Effects of Cr element on the crystal structure, microstructure, and mechanical properties of FeCrAl alloys

In the present work, on the foundation of Fe-13Cr-4.5Al-2Mo-1Nb-0.2Si alloy, FeCrAl alloys with low Cr content (7, 8, 9 and 10 wt%) and other minor alloying elements (Ta, Zr and Ni) were prepared. The crystal structure, microstructure, tensile properties and oxidation resistance to high-temperature steam of lean-Cr FeCrAl alloys were investigated. As with the decrease of Cr content, the matrix phase of FeCrAl alloys still exhibited the a-ferrite phase, but the lattice parameter of the matrix phase gradually increased. After annealing, the 13Cr alloy occurred complete recrystallization with an average grain size of 33.5 mu m. Meanwhile, the amount of Fe2Nb-type Laves phase in FeCrAl alloys gradually decreased with the decrease of Cr content below 9 wt%. Owing to the weakest pinning effect from the small amount of Laves phase particles, many coarse equiaxed grains were observed in 7Cr alloy. 10Cr alloy did not occur full recrystallization due to relatively slow diffusion of elements resulting from the high content of alloying elements and recovered microstructure. Reducing the Cr content did not damage tensile properties of FeCrAl alloys at both room temperature and 800 degrees C. Due to the incomplete recrystallization, the 10Cr alloy retained higher strength and relatively poor ductility than other low Cr content alloys at room temperature. Decreasing the content of Cr made the oxidation resistance of lean-Cr alloys worse, which was still better than the traditional Zr alloy. The present work showed that small changes in Cr will not have a remarkable impact on tensile properties and oxidation resistance to high-temperature steam, and low-Cr FeCrAl alloys can be used as an accident-tolerant fuel cladding in light water reactors.