Long term stability of MX precipitation strengthening mechanism in high chromium steel under creep deformation

Onizawa, Takashi  ; Wakai, Takashi ; Kato, Shoichi ; Asayama, Tai 

High Cr steel for structural material of fast breeder reactors request high ductility and toughness during long term. V and Nb are believed to improve the high temperature strength of high Cr steels by precipitating as carbides and/or nitrides, namely fine MX particles. However, the long term efficiency and stability of such precipitation strengthening mechanisms provided by the fine MX particles have not been clarified yet. A series of trial products controlling V and Nb contents is produced and mechanical tests are conducted to investigate the effect of these elements on the mechanical properties and the long term stability of the MX strengthening mechanism. In this study, stability of MX in high Cr steel during long-term creep was examined.