Study of the formation and intergrowth of granular eutectic in austenitic steel matrix composite by directional solidification technology

The formation and intergrowth of granular eutectic in austenitic steel matrix composite has been studied by directional solidification technology. The results indicate that the modifying element Si enhances the dendritic segregation of C and Mn. The surface active elements, such as Y and Ca, concentrate highly ahead of the solid-liquid (S-L) interface of the composite due to the nonequilibrium solidification. As a result, the S-L interface of the composite is unstable during solidification. The spatiotemporal condition of the formation and the growth of the granular eutectic is the formation of granular eutectic between austenitic dendrite arms at the end of solidification and its growth restricted by the austenitic dendrites. By the simulating eutectic growth of the granular eutectic by Fe−C−Mn alloy, the Si, Ca, and Y adsorb and enrich on the growing surface of the eutectic during crystallization, which makes the crystallization model of the eutectic turn from facet/nonfacet to nonfacet/nonfacet. The intergrowth of the eutectic can be explained by (1) the influence of the modifying elements on the crystallization of the eutectic, (2) the coarse solidification growth interface of the eutectic and the same growth rate for austenite and cementite ((Fe, Mn)₃C), and (3) the austenite and cementite ((Fe, Mn)₃C) have not lateral branch during eutectic growth.