超声冲击处理对厚板接头组织、应力和力学性能的影响

发布时间：2018-05-19 04:03

本文选题：分层超声冲击处理 + 厚板焊缝　；参考：《江苏科技大学》2017年硕士论文

【摘要】：焊接熔池温度高及冷却速度大的特点使焊缝容易产生柱状晶。粗大的柱状晶颗粒协同变形能力差,使接头在形变过程中容易发生裂纹扩展,同时焊接造成的接头中高残余拉应力容易导致其载能力和疲劳寿命下降。因此,优化焊缝内部组织,改善焊缝力学性能,有效评价和调控焊接残余应力尤为重要。本文以55mm厚Q345钢板接头为研究对象,进行了无超声冲击处理、分层超声冲击处理和盖面前超声冲击处理工艺实验,分析了焊缝内部组织变化,结合轮廓法、冲击试验、微冲剪试验和显微硬度试验,研究了焊缝残余应力分布和力学性能,分析了超声冲击处理对焊缝内部组织、性能的影响及影响机理,研究了厚板内部残余应力分布特征,提出了分层超声冲击处理结合焊缝表面超声冲击处理的调控方法。组织分析表明:经分层超声冲击处理后焊缝内部组织细化明显,晶粒由粗大的柱状晶转变为细小的等轴晶,同时组织的细化也导致硬度值升高。经能谱测试发现分层超声冲击处理可以提高焊缝内部氧含量,同时促进了金属氧化物的生成过程,在焊道超声冲击处理表层产生的金属氧化物,这些氧化物可以为后续焊道凝固过程提供大量的形核质点,促进非自发形核,从而改变后续焊道凝固结晶过程,促使焊缝内部生长为等轴晶。二次切割轮廓法残余应力测试结果表明:焊态高残余应力主要分布在焊缝坡口内部及其附近,残余拉应力峰值出现在上下表面焊缝内部。盖面前超声冲击处理和分层超声冲击处理对焊缝内部残余应力分布趋势影响不大,但是在厚度上的水平方向上拉应力峰值有所下降,但是下降幅度有限。冲击试验结果表明:分层超声冲击处理后,由于焊缝组织细化,焊缝冲击吸收功提高13.6%,盖面前超声冲击处理后焊缝冲击吸收功无明显变化。基于微冲剪试验方法测试结果表明:焊缝经分层超声冲击处理后由于组织改善的原因剪切性能提高,尤其是焊缝内部薄弱区域提高明显。微冲剪试样断口照片显示,断裂韧窝分层超声冲击处理后大而深,韧窝内第二相粒子明显。维氏硬度测试结果表明:三组焊缝分布规律与微冲剪结果存在一致性,分层超声冲击焊缝硬度提高。
[Abstract]:The characteristics of high weld pool temperature and high cooling speed make it easy to produce columnar crystals. The poor synergetic deformation ability of the coarse columnar grain makes the crack propagation easily occur in the deformation process of the joint and the high residual tensile stress caused by welding can easily lead to the decrease of the loading capacity and fatigue life of the joint. Therefore, it is very important to optimize the internal structure of the weld, improve the mechanical properties of the weld and effectively evaluate and regulate the welding residual stress. In this paper, the 55mm thick Q345 steel plate joint is studied. The process experiments of non-ultrasonic impact treatment, stratified ultrasonic impact treatment and ultrasonic impact treatment before the cover are carried out. The changes of the internal structure of the weld are analyzed, combined with the contour method and the impact test. The residual stress distribution and mechanical properties of weld were studied by micro-impact shear test and microhardness test. The influence of ultrasonic impact on the microstructure and properties of weld and the mechanism of influence were analyzed. The distribution characteristics of residual stress in thick plate were studied. The control method of laminated ultrasonic impact treatment combined with ultrasonic impact treatment of weld surface was proposed. The microstructure analysis showed that the microstructure of the weld was refined obviously and the grain changed from the coarse columnar to the fine equiaxed grain after the laminated ultrasonic impact treatment. Meanwhile the microstructure refinement also led to the increase of hardness value. The energy spectrum test shows that the layered ultrasonic shock treatment can increase the oxygen content in the weld and promote the formation process of metal oxide. The metal oxide produced in the surface layer of the weld is treated by ultrasonic impact treatment. These oxides can provide a large number of nucleation particles for the subsequent weld solidification process, promote non-spontaneous nucleation, thus change the subsequent solidification crystallization process and promote the internal growth of equiaxed crystal in the weld. The results of residual stress measurement by secondary cutting contour method show that the high residual stress in welding is mainly distributed in and around the groove of weld, and the peak value of residual tensile stress appears in the upper and lower surface of weld. Ultrasonic impact treatment and stratified ultrasonic impact treatment have little effect on residual stress distribution in weld, but the peak value of tensile stress in horizontal direction of thickness decreases, but the extent of decrease is limited. The results of impact test show that the impact absorption energy of the weld increases by 13.6 due to the refinement of the weld structure after the treatment of stratified ultrasonic impact, but the impact absorption energy of the weld does not change obviously after the ultrasonic impact treatment before the cover. The results of micro-impact shear test show that the shear properties of the weld are improved due to the microstructure improvement, especially the weak area inside the weld. The fracture photographs of micro-impact shear specimens show that the fracture dimples are large and deep after ultrasonic impact treatment, and the second phase particles in the dimples are obvious. The results of Vickers hardness test show that the distribution of three groups of welds is consistent with the results of micro-impact shear, and the hardness of layered ultrasonic impact welds is increased.
【学位授予单位】：江苏科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG407;TG663

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