Creep And Microstructure Of 9cr-0.5mo-2w-V-Nb-B Steels For A Sfr Fuel Cladding

In this paper we evaluated the creep and microstructural properties of experimental 9Cr-0.5Mo-2W-V-Nb-B ferritic/martensitic steels for a Gen-IV sodium-cooled fast reactor (SFR) fuel cladding. As such a fuel cladding would operate under higher temperatures than 600 degrees C, while in contact with liquid sodium, and be irradiated by neutrons to as high as 200 dpa, this cladding should thus sustain both superior irradiation and thermal stabilities during an operational life. These experimental steels for a fuel cladding material should overcome a severe condition, especially their mechanical properties for creep, which deteriorate at higher temperatures of over 600 degrees C. The experimental steels, in this study, had a higher creep resistance than the commercial ASTM Grade T92 steels, and a boron addition could improve their creep properties at 650 degrees C. After the creep tests, Laves and Z phase precipitates were observed in the necking section and the M(2)X precipitates had disappeared. The M(23)C(6) carbides were coarsened to a larger size when compared with those at the normalized and tempered states. Creep voids were detected in the necking section during a long-term creep exposure. And the Z phase precipitates could also affect the creep properties by the consumption of important strengtheners, such as the MX precipitates, and a preferential recovery of the martensitic microstructure.