The Experts below are selected from a list of 132 Experts worldwide ranked by ideXlab platform
Nobuhiro Tsuji - One of the best experts on this subject based on the ideXlab platform.
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Effect of Hydrogen on the Substructure of Lenticular Martensite in Fe-31Ni Alloy
Metallurgical and Materials Transactions A, 2019Co-Authors: Akinobu Shibata, Nobuhiro Tsuji, Masanori Enoki, Nahoko Saji, Hirotaka Tai, Motomichi Koyama, Hiroshi Ohtani, Kaneaki TsuzakiAbstract:This study investigated the effect of Hydrogen on the substructure of martensite in Fe-31Ni alloy. In both the Hydrogen-Charged and unCharged Specimens, typical lenticular martensite plates formed after subzero cooling. However, we found that the fraction of twinned region (including the area of midrib) in lenticular martensite plate increased with increasing Hydrogen content. In addition, the width of individual twins in the Hydrogen-Charged Specimen was slightly smaller than that in the unCharged Specimen. These results indicated that the existence of Hydrogen facilitated twinning deformation as a lattice invariant deformation. We presented a comprehensive discussion about the reason why Hydrogen enhanced twinning deformation. Even though tetragonality of martensite in the Hydrogen-Charged Specimen could not be confirmed by X-ray diffraction, the transmission electron microscopy observations and the first-principles calculations suggested that Hydrogen might increase the tetragonality of martensite. We proposed that solid solution hardening and an increase in the tetragonality of martensite by the existence of Hydrogen were the possible reasons for facilitating twinning deformation as a lattice invariant deformation in martensitic transformation.
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Effect of strain rate on Hydrogen embrittlement in low-carbon martensitic steel
International Journal of Hydrogen Energy, 2017Co-Authors: Yuji Momotani, Akinobu Shibata, Daisuke Terada, Nobuhiro TsujiAbstract:Abstract This study investigated the effect of strain rate on Hydrogen embrittlement behavior in a low-carbon martensitic steel. Elongation of the Hydrogen-Charged Specimen decreased significantly with decreasing the strain rate. The characteristics of the Hydrogen-related fracture behavior also changed with the strain rate. Hydrogen micro-print technique and electron backscattering diffraction analysis revealed that the deformation at a lower strain rate facilitated Hydrogen to accumulate mainly on prior austenite grain boundaries. This Hydrogen accumulation led to the formation of micro-cracks along prior austenite grain boundaries and brittle fracture on or in the vicinity of prior austenite grain boundaries. On the other hand, in the case of a higher strain rate, micro-cracks formed mainly inside prior austenite grains and transgranular fracture occurred. This is presumably because there was not enough time for Hydrogen to accumulate on prior austenite grain boundaries during tensile test.
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effect of prior austenite grain size on Hydrogen embrittlement behaviors in 8ni 0 1c steel
PRICM: 8 Pacific Rim International Congress on Advanced Materials and Processing, 2013Co-Authors: Akinobu Shibata, Takahiro Matsuoka, Nobuhiro TsujiAbstract:The present study investigated the effect of prior austenite grain size on Hydrogen embrittlement in an 8Ni-0.1C martensitic steel. The prior austenite grain size was refined from 124 μm to 4.7 μm through cyclic heat treatment of austenitizing and water quenching. Slow strain rate tensile tests revealed that the Hydrogen embrittlement was improved by the refinement of prior austenite grains. The macroscopic fracture surfaces of both the Hydrogen-Charged Specimens with coarse prior austenite grains and fine prior austenite grains were characterized by intergranular fracture surfaces. The area fraction of the macroscopic intergranular fracture surfaces in the Hydrogen-Charged Specimen with fine prior austenite grains was smaller than that in the Hydrogen-Charged Specimen with coarse prior austenite grains. This suggested that the refinement of prior austenite grains reduced the frequency of the fracture by Hydrogen embrittlement.
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PRICM: 8 Pacific Rim International Congress on Advanced Materials and Processing - Effect of Prior Austenite Grain Size on Hydrogen Embrittlement Behaviors in 8Ni‐0.1C Steel
Proceedings of the 8th Pacific Rim International Congress on Advanced Materials and Processing, 2013Co-Authors: Akinobu Shibata, Takahiro Matsuoka, Nobuhiro TsujiAbstract:The present study investigated the effect of prior austenite grain size on Hydrogen embrittlement in an 8Ni-0.1C martensitic steel. The prior austenite grain size was refined from 124 μm to 4.7 μm through cyclic heat treatment of austenitizing and water quenching. Slow strain rate tensile tests revealed that the Hydrogen embrittlement was improved by the refinement of prior austenite grains. The macroscopic fracture surfaces of both the Hydrogen-Charged Specimens with coarse prior austenite grains and fine prior austenite grains were characterized by intergranular fracture surfaces. The area fraction of the macroscopic intergranular fracture surfaces in the Hydrogen-Charged Specimen with fine prior austenite grains was smaller than that in the Hydrogen-Charged Specimen with coarse prior austenite grains. This suggested that the refinement of prior austenite grains reduced the frequency of the fracture by Hydrogen embrittlement.
Akinobu Shibata - One of the best experts on this subject based on the ideXlab platform.
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Effect of Hydrogen on the Substructure of Lenticular Martensite in Fe-31Ni Alloy
Metallurgical and Materials Transactions A, 2019Co-Authors: Akinobu Shibata, Nobuhiro Tsuji, Masanori Enoki, Nahoko Saji, Hirotaka Tai, Motomichi Koyama, Hiroshi Ohtani, Kaneaki TsuzakiAbstract:This study investigated the effect of Hydrogen on the substructure of martensite in Fe-31Ni alloy. In both the Hydrogen-Charged and unCharged Specimens, typical lenticular martensite plates formed after subzero cooling. However, we found that the fraction of twinned region (including the area of midrib) in lenticular martensite plate increased with increasing Hydrogen content. In addition, the width of individual twins in the Hydrogen-Charged Specimen was slightly smaller than that in the unCharged Specimen. These results indicated that the existence of Hydrogen facilitated twinning deformation as a lattice invariant deformation. We presented a comprehensive discussion about the reason why Hydrogen enhanced twinning deformation. Even though tetragonality of martensite in the Hydrogen-Charged Specimen could not be confirmed by X-ray diffraction, the transmission electron microscopy observations and the first-principles calculations suggested that Hydrogen might increase the tetragonality of martensite. We proposed that solid solution hardening and an increase in the tetragonality of martensite by the existence of Hydrogen were the possible reasons for facilitating twinning deformation as a lattice invariant deformation in martensitic transformation.
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Effect of strain rate on Hydrogen embrittlement in low-carbon martensitic steel
International Journal of Hydrogen Energy, 2017Co-Authors: Yuji Momotani, Akinobu Shibata, Daisuke Terada, Nobuhiro TsujiAbstract:Abstract This study investigated the effect of strain rate on Hydrogen embrittlement behavior in a low-carbon martensitic steel. Elongation of the Hydrogen-Charged Specimen decreased significantly with decreasing the strain rate. The characteristics of the Hydrogen-related fracture behavior also changed with the strain rate. Hydrogen micro-print technique and electron backscattering diffraction analysis revealed that the deformation at a lower strain rate facilitated Hydrogen to accumulate mainly on prior austenite grain boundaries. This Hydrogen accumulation led to the formation of micro-cracks along prior austenite grain boundaries and brittle fracture on or in the vicinity of prior austenite grain boundaries. On the other hand, in the case of a higher strain rate, micro-cracks formed mainly inside prior austenite grains and transgranular fracture occurred. This is presumably because there was not enough time for Hydrogen to accumulate on prior austenite grain boundaries during tensile test.
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effect of prior austenite grain size on Hydrogen embrittlement behaviors in 8ni 0 1c steel
PRICM: 8 Pacific Rim International Congress on Advanced Materials and Processing, 2013Co-Authors: Akinobu Shibata, Takahiro Matsuoka, Nobuhiro TsujiAbstract:The present study investigated the effect of prior austenite grain size on Hydrogen embrittlement in an 8Ni-0.1C martensitic steel. The prior austenite grain size was refined from 124 μm to 4.7 μm through cyclic heat treatment of austenitizing and water quenching. Slow strain rate tensile tests revealed that the Hydrogen embrittlement was improved by the refinement of prior austenite grains. The macroscopic fracture surfaces of both the Hydrogen-Charged Specimens with coarse prior austenite grains and fine prior austenite grains were characterized by intergranular fracture surfaces. The area fraction of the macroscopic intergranular fracture surfaces in the Hydrogen-Charged Specimen with fine prior austenite grains was smaller than that in the Hydrogen-Charged Specimen with coarse prior austenite grains. This suggested that the refinement of prior austenite grains reduced the frequency of the fracture by Hydrogen embrittlement.
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PRICM: 8 Pacific Rim International Congress on Advanced Materials and Processing - Effect of Prior Austenite Grain Size on Hydrogen Embrittlement Behaviors in 8Ni‐0.1C Steel
Proceedings of the 8th Pacific Rim International Congress on Advanced Materials and Processing, 2013Co-Authors: Akinobu Shibata, Takahiro Matsuoka, Nobuhiro TsujiAbstract:The present study investigated the effect of prior austenite grain size on Hydrogen embrittlement in an 8Ni-0.1C martensitic steel. The prior austenite grain size was refined from 124 μm to 4.7 μm through cyclic heat treatment of austenitizing and water quenching. Slow strain rate tensile tests revealed that the Hydrogen embrittlement was improved by the refinement of prior austenite grains. The macroscopic fracture surfaces of both the Hydrogen-Charged Specimens with coarse prior austenite grains and fine prior austenite grains were characterized by intergranular fracture surfaces. The area fraction of the macroscopic intergranular fracture surfaces in the Hydrogen-Charged Specimen with fine prior austenite grains was smaller than that in the Hydrogen-Charged Specimen with coarse prior austenite grains. This suggested that the refinement of prior austenite grains reduced the frequency of the fracture by Hydrogen embrittlement.
Hisao Matsunaga - One of the best experts on this subject based on the ideXlab platform.
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Comprehensive Understanding of Ductility Loss Mechanisms in Various Steels with External and Internal Hydrogen
Metallurgical and Materials Transactions A, 2017Co-Authors: Osamu Takakuwa, Hisao Matsunaga, Junichiro Yamabe, Yoshiyuki Furuya, Saburo MatsuokaAbstract:Hydrogen-induced ductility loss and related fracture morphologies are comprehensively discussed in consideration of the Hydrogen distribution in a Specimen with external and internal Hydrogen by using 300-series austenitic stainless steels (Types 304, 316, 316L), high-strength austenitic stainless steels (HP160, XM-19), precipitation-hardened iron-based super alloy (A286), low-alloy Cr-Mo steel (JIS-SCM435), and low-carbon steel (JIS-SM490B). External Hydrogen is realized by a non-Charged Specimen tested in high-pressure gaseous Hydrogen, and internal Hydrogen is realized by a Hydrogen-Charged Specimen tested in air or inert gas. Fracture morphologies obtained by slow-strain-rate tensile tests (SSRT) of the materials with external or internal Hydrogen could be comprehensively categorized into five types: Hydrogen-induced successive crack growth, ordinary void formation, small-sized void formation related to the void sheet, large-sized void formation, and facet formation. The mechanisms of Hydrogen embrittlement are broadly classified into Hydrogen-enhanced decohesion (HEDE) and Hydrogen-enhanced localized plasticity (HELP). In the HEDE model, Hydrogen weakens interatomic bonds, whereas in the HELP model, Hydrogen enhances localized slip deformations. Although various fracture morphologies are produced by external or internal Hydrogen, these morphologies can be explained by the HELP model rather than by the HEDE model.
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Ductility Loss in Ductile Cast Iron with Internal Hydrogen
Metallurgical and Materials Transactions A, 2014Co-Authors: Hisao Matsunaga, Teruki Usuda, Keiji Yanase, Masahiro EndoAbstract:Hydrogen-induced ductility loss in ductile cast iron (DCI) was studied by conducting a series of tensile tests with three different crosshead speeds. By utilizing the thermal desorption spectroscopy and the Hydrogen microprint technique, it was found that most of the solute Hydrogen was diffusive and mainly segregated at the graphite, graphite/matrix interface zone, and the cementite of pearlite in the matrix. The fracture process of the non-Charged Specimen was dominated by the ductile dimple fracture, whereas that of the Hydrogen-Charged Specimen became less ductile because of the accompanying interconnecting cracks between the adjacent graphite nodules. Inside the Hydrogen-Charged Specimen, the interspaces generated by the interfacial debonding between graphite and matrix are filled with Hydrogen gas in the early stage of the fracture process. In the subsequent fracture process, such a local Hydrogen gas atmosphere coupled with a stress-induced diffusion attracts Hydrogen to the crack tip, which results in a time-dependent ductility loss.
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Hydrogen-Induced Ductility Loss in Cast Irons
Materials Science Forum, 2013Co-Authors: Teruki Usuda, Hisao Matsunaga, Keiji Yanase, K. Matsuno, Masahiro EndoAbstract:Effect of Hydrogen-charging was investigated with respect to the tensile properties of three types of cast irons: JIS FCD400, FCD450 and FCD700. In this study, Hydrogen charging led to a marked ductility loss in all the cast irons. The thermal desorption spectroscopy and the Hydrogen microprint technique revealed that, in the Hydrogen-Charged Specimens, most of solute Hydrogen was diffusive and mainly segregated at graphite, graphite/matrix interface zone and pearlite. In the fracture process of non-Charged Specimen, neighboring graphites were interconnected with each other mainly by ductile dimple fracture. On the other hand, in the fracture process of Hydrogen-Charged Specimen, the graphites were interconnected by cracks. The difference in the fracture morphology between the non-Charged and the Hydrogen-Charged Specimens is attributed to the presence of diffusive Hydrogen in graphite and graphite/matrix interface. During early stage of fracture process in Hydrogen-Charged Specimen, the interspace between graphite and matrix is filled with Hydrogen gas, which leads to the ductility loss of matrix in the vicinity of graphite. Even after the initiation of crack from graphite, Hydrogen is continuously outgassed from graphite and supplied to the crack tip. Therefore, concerning the Hydrogen effect on the strength of cast irons, a role of subsurface graphite as a “local Hydrogen supplier” should be taken into consideration.
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EFFECT OF Hydrogen ON UNIAXIAL TENSILE BEHAVIORS OF A DUCTILE CAST IRON
2012Co-Authors: K. Matsuno, Hisao Matsunaga, Masahiro Endo, Keiji YanaseAbstract:Effect of the Hydrogen-charging on the uniaxial tensile behaviors of a ductile cast iron was investigated. It was found that the Hydrogen-charging accelerated the process of crack growth from graphite in the uniaxial tensile loading condition. Further, the accelerated crack growth had a marked influence on the reduction of area at the final fracture (RA) of Specimens. For instance, for the unCharged Specimens, the RA was nearly constant irrespective of the strain rate. In contrast, for the Hydrogen-Charged Specimens, the RA gradually decreased as the strain rate decreased. Thermal desorption spectroscopy and Hydrogen microprint technique revealed that, in the Hydrogen-Charged Specimen, most of solute Hydrogen was diffusive one, which was mainly segregated at graphite, graphite/matrix interface zone and pearlite. Based on these experimental observations, we consider that the Hydrogen-induced degradation behavior was caused mainly by a combination of the following three mechanisms: (i) supplement of Hydrogen to the crack tip from graphite and graphite–matrix interface, (ii) Hydrogen-enhanced pearlite cracking and, (iii) successive Hydrogen-emission from graphite and additional Hydrogen-supplement to the crack tip.
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Visualization of Hydrogen Diffusion in a Hydrogen-Enhanced Fatigue Crack Growth in Type 304 Stainless Steel
Metallurgical and Materials Transactions A, 2011Co-Authors: Hisao Matsunaga, Hiroshi NodaAbstract:To study the influence of Hydrogen on the fatigue strength of AISI type 304 metastable austenitic stainless steel, Specimens were cathodically Charged with Hydrogen. Using tension-compression fatigue tests, the behavior of fatigue crack growth from a small drill hole in the Hydrogen-Charged Specimen was compared with that of nonCharged Specimen. Hydrogen charging led to a marked increase in the crack growth rate. Typical characteristics of Hydrogen effect were observed in the slip band morphology and fatigue striation. To elucidate the behavior of Hydrogen diffusion microscopically in the fatigue process, the Hydrogen emission from the Specimens was visualized using the Hydrogen microprint technique (HMT). In the Hydrogen-Charged Specimen, Hydrogen emissions were mainly observed in the vicinity of the fatigue crack. Comparison between the HMT image and the etched microstructure image revealed that the slip bands worked as a pathway for Hydrogen to move preferentially. Hydrogen-charging resulted in a significant change in the phase transformation behavior in the fatigue process. In the nonCharged Specimen, a massive type α′ martensite was observed in the vicinity of the fatigue crack. On the other hand, in the Hydrogen-Charged Specimen, large amounts of ε martensite and a smaller amount of α′ martensite were observed along the slip bands. The results indicated that solute Hydrogen facilitated the ε martensitic transformation in the fatigue process. Comparison between the results of HMT and EBSD inferred that martensitic transformations as well as plastic deformation itself can enhance the mobility of Hydrogen.
Yuji Momotani - One of the best experts on this subject based on the ideXlab platform.
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Effect of strain rate on Hydrogen embrittlement in low-carbon martensitic steel
International Journal of Hydrogen Energy, 2017Co-Authors: Yuji Momotani, Akinobu Shibata, Daisuke Terada, Nobuhiro TsujiAbstract:Abstract This study investigated the effect of strain rate on Hydrogen embrittlement behavior in a low-carbon martensitic steel. Elongation of the Hydrogen-Charged Specimen decreased significantly with decreasing the strain rate. The characteristics of the Hydrogen-related fracture behavior also changed with the strain rate. Hydrogen micro-print technique and electron backscattering diffraction analysis revealed that the deformation at a lower strain rate facilitated Hydrogen to accumulate mainly on prior austenite grain boundaries. This Hydrogen accumulation led to the formation of micro-cracks along prior austenite grain boundaries and brittle fracture on or in the vicinity of prior austenite grain boundaries. On the other hand, in the case of a higher strain rate, micro-cracks formed mainly inside prior austenite grains and transgranular fracture occurred. This is presumably because there was not enough time for Hydrogen to accumulate on prior austenite grain boundaries during tensile test.
En-hou Han - One of the best experts on this subject based on the ideXlab platform.
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Hydrogen assisted fracture features of a high strength ferrite pearlite steel
Journal of Materials Science & Technology, 2019Co-Authors: Jianqiu Wang, Yuefeng Jiang, Bo Zhang, Dongying Wang, Yu Zhou, En-hou HanAbstract:Abstract Up to now, the exact reason of Hydrogen-induced fracture for ferrite-pearlite (FP) steel is still not fully understood. This study presents detail observations of the feature beneath the fracture surface with the aim to reveal the Hydrogen-induced cracking initiation and propagation processes. Slow strain rate tensile (SSRT) testing shows that the FP steel is sensitive to Hydrogen embrittlement (HE). Focused ion beam (FIB) was used to prepare samples for TEM observations after HE fracture. The corresponding fractographic morphologies of Hydrogen Charged Specimen exhibit intergranular (IG) and quasi-cleavage (QC) fracture feature. Pearlite colony, ferrite/pearlite (F/P) boundary and the adjacent ferrite matrix are found to be responsible for the initial HE fracture and the subsequent propagation. With increasing of the stress intensity factor, fracture mode is found to change from mixed IG and QC to entire QC feature which only occurs at the ferrite matrix. No crack is observed at the ferrite/cementite (F/C) interface. This may be mainly due to the limited pearlite lamella size and relatively low interface energy.
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Atom probe tomographic observation of Hydrogen trapping at carbides/ferrite interfaces for a high strength steel
Journal of Materials Science & Technology, 2018Co-Authors: Youlin Jiang, B. Zhang, Yuwei Zhou, J.q. Wang, En-hou HanAbstract:Abstract A three-dimensional atom probe (3DAP) technique has been used to characterize the Hydrogen distribution on carbides for a high strength AISI 4140 steel. Direct evidence of H atoms trapped at the carbide/ferrite interfaces has been revealed by 3DAP mapping. Hydrogen is mainly trapped on carbide/ferrite interfaces along the grain boundaries. Slow strain rate tensile (SSRT) testing shows that the AISI 4140 steel is highly sensitive to Hydrogen embrittlement. The corresponding fractographic morphologies of Hydrogen Charged Specimen exhibit brittle fracture feature. Combined with these results, it is proposed that the Hydrogen trapping sites present in the grain boundaries are responsible for the Hydrogen-induced intergranular fracture of AISI 4140. The direct observation of Hydrogen distribution contributes to a better understanding of the mechanism of Hydrogen embrittlement.
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Effects of Hydrogen on the anodic behavior of Alloy 690 at 60 °C
Corrosion Science, 2010Co-Authors: Tichun Dan, Tetsuo Shoji, Kazuhiko Sakaguchi, Jianqiu Wang, En-hou HanAbstract:Abstract Polarization and electrochemical impedance spectroscopy (EIS) measurements, Mott–Schottky (M–S) analysis and X-ray photoelectron spectroscopy (XPS) were used to investigate the effects of Hydrogen on the anodic behavior of a one-dimensionally (1D) 25% cold worked (CW) Alloy 690 thermal treated (TT) in a boric acid and sodium sulphate solution at 60 °C. The pre-Hydrogen-Charged Specimen exhibited a higher anodic current than that of the unCharged Specimen below the transpassive potential. The Charged Hydrogen can be trapped in the metal. Electrochemical impedance spectroscopy (EIS) showed that the resistance capacitance loop of the Hydrogen-Charged Specimen was significantly smaller than that of the unCharged Specimen. Mott–Schottky analyses indicated that the passive film formed on Alloy 690 at −0.2 V SCE was an n-type semiconductor, with a p–n hetero-junction at 0.2 V SCE . Charged Hydrogen increased the carrier density and the thickness of the passive film both at −0.2 V SCE and 0.2 V SCE . The Ni/Cr ratio in the surface film decreased after Hydrogen charging, indicating that Charged Hydrogen could enhance the oxide film growth by increasing the OH − (O 2− ) concentrations through its reaction with vacancies.
