Relating Cleavage Crack Nucleation to Cracked Carbides in A533B Steel

Abstract

At low temperatures, ferritic steels exhibit a change in fracture behaviour, from ductile fracture with high fracture energies accompanied by a high degree of plasticity, to brittle cleavage fracture whereby fracture occurs at transonic speeds at low fracture energies accompanied by very low degree of plasticity [1, 2]. This change from ductile to brittle cleavage fracture behaviour occurs over a range of temperatures, over which the behaviour is characterised by a competition of ductile microvoid coalescence and brittle cleavage fracture. The ductile to brittle transition temperature is dependant on strain rate, stress triaxiality due to notch acuity, microstructural and compositional factors [1, 2, 3]. The pervasiveness of ferritic steels in structural engineering and the nuclear power industry, means that a thorough understanding of the micromechanism of cleavage fracture is fundamental for the development of accurate models for predicting fracture stresses and lifetimes of components.