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The role of gray cast iron graphite covers

Gray cast iron Graphite is flake in the metal body, due to the chemical composition of cast iron and cooling conditions are different, thus changing the crystallization conditions of graphite (carbon atoms and the diffusion of iron atoms from the diffusion rate), leading to stone Type, size and distribution.
Under the microscope, gray cast iron graphite was flaky, which is the shape of the three-dimensional stone star, the actual graphite in the three-dimensional shape can be a variety of.
The distribution pattern of flake graphite can be divided into five categories.
A type of graphite: graphite film uniform distribution of non-directional, can not see any trace of dendritic crystal, that is, eutectic austenite. In the solidification and dendritic primary crystal into a continuous whole. The graphite sheet is long and tortuous. This is the most common form of graphite, especially when the sub-eutectic cast iron crystallizes when the subcooling is not large when the graphite is organized. Type B graphite: uniform non-directional distribution. Each chrysanthemum (rose) center of the graphite sheet is small, which is ordinary gray cast iron in the eutectic crystal when the degree of subcooling slightly larger when the formation of graphite distribution type. In the case of eutectic crystallization when the degree of subcooling is slightly larger, the austenite-graphite aggregate (eutectic) obtains a thin eutectic structure, and the graphite is distributed in a large number of flaky aggregates in the globular aggregates, The graphite grows radially outwardly from the center (ie, to the liquid). Ductile iron covers because the graphite side of the austenite surrounded by, so the liquid to grow faster, it was chrysanthemum-like, or rose-like. As the stone is gathered, the strength of the cast iron is reduced. '
C-type graphite: uniform non-directional distribution, coarse graphite. This graphite is often found in the cast iron eutectic degree, that is, the primary graphite. The strength of cast iron is very low when this graphite is present.
D-type graphite: uniform non-directional distribution. This is the sub-eutectic cast iron produced in the case of undercooling greater. At this time the obtained austenite-graphite set off (eutectic) is thinner. Because in the case of greater undercooling conditions, the liquid is rapidly carbon-rich on the surface of the growing austenite, where a new graphite core is produced, at which time the carbon is hindered from the previously generated adjacent graphite inclusions Also stopped their own growth, so the graphite into a small flaky distribution in the dendrites. Usually referred to as chilled graphite or eutectic graphite.
E-type graphite: a directional distribution of wealth. This kind of graphite structure is produced in the case of large eutectic crystal eutectic crystal when the cooling rate is very large, when the austenite is very developed, sandwiched between the austenite dendrites between the residual liquid Crystal crystal, and liquid contact with the direction of growth, graphite growth with a directional, so was a small and directional distribution.
Export ductile iron square covers mainly by the ductile iron to build out of the covers, the quality of this well covers the ball to the rate of the problem. Casting commonly used paint is rust-proof asphalt paint, of course, the surface of the ductile iron cover is also treated by spraying rust-proof asphalt paint. Ductile iron covers have an advantage, is due to ductile iron high strength, good toughness, making the ductile castings than the same type of gray cast iron covers light about 30%.


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