55钢热形变再结晶行为研究与晶粒度预报

发布时间：2018-01-29 16:27

本文关键词： 55钢热锻件再结晶行为晶粒度预报双向控制　出处：《江苏大学》2017年硕士论文　论文类型：学位论文

【摘要】：评价金属热锻件产品质量的两个主要指标:成形尺寸和组织性能。成形尺寸满足装配的要求,确保产品能正常使用;而组织性能的好坏直接影响着使用寿命,从某方面上讲,产品组织性能具有更重要的意义。晶粒度是评价热锻件微观组织的重要参数,根据经典Hall-Petch公式,细小的晶粒度组织可显著提高金属材料的综合力学性能。因此通过合理的方法对材料热成形的晶粒度演变进行预报,这可为实际锻件生产的质量控制提供理论依据。本文利用有限元数值分析与物理实验相结合的微观组织模拟方法,系统研究55钢热压缩以及某异形锻件热成形的晶粒度变化规律,同时为在Deform-3D软件后处理窗口中实现有效的晶粒度预报结果,需先在型号-3800热/力模拟机上进行单、双道次热压缩实验并结合金相实验数据,建立55钢热形变的微观组织演变包括动态、静态再结晶的Yada唯象模型,具体研究工作如下:(1)采用单道次实验研究了55钢热形变的动态再结晶行为规律,主要包括:确立了55钢动态再结晶形变激活能和热塑性变形本构关系;采用Poliak和Jonas提出的应变硬化率(?)模型,得到了动态再结晶临界条件下应力、应变比值;建立了与初始奥氏体晶粒大小相关的峰值应变模型,及动态再结晶动力学方程。(2)采用双道次实验研究了55钢热形变的静态再结晶行为,得出不同工艺参数条件下对静态再结晶行为的影响可概括为:随压缩温度升高,或应变速率增大,或第一道次应变量增大,或初始奥氏体晶粒越细小,按式计算得的静态再结晶百分数就越高。并通过实验数据回归建立了静态再结晶动力学方程。(3)通过将建立的相关参数嵌入到Deform-3D软件中完成该材料热压缩变形的晶粒度预报有限元模拟系统建立,从直观层面上对热压缩实验的微观组织演变包括动态、静态再结晶以及晶粒长大的晶粒度变化进行预报与分析。(4)结合热塑性变形宏观与微观多尺度的有限元耦合系统,针对某异形锻件产品实例,对其热成形过程进行了宏微观模拟分析,并通过对比A、B两处实际的空冷晶粒组织,发现A处的晶粒组织明显要细小,这与晶粒度预报结果一致,从而验证了所采用的唯象模型对晶粒度预报的有效性。研究结果表明:基于建立的Yada唯象模型用于55钢热成形的晶粒度预报是有效的,这可为实现锻件产品的宏观成形尺寸与微观组织性能双向控制提供重要的工具。
[Abstract]:There are two main indexes to evaluate the product quality of hot metal forgings: forming size and microstructure and properties. The forming dimensions meet the requirements of assembly and ensure the products can be used normally. The quality of microstructure and properties directly affect the service life, from a certain point of view, the structure and properties of products have more important significance. Grain size is an important parameter to evaluate the microstructure of hot forgings. According to the classical Hall-Petch formula, fine grain size structure can significantly improve the comprehensive mechanical properties of metal materials. Therefore, the grain size evolution of hot forming materials is predicted by a reasonable method. This can provide a theoretical basis for the quality control of actual forgings. In this paper, the microstructure simulation method combining finite element numerical analysis with physical experiments is used. The grain size variation of hot compression of 55 steel and hot forming of a special-shaped forgings was studied systematically, and the results of grain size prediction were realized in the post-processing window of Deform-3D software. The microstructure evolution of 55 steel thermal deformation including dynamics should be established by single and double pass thermal compression test on the model -3800 thermal / mechanical simulator combined with metallographic experimental data. The Yada phenomenological model of static recrystallization, the specific research work is as follows: 1) the dynamic recrystallization behavior of 55 steel is studied by single pass experiment. The dynamic recrystallization activation energy and thermoplastic deformation constitutive relation of 55 steel are established. Strain hardening rate proposed by Poliak and Jonas? The ratio of stress and strain under the critical condition of dynamic recrystallization is obtained. The peak strain model related to the initial austenite grain size and the dynamic recrystallization kinetics equation. It is concluded that the effect of different process parameters on the static recrystallization behavior can be summarized as follows: with the increase of compression temperature, the strain rate increases, or the first secondary strain increases, or the initial austenite grain becomes smaller. The higher the percentage of static recrystallization is calculated by the formula, and the equation of static recrystallization kinetics is established by regression of experimental data. By embedding the relevant parameters into the Deform-3D software, the finite element simulation system of grain size prediction for the hot compression deformation of the material is established. The microstructure evolution of the thermal compression experiment includes the dynamics from the visual level. Static recrystallization and grain growth grain size change prediction and analysis. 4) combined with thermoplastic deformation macro and micro multi-scale finite element coupling system for a special-shaped forgings product example. The hot forming process was analyzed by macro and micro simulation, and by comparing the two actual air-cooled grain structures in A and B, it was found that the grain structure at A was obviously fine, which was consistent with the prediction results of grain size. The results show that the proposed Yada phenomenological model is effective in predicting the grain size of 55 steel in hot forming. This can provide an important tool for realizing the bidirectional control of macro forming size and microstructure and properties of forgings.
【学位授予单位】：江苏大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG142.1

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