Abstract
Kinetics of the precipitation of ε-carbide from the ferrite matrix are investigated in detail by means of electrical resistivity measurement and transmission electron microscopy. The aging temperature is between 50°C and 100°C. It is found that the nucleation of precipitates is completed during quenching and during aging, if any, at its very initial stage. The number of nuclei is independent of the quenching or aging temperature. These results are difficult to be explained by any existing theories of homogeneous nucleation. Quenched-in vacancies are shown not to be the predominant nucleation site. It is concluded that impurity atoms, single or pairs, are the most likely nucleation sites.
