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F82H鋼$$cdot$$HIP接合材の衝撃特性

Impact properties of reduced activation ferritic/martensitic steel, F82H joined by hot isostatic pressing

荻原 寛之; 谷川 博康; 廣瀬 貴規; 榎枝 幹男; 香山 晃*

Ogiwara, Hiroyuki; Tanigawa, Hiroyasu; Hirose, Takanori; Enoeda, Mikio; Koyama, Akira*

核融合炉第一壁作製における課題は、衝撃特性向上を克服したうえでのHIP接合条件の最適化である。第一壁作製においては、部材作製にいたるプロセスの簡約化が必要となる。現在までに得られた結果から、HIP後の接合界面への酸化物の形成により、母材と比較して、接合面の衝撃特性が低下することが報告されている。したがって、HIP後の接合界面に存在する酸化物形成を低減させる必要がある。そこで、本研究では、衝撃特性向上を目的とし、HIPプロセスにおける接合面制御性について検討した。衝撃試験の結果から、接合部の室温における衝撃特性は、母材部のものと比較し、50%程度であった。HIP接合面の組織観察の結果から、ボイド等の形成は確認されず、良好な接合面を有することが確認された。延性脆性遷移温度については、明確な違いは見られず、-60$$sim$$-40$$^{circ}$$Cの値を示した。接合部の衝撃試験後の破面観察を行った結果、破壊の起点と考えられる成長した酸化物の存在は確認されなかった。衝撃特性低下に起因する酸化物の抑制は、脱気条件の改善により図ることができたが、さらなる衝撃特性の向上が必要である。

Reduced-activation ferritic/martensitic steels are leading candidate structural material for the blanket system of fusion reactors. The important issue in current stage is the finalization of detailed manufacturing specification for ITER test blanket module. Hot isostatic pressing (HIP) process is one of the most important methods to fabricate the first wall with cooling channels. The objective of this paper is to optimize HIP condition to obtain the excellent joints mechanical properties. The materials used were F82H steels. The joint was produced by solid state HIP method. Before HIP treatments, specimens were heated in vacuum condition to out-gas. This treatment was conducted to decrease oxidation on the surfaces. HIP treatments were carried out for 2 h at 1100 $$^{circ}$$C - 140 MPa. The specimens were normalized at 960 $$^{circ}$$C for 0.5 h and tempered at 750 $$^{circ}$$C for 1.5 h. The bonding interface was characterized by scanning electron microscope. Charpy impact tests and tensile tests were conducted to evaluate the mechanical properties of HIP joint. Impact tests revealed that there were no significant difference in ductile-brittle transition temperatures of HIP jointed specimens and base metal specimens, but upper-shelf energy (USE) of HIP joint specimens at room temperature was about 10 % of that of base metal specimens. SEM observation on the fracture surface of HIP joint specimen revealed that a large number of oxides were formed on the HIP joint. This result indicates that oxides formed on the HIP joint are the dominant factor of the impact properties. Based on the results, the pre-HIP treatment conditions had been optimized to reduce the number of oxides, and USE of HIP joint specimen become about 50 % of base metal. The detailed analyses on HIP joint microstructure will be reported.

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