Differences of Elastic-Plastic Fracture Toughness and R curve in Carbon Steel Pipes due to Specimen Cut-out Orientations

摘要

Regarding Charpy impact values on rolled plates, many papers discussed the effects of specimen orientation and concluded that the impact value strongly depends on the specimen orientation. Although similar results are assumed on the fracture toughness, this point has not frilly discussed, especially on the specimens cut out of pipes. In this study, to confirm the orientation effects, comparative fracture toughness tests were carried out using two carbon steel pipes. Two types of specimens were subjected to the fracture toughness tests. One is the specimen with the crack orientation parallel to the longitudinal direction of pipe (C-L specimen), and the other is the specimen with its orientation coincident with the circumferential direction (L-C specimen). As a result, L-C specimens showed higher fracture toughness value by more than 18% primarily because of the difference of microstructure.