Brittle intergranular fracture at elevated temperatures in low–alloy steel

Abstract

AbstractRecent studies of stress-relief cracking in low-alloy steels have focused attention on a novel mode of brittle intergranular fracture which occurs at elevated temperatures (300–650°C) in hard, coarse–grained heat–affected–zone microstructures. Fracture initiates at stress concentrators such as sharp cracks or inclusions, and can propagate under static loading at rates of 10−11−10−5 ms−1 to produce intergranular facets with very little associated plastic deformation. The stress-intensity parameter K has been used to characterize crack growth, and three regimes of behaviour have been observed: (i) a threshold region at growth rates of 10−11−10−10 m S−1, (ii)a plateau region, in which growth rates are independent of K between 10−10 and 10−8 m S−1, and (iii) a region of highly K-sensitive crack growth between 10−8 and −5 m S−1. Independent Auger electron spectroscopy analyses have demonstrated that sulphur segregates locally to the high-temperature crack tip, giving rise to the embrittlement of a limi...