| Low alloy high strength steel has high strength, high toughness, excellent low temperature performance and good comprehensive performance. It is widely used in national defense and civil area. Laser-MAG hybrid multi-pass welding has high stability, deep penetration, low heat input and good gap bridging ability. It can visibly reduce problems such as large heat input, large deformation and weld defect which are occurred in conventional welding method on medium and thick plate.In this paper, the influence of microstructure on the mechanical properties was studied during Laser-MAG hybrid multi-pass welding of low alloy high strength steel (11CrNi3MnMoV) of 16 mm in thickness. Furthermore, the relation between the fracture behavior and rupture characteristics was also investigated.Y-groove was used in the Laser-MAG hybrid multi-pass welding and good welded seam was obtained by optimum parameter of welding process. macrostructure of the welded joint was studied by light microscope. Microstructure of the welded joint was investigated by SEM and TEM. Furthermore, the sub structure of bainite and martensite in the ferrite of weld seam was also studied.The results indicated that the hardness of weld zone and heat affected zone varies between 285HV and 325HV, which are higher than that of base metal. Fracture occurred in the base metal during the tensile test. The fracture behavior of the welded joint was effected slightly by residual stress , while microstructure was a key factor affecting the fracture behavior of the welded joint. Weld defect was not occurred on the weld appearance during front, root and side bend tests. The impact energy of the welded joint was lower than that of the base metal during series impact test and the temperature of ductile-to-brittle was at about 40℃.The fracture in tensile test was typical ductile rupture and the fracture in impact test were ductile and quasi-cleavage rupture. the relation between the fracture behavior and mechanical properties was investigated. |
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