Effect of precipitates on the cryogenic fracture toughness of 9%Ni steel flux cored arc weld

The microstructure and fracture toughness of 9%Ni steel flux cored arc welds with different heat input were investigated. CTOD results showed that the fracture toughness of the weld decreased with the increasing amount of precipitates at room temperature and at cryogenic temperature. Micro-regional force and deformation (MRFD) of the weld was investigated by finite element analysis. Precipitates have a significant impact on MRFD. In the stretching process, high stress concentration and local plastic deformation occurred around precipitates, which decreased crack propagation resistance in interdendritic region. The increment of precipitate amount enhanced the stress concentration and local plastic deformation. The effect of rod-shaped Laves phase on MRFD is much higher than globular-shaped carbide. For Laves phase, the maximum local plastic strain and peak stress has close relationship with its aspect ratio and its angle between long-axis direction and load-direction. The size of carbide has little influence on MRFD. Due to the high local plastic deformation and peak stress, microcracks formed at interdendritic region near precipitates during stretching at cryogenic temperature.