Microstructures of dynamically undercooled (melt spun) Fe-base alloys characterized by a post-dendritic needle-like growth morphology were shown to be essentially identical to those of bulk undercooled samples with DeltaT > 190-200 K. Nonequilibrium crystallization is accompanied by the formation of internal stresses and defects which can lead to relaxation processes (polygonization, recrystallization) during the cooling procedure changing the asquenched microstructure. The mechanism and degree of these transformation processes are determined by the level of frozen-in microstresses, the cooling rate in the solid state, and the lattice structure of the alloys.