TWIP钢屈服准则的应用与变形抗力研究

发布时间：2019-01-28 09:26

【摘要】：孪晶诱发塑性变形钢,又称TWIP钢,是近些年来所发展起来的新型汽车用钢。在力学性能上,有着很高的强塑积,能够在保证强度的情况下,有着更高的塑性,同时,其对冲击功的吸收能力更优于传统钢种。从TWIP钢塑性变形阶段的本构关系和变形抗力角度出发,对钢种的各向异性程度、TWIP效应机理、屈服准则应用以及整个变形阶段的应变硬化行为进行了研究。通过单向拉伸实验和XRD观察,得到实验钢为室温奥氏体钢,在0°、45°和90°方向上的屈服应力差异很大,其中在90°方向和45°方向上,屈服强度相差约为165MPa,厚向各向异性指数r值均大于1,存在有明显的各向异性。通过不同变形量的单向拉伸实验,然后分别用金相显微镜和透射显微镜对纵向截面的微观组织结构进行观察,发现该钢种在形变时形成很大数量的形变孪晶,并对颈缩的出现起到了显著的推迟作用,从而证明该钢种在塑性形变中发生了较为显著的TWIP效应。通过与轧制方向成不同角度的单向拉伸实验,以及在自主设计制造的用于实现等比例双向拉伸的简易机械式实验装置上所做的等双拉实验,分别对Hill48和Barlat89两种屈服函数中的未知参数进行了计算,计算方法有变形各向异性r值求解法和应力各向异性求解法。将所求结果分别对TWIP钢的r值、屈服轨迹和等双拉应力应变曲线进行了预测,根据预测结果的误差分析,可以得到,由各向异性系数r值计算屈服函数中未知参数所得的Hill48屈服函数能够更加准确的描述TWIP钢的屈服行为。通过对室温下单向拉伸应力—应变曲线做相应的数据处理,获得TWIP钢的应变硬化率—应变曲线,结果表明,TWIP钢在塑性变形阶段,其应变硬化行为分为三个阶段,也即随着应变的逐渐增加,应变硬化率呈现为“迅速下降—上升—再下降”的整体趋势,而在金相显微镜下和透射电子显微镜下的观察表明,这是试验钢在塑性阶段的变形中,形变孪晶和位错各自及相互之间的交互作用共同影响的结果。
[Abstract]:Twin induced plastic deformation steel, also known as TWIP steel, is a new type of automobile steel developed in recent years. In terms of mechanical properties, it has a high strong plastic product, which can ensure the strength of the steel and has a higher plasticity. At the same time, its absorptive capacity of impact work is better than that of the traditional steel. The anisotropy of TWIP steel, the mechanism of TWIP effect, the application of yield criterion and the strain hardening behavior of the whole deformation stage were studied from the point of view of constitutive relation and deformation resistance of TWIP steel during plastic deformation. Through uniaxial tensile test and XRD observation, it is found that the experimental steel is austenitic steel at room temperature. The yield stress in 0 掳, 45 掳and 90 掳directions is very different, and the difference of yield strength in 90 掳direction and 45 掳direction is about 165 MPA. The thickness anisotropy exponent r is greater than 1, and there is obvious anisotropy. The microstructure of the longitudinal section was observed by means of metallographic microscope and transmission microscope. It was found that a large number of deformation twins were formed when the steel was deformed. It is proved that the TWIP effect is significant in plastic deformation of the steel. Through the uniaxial tensile experiment with different angle to the rolling direction, and on the simple mechanical experiment device designed and manufactured by ourselves to realize the equal proportion biaxial tension, the equal double pull experiment was done. The unknown parameters in Hill48 and Barlat89 yield functions are calculated respectively. The calculation methods include deformation anisotropy r value method and stress anisotropy method. The values of r, yield trajectory and iso-double tensile stress-strain curves of TWIP steel are predicted by the calculated results. According to the error analysis of the prediction results, the results can be obtained. The Hill48 yield function calculated from the anisotropic coefficient r value of the yield function can more accurately describe the yield behavior of TWIP steel. The strain-hardening rate-strain curve of TWIP steel was obtained by processing the stress-strain curve of uniaxial tension at room temperature. The results show that the strain hardening behavior of TWIP steel is divided into three stages during plastic deformation. That is to say, with the increasing of strain, the strain hardening rate shows the whole trend of "rapid descending, rising and falling", and the observation under metallographic microscope and transmission electron microscope shows that this is the deformation of the test steel in the plastic stage. The results of the interaction between deformation twins and dislocations.
【学位授予单位】：华北理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG142.1

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