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伊東 達矢; 小川 祐平*; Gong, W.; Mao, W.*; 川崎 卓郎; 岡田 和歩*; 柴田 曉伸*; Harjo, S.
Acta Materialia, 287, p.120767_1 - 120767_16, 2025/04
Incorporating solute hydrogen into Fe-Cr-Ni-based austenitic stainless steels enhances both strength and ductility, providing a promising solution to hydrogen embrittlement by causing solid-solution strengthening and assisting deformation twinning. However, its impacts on the relevant lattice defects evolution (, dislocations, stacking faults, and twins) during deformation remains unclear. This study compared the tensile deformation behavior in an Fe-24Cr-19Ni (mass%) austenitic steel with 7600 atom ppm hydrogen-charged (H-charged) and without hydrogen-charged (non-charged) using
neutron diffraction. Hydrogen effects on the lattice expansion, solid-solution strengthening, stacking fault probability, stacking fault energy, dislocation density, and strain/stress for twin evolution were quantitatively evaluated to link them with the macroscale mechanical properties. The H-charged sample showed improvements in yield stress, flow stress, and uniform elongation, consistent with earlier findings. However, solute hydrogen exhibited minimal influences on the evolution of dislocation and stacking fault. This fact contradicts the previous reports on hydrogen-enhanced dislocation and stacking fault evolutions, the latter of which can be responsible for the enhancement of twinning. The strain for twin evolution was smaller in the H-charged sample compared to the non-charged one. Nevertheless, when evaluated as the onset stress for twin evolution, there was minimal change between the two samples. These findings suggest that the increase in flow stress due to the solid-solution strengthening by hydrogen is a root cause of accelerated deformation twinning at a smaller strain, leading to an enhanced work-hardening rate and improved uniform elongation.
Mao, W.*; Gao, S.*; Gong, W.; 川崎 卓郎; 伊東 達矢; Harjo, S.; 辻 伸泰*
Acta Materialia, 278, p.120233_1 - 120233_13, 2024/10
被引用回数:1 パーセンタイル:63.56(Materials Science, Multidisciplinary)Using a hybrid method of in situ neutron diffraction and digital image correlation, we found that ultrafine-grained 304 stainless steel exhibits Luders deformation after yielding, in which the deformation behavior changes from a cooperation mechanism involving dislocation slip and martensitic transformation to one primarily governed by martensitic transformation, as the temperature decreases from 295 K to 77 K. Such martensitic transformation-governed Luders deformation delays the activation of plastic deformation in both the austenite parent and martensite product, resulting in delayed strain hardening. This preserves the strain-hardening capability for the later stage of deformation, thereby maintaining a remarkable elongation of 29% while achieving a high tensile strength of 1.87 GPa at 77 K.
松下 慧*; 土田 紀之*; 石丸 詠一郎*; 平川 直樹*; Gong, W.; Harjo, S.
Journal of Materials Engineering and Performance, 33(13), p.6352 - 6361, 2024/07
被引用回数:0 パーセンタイル:0.00(Materials Science, Multidisciplinary)This study investigated the anisotropy of the tensile properties in a duplex stainless steel of 24Cr-5Ni-0.18N based on in situ neutron diffraction experiments. The 24Cr-5Ni-0.18N steel showed a better balance of tensile strength (TS) and uniform elongation (U.El) compared with 329J4L and 329J1 steels. The Lankford value (-value) of the 24Cr-5Ni-0.18N steel was comparable to other duplex stainless steels while showing a larger TS. Regarding the anisotropy of the mechanical properties, the results for a test specimen oriented at 45
showed a low yield strength (YS) and TS, but a better U.El and
-value. The neutron diffraction results are discussed to explain the mechanical properties.
江村 優軌; 高井 俊秀; 菊地 晋; 神山 健司; 山野 秀将; 横山 博紀*; 坂本 寛*
Journal of Nuclear Science and Technology, 61(7), p.911 - 920, 2024/07
被引用回数:0 パーセンタイル:0.00(Nuclear Science & Technology)Boron carbide (BC)- stainless steel (SS) eutectic reaction behavior is one of the most important issues in the core disruptive accidents (CDAs) of sodium-cooled fast reactors (SFRs). In this study, the immersion experiments using B
C pellets with molten SS were conducted to evaluate the CDA sequences such as contact event of solid B
C with degraded core materials including SS at very high temperature. The immersion experiment aims at understanding the kinetic behavior of solid B
C-liquid SS reaction based on the reduced thickness of B
C pellet after the experiment in the temperature ranges from 1763 to 1943 K, which is higher than the temperature of solid B
C-solid SS reaction. Based on the kinetic consideration of the reaction rate constants for solid B
C-liquid SS reaction, it was found that similar temperature dependency was identified between solid B
C-liquid SS and solid B
C-solid SS. Besides, the reaction rate constants of solid B
C-liquid SS were smaller than those of solid B
C-solid SS extrapolated in higher temperature region by two or more orders of magnitude due to two different evaluation method for B
C side/SS side. It was confirmed that this difference was reasonable through the consideration of previous reaction tests in solid-solid contact for B
C side/SS side.
Negyesi, M.*; 山口 義仁; 長谷川 邦夫; Lacroix, V.*; Morley, A.*
Proceedings of ASME 2024 Pressure Vessels & Piping Conference (PVP 2024) (Internet), 8 Pages, 2024/07
Fatigue crack growth rates da/dN for stainless steels in air environment are provided by the ASME Code Section XI. The fatigue crack growth rates are given by da/dN = C(
K)
, where C
is the fatigue crack growth rate coefficient, n is the fatigue crack growth rate exponent and
K is the stress intensity factor range. The coefficient C
contains a temperature parameter S
, and a scaling parameter, S
, which is a function of the stress ratio R. When the stress ratio R is positive from 0 to 1, the parameter S
increases with increasing the ratio R, and da/dN increases with increasing stress ratio R. When R is less than 0, the parameter is given by S
= 1.0. Accordingly, fatigue crack growth rates under negative stress ratio are always constant, independent of stress ratios. This means that a cyclic stress state with a minimum that is compressive is considered to cause the same degree of crack growth as one with the same range but a zero minimum. However, from the results of literature survey, experimental data reveal that the fatigue crack growth rates decrease with decreasing R ratios below zero, i.e. negative stress ratios. The objective of this paper is to assess fatigue crack growth rates under such negative stress ratios for stainless steels in air environment. An equation determined from trends in experimental data is proposed for negative R ratios for calculating the parameter S
for the ASME Code Section XI, Appendix Y, based on the literature surveyed in this study.
Li, S.; 山口 義仁; 勝山 仁哉; Li, Y.
Proceedings of ASME 2024 Pressure Vessels & Piping Conference (PVP 2024) (Internet), 8 Pages, 2024/07
Flaws due to stress corrosion cracking (SCC) were recently detected in welded joints of austenitic stainless steel piping lines in pressurized water reactors. Welding-induced high hardness and tensile residual stress are known as one of the main factors affecting SCC. In this work, thermal-elastic-plastic coupled three-dimensional finite element analyses were performed to investigate the distributions of welding residual stress and hardness in butt-welded joints of Type 316 stainless steel. Different heat inputs were applied to the pipe welds, including normal heat input, high heat input and very high heat input. Two different constraint conditions were considered for the welded joints, i.e., both ends free or clamped, the latter indicating that the welded joint is constrained by the surrounding piping system. Simulation results were compared with experimental data such as welding thermal cycle, axial shrinkage and residual stress for validation. The effects of heat input and constraint condition on the welding residual stress and hardness at different sections of the welded joints including the weld start/end location were discussed in detail.
Ma, Y.*; Naeem, M.*; Zhu, L.*; He, H.*; Sun, X.*; Yang, Z.*; He, F.*; Harjo, S.; 川崎 卓郎; Wang, X.-L.*
Acta Materialia, 270, p.119822_1 - 119822_13, 2024/05
被引用回数:4 パーセンタイル:81.14(Materials Science, Multidisciplinary)We report an in situ neutron diffraction study of 316 L that reveals an extraordinary work-hardening rate (WHR) of 7 GPa at 15 K. Detailed analyses show that the major contribution to the excellent strength and ductility comes from the transformation-induced plasticity (TRIP) effect, introduced by the austenite-to-martensite (
-to-
') phase transition. A dramatic increase in the WHR is observed along with the transformation; the WHR declined when the austenite phase is exhausted. During plastic deformation, the volume-fraction weighted phase stress and stress contribution from the
'-martensite increase significantly. The neutron diffraction data further suggest that the
-to-
' phase transformation was mediated by the
-martensite, as evidenced by the concurrent decline of the
phase with the
phase.
Chae, H.*; Huang, E.-W.*; Jain, J.*; Lee, D.-H.*; Harjo, S.; 川崎 卓郎; Lee, S. Y.*
Metals and Materials International, 30(5), p.1321 - 1330, 2024/05
被引用回数:4 パーセンタイル:58.10(Materials Science, Multidisciplinary)In situ neutron diffraction during tensile deformation was performed for the stainless steels prepared by the additive manufacturing (AM) processes with two strategies: vertically built and horizontally built. The AM steels were further aged without solid solution treatment. As the results, the retained austenite was found to be more stable because the chemical composition became homogeneous by aging, and the onset of deformation induced martensitic transformation was delayed.
入澤 恵理子; 加藤 千明
Journal of Nuclear Materials, 591, p.154914_1 - 154914_10, 2024/04
被引用回数:2 パーセンタイル:90.90(Materials Science, Multidisciplinary)核燃料再処理施設における濃縮運転時の溶液組成及び沸騰の変化を考慮して、オーステナイト系ステンレス鋼R-SUS304ULCの腐食量を評価した。オーステナイト系ステンレス鋼R-SUS304ULCは、日本の使用済燃料再処理施設の高放射性廃液濃縮装置の構造材料であり、濃縮運転時に腐食性の高い硝酸溶液を処理する。本研究の結果、カソード反応活性化によるステンレス鋼の腐食速度を加速する要因として、硝酸濃度、酸化性金属イオン濃度、減圧沸騰に着目する必要があることがわかった。
鈴木 誠矢; 荒井 陽一; 岡村 信生; 渡部 雅之
Journal of Nuclear Science and Technology, 60(7), p.839 - 848, 2023/07
被引用回数:0 パーセンタイル:0.00(Nuclear Science & Technology)福島第一原子力発電所の事故で発生した燃料デブリは、溶融した核燃料物質と原子炉の構造材等で構成された酸化物が多くを占めているため、環境温度の変化により岩石のように劣化する可能性が高い。燃料デブリは10年以上水冷されているが、季節や昼夜の温度変化の影響を少なからず受けていることから、燃料デブリの経年変化挙動を評価するためには環境温度の変化を考慮することが不可欠である。仮に燃料デブリの劣化が進んでいる場合、微粉化した放射性物質が冷却水中に溶出して取出し作業に影響を及ぼす可能性がある。本研究では、環境温度の繰り返し変化がクラックの発生に与える影響に着目して、燃料デブリの模擬体を用いた加速試験を実施した。その結果、クラックは温度変化を重ねることで増加することを確認し、燃料デブリの簿擬態は熱膨張と収縮による応力により脆化することが判明した。燃料デブリの物理学的な劣化挙動は岩石や鉱物に類似していることが確認され、模擬燃料デブリと環境のモデルでクラックの増加挙動を予測することが可能となった。
Li, S.; 山口 義仁; 勝山 仁哉; Li, Y.; Deng, D.*
Proceedings of ASME 2023 Pressure Vessels and Piping Conference (PVP 2023) (Internet), 7 Pages, 2023/07
In this work, a framework was proposed on the comprehensive assessment of hardness and welding residual stress in Type 316 austenitic stainless steel welded joints. Firstly, an 8-pass butt-welded joint made of Type 316 stainless steel was fabricated. Finite element analysis of the welded joint was performed to investigate hardness and welding residual stress distributions. The grain growth model was developed for the hardness prediction. The Chaboche combined isotropic-kinematic strain hardening model and time-temperature dependent annealing model were adopted. The relationships between the Vickers hardness and the uniaxial plastic strain as well as grain size were collected from published literatures. The simulation results of the grain size and accumulated equivalent plastic strain were used for the hardness prediction of the welded joint. The predicted hardness was compared with the experimental data of hardness mapping. The distribution of welding residual stress on the outer surface of the welded pipe was measured by using the X-ray diffraction method and strain gauge method, respectively. The predicted welding residual stresses were compared with the measurements. The results obtained showed that the developed numerical approach can predict the hardness and welding residual stress of Type 316 stainless steel welded joints with satisfactory accuracy. The effects of structural constraint and heat input on the hardness and welding residual stress will be investigated as further works, as described in the proposed framework.
鈴木 賢治*; 三浦 靖史*; 城 鮎美*; 豊川 秀訓*; 佐治 超爾*; 菖蒲 敬久; 諸岡 聡
材料, 72(4), p.316 - 323, 2023/04
Residual stresses in small-bore butt-welded pipe of austenitic stainless steel have never been measured. It is difficult to obtain a detailed residual stress map of the root welded part, because the gauge volume in neutron diffraction is large. The stress evaluation of the welded part by synchrotron X-rays was also difficult due to the dendritic structure. In this study, a double exposure method (DEM) with high-energy synchrotron X-rays was applied to measuring the details of the residual stress of the welded part, and we succeeded in obtaining the detailed axial and radius stress maps of the root welded part of the plate cut from the welded pipe, though the stress map was under the plane stress condition. The hoop stress map of the butt-welded pipe was obtained using the strain scanning method with neutrons under the triaxial stress state. The axial and radius stress maps under triaxial stress state were made up using the complementary use of the synchrotron X-ray and neutron. As a result, the detailed stress maps of the root welded part of the butt-welded pipe were obtained. The obtained map sufficiently explained the initiation and propagation of SCC.
Mohamad, A. B.; 中島 邦久; 三輪 周平; 逢坂 正彦
Journal of Nuclear Science and Technology, 60(3), p.215 - 222, 2023/03
被引用回数:0 パーセンタイル:0.00(Nuclear Science & Technology)The distribution of Sr in the reactor would be influenced by a chemical reaction of Sr vapor species with a structural material of internal reactor and fuel cladding materials; stainless steel (SS) or Zircaloy (Zry) cladding during 1F-NPS accident. The chemical interaction between Sr-Zry and Sr-SS has been described. The reaction tests have been performed to investigate the chemical interaction behavior under possible severe accident conditions. The tests have been conducted up to 1523 K under steam atmosphere. It was confirmed that Sr-Zr-O and Sr-Si-O compounds were formed through 2 kinds chemical interactions; gas-solid reaction and liquid-solid reaction. The gas and liquid species of Sr in a good contact with the solid Zry and SS to form Sr-Zr-O and Sr-Si-O compounds, respectively. Sr was deposited onto the Zry and SS surfaces and lead to the formation of reaction product. Thus, this study highlights the possibility that Sr was deposited and retained in the core structure where the temperature was elevated during the accident in the 1F-NPS.
青山 高士; 加藤 千明
Corrosion Science, 210(2), p.110850_1 - 110850_10, 2023/01
被引用回数:6 パーセンタイル:43.90(Materials Science, Multidisciplinary)Cuのキレート錯体: [Cu(EDTA)]
を用いて、Cu
を隙間の外側から内側へ導入した。導入されたCu
は、ステンレス鋼の隙間腐食の抑制剤として作用することが期待される。隙間腐食試験により、[Cu(EDTA)]
のエレクトロマイグレーションによりCu
が隙間内部へ導入されることが確認された。移行した[Cu(EDTA)]
はH
と反応して隙間内部のpH低下を抑制し、Cu
と[Cu(EDTA)]
は分離してステンレス鋼の活性溶解が抑制されることが確認された。
入澤 恵理子; 加藤 千明; 山下 直輝; 佐野 成人
材料と環境, 71(3), p.70 - 74, 2022/03
使用済核燃料再処理溶液施設でのステンレス鋼の腐食評価として、放射性核種であるNpを含む硝酸水溶液中でのステンレス鋼R-SUS304ULC鋼の浸漬腐食試験と分極測定を行った。328K以上の温度では硝酸水溶液中よりも高い腐食電位を示し、過不動態域近傍となることがわかった。また、浸漬腐食試験により腐食量と分極抵抗との比較から換算係数として
=0.018V
0.025Vの値を取得し、電気化学測定からの腐食量算出が可能であるかを検討した。
加藤 千明; 山岸 功; 佐藤 智徳; 山本 正弘*
材料と環境, 70(12), p.441 - 447, 2021/12
ゼオライト粒子は福島第一原子力発電所(1F)の汚染水の浄化のためのセシウム吸着塔内で用いられている。使用後のセシウム吸着塔は敷地内で保管されているが、ステンレス鋼製胴部の局部腐食が懸念された。この腐食リスクに対し、線による影響データを照射下電気化学試験装置で取得した。また、内溶液の変化状態を実規模サイズのモックアップ試験装置で検討した。それらの結果から、過酸化水素による電位の上昇がゼオライト粒子の存在で防ぐことができ、塩化物イオンの濃化もそれほど生じないことを明らかにし、局部腐食が相当に小さく抑えられることを示した。
高井 俊秀; 古川 智弘; 山野 秀将
Mechanical Engineering Journal (Internet), 8(4), p.20-00540_1 - 20-00540_11, 2021/08
炉心損傷事故時には、制御棒材である炭化ホウ素と構造材であるステンレス鋼が共晶反応を起こし、ステンレス鋼の融点より低い温度で溶融(液化)すると考えられる。こうして生成された制御棒溶解材は流動性があるため、崩壊炉心内を広範に移行し、崩壊炉心物質に混ざり込むことで、崩壊炉心物質の反応度抑制に顕著な効果をもたらすと考えられる。しかしながら、このような制御棒溶解材の共晶溶融反応やその移行挙動については、これまでの重大事故解析では何ら考慮されていない。本研究では、シビアアクシデント解析コードの高度化に資するため、炭化ほう素溶解量の異なる制御棒溶解材について固相物性測定を実施し、温度(及び炭化ホウ素濃度)依存性を示す物性評価式として整備した結果について報告する。
春日井 好己; 佐藤 浩一; 高橋 一智*; 宮本 幸博; 甲斐 哲也; 原田 正英; 羽賀 勝洋; 高田 弘
JPS Conference Proceedings (Internet), 33, p.011144_1 - 011144_6, 2021/03
J-PARCの物質・生命科学実験施設では、2008年より水銀を使った核破砕中性子源を運用している。水銀を内包するステンレス製の水銀標的容器は、放射線損傷等のため定期的な交換が必要である。本件では、2011年に実施した最初の標的容器交換にともなう一連の作業で観測された標的容器等からのトリチウムの放出挙動とその解析結果について報告する。
高井 俊秀; 古川 智弘; 山野 秀将
Proceedings of 2020 International Conference on Nuclear Engineering (ICONE 2020) (Internet), 6 Pages, 2020/08
Eutectic melting behavior between boron carbide (BC) as control rod material and stainless steel (SS) as structural material and subsequent relocation behavior plays an important role to achieve an in-vessel retention concept which ensures long-term coolability of degraded core under core disruptive accident, because these behaviors are expected to reduce the neutronic reactivity significantly. However, these behaviors have never been simulated in severe accident computer codes before. Since 2016, JAEA has been conducting a research project to develop physical models that describe these behaviors. For the physical models' development, it is necessary to obtain thermophysical properties of SS-B
C eutectic mixture with various B
C concentration and maintain them as a database. In this work, the density and specific heat of SS-17 mass%B
C in a solid state are obtained and compared with these of stainless steel containing 0 and 5 mass%B
C.
中島 邦久; 西岡 俊一郎*; 鈴木 恵理子; 逢坂 正彦
Mechanical Engineering Journal (Internet), 7(3), p.19-00564_1 - 19-00564_14, 2020/06
軽水炉シビアアクシデント時、ステンレス鋼(SS304)に化学吸着したセシウム量を推定するために、セシウム化学吸着モデルが構築されている。しかし、既存の化学吸着モデルは、実験結果をうまく再現することができていない。そのため、本研究では、化学反応を伴う気液系の物質移動理論(浸透説)や気相固相界面における水酸化セシウム(CsOH)の分解反応に対する質量作用の法則を組合せることで、SS304中のケイ素濃度や気相中の水酸化セシウム濃度の影響を考慮したモデルを構築した。その結果、既存モデルを用いた場合よりも、本研究で得られた修正モデルの方が、実験データをより正確に再現できることが分かった。