Effect of hydrogen on Cr-Mo-V steel fracture under constant load

Decelerated fracture was studied using a round notched test bar made of rolled and heat treated Cr-Mo-V steel in non-irradiated state. Hydrogen charging was performed in galvanostatic connection in 1N H2SO4 with the addition of 30 mg/l As2O3. Current densities i=0, 10, 30, 100, 300 and 3000 A/m2 were used. The measured time to fracture for the various current densities in dependence on initial stress are presented graphically. The test was terminated in case fracture of the test bar did not occur in 105s. It was found that a minimum threshold value of stress exists under which no fracture occurs. For Cr-Mo-V steel this is 210 MPa. The content of hydrogen increased from 3.7 for i=10 A/m2 to 5.7 ppm for i=300 A/m2. It was found fractographically that intercrystalline separation is the control mechanism of fracture. (E.S.)