Effect of Strain Heterogeneity on the Recrystallization Behavior of an Oxide Dispersion Strengthened Ferritic Alloy

Abstract

Oxide Dispersion Strengthened (ODS) Fe-based alloys often contain 0.5wt% of fine, uniformly dispersed, yttrium oxide particles in a Fe-Cr-Al matrix. They are ideal candidates for high temperature applications such as high temperature heat exchangers or nuclear power plants due to their good combination of creep and oxidation resistance. Numerous studies of annealing phenomena have shown that nucleation and growth of recrystallized grains, as well as the recrystallization texture, strongly depend on the deformed state of a previously cold worked alloy. In the present work, we examined the effect of strain heterogeneity on the development of recrystallized grain structures using bend samples. A bend test introduces a stress gradient and both compressive and tensile deformation. After a further heat treatment at 1380°C for 1 hour in air, the recrystallization behavior was characterized on both the tension and compression sides of the samples at varied levels of strain. Electron backscattering diffraction (EBSD) was used to analyze recrystallization behavior and texture. The results demonstrated that: recrystallized grains only formed in areas of sample subject to plastic compression; maximum grain size increased with increasing severity of bending deformation; there was heterogeneity in the recrystallized grain size, which varied with distance from the bending neutral axis. This indicates that the strain heterogeneity conducive to recrystallization was introduced by the non-uniform plastic strains in the compression region. However, the regions of tensile bending in all samples remained unrecrystallized and strong shear banding was evident.