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酸化物分散強化型(ODS)鋼被覆管の高温酸化試験

High temperature oxidation test of oxide dispersion strengthened (ODS) steel claddings

成田 健; 鵜飼 重治; 皆藤 威二; 大塚 智史; 松田 恭司*

Narita, Takeshi; Ukai, Shigeharu; Kaito, Takeji; Otsuka, Satoshi; Matsuda, Yasushi*

酸化物分散強化型(ODS)フェライト鋼被覆管の実用化見通しを評価する一環で、耐高温酸化性を評価した。一般に耐水高温酸化性の改善にはCrの添加が有効であるが、Cr添加量が多くなり過ぎると$$alpha$$'相が析出して脆化が促進される。このため、日本原子力研究開発機構(JAEA)で開発した9Crマルテンサイト系及び12Crフェライト系ODS鋼被覆管の高温酸化試験を行い、従来材のオーステナイト及びフェライト-マルテンサイト鋼と比較した。得られた結果は以下の通りである。(1)9Cr, 12CrODS鋼は、同Cr量(11mass%)のPNC-FMS及び高Cr量(17mass%)のSUS430と比較して耐高温酸化性が大幅に優れ、オーステナイト鋼であるPNC316と同等であった。(2)ODS鋼の良好な耐高温酸化性は、保護機能の強いCr$$_{2}$$O$$_{3}$$層が母材/スケール界面に形成したことに起因する。これは、ODS鋼の結晶粒は微細であるため、Crの粒界拡散が促進され、Cr$$_{2}$$O$$_{3}$$層が形成された可能性が考えられる。またODS鋼中に分散するY酸化物が、母材/Cr$$_{2}$$O$$_{3}$$の密着性改善に寄与している可能性が考えられる。

In a feasibility study of ODS steel cladding, its high temperature oxidation resistance was evaluated. Although addition of Cr is effective for preventing high temperature oxidation, excessively higher amount of Cr leads to embrittlement due to the Cr-rich $$alpha$$' precipitate formation. In the ODS steel developed by the Japan Atomic Energy Agency (JAEA), the Cr content is controlled in 9Cr-ODS martensite and 12Cr-ODS ferrite. In this study, high temperature oxidation test was conducted for ODS steels, and their results were compared with that of conventional austenitic stainless steel and ferritic-martensitic stainless steel. Following results were obtained in this study. (1)9Cr-ODS martensitic and 12Cr-ODS ferritic steel have superior high temperature oxidation resistance compared to 11mass%Cr PNC-FMS and even 17mass% SUS430 and equivalent to austenitic PNC316. (2)The superior oxidation resistance of ODS steel was attributed to earlier formation of the protective alpha-Cr$$_{2}$$O$$_{3}$$ layer at the matrix and inner oxide scale interface. The grain size of ODS steel is finer than that of PNC-FMS, so the superior oxidation resistance of ODS steel can be attributed to the enhanced Cr-supplying rate throughout the accelerated grain boundary diffusion. Finely dispersed Y2O3 oxide particles in the ODS steel matrix may also stabilized the adherence between the protective alpha-Cr$$_{2}$$O$$_{3}$$ layer and the matrix.

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