Eutectic growth in as-cast medium manganese steel

Eutectic growth in as-cast medium manganese steel modified by a Mg–Ce–Ti–Si compound was investigated by means of transmission electron microscopy (TEM), scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). Results show that the eutectic ((Fe, Mn)3C and austenite) is formed between austenite dendrites at the end of solidification due to the segregation of C and Mn which is enhanced by modifying elements. MgS and CeO2 are formed preferentially during solidification to act as heterogeneous nuclei for the crystallization of the eutectic. The Mg, Ce and Si adsorb and enrich on the growing surface of the eutectic during crystallization, which makes the crystallization model of the eutectic turn from facet–non-facet to non-facet–non-facet. The mechanism of the nodularization of the eutectic can be explained by (1) the heterogeneous nuclei, (2) the influence of the modifying elements on the crystallization of the eutectic and (3) the eutectic growth limited by the small melting pool between austenitic dendrite arms and austenitic grains.