Mechanical tests on the welding part of SS316LN after heat treatment for NbSn superconducting conductor

Kudo, Yusuke; Sakasai, Akira; Hamada, Kazuya; Takano, Katsutoshi*; Nakajima, Hideo; Okuno, Kiyoshi; Matsukawa, Makoto; Tamai, Hiroshi; Ishida, Shinichi

Japan Atomic Energy Research Institute (JAERI) has a plan to construct a tokamak fusion device called JT-60SC in which superconducting magnet system will be used. The objectives of this study are to clarify applicability of conventional austenitic stainless steel wire for the SS316LN to the conduit material of the Nb3Sn cable-in-conduit conductor for the central solenoid (CS) of JT-60SC. Tensile properties, fracture toughness and fatigue crack growth rate of both as-weld and aged (923 K 240 hours) weld metals were evaluated at 4 K. The measured tensile properties of aged weld metal satisfied the requirement of JT-60SC. Fatigue crack growth property was enough to ensure the required operation cycles of 9.0 10e4. However, fracture toughness of aged weld metal could not be validated due to unstable crack extension. It was concluded that improvement of fracture toughness after aging was required to ensure the structural integrity of the CS conduit.