1995 Volume 36 Issue 5 Pages 601-609
Elements interacting attractively with carbon are considered to have two effects opposite to each other on the rate of ε-carbide precipitation: (a) they may decrease the diffusion rate of carbon and hence the rate of ε-carbide precipitation, and (b) they may act as preferential nucleation sites to increase the number density of the precipitates and hence the rate of precipitation. However, the whole effects of such elements on the rate of ε-carbide precipitation has not been determined as yet. The purpose of the present paper is to investigate the effects of small addition of titanium, vanadium and chromium, which interact attractively with carbon, on the rate of ε-carbide precipitation. High purity alloys made from 99.99% electrolytic iron were used to minimizes the effect of impurity atoms on the precipitation kinetics of ε-carbide. The kinetics of ε-carbide precipitation was investigated by measuring at 77 K the change in the electrical resistivity due to precipitation. The number density of precipitates was investigated by TEM. The activation energy for carbon atom diffusion was determined by slope change method.
For the concentration investigated, only titanium increases the rate of ε-carbide precipitation by increasing the number density of ε-carbide particles. In the titanium containing alloys, fine precipitates of TiC which are present in the as-quenched condition act as the preferential nucleation sites for ε-carbide. Solute titanium after quenching decreases the rate of carbon diffusion. The decreasing effect, however, is small and the whole effect of tatanium addition is to increase the rate of ε-carbide precipitation.
