Aspects of orientation-dependent grain growth in extra-low carbon and interstitial-free steels during continuous annealing

The present work concentrates on the application of orientation imaging microscopy (OIM) based on the electron backscattered diffraction (EBSD) technique to the investigation of the microstructural evolution of an extra-low carbon (ELC) steel and a Ti-Nb-bearing interstitial-free (IF) steel, during continuous annealing. Aspects like the nucleation, the evolution of the recrystallized volume fraction and grain size of grains with different orientations, the interface area limiting recrystallized {111} regions, and the apparent growth rates have been considered. Different criteria have been applied in order to identify crystallites produced during annealing. During the first stages. of annealing, a network of grain boundaries with misorientations higher than 10 deg is produced, mainly inside the deformed gamma-fiber grains. The crystallites formed within this network, free from cells or subgrains at their interiors, can be considered as potential nuclei. However, among all, only some of them become effective due to an important selection. The {111} recrystallized grains have a significant size and number advantage as compared with other texture components, and a hard impingement between clusters of {111} grains is produced during grain growth. The effect of grain growth behind the recrystallization front seems to be negligible as compared with the grain coarsening produced by the migration of this front, driven by the cold-work stored energy.