大型轧辊用钢Cr5动态再结晶行为及元胞自动机法研究

发布时间：2018-10-31 11:47

【摘要】：大型锻件一般是重型装备上的核心零部件,由于工作环境特殊,要求其具有优良的综合力学性能。而金属的宏观力学性能由其最终微观组织结构决定,在热加工的过程中,金属的宏观塑性变形引起了内部微观组织的复杂变化。在工业生产中,利用动态再结晶机制来改善材料在热变形中的微观组织,是提高产品质量的重要途径。因此,了解和掌握金属在热变形时的微观组织演变规律,对提高其综合性能及控制产品质量具有非常重要的意义。本文以大型轧辊用钢Cr5为研究对象,将宏观工艺参数与元胞自动机结合,以位错密度为内变量,建立能够从本质上反应Cr5钢热塑性变形过程的微观组织演化模型,研究了Cr5钢动态再结晶行为的演化规律与其变形参数之间的关系,从而可以达到预测组织性能和优化工艺参数的目的。具体开展的研究工作如下:通过热压缩物理模拟实验、初始位错密度测量实验以及母相初始晶粒尺寸测量实验,分析了不同变形条件下Cr5钢的流变应力行为和组织演化规律,建立了Cr5钢高温流变峰值应力模型,并获取了元胞自动机(CA)模拟所需的材料参数。基于材料热变形过程中的位错密度变化、再结晶形核及晶粒长大等材料学物理冶金理论,通过追踪唯一内变量—位错密度的变化,建立了用于模拟Cr5钢动态再结晶行为的CA模型。利用所建立的动态再结晶CA模型,模拟了Cr5钢在各个变形条件下的高温流变应力曲线和动态再结晶动力学行为,并与实验结果进行对比,验证了模型的准确性。通过改变应变速率、变形温度以及应变量三大热变形参数,研究了各热力参数对Cr5钢动态再结晶行为的影响规律。结果表明,基于材料学物理冶金原理所建立的CA模型,可以准确模拟和预测Cr5钢动态再结晶微观组织和流变应力的演变特征,从而为预测组织演变和控制产品质量提供合理依据。
[Abstract]:Large forgings are generally the core parts of heavy equipment. Because of the special working environment, they are required to have excellent comprehensive mechanical properties. The macroscopic mechanical properties of metals are determined by their final microstructure. During the process of hot working, the macroscopic plastic deformation of metals causes complex changes of internal microstructure. In industrial production, it is an important way to improve the product quality by using dynamic recrystallization mechanism to improve the microstructure of materials in hot deformation. Therefore, it is of great significance to understand and master the law of microstructure evolution of metals during hot deformation in order to improve their comprehensive properties and control the quality of products. In this paper, taking Cr5 steel for large roll as the research object, combining macroscopic process parameters with cellular automata, taking dislocation density as internal variable, a microstructure evolution model which can essentially reflect the thermoplastic deformation process of Cr5 steel is established. The relationship between the evolution of dynamic recrystallization behavior of Cr5 steel and its deformation parameters is studied, which can be used to predict the microstructure and properties and optimize the process parameters. The research works are as follows: the rheological stress behavior and microstructure evolution of Cr5 steel under different deformation conditions are analyzed by means of thermal compression physical simulation experiment, initial dislocation density measurement experiment and parent phase initial grain size measurement experiment. The peak rheological stress model of Cr5 steel at high temperature was established and the material parameters needed for (CA) simulation of cellular automata were obtained. Based on the dislocation density change during hot deformation of materials, recrystallization nucleation and grain growth and other physical metallurgical theories of materials, the change of dislocation density, which is the only internal variable, is traced. A CA model was established to simulate the dynamic recrystallization behavior of Cr5 steel. The dynamic recrystallization CA model is used to simulate the high temperature rheological stress curve and dynamic recrystallization kinetic behavior of Cr5 steel under various deformation conditions. The experimental results are compared to verify the accuracy of the model. The effect of thermal parameters on the dynamic recrystallization behavior of Cr5 steel was studied by changing the strain rate, deformation temperature and strain. The results show that the CA model based on the principle of material physics metallurgy can accurately simulate and predict the evolution characteristics of dynamic recrystallization microstructure and rheological stress of Cr5 steel. Therefore, it provides reasonable basis for predicting organizational evolution and controlling product quality.
【学位授予单位】：河南科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG142.1

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