采用MAG（熔化极活性气体保护焊）对25 mm厚10Ni5CrMoV钢进行了焊接，观察了接头显微组织与冲击断口形貌，并对其硬度、冲击性能和拉伸性能进行了研究。结果表明：接头焊缝区组织主要为板条马氏体/贝氏体+粒状贝氏体，且存在较多的沿奥氏体晶界分布的M-A组元，硬度接近于母材，冲击韧性较低，-50 ℃时的平均冲击功为42 J；随着距焊缝中心距离的增大，热影响区组织依次为淬火马氏体、板条马氏体/贝氏体+铁素体+粒状贝氏体，且临界区碳化物积聚并长大，硬度先升高后降低，最低硬度为286.4 HV，冲击韧性较高，-50 ℃时的平均冲击功为188 J；焊接接头的平均抗拉强度达到920 MPa，拉伸试样的断裂位置均在母材；M-A组元及碳化物是影响接头性能的主要因素。

10Ni5CrMoV steel with thickness of 25 mm was welded by MAG (melting pole active gas shielded welding). The microstructure and impact fracture morphology of joint were observed, and hardness, impact property and tensile property were studied. The results show that the microstructure of joint weld zone was mainly lath martensite/bainite+granular bainite, and there was much M-A component distributed along austenite grain boundary. The hardness of the weld zone closed to that of base metal, and average impact energy at -50℃ was 42 J which represented low impact toughness. With the increase of distance from center of weld, the microstructure of heat affected zone was quench martensite, lath martensite/bainite+ferrite+granular bainite in sequence, and the carbide of critical zone accumulated and grew up. Hardness increased first and then decreased with the minimum hardness of 286.4 HV. The impact toughness was relatively high and the average impact toughness was 188 J at -50℃. The tensile strength of welded joint was 920 MPa and the location of fracture in tensile test was base metal. M-A component and carbide were the main factors that affected the performance of joint.