掺杂钨连轧棒材的微观组织及有限元分析

发布时间：2018-08-25 08:34

【摘要】：掺杂钨具有熔点高、膨胀系数低和良好的高温抗下垂性能等优点,被广泛用作于照明、气体放电光源以及电子管的阴极材料。通过热变形方法,获得组织与性能优异的细晶掺杂钨棒是制备掺杂钨丝的重要步骤,传统的旋锻工艺虽能获得较大变形量,但加工后的组织不均匀且耗能较大;三辊轧机轧制掺杂钨棒材,轧件咬入能力较弱,且结构复杂,维护较为繁琐。本文通过高速连轧机,采用一火次十道连轧的连轧工艺,将直径为18.5mm的掺杂钨烧结棒连轧为直径9mm的掺杂钨杆,研究了掺杂钨棒的显微组织及连轧过程的应力和应变场。利用金相显微镜、扫描电子显微镜等方法观察了四道、六道、十道次连轧后掺杂钨棒材横截面的组织。结果发现:掺杂钨棒材连轧后,显微组织显著细化,道次越多,晶粒细化越显著。经过十道次连轧后,晶粒平均直径约为3~5μm,烧结孔被压缩甚至闭合,掺杂钨棒横截面边缘区域晶粒比中心区域更加细小。部分连轧后的掺杂钨棒出现了区域性的晶粒异常长大,其内部钾泡及钾管较多。随着连轧道次的增加,掺杂钨棒的显微硬度明显提高。通过Abaqus软件对掺杂钨棒的四道次、六道次、十道次连轧过程进行有限元模拟,对模拟后的轧件网格变形、温度场、应力场、应变场以及轧制力进行了分析。结果表明,连轧过程中掺杂钨棒横截面上心部温度最高,表面温度最低。在变形区内,轧件表面的等效应力和残余等效应力最大,向心部递减,中心处的等效应力和残余等效应力最小;四道次、六道次连轧的轧件心部等效应变最大,向表面递减,经过十道次连轧后,轧件等效应变的分布为表面最高,心部最低。残余等效应变从轧件表面向中心逐渐减小,最小值出现在约2/5R处,其后又逐渐增大。残余等效应变最小值出现的区域,与部分连轧后掺杂钨棒的晶粒异常长大区域相符,是导致掺杂钨棒晶粒异常长大的主要原因。随着连轧道次的增加,各道次稳态轧制阶段的轧制力波动逐渐变大,说明轧制的稳定性降低。通过对不同初轧温度和摩擦系数下残余应力、残余应变及轧制力的变化分析,发现随着初轧温度和初轧速度的升高,十道次连轧的轧制力和轧件的残余应力逐渐降低,残余应变增加;残余应力、残余应变和轧制力均随着摩擦系数的增大而增大。
[Abstract]:Doped tungsten has many advantages such as high melting point, low expansion coefficient and good sag resistance at high temperature. It is widely used as cathode material for lighting, gas discharge light source and electron tube. By hot deformation method, it is an important step to obtain fine doped tungsten rod with excellent microstructure and properties. Although the traditional rotary forging process can obtain a large amount of deformation, the microstructure after processing is not uniform and energy consumption is large. The rolling of Tungsten bar by three high rolling mill has weak bite ability, complex structure and complicated maintenance. In this paper, the microstructures and stress and strain fields of doped tungsten bars with diameter 18.5mm are studied by using the continuous rolling process of a high speed continuous rolling mill with ten passes. The doped tungsten sintered bar with diameter 18.5mm has been continuously rolled into doped tungsten rods with diameter 9mm. The microstructures of the doped tungsten bars and the stress and strain fields in the continuous rolling process have been studied in this paper. The microstructure of four, six and ten passes of doped tungsten bar cross section was observed by metallographic microscope and scanning electron microscope (SEM). The results show that after continuous rolling of doped tungsten bar, the microstructure is significantly refined, and the more passes, the more the grain refinement. After ten times of continuous rolling, the average diameter of the grain is about 3 ~ 5 渭 m, the sintered hole is compressed or even closed, and the grain size in the edge of cross section of doped tungsten rod is smaller than that in the center region. After partial continuous rolling, regional grain growth occurs in the doped tungsten rods, and there are more potassium bubbles and potassium tubes in the interiors. The microhardness of doped tungsten rod increases with the increase of continuous rolling pass. The four, six and ten passes continuous rolling process of doped tungsten rod was simulated by Abaqus software. The mesh deformation, temperature field, stress field, strain field and rolling force were analyzed. The results show that the temperature of the top center of the cross section of doped tungsten rod is the highest and the surface temperature is the lowest during the continuous rolling process. In the deformation zone, the equivalent stress and residual equivalent stress on the surface of the rolling piece are the largest, the concentric part decreases, the equivalent stress and the residual equivalent stress at the center are the smallest, and the equivalent strain in the center of the workpiece with four passes and six passes continuous rolling is the largest and decreases to the surface. After ten times of continuous rolling, the distribution of equivalent strain is the highest on the surface and the lowest at the center. The residual equivalent strain decreases gradually from the surface to the center of the workpiece, and the minimum appears at about 2 / 5R, and then increases gradually. The region where the minimum value of residual equivalent strain appears is consistent with the abnormal grain growth region of the doped tungsten rod after continuous rolling, which is the main reason for the abnormal growth of the doped tungsten rod grain. With the increase of continuous rolling pass, the rolling force fluctuates gradually in each pass steady state rolling stage, which indicates that the rolling stability is decreased. By analyzing the variation of residual stress, residual strain and rolling force at different temperature and friction coefficient, it is found that the rolling force and the residual stress of the rolling piece decrease gradually with the increase of the temperature and speed of the first rolling. The residual strain, residual stress, residual strain and rolling force increase with the increase of friction coefficient.
【学位授予单位】：烟台大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG146.411;TG335.9

【参考文献】