| 研究実績の概要 |
For ultrahigh strength steels and pressure vessel steels, the prevention of hydrogen embrittlement is one of important research topics.Different with the ultrahigh strength steel bars/bolts and thin steel sheets already available in commercial products, ultrahigh strength steel plates with a tensile strength TS=1200 MPa are still under developing.
Though there are several hypotheses about hydrogen embrittlement, the in-situ hydrogen embrittlement evaluation studies are highly expected to make them clear, especially using neutron diffraction as an accurate probe for bulk microstructure/ texture evaluation of materials because its large spot size and high penetration compared to the X-ray diffraction and the electron diffraction.
In our study, the anisotropic characteristics of high strength steel plate were evaluated through the neutron diffraction, and the mutual effects of texture and hydrogen charging on elastoplastic deformation of high strength steel plates were investigated for their future application to heavy engineering trucks, huge bridges, ocean infrastructures, etc. The results show that neutron diffraction is suitable for monitoring the plastic deformation of hydrogen-charged high strength steel. The anisotropy of elastoplastic deformation behaviors of high strength steel plate has been confirmed and the effect of hydrogen charging on total elongation and reduction in the area has been confirmed. Moreover, the direction susceptibility of hydrogen embrittlement from low to high is rolling direction, diagonal direction, transverse direction, respectively.
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| 現在までの達成度 (区分) |
現在までの達成度 (区分)
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理由
In this budget year, together with necessary off-line macroscopic mechanical property measurements, the in-situ neutron diffraction experiments were carried out for the anisotropic tensile deformation of high strength steel samples without and with hydrogen pre-charging. The Neutron diffraction is suitable for monitoring the plastic deformation of hydrogen-charged high strength steel. The anisotropy of elastoplastic deformation behaviors of high strength steel plate has been confirmed and the effect of hydrogen charging on the total elongation and the reduction in the area has been confirmed. It is found that the direction susceptibility of hydrogen embrittlement from low to high is the rolling direction, the diagonal direction, the transverse direction of the investigated high strength steel plate, respectively.
Moreover, in order to improve the instrumental accessibility, the neutron diffraction measurement technique based on RIKEN compact neutron source has been upgraded and it is found that such compact neutron source is possible to be applied to the quantitative crystallographic textures of steel materials.
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| 今後の研究の推進方策 |
In the next budget year, the additional tensile deformation experiments will be carried out to get more reliable measurement data to further confirm the results from the neutron diffraction studies. Moreover, the microstructure and fracture morphology will be analyzed together with the crystallographic orientation analysis, especially near the fracture surface and the nearby sub-layer. The microstructure and texture changes will be strengthened and weakened through some preliminary deformation to investigate the effect of crystallographic texture on the hydrogen embrittlement phenomenon and discuss the possibility of texture control to improve the hydrogen embrittlement resistance.
If the RIKEN beam time is available, the compact neutron diffraction technique will be employed to compare the neutron diffraction profiles related to the direction susceptibility of hydrogen embrittlement.
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