The delayed fracture characteristics of V-bearing steel were evaluated using the CSRT method, and the hydrogen trapping and de-trapping behavior was studied with the specimens hydrogen-charged and then held in air for up to 2.5 months.
The CSRT tests were carried out at two test sites and nearly the same delayed fracture characteristics were obtained using the V-bearing steel. The fracture appearance changed from quasi-cleavage to inter-granular fracture with an increase of hydrogen content. The boundary hydrogen content of the fracture appearance change is around 4 mass ppm.
The hydrogen charged in V-bearing steel was composed of diffusible one, which comes out in 24 h when held in air of 30°C and two kinds of (weakly and strongly) trapped ones. The strongly trapped hydrogen remained in specimen after 2.5 months held in air. By analyzing the thermal desorption profiles with Gaussian function, the peak temperatures of these hydrogen were 100°C, 167°C and 198°C, which corresponds to diffusible, weakly and strongly trapped hydrogen.
The specimens hydrogen-charged more than 4 mass ppm were fractured in inter-granular mode. After held in air and the hydrogen content became less than 4 mass ppm the fracture mode changed to quasi-cleavage. Re-charging the hydrogen more than 4 mass ppm, the fracture mode became inter-granular again.
