Cost-Effective Alternatives to Conventional Charpy Tests for Measuring the Impact Toughness of Very-High-Toughness Steels

For modern plate steels exhibiting high toughness and ductility, the conventional Charpy test is ostensibly stretched beyond its limits of applicability. Impact tests yield absorbed energy values in excess of 300 J – 400 J, which are associated with limited material fracture and mostly derive from plastic deformation of the specimen (bending), friction and vibrations of the swinging hammer. It would be therefore very desirable to measure the actual fracture toughness of very-high-toughness steels by means of an alternative specimen and/or methodology, entailing just a moderate increase of cost and test complexity with respect to Charpy testing. The investigation presented here was aimed at establishing a reasonable, yet cost-effective test procedure utilizing Charpy-type specimens for measuring the dynamic toughness of high-toughness steels, such as line pipe steels. Promising results have been obtained from notches cut by Electrical-Discharge Machining (EDM) using a thin wire of 0.1 mm diameter, as compared to specimens where an actual crack was generated and propagated by fatigue at the root of the machined notch.