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論文

TRIP effect in a constant load creep test at room temperature

土田 紀之*; Harjo, S.

Proceedings of International Conference on Martensitic Transformations: Chicago, p.43 - 46, 2018/00

In order to investigate TRIP (transformation induced plasticity) effect in different deformation style, a room temperature creep test under the constant load was conducted by using a TRIP-aided multi-microstructure steel. As a result, the volume fraction of deformation-induced martensite in the constant load creep test was larger than that in the tensile test. In situ neutron diffraction experiments during the constant load creep test were performed to discuss its reason. It is found from the in situ neutron diffraction experiments during the constant load creep tests that the phase strain of the austenite phase in the creep tests was larger than that in the tensile tests at the same applied stress.

論文

Martensite phase stress and the strengthening mechanism in TRIP steel by neutron diffraction

Harjo, S.; 土田 紀之*; 阿部 淳*; Gong, W.*

Scientific Reports (Internet), 7(1), p.15149_1 - 15149_11, 2017/11

AA2017-0453.pdf:3.62MB

 被引用回数:30 パーセンタイル:13.23(Multidisciplinary Sciences)

Two TRIP-aided multiphase steels with different carbon contents were analyzed in situ during tensile deformation by time-of-flight neutron diffraction to clarify the deformation induced martensitic transformation behavior and its role on the strengthening mechanism. The difference in the carbon content affected mainly the difference in the phase fractions before deformation, where the higher carbon content increased the phase fraction of retained austenite ($$gamma$$). However, the changes in the relative fraction of martensitic transformation with respect to the applied strain were found to be similar in both steels since the carbon concentrations in $$gamma$$ were similar. The stress contribution from martensite was observed increasing during plastic deformation while that from bainitic ferrite hardly changing and that from $$gamma$$ decreasing.

論文

Room-temperature creep tests under constant load on a TRIP-aided multi-microstructure steel

土田 紀之*; Nagahisa, N.*; Harjo, S.

Materials Science & Engineering A, 700, p.631 - 636, 2017/07

 被引用回数:2 パーセンタイル:87.67(Nanoscience & Nanotechnology)

This study investigated room-temperature creep tests using a low-carbon TRIP steel to clarify the TRIP effect on tensile deformation behavior under constant load. Nominal strain and strain rate increased with an increase in applied stress and those were almost stagnated at holding times of about $$3.0 times 10^4$$ s. The volume fractions of deformation-induced martensite ($$alpha'$$) at a given true strain obtained from constant load creep tests were larger than those from tensile tests. From the in situ neutron diffraction experiments during the constant load creep tests, the phase strain of the austenite ($$gamma$$) phase in the creep tests was found to be larger than that in the tensile tests at the same applied stress. This means that the phase strain or true stress of the $$gamma$$ phase in the TRIP steel was associated with the difference in the volume fraction of $$alpha'$$ between the creep and the tensile tests.

論文

Static tensile deformation behavior of a lean duplex stainless steel studied by in situ neutron diffraction and synchrotron radiation white X-rays

土田 紀之*; 川畑 拓司*; 石丸 栄一郎*; 高橋 明彦*; 鈴木 裕士; 菖蒲 敬久

ISIJ International, 53(7), p.1260 - 1267, 2013/07

 被引用回数:12 パーセンタイル:38.61(Metallurgy & Metallurgical Engineering)

二相ステンレス鋼の引張変形挙動を明らかにするため、中性子と放射光白色X線を利用したその場測定を行った。放射光白色X線の結果から、引張変形中でS32101の硬い相がフェライトからオーステナイトに変化した。これはより大きな力により後半の相へ変化したためであるといえる。中性子実験からは、S32101中のより高い応力下での$$gamma$$相の応力分配が見つかった。ゆえに、S32101中の加工硬化率は$$gamma$$相と$$alpha$$相の応力分配により説明することができる。

論文

TRIP steel deformation behavior by neutron diffraction

Harjo, S.; 土田 紀之*; Gong, W.; 阿部 淳; 相澤 一也

Materials Research Society Symposium Proceedings, Vol.1528 (Internet), 7 Pages, 2013/01

鉄鋼材料の強化機構の中で、高強度,高延性、優れた高速変形挙動が期待されるものにTRIP効果がある。TRIP効果は鉄鋼材料に発現する特徴的な強化機構であり、オーステナイト組織($$gamma$$)の一部が強度の高いマルテンサイト組織($$alpha$$')に変態する(加工誘起変態)ことにより高強度,高延性が得られると言われている。ところが、TRIP効果にもたらす変形中の加工誘起変態挙動, $$gamma$$,フェライト組織($$alpha$$)及び$$alpha$$'組織の役割に関する定量的な研究がほとんどないため、TRIP鋼の変形中のその場中性子回折実験を行った。実験及び結果の詳細を紹介し議論する。

口頭

中性子回折によるTRIP鋼の変形挙動

Harjo, S.; Gong, W.; 阿部 淳; 相澤 一也; 土田 紀之*

no journal, , 

鉄鋼材料の強化機構の中で、高強度,高延性、優れた高速変形挙動が期待されるものにTRIP効果がある。TRIP効果は鉄鋼材料に発現する特徴的な強化機構であり、オーステナイト組織($$gamma$$)の一部が強度の高いマルテンサイト組織($$alpha$$')に変態する(加工誘起変態)ことにより高強度,高延性が得られると言われている。ところが、TRIP効果にもたらす変形中の加工誘起変態挙動,$$gamma$$,フェライト組織($$alpha$$)及び$$alpha$$'組織の役割に関する定量的な研究がほとんどないため、TRIP鋼の変形中のその場中性子回折実験を行った。本発表では実験結果を中心に紹介し、他の手法では得られない知見を議論する。

口頭

加工誘起変態中のTRIP鋼のその場中性子回折

Harjo, S.; 土田 紀之*; Gong, W.; 阿部 淳; 相澤 一也

no journal, , 

2種類のTRIP型複相の炭素鋼、0.4C TRIP鋼及び0.2C TRIP鋼を用意し、室温引張変形中のその場測定をJ-PARC物質・生命科学実験施設(MLF)工学材料回折装置「匠」を用いて行った。試験片を横にして、入射ビームに対して45$$^{circ}$$水平方向に置き、外力を加えて、引張軸方向とその垂直方向からの回折パターンを散乱角2$$theta$$が90$$^{circ}$$のペアの検出器バンクで同時に収集した。引張試験は、弾性域では5分間の段階的な荷重制御、塑性域ではクロスヘッド一定の連続試験を行った。塑性域での回折パターンは実験後に5分間ごとにスライスし、解析を行った。本発表では、得られた実験結果を紹介し、TRIP効果に伴う強化機構及び本試料における炭素量の影響等についての議論を行う。

口頭

Neutron diffraction measurement during stress induced phase transformation

Harjo, S.; 土田 紀之*; 中本 建志*; 相澤 一也; 阿部 淳*; Gong, W.

no journal, , 

Stress Induced Phase Transformation is one of the strengthening mechanisms in steels for the improvement in strength and ductility, which is well known as a TRIP effect. Two kinds of steels, type 304 stainless steel and TRIP-type multiphase carbon steel, were used in neutron diffraction measurements during tensile deformations. The type 304 stainless steel samples were deformed at RT and at 50K. There was no TRIP effect observed during the deformation at RT, while TRIP effects were observed at the onset of plastic region during deformation at 50K. The TRIP-type carbon steel was deformed at RT, and TRIP effects started at the onset of plastic deformation. The phases formed during TRIP effects were determined and stress partitioning among the constituent phases were evaluated. The details will be reported and the strengthening mechanisms of both steels during the TRIP effects will be discussed in the presentation.

口頭

中性子を利用した先端鉄鋼材料の加工誘起相変態挙動の解明

Harjo, S.; 土田 紀之*; 相澤 一也

no journal, , 

鉄鋼材料の強化機構の中で、高強度,高延性、優れた高速変形挙動が期待されるものにTRIP効果がある。TRIP効果は準安定な組織(オーステナイト:A)を有する鉄鋼材料において塑性変形に伴い強度がより高い組織(マルテンサイト:M)に相変態することによって起こる。ところが、TRIP効果にもたらす変形中の加工誘起相変態挙動、すなわち、M相の強度への寄与に関する定量的な研究がほとんどないため、中性子回折法を使って変形中のその場測定を行い解明を試みた。匠は従来の装置に比べて約3倍も分解能が高いため今まで分離が難しかったフェライト母相とM相の回折情報を識別でき、全構成相の相ひずみの観察に成功した。加工誘起相変態で形成されたM相は最も高い応力を負担していることが実証できた。

口頭

Monitoring martensitic transformation and the strengthening behavior during tensile deformation in TRIP steel using neutron diffraction

Harjo, S.; 土田 紀之*; 阿部 淳*; 川崎 卓郎

no journal, , 

TRIP steels contain several tens of percent of metastable retained austenite ($$gamma$$) that transform to martensite ($$alpha$$') during deformation, leading to the improvement of strength and ductility. Deformation induced martensitic transformation behavior and its effect on the strengthening mechanism in two TRIP-aided multiphase steels with different carbon contents (0.2 and 0.4 wt.%) were monitored using in situ neutron diffraction experiments during tensile tests to clarifying the effect of TRIP on the improvement of strength. The results suggest that $$alpha$$' plays an important role in increasing the strength during tensile deformation.

口頭

TRIP behavior observation during creep test using neutron diffraction

Harjo, S.; 土田 紀之*; 川崎 卓郎

no journal, , 

Transformation Induced Plasticity (TRIP) effect is one of important strengthening mechanism of advanced steels, to achieve high strength and relatively large ductility in the same time. TRIP occurs and uses the deformation induced martensitic transformation. It is well known that the retained austenite still exists in TRIP steels near the fracture in tensile deformation. Recently we have found that the amount of transformed martensite was much larger in a creep test under constant load than in tensile deformation of a metastable austenitic 304 steel that shows also TRIP phenomenon. In this study, we will pay attention on crystallographic microstructure properties including dislocation information during tensile and creep deformations, by means of in situ neutron diffraction, to clarify the relationship among martensitic transformation, crystallographic properties and mechanical properties.

口頭

Monitoring martensitic transformation during tensile test in TRIP steels using neutron diffraction

Harjo, S.; 土田 紀之*

no journal, , 

TRIP-aided multiphase steels with different carbon contents were analyzed in situ during tensile deformation by TOF neutron diffraction to clarify the deformation induced martensitic transformation behavior and its role on the strengthening mechanism. The difference in the carbon content affected mainly the difference in the phase fractions, where the higher carbon content increased the fraction of retained austenite ($$gamma$$). However, changes in the relative fraction of martensitic transformation during deformation were found to be similar in both steels. The relative fraction of martensitic transformation increased with increasing of $$gamma$$ phase stress. The martensite phase stress was much larger than that of $$gamma$$ or bainitic ferrite since the martensite was generated at the beginning of plastic deformation. The stress contribution from martensite increased during plastic deformation while that from bainitic ferrite hardly changed and that from $$gamma$$ decreased.

口頭

中性子回折によるTRIP鋼における変形中のマルテンサイト変態の観察

Harjo, S.; 土田 紀之*; 川崎 卓郎; 諸岡 聡

no journal, , 

TRIP鋼のマルテンサイト変態において、ひずみ誘起相変態が支配的であるか、変形中のその場中性子回折によって検証した。引張変形中のその場中性子回折実験をJ-PARCのBL19匠にて実施し、ピーク積分強度, 格子ひずみ等の解析をRietveld法等で行った。マクロ降伏の後にマルテンサイト変態の相対量が増加しはじめ、負荷応力の増加に伴い増加し続けた。この負荷応力にはベイナイト-フェライト及び変態で発生したマルテンサイトも寄与している。また、マルテンサイト変態量に$$gamma$$相応力との相関があることを示唆している。

口頭

Martensitic transformation in metastable iron alloys monitored by neutron diffraction

Harjo, S.; 川崎 卓郎; 土田 紀之*; 諸岡 聡; 相澤 一也

no journal, , 

Transformation induced plasticity (TRIP) phenomenon is paid attention because it gives a high work-hardening rate and a large uniform elongation as a result of deformation induced martensitic transformation during plastic loading. The deformation induced martensitic transformations in most metastable iron alloys occur after macro-yielding during deformation at room temperature (RT). There are arguments to explain whether the martensitic transformation during plastic loading is controlled by strain (the strain-induced transformation) or stress (the stress-assisted transformation). In this paper, we tried to observe the trigger of deformation induced martensitic transformation during tensile deformation by in situ tensile loading neutron diffraction (ND) of metastable iron alloys. In situ ND measurements during deformation have been confirmed as powerful tools to understand the strengthening mechanism during deformation of multiphase alloys.

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