We describe our optical and electron-microscopy observations of pearlite structures in eutectoid steels which seem to imply that the mechanisms of formation of pearlite colonies in these steels differ from those observed earlier for non-eutectoid steels. A simple theoretical model to study kinetics of pearlite transformations is suggested. Simulations of growth of pearlite colonies based on this model reveal that for the volume carbon diffusion mechanism usually-supposed such growth is always unstable, and the steady-state growth can be realized only via the interfacial carbon diffusion mechanism. A model of formation of pearlite colonies based on the assumption of a strong enhancement of carbon diffusion near grain boundaries is also suggested. The model can be applicable to the plastically deformed steels, and the results of simulations based on this model qualitatively agree with some microstructural features of formation of pearlite colonies observed in such steels.

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The dislocation gliding in crystals with impurities is investigated by computer simulations for the two dimensional Frenkel-Kontorova model. It is shown that the impurity-dislocation interaction can result in both the stimulation of the double-kink formation (which increases the dislocation mobility) and the trapping of moving kinks by the impurities with the following kink-antikink recombination (which slows down the dislo cation motion). The relative importance of these competing mechanisms depend mostly on the temperature as well as the type of impurity. Here we demonstrate that the presence of impurities can increase the dislocation velocity at low temperatures which leads to the solid solution softening. With increasing temperature, a transition from the solid solution softening to the solid solution hardening regime takes place.

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