High nitrogen steel welded joints are prone to problems such as porosity defects and coarse grain size. To address these issues, ultrasonic-assisted laser-arc hybrid welding experiments were conducted on 8 mm-thick high nitrogen steel plates. The effect of ultrasonic vibration on the porosity defects, microstructure, and properties of welded joints was studied. The results indicate that with the increase of ultrasonic power, the pore ratio of the weld first decreases and then increases. The effects generated due to ultrasound such as cavitation and sound flow caused grain refinement while weakening the directionality of grain growth. The refined microstructure of the weld increased the microhardness. However, when the ultrasonic power was 240 W, the microhardness of the welded joint decreased due to the low nitrogen content. As the ultrasonic power was increased, the tensile strength and impact toughness initially exhibited an enhancement followed by a declining trend. The best mechanical properties were obtained when the ultrasonic power was 180 W. In contrast, the worst performance was obtained when the ultrasonic power was 240 W, which was due to higher porosity and severe nitrogen loss. Ultrasonic impact can reduce welding residual stress and improve the corrosion resistance of welds, and the effect becomes more pronounced with the increase of ultrasound power.

中文翻译：

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超声波振动对高氮钢激光电弧复合焊接头气孔及性能的影响

高氮钢焊接接头容易出现气孔缺陷、晶粒粗大等问题。为了解决这些问题，在8毫米厚的高氮钢板上进行了超声波辅助激光电弧复合焊接实验。研究了超声波振动对焊接接头气孔缺陷、显微组织和性能的影响。结果表明，随着超声功率的增大，焊缝气孔率先减小后增大。超声波产生的空化和声流等效应导致晶粒细化，同时削弱了晶粒生长的方向性。焊缝显微组织的细化提高了显微硬度。然而，当超声功率为240 W时，由于氮含量较低，焊接接头的显微硬度下降。随着超声功率的增加，拉伸强度和冲击韧性呈现先增强后下降的趋势。当超声波功率为180 W时，获得了最好的机械性能。相反，当超声波功率为240 W时，获得了最差的性能，这是由于较高的孔隙率和严重的氮损失。超声波冲击可以降低焊接残余应力，提高焊缝的耐腐蚀性能，且随着超声波功率的增大，效果更加明显。