Statistical aspects of cleavage fracture in steel

Abstract

The fracture of mild steel in the cleavage range has been evaluated using a weakest link statistical model, assuming the preexistence of a distribution of cracked carbides. The model provides a rationale for the critical fracture distance, viz., the distance from the crack tip at which the probability of cleavage cracking exhibits a maximum. The critical distance depends on the size distribution and volume fraction of carbides. The model also predicts trends in K,ic with material properties: flow strength, cracked carbide size and volume fraction, and grain size. The resultant temperature dependence of K,ic is shown to derive exclusively from the temperature dependence of the flow stress, as in prior models. The effects of microstructure on K,ic depend primarily on the size distribution of cracked carbides, with additional influences of the grain size and of the volume fraction of carbides.