Mechanical tests on two batches of oxide dispersion strengthened RAFM steel (EUROFER97)

EUROFER97 is a 9CrWVTa reduced-activation ferritic/martensitic (RAFM) steel, modelled after the conventional T91 alloy (9Cr/1Mo/0.2V/0.08Nb); some of the elements in T91 that will transmute in a fusion neutron spectrum into high-energy radiation emitters with long-half life have been selectively replaced by other elements (W has replaced Mo and Ta has replaced Nb). Such replacements do not influence the mechanical properties but are beneficial from a reduced-activation point of view. The latest developments in the ferritic/martensitic steels for nuclear applications tend toward a fine microstructure with small prior austenite grains and a low number of inclusions, in order to achieve an optimal combination of toughness, strength and high-temperature properties. On the other hand, higher operating temperatures may translate into a better efficiency of power reactors; oxide dispersion strengthening (ODS) offers the potential of increasing the operating temperature of RAFM steels from 550 °C to about 625 °C, while retaining satisfactory mechanical properties. A mechanical characterisation of two ODS versions of EUROFER97 has been carried out at SCK-CEN by means of tensile and instrumented KLST Charpy tests. The two alloys, which contain different weight percentages of Y2O3 (0.3 and 0.5%), have been characterised in two orientations in the ‘as-HIPped’ state, that is without any post-HIPping heat treatment.