超声冲击对P355NL1钢焊接接头超高周疲劳性能影响

 通过超声疲劳试验探究超声冲击对P355NL1钢焊接接头超高周疲劳性能的影响。结果表明，由疲劳S-N]曲线可知，在105～109寿命区间内，冲击态试样的疲劳性能要高于焊态试样，在1.0×108的疲劳寿命下，焊态试样的疲劳强度为139 MPa，冲击态的疲劳强度为217 MPa，冲击态疲劳强度相较于焊态提高了56%，这表明超声冲击可以明显提高焊接接头的疲劳强度。利用扫描电镜（SEM）观察断口形貌可以发现，裂纹源位于焊接接头焊根区表面。P355NL1钢焊接接头疲劳断裂为准解理断裂，超声冲击可以提高焊接接头的疲劳强度，但不会改变其疲劳失效机理。超声冲击可以降低焊根处应力集中，引入有益压应力和表面晶粒细化，从而提高焊接接头的疲劳强度。

Effects of ultrasonic impact treatment on very high cycle fatigue properties of P355NL1 steel welded joint

The effect of ultrasonic impact treatment （UIT） on very high cycle fatigue properties of P355NL1 steel welded joint was investigated through ultrasonic fatigue test and UIT test. The results show that theS-N]curve of the fatigue life，in the 105-109 cycles range，the fatigue properties of impact specimens are higher than that of the as-welded specimens. Under the fatigue life of 1.0×108 cycles，the fatigue strength of as-welded specimen is 139 MPa，the fatigue strength of treated specimen is 217 MPa，the fatigue strength of the treated specimen is improved by 156% compared with the as-welded specimen. This shows that UIT can significantly improve the fatigue strength of welded joint. The fracture surface was observed using scanning electron microscope （SEM），it can be found that the crack is initiated in the welded root surface of specimen. The fatigue fracture of P355NL1 steel welded joint is quasi cleavage fracture. The UIT can improve the fatigue strength of welded joint，but it will not change the fatigue failure mechanism. UIT can reduce the stress concentration at the weld root，and bring in the beneficial compressive stress and the surface grain refinement，so as to improve the fatigue strength of the welded joint.