热连轧钛合金棒材损伤机理研究

发布时间：2018-03-23 19:46

  本文选题：钛合金棒材　切入点：有限元模拟　出处：《太原科技大学》2017年硕士论文

【摘要】：钛合金棒材产品是国民经济领域中的关键工程材料,具有高的机械强度和韧性,同时具备良好的冷加工工艺性能,以满足后续加工的要求。然而,由于目前钛合金产品生产过程中存在裂纹或者断裂的缺陷,使得产品成材率较低,本文通过损伤分析对裂纹的产生进行了预测,从而降低了钛合金生产过程中的损耗率。本文制定了合理的三辊连轧TC4棒材的工艺制度,用有限元软件模拟棒材损伤值,对连轧过程中裂纹敏感区进行预测,并研究不同工艺参数对棒材最大损伤值的影响。改进了连轧孔型系统,在三辊热连轧机组上进行了相关试验,获得了几何尺寸精确、表面质量好的试样,随后进行了微观组织观察。具体研究内容如下:(1)利用Deform有限元模拟技术,对棒材三辊热连轧过程中的损伤值分布进行了模拟,通过对比,确定了损伤值最大的区域,即与轧辊接触的区域,此区域金属变形最大;比较了轧辊偏角、摩擦因数、温度对棒材最大损伤值的影响,为后续参数优化提供理论基础;采用CA模型,线性拟合了位错密度模型、动态再结晶模型等,进一步模拟了最大损伤区域晶粒的组织演变。(2)基于断裂力学理论,对适用于低温与等温的Ayada损伤模型进行了优化,考虑了轧制温度(850℃、900℃、950℃、1000℃)、应变速率(0.01 s-1、0.1s-1、1s-1)的影响,推导了TC4钛合金高温累积损伤值的数学模型;并比较了模拟损伤值与计算损伤值的计算偏差,最大偏差值为9%。(3)孔型连轧稳定是实现产品顺利变形的关键,在传统孔型基础上,采用正交分析法与有限元模拟,以降低棒材横截面温度梯度、减小表面裂纹为目标,优化了“多线段三角—圆”孔型系统,确定了第一道次、第三道次凸起轧槽的最佳几何尺寸,即,第一道次长轴长4.30mm,短轴长0.80mm,第二道次长轴长3.34mm,短轴长0.80mm。(4)在三辊热连轧机组上进行了TC4棒材轧制试验,获得了几何尺寸精确、表面质量好的试样,进一步确认了新型孔型的优越性;随后微观组织观察发现,在轧制第三道次,棒材组织开始发生组织转变,即由细条状逐渐转变为等轴状,这与有限元模拟结果相吻合。说明本文制定的工艺参数、设备参数是合理的,从而为同类金属材料轧制提供可靠的技术依据。
[Abstract]:Titanium alloy bar is a key engineering material in the field of national economy. It has high mechanical strength and toughness, and has good cold processing performance to meet the requirements of subsequent processing. Due to the defects of crack or fracture in the process of titanium alloy production at present, the yield of finished product is low. In this paper, the production of crack is predicted by damage analysis. In order to reduce the loss rate of titanium alloy in the process of production, a reasonable process system of three-roll continuous rolling TC4 bar is established in this paper. The damage value of the bar is simulated by finite element software, and the crack sensitive zone in continuous rolling process is predicted. The influence of different process parameters on the maximum damage value of the bar was studied. The pass system of continuous rolling was improved, and the related tests were carried out on the three high hot strip mill. The samples with accurate geometry and good surface quality were obtained. Then the microstructure was observed. The specific research contents are as follows: (1) using Deform finite element simulation technology, the damage value distribution in the process of three-roll hot continuous rolling of bar is simulated. By comparison, the region with the largest damage value is determined. The influence of roll angle, friction coefficient and temperature on the maximum damage value of the bar is compared, which provides the theoretical basis for the optimization of the following parameters. The dislocation density model and dynamic recrystallization model are fitted linearly, and the microstructure evolution of grain in the maximum damage region is further simulated. Based on the theory of fracture mechanics, the Ayada damage model suitable for low temperature and isothermal temperature is optimized. Considering the influence of rolling temperature (850 鈩，

本文编号：1654909