抄録
Based on the recent results of material testing in high pressure hydrogen environment, mechanisms of the hydrogen induced cracking are discussed as follows.
(1) The hydrogen induced cracking shows the morphology of multiple-site cracks on the metal surface and grows continuously into the inner of metal. The terminology of hydrogen embrittlement is not correct use in this case.
(2) The origin is the plastic deformation by loading. An active slip band results in localized rupture of the oxide film on the metal surface and creates freshly slip steps. Therefore, there is no effect of hydrogen during the elastic deformation by loading.
(3) The dissociation of hydrogen molecule into atomic hydrogen takes place easily on the freshly created slip step. At the same time, rupture of the oxide film generates the dislocation source and the slip is localized by the dislocation emission.
(4) The dislocation emission operates as a hydrogen intake mechanism and hydrogen operates in parallel the activity of mobile dislocations. Therefor, hydrogen can enter the metal by the plastic deformation and hydrogen entry can activate the plastic deformation.
(5) Two models of hydrogen induced cracking are shown;one is a mechanics model and the other a crystallographic model. Both models constitute a pair of intersecting two slip planes and a crack plane divided by the two slip planes. It is also shown that the difference of body centered cubic metal from face centered cubic metal in the crystallographic model.
