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 g fibre ND || < 1 1 1 > and equiaxed cells for the {1 1 1} < 110 > orientation that belong to both gamma and alpha fibres (alpha fibre RD|| < 110 > ). 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} < 112 > 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.