Precipitation from Solid Solutions of C and N in α-Iron

Abstract

The formation of precipitates from the solid solutions of C and N in α‐iron has been studied by means of the internal friction peak associated with the stress‐induced interstitial diffusion of the solute atoms. A transformation law has been found to fit the experimental data. The data are interpreted as showing the following: (1) Fe₃C precipitates in the shape of spheres; (2) an intermediate phase in the precipitation of nitrogen forms in the shape of disks; and (3) within the experimental error there is indicated no continuous nucleation. Using the results of a derivation made by Zener, the mean distance between nuclei is calculated for Fe₃C. For carbon concentrations of about 0.016 wt. percent, this distance is about 800, 2000, and 7000 Angstroms at 27°C, 102°C, and 312°C, respectively. With appropriate experimental conditions, the temperature dependence of the precipitation rate is found to be about the same as the temperature dependence of the diffusion rate of the solute atoms.