TEM study of recovery and recrystallization mechanisms after 40% cold rolling in an IF-Ti steel

The deformed microstructure of an IF-Ti steel has been characterized by TEM observations after 40% cold rolling. Different substructures can be distinguished: lamellar bands for the {1 1 1}〈1 1 2〉 grains belonging to the γ fibre ND∥〈1 1 1〉 and equiaxed cells for the {1 1 1}〈1 1 0〉 orientation that belong to both γ and α fibres (α fibre RD∥〈1 1 0〉). Whatever the initial dislocation structure, the first steps of nucleus formation is characterized by coalescence and growth of existing cells in the recovered matrix. Then, nucleus growth occurs by sub-boundary migration. Nucleation is mainly intragranular for the {1 1 1}〈1 1 2〉 grains and it is widely observed at the grain boundaries or at the vicinity of the grain boundaries for the {1 1 1}〈1 1 0〉 grains. Therefore, first steps of recrystallization mainly take place by continuous growth of subgrains followed quickly or not by bulging of grain boundaries.