Doel 3 & Tihange 2 - Some Peer-reviewed Scientific Papers & Reports

J. Koutskp, K. ~plichal

20

R [MPo]

Cr -Ni -Mo -V

1000

~ o - -

500

• 0 A.~ 2 A 10 AI~ z o100 Arn2 • 300 Arn2 ~- 3000 Arn2

I

I

I

103

104

105

106

Fig. 7. t is] Effect of applied stress intensity on time to failure of unirradiated CrNiMoV steel. For the CrMoV and CrNiMoV steels Rit equals 210 MPa and 410 MPa, respectively. A fractographic investigation proved that the controlling mechanism of fracture was intercrystalline separation, the relative area of which on the fracture face was inversely proportional to the initial stress, as found by Axamit e t al . 3 Hydrogen trapping is affected by the presence and activity of structural defects. Up to 2.0 ppm hydrogen, the hydrogen distribution on the cross- section can be assumed to be uniform. Further increase of hydrogen content is observed mostly on traps, i.e. the initial austenitic grain boundaries, inclusions, and interphase boundaries. At tainment of local critical hydrogen concentration can then lead to crack formation even in non-deformed specimens (Fig. 9). For example, electrolytic charging of unirradiated samples at current densities over 300-500 A m -2 and for periods longer than 1h causes irreversible changes resulting in internal cracks, oriented along the grain boundaries and along the interphase of non-metallic inclusion and matrix. The r61e of the grain structure is particularly important after hydrogen charging of specimens irradiated at lower temperature and in delayed Interaction of hydrogen with steel structure