Grey Iron and Ductile Iron are two different types of Cast Irons
with differences in the type or structure of the carbon present
Cast Iron: Cast Iron is an Iron alloy prepared by heating the
Iron till it liquefies and then adding the alloy component. It
is then poured into a mould where it cools down and solidifies.
The Differences Between Grey Iron And Ductile Iron Are:
Process of Formation: Both Grey Iron and Ductile Iron are
prepared by adding carbon in the hot beds where they are
liquefied but in the case of Ductile Iron, magnesium is also
Structure of Graphite: The graphite found in Grey Iron
has a rod-like or a random flaky pattern while the graphite
found in Ductile Iron is shaped like nodules or spheres.
Ductility: Due to the nodular or spherical shape of the
graphite in Ductile Iron, its molecules have lesser
discontinuities and give rise to the property of Ductility.
Ductility is the ability of a metal to be shaped into wires. The
A395 is the most Ductile of the Ductile Irons and has a
Ductility of 18 to 30 percent elongation. Grey Iron does not
have any recognizable elongation.
Tensile and Yield Strength: The Tensile Strength of Grey
Iron is approximately 20,000 psi (pound per square inch) and its
Yield Strength is not measurable. In contrast, the minimum
Tensile Strength of Ductile Iron is 60,000 psi and its minimum
Yield Strength is 40,000 psi.
Resistance to Impact: Ductile Iron is more resistant to
impacts than Grey Iron. Ductile Iron Casting can resist a
minimum of 7 foot-pounds of impact while Grey Iron can survive a
maximum of only 2 foot-pounds of impact. This higher resistance
is also due to the nodular or the spherical shape of the
Graphite in Ductile Irons.
Thermal Conductivity: The thermal conductivity of Grey
Iron is 46 Watts per meter while the thermal conductivity of
Ductile Iron is 36 Watts per meter. Due to this lesser thermal
conductivity, Ductile Iron is used in the manufacture of gas
cylinders while Grey Iron is used in making utensils.
Vibration: Grey Iron dampens vibrations more effectively
than Ductile Iron. Thus, Grey Iron is used in the machineries
like the milling machines etc.
Ductile Iron, owing to its better strength and Ductility, is
considered the upgraded version of Grey Iron Casting. However,
it has not been able to completely replace Grey Iron as Grey
Iron is still preferred for the manufacture of lot of tools and
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