Development of high-Cr steel for FBR structure having both high temperature strength and long-term stability; Possibility of alloys with ultra high purity

高温強度と長時間組織安定性に優れた高速増殖炉用高クロム鋼の開発; 超高純度合金の可能性

若井 隆純 ; 菱沼 章道*; 高木 清一*; 安彦 兼次*

Wakai, Takashi; Hishinuma, Akimichi*; Takaki, Seiichi*; Abiko, Kenji*

This paper studies applicability of ultra high purity (UHP) alloys to the structural materials for the sodium cooled fast reactor (SFR). Although, for the demonstration plant, conventional modified 9Cr-1Mo steel will be employed as the main structural material, innovative structure material having excellent high temperature strength and long-term microstructure stability is required for the future plant. The authors performed a series of mechanical tests of the alloys with UHP. As a result, it was clarified that some UHP alloys showed sufficient high temperature strength and liquid sodium resistance comparable to conventional steels. The authors also investigated the influence of trace elements on the mechanical properties and on the microstructure stability for long time, by using scanning electron microscopy. Laves phase was observed uniformly in grains of UHP alloys because there were few nucleation sites on grain boundaries. It was clarified that precipitation behavior of Laves phase strongly depends on the amount of trace elements. The long-term stability and efficiency of solid solution strengthening mechanism can be enhanced by UHP alloying technology. In some cases, strength and ductility were improved both together by UHP alloying technology. Although the further experimental validation of efficiency and stability of such mechanism is needed and economic competitiveness of UHP alloys with conventional steels carefully should be considered, there are some possibilities to improve the material characteristics suitable for SFR components by UHP alloying technology.