抄録
P91 steel is a new heat-resistant material developed for the next-generation power plant and shows the good performance in mechanical properties under elevated temperatures. However, it is well known that the so-called type- IV creep damage/crack occurs in a Heat Affected Zone (HAZ) of the P91 weld joint, and that it reduces the rupture life of structural components remarkably. The HAZ area becomes to be a multi-axial stress state due to the restriction by the base and the weld metals. Although it is supposed that the multi-axial stress state has a close relation to the nucleation of creep voids, experimental studies on the creep damage under the multi-axial stress state have not been conducted enough so far. This is because these tests usually have some difficulties due to intricate and large-scale equipments. Circumferentially notched bar specimens can make various multi-axis stress states inside the notch root. In this study, creep damage tests were carried out over a long period of time employing the notched specimen of P91 steel. Subsequently, the development and distributions of creep voids inside the notch root were examined interrupting creep tests three times. Furthermore, coefficient of the multi-axial stress state in the notch root was calculated using an FEM and compared with the distribution of creep void ratio per unit area. It was shown that there was a good relation between the multi-axis stress state and the distribution of creep voids.
