Study of Precipitate Nucleation in Iron Carbone Alloys

It is shown that the process of precipitation of carbon into Fe C is in accordance with the Damask, Danielson, and Dienes scheme and that two different stages can be pointed out. In the f irst one, exchanges between solute atoms and clusters (nucleation phase) are reversible. In the second they become irreversible (growth phase). The transition from one stage to the other corresponds exactly to the maximum of precipitation rate as a function of time dX,/dt = f(t). A theoretical investigation of the time tm at which the maximum occurs as a function of T-V(-1) (T-v ageing temperature) gave the value of carbon diffusion energy. The experimentally determined value was 18 kcal/mol which is near to the theoretical one. The nucleation process was markedly influenced by the formation of nuclei at a temperature differing from ageing temperature and fairly shortened by cold working after quenching.