On the impact bending test technique for high-strength pipe steels

It is shown that the impact toughness (KCV –40 = 250 J/cm 2 ) accepted for pipe steels of strength class K65 (σ y ≥ 550 MPa) intended for large-diameter gas line pipes is ineffective to classify steels in fracture strength. The results obtained upon testing of specimens with a fatigue crack and additional sharp lateral grooves seem to be more effective. In energy consumption, a macrorelief with splits is found to be intermediate between ductile fracture and crystalline brittle fracture. A split formation mechanism is considered and a scheme is proposed for split formation.