| Project/Area Number |
11650717
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Structural/Functional materials
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| Research Institution | YOKOHAMA NATIONAL UNIVERSITY |
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Principal Investigator |
ENDO Takao YOKOHAMA NATIONAL UNIVERSITY, Faculty of Engineering, PROFESSOR, 工学部, 教授 (40018007)
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| Project Period (FY) |
1999 – 2000
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| Project Status |
Completed (Fiscal Year 2000)
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| Budget Amount *help |
¥2,200,000 (Direct Cost: ¥2,200,000)
Fiscal Year 2000: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1999: ¥1,700,000 (Direct Cost: ¥1,700,000)
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| Keywords | stain less steel / high temperature / creep / stress relaxation / creep life / solid solution strengthening / precipitation strengthening / nitrogen / creep / nitrogen / I-S cluster / effective stress / stress relaxation / staineless steel / heatreststant steel |
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| Research Abstract |
Forcibly introduced nitrogen has been regarded as the last element for the improvement of heat resistant steels because it improves the mechanical properties without any adverse effect on creep rupture strain. However, the most beneficial effect of nitrogen can be seen when nitrogen is added with a small amount of niobium and/or vanadium. In order to elucidate the combined effect of nitrogen and niobium on creep characteristics, aSUS310S and a 25Cr-20NiNbN steel containing 0.2 mass % of N and 0.45 mass % of Nb were selected for the present study.
Creep tests showed that the creep life of the 25Cr-20NiNbN was one hundred times longerthan that of the SUS310S notwithstanding that the chemical compositions were about the same except for a small amount of these additions. In order to describe the stress and temperature dependence of the imaginary strain rate, the constitutive equations for these steels were derived.
Although the main substitutional elements in these steels can hardly interact with dislocations, some pieces of evidence were obtained that an atmosphere of Cr-N clusters was formed around moving dislocations in the25Cr-20NiNbN steel. Besides the solid solution hardening due to clustering, it was made clear that the precipitation hardening played an important role in the 25Cr-20NiNbN steel. The analysis of stress relaxation and stress change tests revealed that the fraction of effective stress was about 16% and the threshold stress was about 190 MPa. Using the data on the distribution of particle radius determined by TEM, the threshold stress of about the same magnitude of experimental one was obtained from calculation based on the void strengthening theory.
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