The influence of boron on the ferrite formation in pearlite matrix spheroidal graphite cast iron has been investigated using the advanced analytical equipments such as an SEM and a TEM. The surface of spheroidal graphite in the bull's eye structure, produced by the addition of quite small amount of boron, was analyzed for discussing the ferritizing mechanism.
The microstructure in the spheroidal graphite was investigated using the SEM and TEM, and we found the triangular precipitates, consisted of Fe-Si-Cu-B size of 150nm, in the surface layer of the graphite. These precipitates are consisted of the nano-crystal and act as the nucleus sites of flake graphite size of 0.5μm. The formation of the flake graphite due to the ferritizing above their eutectoid temperature, is the key mechanism of the ferrite formation.
