38MnVTi非调质钢热变形过程中微观组织演变的研究

发布时间：2018-04-26 12:04

本文选题：38MnVTi非调质钢 + 织构　；参考：《重庆理工大学》2017年硕士论文

【摘要】：非调质钢由于其后续不需要调质处理,即减少了高能耗的热处理环节,因而能够降低能耗,节约能源。随着非调质钢的发展,当前生产汽车所使用的大多数关键设备如动力部件、连接功能件、车轮转向部件等都使用非调质钢来进行加工。这些汽车零部件在使用过程中会不断的承受拉伸、冲击、弯曲等比较复杂的载荷,因此要求材料在锻造成形后具有较高的强度、较好的韧性、高的抗疲劳性。良好的综合力学性能取决于热锻和锻后冷却组织的演变,因此对非调质钢成形和冷却过程当中显微结构演化规律的研究是比较重要的。通过模型和实际生产情况的结合,可以有效的减少材料的浪费和提高产品的质量,对我国非调质钢的研发和应用具有重大的意义。本文以38MnVTi钢为实验对象,对热压缩过程中的显微组织演化进行了重点探讨。根据单道次热压缩实验的结果建立了高温流动应力模型,然后通过线性回归的方法确定了高温流动应力模型的参数,并根据38MnVTi钢的金相数据,建立了其对应的动态再结晶金相规律和相应的晶粒尺寸模型。在双道次热压缩实验的基础上建立了静态再结晶动力学模型和对应的尺寸模型,并详细讨论了静态再结晶体积分数的影响因素如形变的温度、第一道次的应变量、形变的速率等,得出影响体积分数的主要原因是形变的温度和第一道次的应变量,而形变的速率对其影响不大。通过奥氏体晶粒长大实验重点探讨了奥氏体区保温时间和加热温度对晶粒尺寸的影响,结果显示温度的停留时间变化与晶粒尺寸间近似呈抛物线函数关系;加热温度的高低与晶粒尺寸间近似呈指数函数的关系,最后通过大量晶粒尺寸的平均化处理得到了相应的晶粒尺寸模型。通过物理实验的方法,探讨了冷却终锻温度和冷却速度与非调质钢显微金相组织之间的关系。由于本文采用的钢为典型的铁素体-珠光体型钢,珠光体的层片间距对非调质钢的综合性能有很大的影响,因而借助扫描电镜得出了冷却温度和冷却速度对珠光体层片间距的影响规律。最后借助于EBSD技术研究了冷却速率对38MnVTi非调质钢的晶粒取向差和织构的影响,得出冷却速率对38MnVTi非调质钢的织构是有一定影响,但并没有固定的规律。本文通过大量的实验建立了38MnVTi非调质钢在锻造过程中的微观组织演变模型,并把得到的模型与实验值进行了对比,实验值与模型的吻合程度较高。并用金相技术和EBSD技术研究了冷却工艺参数对热锻完成后冷却过程微观组织的影响,为实际生产过程中的工艺参数优化提供了有效的理论指导。
[Abstract]:Non-quenched and tempered steel can reduce energy consumption and save energy because it does not need to be tempered and tempered in the subsequent process, that is to say, it can reduce the heat treatment link with high energy consumption. With the development of non-quenched and tempered steels, most of the key equipments used in the production of automobiles, such as power components, connection functions, wheel steering parts, etc., are processed by non-quenched and tempered steel. In the process of using these automobile parts will bear more complex loads such as tensile impact bending and so on. Therefore the material must have higher strength better toughness and higher fatigue resistance after forging. The good comprehensive mechanical properties depend on the evolution of hot forging and cooling microstructure after forging, so it is important to study the evolution of microstructure in the forming and cooling process of non-quenched and tempered steel. Through the combination of the model and the actual production conditions, the waste of materials and the quality of products can be effectively reduced, which is of great significance to the research and development and application of non-quenched and tempered steels in China. In this paper, the microstructure evolution of 38MnVTi steel during hot compression is discussed. A high temperature flow stress model is established based on the results of a single pass thermal compression experiment. Then the parameters of the high temperature flow stress model are determined by linear regression, and the metallographic data of 38MnVTi steel are obtained. The corresponding dynamic recrystallization metallography and the corresponding grain size model were established. Based on the two-pass thermal compression experiment, the static recrystallization kinetic model and the corresponding dimension model are established, and the influence factors of the static recrystallization volume integral number such as the deformation temperature, the first order dependent variable are discussed in detail. It is concluded that the temperature and the first strain of the deformation are the main factors influencing the volume fraction, but the rate of deformation has little effect on the deformation. The effect of holding time and heating temperature in austenitic region on grain size is discussed through austenite grain growth experiment. The results show that the relationship between temperature residence time and grain size is approximately parabola function. The relationship between the heating temperature and the grain size is approximately exponential function. Finally, the corresponding grain size model is obtained through the average treatment of a large number of grain sizes. The relationship between the final forging temperature, cooling rate and microstructure of non-quenched and tempered steel was investigated by physical experiments. Because the steel used in this paper is a typical ferrite-pearlite section steel, the interlaminar spacing of pearlite has a great influence on the comprehensive properties of non-quenched and tempered steel. The influence of cooling temperature and cooling rate on the lamellar spacing of pearlite was obtained by SEM. Finally, the effect of cooling rate on the grain orientation and texture of 38MnVTi non-quenched and tempered steel is studied by means of EBSD technology. It is concluded that the cooling rate has a certain effect on the texture of 38MnVTi non-quenched and tempered steel, but there is no fixed rule. In this paper, the microstructure evolution model of 38MnVTi non-quenched and tempered steel in forging process is established by a large number of experiments, and the obtained model is compared with the experimental value, and the experimental value is in good agreement with the model. The effect of cooling process parameters on the microstructure of cooling process after hot forging was studied by metallography and EBSD technology, which provided an effective theoretical guidance for the optimization of process parameters in actual production process.
【学位授予单位】：重庆理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG142.1

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