Abstract
The delayed fracture characteristics of V-bearing steel were evaluated using conventional strain rate test (CSRT) and the hydrogen absorption and desorption behaviors were studied with the specimens hydrogen-charged and then exposed to air of 30°C for up to 2.5 months. CSRT was carried out at two test sites, and nearly the same delayed fracture resistance was obtained for the V-bearing steel. The fracture appearance changed from quasicleavage to intergranular with increasing hydrogen content. The hydrogen content of the boundary between fracture appearances was approximately 4 mass ppm. The hydrogen introduced into the V-bearing steel was composed of a diffusible one which decreased in concentration in 24 h when exposed to air of 30°C, and two types (weakly and strongly) of trapped ones. The strongly trapped hydrogen remained in the specimen after 2.5 months of exposure in air. By analyzing the thermal desorption profiles with Gaussian function, the peak temperatures of these hydrogen types were 100°C, 167°C and 198°C, corresponding to diffusible, weakly and strongly trapped hydrogen, respectively. The hydrogen-charged specimens of more than 4 mass ppm were fractured in the intergranular mode. After exposure in air and the hydrogen content became less than 4 mass ppm, the fracture mode changed to quasicleavage. After recharging the hydrogen to more than 4 mass ppm, the fracture mode became intergranular again.
