Development of ODS ferritic steel claddings

Mizuta, Shunji ; Fujiwara, Masayuki; not registered  

Oxide dispersion strengthened (ODS) ferritic steels have been developing as a long life fuel claddings, because they are expected to be superior structure stability and high temperature strength up to high neutron dose. In order to improve a strength anisotropy induced by an elongated grain structure along rolling direction, the effects of manufacturing process and added elements have been studied by means of recrystallization technique. The feasibility study was also conducted for economical manufacturing process with capable of large scale production. Following results were obtained in this study. (1)From cold rolling manufacturing study as a parameter of Ti and YO contents, claddings have been successfully manufactured through softening by recrystallization heat treatment. The grains tend to elongate along rolling direction with increasing Ti and YO contents. (2)The ring tensile tests show the improved strength with increasing Ti and YO contents: 0.3Ti-0.23YO has the highest strength. The uniform elongation and ductility in circumferential direction is maintained at entire temperature range. (3)The internal creep rupture strength is also improved by finely distributed YO-TiO complex oxides. The manufactured cladding with 0.3Ti-0.23YO is expected to attain the target strength (120MPa at 700C for 10,000h). (4)At the cladding manufacturing test with four times rolling, recrystallization structure was realized at the final heat treatment by suppressing heat treatment temperature up to recovery stage at intermediate heat treatment.