Development of high chromium steel for fast breeder reactors with high-temperature strength, ductility, and microstructural stabilit

高温強度,延性,組織安定性に優れた高速炉用高クロム鋼の開発

鬼澤 高志  ; 浅山 泰 ; 菊地 賢司*

Onizawa, Takashi; Asayama, Tai; Kikuchi, Kenji*

本研究は、V, Nb添加量を調整した高クロム鋼に対して、クリープ試験を実施し、FBR使用条件(最高使用温度550Cで約50万時間)におけるクリープ特性とV, Nbそれぞれの関係を明らかにした。また、特にMX粒子やZ相に着目した組織観察・分析により長時間クリープで生じる強度低下の原因を考察し、FBR用高クロム鋼に最適なV, Nb添加量を提示した。

The applicability of high chromium (Cr) steel as the main structural material in fast breeder reactors (FBR) has been explored to enhance the safety, the credibility and the economic competitiveness of FBR power plants. Vanadium (V) and Niobium (Nb) are believed to improve the high-temperature strength of high Cr steels by precipitating as carbides and/or nitrides, namely fine MX particles, although the long-term efficiency and stability of such precipitation strengthening mechanisms resulting from the fine MX particles have not been clarified yet. The effects of V and Nb on degradation of creep properties were investigated under FBR operating conditions, e.g., at 550 C for 500,000 h, and the relationship between the long-term creep properties and microstructural changes was investigated considering the MX particles and the Z-phase. It was found that the optimal V and Nb contents for excellent high Cr steel of FBR grade are 0.2 mass% and 0.01 mass%, respectively, under FBR operating conditions.