采用不同的激光功率和离焦量对低合金高强钢HC420LA进行光纤激光焊接, 研究了功率和离焦量对接头形貌、显微组织、硬度分布和拉伸性能的影响。结果表明, HC420LA钢板进行光纤激光焊接, 可获得无气孔和裂纹的焊接接头。当激光焊接功率为1 000 W时焊缝外观成形良好, 随着激光功率的增加, 熔宽增大, 下表面略有弧坑; 采用负离焦焊接对焊缝截面形状影响显著, 随着负离焦量的增加, 上下熔宽比增大; 激光焊接HC420LA钢焊缝区主要由马氏体、铁素体和贝氏体组织组成; 焊接接头未出现软化现象, 焊缝的硬度值均高于热影响区和母材; 随着激光功率的增加, 焊缝区硬度值逐渐降低; 在较大的负离焦量下的焊缝硬度略高于正离焦量。焊接接头的拉伸强度在垂直于焊缝方向上高于母材; 焊缝区的强塑积随着功率的增加略有增大, 离焦量的变化对强塑积的影响显著, 但无明显规律。

Fiber laser welding of low alloy high strength steel HC420LA was carried out with different laser power and defocusing distance. The effects of power and defocusing distance on the morphology, microstructure, hardness distribution and tensile properties of the joints were studied. The results show that the welded joints without porosity and crack can be obtained by fiber laser welding of the steel plate of HC420LA. When the laser welding power is 1 000 W, the weld formation is better. With the increase of laser power, the weld width increases, and the lower surface has a slight arc pit. The negative defocusingdistance has a significant effect on the weld section shape, and the ratio of upper and lower melting width increases with the increase of negative defocusingdistance.The main microstructure in the weld zone of laser welded HC420LA steel consists of martensite, ferrite and bainite. There is no softening zone in welded joint, and the hardness of weld is higher than that of heat affected zone and base metal. With the increase of power, the hardness of weld decreases gradually. The hardness of weld with larger negative defocusing distance is slightly higher than that with positive defocusing distance. In the direction perpendicular to the weld, the tensile strength of the welded joint is higher than that of the base metal. The strength-ductility balance of the weld increases slightly with the increase of power, and the change of the defocusing distance has a great influence on the strength-ductility balance, but there is no obvious rule.