(FT/P2-2) Microstructure and Tensile Properties in Reduced Activation 8 - 9% Cr Steels at Fusion Relevant He/dpa Ratios, dpa Rates and Irradiation Temperatures

E. Materna-Morris1), A. Möslang1), H.-C. Schneider2), R. Rolli2)
 
1) Kernforschungszentrum Karlsruhe IMF I, Karlsruhe, Germany
2) Kernforschungszentrum Karlsruhe IMF II, Karlsruhe, Germany

Abstract.  Helium production by irradiation in reduced-activation martensitic/ferritic 8 - 10 Cr-WTaV steels and their impact on mechanical properties are primary subjects of fusion materials research. In this connection, three heats were melted with different contents of B-nat (natural boron) and the isotope B-10 on the basis of the chemical composition of EUROFER97. The alloy EUROFER97 had the lowest content of B-nat <10 ppm. Two experimental heats were alloyed with boron, one with 82 ppm B-nat and the other with 83 ppm B-10, and a third heat with a very high concentration of 1160 ppm B-10. Tensile specimens were fabricated of the heats and irradiated. The thermal neutron irradiation was carried out in 771 full power days up to 16.3 dpa, and was set between 250 and 450oC. The post-irradiation tensile tests showed the typical strengthening in the temperature range of 250 and 350oC. The achieved He contents by B-10(n,α )Li-7 reaction were < 10 appm, ∼80 appm, ∼415 appm, and ∼5800 appm. Effect of the dpa and irradiation temperature was explained by microstructural changes, such as dislocation loops, α `-precipitates, and He bubbles. The lower B-10 containing specimens broke all ductile, but with a loss in elongation. The specimens with the highest concentration of B-10 broke always brittle. The phenomena observed in the microstructures and fractures were correlated with the mechanical properties. The significant implications of these results are obvious. Even at higher He levels of 400 appm, despite moderate uniform elongations, good levels of tensile ductility have been found in the entire temperature range of irradiation hardening ( < 400oC). In addition, the results supported the hypothesis that at least up to ∼400 appm He, doping with B-10 can be used to simulate He embrittlement effects, at least as long IFMIF with fusion relevant neutron spectra is not yet available.

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