超声冲击处理工艺对Q345焊接热影响区残余应力的影响

目的降低Q345焊接热影响区的残余应力。方法假设Q345对接焊缝两侧热影响区对称位置的表面残余应力一致,并采用盲孔法测量进行验证。采用超声冲击设备对焊缝一侧热影响区进行不同工艺参数的冲击处理,并测量焊缝两侧的残余应力值。对比焊缝两侧残余应力大小,并以消减率评价残余应力的消除效果。结果焊缝两侧热影响区对称位置的表面残余应力差值不超过最大主应力值的7.5%。超声冲击处理使热影响区的表面拉应力转变为压应力,消减率达到88%~130%。冲击时间一定,冲击电流的增大使残余应力消减率增大,但消减率增加的趋势变小。冲击电流一定,冲击时间增大时,残余应力的消减率变化不明显。结论可以认为焊缝两侧热影响区对称位置的应力值相等。提高冲击电流能够提高冲击力,使热影响区发生更大的塑性变形及位错结构变化,进而提高残余应力的消减率。但由于加工硬化的影响,消减率增加的趋势减小。超声冲击电流一定时,冲击力是一定的,提高冲击时间对消除率并没有明显的影响。

Effect of Ultrasonic Impact Treatment Technology on Residual Stress of Q345 HAZ

The work aims to reduce residual stress of Q345 HAZ. The residual stresses of the HAZ symmetrical position on both weld sides were assumed to be consistent, then residual stresses were measured in blind-hole method for verification. HAZ on one side of weld was subject to shock treatment using ultrasonic impact machine with different technological parameters, then residual stresses on both sides were measured and compared. Removal rate was used to evaluate elimination effect. Difference between residual stresses on both sides of weld fell within 7.5% of maximum principal stress. Surface tensile stress of HAZ could be transformed into compressive stress by UIT, removal rate was 88%~130%. When impact time was unvarying, as removal rate of impact current increased, but the trend became slower. When impact current was unvarying, impact time had slight effects on removal rate. The stresses in HAZ symmetrical position on both sides of weld can be deemed to be equal. Impact current increase can bring about UIT impact increase, leading to further plastic deformation and dislocation motion on HAZ surface, and further improve removal rate of residual stress. Work hardening slowed down the increase trend of removal rate. UIT impact is unvarying when current is unvarying, increasing impact time don''t affect removal rate significantly.