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Li, L.*; 宮本 吾郎*; Zhang, Y.*; Li, M.*; 諸岡 聡; 及川 勝成*; 友田 陽*; 古原 忠*
Journal of Materials Science & Technology, 184, p.221 - 234, 2024/06
被引用回数：0 パーセンタイル：0(Materials Science, Multidisciplinary)Dynamic transformation (DT) of austenite (
) to ferrite (
) in the hot deformation of various carbon steels was widely investigated. However, the nature of DT remains unclear due to the lack of quantitative analysis of stress partitioning between two phases and the uncertainty of local distribution of substitutional elements at the interface in multi-component carbon steels used in the previous studies. Therefore, in the present study, a binary Fe-Ni alloy with + duplex microstructure in equilibrium was prepared and isothermally compressed in + two-phase region to achieve quantitative analysis of microstructure evolution, stress partitioning and thermodynamics during DT. to DT during isothermal compression and to reverse transformation on isothermal annealing under unloaded condition after deformation were accompanied by Ni partitioning. The lattice strains during thermomechanical processing were obtained via in-situ neutron diffraction measurement, based on which the stress partitioning behavior between and was discussed by using the generalized Hooke's law. A thermodynamic framework for the isothermal deformation in solids was established based on the basic laws of thermodynamics, and it was shown that the total Helmholtz free energy change in the deformable material during the isothermal process should be smaller than the work done to the deformable material. Under the present thermodynamic framework, the microstructure evolution in the isothermal compression of Fe-14Ni alloy was well explained by considering the changes in chemical free energy, plastic and elastic energies and the work done to the material. In addition, the stabilization of the soft phase in Fe-14Ni alloy by deformation was rationalized since the to transformation decreased the total Helmholtz free energy by decreasing the elastic and dislocation energies.
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
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 L
ders 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.
Zhang, Y.*; 丸澤 賢人*; 工藤 航平*; 諸岡 聡; Harjo, S.; 宮本 吾郎*; 古原 忠*
ISIJ International, 64(2), p.245 - 256, 2024/01
As-quenched martensite in carbon steels needs to be tempered to restore its ductility and toughness for practical applications. During tempering of martensite, microstructural evolutions induced by a series of reactions relevant to carbon diffusion is known to occur. In this study, multi-aspect characterization using advanced techniques such as in-situ neutron diffraction, transmission electron microscopy and three-dimensional atom probe tomography, was performed to investigate the changes in tetragonality, physical properties, microstructure and solute carbon content in high-carbon martensite, with an aim to clarify its low-temperature tempering behaviors. A binary alloy with a chemical composition of Fe-0.78 mass%C was austenitized and quenched to prepare the as-quenched martensite, followed by tempering in continuous heating at different heating rates. It was found that various reactions occurred sequentially during tempering, starting from the structure modulation generated by carbon clustering in the 0th stage, then followed by the precipitation of metastable 
-carbide particles on linear features in the 1st stage, towards the later decomposition of retained austenite and precipitation of cementite in the 2nd and 3rd stages, respectively. After analyzing the experimental results, the solute carbon content in martensite tempered under various conditions was found to be in good agreement with that estimated from the lattice volume expansion, whereas the evaluation based on the tetragonality might lead to some underestimation of the solute carbon content in martensite tempered at high temperatures.
岩井 紘基; 副島 吾郎; 瀧谷 啓晃; 粟谷 悠人; 荒谷 健太; 宮本 勇太; 手塚 将志
デコミッショニング技報, (61), p.12 - 19, 2020/03
新型転換炉原型炉ふげんは、2008年2月に廃止措置計画の認可を受け、廃止措置に取り組んでいる。2018年3月に廃止措置の第1段階(重水系・ヘリウム系等の汚染の除去期間)を終了し、現在第2段階(原子炉周辺設備解体撤去期間)に移行している。本報告では、第3段階における原子炉本体解体撤去に向けて実施した原子炉内部の構造材からの遠隔試料採取に係る技術実証について紹介する。
岩井 紘基; 副島 吾郎; 粟谷 悠人; 宮本 勇太
no journal, ,
「ふげん」の原子炉構造材から試料採取を実施するため、原子炉本体へのアクセスに接続配管を活用した遠隔試料採取装置の開発・製作を行った。開発した装置による試料採取を安全かつ確実に実施するため、モックアップ試験を行い、実試料採取に着手した。本発表では試料採取モックアップ試験及び実試料採取状況について報告する。
諸岡 聡; 宮本 吾郎*; 大場 洋次郎; 大石 一城*; 高田 慎一
no journal, ,
The formation of carbon clusters (C clusters) has an evidently influence on the mechanical properties of martensitic steels containing carbon atoms. In the present work, the formation of C clusters during low-temperature tempering of Fe-25Ni-0.5C alloy was investigated by means of a combined technique including small angle neutron scattering (SANS) and three-dimensional atom probe tomography (3D-AP). Here, the SANS instrument TAIKAN at J-PARC MLF has installed a large number of detectors with a wide angular range to simultaneously collect SANS patterns with Bragg diffractions. The SANS measurement indicates the evolution of C clusters in a low-temperature-annealed high-Ni-C steel during tempering. The results show that a mean size and the number density of C clusters both increase with an increase in annealing time. In addition, the axis ratio (c/a) of the martensitic phase decreases with an increase of the annealing time. On the other hand, the large scattering of magnetic domain reported by V.M. Nadutov et al. can be observed from initial SANS profile of the austenite single phase. The 3D-AP well describes the formation of C clusters and concentration of carbon elements in the Fe-25Ni-0.5C alloy. In this study, a type of the carbide is identified from the correlation among an average size of C clusters, number density, and carbon atom concentration.
小山 元道*; 北條 智彦*; 宮本 吾郎*; 諸岡 聡; 山下 享介; 澤口 孝宏*; 峯 洋二*; 眞山 剛*; 興津 貴隆*; 榊原 睦海*; et al.
no journal, ,
高強度-高延性鋼を開発するために近年盛んに研究されてきた対象は、高Mn鋼と変態誘起塑性(TRIP)鋼である。高Mn鋼の研究を通して、Mn利用による積層欠陥エネルギーおよび相変態挙動の制御の重要性が再認識された。また、素材コストも睨みながら、従来の延性強度バランスを打破するには、未変態オーステナイトのTRIP効果を利用することが有効であるとの見方も広く受け入れられてきた。これら高Mn鋼とTRIP鋼の研究が合流する形で、TRIP効果を示す中Mn鋼が注目されている。中Mn鋼は優れた延性強度バランスを示す。しかし、複相であること、化学組成や熱処理条件に敏感であること、変形誘起マルテンサイト変態を示すこと、大きなリューダース変形を示すこと、応力ひずみ応答においてセレーションが現れること等に起因して、非常に複雑な塑性変形挙動を呈する。そのため、その優れた力学特性発現の機構は未だ不明瞭である。本講演では、その優れた力学特性の原因を組織発達および塑性変形挙動解析に基づいて明らかとするための研究戦略を示し、その妥当性と応用展開を広く議論する。
)組織中の不均一な炭素分布との熱的安定性の関係渡邊 未来*; 宮本 吾郎*; 諸岡 聡; 古原 忠*
no journal, ,
TRIP鋼では、オーステンパー処理中のベイナイト変態を活用して未変態オーステナイトに炭素を濃化させて安定化し、室温でオーステナイトを残留させている。残留オーステナイトの安定性はその粒径,形態および組成に依存するが、その定量的な理解は進んでいない。そこで、本研究では中性子回折を用いたベイナイト変態中の炭素濃化挙動のその場観察および、FE-EPMAとEBSDの同視野観察により、炭素濃度分布および粒径の不均一性がオーステナイトの熱的安定性に及ぼす関係を調査した。中性子回折の結果として、673K保持におけるオーステナイトの回折プロファイルの変化から、変態後期では、低炭素のオーステナイトが優先的にベイナイト変態することが分かる。一方で、微視組織観察の結果として、粒径の小さいオーステナイトほど炭素濃縮しやすいことがわかる。また、同じ炭素濃度でも粒径が小さいほどオーステナイトとして残留していることから、粒径微細化によるMs点の低下が現れたことが示唆される。
梅田 岳昌*; Zhang, Y.*; 宮本 吾郎*; 古原 忠*; 諸岡 聡
no journal, ,
パーライトは、鋼の共析変態によって得られ、冷却によって生じた駆動力は炭素の拡散や、フェライト/セメンタイトラメラの形成、パーライト/オーステナイト界面の移動に消費されると考えられてきた。実際には、パーライト変態時に生じるひずみや、成長先端における合金元素の分配や界面偏析によっても駆動力が消費され、より複雑なエネルギー散逸が起こっていると推測される。エネルギー散逸によって界面の移動に寄与できる駆動力が減少し、成長速度も遅くなるが、その定量的な理解がパーライト鋼の組織制御において重要である。しかし変態kineticsに影響を及ぼすエネルギー散逸因子の検討はパーライト変態の場合にはあまり行われていない。そこで本研究では、Fe-C-Mn合金をモデル系として選択し、パーライトの成長界面の移動時におけるエネルギー散逸について定量的評価することを目的とした。
梅田 岳昌*; Zhang, Y.*; 宮本 吾郎*; 古原 忠*; 諸岡 聡
no journal, ,
共析変態によって得られるパーライト鋼は、フェライトとセメンタイトが層状に積層した微細なラメラ組織を有し、鉄道用レールやピアノ線、橋梁用ワイヤなどに幅広く用いられる重要な鉄鋼材料である。強度特性と大きく関係するラメラ間隔は、パーライト変態の駆動力および成長速度に依存することから、その制御にはパーライト変態の熱力学的な理解が重要である。パーライト変態の駆動力は炭素拡散、界面移動に伴う摩擦、ラメラ界面形成の3つの素過程に消費されると考えられてきた。しかし近年、フェライト/セメンタイト間の格子ミスフィットによって変態時に弾性ひずみエネルギーが蓄積することで、駆動力が消費されることが報告されている。また合金元素を添加すると、界面近傍における拡散や界面偏析が起こることで実質的な変態の駆動力もさらに変化すると考えられる。変態挙動に影響を与えるこれらの現象には未だ不明点が多く、特に成長界面における合金元素の分布を直接観察した例が少なく、さらに上記因子の効果を定量評価した例もほとんどない。よって本研究では、Fe-C-Mn合金のパーライト成長時の駆動力消費を様々な組織解析技術を用いて解明することを目的とした。その結果、Mn添加材では、/界面でのMn偏析によるソリュートドラッグ効果が最も駆動力を消費する大きな要因であることが示唆され、界面移動に伴う摩擦によるエネルギー散逸や、その場中性子回折実験より評価した変態ひずみの効果など他因子も少なからず影響していることが判明した。
Zhang, Y.*; 梅田 岳昌*; 諸岡 聡; 宮本 吾郎*; 古原 忠*
no journal, ,
Essential understanding of the pearlite growth kinetics is of great significance to predict the lamellar spacing and the resultant mechanical properties of pearlitic steels. In this study, a series of eutectoid steels with Mn addition up to 2mass% were isothermally transformed at a temperature range from 873K to 973K to investigate the growth kinetics and the underlying thermodynamics at the migrating interface during pearlite transformation. The microscopic observation revealed that the pearlite growth rate in each alloy becomes increased while the lamellar spacing becomes decreased by lowering the transformation temperature. Mn addition decelerates the growth rate, accompanied by a relatively wider lamellar spacing at each temperature. After analyzing the element distribution in the vicinity of migrating austenite/pearlite interface via three-dimensional atom probe, Mn was found to be enriched at the austenite/pearlitic ferrite interface, whereas the Mn partitioning among the three phases is negligibly small in the 2mass% Mn added alloy isothermally transformed at 873K. Based on the estimation of energy dissipated by various factors, the driving force for pearlite transformation in the Mn-free alloy was found to be consumed by interface friction, carbon partitioning and ferrite/cementite interfacial energy, whereas neutron diffraction analysis indicated that the influence of transformation strain is relatively small. The retardation effects of pearlite growth kinetics in the Mn-added alloy, which is partly due to the reduced driving force for pearlite transformation, can be well explained by further considering the energy dissipation caused by solute drag effects of Mn.
Zhang, Y.*; 梅田 岳昌*; 宮本 吾郎*; 古原 忠*; 諸岡 聡
no journal, ,
Essential understanding of the pearlite growth kinetics is important to predict the lamellar spacing and the resultant mechanical properties of pearlitic steels. In this study, through quantitatively analyzing the microstructural features in the vicinity of pearlite growth interface, the influence of these factors and the underlying thermodynamics of pearlite growth kinetics were clarified. The pearlite growth rate and lamellar spacing were measured based on the microstructural observation via optical microscopy and scanning electron microscopy, respectively. Three-dimensional atom probe (3DAP) was used to analyze the elemental distribution in the vicinity of pearlite growth front, whereas in-situ neutron diffraction at elevated temperatures was performed at J-PARC, BL19 (TAKUMI) to quantify the elastic strain generated during pearlite transformation. Based on the proposed thermodynamic model, the influence of various factors on the pearlite growth kinetics is estimated using the experimental results obtained in this study. It was found that in most transformation conditions, solute drag effects caused by Mn interfacial segregation have the largest contribution in retarding the pearlite growth rate. In contrast, the magnitude of elastic strain in pearlite measured by neutron diffraction is quite small, which marginally affects the pearlite growth kinetics.
丸澤 賢人*; Zhang, Y.*; 宮本 吾郎*; 古原 忠*; 諸岡 聡
no journal, ,
マルテンサイトの焼もどし過程は反応熱と熱膨張の物性測定結果よると、合金元素添加により反応が遅延される傾向があると報告されているが、ミクロ組織変化との対応には不明な点が多く残されている。本研究では種々の組織解析手法を組み合わせることで、低温焼もどし時の組織変化に及ぼす合金元素添加の影響を解明することを目的とした。測定試料に対して、室温から600
Cまで10C/minの連続加熱中および90Cでの等温保持中のその場中性子回折測定を行った。また種々の温度と時間で焼もどし後のX線回折測定およびミクロ組織観察を行った。中性子回折の結果から、焼入れままの状態では残留オーステナイトのピークが確認され、また強制固溶された炭素により正方晶性(軸比)を有するためマルテンサイトの002回折ピークには明瞭なピーク分離が生じている。一方で、昇温に伴って第2段階の終了温度である300C付近で残留オーステナイトのピークは消失し、またピーク分離は徐々に解消され正方晶性が低下した。この傾向は他の合金材についても同様であった。次に、軸比の変化に着目すると、焼入れままではAl添加材はその他の合金材と比べ、最も高い軸比を有しており、その後遅延効果により第1段階後期まで正方晶性が維持され、200CでFe-C2元合金と一致した。一方でFe-C2元合金と比べ、Mn, Cr添加材の軸比変化はほとんど同様で、Si添加材は第0段階で軸比低下がわずかに促進されるという結果が得られた。
Zhang, Y.*; 丸澤 賢人*; 工藤 航平*; 諸岡 聡; 宮本 吾郎*; 古原 忠*
no journal, ,
As-quenched martensite in carbon steels needs to be tempered to restore its ductility and toughness for practical applications. During tempering, a series of reactions relevant to carbon diffusion are known to occur sequentially, causing changes in microstructure in tempered martensite. In this study, multi-aspect characterization using various advanced characterization techniques were performed, with an aim to clarify the low-temperature tempering behaviors of high-carbon martensitic steels. An Fe-0.8 mass% binary alloy was mainly used in this study, and 4 ternary alloys with further 2 at% addition of Mn, Si, Cr or Al, were also investigated for comparison. All the alloys were water quenched after austenitization to obtain the as-quenched martensite as the starting microstructure. Tempering processes were performed either by continuous heating or isothermal holding under various conditions. Afterwards, the changes in physical properties of tempered martensite were analyzed via calorimetry, dilatometry, and resistometry, whereas the microstructural evolutions were characterized via transmission electron microscopy, in-situ neutron diffraction, and three-dimensional atom probe tomography. The experimental results revealed the continuous occurrence of different tempering stages, including carbon clustering, precipitation of metastable iron carbide, decomposition of retained austenite, and precipitation of cementite. In addition, the tetragonality of martensite became continuously lowered due to the reduction in solute carbon content by tempering. Among all the investigated elements, the addition of Al was found to have the largest retardation effects on the tempering kinetics, which was caused by its suppression effect on carbon diffusivity.
Zhang, Y.*; 宮本 吾郎*; 古原 忠*; 丸澤 賢人*; 工藤 航平*; 諸岡 聡
no journal, ,
In this study, following our previous work on low-temperature tempering kinetics, multi-aspect characterization (in-situ neutron diffraction, TEM and 3DAP) via combining various traditional and advanced experimental approaches was performed, with an aim to thoroughly elucidate the low-temperature tempering behaviors and microstructural evolutions in martensite. As the result, the lattice parameters of a- and c-axes of martensite became increased and decreased, respectively, during continuous heating, resulting in continuous weakening of its tetragonality especially in the temperature range of the 1st stage of 
/-carbide precipitation (340 K 
500 K). On the other hand, the lattice parameter of austenite stopped increasing at 450 K much earlier before the onset of the 2nd stage, indicated the occurrence of carbon depletion.
丸澤 賢人*; 工藤 航平*; Zhang, Y.*; 宮本 吾郎*; 古原 忠*; 諸岡 聡
no journal, ,
The objective of this study is to clarify microstructure evolution during low-temperature tempering of high carbon martensite with addition of various third alloying elements, by particularly focusing the early-stage reactions. Fe-0.8mass%C (Base alloy) and Fe-0.8mass%C-2at%M (M alloy: M = Al, Si, Mn, Cr) were used. The as-quenched specimens were either continuously heated to 873 K at various rates of 5-20 K/min, or isothermally held at various temperatures of 333-453 K, whose kinetics were evaluated by calorimetric, dilatometric and resistometric analyses, respectively. Furthermore, in-situ neutron diffraction experiment and microstructure observation using TEM and 3DAP were conducted. As the result, the tetragonality is found to be gradually decreased during heating, especially in the temperature range of the 1st stage of tempering. Its decreasing rate is strongly retarded by Al addition, whereas the effects of other alloying elements are relatively small. Such effects were also recognized by the calorimetric and dilatometric analyses. In these specimens, heterogeneity in carbon distribution is induced by precipitation of metastable iron carbide. When the 
parameter (deviation from the binomial distribution) is used to evaluate the degree of heterogeneity, a much lower value in the Al alloy than the other alloys indicates retarded carbide precipitation by Al addition. This is also consistent with the smaller reduction in solute carbon content in the Al alloy. By assuming the linear relationship between tetragonality and solute carbon content, this observation corresponds to the retardation effect on decreasing rate of tetragonality.
Harjo, S.; 川崎 卓郎; Gong, W.; 宮本 吾郎*
no journal, ,
Pulsed neutron diffraction with the time-of-flight method is suitable for microscopic structural observation as a bulk average behavior because of the simultaneous measurement of multiple Bragg peaks. The large penetrating power of neutrons also allows in-situ investigation of crystallographic information on engineering materials under various environments, including operando monitoring during deformation at a wide temperature range from cryogenic to high temperatures, thermo-mechanical processes, and so on. The pulsed neutron diffraction with the time-of-flight method will be briefly introduced, and a pulsed neutron diffractometer for engineering materials studies in J-PARC with some highlighted researches using operando observations will be introduced.
