Development of Accident-Tolerant FeCrAl Steels Containing Al₂O₃ Particles by Means of Internal Al Oxidation

FeCrAl ferritic steels containing dispersed Al₂O₃ particles instead of Y₂O₃ or Ce₂O₃ particles were developed for accident-tolerant fuel cladding in light-water reactors. Forcible addition of only oxygen through mechanical alloying can create Al₂O₃ particles by precipitation during annealing above 973 K. The oxygen content was controlled to use oxidation of internal aluminum to form Al₂O₃ particles and increase the number density of Al₂O₃ particles with an average diameter of around 40 nm. The size and number density of Al₂O₃ particles are significantly affected by lattice misfit, and thus interfacial energy between Al₂O₃ particles and the matrix, and by aluminum solubility into the ferrite matrix. The estimated Al₂O₃ particle strengthening stress is consistent with measured tensile stress at 973 K. Both stresses are slightly improved with increasing oxygen content, but are half the level of that in steel strengthened by Ce₂O₃ and CeAlO₃ particles.