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Onuki, Somei*; Hashimoto, Naoyuki*; Ukai, Shigeharu*; Kimura, Akihiko*; Inoue, Masaki; Kaito, Takeji; Fujisawa, Toshiharu*; Okuda, Takanari*; Abe, Fujio*
Proceedings of 2009 International Congress on Advances in Nuclear Power Plants (ICAPP '09) (CD-ROM), p.9306_1 - 9306_5, 2009/05
For development of advanced ferritic ODS steels including high concentration of Cr and Al, the effect of minor alloying elements on fine dispersion of oxide particle was investigated. Microstructural analysis for Fe-16Cr-4Al-mY
O
-nZr or mHf due to TEM indicated that 0.3Zr or 0.6Hf are the optimum concentration. The mechanism of nano-sized oxide formation was also discussed.
Okuda, Takanari*; Fujiwara, Masayuki*; Nakai, Tatsuyoshi*; Shibata, Kenichi*; Kimura, Akihiko*; Inoue, Masaki; Ukai, Shigeharu*; Onuki, Somei*; Fujisawa, Toshiharu*; Abe, Fujio*
Proceedings of 2009 International Congress on Advances in Nuclear Power Plants (ICAPP '09) (CD-ROM), p.9229_1 - 9229_4, 2009/05
Oxygen content in ODS ferritic steel is the most important element to determine the mechanical properties. The oxygen contamination from the air is perfectly prevented by using new designed ball mill and the subsequent process control. Zr, Hf and Ti added ODS steels with three oxygen levels for the evaluation tests are fabricated.
Lee, J. H.*; Kimura, Akihiko*; Kasada, Ryuta*; Iwata, Noriyuki*; Kishimoto, Hirotatsu*; Zhang, C. H.*; Isselin, J.*; Dou, P.*; Muthukumar, N.*; Okuda, Takanari*; et al.
Proceedings of 2009 International Congress on Advances in Nuclear Power Plants (ICAPP '09) (CD-ROM), p.9223_1 - 9223_6, 2009/05
Corrosion is a critical issue for cladding materials, especially, in sever corrosion environment as supercritical pressurized water (SCPW). In this work, the effects of alloy elements on the corrosion behavior in SCPW were investigated for a series of oxide dispersion strengthened (ODS) steels to design alloy compositions for corrosion resistant super ODS ferritic steels. Corrosion tests were carried out for the ODS steels with different concentrations of Cr and Al in SCPW at 773 K at 25 MPa with 8 ppm of dissolved oxygen. The corrosion rate of SUS430, which contained 16wt.%Cr, was much higher than 16Cr-ODS steel. This suggests that nano-sized oxide particles dispersion and very fine grains play an important role in suppression of the corrosion. The corrosion of the ODS steel was reduced by an addition of Al in 16wt.%Cr-ODS steel but not in 19Cr-ODS steel. FE-EPMA chemical analysis clearly indicated that the surface of the Al added ODS steels was covered by alumina which suppresses the corrosion in SCPW. It is considered that an adequate combination of the contents of Cr and Al is ranging (14-16)Cr and (3.5-4.5)Al.
Kasada, Ryuta*; Lee, S. G.*; Lee, J. H.*; Omura, Takamasa*; Zhang, C. H.*; Dou, P.*; Isselin, J.*; Kimura, Akihiko*; Inoue, Masaki; Ukai, Shigeharu*; et al.
Proceedings of 2009 International Congress on Advances in Nuclear Power Plants (ICAPP '09) (CD-ROM), p.9072_1 - 9072_5, 2009/05
The newly-developed Al-added ODS ferritic steels with an addition of Zr or Hf, socalled super ODS candidate steels, showed good notch-impact properties in the as-received condition with keeping the excellent creep strength.
Sano, Hiroyuki*; Fujisawa, Toshiharu*; Kimura, Akihiko*; Inoue, Masaki; Ukai, Shigeharu*; Onuki, Somei*; Okuda, Takanari*; Abe, Fujio*
Proceedings of 2009 International Congress on Advances in Nuclear Power Plants (ICAPP '09) (CD-ROM), p.9308_1 - 9308_5, 2009/05
Corrosion of structural materials is one of the serious problems when lead-bismuth eutectic alloy (LBE) is used as a coolant material in next generation nuclear systems. In this study, dissolution experiments of synthetic Fe-Cr-Al alloys and developed super ODS steel candidates into LBE under several partial pressures of oxygen were conducted. Dissolution behaviors of major components in such steels into LBE were investigated. Interfacial behavior between LBE and steels was also observed. In addition, partial potential diagrams of the Fe-Cr-Al-O system at several conditions were established as basic data. From the potential diagrams, the partial pressure range of oxygen was estimated for the stable protective oxide layer formation at the interface. At lower oxygen partial pressure than the pressure that is enough for the formation of the stable oxide layer, a rough oxide layer was formed at the interface in all samples, and the alloy elements dissolved into LBE through it. On the other hand, at the oxygen partial pressure to form stable oxide layer, a dense and very thin oxide layer was formed especially on the higher aluminum content steel, preventing the alloy dissolution into LBE. From the results, aluminum and chromium content in steel were very important for preventing the corrosion by LBE.
Kishimoto, Hirotatsu*; Kasada, Ryuta*; Kimura, Akihiko*; Inoue, Masaki; Okuda, Takanari*; Abe, Fujio*; Onuki, Somei*; Fujisawa, Toshiharu*
Proceedings of 2009 International Congress on Advances in Nuclear Power Plants (ICAPP '09) (CD-ROM), p.9219_1 - 9219_8, 2009/05
The Super ODS steels, having excellent high-temperature strength and highly corrosion resistant, are considered to increase the energy efficiency by higher temperature operation and extend the lifetime of next generation nuclear systems. High-temperature strength of the ODS steels strongly depends on the dispersion of oxide particles, therefore, the irradiation effect on the dispersed oxides is critical in the material development. In the present research, ion irradiation experiments were employed to investigate microstructural stability under the irradiation environment at elevated temperatures. Ion irradiation experiments were performed with 6.4 MeV Fe ions irradiated at 650 
C up to a nominal displacement damage of 60 dpa. Microstructural investigation was carried out using TEM and EDX. No significant change of grains and grain boundaries was observed by TEM investigation after the ion irradiation. Main oxide particles in the 16Cr-4Al-0.1Ti (SOC-1) ODS steel were (Y, Al) complex oxides. (Y, Ti) complex oxides were in 16Cr-0.1Ti (SOC-5) and 15.5Cr-2W-0.1Ti (SOCP-3). (Y, Zr) complex oxides were in 15.5Cr-4Al-0.6Zr (SOCP-1). No significant modification of these complex oxides was detected after the ion irradiation up to 60 dpa at 650 C. The stable complex oxides are considered to keep highly microstructural stability of the Super ODS steels under the irradiation environments.
Onuki, Somei*; Hashimoto, Naoyuki*; Ukai, Shigeharu*; Kimura, Akihiko*; Inoue, Masaki; Kaito, Takeji; Fujisawa, Toshiharu*; Okuda, Takanari*; Abe, Fujio*
Proceedings of 2009 International Congress on Advances in Nuclear Power Plants (ICAPP '09) (CD-ROM), p.9307_1 - 9307_4, 2009/05
The aim of this study is to survey microstructural properties and irradiation response of advanced high Cr and Al ODS steels. The effects of minor element addition and heat-treatment are also investigated. In these steels, black dots-like dislocation loops were formed around oxide particles during electron irradiation, and then the behavior depended on the type of additional elements, but the irradiation resistance was confirmed generally. The irradiation response was not sensitive as the heat-treatment, but the minor element addition (Zr and Hf) showed an intensive suppressing the loop growth. The results suggest that a large number of oxides enhanced the mutual recombination of the irradiation-induced point defects, especially at their surface.
Ukai, Shigeharu*; Onuki, Somei*; Hayashi, Shigenari*; Kaito, Takeji; Inoue, Masaki; Kimura, Akihiko*; Fujisawa, Toshiharu*; Okuda, Takanari*; Abe, Fujio*
Proceedings of 2009 International Congress on Advances in Nuclear Power Plants (ICAPP '09) (CD-ROM), p.9232_1 - 9232_7, 2009/05
The super ODS cladding were manufactured into 8.5 mm outer diameter and 0.5 mm thickness by using pilger.mill rolling and intermediate heat treatment. The final heat treatment was successfully conducted at 1150 C for 1h to make perfectly recrystallized structure. The manufactured cladding exhibits a secondary recrystallized grains with {110} 
100
Goss orientation. As a summary of super ODS steels R&D, the ODS steel, 16Cr-4Al-2W-0.1Ti added with small amount of Hf or Zr, is the prime candidate of "Super ODS steels" which has high strength at elevated temperatures, high resistance to corrosion for SCW and LBE, and high resistance to irradiation.