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SCC initiation susceptibility and corrosion behavior of grain boundaries of long-term thermal aged low carbon austenitic stainless steels in simulated BWR condition

BWR模擬環境下における低炭素オーステナイトステンレス鋼長時間熱時効材の応力腐食割れ発生感受性および粒界の腐食挙動

青木 聡  ; 近藤 啓悦  ; 加治 芳行  ; 山本 正弘 

Aoki, So; Kondo, Keietsu; Kaji, Yoshiyuki; Yamamoto, Masahiro

本研究はBWR模擬環境下における低炭素オーステナイトステンレス鋼長時間熱時効材の応力腐食割れ(SCC)発生感受性、及び粒界の腐食挙動を明らかにすることを目的とした。SCC発生感受性を評価するためにCBB試験を実施し、試験後の試験片の表面及び粒界を分析した。316LのSCC発生感受性は冷間加工と熱時効が組み合わさることで明確に上昇した。316Lの粒界は腐食してCr酸化物が形成されており、酸化物は粒界に沿って深さ方向へ浸食していた。これらの結果に基づき、SCC発生感受性、SCCき裂及び腐食粒界の関係について議論する。

The objective of this study was to clarify stress corrosion cracking (SCC) initiation susceptibility and corrosion behavior of grain boundaries of long-term thermal aged low carbon austenitic stainless steels in simulated BWR condition. Crevice Bent Beam (CBB) test was carried out to estimate the SCC initiation susceptibility under BWR simulated water condition. Surface and grain boundaries analysis of specimens was also carried out after the CBB test. The present results of the CBB tests showed that the SCC initiation susceptibility of Type 316L increased clearly by the combination of the cold work and the long-term thermal aging. Grain boundaries of Type 316L specimen which exhibited the SCC initiation susceptibility corroded with formation of Cr oxide, and the oxide formed along depth direction of grain boundaries. Based on these results, the correlation among SCC initiation susceptibility, SCC crack initiation and corroded grain boundaries will be discussed.

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