【作者】 麻晓飞；

【导师】 关小军；

【作者基本信息】 山东大学 ， 材料加工工程， 2008， 博士

【摘要】 随着材料科学和计算机技术的发展,材料的制备正从传统的正向研究向逆向研究过渡:从材料组分、微观结构或性能出发,借助计算机模拟来设计工艺和预测材料性质或组分、微观结构,以生成满足使用要求的材料。材料中存在的二相粒子主要是加入合金以改善性能的产物。其中,合金化和控轧控冷技术已被普遍用于低碳钢生产中以细化晶粒组织。合金化的作用是在材料中形成足够数量、细小的二相粒子,以影响到热变形材料和冷变形材料的动态再结晶、静态再结晶行为及其相应的组织变化,特别是对于冷变形材料退火期间再结晶和晶粒长大过程的影响直接决定了其最终组织结构和性能。Cellular Automata(CA)模型是近10多年来发展起来的一种材料组织模拟模型,在材料晶粒长大和再结晶模拟中得到广泛应用。但是,对于含有二相粒子变形材料的退火过程计算机模拟应用还未及时开展,这与该模型非常适合于模拟二相粒子与基体之间局部交互作用所引起的组织演变过程的特点是不相称的。事实上,构建含有二相粒子的变形材料CA模型以模拟其再结晶和晶粒长大组织演变过程,不仅可实现二相粒子的体积分数、尺寸及其分布等参数对退火组织影响的模拟研究,实现退火过程微观组织设计、工艺控制及其性能预报,为退火工艺优化和高性能材料设计与开发打下了坚实基础,而且进一步挖掘了CA模型的潜力,拓展了其应用范围。因此,及时开展含有二相粒子的变形材料再结晶退火CA模型及其模拟研究具有重要的理论和实际意义。本文基于CA方法、金属学和材料再结晶等相关理论,提出并建立了具有较强物理基础的单相材料变温回复-再结晶和晶粒长大的CA模型;在这些模型的基础上,创建了二相粒子材料变温回复-再结晶和晶粒长大CA模型,进而得到了二相粒子材料退火组织CA模型;自主开发了相关再结晶模拟的关键技术;采用C++编程语言,编写了上述模型的应用程序,并开展了相关的模拟研究和实验研究,对模型的合理性及其应用效果进行了检验。首先,分析了现有的晶粒长大CA模型的不足,基于曲率和能量机制,提出了元胞取向状态转变的二次判断方式和相应规则,建立了具有更好物理基础的晶粒长大CA模型。该模型将晶界能作为晶粒长大的驱动力,考虑了晶界曲率对晶界移动方向的影响,解决了晶界朝曲率中心运动方向与及能量降低方向不一致的问题,晶粒尺寸分布更为理想。其次,以单相材料正常晶粒长大的CA模型为基础,引入二相粒子影响及其对应的改进转变规则,建立了一个新的二相粒子材料晶粒长大过程CA模型。该模型的模拟结果很好地反映了二相粒子体积分数、尺寸及其分布对晶粒长大的影响规律,并与相关实验结果相符。然后,分析了现有再结晶CA模型存在的储存能均匀分布、形核机制不完善、温度恒定、忽略回复影响等不足,基于相关实验研究,建立了一个新的具有明确物理基础的单相材料变温回复-再结晶CA模型。该模型特点在于:①采用非均匀储能场,初步解决了冷变形材料储存能分布不均匀问题;②基于亚晶异常长大形核机制,并考虑了回复对形核过程的影响;③考虑了温度变化对再结晶过程的影响。与原有模型相比,该模型的模拟结果更正确地反映了退火温度和变形程度对再结晶过程的影响规律,并与相关实验结果更加接近。随后,根据细小及大尺寸二相粒子对再结晶过程影响的相关实验研究,在单相材料变温回复-再结晶CA模型基础上,创建了二相粒子材料变温回复-再结晶CA模型。该模型综合考虑了与二相粒子尺度有关的位错运动及其分布状态,改进了储存能模型和晶核长大模型,较好地模拟了二相粒子对再结晶影响的实验规律。最后,基于二相粒子材料变温回复-再结晶模型和晶粒长大CA模型,得到了一个二相粒子材料退火组织CA模型。为了验证该模型的合理性及其应用效果,分别以两组冷轧钢板为研究对象,实验研究了含有二相粒子和二相粒子含量不同条件下再结晶退火组织变化过程,并与其模拟结果进行了对比。结果表明:本文所建模型能较准确地模拟二相粒子材料的冷轧组织、再结晶形核位置、再结晶完成组织及随后的晶粒长大组织;模拟的二相粒子对再结晶过程的影响规律与退火实验预测结果及相关再结晶理论一致:二相粒子的存在阻碍了再结晶进行,使再结晶形核及晶核长大过程滞后,且粒子含量越多,影响效果越明显。模拟的退火速度与实际值相比存在一定的误差,这与模型假设、实验误差等有关,进一步完善该模型有助于其模拟精度的提高和实际应用的拓展。更多还原

【Abstract】 With the development of material science and computer technology, the science of material preparation is changing from traditional design manner to its reverse one. By the aid of computer simulation, material properties can be predicted based on its components microstructure, vice versa, and the optimum manufacturing techniques can be selected to derive some functional materials which can meet the actual needs.The sceond phase particle in material is mainly the product caused by adding alloy elements to improve the performance of material. Alloying and controlled rolling and cooling technology have been widely used in the process of low-canbon steel manifacture to control the grain growth. The aim of alloying is to generate sufficient amount and fine second phase particles in the material, which affect the behaviors of dynamic recrystallization and static recrystallization and corresponding microstructure changes in the process of thermal deformation and cold one. Especially, the effects of the second phase particle on recrystallization and grain growth during the annealing directly determine the ultimate microstructure and performance of the cold deformed material.Cellular Automata (shortly called CA) model which developed in recent more than ten years has been widely used in the simulation of grain growth and recrystallization, but it has not been applied in the simulation of the deformed material with second phase particle yet. This status is inappropriate to compare with the character of the model which suits to simulate the local interaction between the second phase particle and body organization. Actually, constructing CA model for the deformed material with second phase particle to simulate the grain growth and recrystallization process not only studies the effects of the second phase particle’s size, volume fraction and distribution on annealing microstructure, and achieves the microstructure organizational design and process control of and performance prediction to establish the foundation for the annealing technology optimization and development of better performance material, but also further explores the potential of extending its application. So it has an important significance of theory and practice to study the modeling and simulation of the annealing microstructure evolving for the deformed material with second phase particle by CA method in time .In present thesis, based on the CA method, metallography and recrystallization theory and so on, two CA models for the recrystallization and grain growth for single phase material were proposed with better physical basis, respectively. Based on the models, two CA models for the recovery - recrystallization and grain growth for the material with second phase particle under the change of annealing temperature were constructed, respectively, which formed a CA model for annealing microstructure evolution of the material with second phase particle. According to the new models and the corresponding key technologies for simulation, a computer program was compiled to simulate the annealing microstructure evolving of the material with second phase particle under the change of annealing temperature, and some experiments were finished to verify the rationality of the models.Firstly, the limitations of previous CA models for grain growth were well analyzed, and a new criterion with the judgement of two times was proposed for the attempted transition of cell state and a new CA model was constructed with a better physical basis, based on the mechanisms of grain boundary curvature driving and the thermodynamic one. In the new CA model, the main driving force of grain growth is grain boundary energy and the influence of grain boundary curvature on the direction of grain boundary movement is also considered so that the problem that the direction of grain boundary moving to its curvature center differs to the direction of its energy decrease is solved and the distribution of grain size is more ideal.Secondly, based on the grain growth CA model for single phase material, a new model with a modified transition rule of cell state was constructed to simulate the effects of the second phase particle on grain growth. The results gained by the model correctly reflect the effects of the second phase particle’s volume fraction, size and its distribution on grain growth, which is consistent with the experimental results.Thirdly, the limitations of stored energy distribution, nucleation, temperature change and recovery effect of previous recrystallization CA models were well analyzed, and based on corresponding experimental research and MC models, a recovery-recrystallization CA model for single phase material which has strong physical basis was constructed. The new model has the following advantages: 1) A new stored energy distribution model is constructed by using inhomogeneous distribution of stored energy. 2) A recovery model is built on the basis of subgrain abnormal growth nucleation model and considered the effect of recovery on nucleation. 3) The influences of annealing temperature change on recrystallization process are considered in the new model. In comparison with the results of previous models, the results simulated by the new model more really reflect the influence laws of annealing temperature and deformation degree on recrystallization, which is in good agreement with the experiment results.Then, based on the experimental research on the effects of the small and large second phase particles on recrystallization and the recovery- recrystallization model for single phase material, a new recovery- recrystallization model for the material with second phase particle was proposed by CA method. In the new model, the dislocation movement and its distribution related to the second particle’s size are generally considered, and the modified storage energy model and nucleation one are applied. The results simulated by the new model coincide with the experimental laws which show the effects of the second phase particle on recrystallization.Finally, based on the recovery-recrystallization and grain growth CA models, a new annealing microstructure CA model for the material with second phase particle was obtained. To verify the rationality and application effect of the model constructed in present thesis, the annealing processes of cold-rolled steel plates which contain the second phase particle with different content are investigated in detail. The comparison of experimental results and simulated ones indicate that: 1) The initial microstructure, the nucleation sites, recrystallized microstructure and the subsequent grain growth microstructure can be better simulated by the model constructed in present thesis. 2) The simulation results are consistent with the experimental results and related recrystallization theories. 3) The second phase particle delays the process of nucleation and nucleus growth, and then hinders the whole recrystallization process. There exists definite error between simulated annealing speed and experiment one because of model hypothesis and experimental error, so that it is helpful to perfect this model further for improving its simulation accuracy and practical application.更多还原