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ステンレス鋼の亀裂先端における高温水中酸化に及ぼす荷重付与の影響

Influence of applied load on oxidation in the vicinity of crack tips of stainless steel under high temperature water

笠原 茂樹; 知見 康弘; 端 邦樹; 塙 悟史

Kasahara, Shigeki; Chimi, Yasuhiro; Hata, Kuniki; Hanawa, Satoshi

ステンレス鋼のBWR一次系水中環境助長割れ機構検討の一環として、荷重を付与したCT試験片を290$$^{circ}$$Cの高温水に浸漬し、疲労予亀裂先端近傍の酸化物を観察した。酸化物内層は、Fe, Ni, Crを含むスピネル構造の微細粒、外層はFe$$_{3}$$O$$_{4}$$の結晶粒であった。FEM解析によるCT試験片亀裂先端の応力、ひずみ分布との比較より、塑性変形に伴う転位と弾性ひずみの重畳によって酸化物内層の形成が促進されることが示唆された。

In order to study environment assisted cracking mechanism of stainless steel under BWR primary coolant condition, effects of applied load on oxidation in the vicinity of crack tips of CT specimens were evaluated. Loaded CT specimens were immersed in an aqueous condition at 290$$^{circ}$$C as a simulated BWR coolant condition, and microstructural observation on oxide near the tips of pre-cracks was carried out. Oxide inner layers, which consisted of fine grain magnetite containing Fe and Cr were formed, and oxide outer layers consisting of large grains of Fe$$_{3}$$O$$_{4}$$ were observed to cover the inner layers. FEM analysis of stress and strain in the loaded CT specimen suggests that both of dislocations due to localized plastic deformation and elastic strain could play important roles to accelerate inner oxide formation in the vicinity of the crack tip of the specimens.

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