改良9Cr-1Mo鋼溶接継手のクリープ強度に及ぼす補修溶接の位置及び回数の影響

Effect of repair welding location and number of welds performed on creep strength of Mod. 9Cr-1Mo steel welded joints

山下 勇人 ; 豊田 晃大 ; 鬼澤 高志  ; 山本 賢二*; 久保 幸士*

Yamashita, Hayato; Toyota, Kodai; Onizawa, Takashi; Yamamoto, Kenji*; Kubo, Koji*

本研究では改良9Cr-1Mo鋼の溶接継手及び補修位置と補修回数を変えた補修溶接継手を製作し、それらのクリープ強度を調査した。そして、補修溶接継手がクリープ強度に及ぼす影響を金属組織観察等により考察し、補修溶接法を開発した。

It is planned that Mod.9Cr-1Mo steel will be used as the structural material for the steam generator of the demonstration fast reactor. Creep strength of welded joints of Mod.9Cr-1Mo steel is lower than that of base metal at high temperature and long time. In addition, the creep strength of welded joints of Mod.9Cr-1Mo steel with repair welding is lower than that of without repair welding. In this study, the effects of the location and number of repair welds performed on the creep strength of welded joints of Mod.9Cr-1Mo steel were investigated, and a repair welding method was developed for the construction of the demonstration fast reactor. It was clarified that, regardless of the location and number of repair welds performed, the degradation in creep strength could be greatly reduced by performing the repair welding before post weld heat treatment (PWHT). Furthermore, it was found that the superposition of thermal history and the formation of a heat affected zone (HAZ) on the weld metal promote the coarsening of ferrite grains during creep and cause a slight reduction in creep strength. All repair welding was performed prior to PWHT, and a repair welding method was also developed to minimize thermal history superposition and weld metal HAZ formation.