Hokkaido University · Materials Science
Professor Shigeharu Ukai's research lab specializes in the development and characterization of advanced oxide dispersion strengthened (ODS) ferritic and martensitic steels for extreme nuclear energy applications. The lab focuses on enhancing high-temperature mechanical properties—particularly creep rupture strength and ductility—through microstructural engineering, including grain morphology control via recrystallization and optimization of oxide particle dispersion. Their work centers on designing next-generation cladding materials for fast breeder reactors, such as Japan’s MONJU and Generation IV reactors, with an emphasis on radiation resistance and long-term stability under severe conditions. The lab also investigates the role of complex oxide phases (e.g., Y2Ti2O7, αY2TiO5) and solute elements (Ti, Y) in refining microstructures and improving performance at elevated temperatures.
Figures are computed from collected data and may differ slightly.
For use as fuel cladding of liquid metal fast reactors, Fe-0.12C-9Cr-2W ODS martensitic steel claddings were developed by cold-rolling under the softened ferrite phase induced by slow cooling from austenite phase, subsequently by ferrite to austenite phase transformation to break up substantially elongated grains produced by cold-rolling at the final heat-treatment. The produced claddings showed noticeable improvement in tensile and creep rupture strength that are considerably superior to PNC-FM
The high temperature strengthening mechanism of previously manufactured 12Cr-ODS ferritic steel claddings was clarified. In the recrystallized 12Cr-2W-0.3Ti-0.24Y2O3-ODS ferritic steel cladding, αY2TiO5 type complex oxide formation was responsible for the drastic reduction of oxide particle size and the resulting shortened distance between particles, which led to superior internal creep rupture strength at 973 K because of the high resistance to gliding dislocation. Internal creep deformation wa
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 recry
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 recry
The 9Cr-ODS martensitic steel claddings were developed by cold-rolling and subsequent heat-treatment. The standard chemical composition is Fe-0.13C-9Cr-2W-0.2Ti-0.35Y2O3. The substantially elongated grains formed by cold-rolling turned out to be into equi-axied grains by ferrite to austenite phase transformation at the final heat-treatment. The produced claddings have the tempered martensitic structure and excess oxygen of 0.060 mass%. The superior tensile and creep rupture strength were shown i
AbstractThe development status of 9Cr–oxide dispersion strengthened (ODS) ferritic steels was reviewed, focusing on the authors' activities. This material is the most prospective cladding of the advanced high burn-up fuel elements for Japanese prototype fast breeder reactor MONJU and international Generation IV advanced fast reactors, because of their inherent radiation resistance as well as superior high temperature strength. The Y2Ti2O7 complex oxide particles in nano-scale are precipitated th
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