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Precipitate Evolution in a Modified 25Cr-20Ni Austenitic Heat Resistant Stainless Steel During Creep Rupture Test at 750 degrees C
Hu Guodong1,2; Wang Pei1; Li Dianzhong1; Li Yiyi1
Corresponding AuthorLi Dianzhong(dzli@imr.ac.en)
2018-11-11
Source PublicationACTA METALLURGICA SINICA
ISSN0412-1961
Volume54Issue:11Pages:1705-1714
Abstract25Cr-20Ni austenitic heat resistant stainless steels are widely used as structural materials in nuclear industries and power plants for their excellent corrosion resistance and creep properties at elevated temperature. It is generally accepted that the precipitation during creep is a key factor influencing the creep properties. However, the evolution of precipitates is complicated due to the interaction of the alloy elements. To investigate the precipitation behaviors, a modified 25Cr-20Ni austenitic heat resistant stainless steel has been crept at 750 C under different stresses varying from 100 MPa to 180 MPa. The microstructure observation indicates that M23C6 and (Nb, V)(C, N) precipitates are formed during 32.6 h creeping deformation under 180 MPa. M23C6 precipitates are mainly generated at grain boundaries and (Nb, V)(C, N) particles are dispersively distributed in austenitic matrix. The grain boundary M23C6, carbides are significantly coarsened and Ostwald ripening process happens during 98.1 h creeping deformation under the stress of 150 MPa and 353.0 h creeping deformation under stress of 120 MPa, while (Nb, V)(C, N) carbonitrides show high dimensional stability. With the creep rupture time further prolonging to 353.0 h and 752.3 h under the creep stress of 120 and 100 MPa, respectively, sigma-phases are generated first at grain boundaries and then at inner grains. Meanwhile, large amounts of sigma- phases are formed around (Nb, V)(C, N) particles, indicating the sigma-phase precipitation is accelerated by (Nb, V)(C, N) carbonitrides. Composition analysis and thermodynamic calculation are subsequently performed to elucidate the precipitation mechanism of sigma-phase. Carbon and nitrogen depleted zone is detected at the interface between (Nb, V)(C, N) precipitates and austenitic matrix. A correlation between sigma-phase and C/N contents has been calculated by Thermo-Calc, which shows that the mass fraction of sigma-phase increases with the decreasing C/N contents. According to the thermodynamic calculations and experimental results, it is reasonably inferred that the formation of sigma-phase is induced by the carbon and nitrogen depletion in austenitic matrix. Additionally, the fracture surfaces of creep specimens show intergranular fracture under all creep stresses. When the creep time is comparatively short, cracks are inclined to propagate along grain boundaries owing to the low cohesion between grain boundary M23C6 precipitates and austenitic matrix, resulting in intergranular creep fracture. With the precipitation of sigma-phase at grain boundaries after long time creep, the cracks are primarily generated from sigma-phase, further deteriorating the creep elongation.
Keywordaustenitic heat resistant stainless steel creep rupture precipitate evolution sigma-phase MX
Funding OrganizationNational Natural Science Foundation of China
DOI10.11900/0412.1961.2018.00361
Indexed BySCI
Language英语
Funding ProjectNational Natural Science Foundation of China[U1708252]
WOS Research AreaMetallurgy & Metallurgical Engineering
WOS SubjectMetallurgy & Metallurgical Engineering
WOS IDWOS:000447845000020
PublisherSCIENCE PRESS
Citation statistics
Cited Times:1[WOS]   [WOS Record]     [Related Records in WOS]
Document Type期刊论文
Identifierhttp://ir.imr.ac.cn/handle/321006/129794
Collection中国科学院金属研究所
Corresponding AuthorLi Dianzhong
Affiliation1.Chinese Acad Sci, Inst Met Res, Shenyang 110016, Liaoning, Peoples R China
2.Univ Sci & Technol China, Sch Mat Sci & Engn, Shenyang 110016, Liaoning, Peoples R China
Recommended Citation
GB/T 7714
Hu Guodong,Wang Pei,Li Dianzhong,et al. Precipitate Evolution in a Modified 25Cr-20Ni Austenitic Heat Resistant Stainless Steel During Creep Rupture Test at 750 degrees C[J]. ACTA METALLURGICA SINICA,2018,54(11):1705-1714.
APA Hu Guodong,Wang Pei,Li Dianzhong,&Li Yiyi.(2018).Precipitate Evolution in a Modified 25Cr-20Ni Austenitic Heat Resistant Stainless Steel During Creep Rupture Test at 750 degrees C.ACTA METALLURGICA SINICA,54(11),1705-1714.
MLA Hu Guodong,et al."Precipitate Evolution in a Modified 25Cr-20Ni Austenitic Heat Resistant Stainless Steel During Creep Rupture Test at 750 degrees C".ACTA METALLURGICA SINICA 54.11(2018):1705-1714.
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