Overview of the tensile properties of EUROFER in the unirradiated and irradiated conditions
Introduction
Reduced activation ferritic/martensitic (RAFM) steels are presently considered as primary structural materials for a demonstration fusion plant (DEMO). Although service conditions are not yet fully established in terms of temperatures, stresses or environment, simplified studies are available investigating different concepts [1]. Predictably, irradiation effects are of highest concern amongst environmental conditions in a fusion reactor.
The European Union reference material is a 9Cr–1.1W–0.2V–0.07Ta–0.1C RAFM steel, denominated EUROFER (or EUROFER97), which exhibits a tempered martensitic microstructure and presently allows operation up to 550 °C [2], [3]. Since one of the main issues of RAFM steels is the effect of irradiation at temperatures lower than about 400 °C, the European Fusion Development Agreement (EFDA) has devoted considerable efforts and budget to the characterization of post-irradiation mechanical and microstructural properties of EUROFER. Irradiations have been conducted in test reactors up to a wide range of radiation damage: from 0.3 up to 70–80 dpa [4]. In 2005, EFDA launched an activity aimed at the collection and critical assessment of the mechanical and microstructural property data of irradiated EUROFER, including also properties in the unirradiated condition and comparisons with other RAFM steels, such as F82H, JLF-1, CLAM and others.
This paper presents an overview of the tensile property data of EUROFER in the unirradiated and irradiated conditions, conducted by SCK•CEN within the above mentioned activity [5].
Section snippets
Database of RAFM steels tensile properties
The first phase of the activity consisted in the collection of available tensile test results for EUROFER in the unirradiated and irradiated conditions, using all available sources, including ‘informal’ contacts with investigators in the case of yet unpublished data.
An EXCEL97 database was compiled in order to facilitate the analysis of the available information. The database contains more than 1000 records, each record corresponding to the results of an individual tensile test. It includes
Strategy used and materials considered
In the unirradiated condition, EUROFER tensile properties have been analyzed as a function of test temperature (Ttest) and compared to equivalent information for other relevant RAFM steels (F82H, JLF-1, CLAM and OPTIFER).
As far as irradiated properties are concerned, the collected information allows tensile results to be analyzed as a function of irradiation temperature (Tirr) and accumulated dose (dpa). Data pooling was necessary in order to detect and investigate the influence of each
Unirradiated tensile properties
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No influence of product form (plates of different thickness or bars) is observed for EUROFER-1 (first batch), except for a slightly lower strength of the 25 mm plate at temperatures below RT.
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For EUROFER-2 (second batch), more scatter is observed between product forms, with the bars and the 8 mm plate delivering the worst and the best tensile properties, respectively.
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The two EUROFER batches are equivalent in terms of mechanical resistance (yield strength in Fig. 1), but EUROFER-2 exhibits better
Dose dependence
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A steep increase with dose of irradiation hardening up to ∼10 dpa is observed, followed by a tendency to saturation; based on the presently available data, it is not possible yet to exactly define the saturation dose or level.
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For Tirr = 300 °C and above ∼0.7 dpa, strain hardening capability vanishes and uniform elongation is significantly reduced (below 0.5%, Fig. 3). On the other hand, reduction of area appears to remain at sufficient levels (above 65% at 9 dpa, Fig. 4).
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Based on the limited
Comparisons with other RAFM steels
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In the unirradiated condition, EUROFER shows equivalent tensile properties (strength and ductility) to other RAFM steels, such as F82H-mod, JLF-1, CLAM and OPTIFER.
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In the irradiated condition, only very limited comparisons could be made due to the scarcity of available data under comparable irradiation conditions. Nevertheless, it appears that EUROFER irradiated at 300 °C exhibits more hardening and comparable ductility as compared to F82H-mod and JLF-1. Further comparisons between EUROFER and
Future perspectives
Further insight into the tensile properties of irradiated EUROFER will be gained once post-irradiation results from recently concluded irradiation experiments (namely, SPICE and ARBOR-2) are made available.
Acknowledgements
The authors are gratefully indebted to all the colleagues who have kindly provided tensile data, even when still unpublished, namely: Jan-Willem Rensman (NRG), Ana Alamo, Fahrad Tavassoli and Jean Henry (CEA), Edeltraud Materna-Morris (FZK), Philippe Spätig (PSI), Claus Petersen (FZK) and H. Tanigawa (JAERI). This work, supported by the European Communities under the contract of Association between EURATOM/SCK•CEN, was carried out within the framework of the European Fusion Development
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