Jun'ya KOBAYASHIAssociate Professor
■Researcher basic information
Organization
- College of Engineering Department of Mechanical Systems Engineering
- Graduate School of Science and Engineering（Master's Program） Major in Mechanical Systems Engineering
- Graduate School of Science and Engineerin（Doctoral Program） Major in Complex Systems Science
- Faculty of Applied Science and Engineering Domain of Mechanical Systems Engineering
Research Areas
Research Keyword
Educational Background
■Research activity information
Award
- Jun. 2022, 日本塑性加工学会新進賞, 塑性加工性および塑性加工を利用したプロセス技術に関する研究, 一般社団法人日本塑性加工学会
小林 純也
Official journal - Nov. 2021, 第39回軽金属奨励賞, 一般社団法人 軽金属学会
小林純也
Japan society - Mar. 2021, 研究奨励賞, 高強度低合金TRIP鋼に関する研究, 一般社団法人日本鉄鋼協会
小林純也
Others - Jan. 2021, 令和３年度 茨城⼤学学⻑学術表彰, 高強度低合金TRIP鋼に関する研究, 国立大学法人 茨城大学
小林純也
Others - 2014, Gilbert R. Speich Award for Best Paper(AIST), Advanced Ultrahigh-Strength TRIP-Aided Martensite Steels for Automotive Applications
Koh-ichi Sugimoto;J. Kobayashi;D.V. Pham
Official journal - 2010, 2010年度 日本機械学会三浦賞, 日本機械学会
Others - 2008, 2008年度 日本機械学会畠山賞, 日本機械学会
Others
Paper
- Warm V-Bendabilites and Hydrogen Embrittlement Properties of Ultrahigh-Strength Quenching and Partitioning-TRIP Steel Sheets
Tomohiko Hojo; Akihiko Nagasaka; Chihaya Tabata; Yuki Shibayama; Junya Kobayashi; Eiji Akiyama, Iron and Steel Institute of Japan
Tetsu-to-Hagane, May 2024, [Reviewed] - Severe plastic deformation for producing Superfunctional ultrafine-grained and heterostructured materials: An interdisciplinary review
Kaveh Edalati; Anwar Q. Ahmed; Saeid Akrami; Kei Ameyama; Valery Aptukov; Rashid N. Asfandiyarov; Maki Ashida; Vasily Astanin; Andrea Bachmaier; Victor Beloshenko; Elena V. Bobruk; Krzysztof Bryła; José María Cabrera; Amanda P. Carvalho; Nguyen Q. Chinh; In-Chul Choi; Robert Chulist; Jorge M. Cubero-Sesin; Gregory Davdian; Muhammet Demirtas; Sergiy Divinski; Karsten Durst; Jiri Dvorak; Parisa Edalati; Satoshi Emura; Nariman A. Enikeev; Ghader Faraji; Roberto B. Figueiredo; Ricardo Floriano; Marjan Fouladvind; Daniel Fruchart; Masayoshi Fuji; Hiroshi Fujiwara; Marcell Gajdics; Diana Gheorghe; Łukasz Gondek; Joaquín E. González-Hernández; Alena Gornakova; Thierry Grosdidier; Jen Gubicza; Dmitry Gunderov; Liqing He; Oscar Fabian Higuera; Shoichi Hirosawa; Anton Hohenwarter; Zenji Horita; Jelena Horky; Yi Huang; Jacques Huot; Yoshifumi Ikoma; Tatsumi Ishihara; Yulia Ivanisenko; Jae-il Jang; Alberto M. Jorge; Mie Kawabata-Ota; Megumi Kawasaki; Tarek Khelfa; Junya Kobayashi; Lembit Kommel; Anna Korneva; Petr Kral; Natalia Kudriashova; Shigeru Kuramoto; Terence G. Langdon; Dong-Hyun Lee; Valery I. Levitas; Cong Li; Hai-Wen Li; Yongtao Li; Zheng Li; Huai-Jun Lin; Klaus-Dieter Liss; Ying Liu; Diana Maritza Marulanda Cardona; Kenji Matsuda; Andrey Mazilkin; Yoji Mine; Hiroyuki Miyamoto; Suk-Chun Moon; MullerTimo Müller; Jairo Alberto Muñoz; Maxim Yu. Murashkin; Muhammad Naeem; Marc Novelli; Dániel Olasz; Reinhard Pippan; Vladimir V. Popov; Elena N. Popova; Gencaga Purcek; Patricia de Rango; Oliver Renk; Delphine Retraint; Ádám Révész; Virginie Roche; Pablo Rodriguez-Calvillo; Liliana Romero-Resendiz; Xavier Sauvage; Takahiro Sawaguchi; Hadi Sena; Hamed Shahmir; Xiaobin Shi; Vaclav Sklenicka; Werner Skrotzki; Nataliya Skryabina; Franziska Staab; Boris Straumal; Zhidan Sun; Maciej Szczerba; Yoichi Takizawa; Yongpeng Tang; Ruslan Z. Valiev; Alina Vozniak; Andrei Voznyak; Bo Wang; Jing Tao Wang; Gerhard Wilde; Fan Zhang; Meng Zhang; Peng Zhang; Jianqiang Zhou; Xinkun Zhu; Yuntian T. Zhu, Elsevier BV
Journal of Alloys and Compounds, May 2024, [Reviewed] - Evaluation of Shear-Punched Surface Layer Damage in Three Types of High-Strength TRIP-Aided Steel
Koh-ichi Sugimoto; Shoya Shioiri; Junya Kobayashi, The damage properties in the shear-punched surface layer, such as the strain-hardening increment, strain-induced martensite fraction, and initiated micro-crack/void characteristics at the shear and break sections, were experimentally evaluated to relate to the stretch-flangeability in three types of low-carbon high-strength TRIP-aided steel with different matrix structures. In addition, the surface layer damage properties were related to the mean normal stress developed on shear-punching and microstructural properties. The shear-punched surface damage of these steels was experimentally confirmed to be produced under the mean normal stress of negative to 0 MPa. TRIP-aided bainitic ferrite (TBF) steel had the smallest surface layer damage, featuring a significantly suppressed micro-crack/void initiation. This was due to the fine bainitic ferrite lath matrix structure, a low strength ratio of the second phase to the matrix structure, and the high mechanical stability of the retained austenite. On the other hand, the surface layer damage of TRIP-aided annealed martensite (TAM) steel was suppressed next to TBF steel and was smaller than that of TRIP-aided polygonal ferrite (TPF) steel. The surface layer damage was also characterized by a large plastic strain, a large amount of strain-induced martensite transformation, and a relatively suppressed micro-crack/void formation, which resulted from an annealed martensite matrix and a large quantity of retained austenite. The excellent stretch-flangeability of TBF steel might be caused by the suppressed micro-crack/void formation and high crack propagation/void connection resistance. The next high stretch-flangeability of TAM steel was associated with a small-sized micro-crack/void initiation and high crack growth/void connection resistance., MDPI AG
Metals, 30 Apr. 2024, [Reviewed] - Effect of Hydrogen on Fatigue Life and Fracture Morphologies of TRIP-Aided Martensitic Steels with Added Nitrogen
Tomohiko Hojo; Akihiko Nagasaka; Junya Kobayashi; Yuki Shibayama; Eiji Akiyama, The effects of hydrogen on the tensile properties, fatigue life, and tensile and fatigue fracture morphologies of nitrogen-added ultrahigh-strength transformation-induced plasticity (TRIP)-aided martensitic (TM) steels were investigated. The total elongation and number of cycles to failure (Nf) of the hydrogen-charged TM steels decreased with the addition of nitrogen; in particular, adding 100 ppm of nitrogen decreased the total elongation and Nf of the TM steels. The quasi-cleavage cracking around the AlN occurred near the sample surface, which is the crack propagation region, although dimples appeared at the center of the fracture surface in the tensile samples. The initial fatigue crack initiated at the AlN precipitate or matrix/AlN interface, located at the notch root. During crack propagation, new cracks were initiated at the AlN precipitates or matrix/AlN interfaces, while quasi-cleavage crack regions were observed around the AlN precipitates. The decrease in the total elongation and Nf of the hydrogen-charged TM steel with 100 ppm of added nitrogen might be attributable to the crack initiation around the AlN precipitates formed by a large amount of hydrogen trapped at the AlN precipitates and matrix/AlN interfaces, and to the dense distribution of AlN, which promoted crack linkage., MDPI AG
Metals, 17 Mar. 2024, [Reviewed] - Visualization of Hydrogen and Hydrogen-induced Defects in Tensile-deformed Pure Iron Using Hydrogen Microprint and Tritium Autoradiography
Toshiaki Manaka; Goroh Itoh; Junya Kobayashi; Shigeru Kuramoto; Yuji Hatano, Iron and Steel Institute of Japan
ISIJ International, 28 Feb. 2024, [Reviewed] - Effect of the Microstructures Adjacent to the Grain Boundaries on the Mechanical Properties and Hydrogen Embrittlement Susceptibilities of Al–Cu Alloys
Yuki Ishii; Junya Kobayashi; Shigeru Kuramoto; Goroh Itoh, Japan Institute of Metals
MATERIALS TRANSACTIONS, 01 Feb. 2024, [Reviewed] - Warm V-Bending and Hydrogen Embrittlement Properties of Ultrahigh-Strength TRIP-Aided Bainitic Ferrite Steel Sheets
Akihiko Nagasaka; Tomohiko Hojo; Junya Kobayashi; Chihaya Tabata
14th International Conference on the Technology of Plasticity ICTP-734 (2023.9), Springer Nature Switzerland AG 2024 K. Mocellin et al. (Eds.): ICTP 2023, LNME, 2024, [Reviewed] - Long Term and in situ Measurements of Nanostructure Evolution of Al-3.9Cu-1.5Mg Alloys by Laboratory High Energy Small-Angle X-Ray Scattering
Shin Fukuda; Masato Ohnuma; Goroh Itoh; Shigeru Kuramoto; Junya Kobayashi; Equo Kobayashi, Elsevier BV
2024 - Effect of alloy compositions and aging conditions on tensile properties of cold-rolled Al-Mg-Si alloys
Hiroki Fukuzawa; Yuki Ishii; Junya Kobayashi; Equo Kobayashi; Masato Ohnuma; Shigeru Kuramoto; Goroh Itoh, Japan Institute of Light Metals
Journal of Japan Institute of Light Metals, 15 Dec. 2023 - Effect of Process Condition and Test Environment on Tensile Properties in Cold-Rolled Al-Cu-Mg Alloys
Yuki Ishii; Junya Kobayashi; Equo Kobayashi; Masato Ohnuma; Shigeru Kuramoto; Goroh Itoh, Severe plastic deformation processing and subsequent aging treatment have been known to be effective for achieving higher strength than the conventional aging treatment in aluminum alloys. This study prepared the Al-Cu-Mg-based alloy sample, Al-5.3Cu-2.8Mg (mass%). The alloys were solution treated at 480, 495 and 505°C, and cold-rolled by 90%. The effect of process condition and test environment on tensile properties in cold-rolled Al-Cu-Mg alloys was investigated. Results confirm that strength and ductility were improved with increasing the solution heat treatment temperature regardless of test environment. 0.2% proof stress and ultimate tensile strength were higher than aging treatment specimens, but elongation to failure was lower than aged one. Hydrogen embrittlement susceptibility increased with increasing solution treatment temperature. Ductile fracture with many dimples is observed in both cold-rolled and aged specimens. Second-phase particles were observed at the bottom of the dimples. There was no significant difference in fracture surface between the different test environments., Trans Tech Publications, Ltd.
Solid State Phenomena, 05 Dec. 2023, [Reviewed] - Effect of Thermomechanical Rolling on Mechanical Properties of TRIP-Aided Steel Sheet
Junya Kobayashi; Taichi Kimura; Shun Kudo; Genta Kojima; Tomohiko Hojo; Shigeru Kuramoto; Goroh Itoh
Materials Science Forum, Dec. 2023, [Reviewed] - Fe-Ni-Al-C 系合金冷間圧延材のリューダース型変形挙動に及ぼすγ相安定性の影響
森 柚和; 河野 悠太; 小林 純也; 倉本 繁; 江村 聡; 澤口 孝宏,The effect of stability of austenite (γ) phase on Lüders-like deformation behavior of cold-rolled Fe-Ni-Al-C alloys was investigated by digital image correlation (DIC) analysis, magnetic measurements and electron backscatter diffraction (EBSD) analysis. In this study, cold-rolled Fe-23Ni-5.0Al-0.5C (mass%) alloy (23Ni alloy) and Fe-25Ni-5.0Al-0.5C (mass%) alloy (25Ni alloy) were used. The tensile strength increased and the total elongation decreased with decreasing Ni content. Lüders-like deformation after yielding was observed up to a nominal strain of approximately 0.04 for the 23Ni alloy and approximately 1.0 for the 25Ni alloy. The transformation from γ to martensite (α') with a specific crystal orientation relationship was observed during tensile deformation, and it was found that the volume fraction of α' during tensile deformation increased more easily in 23Ni alloy than in 25Ni alloy. In addition, the increment of α' phase in 25Ni alloy was higher during Lüders-band propagation than after the band propagation. These results suggested that change of the Lüders-like deformation behavior was due to the change in γ stability.
, 一般社団法人 日本鉄鋼協会
鉄と鋼, 01 Aug. 2023, [Reviewed] - Mechanical Properties and Deformation Behavior in Severely Cold-Rolled Fe-Ni-Al-C Alloys with Lüders Deformation - Overview with Recent Experimental Results -
Shigeru Kuramoto; Yuta Kawano; Yuwa Mori; Junya Kobayashi; Satoshi Emura and Takahiro Sawaguchi, 日本金属学会
Materials Transactions, Jul. 2023, [Reviewed] - Nanoscale Analysis of Solute Distribution in Ultrahigh-Strength Aluminum Alloys
Equo Kobayashi; Masato Ohnuma; Shigeru Kuramoto; Junya Kobayashi and Goroh Itoh, 日本金属学会
Materials Transactions, Jul. 2023, [Reviewed] - 〔Major achievements〕Effects of Partial Replacement of Si by Al on Impact Toughness of 0.2%C-Si-Mn-Cr-B TRIP-Aided Martensitic Steel
K. Sugimoto; Y. Nakashima; J. Kobayashi; and T. Hojo
Metals, Jul. 2023, [Reviewed] - Effects of Thermomechanical Processing on Hydrogen Embrittlement Properties of UltraHigh-Strength TRIP-Aided Bainitic Ferrite Steels
Tomohiko Hojo; Yutao Zhou; Junya Kobayashi; Koh-ichi Sugimoto; Yoshito Takemoto; Akihiko Nagasaka; Motomichi Koyama; Saya Ajito and Eiji Akiyama, The effects of thermomechanical processing on the microstructure and hydrogen embrittlement properties of ultrahigh-strength, low-alloy, transformation-induced plasticity (TRIP)-aided bainitic ferrite (TBF) steels were investigated to apply to automobile forging parts such as engine and drivetrain parts. The hydrogen embrittlement properties were evaluated by conducting conventional tensile tests after hydrogen charging and constant load four-point bending tests with hydrogen charging. The 0.4 mass%C-TBF steel achieved refinement of the microstructure, improved retained austenite characteristics, and strengthening, owing to thermomechanical processing. This might be attributed to dynamic and static recrystallizations during thermomechanical processing in TBF steels. Moreover, the hydrogen embrittlement resistances were improved by the thermomechanical processing in TBF steels. This might be caused by the refinement of the microstructure, an increase in the stability of the retained austenite, and low hydrogen absorption of the thermomechanically processed TBF steels., MDPI AG
Metals, 31 Jan. 2022, [Reviewed] - Effect of 90% cold rolling on precipitation behavior of Al-0.6Mg-1.0Si-0.5Cu alloy
Naoto Kirekawa; Minho O; Jun’ya Kobayashi; Masato Ohnuma; Shigeru Kuramoto; Goroh Itoh; Equo Kobayashi, Since 6000 series aluminum alloys have high hardness based on precipitation strengthening and good corrosion resistance, they are utilized as automobile body sheet panels in the industry. In order to reduce the weight of automobiles, further improvement of hardness is required. To improve the hardness, the process of severe plastic deformation before artificial aging (T8 treatment) was suggested. However, the effect of severe plastic deformation on the precipitation behavior of the alloys is not clear. In this study, 90% cold rolling was conducted for an Al-0.6Mg-1.0Si-0.5Cu alloy as the thermo-mechanical treatment. It was compared that precipitation behavior between T6 and T8 treated alloys by Micro Vickers hardness test, electrical conductivity measurement, differential scanning calorimetry and transmission electron microscopy. As the results, in T8 treated alloys, both precipitation strengthening and recovery softening happened during aging. However, the peak hardness of T8 treatment was larger than that of T6 treatment. The precipitation process was accelerated by lattice defects such as vacancies and dislocations introduced during 90% cold rolling. The precipitations in T8 treatment aged for 10.8 ks were identified as β'', β' and Q'. It was confirmed that β' (Q') phases precipitated directly along dislocations in 90% cold-rolled alloys., Japan Institute of Light Metals
Journal of Japan Institute of Light Metals, 15 Dec. 2021, [Reviewed] - 超高強度アルミニウム合金中の溶質配置のナノスケール解析 : 軽金属奨学会2019年度統合的先端研究の成果
小林 郁夫; 大沼 正人; 倉本 繁; 小林 純也; 伊藤 吾朗, 軽金属学会
軽金属, Dec. 2021 - 〔Major achievements〕Cold Formabilities of Martensite-Type Medium Mn Steel
K. Sugimoto; H. Tanino; and J. Kobayashi, Last, MDPI
Metals, Aug. 2021, [Reviewed] - 〔Major achievements〕Effects of Matrix Structure and Nitrogen Content on Fatigue Properties of Ultrahigh-Strength Low Alloy TRIP-Aided Steels
Tomohiko Hojo; Junya Kobayashi; Koh-ichi Sugimoto; Yoshito Takemoto; Akihiko Nagasaka; Motomichi Koyama; Eiji Akiyama, Iron and Steel Institute of Japan
Tetsu-to-Hagane, Aug. 2021, [Reviewed] - 〔Major achievements〕Effects of Retained Austenite on Hydrogen Embrittlement in TRIP-aided Bainitic Ferrite Steel Sheet
Junya Kobayashi; Ryo Sakata; Naoya Kakefuda; Goroh Itoh; Tomohiko Hojo, Lead, In order to suppress global warming, it is necessary to reduce the weight of autobodies, whereas improvement of the collision safety of automobiles is required which results in a weight increase. Research and development of high-strength steel sheets for autobodies are being carried out to achieve both two objectives. Among various high-strength steel sheets, low alloy steels utilizing transformation-induced plasticity of retained austenite (TRIP-aided steels) have attracted attention as body frame and automotive parts materials because of their high strength and ductility. However, there is concern about hydrogen embrittlement in low alloy TRIP-aided steels with a tensile strength exceeding 1 000 MPa, as in conventional high-strength steels. In this study, in order to reveal the role of retained austenite for hydrogen embrittlement on TRIP-aided bainitic ferrite steel (TBF steel), (i) several TBF steel sheets with different volume fraction and carbon concentration of retained austenite were prepared by austempering the original sheet for different durations, and (ii) slow strain rate technique tensile tests were carried out on hydrogen-charged and uncharged test pieces of the sheets together with microstructure observations and X-ray diffractions. It was revealed that hydrogen embrittlement of TBF steel sheet became suppressed with increasing austempering time, which was attributable to the increase of surface area of lath and/or filmy metastable retained austenite acting as a trapping site for hydrogen., IRON STEEL INST JAPAN KEIDANREN KAIKAN
ISIJ International, Apr. 2021, [Reviewed] - Effects of Matrix Structure and Nitrogen Content on Fatigue Properties of Ultrahigh-Strength Low Alloy TRIP-Aided Steels
Tomohiko Hojo; Junya Kobayashi; Koh-ichi Sugimoto; Yoshito Takemoto; Akihiko Nagasaka; Motomichi Koyama; Eiji Akiyama, To develop ultrahigh-strength steels for automotive impact safety parts, the effects of the microstructure and nitrogen content on the fatigue properties of ultrahigh-strength low alloy transformation-induced plasticity (TRIP)-aided steels with martensite (TM), bainitic ferrite-martensite (TBM), and bainitic ferrite (TBF) matrices were investigated. Compared to TBF steels, both the TM and TBM steels achieved high tensile strength, of more than 980 MPa, and excellent fatigue properties. This results from the suppression of crack propagation due to the effective TRIP of the relatively stable interlath retained austenite and the increase in tensile and yield strengths attributed to the low isothermal transformation treatment. The fatigue strengths of the ultrahigh-strength low alloy TRIP-aided steels were slightly increased by the addition of 100 ppm of nitrogen. The increase in fatigue strength of TM, TBM, and TBF steels with 100 ppm of nitrogen was caused by the fine and uniform martensite and bainitic ferrite matrices and retained austenite, along with the increase in carbon concentration in the retained austenite due to the precipitation of AlN., IRON STEEL INST JAPAN KEIDANREN KAIKAN
ISIJ International, Feb. 2021, [Reviewed] - Effect of Cooling Rate below Ms Temperature on Hydrogen Embrittlement of TRIP-Aided Martensitic Steels
Naoya Kakefuda; Shintaro Aizawa; Ryo Sakata; Junya Kobayashi; Goroh Itoh and Tomohiko Hojo, Corresponding, Trans Tech Publications Ltd.
Materials Science Forum, Jan. 2021, [Reviewed] - 〔Major achievements〕Microstructure and Tensile Properties of TRIP-Aided Steel Sheet Subjected to Hot-Rolling and Austempering
Junya Kobayashi; Hiroto Sawayama; Naoya Kakefuda; Goroh Itoh; Shigeru Kuramoto and Tomohiko Hojo, Lead, Trans Tech Publications Ltd.
Materials Science Forum, Jan. 2021, [Reviewed] - Spinning Formability of Al-Mg-Si Alloy
Shota Seta; Junya Kobayashi and Goroh Itoh, Corresponding, Trans Tech Publications Ltd.
Materials Science Forum, Jan. 2021, [Reviewed] - Suppression of Intergranular Fracture in 7000 Series Aluminum Alloys
Goroh Itoh; Keisuke Hiyama; Bofan Lyu; Junya Kobayashi and Shigeru Kuramoto, Trans Tech Publications Ltd.
Materials Science Forum, Jan. 2021, [Reviewed] - Assessment of hydrogen embrittlement susceptibility of an Al-Cu-Mg alloy in humid air
Toshiaki Manaka; Takahiro Suzuki; Keisuke Hiyama; Junya Kobayashi; Shigeru Kuramoto; Goroh Itoh, In the present study, we investigated the hydrogen embrittlement susceptibility of Al-4%Cu-1.5%Mg alloys subjected to several heat treatments by means of SSRT tensile test and humid gas stress corrosion cracking(HG-SCC) test. For SSRT tensile test, the tensile test pieces were cut from cold-rolled sheets of 1mm thickness. The test pieces were solution-treated at 500 °C for 1h, water-quenched and aged at 140oC for 72h or 360h. SSRT tensile test was performed in two environments, humid air (HA) and dry nitrogen gas (DNG) at a strain rate of 1.39×10-6s-1. Fracture surfaces were observed with a scanning electron microscopy(SEM). For HG-SCC test, compact tension(CT) test pieces were cut from hot-rolled plate of 6mm thickness. The CT test pieces were solution-treated, water-quenched and aged at 190 °C for 9h, 50°C for 96h or 140°C for 72h. HG-SCC test was carried out based on High Pressure Institute of Japan standards; HPIS E103:2018. The pre-cracked CT specimens with stress loading were kept for 90 days in two environments, HA and DNG. After 90 days, in order to observe whether cracks propagated due to HG-SCC, the specimens were loaded up to fracture rapidly, followed by SEM observation. Tensile properties obtained by SSRT tensile tests were almost the same in two environments. Also, fracture surfaces were not affected by test environments. Moreover, in HG-SCC tests, crack propagation was not observed at each test conditions. Therefore, Al-4%Cu-1.5%Mg alloy had high-resistance to hydrogen embrittlement., EDP Sciences
MATEC Web of Conferences, 2020 - Effects of Alloying Elements Addition on Delayed Fracture Properties of Ultra High-Strength TRIP-Aided Martensitic Steels
Tomohiko Hojo; Junya Kobayashi; Koh-ichi Sugimoto; Akihiko Nagasaka; Eiji Akiyama
Metals, Dec. 2019, [Reviewed] - Effects of Cr and Mo on Mechanical Properties of Hot-Forged Medium Carbon TRIP-Aided Bainitic Ferrite Steels
Koh-ichi Sugimoto; Sho-hei Sato; Junya Kobayashi; Ashok Kumar Srivastava
Metals, 30 Sep. 2019, [Reviewed], [Invited] - Al-8%Zn-2%Mg-2%Cu-0.15%Zr合金の強度と水素脆化特性に及ぼす冷間圧延の影響
蓼沼宏樹; 倉本 繁; 小林純也; 伊藤吾朗; 青井一郎; 清水吉広
軽金属, Jun. 2019, [Reviewed] - 7075アルミニウム合金圧延材の引張特性に及ぼす試験雰囲気の影響
中島 祐樹; 倉本 繁; 小林 純也; 伊藤 吾朗; 大石 敬一郎; 青井 一郎; 清水 吉広
軽金属, Nov. 2018, [Reviewed] - Hot spinning formability of aluminum alloy tube
Shunichiro Nakasato; Junya Kobayashi; Goroh Itoh
Procedia Manufacturing, 2018, [Reviewed] - Critical assessment of TRIP-aided bainitic ferrite steels
Koh-ichi Sugimoto; Tomohiko Hojo; Junya Kobayashi, Transformation-induced plasticity (TRIP)-aided bainitic ferrite steels developed for automotive applications have attractive mechanical properties such as ductility, formability, toughness, fatigue strength and delayed fracture strength. These mechanical properties are principally associated with a ductile lath-structure matrix and the strain-induced transformation of the metastable-retained austenite films of 3–20 vol.%. In this paper, data on the microstructural and mechanical properties of the low-carbon TRIP-aided bainitic ferrite steels are critically assessed, as well as their deformation mechanism., Taylor and Francis Ltd.
Materials Science and Technology (United Kingdom), 22 Nov. 2017, [Reviewed] - Warm Formability of 0.2 Pct C-1.5 Pct Si-5 Pct Mn Transformation-Induced Plasticity-Aided Steel
Koh-ichi Sugimoto; Shin-nosuke Hidaka; Hikaru Tanino; Junya Kobayashi, The warm stretch formability and flangeability of 0.2 pct C-1.5 pct Si-5 pct Mn transformation-induced plasticity-aided sheet steel with annealed martensite matrix were investigated for automotive applications. Both formabilities were enhanced by warm forming at peak temperatures of 423 K to 573 K and 423 K to 523 K (150 A degrees C to 300 A degrees C and 150 A degrees C to 250 A degrees C), respectively. The superior warm formabilities were mainly due to the stabilization of a large amount of retained austenite by warm forming and the consequent considerably suppressed void growth at the interface between the matrix and transformed martensite, despite there being large hole punching damage for the stretch flangeability. High peak temperatures for stretch formability and flangeability were associated with apparently increased M (S) of the retained austenite resulting from the increased mean normal stress on stretch forming and hole expansion., SPRINGER
METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE, May 2017, [Reviewed] - Effects of Mn Content on the Warm Stretch-Flangeabiliy of C-Si-Mn TRIP-Aided Steels
Koh-ichi Sugimoto; Shin-nosuke Hidaka; Hikaru Tanino; Junya Kobayashi, Effects of Mn content on warm stretch-flangeability are investigated using 0.2% C-1.5% Si(1.5-5.0)% Mn transformation-induced plasticity (TRIP)-aided sheet steels with annealed martensite matrix. Warm hole-expansion at 150- 250 degrees C after hole-punching at 25 degrees C enhances the stretch-flangeability of 3 and 5% Mn steels. The warm stretchflangeability increases with the Mn content. The superior warm stretch-flangeability of hole-punched 5% Mn steel is caused by its large localized ductility on expanding, which results primarily from the stabilization of its large quantity of retained austenite and its fine microstructure. Use of hole-drilling instead of hole-punching at 25 degrees C further increases the stretch-flangeability and raises the optimum expanding temperature to 250-300 degrees C., WILEY-V C H VERLAG GMBH
STEEL RESEARCH INTERNATIONAL, Mar. 2017, [Reviewed] - Warm ductility of 0.2% C-1.5% Si-5% Mn TRIP-aided steel
Koh-ichi Sugimoto; Hikaru Tanino; Junya Kobayashi, Warm tensile properties of 0.2% C-1.5% Si-5.0% Mn transformation-induced plasticity (TRIP)-aided steel sheets with annealed martensite matrix and retained austenite of 39.4 vol% were investigated for automotive applications. The product of tensile strength and total elongation (TSxTEI) of the TRIP-aided steel was enhanced to 50 GPa% by warm deformation at 150 and 200 degrees C which is significantly higher than that (30 GPa%) required for third generation advanced high-strength steels. The thermal stability of the retained austenite was low, because the low stacking fault energy promotes the epsilon-martensitic transformation. The mechanical stability of the retained austenite, however, increased with an increase in the deformation temperature of the steel, because the epsilon-martensitic and the strain-induced alpha'-martensitic transformations were suppressed with increasing deformation temperature. Therefore, the high value of the TS x TEl of the steel subjected to warm deformation is principally associated with the high volume fraction of the retained austenite and its optimum metastability which maximizes the TRIP effect., ELSEVIER SCIENCE SA
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, Mar. 2017, [Reviewed] - Microstructure and Mechanical Properties of Ultrahigh-Strength TRIP-aided Steels
Koh-ichi Sugimoto; Junya Kobayashi; Tomohiko Hojo, This. paper introduces the microstructure, retained austenite characteristics, strain-induced transformation-deformation mechanism and mechanical properties of transformation-induced plasticity (TRIP)-aided martensitic (TM) steels for the automotive applications. Because the microstructure consists of a wide lath-martensite structured matrix and a mixture of narrow lath-martensite and metastable retained austenite (MA-like phase), the TM steel produced a good combination of tensile strength and cold formability. If Cr and/or Mo were added into 0.2%C-1.5%Si-1.5%Mn steel to enhance its hardenability, the resultant TM steel achieved superior notch fatigue strength and impact and fracture toughness to conventional structural steel such as SCM420. These enhanced mechanical properties were found to be mainly caused by: (I) plastic relaxation of the stress concentration, which results from expansion strain on the strain-induced transformation of the metastable retained austenite; and (2) the presence of a large quantity of finely dispersed MA-like phase, which suppresses crack or void initiation and subsequent connection., IRON STEEL INST JAPAN KEIDANREN KAIKAN
TETSU TO HAGANE-JOURNAL OF THE IRON AND STEEL INSTITUTE OF JAPAN, 2017, [Reviewed] - Spinning workability of Al-Mg-Si alloy extruded tube using the forming die
Fumiya Nanjo; Junya Kobayashi; Goroh Itoh, Spinning processing is used to produce the seamless liner of high-pressure hydrogen gas container. Currently, Al-Mg-Si alloys are applied for the hydrogen high-pressure gas container, where the formation of surface defects such as wrinkles and cracks on the inner surface of the liner is a crucial problem. In this study, spinning is performed on Al-Mg-Si (A6063) alloy by changing processing conditions. Then, surface defects and texture of test pieces affected by processing conditions. The results are followings, in the larger number of spinning pass, good surface properties can be obtained on the contacting surface of the roller. On the other hand, in the smaller number of pass, irregularities on the inner surface, the length of the processed portion, and the reduction of thickness are decreased. The decrease of irregularities on the inner surface may be caused by a small number of continuous deep drawing processes without decreasing thickness.The irregularities on the inner surface of test pieces are reduced by using the forming die., Elsevier Ltd
Procedia Engineering, 2017, [Reviewed] - Formabilities of C-Si-Al-Mn transformation-induced plasticity-aided martensitic sheet steel
Junya Kobayashi; Yumenori Nakashima; Koh-Ichi Sugimoto; Goroh Itoh, The substitution of Si with Al in 0.2%C-1.5%Si-1.25%Mn-0.2%Cr ultrahigh strength transformation-induced plasticity (TRIP)-aided martensitic (TM) sheet steel improves galvanization. The effect of Al content on the microstructure and formabilities of the TM steel was therefore investigated. Replacement of Si with Al maintained the high volume fraction of the retained austenite and the high stretch-formability and stretch-flangeability, whereas it decreased the tensile strength. Complex addition of Si and Al yielded the best formabilities with 1.5 GPa tensile strength grade. The superior formabilities of Si-Al bearing TM steel were attributed to the strain-induced transformation of the metastable retained austenite and the relatively soft lath-martensite structure matrix. The former leads to plastic relaxation of the localized stress concentrations, thus suppressing void formation., Trans Tech Publications Ltd
Materials Science Forum, 2016, [Reviewed] - Deformation characteristics of 6066 and 6069 aluminum alloys at elevated temperatures
Shohei Koizumi; Junya Kobayashi; Goroh Itoh, Currently liners of high-pressure hydrogen storage container for fuel cell vehicles are manufactured from the 6061 aluminum alloy pipes through spinning at elevated temperatures. Since the surroundings of the containers are reinforced with a large amount of high-cost CFRP, the use of 6066 or 6069 aluminum alloy with higher strength than 6061 is demanded to lower the cost of the container. However, the formability of these aluminum alloys at elevated temperatures has not been elucidated yet. In this study, tensile deformation characteristics of 6066 and 6069 aluminum alloys at temperatures ranging from 25 to 550°C were investigated. The total elongation of 6066 aluminum alloy was higher than that of 6069 aluminum alloy at 450°C. This may be caused by the lower volume fraction of constituent particles. The flow stresses of the two alloys were almost the same, and were decreased with increasing testing temperature. The increase in elongation and decrease in strength observed in the two alloys were attributable to dynamic recovery., Trans Tech Publications Ltd
Materials Science Forum, 2016, [Reviewed] - Tensile properties of recrystallized and unrecrystallized tungsten at elevated temperatures
Nobuatsu Tano; Junya Kobayashi; Goroh Itoh; Akira Kurumada; Shingo Mukae, As a fundamental study to prolong the lifetime of tungsten electrode for fusing joining, i.e., a kind of resistance welding for conducting metals such as copper and aluminum, deformation and fracture behaviors have been studied as a function of temperature, strain rate and microstructure. Specimens of recrystallized and unrecrystallized tungsten sheets were tensile-tested at temperatures ranging from 300 to 600°C and at strain rates from 1.4×10-3 to 1.4×10-1s-1 in air. In the recrystallized tungsten tested at 400°C, elongation to failure was decreased from 80% to 10% while yield stress was increased by 50%, when strain rate was increased from 1.4×10-2 s-1 to 1.4×10-1 s-1. This was presumed to be based on the fact that ductile/brittle transition in BCC metal is affected by strain rate as well as temperature, which is attributable to the thermally activated manner of the close slip of screw dislocations. In contrast, in the recrystallized tungsten tested at 600°C, elongation to failure was increased by approximately 10%, when the strain rate was increased from 1.4×10-3 s-1 to 1.4×10-1 s-1. This may be caused by alleviation of some environmental embrittlement, probably associated with oxygen in air. Intergranular fracture took place in almost all conditions within the experiments, even in the unrecrystallized tungsten where majority of the grain boundaries are parallel to the tensile direction., Trans Tech Publications Ltd
Materials Science Forum, 2016, [Reviewed] - Impact properties of low-alloy transformation-induced plasticity-steels with different matrix
T. Hojo; J. Kobayashi; K. Sugimoto, The effects of matrix types on Charpy impact properties were investigated in Fe-0.2% C-1.5% Si-1.5% Mn (mass%) transformation-induced plasticity steels. The steels with annealed martensite and bainitic ferrite matrix possessed higher upper shelf Charpy impact absorbed energy than the steel with polygonal ferrite and martensitic matrix. In addition, the low ductile-brittle fracture appearance transition temperatures were achieved in annealed martensite and martensite types in comparison with those of other steels., TAYLOR & FRANCIS LTD
MATERIALS SCIENCE AND TECHNOLOGY, 2016, [Reviewed] - Impact Toughness of Medium-Mn Transformation-Induced Plasticity-Aided Steels
Koh-ichi Sugimoto; Hikaru Tanino; Junya Kobayashi, The impact toughness of 0.2% C-1.5% Si-(1.5-5.0)% Mn (mass%) transformation-induced plasticity (TRIP)-aided steels with bainitic ferrite and/or martensite structure matrices produced by isothermal transformation process is investigated for automotive body applications. The highest impact toughness, highest Charpy impact absorbed value (CIAV) at 298 K (130 J cm(-2)), and lowest ductile-brittle transformation temperature (DBTT, 203 K) is achieved in 1.5% Mn steel subjected to an isothermal transformation process at a temperature below the martensite start temperature M-S - (50-100) K. An increase in the Mn content results in a small decrease in the CIAV (5-40 J cm(-2)) and an increase in the DBTT (20 K). The highest CIAV of 1.5% Mn steel compared with steels containing higher Mn content is mainly caused by (i) a more softened matrix structure consisting of wide lath-martensite and bainitic ferrite, (ii) a smaller amount of the narrow-lath martensite-retained austenite-like phase, and (iii) more stable retained austenite. The lowest DBTT of 1.5% Mn steel compared with the other steel compositions is mainly associated with the low Mn concentration of the matrix in this steel., WILEY-V C H VERLAG GMBH
STEEL RESEARCH INTERNATIONAL, Oct. 2015, [Reviewed] - Effects of Thermomechanical Processing on Microstructure and Shear Properties of 22SiMnCrMoB TRIP-aided Martensitic Steel
Tomohiko Hojo; Junya Kobayashi; Takuya Kochi; Koh-ichi Sugimoto
Proceedings of The Iron & Steel Technology Conference and Exposition (AISTech2015), 2015, [Reviewed] - Effects of cooling rate on impact toughness of an ultrahigh-strength TRIP-aided martensitic steel
Junya Kobayashi; Yuji Nakajima; Koh Ichi Sugimoto, The effects of variations in the rate of post-austenitization cooling of a 0.2%C-1.5%Si-1.5%Mn-1.0%Cr-0.2%Mo-1.5%Ni-0.05%Nb (mass%) transformation-induced plasticity (TRIP)-aided steel with a lath martensite structure matrix on the Charpy impact toughness were investigated, with the aim of improving the material properties for automotive body applications. When cooled at 1.2°C/s after austenitization, the TRIP-aided steel showed a higher upper-shelf Charpy impact absorbed value (90 J/cm2) and a lower ductile-brittle fracture appearance transition temperature (-126°C), compared with the values determined (82 J/cm2, -98°C) for steel cooled at 53.5°C/s. The lower cooling rate yielded a higher volume fraction and carbon concentration of metastable retained austenite, finer martensite-austenite constituents, and a lower carbide fraction in the wide lath martensite structure in the TRIP-aided steel. These improved microstructural characteristics resulted in superior impact toughness. © (2014) Trans Tech Publications, Switzerland., Trans Tech Publications
Advanced Materials Research, 2014, [Reviewed] - Fracture Toughness of an Advanced Ultrahigh-strength TRIP-aided Steel
Junya Kobayashi; Daiki Ina; Asahiko Futamura; Koh-ichi Sugimoto, The fracture toughness of an advanced ultrahigh-strength 0.2%C-1.5%Si-1.5%Mn-1.0%Cr-0.05%Nb (in mass%) transformation-induced plasticity (TRIP)-aided steel with a bainitic ferrite and/or martensite structure matrix was investigated for applications in automobiles, construction machines, and pressure vessels. After the steel was austenitized and isothermally transformed via heat treatment at temperatures between 200 degrees C and 350 degrees C below the martensite-finish temperature, it exhibited a good combination of tensile strength (1.4 GPa) and total elongation (15%). In addition, the steel achieved a much higher plane-strain fracture toughness (K-IC = 129-154 MPa m(1/2)) than conventional structural steel such as SCM420 steel (K-IC = 57-63 MPa m(1/2)). Surprisingly, the fracture toughness was nearly the same as that of a maraging steel. Our results indicate that the high fracture toughness was associated with (1) a softened wide lath-martensite matrix with a low carbide content and carbon concentration and (2) effective plastic relaxation of localized stress concentration by the strain-induced transformation of fine metastable retained austenite in the narrow lath-martensite and retained austenite mixture, which suppresses void formation and cleavage crack initiation at the pre-crack tip., IRON STEEL INST JAPAN KEIDANREN KAIKAN
ISIJ INTERNATIONAL, 2014, [Reviewed] - Effects of Microalloying on Stretch-flangeability of Ultrahigh-strength TRIP-aided Martensitic Steel Sheets
Duc Van Pham; Junya Kobayashi; Koh-ichi Sugimoto, The effects of Cr, Mo, and Ni addition on the microstructure and stretch-flangeability of a 0.2%C-1.5%Si-1.5%Mn-0.05%Nb (mass%) transformation-induced plasticity (TRIP)-aided martensitic steel sheet produced by an isothermal transformation process at a temperature below martensite transformation-finish temperatures were investigated in order to develop third-generation steel sheet for automobiles requiring high hardenability. When 0.5% or 1.0% Cr was added to the base steel, a tensile strength of 1.5 GPa and a hole-expanding ratio of 40% was attained. On the other hand, the addition of Cr-Mo or Cr-Mo-Ni had a minimal influence on stretch-flangeability and stretch-formability, although it increased the yield and tensile strengths as compared to the base steel. The good balance of the Cr-bearing steel was mainly caused by a suitable combination of (1) volume fraction and (2) interparticle path of a finely dispersed martensite-austenite complex phase, which suppressed void initiation at the matrix/complex-phase interface on hole-punching and void coalescence or crack extension on hole-expanding., IRON STEEL INST JAPAN KEIDANREN KAIKAN
ISIJ INTERNATIONAL, 2014, [Reviewed] - The Effects of Cooling Rate on Retained Austenite Characteristics of a 0.2C-1.5Si-1.5Mn-1.0Cr-0.05Nb TRIP-aided Martensitic Steel
Koh-ichi Sugimoto; Junya Kobayashi; Yuji Nakajima
Materials Science Forum, 2014, [Reviewed] - Fracture Toughness of Advanced TRIP-Aided Martensitic Steels
Koh-ichi Sugimoto; Junya Kobayashi; Daiki Ina, The effects of microalloying on the fracture toughness of 0.2%C-1.5%Si-1.5%Mn -0.05%Nb (mass%) transformation-induced plasticity-aided steel with a lath-martensite structure matrix were investigated. When 0.002% B or 1.0% Cr was added to the base steel, the steel achieved a fracture toughness that was as high as that of 18%Ni maraging steel. Based on our results, the high fracture toughness was essentially caused by (i) a matrix with a softened lath-martensite structure, low carbide content and low carbon concentration; (ii) the effective plastic relaxation of localized stress concentration by the strain-induced transformation of metastable retained austenite of about 3 vol% in the martensite-austenite constituent or phase., TRANS TECH PUBLICATIONS LTD
Key Engineering Materials, 2014, [Reviewed] - Cold formability of 22SiMnCrB TRIP-aided martensitic sheet steel
Junya Kobayashi; Hiroki Tonegawa; Koh-ichi Sugimoto, This study investigates whether the transformation-induced plasticity (TRIP) of metastable retained austenite, and a finely dispersed MA-like phase (narrow-lath martensite-retained austenite complex phase), produced by the addition 1.5% Si or 1.5% Si-1.0% Cr (mass%) can improve the cold formability of 22MnB martensitic sheet steel. The best combination of tensile strength and formability was achieved with 22SiMnCrB steel that was subjected to isothermal transformation at a temperature between 25 and 250 degrees C after austenitizing. This optimal combination is attributed to strain-induced transformation of metastable retained austenite in the MA-like phase, which subsequently leads to plastic relaxation of localized stress concentrations. (C) 2014 The Authors. Published by Elsevier Ltd., ELSEVIER SCIENCE BV
Procedia Engineering, 2014, [Reviewed] - Mechanical Properties of TRIP-aided Martensitic Steels for Hot-Worked Automotive Drivetrain Components
Koh-ichi Sugimoto; Junya Kobayashi; Tomohiko Hojo
Proceedings of 4th International Conference on Steels in Cars and Trucks, (June 15-19, 2014), 2014, [Invited] - Stretch-flangeability of 0.2%C–1.5%Si–(1.5–5)%Mn TRIP-aided martensitic steels
Koh-ichi Sugimoto; Hikaru Tanino; Junya Kobayashi
Proceedings of Materials Science and Technology 2014 (MS&T 2014), 2014, [Reviewed] - Effects of Microalloying on the Impact Toughness of Ultrahigh-Strength TRIP-Aided Martensitic Steels
Junya Kobayashi; Daiki Ina; Yuji Nakajima; Koh-Ichi Sugimoto, The effects of the addition of Cr, Mo, and/or Ni on the Charpy impact toughness of a 0.2 pct C-1.5 pct Si-1.5 pct Mn-0.05 pct Nb transformation-induced plasticity (TRIP)-aided steel with a lath-martensite structure matrix (i.e., a TRIP-aided martensitic steel or TM steel) were investigated with the aim of using the steel in automotive applications. In addition, the relationship between the toughness of the various alloyed steels and their metallurgical characteristics was determined. When Cr, Cr-Mo, or Cr-Mo-Ni was added to the base steel, the TM steel exhibited a high upper-shelf Charpy impact absorbed value that ranged from 100 to 120 J/cm(2) and a low ductile-brittle fracture appearance transition temperature that ranged from 123 K to 143 K (-150 A degrees C to -130 A degrees C), while also exhibiting a tensile strength of about 1.5 GPa. This impact toughness of the alloyed steels was far superior to that of conventional martensitic steel and was caused by the presence of (i) a softened wide lath-martensite matrix, which contained only a small amount of carbide and hence had a lower carbon concentration, (ii) a large amount of finely dispersed martensite-retained austenite complex phase, and (iii) a metastable retained austenite phase of 2 to 4 vol pct in the complex phase, which led to plastic relaxation via strain-induced transformation and played an important role in the suppression of the initiation and propagation of voids and/or cleavage cracks., SPRINGER
METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE, Nov. 2013, [Reviewed] - Effects of Microalloying on Stretch-flangeability of TRIP-aided Martensitic Sheet Steel
Duc Van Pham; Junya Kobayashi; Koh-ichi Sugimoto, The effects of Cr, Mo and Ni additions on the microstructure and stretch-flangeability of 0.2%C-1.5%Si-1.5%Mn-0.05%Nb, in mass%, TRIPaided martensitic sheet steel produced by isothermal transformation process at a temperature below martensite-finish temperatures were investigated to develop the 3rd-generation sheet steel for automobile requiring high hardenability. When 0.5% or 1.0% Cr was added to the base steel, the combination of tensile strength of 1.5 GPa and hole-expanding ratio of 40% was attained. On the other hand, the Cr-Mo or Cr-MoNi addition hardly influenced the stretch-flangeability and stretch-formability, although it increased the yield and tensile strengths, comparing to the base steel. The good balance of Cr-bearing steel was mainly caused by suitable combination of (1) volume fraction and (2) interparticle path of finely dispersed martensite-austenite complex phase (M-A phase), which suppressed a void initiation at the matrix/M-A phase interface on hole-punching and void coalescence or crack extension on hole-expanding., IRON STEEL INST JAPAN KEIDANREN KAIKAN
TETSU TO HAGANE-JOURNAL OF THE IRON AND STEEL INSTITUTE OF JAPAN, 2013, [Reviewed] - Notch-fatigue Strength of Advanced TRIP-aided Martensitic Steels
Junya Kobayashi; Nobuo Yoshikawa; Koh-ichi Sugimoto, The notch-fatigue limit and notch sensitivity of 0.1-0.6%C-1.5%Si-1.5%Mn transformation-induced plasticity (TRIP)-aided martensitic steels (TM steels) were investigated for use as common rails in next-generation automotive diesel engines. Also, these properties were related to the microstructural and retained austenite characteristics. When TM steels containing 0.2% to 0.4% C were subjected to heat treatment for isothermal transformation at 50 degrees C and subsequent partitioning at 250 degrees C, the steels achieved much higher notch-fatigue limits and lower notch sensitivities than those of conventional 0.2-0.4%C-1.0%Cr-0.2%Mo structural steels. This was principally associated with (i) plastic relaxation of localized stress concentration as a result of strain-induced transformation of 3-5 vol% metastable retained austenite and (ii) a large amount of finely dispersed martensite-austenite phase along prior austenitic, packet and block boundaries, as well as (Hi) a small amount of carbide only in the wide lath-martensite structure, which may contribute to making fatigue crack initiation and/or propagation difficult., IRON STEEL INST JAPAN KEIDANREN KAIKAN
ISIJ INTERNATIONAL, 2013, [Reviewed] - TRIP型マルテンサイト鋼板の伸びフランジ性に及ぼす合金元素添加の影響
ファム バン ドック; 小林 純也; 杉本 公一, Corresponding, The Iron and Steel Institute of Japan
鉄と鋼, 2013, [Reviewed] - Advanced Ultrahigh-Strength TRIP-aided Martensitic Sheet Steels for Automotive Applications
Koh-ichi Sugimoto; Junya Kobayashi, Association for Iron & Steel Technology, Warrendale, PA, USA
Proceedings on the International Symposium on New Developments in Advanced High Strength Sheet Steels (AIST 2013), 2013, [Reviewed] - Hydrogen Embrittlement Properties of Ultra High-Strength Low Alloy TRIP-Aided Steels with Hot Forging Process
Tomohiko Hojo; Junya Kobayashi; 他5名, The Chinese for Metals, China
Proceedings of The 2nd International Symposium on Automobile Steel (ISAS2013), 2013, [Reviewed] - Fatigue Properties of Nitrogen Added Ultra High-Strength Low Alloy TRIP-Aided Steels
Tomohiko Hojo; Junya Kobayashi; Koh-ichi Sugimoto
Proceedings of Materials Science & Technology 2013 Conference (MS&T’2013), 2013, [Reviewed] - Effects of Cr and Mo on Retained Austenite Characteristics and Tensile Properties of TRIP-aided Annealed Martensitic Steel
Junya Kobayashi; Nobuo Yoshikawa; Toshio Murakami; Koh-ichi Sugimoto, The effects of Cr and Mo on microstructure, retained austenite characteristics and tensile properties of a 0.2%C, 1.5%Si, 1.5%Mn, 0.05%Nb TRIP-aided steel with annealed martensite matrix, "TRIP-aided annealed martensitic steel; TAM steel", were investigated to enhance the hardenability. Volume fraction and carbon concentration of retained austenite were decreased with increasing hardenability, although the volume fraction was increased in a 0.5% Cr bearing steel. Simultaneously, blocky second phase consisting of carbon-enriched martensite and retained austenite increased with increasing hardenability. These interesting characteristics were mainly caused by preferential nucleation of austenite on prior austenitic grain and packet boundaries on intercritical annealing and delayed bainitic transformation during austempering. Tensile strength of the steels was increased with increasing hardenability, accompanied with the decreased yield stress. Combination of tensile strength and total elongation decreased with increasing hardenability due to the increased blocky second phase., IRON STEEL INST JAPAN KEIDANREN KAIKAN
TETSU TO HAGANE-JOURNAL OF THE IRON AND STEEL INSTITUTE OF JAPAN, Nov. 2012, [Reviewed] - Notch-Fatigue Properties of Advanced TRIP-Aided Bainitic Ferrite Steels
Nobuo Yoshikawa; Junya Kobayashi; Koh-ichi Sugimoto, To develop a transformation-induced plasticity (TRIP)-aided bainitic ferrite steel (TBF steel) with high hardenability for a common rail of the next generation diesel engine, 0.2 pct C-1.5 pct Si-1.5 pct Mn-0.05 pct Nb TBF steels with different contents of Cr, Mo, and Ni were produced. The notch-fatigue strength of the TBF steels was investigated and was related to the microstructural and retained austenite characteristics. If Cr, Mo, and/or Ni were added to the base steel, then the steels achieved extremely higher notch-fatigue limits and lower notch sensitivity than base TBF steel and the conventional structural steels. This was mainly associated with (1) carbide-free and fine bainitic ferrite lath structure matrix without proeutectoid ferrite, (2) a large amount of fine metastable retained austenite, and (3) blocky martensite phase including retained austenite, which may suppress a fatigue crack initiation and propagation., SPRINGER
METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE, Nov. 2012, [Reviewed] - Fracture toughness of A 1.5 GPa grade C-Si-Mn-Cr-Nb trip-aided martensitic steel
Junya Kobayashi; Daiki Ina; Koh-Ichi Sugimoto, Fracture toughness of an ultrahigh-strength TRIP-aided steel with lath-martensite structure matrix or "a TRIP-aided martensitic steel" was investigated for some applications to automobiles, construction machines, ships and so on. When the steel with a chemistry of 0.2%C, 1.5%Si, 1.5%Mn, 1.0%Cr and 0.05%Nb (in mass%) was subjected to partitioning at 200 through 350°C after quenching, much higher fracture toughness (139-166 MPa.m 1/2) than a conventional structural SCM420 steel (57-63 MPa.m 1/2) was achieved with a tensile strength of 1.47-1.56 GPa GPa. The fracture toughness was the same level as those of typical maraging steels and was superior to "a TRIP-aided bainitic ferrite steel". The superior fracture toughness was associated with (1) softening of wide lath-martensite matrix, (2) a large amount of M-A constituent on prior austenitic grain, packet and block boundaries, (3) metastable retained austenite of 2-3 vol% in the M-A constituent, and (4) a small amount of fine carbide, which suppress a cleavage fracture.
AIST Steel Properties and Applications Conference Proceedings - Combined with MS and T'12, Materials Science and Technology 2012, 2012 - Microstructure and Retained Austenite Characteristics of Ultra High-strength TRIP-aided Martensitic Steels
Junya Kobayashi; Sung-Moo Song; Koh-ichi Sugimoto, A new type of 0.2%C-1.5%Si-1.5%Mn ultra high-strength low alloy TRIP-aided steel consisting of lath martensite structure matrix and metastable retained austenite films, "TRIP-aided martensitic steel; TM steel", was developed by means of quenching and partitioning process. In addition, effects of partitioning temperature and time on the microstructure and retained austenite characteristics were investigated. The matrix structure was composed of two kinds of lath martensite structures, or wide and narrow lath martensite structures. Most of the retained austenite of about 3 vol% was located along the narrow martensite lath boundary. On the other hand, a small amount of fine and needle-like carbides precipitated only in wider lath martensite structure. Partitioning at temperatures lower than 250 degrees C for 1 000 s after quenching in oil or ice brine considerably increased carbon concentration of the retained austenite phase to about 1.0 mass%, maintaining volume fractions of retained austenite and carbide. Also, the carbon-enrichment mechanism in the retained austenite was proposed through TEM observation, as well as the carbide precipitation and coarsening mechanisms., IRON STEEL INST JAPAN KEIDANREN KAIKAN
ISIJ INTERNATIONAL, 2012, [Reviewed] - Effects of the Addition of Cr, Mo and Ni on the Microstructure and Retained Austenite Characteristics of 0.2% C-Si-Mn-Nb Ultrahigh-strength TRIP-aided Bainitic Ferrite Steels
Junya Kobayashi; Daiki Ina; Nobuo Yoshikawa; Koh-ichi Sugimoto, Cr, Mo and/or Ni were added to TRIP-aided bainitic ferrite (TBF) steel (0.2% C, 1.5% Si, 1.5% Mn and 0.05% Nb ultrahigh-strength TBF steel) in order to increase its hardenability. In addition, the effects of the alloying elements on the Vickers hardness, microstructure and retained austenite characteristics of the TBF steels were investigated. When the TBF steels were austempered at temperatures between M-S and M-f, the Vickers hardness increased from HV300 to HV430 with increasing hardenability. The microstructure consisted of martensite and bainitic ferrite lath structures and retained austenite phases and the volume fraction of retained austenite increased with increasing hardenability. Conversely, the carbon concentration of the retained austenite decreased with increasing hardenability. Simultaneously, the quantity of the hard blocky martensite phase (M-A constituent) with refined interlath retained austenite films increased with increasing hardenability. These characteristics are mainly caused by the delayed bainite transformation during austempering through the addition of Cr, Mo and/or Ni. The addition of Ni lowered the To line further. The retained austenite phases of Cr- and/or Mo-bearing TBF steels were relatively stable against straining, despite their low carbon concentrations., IRON STEEL INST JAPAN KEIDANREN KAIKAN
ISIJ INTERNATIONAL, 2012, [Reviewed] - TRIP型焼鈍マルテンサイト鋼の残留オーステナイト特性と引張特性に及ぼすCrとMoの影響
小林 純也; 吉川 伸麻; 村上 俊夫; 杉本 公一, Lead, The Iron and Steel Institute of Japan
鉄と鋼, 2012, [Reviewed] - Effects of hot-forging process on combination of strength and toughness in ultra high-strength TRIP-aided martensitic steels
Junya Kobayashi; Koh-Ichi Sugimoto; Goro Arai, Recently developed ultra high-strength low alloy transformation-induced plasticity (TRIP)-aided steel with martensitic lath structure matrix or "TRIP-aided Martensitic steel
TM steel" possesses a high impact toughness. In this study, to apply the TM steel to some hot-forging parts, the effects of hot-forging on microstructure, retained austenite characteristics, tensile properties and toughness in the TM steels with chemical composition of 0.3-0.4%C, 1.5%Si, 1.5%Mn, 0.002%B, 0.02Ti, 0.05Nb (mass%) were investigated. The hot forging brought on an excellent combinations of tensile strength of 1500-2000 MPa or 0.2% offset proof stress of 1200-1560 MPa and Charpy impact absorbed value of 35-80 J/cm 2 when partitioned at 250-350°C after quenching in oil. The combinations exceeded so much those of the conventional quench and tempering structural steels. From examinations of microstructure and retained austenite characteristics, it was found that the excellent combinations are mainly caused by (i) refined and uniform martensitic lath structure matrix with a small amount of carbide, (ii) increasing narrow martensite with high dislocation density and (iii) the increased stability of retained austenite, resulting from the FQP process. © (2012) Trans Tech Publications, Switzerland.
Advanced Materials Research, 2012, [Reviewed] - Stretch Flangeability and Bendability of a 0.2C-1.5Si-1.5Mn-0.05Nb Ultrahigh-Strength TRIP-Aided Martensitic Sheet Steel
Junya Kobayashi; Duc Van Pham; Koh-ichi Sugimoto
Steel Research International, 2012, [Reviewed] - Fracture Toughness of a 1.5GPa Grade C-Si-Mn-Cr-Nb TRIP- Aided Martensitic Steels
Junya Kobayashi; Daiki Ina; Koh-ichi Sugimoto, MS&T Partner Societies, Pittsburgh, PA, USA
Proceedings of Materials Science and Technology 2012 (MS&T2012), 2012, [Reviewed] - Hydrogen Embrittlement Resistances of Alloying Elements Adding Ultra High Strength Low Alloy TRIP-aided Steels
Tomohiko Hojo; Junya Kobayashi; Koh-ichi Sugimoto, MS&T Partner Societies, Pittsburgh, PA, USA
Proceedings of Materials Science and Technology 2012 (MS&T2012), 2012, [Reviewed] - Stretch-flangeability of 1.5GPa Grade TRIP-aided Martensitic Cold Rolled Sheet Steels
Junya Kobayashi; Duc Van Pham; Koh-ichi Sugimoto
Steel Research International, 2011, [Reviewed] - Stretch-flangeability of Ultra High-strength Low Alloy TRIP-aided Sheet Steels with Mixed Structure Matrix of Bainitic Ferrite and Martensite
Muneo MURATA; Junya KOBAYASHI and Koh-ichi SUGIMOTO, The microstructure, retained austenite characteristics, tensile properties and stretch-flangeability of ultra high-strength 0.2%C-1.5%Si-1.5%Mn (mass%) TRIP-aided bainitic ferrite cold-rolled sheet steel, "TBF steel", were investigated for automotive applications. When isothermally held at temperatures less than martensite-start temperature for 300-3000 s after annealing or austenitizing, the TBF steel possessed mixed matrix structure of bainitic ferrite and martensite, with retained austenite of about 4 vol%. The TBF steel achieved the tensile strength higher than 1400 MPa and hole-expanding ratio of 40%. The good combination of tensile strength and hole-expanding ratio was mainly Caused by highly carbon-enriched retained austenite and softened matrix structure composing of bainitic ferrite and martensite., IRON STEEL INST JAPAN KEIDANREN KAIKAN
TETSU TO HAGANE-JOURNAL OF THE IRON AND STEEL INSTITUTE OF JAPAN, 2010, [Reviewed] - Development of Ultra High-Strength Low Alloy TRIP-Aided Steel for Hot-Forging Parts
Koh-ichi Sugimoto; Junya Kobayashi; Goro Arai, An ultra high-strength TRIP-aided steel consisting of bainitic ferrite lath structure matrix and interlath retained austenite films possesses high toughness and fatigue strength, as well as high resistance against hydrogen embrittlement. In this study, to develop the ultra high-strength TRIP-aided steel for hot-forging parts, the effects of hot-forging and subsequent austempering process on the microstructure, retained austenite characteristics, tensile properties and impact toughness of 0.2% C-1.5% Si-1.5% Mn-Cr-Mo-B TRIP-aided steels were investigated. The process achieved an excellent combination of yield strength of 700-800MPa and Charpy impact absorbed value of 110-130 J/cm(2) in these steels, as well as a good balance of yield strength and total elongation when subjected to austempering at temperatures between 325 degrees C and 375 degrees C below martensite-start temperature (Ms). These combinations exceeded so much those of the steel subjected to the conventional austempering without hot-forging. From examinations of microstructure and retained austenite characteristics, it was found that these combinations are mainly caused by (i) refined mixed structure of bainitic ferrite and retained austenite without pro-eutectoid ferrite (ii) high uniformity of the mixed structure and (iii) the increased volume fraction of metastable retained austenite., WILEY-V C H VERLAG GMBH
Steel Research International, 2010, [Reviewed] - Newly Developed TRIP-aided Martensitic Steels
Koh-ichi Sugimoto; Junya Kobayashi, The Minerals, Metals & Materials Society (TMS), Warrendale, PA, USA
Materials Science & Technology 2010 Conference & Exhibition (Recent Developments in Steel Processing), 2010, [Reviewed] - Toughness of Ultra High-Strength TRIP-Aided Steels with high Hardenability
Koh-ichi Sugimoto; Junya Kobayashi; Daiki Ina, Metallurgical Industry Press, Beijing, China, Abstract and Manuscript
The International Conference on Advanced Steels 2010 (ICAS 2010), 2010, [Reviewed]
MISC
- Mechanical Properties and Deformation Behavior in Severely Cold-Rolled Fe-Ni-Al-C Alloys with Lüders Deformation -Overview with Recent Experimental Results -
Shigeru Kuramoto; Yuta Kawano; Yuwa Mori; Junya Kobayashi; Satoshi Emura; Takahiro Sawaguchi
Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals, 2025 - History of microstructural control and some recent topics aiming strengthening of aluminum alloys
G. Itoh; S. Kuramoto; J. Kobayashi
Journal of the Japan Institute of Light Metals, Dec. 2023, [Reviewed] - 圧縮水素容器用アルミニウム合金の湿潤ガス応力腐食割れ試験方法
伊藤吾朗; 倉本 繁; 車田 亮; 小林純也; 浅見重則; 小川武史
圧力技術, 2019 - 超高強度低合金TRIP鋼の組織と機械的性質
杉本公一; 小林純也; 北條智彦
鉄と鋼, 2017, [Invited] - Hydrogen Embrittlement Properties of 0.2-0.4%C Ultra High-Strength TRIP-Aided Bainitic Ferrite Steels with Hot Forging Process
北條 智彦; 小林 純也; 山本 浩介
材料とプロセス 日本鉄鋼協会 編, 17 Sep. 2013 - Hydrogen Embrittlement Properties of Cr added Ultra High-Strength TRIP-Aided Martensitic Steels
北條 智彦; 小林 純也; 杉本 公一
材料とプロセス 日本鉄鋼協会 編, 17 Sep. 2013 - 317 Delayed Fracture Properties of Nitrogen Added Ultra High Strength Low Alloy TRIP-Aided Sheet Steels
HOJO Tomohiko; KOBAYASHI Junya; SUGIMOTO Koh-ichi
講演論文集, 28 Feb. 2012 - 713 Fatigue Properties of Nitrogen added Ultra High Strength Low Alloy TRIP-Aided Sheet Steels
HOJO Tomohiko; KOBAYASHI Junya; SUGIMOTO Koh-ichi
学術講演会講演論文集, 2012
Lectures, oral presentations, etc.
- 高強度低合金TRIP鋼に関する研究
小林純也
令和３年度茨城⼤学学⻑学術表彰 表彰式及び受賞記念講演会, 26 Jan. 2022, 茨城大学, [Invited]
20220126, 20220126 - アルミニウム合金の塑性加工と水素脆化特性
小林純也
一般社団法人 軽金属学会 創立70周年記念 第141回秋期大会, 14 Nov. 2021, 一般社団法人 軽金属学会, [Invited]
20211114, 20211114 - 高強度低合金TRIP鋼に関する研究
小林純也
一般社団法人 日本鉄鋼協会 第181回春季講演大会, 17 Mar. 2021, 一般社団法人 日本鉄鋼協会, [Invited]
20210317, 20210319 - 学生が運営するファブラボ鋳造クラブ構想
益子 雄行; 伊藤 伸英; 伊藤 吾朗; 小林 純也
精密工学会学術講演会, 2017, 精密工学会 - 難燃性マグネシウム合金の疲労特性評価
橋本 拳志; 山田 隆一; 鬼澤 海; 伊藤 吾朗; 車田 亮; 倉本 繁; 小林 純也; 伊藤 友美; 野田 雅史
茨城講演会, 2017, 日本機械学会関東支部 - Al-Mg-Si 合金の耐湿潤ガス応力腐食割れ特性に及ぼす Pb,Bi の影響
杢家 弘樹; 青島 翔平; 秋篠 亮太; 大渕 知之; 車田 亮; 伊藤 吾朗; 倉本 繁; 小林 純也
茨城講演会, 2017, 日本機械学会関東支部 - 冷間圧延した 7000 系アルミニウム合金の機械的特性
蓼沼 宏樹; 中島 祐樹; 小林 純也; 倉本 繁; 伊藤 吾朗; 青井 一郎; 清水 吉広
茨城講演会講演論文集, 2017, 一般社団法人 日本機械学会 - Al-Mg-Si 合金の耐湿潤ガス応力腐食割れ特性に及ぼす主成分の影響
大渕 知之; 秋篠 亮太; 青島 翔平; 杢家 弘樹; 車田 亮; 伊藤 吾朗; 倉本 繁; 小林 純也
茨城講演会講演論文集, 2017, 一般社団法人 日本機械学会 - SSRT 試験法による難燃性マグネシウム合金の水素脆化特性の評価
佐野 亮太; 井出 一平; 伊藤 吾朗; 倉本 繁; 小林 純也; 伊藤 友美; 野田 雅史
茨城講演会講演論文集, 2017, 一般社団法人 日本機械学会 - トリチウムオートラジオグラフィによる金属材料中の水素の挙動解析
伊藤吾朗; 小林純也; 真中俊明; 波多野雄治
2017 - 414 冷間加工したSUS301鋼の機械的特性(OS4-(4),OS4 オーガナイズドセッション≪材料・組織と加工≫)
沼賀 慎; 倉本 繁; 小林 純也
茨城講演会講演論文集 : Ibaraki district conference, 27 Aug. 2015, 一般社団法人日本機械学会 - 421 6000系アルミニウム合金の長期負荷割れ(OS4-(5),OS4 オーガナイズドセッション≪材料・組織と加工≫)
青島 翔平; 楊 帆; 望月 健吾; 伊藤 吾朗; 車田 亮; 小林 純也
茨城講演会講演論文集, 2015, 一般社団法人 日本機械学会 - 418 高圧水素貯蔵容器用アルミニウム合金のスピニング加工性(OS4-(4),OS4 オーガナイズドセッション≪材料・組織と加工≫)
南條 郁弥; 小泉 彰平; 小林 純也; 伊藤 吾朗
茨城講演会講演論文集, 2015, 一般社団法人 日本機械学会 - 高圧水素貯蔵容器用アルミニウム合金の高温変形特性に関する研究
小林純也
茨城大学工学部付属教育研究センター 公開シンポジウム, 2014 - Effects of Aluminum and Niobium on Impact Properties of Ultra High-Strength TRIP-aided Bainitic Ferrite Steels
HOJO Tomohiko; KOBAYASHI Junya; KAJIYAMA Tomohiro
津山工業高等専門学校紀要, 2012, 津山工業高等専門学校 - 317 窒素添加した超高強度低合金TRIP鋼板の遅れ破壊特性(機械材料・材料加工III)
北條 智彦; 小林 純也; 杉本 公一
中国四国支部総会・講演会 講演論文集, 2012, 一般社団法人 日本機械学会 - 713 N添加超高強度低合金TRIP鋼板の疲労特性(疲労強度特性,疲労損傷観察ならびに強度評価,オーガナイスドセッション1)
北條 智彦; 小林 純也; 杉本 公一
学術講演会講演論文集, 2012, 日本材料学会
Courses
- Apr. 2022 - Present
茨城大学大学院 理工学研究科 - Apr. 2020 - Present
茨城大学 工学部 機械システム工学科 - Apr. 2020 - Present
茨城大学 工学部 機械システム工学科 - Apr. 2020 - Present
茨城大学 工学部 機械システム工学科 - Apr. 2019 - Present
茨城大学 工学部 機械システム工学科 - Apr. 2015 - Present
茨城大学大学院 理工学研究科 機械システム工学専攻 - Apr. 2022 - Mar. 2024
茨城大学 工学部 機械システム工学科 - Apr. 2015 - Mar. 2020
茨城大学 工学部 機械工学科 - Apr. 2015 - Mar. 2020
茨城大学 工学部 機械工学科 - Apr. 2015 - Mar. 2020
茨城大学 工学部 機械工学科 - Apr. 2015 - Mar. 2017
茨城大学 工学部 機械工学科
Affiliated academic society
Research Themes
- セラミックスの高温変形及び接合に対する通電効果の原理解明
Grant-in-Aid for Scientific Research (B)
Apr. 2020 - Mar. 2024 - Analysis on the sites of existence and paths of migration for hydrogen in metallic materials for structural use by means of some visualization techniques
Grant-in-Aid for Scientific Research (C)
Apr. 2020 - Mar. 2023 - 熱間圧延により残留オーステナイトを微細分散させた微細粒を有する超高強度低合金TRIP鋼の成形性
Oct. 2018 - Mar. 2022 - 粒界析出組織制御によるアルミニウム合金の信頼性の向上
Grant-in-Aid for Scientific Research (C)
Apr. 2017 - Mar. 2020 - Suppression of environmental embrittlement in cold worked aluminum alloys with deformation-induced nano clusters
Grant-in-Aid for Scientific Research (B)
Ibaraki University
Apr. 2017 - Mar. 2020
Industrial Property Rights
Academic Contribution Activities
- 一般社団法人日本塑性加工学会 企画委員
Planning etc
一般社団法人日本塑性加工学会, 01 Apr. 2018 - Present - 軽金属学会 アルミニウム中の水素と材料物性研究部会
Academic research planning
一般社団法人軽金属学会, Apr. 2016 - Present - 日本塑性加工学会東関東支部 企画・会計幹事
Planning etc
01 Apr. 2014 - Present - 学術部会創形創質工学部会運営委員会委
Planning etc
一般社団法人日本鉄鋼協会, 01 Apr. 2023 - 31 Mar. 2025 - 日本機械学会関東支部茨城ブロック商議員
Planning etc
一般社団法人日本機械学会 関東支部, 11 Apr. 2023 - 31 Mar. 2024 - 日本アルミニウム協会 個別ロードマップ若手検討会 委員
Planning etc
01 Apr. 2021 - 31 Mar. 2022
