1. The change in the structure of the boundaries of recrystallized austenite grains during heating and the development of breaks in the boundaries are due to annealing twins growing from the breaks in the boundaries or near them. 2. Large numbers of annealing twins not connected with the boundaries of the matrix are observed in large grains. Their appearance is explained by the "explosive" kinetics of the breakup of boundaries. Such twins are unstable and disappear due to migration of noncoherent boundaries or breakup of low-mobility coherent twin boundaries. 3. The formation of annealing twins should be regarded as an intermediate stage in the disappearance of intergranular boundaries and anomalous grain growth by union of grains in metals and alloys with low stacking fault energies. The total grain-boundary energy decreases as the result of this process.