抄録
With a view to clarifing the mechanism of the graphite retardation during solidification of cast iron, the effect of bismuth on the morphological change of primary graphite in hypereutectic Fe-C-Si alloy was studied. SEM observation shows the change of primary graphite from normal flake to hexagonal type with bismuth addition, and EPMA analysis clarifies that bismuth is segregated both in the interface between graphite and molten metal and in the subgrain boundary within graphite. Furthermore, graphite separated by quenching of melt at various temperatures shows a hexagonal outline and a hexagonal step pattern decorated by adhered bismuth. This suggests that bismuth existing along the step of graphite crystal controls the graphite step movement which is caused by the attachment of carbon atom to the growing front of graphite crystal from the melt. Therefore, it is assumed that the change of graphite to hexagonal shape is caused by the change of graphite step from random to hexagonal crystal having a structure-sensitive prism plane.
