连铸坯基体高温磁性及相关性能演化规律的基础研究

The properties of continuous casting blank at elevated temperature directly depends on the microstructure associated with various thermal-mechanical effect, and it is basically determined by the intrinsic properties of primary phases which show different magnetic state and electronic structure. The magnetism and crystal structure is of importance for the evolution of casting blank performance at high temperature. Ab Initio investigation on properties of continuous casting blank at elevated temperature based on electronic structure calculation has been a scientific challenge, because there are complex thermo-magneto and lattice vibration couplings in the magnetic system of casting blank especially in the paramagnetic (PM) system. In the project, the task is to study the high temperature magnetism, spin fluctuation distribution and their effects on the properties at elevated temperature of Fe matrix in continuous casting blank by using first-principles method; With the consideration of spin fluctuation and the evolution of magnetism at high temperature, the prediction methods for lattice expansion and properties at elevated temperature of continuous casting blank matrix will be obtained by using first-principles calculation, combining with experimental measurement; Accurate calculation of high temperature properties for primary phases in casting blank matrix under disorder paramagnetic state will be achieved; Fundamental of high temperature magnetism and related temperature-dependent properties of continuous casting blank of steel will be explained from electronic structure calculations, which could aid in the effective application of Ab Initio calculation to the studying of high temperature properties of complex magnetism system alloy, and it would also provide foundation for the properties control of continuous casting blanks and the development of high quality new steel grade based on quantum calculations.

高温下连铸坯的性能直接依赖于不同热、力作用下的显微组织状态，并最终取决于具有不同磁性状态及电子结构的基本相性能；基本相磁性和晶体结构的演化是决定连铸坯高温性能演变规律的关键。由于连铸坯磁性体系，尤其是高温无序顺磁体系，存在复杂的热、磁、晶格振动相互作用，基于电子结构计算的连铸坯高温性能的第一性原理研究一直是个科学难题。本项目拟对连铸坯基体高温磁性、电子自旋涨落分布及其对高温性能的影响进行第一性原理计算研究；结合实验研究分析，建立考虑电子自旋涨落与高温磁性演变的连铸坯基体晶格膨胀及高温性能的第一性原理预测计算方法；实现高温无序顺磁状态下连铸坯基体各相性能的准确计算；从电子结构计算出发认识和诠释高温下连铸坯基体及其多元合金体系高温磁性与相关性能的演化规律及其物理本质；为第一性原理在复杂磁性体系高温性能研究中的有效应用奠定基础，也为基于量子力学计算的连铸坯性能调控及高品质钢种开发提供依据。

高温连铸坯的性能直接依赖于复杂热力作用下的显微组织状态，并最终取决于具有不同磁性状态和晶体结构的基体相性能。相较于困难、复杂和昂贵的单相晶体性能测试，基于密度泛函理论的计算模拟是诠释和掌握连铸坯高温性能演化规律的重要方法。由于复杂的热-磁-晶格振动的相互作用，高温态(热激发态)连铸坯基体相性能的第一性原理计算、复杂的磁性体系的准确描述一直是材料领域的科学难题。.本项目应用EMTO方法，考虑晶体结构和磁性状态的变化，构建了连铸坯基体相性能的第一性原理计算模型，研究讨论了铸坯基体相弹性性能的高温演化规律；明确了高温顺磁状态下磁-弹及体积-弹性耦合作用对基体相性能的影响。以绝热近似为基础，基于Boltzmann分布理论，构建了准确的电子自旋涨落分布模型；研究了热-磁耦合作用下基体相电子自旋密度分布、局域磁矩、弹性性能的高温演变规律，量化分析了电子自旋涨落对基体相性能的影响。基于电子自旋涨落的量化研究，考虑晶格膨胀、温度和磁性的耦合作用，自编程实现了体系Helmholtz自由能及晶格振动能的自洽计算；深入研究了高温顺磁状态下连铸坯基体相的晶格热膨胀和相关内禀性能的演化规律，探讨了局域磁矩及晶格膨胀对内禀属性高温演化的作用机理。此外，模拟研究了超低碳IF钢铸坯在高温下力学性能的演变规律，探究了IF钢连铸坯第III脆性区的形成机理；结合奥氏体分解过程中基体相转变、特征温度演变的规律，建立了不同冷速下铸坯相分数变化和裂纹敏感温度区域的预测模型。最后，基于第一性原理计算及奥氏体相变和晶体结构演变，构建了铸坯奥氏体相变区内禀属性连续演化的预测模型，预测了延/脆性演变行为、杨氏模量及各向异性指数的变化，为量子力学在钢铁材料中的应用提供了一种新思路。.本项目在基体相性能量子力学计算的基础上，结合高温性能及显微组织的实验研究，揭示了高温铸坯性能演化的物理本质，为实现连铸坯性能调控及高品质钢种开发提供了理论基础和科学依据。