核心技术；授权国家发明专利15项，主持制定国家和企业标准各1项，并在油气开采、高铁等重大工程中获重要应用。相应成果获2019年度教育部自然科学奖一等奖。由傅恒志院士、刘维民院士、魏炳波院士等9名行业知名教授组成的专家组一致评价，“该项目丰富和发展了金属材料相变理论，在非平衡凝固与固态相变一体化调控和相变热-动力学相关性等方面处于国际引领地位”。