溶接熱影響部の破壊挙動に及ぼす島状マルテンサイトの影響

80及び100キロ級高張力鋼大入熱溶接HAZ部の靭性劣化とその改善に関する研究(第5報)

抄録

The effects of M-A constituent on initiation and propagation of cracks has been investigated by the observation of fracture morphology and crack around M-A constituent. Energies for the crack initiation and propagation have been estimated by using an instrumented-Charpy impact testing machine. Furthermore, concentration and distribution of tensile plastic-distortion introduced in a soft phase around hard phase have been qualitatively analyzes with FEM in order to explain the effect of the M-A constituent on the crack initiation and propagation. As the result, remarkable decrease in the crack initiation energy and propagation energy were observed, as the area fraction of the massive M A constituent was increased. The FEM analysis have suggested that the greater hard phase decreases the energy for crack initiation in the surrounding soft phase and this can explained the observed decrease in the crack initiation energy by the increase in the area fraction of the massive M-A constituent. It has also been suggested that the decrease in the crack propagation energy is caused by the increase in the interfacial area between the massive M-A constituent and matrix, since the crack was observed to propagate preferentially along the interface between the M-A constituent and matrix.