Kazutaka Asabe

Alloying design of oxide dispersion strengthened ferritic steel for long life FBRs core materials

Abstract Oxide dispersion strengthened (ODS) ferritic steels with excellent swelling resistance and superior high temperature strength are prospective cladding materials for advanced fast breeder reactors. The addition of Ti in 13Cr-3W ODS ferritic steels improved the high temperature strength remarkably by the formation of uniformly distributed ultra-fine oxide particles. ODS ferritic steels have a bamboo-like grain structure and a strong deformation texture. The decrease of creep rupture strength in the bi-axial direction compared to the uni-axial direction is attributed mainly to this unique bamboo grain structure. Nearly equivalent creep rupture strength for both bi-axial and uni-axial direction was successfully attained by introducing the α to γ transformation in ODS martensitic steel.

Tube manufacturing and mechanical properties of oxide dispersion strengthened ferritic steel

Abstract In order to apply the ODS ferritic steels for the prospective cladding materials of advanced fast breeder reactors, fabrication tests of thin-walled cladding tubes were carried out from a viewpoint of future industrial manufacturing. The manufactured claddings within the specification limit exhibited a superior high temperature strength and sufficient Charpy impact properties. The degradation of creep rupture strength in the bi-axial direction, as compared with the uni-axial direction, is mainly attributed to the grain boundary fracture mode within the elongated bamboo grain structure.

Development of Oxide Dispersion Strengthened Ferritic Steels for FBR Core Application, (I): Improvement of Mechanical Properties by Recrystallization Processing

As to an oxide dispersion strengthened (ODs) ferritic steel cladding as the promising candidate for long-life core materials of the fast reactors, previously fabricated claddings had inferior internal creep rupture strength in hoop direction and inferior formability due to less ductility. Those unexpected features of ODs claddings are substantially ascribed to the needle-like grain structure excessively elongated along the forming direction. Controlling the grain morphology by applying the recrystallization method to ODs ferritic steel made possible to improve those inferior features. The ranges of Y2O3 and excessive oxygen contents for possibly cold-rolling and recrystallization were revealed, and the effects of extruded temperature and deformation texture on recrystallization characteristics were evaluated. The recrystallized ODs ferritic steel showed superior internal creep rupture strength and ductility. It was demonstrated from those results that cold-rolling manufacturing of ODs cladding at room tem...