高速炉燃料用SUS316相当鋼の高温強度及び照射特性評価

宮澤 健; 上羽 智之; 矢野 康英; 丹野 敬嗣; 大塚 智史; 鬼澤 高志; 安藤 勝訓; 皆藤 威二

JAEA-Technology 2024-009, 140 Pages, 2024/10

JAEA-Technology-2024-009.pdf:8.03MB

SUS316相当鋼を用いた高速炉燃料設計の高信頼性化に向けて、SUS316相当鋼被覆管及びラッパ管の高温強度及び照射データを材料学的及び統計学的な観点で評価・解析することで、高温強度及び高照射量までの照射特性に係る設計用強度式を導出した。異常な過渡変化の上限温度を超える900CまでのSUS316相当鋼被覆管及びラッパ管(非照射材)の高温引張試験データ及び高温クリープ試験データを拡充し、0.2%耐力、引張強さ、クリープ破断強度の最適近似式と下限式並びに熱クリープひずみの最適近似式と上下限式を導出した。また、高速実験炉「常陽」、仏国・高速原型炉Phenix及び米国・FFTFで高照射量まで中性子照射したSUS316相当鋼被覆管及びラッパ管の照射後引張試験データ及びSUS316相当鋼被覆管の炉内クリープ破断試験データを解析することで、炉内Na中照射による引張強度及びクリープ強度の低下を表す強度補正係数を導出した。導出した式を実測値と比較することで、その妥当性を確認した。

Anisotropic creep property related to non-spherical shape of mechanically alloyed powder of oxide dispersion strengthened F82H

酒瀬川 英雄; 中島 基樹*; 加藤 太一朗*; 野澤 貴史*; 安堂 正己*

Materials Today Communications (Internet), 40, p.109659_1 - 109659_8, 2024/08

https://doi.org/10.1016/j.mtcomm.2024.109659

酸化物分散強化型鋼鋼のナノメートルサイズの酸化物粒子はクリープ強度の向上に対して重要な役割を持つ。以前の研究では旧粉末境界という焼結前に機械的合金粉末の表面であった組織因子に注目した。その結果、より小さなサイズの粉末で製作され微細な旧粉末境界を持つ酸化物分散強化型鋼は、より大きなサイズの粉末で製作され粗大な旧粉末境界を持つ酸化物分散強化型鋼よりも、短いクリープ寿命を示すことを確かめた。これより、機械的合金粉末の大きさがクリープ強度特性に影響を及ぼすことを明らかとなった。本研究では非球状である機械的合金粉末の形状がクリープ強度特性に及ぼす影響に注目した。このような形状がクリープ強度特性に異方性を生じさせる可能性が考えられたからである。ここでは異なった切り出し方位を持つ試験片に対してスモールパンチクリープ試験を実施することで異方性に注目した。これより、クリープ寿命は試験片の切り出し方位によって変化することを確かめて、形状がクリープ強度特性に及ぼす影響を明らかとした。

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

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

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.

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

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

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.

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

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

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.

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

https://doi.org/10.1007/s12540-023-01575-8

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.

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*

鉄と鋼, 110(3), p.241 - 251, 2024/02

https://doi.org/10.2355/tetsutohagane.TETSU-2023-059

A Fe-0.15C-5Mn-0.5Si-0.05Nb medium Mn steel annealed at 660C and 685C both exhibited inhomogeneous deformation with Luders deformation and extremely high work hardening rates, but with different Luders strain and work hardening behavior. neutron diffraction measurements during tensile test were performed to investigate changes in the phase stresses and in the contributed stresses to the strength of the constituent phases, and crystal orientation of austenite. The role of each constituent phase in the deformation and the effect of crystallographic orientation on austenite stability were discussed. Deformation induced martensite showed excellent phase stress and contributed to the strength approximately 1000 MPa, which is close to macroscopic tensile strength.

残留オーステナイトを含有する中Mn複合組織鋼の高速変形特性

興津 貴隆*; 北條 智彦*; 諸岡 聡; 宮本 吾郎*

鉄と鋼, 110(3), p.260 - 267, 2024/02

https://doi.org/10.2355/tetsutohagane.TETSU-2023-065

We have investigated the dynamic tensile properties of 4, 5, 6-mass%-Mn-containing low carbon steels with multi-phase microstructures containing retained austenite. The five materials used were classified into two groups. The first group of materials, with around 10% of retained austenite, showed normal strain rete dependence of yield strength (YS) and tensile strength (TS) as in conventional high strength steels. The second group of materials, containing 25-36% of retained austenite, exhibited Lders elongation showed also normal strain rate dependence in YS and flow stress at Lders deformation, but TS varied in a complex manner. Among the second group, in the 4 Mn steel, TS was nearly constant at strain rates below 1 s but increased slightly at higher strain rates. In the 5 and 6 Mn steels, TS once decreased up to the strain rate of 1 or 10 s, and then began to increase at higher strain rates. These behaviors were discussed in terms of temperature rise during plastic deformation causing suppression of martensitic transformation, and thermal stability of retained austenite. In the 4 Mn steel with relatively unstable retained austenite, almost all the austenite transforms regardless of strain rate. In the 5 and 6 Mn steels, where the retained austenite is moderately stable, strain induced transformation of austenite continues up to high plastic strain, providing a good balance of strength and ductility. At high strain rate, TS decreases slightly due to temperature rise, but at higher strain rates than 1 s, the strain rate sensitivity of flow stress in ferrite become prominent and the flow stress increases.

Synergistic effect of aluminum lactate and sodium molybdate on freshwater corrosion of carbon steel under irradiation

大谷 恭平; 加藤 千明; 五十嵐 誉廣

Corrosion, 79(11), p.1277 - 1286, 2023/11

https://doi.org/10.5006/4386

A novel corrosion inhibitor of carbon steel in fresh water using Al lactate was proposed and its corrosion-inhibition mechanism was investigated. 0.75 mM Al lactate and 0.25 mM sodium molybdate were the most inhibitive to the corrosion of carbon steel in 3 mM NaCl. Al and MoO in solution formed the metal cation layer on carbon steel with few defects, and the layer did not contain Fe. The metal cation layer on carbon steel inhibited both the cathodic oxygen reduction reaction and anodic iron dissolving reaction and thus enhances the corrosion protection of carbon steel in fresh water.

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

https://doi.org/10.1115/PVP2023-103449

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.