Directional solidification of white cast iron

Several studies of the ledeburite eutectic (Fe-Fe sub 3 C), 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-Fe sub 3 C form, because at the slow growth rates required for plane front growth, the Fe sub 3 C 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.%. It was found that the growth morphology became a faceted rod morphology at 1 wt.% Si, but in contrast to the usual rod morphology of white cast irons, the rod phase was Fe sub 3 C 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 lambda exp 2 V=constant relation of regular eutectics.