Orientation imaging microscopy studies of recrystallization in interstitial-free steel

The origin of the gamma fiber recrystallization texture in interstitial-tree (IF) steel developed during continuous annealing has been investigated by scanning electron microscopy (SEM) and orientation imaging microscopy (OlM). Nucleation of {111}<uvw > oriented crystals occurs in deformation banded gamma grains and therefore a comprehensive Study of microstructure of cold-rolled IF steel in the sections perpendicular to the rolling and transverse directions (TDs) and the rolling plane (RP) has been carried out to understand the formation, geometry, and microstructural features of recrystallization. The RP section gave abundant evidence of orientation gradients formed in gamma oriented grains that had been subject to orientation splitting to give deformation bands. These orientation gradients across a single grain are around 5 to 30 deg and this orientation difference is sufficient to forth nuclei with mobile interfaces during annealing and hence to create chains of gamma oriented new grains in the original hot band gamma grain envelopes. A grain impingement model requiring orientation pinning is then proposed to explain how these grains, contained in deformed gamma grain envelopes, grow out into their neighbors to dominate the final recrystallization texture of IF steel. The alpha deformed grains contain only small lattice curvatures, and therefore in-grain nucleation is rare. These grains are mostly consumed by invading gamma grains toward the end of the recrystallization process.