On the Relationship of Toughness, Fracture Initiation Energy, and Specimen Deflection in Charpy Tests of 4340 Steel

Abstract The toughness of quenched 4340 steel (American Iron and Steel Institute designation) has been studied as a function of notch root radius and tempering temperature for several testing conditions (such as room temperature slow-bend Charpy, room temperature instrumented Charpy). The toughness, the square root of the fracture initiation energy, and the specimen deflection at fracture initiation follow similar trends under identical conditions in each type of testing. Thus fracture initiation energy and the specimen deflection in Charpy testing can be measures of toughness. These three macroscopic relationships are independent of fracture morphology, grain size, or plastic zone size. Theoretical relationships among the three are proposed.