PSI - Issue 68

Akihiko Fukunaga et al. / Procedia Structural Integrity 68 (2025) 1059–1065 Akihiko Fukunaga / Structural Integrity Procedia 00 (2025) 000–000

1064

6

directly weakened the bonding strength within the grains and caused the transgranular fracture. Then, we investigated the difference in KAM distributions between the hydrogen uncharged and the charged specimens. In the hydrogen uncharged specimen, the average misorientation of crystalline in core, 1.46 ° was larger than that in outer layer 1.19 °. This difference seems to be due to the larger deformation occurred in the core at general ductile fracture. On the other hand, after hydrogen charging, the average misorientation in the core decreased to 1.18 ° from 1.46 ° and was rather less than that in the outer layer of 1.23 °. This indicate that the intrinsic deformation ability of the core was reduced by hydrogen charge. 3.3. Hydrogen embrittlement behavior

Fig. 4. Side surface morphology near fracture surface for (a) A286 in 70 MPa gaseous hydrogen, and (b) 56 ppm hydrogen charged A286.

Side surface morphology of specimen in 70 MPa gaseous hydrogen and 56 ppm hydrogen charged specimen of A286 near fracture surface was observed by SEM as shown in Fig. 4. For the specimens in 70 MPa gaseous hydrogen, cracks inclined at 45° could be easily found. On the other hand, no cracks were observed for 56 ppm hydrogen charged specimen and only micro voids were found.

Fig.5. Hydrogen embrittlement behavior (a) A286 in 70 MPa, and (b) 56 ppm hydrogen charged A286.

Through these investigations, the hydrogen embrittlement behavior of each specimen is considered to be as follows. Under high pressure gaseous hydrogen, hydrogen migration is accelerated along the surface cracks, which enhances local plasticity (HELP or HESIV mechanism) and promotes QC fracture (Fig. 5 (a)). On the other hand, hydrogen