Microstructural stability of an as-fabricated 12Cr-ODS steel under elevated-temperature annealing

The effect of elevated-temperature annealing in the range of 1473 K–1673 K on the coarsening kinetics of nanoparticles and microstructural evolution in an as-fabricated 12Cr-ODS steel was systematically investigated. Results show that the nanoparticles were extremely stable and continued precipitating during annealing at 1473 K, whereas, significant coarsening took place during exposure at 1673 K, increasing by 177% and 423% in diameter for 1 h and 24 h, respectively. Furthermore, heterogeneously distributed voids were developed, sizes of which increased distinctly at 1573 K and 1673 K for longer holding time. This is probably due to the growth and/or aggregation of Ar-entrapped and pre-existed voids in the as-fabricated condition. Additionally, no obvious changes were observed in microstructure and texture at 1473 K, nevertheless, full recrystallization were achieved at 1673 K for 24 h, and the major texture was not altered except reduction of the intensity. The apparent activation energy for recrystallization was experimentally calculated as 424 ± 22 kJ/mol, which was almost the same as that for nanoparticle coarsening, i.e., 412 ± 55 kJ/mol, suggesting that recrystallization proceeded accompanying with nanoparticle coarsening that would in turn stimulate the recrystallization process. It was deduced that recrystallization in the as-fabricated 12Cr-ODS steel was presumably not able to occur until the nanoparticles were dissolving and/or coarsening during annealing.