Microstructure and texture evolution and ring-tensile properties of recrystallized FeCrAl ODS cladding tubes

Abstract

Oxide dispersion strengthened (ODS) FeCrAl ferritic steels are being developed as potential accident tolerance fuel cladding materials for the light water reactors (LWRs) due to significant improvement in steam oxidation by alumina forming scale and good mechanical properties up to high temperatures. In this study, the microstructural characteristics and tensile properties of the two FeCrAl ODS cladding tubes with different extrusion temperatures of 1100 °C and 1150 °C were investigated during processing conditions. While the hot extruded sample showed micron sized elongated grains with strong α-fiber in <110> texture, cold pilger rolling process change the microstructure to submicron/micron size grain structure along with texture evolution to both α-fiber (<110> texture) and γ-fiber ({111} texture) via crystalline rotations. Subsequently, final annealing resulted in evolution of microstructure to large grain recrystallized structure starting at recrystallization temperature of ~810–850 °C. Two distinct texture development happened in recrystallized cladding tubes, i.e., only large elongated grains of (110) <211> texture following extrusion temperature of 1100 °C; and two texture components of (110) <211> and {111} <112> following higher extrusion temperature of 1150 °C. The different texture development and retarding of recrystallization progress in 1100°C-extruded cladding tubes were attributed to higher distribution of oxide particles. Furthermore, the ring-tensile test properties of recrystallized FeCrAl ODS cladding tubes were evaluated in the temperature range of 25–800 °C and showed a very good combination of strength-ductility with a lower strength and higher ductility for 1150 °C extruded tube up to ~500 °C and opposite properties at higher temperatures.