研究了外加纵向恒定磁场对10 mm厚SUS316L奥氏体不锈钢窄间隙激光-MIG多层焊接接头成形、奥氏体和铁素体微观组织以及疲劳裂纹扩展的影响。结果表明:在磁场作用下,接头上部复合焊接层的熔深减小,熔宽增大,下部复合焊接层的对称性提高,但上、下部焊接层的面积和层间重熔面积无明显变化;磁场的加入导致了不同的熔合线形状,改变了熔合线附近组织的生长方向,改善了熔合线附近母材的热循环,减小了焊接热影响区的宽度并抑制了晶粒的粗化;磁场可以促进层间胞状晶向树枝晶转变,改变铁素体枝晶的形态,细化层间和层内奥氏体组织;焊缝组织细化可以增大层间组织疲劳裂纹扩展的阻力,降低接头的裂纹敏感性。

In this study, we investigate the effects of longitudinal magnetic field on the welded joint formation characteristics, ferrite/austenite microstructures, and fatigue crack propagation in the laser-MIG welding of 316L austenitic stainless steels. The experimental results indicate that the upper hybrid layer exhibits shallower penetration and larger width, whereas the lower hybrid layer exhibits a better symmetry with the addition of the magnetic field. Further, the melting area of the two hybrid layers and the remelted area between the two hybrid layers remain almost constant. The agitation of the solid-liquid front of the molten pool is promoted by the addition of the magnetic field, resulting in different fusion line shape characteristics. Furthermore, the addition of the magnetic field changes the growth direction of the microstrucuture near the fusion line, improves the thermal cycle of the base metal near the fusion line, reduces the width of the heat-affected zone, and restrains the coarsening of the grains. The magnetic field can promote the transition of cellular grains to the dendrites in the interlayer, change the ferrite dendritic morphology, and refine the interlayer and intralayer austenite structures. The fatigue crack growth resistance increases owing to the refinement of the microstructure, reducing the crack sensitivity of the joint.