SEM study on the M7C3 carbide nucleation during eutectic solidification of high-chromium white irons

This work shows the nature of nucleation and growth of M7C3 carbides in high-chromium white irons during eutectic solidification using scanning electron microscopy. Different chemical compositions of hypoeutectic high-chromium irons were used for the present study. Imaging was undertaken on a JEOL 6400 scanning electron microscope (SEM) on samples where solidification was interrupted by decantation techniques. Bar- and plate-like carbides, which seemed to nucleate on the surface of primary dendrites and at the solute-rich areas between secondary arms, were observed in these irons. The final carbide morphology in the alloys is discussed in terms of the eutectic nucleation and the preferred crystallographic growth direction of the carbide phase.