Creep and damage anisotropies of 9%Cr and 14%Cr ODS steel cladding

Two Oxide Dispersion Strengthened (ODS) steel tubes, obtained by means of hot extrusion and cold rolling, are studied as potential materials for cladding applications in sodium-cooled fast reactors. A 9%Cr martensitic tube (Fee9Cre1W-0.3Ti-0.25Y2O3) with isotropic microstructure is compared to a 14%Cr ferritic tube (Fee14Cre1W-0.3Ti-0.25Y2O3) with elongated grains and a strong texture. Tile and notched ring specimens are used to perform uniaxial creep tests at 650C in the longitudinal and transverse directions of the tubes. The 14%Cr ODS steel tube exhibits strong mechanical anisotropies, while the 9%Cr presents only a slight anisotropy in creep resistance, presumably due to the influence of specimen ge- ometry on mechanical fields. Both intergranular and ductile zones have been observed on the fracture surfaces of the uniaxial creep specimens, suggesting the competition of two damage mechanisms. Damage for both tubes appeared anisotropic, with orientated cracks in the rolling directions on the ring specimens and the 14%Cr tile specimens. Internal pressure creep tests also performed at 650C show complementary results for both tubes in agreement with ring specimens’ ones, validating their use for hoop properties assessment. Overall, while the 14%Cr ODS steel tube is strong in the longitudinal di- rection, the 9%Cr tube proves almost no remarkable anisotropy in creep strength.