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.