2019 Fiscal Year Final Research Report
Improvement in creep strength of over 700 C grade ferritic heat-resistant steels by control of precipitation
| Project/Area Number |
17K06851
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Multi-year Fund |
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| Section | 一般 |
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| Research Field |
Structural/Functional materials
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| Research Institution | National Institute for Materials Science |
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Principal Investigator |
TODA Yoshiaki 国立研究開発法人物質・材料研究機構, 構造材料研究拠点, 主幹研究員 (60343878)
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| Project Period (FY) |
2017-04-01 – 2020-03-31
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| Keywords | クリープ / 析出 / 炭化物 / 炭素 / 窒素 / フェライト鋼 / ラーベス相 / Z相 |
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| Outline of Final Research Achievements |
In order to improve in the high-temperature creep strength of new heat-resistant steels the ferritic parent phase of which is precipitation-strengthened by carbonitrides and Laves phase, the creep strength at 700 C of the steels with various carbon and nitrogen contents was investigated. 0.02 % or more of nitrogen is necessary, and the creep strength was improved with increase in the nitrogen content by the solute strengthening and precipitation of Z phase. The long-term creep strength of the steels with 0.05 % carbon content was decreased, because voids were formed at the interfaces between the parent phase and the carbide on the grain boundaries. The slopes of creep stress vs. time to rupture curves of 0.02C-0.03N steel was low, then it was found that they were optimum contents for improving in the creep strength at 700 C of the new ferritic heat-resistant steels.
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| Free Research Field |
高温材料設計
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| Academic Significance and Societal Importance of the Research Achievements |
発電・化学プラントの高温構造部材に使用されている既存の高クロムフェライト耐熱鋼の重要な析出強化因子である炭化物が、開発鋼では母相との低い整合性からクリープ破断の原因になり得ること、既存鋼では有害相とされている窒化物が、開発鋼における安定な析出強化因子であることが分かり、700℃以上のクリープ強度を向上させるための新しい耐熱材料設計指針を示すことができた。
これにより、700 ℃級先進超々臨界圧火力発電や超臨界地熱発電、次世代核融合炉、固体酸化物型燃料電池等に安価で熱的性質の優れたフェライト開発鋼を応用でき、高効率なエネルギー変換機器により、今までよりも進んだ低炭素化社会を築くことができる。
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