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

Abstract

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 (Fe-9Cr-1W-0.3Ti-0.25Y2O3) with isotropic microstructure is compared to a 14%Cr ferritic tube (Fe-14Cr-1W-0.3Ti-0.25Y2O3) with elongated grains and a strong texture. Tile and notched ring specimens are used to perform uniaxial creep tests at 650°C 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 geometry 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 650°C 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 direction, the 9%Cr tube proves as resistant in the transverse direction.

Strengthening mechanisms of reduced activation ferritic/martensitic steels: A review

“…Fig. 7 shows a comparison of the high-temperature creep performance and radiation resistance between ODS and RAFM steels in recent years [100][101][102][103]. The creep life of the 9Cr ODS steel is ~1000 times longer than that of the F82H and Eurofer 97 steels under 650°C/130 MPa.…”

Effect of Oxygen Content on Microstructure and Tensile Properties of a 22Cr-5Al ODS Steel

“…The high density of nanoscale oxides provides ODS steels with excellent mechanical performance by blocking dislocation slipping and hindering grain boundaries movement [ 5 , 6 , 7 , 8 , 9 ]. Several studies have reported that fine and thermo-stable oxides improve the creep resistance of ferritic steels [ 10 , 11 , 12 , 13 ] and trap He in fine bubbles, thereby limiting He movement and restraining He brittleness [ 2 , 3 , 4 ]. The common processes to fabricate ODS steels are powder metallurgy (PM) with mechanical alloying (MA) and heat consolidation [ 14 ], including hot isostatic pressure (HIP) [ 9 ], hot extrusion (HE) [ 15 , 16 ], and spark plasma sintering (SPS) [ 17 ], and ODS steels have a high density and an excellent tensile strength.…”

Creep Properties of 9Cr and 14Cr ODS Tubes Tested by Inner Gas Pressure

“…However, the ODS steel microstructures are known to be very anisotropic, which depends on the used manufacturing and forming processes [13]. Thus, creep results are very dependent on both the microstructure and testing direction [14], [15].…”

“…However, ODS-materials lose their creep strength when melted, which must be taken into account when designing the test set-up. Rather little openly available information on ODS tube material internal pressure tests and plugging techniques was found in literature [18], [15]. Different methods for plugging have been prospected in earlier study [19].…”