Probability of brittle fracture in low alloy steels

This paper presents a method for quantifying probability of brittle fracture in low alloy steels. The proposed method shows how the probability of brittle fracture varies with stress intensity factor, temperature, deformation characteristics and microstructural parameters of low-alloyed steel. Application of this method on Ni-Cr steel demonstrated very good agreement of predicted temperature dependence of scatter in brittle fracture toughness values with experimental results. The method enables also to calculate characteristic distance as a radial dimension from the crack tip where microcrack initiation is the most probable. The characteristic distance of investigated Ni-Cr steel was found to decrease with increasing temperature. Microstructural mechanisms of initiation and propagation of brittle fracture were identified from results of fractography analysis. The proposed procedure represents a foundation for systematic control of relationship between stress-strain behaviours, toughness and reliability of steel engineering parts.