Cleavage cracking resistance of high angle grain boundaries in Fe–3%Si alloy: experiments and modeling

High angle grain boundaries in steel offer an important resistance to the propagation of cleavage cracks that affects the fracture toughness and can modulate the ductile to brittle transition temperature of fracture downward. This behavior has been studied now in bicrystals of Fe-3%Si alloy in detail. It was noted that the twist misorientation across a high angle boundary has a more profound effect on cleavage fracture resistance than the tilt misorientation. Specific measurements of such resistance at –20oC over a random selection of high angle grain boundaries in bicrystals and associated fractographic studies have led to quantitative models of this resistance. The study has also revealed a transition from pure cleavage to mixed cleavage around 0oC for this alloy above which the observed increment of fracture work could be associated with the sigmoidal plastic bending and rupture of ligaments left between separate primary cleavage strips in the adjoining grain