核融合炉超伝導マグネット構造材JN1鋼の極低温破壊靱性に及ぼす加熱時効の影響

概要

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Elastic-plastic fracture toughness tests were conducted at 77K and 4K to examine an influence of thermal aging on fracture properties of an austenitic stainless steel JN 1 at cryogenic temperature, which is a candidate material for superconducting magnet structures of fusion reactors. The tests were applied to solution-treated material and materials aged at 923〜1073K for 5h. The experimental results showed that the fracture toughness J_<IC> measured on the thermally aged materials were smaller than that on the solution-treated material and decreased with increasing aging temperature. This decrease in fracture toughness due to thermal aging was caused by precipitation and coarsening of grain boundary M_<23>C_6 carbides. Additionally, small punch (SP) tests were conducted at cryogenic temperatures to investigate the relationship between the obtained J_<IC> and SP properties. It was found that the equivalent fracture strain ε_<qf> in SP specimens was linearly correlated with J_<IC>, irrespective of testing temperature. This correlation suggests that the SP testing technique provides a useful tool for evaluating J_<IC> at cryogenic temperature.
社団法人日本機械学会の論文
2004-02-25