Microstructure Observations of Graphite in Gray Cast Iron Using TEM

Abstract

Cast iron is an iron alloy mainly composed of carbon and silicon, the amount of carbon is more than 2.1 mass%. Cast irons, gray cast iron and ductile cast iron, have been used as industrial parts and automobile parts widely because they have a good wear resistance and an excellent machinability. Graphite formation mechanism have been proposed, but, it is not established clearly yet. In this study, the microstructure of flake graphite was investigated to reveal the graphite formation mechanisms using FC250 alloy. Transmission electron microscopy (TEM) samples were prepared using focused ion beam (FIB). In the case of a cross section of flake graphite taken perpendicular to its elongated direction using TEM, internal microstructure of flake graphite was observed layered structure. In the case of a cross section of flake graphite taken parallel to its elongated direction, clear microstructure was not observed. Selected area electron diffraction (SAED) from flake graphite showed <0001> direction of graphite are mostly parallel to their thickness.