Recovery, recrystallization and precipitation behavior in an ATF FeCrAl alloy during annealing treatment

Microstructure evolution of FeCrAl alloy during annealing is critical to the properties and fabrication of the accident-tolerant fuel cladding tubes. In this study, the recovery/recrystallization behavior and the accompanying precipitation process in a warm-rolled Fe-13Cr-4Al-1.85Mo-0.85Nb alloy subjected to annealing at 500–1100 °C were systematically studied. Three distinctly different stages during the annealing treatment were identified: recovery, extended recovery and discontinuous recrystallization. The alloy was always in the recovery state when annealed at 500–600 °C until 6480 min, and it maintained the extended recovery state at 700 °C until 5040 min. During annealing at 800–1100 °C, it successively experienced the recovery, extended recovery and discontinuous recrystallization stages. The simultaneously formed Laves phase had a stronger pinning effect to dislocations rearrangement and subgrain boundaries migration, thus delaying the recrystallization process. When the alloy was annealed at higher temperatures, the precipitates notably coarsened and even re-dissolved into the matrix. The mechanical properties of the alloy were dependent by the precipitation strengthening and recovery or recrystallization softening. The recovery microstructure provided the best tensile strength with good plasticity, and the discontinuous recrystallization microstructure provided the optimal plasticity with a notably decreased strength. The discontinuous recrystallized alloy exhibited the least degradation of mechanical properties at service temperature. The recrystallization and precipitation kinetics were also studied in detail, and the relationship between the microstructure and properties was discussed.