The fracture properties and susceptibility to crack-divider delamination (or splitting) of three commercially produced high-toughness X70 pipeline steels are evaluated with Charpy impact test samples modified to incorporate side grooves. Temperature-dependent impact data are compared with standard Charpy V-notch (CVN) and drop weight tear test data (DWTT). It is shown that the modified geometry prevents the accumulation of plastic deformation at upper shelf energy temperatures and improves the accuracy of impact properties measurements. It also promotes splitting, mirroring the splitting behavior assessed with DWTT samples. To demonstrate the effects of splitting on fracture characteristics and impact energies, steels with similar tensile properties but different splitting susceptibilities are considered. Splitting severity is maximum close to the ductile-brittle transition temperature. However, the effect of splitting on impact energy is minimum at such temperature, as this type of delamination increases energy absorption at lower temperatures and decreases it by a similar extent at higher temperatures. This finding is discussed by examination of force-displacement curves from the instrumented impact tests.
Keywords: Delamination; Fracture toughness; Impact testing; Pipeline steels; Side grooves.