High-temperature strength characterization of advanced 9Cr-ODS ferritic steels

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Vol. 510; pp. 115 - 120
• Main Authors: Ukai, S., Ohtsuka, S., Kaito, T., Sakasegawa, H., Chikata, N., Hayashi, S., Ohnuki, S.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Kidlington Elsevier B.V 15.06.2009; Elsevier
• Subjects: Applied sciences; Creep; Exact sciences and technology; Ferritic steels; Grain boundary sliding; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metals. Metallurgy; Nanoindentation measurement; Oxide dispersion strengthening (ODS); Oxide particle–dislocation interaction; Residual ferrite; Ferritic steels; Grain boundary sliding; Residual ferrite; Nanoindentation measurement; Oxide particle–dislocation interaction; Oxide dispersion strengthening (ODS); Oxide particle-dislocation interaction; Creep; Nanoindentation; Oxides; Creep strength; High temperature; Dispersion strengthened metal; Dislocation; Grain boundary slide; Yield strength; Martensitic transformation; Ferritic steel; Microstructure
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2008.04.126

Oxide dispersion strengthened (ODS) ferritic steels, which are the most promising candidate materials for advanced fast reactor fuel elements, have exceptional creep strength at 973 K. The superior creep property of 9Cr-ODS ferritic steels is ascribed to the formation of a nonequilibrium phase, designated as the residual ferrite. The yield strength of the residual ferrite itself has been determined to be as high as 1360 MPa at room temperature from nanoindentation measurements. The creep strength is also enhanced by minimizing the number of packet boundaries induced by the martensitic phase transformation. The creep strain occurs at a lower stress than that necessary for the deformation of the intragrain regions, which are strengthened by an interaction between nanosize oxide particles and dislocations; this occurs by sliding at weaker regions such as at the grain boundaries and packet boundaries. It is found that 9Cr-ODS ferritic steels behave as fiber composite materials comprising the harder residual ferrite and the softer tempered martensite.