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

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

Ferrite-austenite duplex stainless steels offer excellent strength and ductility, making them suitable for extreme environments. In this study, 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.

Temperature-dependent deformation behavior of dual-phase medium-entropy alloy; In-situ neutron diffraction study

Gu, G. H.*; Jeong, S. G.*; Heo, Y.-U.*; Harjo, S.; Gong, W.; Cho, J.*; Kim, H. S.*; 他4名*

Journal of Materials Science & Technology, 223, p.308 - 324, 2025/07

https://doi.org/10.1016/j.jmst.2024.11.057

Face-centered cubic (FCC) equi-atomic multi-principal element alloys (MPEAs) exhibit excellent mechanical properties from cryogenic to room temperatures. At room temperature, deformation is dominated by dislocation slip, while at cryogenic temperatures (CTs), reduced stacking fault energy enhances strain hardening with twinning. This study uses in-situ neutron diffraction to analyze the temperature-dependent deformation behavior of Al(CoNiV), a dual-phase (FCC/BCC) medium-entropy alloy (MEA). At liquid nitrogen temperature (LNT), deformation twinning in the FCC matrix leads to additional strain hardening through the dynamic Hall-Petch effect, giving the appearance of improved strengthening at LNT. In contrast, BCC precipitates show dislocation slip at both 77 K and 298 K, with temperature-dependent lattice friction stress playing a significant role in strengthening. The study enhances understanding of deformation behaviors and provides insights for future alloy design.

Input data preparation for PWR large-break LOCA analysis with RELAP5/MOD3.3 code

竹田 武司

JAEA-Data/Code 2025-005, 106 Pages, 2025/06

JAEA-Data-Code-2025-005.pdf:2.93MB

JAEAでは、加圧水型軽水炉(PWR)解析のためのRELAP5/MOD3.3コードの入力データを、主に大型非定常実験装置(LSTF)の参照4ループPWRである敦賀発電所2号機の設計情報を基に作成してきた。PWR解析に関する代表的なOECD/NEAの活動として、BEMUSEプログラムの枠組みにおける低温側配管大破断冷却材喪失事故(LBLOCA)の計算が挙げられる。また、わが国の新規制基準に係るPWRの炉心損傷防止対策の有効性評価事象には、低温側配管LBLOCA時の非常用炉心冷却系(ECCS)の再循環機能喪失事象が含まれる。本検討において、PWRの安全設計上想定すべき設計基準事故の一つであるLBLOCAを解析するための入力データを整備した。本報告書では、PWRLBLOCA解析の入力データの主な特徴を示す。PWRの原子炉容器、加圧器(PZR)、高温側配管、蒸気発生器(SG)、SG二次系、クロスオーバーレグ、低温側配管、ECCSなどをモデル化し、参照4ループPWRを2ループで模擬した。その際、PZRは3ループ分を模擬するループAに接続し、破断口は1ループ分を模擬するループBに設置した。PWRのコンポーネントのノード分割は、LSTFのコンポーネントのノード分割を参照した。また、PWRLBLOCA解析の主な入力データに対して、解釈を加えるとともに、設定根拠などの付加情報を提供した。さらに、整備した入力データを用いて、ECCS再循環機能喪失事象を対象とした過渡解析を実施した。RELAP5/MOD3.3コードによる既往研究の計算と比較することにより、過渡解析は概ね妥当であることを確認した。加えて、RELAP5/MOD3.3コードを用いて感度解析を実施し、破断口の流出係数や代替再循環注水流量が燃料棒被覆管表面温度に及ぼす影響を明らかにした。本報告書では、設定した条件の範囲内での感度解析結果について示し、ECCS再循環機能喪失事象に対する既往研究の計算内容の一部を補完する。

Experimental investigation of phase transformations in steel using X-ray and neutron diffraction

友田 陽*; Harjo, S.; 徐 平光; 諸岡 聡; Gong, W.; Wang, Y.*

Metals, 15(6), p.610_1 - 610_19, 2025/05

https://doi.org/10.3390/met15060610

Lattice parameters of product and matrix phases in steels have been measured using in situ X-ray and neutron diffraction during forward and reverse transformations. These parameters are influenced by temperature, transformation-induced internal stresses, alloying element partitioning, crystal defects, and magnetic strains. Disentangling these contributions is essential for understanding lattice behavior. This review explores internal strain (stress) associated with ferrite, pearlite, bainite, martensite, and reverse austenite transformations, emphasizing the distinction between diffusional and displacive mechanisms. It also examines how plastic deformation of austenite affects subsequent bainite or martensite formation. The roles of dislocations and vacancies are identified as critical areas for further research.

Enhanced strength and ductility in an additively manufactured Al10SiMg alloy at cryogenic temperatures

Naeem, M.*; Rehman, A. U.*; Romero Resendiz, L.*; Salamci, E.*; Aydin, H.*; Ansari, P.*; Harjo, S.; Gong, W.; Wang, X.-L.*; 他3名*

Communications Materials (Internet), 6, p.65_1 - 65_13, 2025/04

https://doi.org/10.1038/s43246-025-00793-4

The need for lightweight materials with mechanical integrity at ultralow temperatures drives the development of advanced alloys for cryogenic use. Additive manufacturing via laser powder bed fusion (LPBF) offers a scalable way to create alloys with tailored properties. Here, we show that LPBF-processed Al10SiMg exhibits a high ultimate tensile strength (395 MPa) and uniform elongation (25%) at 15 K. These enhancements stem from grain refinement, increased geometrically necessary dislocations, and stress partitioning between the Al matrix and the stiffer Si phase, aiding strain accommodation. neutron diffraction reveals that the Si phase, with its higher yield strength, bears most of the load, while the Al matrix undergoes continuous strain hardening, extending deformation capacity. These results highlight Al10SiMg's promise for cryogenic applications such as hydrogen storage, aerospace, and quantum computing hardware.

Stress and plastic strain partitioning behaviors and those contributions to martensitic transformation of retained austenite in medium manganese and transformation-induced plasticity-aided bainitic ferrite steels

北條 智彦*; 小山 元道*; 熊井 麦弥*; Zhou, Y.*; 柴山 由樹; 城 鮎美*; 菖蒲 敬久; 齋藤 寛之*; 味戸 沙耶*; 秋山 英二*

ISIJ International, 65(2), p.284 - 296, 2025/02

https://doi.org/10.2355/isijinternational.ISIJINT-2024-268

Stress and plastic strain distributions and those partitioning behaviors of ferrite and retained austenite were investigated in the medium manganese (Mn) and the transformation-induced plasticity-aided bainitic ferrite (TBF) steels, and the martensitic transformation behaviors of retained austenite during Luders elongation and work hardening were analyzed using synchrotron X-ray diffraction at SPring-8. The stress and plastic strain of retained austenite and volume fraction of retained austenite were remarkably changed during Luders deformation in the medium Mn steel, implying that the medium Mn steel possessed inhomogeneous deformation at the parallel part of the tensile specimen. On the other hand, the distributions of the stress, plastic strain and volume fraction of retained austenite were homogeneous and the homogeneous deformation occurred at the parallel part of the tensile specimen at the plastic deformation regime with work hardening in the medium Mn and TBF steels. The martensitic transformation of retained austenite at uders deformation in the medium Mn steel was possessed owing to the application of high stress and preferential deformation at retained austenite, resulting in a significant increase in the plastic deformation and reduction of stress in the retained austenite. The martensitic transformation of retained austenite at the plastic deformation regime with work hardening was induced by the high dislocation density and newly applied plastic deformation in retained austenite in the medium Mn steel whereas the TBF steel possessed gradual transformation of retained austenite which is applied high tensile stress and moderate plastic deformation.

Hybrid data assimilation methods for nuclear-data-induced uncertainties

丸山 修平; 山本 章夫*; 遠藤 知弘*

Journal of Nuclear Science and Technology, 14 Pages, 2025/00

https://doi.org/10.1080/00223131.2025.2500579

This study proposes new hybrid data assimilation (DA) methods to effectively use experimental data represented in two different ways in the DA process for reducing nuclear-data-induced uncertainties. Conventional DA methods often assume a linear model, where data in a DA database are represented by their differential coefficients, i.e., nuclear data sensitivity coefficients. In contrast, more rigorous and versatile DA methods based on sampling techniques have been proposed recently. These sampling-based DA methods describe data for DA using results derived from direct transport calculations performed with perturbed nuclear data samples. The proposed hybrid DA methods simultaneously use both types of data described by sensitivity coefficients and sampling results and thus are called "hybrid." Two hybrid DA methods are proposed herein: the simple hybrid DA and efficient hybrid DA methods. Among these, the simple method is based on a straightforward concept that uses a random sampling technique. In contrast, the efficient method employs a more technical method that effectively combines a new deterministic sampling technique with sensitivity coefficients to reduce statistical uncertainties associated with the simple method. The efficient method is expected to be a candidate to achieve high precision and rigorous DA with a realistic sample size.

Role of retained austenite and deformation-induced martensite in 0.15C-5Mn steel monitored by neutron diffraction measurement during tensile deformation

山下 享介*; 諸岡 聡; Gong, W.; 川崎 卓郎; Harjo, S.; 北條 智彦*; 興津 貴隆*; 藤井 英俊*

ISIJ International, 64(14), p.2051 - 2060, 2024/12

https://doi.org/10.2355/isijinternational.ISIJINT-2024-196

An Fe-0.15C-5Mn-0.5Si-0.05Nb steel annealed at 660C and 685C showed Lders deformation followed by high work hardening, with variations in Lders strain and hardening behavior. neutron diffraction during tensile tests analyzed phase stresses, strength contributions, and austenite orientation. Deformation-induced martensite contributed 1000 MPa to strength near tensile failure, while austenite mainly enhanced ductility via transformation-induced plasticity. Austenite transformed to martensite during Lders deformation regardless of orientation, though 311-oriented grains tended to remain along the tensile direction.

Deformation behavior of ultrafine-grained TRIP steel observed by neutron diffraction

Harjo, S.; Mao, W.*; Gong, W.; 川崎 卓郎

Proceedings of the 7th International Symposium on Steel Science (ISSS 2024), p.205 - 208, 2024/11

https://doi.org/10.2355/isijisss.2024.0_205

This study aimed to elucidate the effect of grain size on the deformation behavior of TRIP steel. We prepared metastable austenitic Fe-24Ni-0.3C steel samples with average grain sizes of 35 m (coarse grain: CG) and 0.5 m (ultrafine-grain: UFG) for in situ neutron diffraction studies during tensile deformation at room temperature. Our observations revealed increases in dislocation density in both samples prior to DIMT, indicating that plastic deformation precedes DIMT regardless of grain size. In the UFG sample, a significant rise in dislocation density occurred just around the yielding point with minimal increases in macroscopic plastic strain. Additionally, the dislocations exhibited strong dipole arrangements.

Stress-controlled hydrogen embrittlement failure in U-bend high-strength steel

柴山 由樹; 北條 智彦*; 小山 元道*; 秋山 英二*

International Journal of Hydrogen Energy, 88, p.1010 - 1016, 2024/10

https://doi.org/10.1016/j.ijhydene.2024.09.123

The effect of plastic deformation on the hydrogen embrittlement behavior of high-strength martensitic steels was investigated using a U-bend test. The hydrogen embrittlement susceptibility appeared to be enhanced with increasing plastic strain. Based on fractographic and stress-strain analyses, the maximum principal stress dominated the hydrogen embrittlement fracture. Although the apparent enhancement with increasing plastic deformation was observed, the origin of the enhancement was increased residual stress arising from the evolution of graded plastic strain during U-bending. We conclude that residual stress rather than plastic strain induced by plastic deformation strongly affects hydrogen embrittlement susceptibility in deformed high-strength steel components.