Different mechanical behavior of MA957 ODS and Eurofer’97 steels exposed to flowing helium of 720˚C

Result code in IS VaVaI

<a href="https://www.isvavai.cz/riv?ss=detail&h=RIV%2F26722445%3A_____%2F15%3AN0000007" target="_blank" >RIV/26722445:_____/15:N0000007 - isvavai.cz</a>

Result on the web

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DOI - Digital Object Identifier

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Result language

angličtina

Original language name

Different mechanical behavior of MA957 ODS and Eurofer’97 steels exposed to flowing helium of 720˚C

Original language description

Presentation at the ICM12 conference, 10.5.2015 – 14.5.2015 Since ODS steels have been developed for the use of high temperature applications in the range from 400 to 700˚C, thermal aging related problems at prolonged service times need to be intensively studied. The aim of the work was to describe fracture behaviour of MA957 ODS steel (14%Cr, 0,3Mo, 0,9Ti, 0,25%Y2O3 produced by mechanical alloying process) after high temperature exposure in comparison to the Eurofer’97 plate steel (9%Cr, 1%W) behavior. The both materials are considered for future nuclear energy systems. Due to microstructural characteristics, the MA957 steel embodies excellent combination of high-temperature strength and oxidation resistance. The fine oxide dispersion also serves as trapping sites for point defects induced by radiation displacement and thus reduces remarkably irradiation swelling of the MA957 steel [1]. For space nuclear reactors cooled by a gas mixture of He and Xe at reactor temperatures <1100˚C, the MA-ODS steels are particularly very attractive as structure materials [2]. It is well known that thermal aging of high Cr ferritic steels can result in the formation of coherent particles of a’ (Cr-rich ferrite) with an increase in yield and tensile strength, and a reduction in ductility associated with embrittlement when exposed at temperatures above 400˚C [3]. The degree of the embrittlement, manifested in lower impact and fracture toughness, increases with Cr content; for 14 Cr ODS it had been indicated already at 440˚C after 320 hours of exposure. The main problems of the MA957 type ODS are connected to lower toughness and heterogenuity of behaviour as well as transition temperature behaviour of ferritic matrix of the steel and strengthening by oxide dispersion. Whereas, the long-term exposure of the Eurofer’97 steel at high temperatures leads to different microstructural changes [4]; the coarsening of the M23C6 (Cr rich) precipitates and recrystallization of subgrains were found after ageing at 550˚C/5000 h [5]. Small specimens (MicroCharpy, 3x4x27 mm3 and miniTensile ø2 mm) were exposed to helium gas flowing in the High Temperature Furnace at 720˚C for 500 hours. Then, the specimens were tested for the impact and tensile behavior. The test results are compared to the other two sets of specimens of the previous tests, as received and isotermally annealed at 650˚C in the case of the ODS steel. The He exposed materials showed positive shift of transition temperature and change of the upper shelf value. While the upper shelf value decreased in the exposed Eurofer’97, it significantly increased in the ODS steel. The difference is discussed in terms of microscopy observation in the paper.

Czech name

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Czech description

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Type

O - Miscellaneous

CEP classification

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OECD FORD branch

20305 - Nuclear related engineering; (nuclear physics to be 1.3);

Project

<a href="/en/project/GA14-25246S" target="_blank" >GA14-25246S: Advanced ODS steels for applications in heavy liquid metals environments</a><br>

Continuities

P - Projekt vyzkumu a vyvoje financovany z verejnych zdroju (s odkazem do CEP)

Publication year

2015

Confidentiality

S - Úplné a pravdivé údaje o projektu nepodléhají ochraně podle zvláštních právních předpisů