Influence of dislocation density on the fracture behavior of pipeline steel after plastic deformation damage

Abstract

Plastic deformation damage is one of the key factors affecting the safety of pipeline steel in service. In this paper, the fracture behavior of steels after plastic damage is revealed, as well as the mechanism of action between dislocation motion and micro-voids growth is clarified. It shows that the fracture mechanisms of steels are related to the dislocation density after plastic damage. When the dislocation density of steel is low (1.75 $\times$ 10¹¹ ∼ 3.98 $\times$ 10¹³ m⁻²), it provides favorable conditions for the dislocation movement at plastic zone, and promotes intergrowth between neighboring microvoids. As the dislocation density increases to 1.29 $\times$ 10¹⁴ ∼ 2.72 $\times$ 10¹⁴ m⁻², it inhibits growth and coalescence between neighboring voids due to the lack of movable dislocations at plastic zone, which is not conductive to crack blunting by dislocation slip. The crack tip is connected to the micro-voids by cleavage planes, and the main crack will grow along the interface through the micro-voids in a relatively flat path, accelerating the fracture of pipeline steels. This work will contribute to better understand the failure mechanisms of steel materials and provide a new idea for the protection after plastic deformation damage.