在对16 mm厚11CrNi3MnMoV低合金高强钢采用激光-熔化极活性气体保护焊（MAG）复合多层焊技术实现可靠连接的基础上，对焊缝和母材的硬度、拉伸、冲击性能进行分析，并从断口特征方面对其断裂原因和机制进行研究。结果表明，焊缝抗拉强度达到817 MPa，比母材高13%，其断口韧窝相对细小均匀，而母材断口的粗大韧窝明显多于焊缝，表明焊缝强度高，母材韧性好。冲击试验中随着温度降低，母材冲击功保持稳定，而焊接接头冲击功逐渐减小，-40 ℃左右发生延脆性转变。焊缝断口主要存在韧性断裂区和脆性断裂区，而母材只存在韧性断裂区。

A low alloy high strength steel (11CrNi3MnMoV) of 16 mm in thickness is well joined by laser-metal active gas (MAG) hybrid welding and the hardness, tensile and impact properties of weld seam and base metal are analyzed, respectively. Furthermore, the fracture mechanism is investigated through fractography. The results of the tensile test indicate that the strength of weld seam is about 817 MPa, which is 13% higher than that of base metal. The dimples in the fracture of weld seam are fine and uniform, whereas that of base metal are large, which shows that the tensile strength of weld seam is much higher, while the tenacity of base metal is much better. The results of the impact test indicate that the impact energy of base metal changed slightly, while that of weld seam decreases gradually as the testing temperature reduced. In addition, the tenacity-fragility transformation occurres in weld seam as the testing temperature decreases to -40 ℃. The fracture of weld seam exists both ductile and brittle rupture zone, while that of base metal only exists ductile rupture zone.