DIRECTIONAL SOLIDIFICATION OF WHITE CAST-IRON

Several studies of the ledeburite eutectic (Fe-Fe3C), in pure Fe-C all oys have shown that it has a lamellar morphology under plane front gro wth conditions. The structure of ledeburite in white cast irons, Fe-C- Si, consists of a rod morphology. It is generally not possible to prod uce 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, t he growth of graphite was suppressed, and the plane front growth of th e ledeburite eutectic in Fe-C-Si alloys was carried out with Si levels up to 1 wt pet. It was found that the growth morphology became a face ted rod morphology at 1 wt pet Si, but in contrast to the usual rod mo rphology 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 solidifi cation to produce the usual rod morphology in Fe-C-Si alloys are discu ssed. Also, data are presented on the spacing of the lamellar eutectic in pure Fe-C ledeburite, which indicates that this system does not fo llow the usual lambda(2)V = constant relation of regular eutectics.