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論文

Enhanced work hardening in ferrite and austenite of duplex stainless steel at 200 K; ${it In situ}$ neutron diffraction study

山下 享介*; 古賀 紀光*; Mao, W.*; Gong, W.; 川崎 卓郎; Harjo, S.; 藤井 英俊*; 梅澤 修*

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

 被引用回数:0

Ferrite-austenite duplex stainless steels offer excellent strength and ductility, making them suitable for extreme environments. In this study, ${it in situ}$ neutron diffraction during tensile testing at 293 K and 200 K was used to investigate stress partitioning and phase-specific deformation. Phase stress was calculated using a texture-compensated method. At both temperatures, ferrite showed higher phase stress than austenite, acting as the harder phase. At 200 K, both phases exhibited increased strength and work hardening. Austenite showed significant stacking fault formation alongside dislocation migration, while ferrite retained its dislocation-based deformation mode, becoming more effective. Stress contributions from both phases were comparable. No martensitic transformation occurred. Strengthening and enhanced work hardening in both phases led to high strength at 200 K, with ductility similar to that at 293 K.

論文

Unique deformation behavior of ultrafine-grained 304 stainless steel at 20 K

Mao, W.*; Gong, W.; 川崎 卓郎; Gao, S.*; 伊東 達矢; 山下 享介*; Harjo, S.; Zhao, L.*; Wang, Q.*

Scripta Materialia, 264, p.116726_1 - 116726_6, 2025/07

 被引用回数:0 パーセンタイル:0.00(Nanoscience & Nanotechnology)

An ultrafine-grained 304 austenitic stainless steel exhibited pronounced serrated Luders deformation at 20 K, with stress and temperature oscillations reaching 200 MPa and 20 K. ${it In-situ}$ neutron diffraction and digital image correlation revealed discontinuous Luders band propagation and burst martensite formation. During deformation, austenite phase stress remained lower than at upper yielding, indicating elastic behavior. Notably, martensite phase stress stayed lower than austenite until fracture, likely due to stress relaxation from burst martensitic transformation at 20 K. The low martensite stress delayed brittle fracture until austenite plastically yielded during uniform deformation.

論文

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

豊田 晃大; 鬼澤 高志; 若井 栄一*

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

316FR steel, a modification of 316 austenitic stainless steel, will be used as a structural material in the sodium cooled fast reactor (SFR), one of the initiatives being developed in Japan to achieve carbon neutrality in order to combat global warming. To withstand the high-temperature operating environment of the SFR, the alloy design of the 316FR steel has been optimized to have high creep strength for a long time with controlled precipitation by optimizing the alloy composition. In order to clarify that 316FR steel can maintain its properties under the high temperature (around 550$$^{circ}$$C) irradiation environment of the SFR, the authors mainly conducted in-situ observations under electron beam irradiation at high temperatures to investigate in detail the irradiation effects on the precipitates (mainly carbides), which are characteristic of 316FR steel. As a result, it was found that the precipitates in 316FR steel are more stable than those in type 304 stainless steel under irradiation without coarsening at grain boundaries or within grains. The characteristics and attractiveness of 316FR steel, the results obtained, and the mechanism of creep behavior under irradiation are also explained.

論文

Role of solute hydrogen on mechanical property enhancement in Fe-24Cr-19Ni austenitic steel; An ${it in situ}$ neutron diffraction study

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

 被引用回数:1 パーセンタイル:0.00(Materials Science, Multidisciplinary)

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 (${it i.e.}$, 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 ${it in situ}$ 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.

論文

Density of a molten stainless steel-B$$_{4}$$C alloy measured in the electrostatic levitation furnace onboard the international space station

石川 毅彦*; 織田 裕久*; 小山 千尋*; 下西 里奈*; 池内 留美子*; Paradis, P.-F.*; 岡田 純平*; 福山 博之*; 山野 秀将

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

Samples of stainless steel (SS) - boron carbide (B$$_{4}$$C) alloys were levitated in the Electrostatic Levitation Furnace onboard the International Space Station (ISS-ELF) to measure the thermophysical properties of their melts. Melting of samples of two different compositions (SS-12.3, and 28 mass% B$$_{4}$$C) were attempted in the furnace. Even though only one sample (SS-12.3 mass% B$$_{4}$$C) could be melted, its density was successfully obtained.

報告書

Elemental composition analysis of main structural materials of JMTR

永田 寛; 河内山 真美; 茅根 麻里奈; 菅谷 直人; 西村 嵐; 石川 譲二; 坂井 章浩; 井手 広史

JAEA-Data/Code 2024-016, 44 Pages, 2025/03

JAEA-Data-Code-2024-016.pdf:3.54MB

原子炉施設の構造材の元素組成は、廃止措置計画の策定などの際に評価を行う放射化計算において、重要なパラメータの一つとして使用されている。このうち、試験研究炉の構造材として使用されているアルミニウム合金などの元素組成については、主要成分以外の元素については十分なデータが得られていない。このことから、材料試験炉「JMTR」の主要な構造材として使用されてきたアルミニウム合金、ベリリウム、ハフニウムなどから試料を採取し、元素組成の分析を実施した。本報告書は、令和5年度に取得した78元素の元素組成データについてまとめたものである。

論文

BWR下のSUS304L鋼で生じる粒内応力腐食割れに及ぼす結晶粒微細化の影響

広田 憲亮; 中野 寛子; 武田 遼真; 井手 広史; 土谷 邦彦; 小林 能直*

材料の科学と工学, 61(6), p.248 - 252, 2024/12

SUS304Lステンレス鋼の0.2%耐力に関する比較分析により、ひずみ速度が低下するほど、温度が上昇するほど、0.2%耐力は著しく低下することが明らかとなった。一方で結晶粒径を68.6$$mu$$mから0.59$$mu$$mに微細化した場合における低ひずみ速度下での0.2%耐力への強度低下率の影響は小さかった。しかし、結晶粒微細化は、室温に比べて原子炉運転温度下での0.2%耐力低下には影響を及ぼした。粒内応力腐食割れ(SCC)を促進する条件下での低ひずみ速度引張試験では、28.4$$mu$$m以下の結晶粒径を持つSUS304Lに対しては、原子炉運転温度下での破断ひずみと同等の値を示したが、粗粒のSUS304Lでは破断ひずみが低下した。微細構造解析では、より結晶粒が微細な材料で87%以上の延性破面が観察され、特に0.59$$mu$$mの結晶粒径を持つSUS304Lでは{111}/$$Sigma$$3粒界が数多く存在する一方で、結晶粒径が大きくなるにつれてその割合が減少していた。これらの結果は、結晶粒微細化により、{111}/$$Sigma$$3粒界の増加を通じて、腐食の進行が遅延し、粒内SCCが抑制されたことを示唆している。

論文

First freezing experiments with a molten mixture of boron carbide and stainless steel in core disruptive accidents of sodium-cooled fast reactors

江村 優軌; 松場 賢一; 菊地 晋; 山野 秀将

Proceedings of 13th Korea-Japan Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS13) (Internet), 8 Pages, 2024/11

Assuming the CDA of SFRs, the eutectic melting between B$$_{4}$$C as a control rod material and stainless steel (SS) as a structural material could occur below their melting points. After that, the mixture produced by eutectic melting between B$$_{4}$$C and SS (B$$_{4}$$C-SS mixture) would relocate inside or outside of the original core region. From the viewpoint of core reactivity changes, the relocation behavior of B$$_{4}$$C-SS mixture induced by its melting/freezing behavior, is one of the key elements to evaluate the CDA consequences. Many experimental studies on freezing behavior using core materials and its simulants, including molten UO$$_{2}$$, SS, tin, wood's metal have been reported in the past. Based on these experimental findings, the freezing/blockage model for the severe accident simulation code was established and discussed through analyses of freezing process. Specifically, it has been considered that the experimental correlation of melt-penetration length was a key indicator to quantitatively describe freezing behavior. However, there was no experimental data for the freezing behavior of actual B$$_{4}$$C-SS mixture. Therefore, the freezing experiments of B$$_{4}$$C-SS mixture were conducted to investigate the freezing and blockage behavior inside a flow path such as fuel pin bundle. In the freezing experiments, B$$_{4}$$C powder and SS block were heated up to around 1,750 K using a graphite heating furnace, then B$$_{4}$$C-SS mixture flowed down into an SS pipe for cooling below 750 K. The experimental results showed that the B$$_{4}$$C-SS mixture solidified and resulted in the blockage in the SS pipe with 4 mm or 6.7 mm in inner diameter, respectively. Furthermore, the observations for cross section of SS pipe suggested that the B$$_{4}$$C-SS mixture penetrated deeper than molten SS. This difference is considered to be influenced by decrease of the melting point.

論文

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.; 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:13 パーセンタイル:96.74(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.

論文

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

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:2 パーセンタイル:9.61(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 ($$r$$-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$$^{circ}$$ showed a low yield strength (YS) and TS, but a better U.El and $$r$$-value. The neutron diffraction results are discussed to explain the mechanical properties.

論文

Thinning behavior of solid boron carbide immersed in molten stainless steel for core disruptive accident of sodium-cooled fast reactor

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 (B$$_4$$C)- 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$$_4$$C pellets with molten SS were conducted to evaluate the CDA sequences such as contact event of solid B$$_4$$C with degraded core materials including SS at very high temperature. The immersion experiment aims at understanding the kinetic behavior of solid B$$_4$$C-liquid SS reaction based on the reduced thickness of B$$_4$$C pellet after the experiment in the temperature ranges from 1763 to 1943 K, which is higher than the temperature of solid B$$_4$$C-solid SS reaction. Based on the kinetic consideration of the reaction rate constants for solid B$$_4$$C-liquid SS reaction, it was found that similar temperature dependency was identified between solid B$$_4$$C-liquid SS and solid B$$_4$$C-solid SS. Besides, the reaction rate constants of solid B$$_4$$C-liquid SS were smaller than those of solid B$$_4$$C-solid SS extrapolated in higher temperature region by two or more orders of magnitude due to two different evaluation method for B$$_4$$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$$_4$$C side/SS side.

論文

Effects of welding and constraint conditions on the welding residual stress and hardness of Type 316 stainless steel pipe

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.

論文

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.*; 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$$_{F}$$($$Delta$$K)$$^{n}$$, where C$$_{F}$$ is the fatigue crack growth rate coefficient, n is the fatigue crack growth rate exponent and $$Delta$$K is the stress intensity factor range. The coefficient C$$_{F}$$ contains a temperature parameter S$$_{T}$$, and a scaling parameter, S$$_{R}$$, which is a function of the stress ratio R. When the stress ratio R is positive from 0 to 1, the parameter S$$_{R}$$ 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$$_{R}$$ = 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$$_{R}$$ for the ASME Code Section XI, Appendix Y, based on the literature surveyed in this study.

論文

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.; 川崎 卓郎; Wang, X.-L.*

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

 被引用回数:10 パーセンタイル:94.16(Materials Science, Multidisciplinary)

We report an in situ neutron diffraction study of 316 L that reveals an extraordinary work-hardening rate (WHR) of $$sim$$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 ($$gamma$$-to-$$alpha$$') 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 $$alpha$$'-martensite increase significantly. The neutron diffraction data further suggest that the $$gamma$$-to-$$alpha$$' phase transformation was mediated by the $$varepsilon$$-martensite, as evidenced by the concurrent decline of the $$varepsilon$$ phase with the $$gamma$$ phase.

論文

Mechanical stability of retained austenite and texture evolution in additively manufactured stainless steel

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:44.33(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.

論文

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

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:4 パーセンタイル:86.15(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。

論文

EBR-II MOX fuel characterization enabling ARES Phase I testing

Bess, J. D.*; Chipman, A. S.*; Pope, C. L.*; Jensen, C. B.*; 小澤 隆之; 廣岡 瞬; 加藤 正人*

Nuclear Science and Engineering, 197(8), p.1845 - 1872, 2023/08

 被引用回数:0 パーセンタイル:0.00(Nuclear Science & Technology)

日米共同研究の一環として、アイダホ国立研究所の過渡照射試験炉TREATにおいて、過去にEBR-IIで照射したMOX燃料を用いた過渡照射試験を計画している。EBR-IIで約134.4GWd/tを達成したMOX燃料ピン3本の内、2本を過渡照射試験に用いることを計画しており、残りの1本について照射試験のための事前解析を行った。事前解析では、燃料ペレットの特性と照射履歴を整理するとともに、崩壊計算や非破壊分析を行った。得られたデータを元に炉心解析を行い、照射試験条件の検討を進めた。

論文

Establishing an evaluation method for the aging phenomenon by physical force in fuel debris

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。

論文

Modeling of hardness and welding residual stress in Type 316 stainless steel components for the assessment of stress corrosion cracking

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.

論文

放射光X線と中性子を相補的に用いた小口径突合せ溶接配管の実応力解析

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.

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