摘要本文采用盖面前超声冲击和分层超声冲击处理55mm厚Q345钢焊接接头，与无超声冲击接头对比了微观组织、显微硬度、剪切强度、冲击韧性和断口组织形貌。试验结果表明：

分层超声冲击焊接接头相比无超声冲击焊接接头，力学性能上在焊缝内部积累强化效应，焊缝内部硬度升高，焊缝整体呈现软夹硬的三明治效果，剪切强度最大可提高15。7%，强化焊缝力学性能；焊缝冲击功提高13。6%；组织上改变了后续焊道的凝固结晶过程，使焊缝组织细化，焊缝组织由粗大的柱状晶转变为细小的等轴晶。冲击试验发现，经分层超声冲击的焊缝，冲击断口有深密的韧窝特征，是冲击断裂过程位错受阻留下的的痕迹，表明经分层超声冲击后，晶粒细化使焊缝韧性提高。86150

盖面前超声冲击接头相比无冲击接头，在焊缝内部10-25mm深度上显微硬度降低；焊缝内部力学性能软化，在焊缝中部25mm处软化效果最明显，剪切强度降低13。2%；其接头冲击功相比无UIT接头冲击功并无无明显变化。

毕业论文关键词：分层超声冲击；显微硬度；焊缝微观组织；剪切强度；冲击韧性

Abstract In this paper,The 55mm thick Q345 welded joint was manufactured without UIT,UIT ahead of cap pass and layered UIT。There were some conclusions through organizational analysis,hardness testing,shear punch test,Impact test and observing fracture morphology。

Layered UIT can create accumulation of strengthening effects in the region of the welding with the weld hardness increased,and strengthen the mechanical properties of weld with the shear strength is increased by 15。7%。Layered UIT also can enhance the impact energy of weld by 13。6% comparing with the weld without UIT。The appearance of welding is soft gripping hard,UIT changed the solidification crystallization process of subsequent weld,the weld structurewas more compact,weld microstructure turns coarse columnar grains into fine equiaxed grains。Characteristics of the fracture,which has deep dimples,are traces of impact fracture dislocations left by blocked。It shows that layered UIT refines grain and enhances weld toughness。

UIT ahead of cap pass made microhardness of region about 25mm away from the weld surface reduced and sofen the interior of the weld and soften properties of interior of the weld,the effect of softening is most pronounced in the region 25mm away from the weld surface。Shear strength is decreased by 13。2%。There was no obvious change on impact energy compring with the joint without UIT。

Keywords:layered ultrasonic;impact treatment;microshardness;microstructure;micr-ostructure of welding;shear strength;impact toughness 

目  录

第一章 绪论 1

1。1 研究背景 1

1。2 超声冲击的应用与发展 3

1。2。1 超声冲击在焊接中的应用 3

1。2。2 超声冲击国内外研究现状 4

1。3微冲剪实验发展概况 5

1。4 课题的主要研究内容与目的 6

第二章 试验方法与设备 7

2。1 课题研究方案 7

2。2 Q345钢焊接工艺方法 8

2。3 超声冲击 9

2。3。1 超声冲击工艺方法 9

2。3。2 超声冲击设备与方法 11

2。4 微观组织观察（SEM）试验 12