Effect of silicon on the kinetics of ε-carbide precipitation in high purity Fe-C alloys

Abstract

Silicon is known to decrease the precipitation rate of ε-carbide. However, the cause of silicon decreasing the rate of ε-carbide precipitation has not been determined yet. The purpose of the present paper is to clarify this cause, especially the relationship between the number density of ε-carbide particles and the rate of its precipitation. High purity alloys made from 99.99% electrolytic iron were used in the present paper to minimize the effect of impurity atoms on the precipitation kinetics of ε-carbide as low as possible. The kinetics of ε-carbide precipitation was investigated by measuring the change in electrical resistivity at 77 K. The number density of ε-carbide particles was investigated by TEM. Silicon decreases the rate of ε-carbide precipitation. This decrease is caused by the decrease in the number density of ε-carbide particles with the addition of silicon. Comparing the precipitation rate of Fe-C alloys with that of the Fe-0.4 at.%Si-C alloy, it is concluded that the heterogeneous nucleation occurs in the present Fe-C alloy. That is, silicon decreases the number of the preferred nucleation sites of ε-carbides and hence the number of the ε-carbide particles.