Effect of repair welding location and number of welds performed on creep strength of Mod. 9Cr-1Mo steel welded joints

Yamashita, Hayato; Toyota, Kodai; Onizawa, Takashi; Yamamoto, Kenji*; Kubo, Koji*

Nihon Kikai Gakkai Rombunshu (Internet), 13 Pages, 2026/00

https://doi.org/10.1299/transjsme.25-00176

It is planned that Mod.9Cr-1Mo steel will be used as the structural material for the steam generator of the demonstration fast reactor. Creep strength of welded joints of Mod.9Cr-1Mo steel is lower than that of base metal at high temperature and long time. In addition, the creep strength of welded joints of Mod.9Cr-1Mo steel with repair welding is lower than that of without repair welding. In this study, the effects of the location and number of repair welds performed on the creep strength of welded joints of Mod.9Cr-1Mo steel were investigated, and a repair welding method was developed for the construction of the demonstration fast reactor. It was clarified that, regardless of the location and number of repair welds performed, the degradation in creep strength could be greatly reduced by performing the repair welding before post weld heat treatment (PWHT). Furthermore, it was found that the superposition of thermal history and the formation of a heat affected zone (HAZ) on the weld metal promote the coarsening of ferrite grains during creep and cause a slight reduction in creep strength. All repair welding was performed prior to PWHT, and a repair welding method was also developed to minimize thermal history superposition and weld metal HAZ formation.

Enhanced work hardening in ferrite and austenite of duplex stainless steel at 200 K; neutron diffraction study

Yamashita, Takayuki*; Koga, Norimitsu*; Mao, W.*; Gong, W.; Kawasaki, Takuro; Harjo, S.; Fujii, Hidetoshi*; Umezawa, Osamu*

Materials Science & Engineering A, 941, p.148602_1 - 148602_11, 2025/09

https://doi.org/10.1016/j.msea.2025.148602

Evaluation of stability of precipitates under irradiation in 316FR steel used as fast reactor structural material

Toyota, Kodai; Onizawa, Takashi; Wakai, Eiichi*

Research & Development in Material Science (Internet), 21(5), p.2632 - 2637, 2025/06

Density of a molten stainless steel-BC alloy measured in the electrostatic levitation furnace onboard the international space station

Ishikawa, Takehiko*; Oda, Hirohisa*; Koyama, Chihiro*; Shimonishi, Rina*; Ikeuchi, Rumiko*; Paradis, P.-F.*; Okada, Jumpei*; Fukuyama, Hiroyuki*; Yamano, Hidemasa

International Journal of Microgravity Science and Application, 42(2), p.420202_1 - 420202_10, 2025/04

https://doi.org/10.15011/jasma.42.420202

Effect of grain refinement on transgranular stress corrosion cracking in SUS304L under boiling water reactor conditions

Hirota, Noriaki; Nakano, Hiroko; Takeda, Ryoma; Ide, Hiroshi; Tsuchiya, Kunihiko; Kobayashi, Yoshinao*

Material Science and Technology of Japan, 61(6), p.248 - 252, 2024/12

A comparative analysis of the 0.2 % yield stress in SUS304L stainless steel revealed that lower strain rates and higher temperatures significantly reduce yield stress. Grain refinement from 68.6 m to 0.59 m minimally impacted the rate of yield stress reduction at slower strain rates. However, finer grains showed a decrease in yield stress at reactor operating temperature compared to room temperature. In slow strain rate tests under conditions promoting intragranular stress corrosion cracking (SCC), SUS304L with grain sizes of 28.4 m or smaller exhibited similar fracture strains comparable to those at reactor operating temperatures, whereas coarse-grained SUS304L showed reduced fracture strain. Microstructural analysis showed that in smaller grains, over 87 % of the fracture surface was ductile. In particular, SUS304L with 0.59 m grains exhibited a higher presence of {111} / 3 boundaries, which decreased with grain growth. These results indicate that grain refinement will suppress intragranular SCC by slowing corrosion progression through increased {111} / 3 boundaries.

Martensitic transformation-governed Luders deformation enables large ductility and late-stage strain hardening in ultrafine-grained austenitic stainless steel at low temperatures

Mao, W.*; Gao, S.*; Gong, W.; Kawasaki, Takuro; Ito, Tatsuya; Harjo, S.; Tsuji, Nobuhiro*

Acta Materialia, 278, p.120233_1 - 120233_13, 2024/10

https://doi.org/10.1016/j.actamat.2024.120233

Effects of loading direction on the anisotropic tensile properties of duplex stainless steels based on phase strains obtained by in situ neutron diffraction experiments

Matsushita, Akira*; Tsuchida, Noriyuki*; Ishimaru, Eiichiro*; Hirakawa, Naoki*; Gong, W.; Harjo, S.

Journal of Materials Engineering and Performance, 33(13), p.6352 - 6361, 2024/07

https://doi.org/10.1007/s11665-023-08424-0

Proposal of negative stress ratio R for fatigue crack growth rates of austenitic stainless steels in air for ASME Code Section XI based on trend in experimental data

Negyesi, M.*; Yamaguchi, Yoshihito; Hasegawa, Kunio; Lacroix, V.*; Morley, A.*

Proceedings of the ASME 2024 Pressure Vessels & Piping Conference (PVP 2024) (Internet), 8 Pages, 2024/07

https://doi.org/10.1115/PVP2024-122614

Microscopic insights of the extraordinary work-hardening due to phase transformation

Ma, Y.*; Naeem, M.*; Zhu, L.*; He, H.*; Sun, X.*; Yang, Z.*; He, F.*; Harjo, S.; Kawasaki, Takuro; Wang, X.-L.*

Acta Materialia, 270, p.119822_1 - 119822_13, 2024/05

https://doi.org/10.1016/j.actamat.2024.119822

Estimating the corrosion rate of stainless steel R-SUS304ULC in nitric acid media under concentrating operation

Irisawa, Eriko; Kato, Chiaki

Journal of Nuclear Materials, 591, p.154914_1 - 154914_10, 2024/04

https://doi.org/10.1016/j.jnucmat.2024.154914

The amount of corrosion of austenitic stainless-steel R-SUS304ULC was evaluated considering the changes in solution composition and boiling during actual concentration operations. Austenitic stainless-steel R-SUS304ULC is the structural material of the highly radioactive liquid waste concentrator in Japanese spent fuel reprocessing plant, which treats highly corrosive nitric acid solutions during enrichment operations. The study results show that it is necessary to focus on nitric acid concentrations, oxidizing metal ion concentrations, and decompression boiling as factors that accelerate the corrosion rate of stainless steel because of cathodic reaction activation.