Influence of Inclusion Morphology on Impact Fracture Behavior in High-Strength Pipeline Steel

Based on the two-dimensional finite element simulation with commercial MSC software, the fracture observation with scanning electron microscope and theoretical analysis, the stress and strain status of X80 pipeline steel during the impact process and the micro-mechanism of inclusion morphology and size on the formation of voids were investigated. The results show that the square inclusions are more sensitive to plastic strain energy density (PSED) than the circular inclusions with the increase in inclusion size. The maximum equivalent strain and the minimum stress triaxial factor ( R σ ) of the circular inclusions appear at the interface of 45° and 135° while that of the square inclusions appear at the sharp interface. And the circular inclusions have much lower strain concentration and damage value than the square inclusions, which make them difficult in separating from the matrix materials. The first generation of voids is mainly formed at the interface of the maximum PSED and the minimum R σ , while the second generation of voids is formed at a certain distance from the interface with the second large PSED. Small-sized inclusions tend to produce the larger size of dimples and absorb more impact energy compared with large sized inclusions.