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Hamada, Kazuya; Nakajima, Hideo; Kawano, Katsumi; Takano, Katsutoshi; Tsutsumi, Fumiaki; Okuno, Kiyoshi; Fujitsuna, Nobuyuki*; Teshima, Osamu*
Teion Kogaku, 43(6), p.244 - 251, 2008/06
Japan Atomic Energy Agency has developed JK2LB conduit for the Nb
Sn conductor of the ITER Central Solenoid. Mechanical requirements for the CS conductor conduit are 0.2% yield strength of more than 900 MPa and fracture toughness K 
(J) of more than 130 MPa
after a compaction and aging heat treatment (650 
C, 240 hours). In the previous work, aged JK2LB conduit has shown high strength and fracture toughness enough to satisfy the requirements. As a next step, work was performed to determine specification of the JK2LB conduit taking account of cold work including compaction and winding, and to simplify its fabrication process. To simulate the cold work effect and aging, mechanical tests were performed at 4.2 K on laboratory scale (20-30kg) ingot samples. It was found that the sum of carbon and nitrogen content should be in a range from 0.11% to 0.18% to achieve the ITER mechanical requirements. To obtain a grain size of conduit as well as that of small ingot sample, applicable solution heat treatment temperature and holding time were studied. In order to simplify the billet production process, we confirmed internal metallurgical qualities of JK2LB cast ingot. Since significant segregation was not observed, we could exclude an electroslag remelting process. Based on above achievements, full size JK2LB conduits were fabricated and satisfied the ITER mechanical requirements.
Hamada, Kazuya; Nakajima, Hideo; Kawano, Katsumi; Takano, Katsutoshi; Tsutsumi, Fumiaki; Okuno, Kiyoshi; Suzuki, Tomio; Fujitsuna, Nobuyuki*
Cryogenics, 47(3), p.174 - 182, 2007/03
Times Cited Count：33 Percentile：73.75(Thermodynamics)no abstracts in English
Hamada, Kazuya; Nakajima, Hideo; Kawano, Katsumi; Takano, Katsutoshi*; Tsutsumi, Fumiaki*; Seki, Shuichi*; Okuno, Kiyoshi; Fujitsuna, Nobuyuki*; Mizoguchi, Mitsuru*
IEEE Transactions on Applied Superconductivity, 16(2), p.787 - 790, 2006/06
Times Cited Count：6 Percentile：37.01(Engineering, Electrical & Electronic)no abstracts in English
Hamada, Kazuya; Nakajima, Hideo; Kawano, Katsumi; Takano, Katsutoshi; Tsutsumi, Fumiaki; Okuno, Kiyoshi; Suzuki, Tomio; Fujitsuna, Nobuyuki*
Teion Kogaku, 41(3), p.131 - 138, 2006/03
no abstracts in English
Sn heat treatmentNakajima, Hideo; Hamada, Kazuya; Takano, Katsutoshi*; Okuno, Kiyoshi; Fujitsuna, Nobuyuki*
IEEE Transactions on Applied Superconductivity, 14(2), p.1145 - 1148, 2004/06
Times Cited Count：35 Percentile：78.42(Engineering, Electrical & Electronic)In ITER, the conductor for the Central Solenoid (CS) uses Incoloy 908, which requires special environment control to prevent cracks caused by Stress Accelerated Grain Boundary Oxidation (SAGBO) during Nb3Sn heat treatment. Use of a stainless steel jacket can simplify the design and fabrication because the special caution is not required for SAGBO. JAERI has already developed high manganese, JK2, whose thermal contraction from 300K to 4 K is almost the same as that of Incoloy: thus no change in the mechanical design of the CS is necessary. However, during the heat treatment, phosphorus enhances embrittlement of JK2. Carbon reduction and boron addition was considered to be a possible solution to mitigate the phosphorus effect. Jackets of low carbon and boron added JK2(JK2LB) were produced and tensile properties, fracture toughness, and crack propagation rate were measured at 4K. Elongation and fracture toughness at 4K after the heat treatment are 33% and 91 MPam
for the final jacket, which satisfy the ITER targets. JK2LB can be applied to the ITER CS.
