Fatigue Performance Influenced By Automatic Ultrasonic Impact Treatment On The Welded Joints

Ultrasonic impact treatment is a surface hardening method,but previous research on ultrasonic impact is limited to manual ultrasonic impact treatment.With the social development changes,the tendency of industrial automation becomes more and more obvious.At the same time,the exposure of the problems of the stability and efficiency of the manual ultrasonic impact treatment makes the research of automatic ultrasonic impact treatment more important.Investigation on the automatic ultrasonic impact treatment and explore its mechanism to improve fatigue performance joints is of great significance.For the low-alloy high-strength steel S690 QL butt joint,the manual ultrasonic impact treatment and automatic ultrasonic impact treatment were used to treat the weld toe of the specimen.The fatigue performance of the specimen treated by manual ultrasonic impact treatment and automatic ultrasonic impact treatment,surface hardening effect,weld toe transition radius,impact profile,surface roughness,residual stress and fold defects were studied.Under the test conditions and process parameters,the main conclusions are as follows:For low-alloy high-strength steel S690 QL,according to the national standard GB / T 33163-2016 on the impact of the weld toe area geometry requirements,the selection of automatic ultrasonic impact process parameters selected: diameter of impact needle 4mm,current 2.5A,amplitude 35?m,speed 60 mm / min,coverage 300%,we can get in line with the requirements of the standard impact.Automatic ultrasonic impact method and manual ultrasonic impact methods can significantly improve the fatigue properties of welded joints.Dispersion of the results obtained using the automated ultrasonic impact method on the welded joints was significantly reduced,with the sum of squared residuals being 31% of the manual impact results.Compared with the manual impact,fatigue performance increased by 58% after auto-impact treatment under the same fatigue strength(342MPa).The surface roughness at the bottom of the groove formed by the auto-impact treatment is reduced by about 27%,the depth of the groove is larger and the width is smaller.The depth of the plastic deformation layer is increased by 33% from the surface 0.2mm,and the hardness is higher.The compressive stress increased by 32%.With the increase of compressive stress,the general trend of compressive stress had a similar rule with that of the manual ultrasonic impacting method.Weld toe transition radius is smaller,the transition radius dispersion is significantly reduced,the standard deviation reduced by 50%.The fold defects are mainly induced by the lateral movement of the impact pin,which would fold the flash produced by the previous impacts;Fold defects in welded joints treated by automatic UIT are less than those treated by manual UIT and reduced by 27% owing to better control of lateral movement of impact pin;Fold defects in weld joints treated by manual UIT randomly distributes throughout the weld toe,appearing alone or concentrated,with defect sizes in the range of 50-300 ?m,while fold defects in weld joints treated by automatic UIT mostly concentrates on the edge of the weld toe,usually parallel to the edge,with defect sizes below 100?m but few larger ones.