Effect of specimen shape on the elongation of 316LN jacket used in the ITER toroidal field coil

Hamada, Kazuya; Kawano, Katsumi; Saito, Toru; Iguchi, Masahide; Nakajima, Hideo; Teshima, Osamu*; Matsuda, Hidemitsu*

The TF coil conductor was composed of 900 NbSn superconducting strands and 522 Cu strands protected by circular sheath tube (jacket) with the outer diameter of 43.7 mm. The jacket section is a seamless tube made of modified 316LN. JAEA tested different types of tensile specimen (Japanese Industrial Standards (JIS) type and ASTM type) cut from jacket. ASTM type specimen has longer and wider reduced section than those of JIS type specimen. Elongation of as received condition is not dependent on specimen shape. But after cold work and aging, the elongation is deteriorated due to a sensitization and scattering of elongation is larger than that of as received condition. Fracture mode of aged jacket is "cup and cone fracture", which have a mixture of inter granular at center area and trans-granular factures in circumference area. It is considered that initiation of fracture is more sensitive on test specimen shape with low ductility.