Mechanical properties of TIG and EB weld joints of F82H

TIGおよび電子ビーム溶接したF82H溶接継手の強度特性

廣瀬 貴規; 酒瀬川 英雄   ; 中島 基樹; 谷川 博康

Hirose, Takanori; Sakasegawa, Hideo; Nakajima, Motoki; Tanigawa, Hiroyasu

ITER計画・幅広いアプローチ活動における核融合炉原型炉ブランケット用の構造材料研究開発の一環として、TIGおよび電子ビーム溶接により製作した低放射化フェライト鋼F82Hの溶接継手を対象とした強度特性評価を実施した。TIG溶接の溶加材には共金を用いた。溶接後熱処理条件としてASME基準に規定されるGrade91鋼(P-No.15Em Group No.1)の条件を適用した。TIGより低入熱の電子ビーム溶接継手では狭小な溶接部を得た。溶接部における硬さ試験の結果、最弱部は両継手とも過時効を受けた熱影響部(180Hv)だったが、最高の高度はTIGでは変態点を超えた熱影響部(280Hv)、電子ビームでは溶接金属(260Hv)となり、硬度の分布に違いが認められた。更に、ブランケット筐体構造の溶接方法検討の一環として、電子ビーム溶接により二重溶接部を作製し硬さの評価を行った結果、二重溶接による軟化は溶接金属部(260Hv)において顕著であったが、熱影響部における軟化は極めて軽微であることを得た。

As a R&D activity on materials engineering for DEMO blanket in ITER-BA activity, characterization of F82H weld joints prepared with Tungsten-Inert-Gas (TIG) and electron beam (EB) have been investigated. In this work, 50 mm thick plates of F82H were welded using both processes. A similar-metal was employed as a filler for TIG welding. Post-weld-heat-treatment was conducted according to the conditions for Grade 91 defined as ASME P-No.15E, Group No.1. Although the maximum and the minimum hardness of the both joint are similar, the hardness distribution is quite different. The width of EB welds were smaller than that of TIG, and the hardness of EB weld metal was 10% higher than that of TIG. In the TIG welds, the strongest part was heat affected zone (HAZ) heated above phase transformation temperature, Ac1 and the hardness was very similar to the weld metal of EB joint, 280Hv. The hardness of TIG weld metal was around 260 Hv. Both welds demonstrated the smallest hardness, 180 Hv in the HAZ heated below Ac1 temperature. As a investigation of manufacturing process of box fabrication, second EB weld bead was perpendicularly put on the first EB bead. As a result, the second weld did not weaken the HAZ, but reduced the hardness of the weld metal to 260 Hv.