38MnVTi非调质钢热变形行为及加工图研究

发布时间：2018-05-22 16:02

本文选题：非调质钢 + 热成形　；参考：《重庆理工大学》2015年硕士论文

【摘要】：非调质钢是一种通过控锻-控冷技术而使钢材不需要经过调质处理就能达到力学性能的材料。38MnVTi非调质钢作为汽车前轴和转向节锻件的常用材料,对它锻造性能要求很高。本文通过热模拟压缩试验研究了该材料在热变形中的变形行为,运用了本构方程、神经网络及显微组织等手段获得了Parasd和Murty判据的加工图,论文的主要研究内容及成果有:(1)分析了38MnVTi非调质钢应力-应变曲线的特征。达到峰值应力的快慢与变形温度的大小有关,变形温度越高达到峰值应力的时间越短;此外,应力达到峰值后曲线的平缓或下降与材料的软化机制有关,动态回复和动态再结晶能使材料发生软化,因而影响应力-应变曲线的走势。(2)研究了变形参数与流变应力的关系。通过回归分析的方法建立了峰值应力的本构方程,用于描述材料在变形过程强度量的最大属性;为了拓展本构方程的适用性,采用应变量的多项式表示材料常数,对Arrhenius双曲正弦形式的表达式通过引入应变进行修正,得到带应变的本构方程。(3)对比了本构方程与BP神经网络模型预测应力的精度。以应变、变形速率和变形温度作为输入信息并将应力作为输出信息,进行神经网络模型建模。训练后的神经网络模型其应力的预测精度比本构方程预测精度高。利用训练好的神经网络对变形温度为1050℃和1150℃下不同应变速率的应力进行预测。(4)构建了Parasd和Murty两种失稳判据的加工图并对其适用性进行了验证。对不同应变的加工图通过功率耗散系数及失稳区特征的分析,结合显微组织、硬度、拉伸测试对加工图进行验证。结果表明:制作加工图的应变必须选取稳态阶段,非稳态阶段的应变不能保证加工图的准确性;两种判据的加工图具有相似性,且Parasd判据的加工图失稳区与低的功率耗散系数有关,工艺设计时应综合考虑二者的失稳区及功率耗散系数特征。对于38MnVTi非调质钢,不能在高应变速率进行高应变量的成形,否则会导致组织失稳。经工艺优化后,该材料的最佳工艺参数为温度1100~1200℃,应变速率0.1~1s-1。
[Abstract]:Non quenched and tempered steel is a material of.38MnVTi non quenched and tempered steel which can achieve mechanical properties without quenching and tempering through controlled forging and controlled cooling technology. The non quenched and tempered steel is used as a common material for the front axle of the car and the forgings of the steering knuckle. It has a high requirement for its forging performance. This paper has studied the deformation of the material in the thermal deformation by thermal simulation test. Parasd and Murty criteria are obtained by using constitutive equations, neural networks and microstructures. The main contents and results of this paper are as follows: (1) the characteristics of stress strain curves of 38MnVTi non quenched and tempered steel are analyzed. The speed of reaching the peak stress is related to the size of the deformation temperature, and the higher the deformation temperature is to the peak stress. The time is shorter; in addition, the slow or decrease of the curve is related to the softening mechanism of the material. Dynamic recovery and dynamic recrystallization can soften the material and affect the trend of the stress-strain curve. (2) the relationship between the deformation parameters and the rheological stress is studied. The peak stress is established by the regression analysis method. The structure equation is used to describe the maximum properties of the strength of the material in the deformation process. In order to extend the applicability of the constitutive equation, the polynomial of the strain is used to express the material constant. The constitutive equation with strain is obtained by modifying the expression of the Arrhenius hyperbolic sine form by introducing strain. (3) comparing the constitutive equation with the BP neural network model. The precision of stress is predicted. The neural network model is modeled by the strain, deformation rate and deformation temperature as the input information and the stress as the output information. The prediction accuracy of the stress is higher than the constitutive equation after training. The trained neural network is used for the deformation temperature of 1050 and 1150. The stress of the strain rate is predicted. (4) two kinds of Instability Criteria of Parasd and Murty are constructed and their applicability is verified. The analysis of the power dissipation coefficient and the characteristics of the instability zone for different strains of the strain is verified by the microscopic structure, hardness and tensile test. The results show that the processing chart is made. The strain must be selected in the steady state. The strain of the unsteady state can not guarantee the accuracy of the processing diagram; the processing diagram of the two criteria has the similarity, and the instability zone of the Parasd criterion is related to the low power dissipation factor. The process design should take into account the instability zone and the power dissipation factor of the two parties. For the non tuning of the process design, the characteristics of the power dissipation factor should be taken into consideration. The high strain rate of high strain rate can not be formed in high strain rate, otherwise the structure will be unstable. The optimum process parameters of the material are temperature 1100~1200 C and the strain rate 0.1~1s-1. after optimization.
【学位授予单位】：重庆理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG142.1

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