In this paper, the in-situ fracture tests were carried out to study the fracture mechanism of different regions (base region, weld region and interface region) in a dissimilar metal welded joint of nuclear power plant. The local microstructural effect on short crack initiation and propagation behavior was investigated. The results indicated that the mechanism of crack initiation and propagation was strongly depended on the microstructures of the difference zone in the dissimilar metal welded joint. There were large numbers of twins in the base region, and the cracks tended to initiate along the twin boundary. The base region exhibited the characteristics of ductile fracture. There was no twin existed in the weld metal. The crack tended to initiate at the slip band and propagate along the columnar grain boundary due to existence of the second phase particles along the grain boundary. The fracture mode of the weld metal was intergranular. In the interface region, the crack tended to propagate from the weld zone to the epitaxial zone, and then along the grain boundary of the epitaxial zone. The fracture mode was the combination of the brittle and ductile fracture. Meanwhile, the weld region has a lower resistance of crack initiation and propagation compared with the base region and interface region.

本文进行了原位断裂试验，研究了核电厂异种金属焊接接头中不同区域（基部区域，焊接区域和界面区域）的断裂机理。研究了局部组织对短裂纹萌生和扩展行为的影响。结果表明，裂纹萌生和扩展的机理在很大程度上取决于异种金属焊接接头不同区域的组织。在基部区域有大量的孪晶，并且裂纹倾向于沿着孪晶边界发生。基部区域表现出韧性断裂的特征。焊缝金属中不存在孪晶。由于第二相粒子沿着晶界的存在，裂纹倾向于在滑移带处萌生并沿着柱状晶界传播。焊缝金属的断裂模式是晶间的。在界面区域中，裂纹倾向于从焊接区扩展到外延区，然后沿着外延区的晶界扩展。断裂模式是脆性断裂和韧性断裂的组合。同时，与基础区域和界面区域相比，焊接区域具有较低的裂纹萌生和扩展阻力。断裂模式是脆性断裂和韧性断裂的组合。同时，与基础区域和界面区域相比，焊接区域具有较低的裂纹萌生和扩展阻力。断裂模式是脆性断裂和韧性断裂的组合。同时，与基础区域和界面区域相比，焊接区域具有较低的裂纹萌生和扩展阻力。