Grain orientation dependence of microstructures in a warm rolled IF steel

The microstructures of an IF steel warm rolled to 10% and 30% reductions have been characterised by transmission electron microscopy. Individual grains of various orientations, namely γ grains within 15° of the γ fibre (1 1 1//ND), α grains within 15° of the α fibre (1 1 0//RD) and R grains with orientations other than γ or α grains, have been analysed. A common microstructural feature observed in all the grains studied is the development of a cell block structure where cell blocks are delineated by extended planar dislocation boundaries. However, the characteristics of the boundaries depend on the grain orientation. The extended dislocation boundaries preferentially form on or close (mostly within 10°) to the 1 1 0 and 1 1 2 active slip planes and they also have macroscopic orientation with respect to the sample axes angles. The mean macroscopic angles are found to depend on the grain orientation. The large deviation of measured macroscopic angles (34° and −36°) from the maximum shear plane orientations (±45°) observed in the γ and α grains, and similar observations reported in the literature can be related to a strong correlation between the planes of the extended dislocation boundaries and the active slip planes.