The effect of tantalum on the mechanical properties of a 9Cr–2W–0.25V–0.07Ta–0.1C steel

Abstract

An Fe–9Cr–2W–0.25V–0.07Ta–0.1C (9Cr–2WVTa) steel has excellent strength and impact toughness before and after irradiation in the Fast Flux Test Facility (FFTF) and the High Flux Reactor (HFR). The ductile–brittle transition temperature (DBTT) increased only 32°C after 28 dpa at 365°C in FFTF, compared to a shift of ≈60°C for a 9Cr–2WV steel the same as the 9Cr–2WVTa steel but without tantalum. This difference occurred despite the two steels having similar tensile properties before and after irradiation. The 9Cr–2WVTa steel has a smaller prior-austenite grain size, but otherwise microstructures are similar before irradiation and show similar changes during irradiation. The irradiation behavior of the 9Cr–2WVTa steel differs from the 9Cr–2WV steel and other similar steels in two ways: (1) the shift in DBTT of the 9Cr–2WVTa steel irradiated in FFTF does not saturate with fluence by ≈28 dpa, whereas for the 9Cr–2WV steel and most similar steels, saturation occurs at <10 dpa, and (2) the shift in DBTT for 9Cr–2WVTa steel irradiated in FFTF and HFR increased with irradiation temperature, whereas it decreased for the 9Cr–2WV steel, as it does for most similar steels. The improved properties of the 9Cr–2WVTa steel and the differences with other steels were attributed to tantalum in solution.