2016 Fiscal Year Research-status Report
Ultra-grain refinement as prevention against hydrogen-assisted crack propagation
| Project/Area Number |
16K17981
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| Research Institution | Kyushu University |
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Principal Investigator |
マカドレ アルノー 九州大学, カーボンニュートラル・エネルギー国際研究所, 学術研究員 (20635891)
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| Project Period (FY) |
2016-04-01 – 2018-03-31
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| Keywords | hydrogen embrittlement / austenite / grain refinement |
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| Outline of Annual Research Achievements |
By producing different grain sizes of austenite (from 1 micron to 21 microns grains), I have shown how hydrogen influences the tensile properties of metastable austenite under tensile loading.
After exposure to 10 MPa hydrogen gas, metastable austenite does not suffer large effects of hydrogen for grain sizes below 6 microns. The ductility of small austenitic grains is only slightly reduced and the fracture remains fully ductile. Larger grains suffer from significant ductility reduction and display embrittled fracture (quasi-cleavage and intergranular).
The increased resistance of fine austenitic grains against hydrogen embrittlement is explained by the limited dislocation pile-up distance within grains as well as uniform distribution of stress and deformation in small grains.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
The heat treatments and hydrogen exposure for grain size and hydrogen content control are all successful, thanks to good procedure control.
A new testing method (in-situ SEM tensile testing) gives precious information for the fracture mechanism.
Both fracture surface analysis and microstructure analysis are yielding reliable data enabling connections between grain size, hydrogen content and fracture.
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| Strategy for Future Research Activity |
Grain boundary analysis is necessary, both with and without hydrogen, under loading, to understand how dislocations interact with hydrogen and grain boundaries, inclusions and martensite-austenite boundaries.
This will be done with EBSD. Dislocation observation would be done with TEM.
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| Causes of Carryover |
The received amount in the first year was not enough to buy the necessary rolling mill
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| Expenditure Plan for Carryover Budget |
With the added amount of both years, the necessary rolling mill will be purchased.
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[Journal Article] Determination of hydrogen compatibility for solution-treated austenitic stainless steels based on a newly proposed nickel-equivalent equation2016
Author(s)
Takaki, S., Nanba, S., Imakawa, K., Macadre, A., Yamabe, J., Matsunaga, H. and Matsuoka, S.
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Journal Title
International Journal of Hydrogen Energy
Volume: 41
Pages: 15095-15100
DOI
Peer Reviewed / Int'l Joint Research
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