F. Eiichi Fujita1, Yutaka Ono2 and Yukio Inokuti3
1Department of Physics, Faculty of Engineering Science, Osaka University, Toyonaka
The effect of addition of a small amount of silicon on the precipitation process of carbon in super-purity iron was examined. The specimens containing 0.02 and 0.2 wt% silicon were made from the zone melted Puron, carburized to 0.009 wt% carbon concentration, and quenched into iced water. The precipitation process during the isochronal and isothermal aging was measured by the electrical resistivity and internal friction. The process was also followed by the direct observation by electron microscopy.
The obtained results and our conclusions were as follows.
(1) The precipitation of carbon was presumably delayed by the temporary trapping of migrating carbon atoms by silicon atoms, and the rate of delay is in proportion to the silicon contents.
(2) This trapping effect was analysed by our theory of precipitation based on the chemical rate determining equations taking account of the impurity interaction, and it was clarified that only the above trapping mechanism feasibly accounted for the delay in the precipitation. Oxygen atoms in α-iron of commercially high purity seem to play the same role as silicon in the process of carbon precipitation, and therefore their effect reported in the previous paper may be analysed by the same theory.
(3) Like the case of the zone melted super purity iron, the silicon impregnated super purity iron showed large descrepancies between the electrical resistivity and the internal friction decay curves. This behavior is quite different from that found in the lower purity α-iron, and we concluded that the influences of silicon and oxygen in the structure of the metastable first phase of carbon precipitation are dissimilar to each other in spite of the same trapping effect.
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