20MnNiMo核电用钢的热变形宏微观演化行为研究

发布时间：2018-06-03 05:09

本文选题：20MnNiMo钢 + 热变形行为　；参考：《重庆大学》2016年硕士论文

【摘要】：核电封头和反应堆压力容器(Reactor Pressure Vessel,RPV)大型锻件是核电站设备上的重要零部件,其长期在高温、高压、流体冲刷和侵蚀的恶劣环境下工作,所以此类大锻件对成形质量及微观组织性能的要求极高。目前,20MnNiMo低碳合金钢是制造核电封头和压力容器的主体材料,为获得优良的微观组织和力学性能,实现控制锻造的目的,研究20MnNiMo核电用钢的热塑性宏观变形行为和微观组织演化规律对于制定合理的热成形工艺参数有着重要的工程实际意义。论文以铸态20MnNiMo钢为研究对象,结合热物理压缩试验研究和有限元仿真模拟,利用数学统计回归分析方法和金相显微实验验证,主要从以下方面系统研究20MnNiMo核电钢的热塑性变形宏微观演化行为及规律:(1)热塑性变形时的宏观流变应力模型研究。通过热模拟压缩试验获得20MnNiMo核电钢的高温流变曲线,分析其宏观流变应力的变化特点,探讨应变量、变形速率和温度等变形工艺参数对20MnNiMo核电钢的热变形行为影响规律;分别基于经典Arrhenius模型、物象模型和人工神经网络模型描述并建立其高温流变应力模型,对比研究各自优缺点,进而确立较精确描述20MnNiMo核电钢热流变宏观力学行为的材料模型。(2)热变形过程中的微观动态再结晶行为研究。根据热物理模拟压缩试验数据建立该低碳低合金核电钢的动态再结晶微观组织演化相关模型,包括再结晶动力学模型、动态再结晶临界应变模型和动态再结晶晶粒尺寸模型。利用DEFORM有限元平台分析20MnNiMo核电钢的动态再结晶微观演化特点,并基于DEFORFM有限元的CA模块,构建用于模拟动态再结晶微观演化的元胞自动机模型。(3)基于有限元的热变形宏微观演化模拟。通过直接和二次开发间接导入材料参数及相关模型,分析20MnNiMo核电钢热塑性变形时的微观组织演化行为,定量、连续、动态和可视化地再现其微观晶粒的演化规律;通过改变温度和变形速率等工艺参数,研究热力参数对20MnNiMo核电钢动态再结晶行为的影响,并与金相实验进行对比以验证所建材料模型的适用性。最后,以某大型核电封头锻件为例,初步实现20MnNiMo核电钢在高温变形过程微观组织演化的模拟和预报。
[Abstract]:The nuclear head and reactor pressure vessel reactor (reactor Pressure vessel) heavy forgings are important components in nuclear power plant equipment. They work in harsh conditions of high temperature, high pressure, fluid erosion and erosion for a long time. Therefore, the forming quality and microstructure and properties of this kind of heavy forgings are very high. At present, 20MnNiMo low carbon alloy steel is the main material for the manufacture of nuclear head and pressure vessel. In order to obtain excellent microstructure and mechanical properties, the purpose of controlling forging is achieved. It is of great practical significance to study the thermoplastic macroscopic deformation behavior and microstructure evolution of 20MnNiMo nuclear power steel for the formulation of reasonable hot forming process parameters. In this paper, the as-cast 20MnNiMo steel is taken as the research object, combined with the thermophysical compression test and finite element simulation, the mathematical statistical regression analysis method and metallographic microscopic test are used to verify the results. The macroscopic rheological stress model of 20MnNiMo nuclear steel during thermoplastic deformation is studied systematically from the following aspects: macroscopic and microscopic evolution behavior of thermoplastic deformation and its law. The high temperature rheological curves of 20MnNiMo nuclear power steel were obtained by thermal simulation compression test. The characteristics of macroscopic rheological stress were analyzed, and the influence of deformation process parameters such as strain, deformation rate and temperature on the thermal deformation behavior of 20MnNiMo nuclear power steel was discussed. Based on the classical Arrhenius model, the object image model and the artificial neural network model, the flow stress model at high temperature is described and established, and the advantages and disadvantages of each model are compared. Furthermore, a more accurate material model for describing the macroscopic mechanical behavior of thermal fluxes of 20MnNiMo nuclear steel was established. The microscopic dynamic recrystallization behavior during hot deformation was studied. The dynamic recrystallization microstructure evolution model including recrystallization kinetics model, dynamic recrystallization critical strain model and dynamic recrystallization grain size model were established based on the data of thermal physical simulation compression test. The characteristics of dynamic recrystallization microevolution of 20MnNiMo nuclear power steel are analyzed by using DEFORM finite element platform, and based on CA module of DEFORFM finite element method, The cellular automata model for simulating dynamic recrystallization microscopic evolution is constructed. (3) the thermal deformation macro and micro evolution simulation based on finite element method is presented. The microstructure evolution behavior of 20MnNiMo nuclear steel during thermoplastic deformation is analyzed by directly and indirectly introducing material parameters and related models to quantitatively, continuously, dynamically and visually reproduce the evolution law of microstructure. The effect of thermal parameters on the dynamic recrystallization behavior of 20MnNiMo nuclear steel was studied by changing the process parameters such as temperature and deformation rate, and compared with the metallographic experiments to verify the applicability of the material model. Finally, taking a large nuclear power head forgings as an example, the simulation and prediction of microstructure evolution of 20MnNiMo nuclear steel during high temperature deformation are preliminarily realized.
【学位授予单位】：重庆大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TM623;TG142.1

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