Directional solidification of white cast iron

Several studies of the ledeburite eutectic (Fe-Fe3C), in pure Fe-C alloys have shown that it has a lamellar morphology under plane front growth conditions. The structure of ledeburite in white cast irons, Fe-C-Si, consists of a rod morphology. It is generally not possible to produce plane front growth of Fe-C-Si eutectic alloys in the Fe-Fe3C form, because at the slow growth rates required for plane front growth, the Fe3C phase is replaced by graphite. By using small additions of Te, the growth of graphite was suppressed, and the plane front growth of the ledeburite eutectic in Fe-C-Si alloys was carried out with Si levels up to 1 wt pct. It was found that the growth morphology became a faceted rod morphology at 1 wt pct Si, but in contrast to the usual rod morphology of white cast irons, the rod phase was Fe3C rather than iron. It was shown that the usual rod morphology only forms at the sides of the two-phase cellular or dendritic growth fronts in Fe-C-Si alloys. Possible reasons for the inability of plane front directional solidification to produce the usual rod morphology in Fe-C-Si alloys are discussed. Also, data are presented on the spacing of the lamellar eutectic in pure Fe-C ledeburite, which indicates that this system does not follow the usual λ2V = constant relation of regular eutectics.