TYPES
OF CAST IRON:
ALLOY
CAST IRON: This
term designates castings containing alloying elements such as nickel, chromium,
molybdenum, copper, and manganese in sufficient amounts to appreciable change
the physical properties. These elements may be added either to increase the
strength or to obtain special properties such as higher wear resistance,
corrosion resistance, or heat resistance. Alloy cast irons are used extensively
for such parts as automotive cylinders, pistons, piston rings, crankcases, brake
drums and for certain machine tool castings.
CAST
IRON: According
to the specifications adopted by the International Association for Testing
Materials, cast iron is defined as iron containing so much carbon that it
is not malleable at any temperature. To conform to this definition, iron
containing more than 2.2 percent of carbon is classified as cast iron.
Generally, commercial cast iron, however, has a carbon content of between 3 and
4 percent. This carbon may be present as graphite, in which case the iron is
known as gray cast iron.
CHILLED
CAST IRON:
Many gray iron castings have wear-resisting surfaces of white cast iron. These
surfaces are designated by the term "chilled cast iron" since they are
produced in molds having metal chills for cooling the molten metal rapidly. This
rapid cooling results in the formation of cementite and white cast iron.
CUPOLA
MALLEABLE IRON: The
production of Cupola Malleable iron involves initially the use of a cupola or a
cupola in conjunction with an air furnace. This type of malleable iron, called
cupola malleable iron, exhibits good fluidity and will produce sound castings.
It is used in making of pipefittings, valves, and similar parts and has the
useful property of being well suited to galvanizing.
MALLEABLE-IRON
CASTINGS: the
annealing or graphitization of white iron castings produces malleable iron. The
graphitization in this case produces temper carbon, which is graphite in the
form of compact round aggregates.
Malleable castings are used for many industrial applications where
strength, ductility, machinability, and resistance to shock are important
factors.
MODULAR
CAST IRON (DUCTILE IRON): A
distinguishing feature of this type of cast iron, also known as spheroid
graphite iron, is that the graphite is present in ball-like form instead of in
flakes as in ordinary gray cast iron.
The special processing produces this spheroid graphite structure and results in
a casting of high strength and appreciable ductility. Its toughness is
intermediate between that of cast iron and steel and its shock resistance is
comparable to ordinary grades of mild carbon steel. It exhibits good pressure
tightness under high stress and can be welded and brazed.
PEARLIC
MALLEABLE IRON: This
type of malleable iron contains some combined carbon in various forms. It may be
produced either by stopping the heat treatment of regular malleable iron during
the production, before the combined carbon contained therein has all been
transformed to graphite or by reheating regular malleable iron above the
transformation range.
WHITE
CAST IRON:
When nearly all of the carbon in a casting is in the combined or cementite form,
it is known as white cast iron. It is so named because it has a silvery-white
fracture. White cast iron is very hard and also brittle, its ductility is
practically zero.
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