| 研究課題/領域番号 |
18K13980
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| 研究機関 | 千葉大学 |
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研究代表者 |
Chiari Luca 千葉大学, 大学院工学研究院, 特任助教 (20794572)
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| 研究期間 (年度) |
2018-04-01 – 2021-03-31
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| キーワード | hydrogen embrittlement / defects / vacancy clusters / hydrogen / iron / stainless steel |
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| 研究実績の概要 |
The behaviour of defects was investigated in pure iron and SUS 304 stainless steel. The samples were simultaneously plastically deformed and hydrogen charged by the electrolytic cathode reaction method at room temperature in order to induce hydrogen embrittlement in the materials.
In pure iron, the thermal behavior of defects was compared between samples stretched up to the same strain value but at different straining rates. The formation of vacancy clusters was observed at all temperatures. However, only in the slowly strained, hydrogen-embrittled material, small vacancy clusters were found to become mobile and agglomerate into larger clusters above 250 K.
In SUS 304 stainless steel, the sample was stretched up to a certain strain value, the hydrogen-charged layer was removed and then it was stretched again up to the fracturing point. The presence of hydrogen embrittlement was confirmed, indicating that hydrogen diffuses into the deeper layers. A new kind of detect was detected in these deeper layers, which is believed to be the embryo of the vacancy clusters. In-situ PALS measurements were also conducted at intermediate strain values at the boundary between the elastic and plastic deformation regions to investigate the role of vacancy clusters in the hydrogen embrittlement process.
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| 現在までの達成度 (区分) |
現在までの達成度 (区分)
2: おおむね順調に進展している
理由
The implementation of the plan for the first year can be considered to have been carried out on time and according to the originally planned schedule. The measurements were carried out on pure iron and stainless steel SUS 304 to investigate the origin of hydrogen embrittlement in both materials.
The temperature dependent behaviour of defects was investigated in pure iron from cryogenic temperatures up to 250 C. Measurements were performed in samples stretched with different straining rates in order to elucidate the role of vacancy cluster defects in driving the hydrogen embrittlement process.
In stainless steel SUS 304, the samples were stretched up to a predetermined strain value, and after removing the hydrogen-charged layer, the samples were stretched again until fracturing. Measurements were performed in all these conditions. To investigate the process of the formation of defects, in-situ measurements were carried out on stainless steel SUS 304 stretched up to various strain values.
The experiments followed in detail the original plan described in the research proposal. The results obtained so far are very satisfactory and overall confirm the outcomes anticipated in the project proposal.
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| 今後の研究の推進方策 |
In the next two years, the plan for the detection and identification of the controlling factor of hydrogen embrittlement in pure iron, stainless steels SUS 304 and SUS 316L is anticipated to continue as scheduled and described in the research proposal.
The plan of the second stage of the project is progressing according to the schedule and we plan to carry it out as detailed in the research project description. In the next year, in-situ measurements on pure iron that is plastically deformed and hydrogen charged at the same time are planned to be carried out at a facility overseas. The details of these in-situ measurements on pure iron are being planned. Hydrogen embrittlement in the highly hydrogen-resistant stainless steel SUS 316L will also be investigated in the next year. In particular, the temperature-dependent behaviour of vacancy defects is planned to be measured while stretching the hydrogen-charged sample up to different strain values.
In the third year of the project, the influence of impurities, such as carbon and nitrogen, on hydrogen embrittlement in pure iron is planned to be investigated. As the vacancy behavior is known to be greatly affected by impurities, in-situ low-temperature measurement will allow to reveal their detailed behaviour.
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| 次年度使用額が生じた理由 |
The reason for the carryover amount of this fiscal year mainly lies in the reallocation of the travel expenses. The amount of travel expenses for international business trips during the fiscal year 2018 that was originally allocated in this kakenhi grant was actually charged to other privately obtained grant accounts. As the usage of those grant accounts were limited to fiscal year 2018 only, priority was given to the usage of those grants. Therefore, the travel expenses to attend the international conferences during the fiscal year 2018 were directly charged to those private grants. The allocated amount for travel expenses of this kakenhi grant was used for the attendance of a domestic conference instead.
The carryover amount from fiscal year 2018 is planned to be used during fiscal year 2019 mainly as equipment and consumable cost, overseas travel expenses and as personnel expenditure and remuneration for the measurements to be carried out at the overseas facility.
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