Abstract
The effect of hydrogen on the crack propagation behavior and the microstmctures around cracks in α-iron has been examined by means of tensile testing with simultaneou scharging of hydrogen and microscopic observation. The results obtained are summarized as follows:
(1) The yield strength and the flow stress at 2% strain increase by absorbing hydmgen, whereas the fracture strain and the total energy spent in the tensile test decrease remarkably.
(2) According to the notch tensile tests, the force for crack initiation does not change so much with the increase in hydrogen content, but the plastic strain induced around crack and the amount of wark required for the propagation of cracks decrease notably with increasing the hydrogen content.
(3) Near the crack edge in notched specimen deformed underuncharged condition, well-defined cell walls which are elongated along the crack edge are observed. As the hydrogen content increases, the distribution of dislocations becomes uniform, the formation of well-developed cell structure is supPressed and the dislocation density slightly increases, indicating the difficulty in relaxation of stress concentration around cracks of α-iron.
(4) It is suggested that the hydrogen embrittlement of α-iron is mainly due to the lowering of deformability in the vicinity of cracks by the absorption of hydrogen and the easy initiation of the grain boundary cracking caused by the segregation and precipitation of absorbed hydrogen.
