Microbands and crystal orientation metastability in cold rolled interstitial-free steel

At low cold rolling reductions microbands form in grains which have either 〈1 1 0〉 or 〈1 1 1〉 parallel to the transverse direction. They appear to form by crystallographic slip and existing theory is sufficient to explain their morphology. Detailed analysis of the mechanics of crystal rotation shows that the orientations belonging to the sets 〈1 1 0〉//TD and 〈1 1 1〉//TD can rotate between two unstable orientations before a stable orientation is reached. This crystallographic metastability is shown to be responsible for the formation of either one or two sets of microbands, and theory and measurement agree that they should form at 20–40° to the rolling direction when measured in the longitudinal section.