Effect of microdefects on the hydrogen embrittllement crack in welded metal of carbon steel

Kobayashi, Masato*; Takahashi, Rieko*; Asano, Hidekazu*; Taniguchi, Naoki ; Naito, Morimasa 

The susceptibility to hydrogen embrittlement of welded metal of carbon steel was evaluated by slow strain rate test (SSRT) at constant current density. In SEM observation, some circle quasi-cleavage fractures with center at microdefects (blowhole, BH) were observed. Such fractures were initiated only in the case of charging hydrogen by cathodic polarization. The area of the quasi-cleavage increased with the radius of BH. As the area of quasi-cleavage fractures increased, the fracture strain became small.