Introduction
Gray cast iron is a kind of cast iron with the main constituent elements of iron, carbon and silicon. It is an alloy material that has been widely used in automobile, machinery, heat exchanger and other fields due to its good casting performance, low cost and good mechanical properties. The unique microstructure of gray cast iron makes it particularly suitable for various components with complicated shapes. The general microstructure of gray cast iron consists of ferrite, pearlite, and graphite.
Characterization of basic organization in gray cast iron
Gray cast iron is composed of iron, carbon and silicon, in which iron is the main component and carbon and silicon are the alloying elements. The ferrite and pearlite are produced by the solidification of the alloy, and the graphite is produced in the later stage. Therefore, gray cast iron has certain differences in the organization of its components from other cast irons.
1. Graphite
The graphite of gray cast iron is lamellar in shape, and its morphology and size are related to the carbon content, cooling rate and alloy composition of the alloy. Low-carbon gray cast iron will not form graphite at all, while high-carbon gray cast iron forms coarse graphite flakes, which are generally flaky, feathery, and globular. Graphite has a cube-shaped hexagonal pattern when observed through an electron microscope, the size of which is mostly below 0.1mm.
2. Ferrite
The shape of ferrite in gray cast iron presents columnar, beach or a combination of columnar and beach, most of which is column-shaped. The ferrite consists of austenite grains, and the size of the grains varies with the cooling rate, alloy composition and other factors. In general, the grain size of grey cast iron is relatively large, mostly in the range of 5~250μm.
3. Pearlite
Pearlite is distributed between graphite and ferrite in both size and shape. It generally consists of spherical or ellipsoidal grains, the size of which is mostly between 1-5μm. The pearlite in gray cast iron has a lamellar structure, with a clear Layered arrangement, and is composed of alternating ferrite and cementite lamellas.
Conclusion
In summary, the basic structure of gray cast iron is composed of ferrite, pearlite and graphite. Their different forms, sizes and distributions are closely related to the alloy composition, cooling rate and other influencing factors. Therefore, in order to get qualified gray cast iron, the selection of alloys and the control of cooling rates should be reasonably adjusted according to different requirements.
