原子炉用HT70鋼大型溶接継手のクリープラプチャに関する研究(第1報)

Abstract

In the foregoing reports, comparison in creep rupture strength between large and small size welded specimens, discussion on the mechanism of creep rupture and the influence of heat treatment after welding were made. In this report, the difference in rupture configuration between large and small size welded specimens, and welding methods viewed from creep rupture configuration are discussed.The large size welded specimens are ruptured at the heataffected zone of base metal (HAZ) near the bond, while the small size welded specimens are ruptured at HAZ near the base metal. The plate thickness of the steel used is 30 mm, and the welded joints are made by multi-layer welding. Therefore, it may be considered that the properties at welded joint of specimens of both sizes are different. It is clear from the foregoing report that creep strength may be proportionate to the absorbed energy to rupture in a high temperature tensile test. Therefore, tensile tests at 450°C on synthetic HAZ specimens, with respect to the coarse grain part near bond and the fine grain part near base metal in HAZ of small size welded specimens, are carried out to measure the absorbed energy. The value of absorbed energy in fine grain part is less than that in coarse grain part. Consequently, it may be considered that small size welded specimens are ruptured at fine grain part of HAZ near base metal, while large size welded specimens are ruptured at coarse grain part of HAZ near bond.The creep rupture configurations of large size specimens are discussed in various ways. As a result, it is believed to be desirable for improving the creep rupture strength of welded joint to make the pentration of the final bead as shallow as possible.