Cast iron generally means grey cast iron, but is identifies a group of ferrous alloys which solidify with a eutectic.
Overview:
Iron accounts for more than 95% the alloy material, while the main
alloying elements are carbon and silicon. The amount of carbon in cast
iron is 2.1-4% while ferrous alloys with less carbon are called carbon
steel by definition. Cast iron has appreciable amount of silicon
normally 1.3%. Therefore, these alloys should be considered ternary
Fe-C-Si alloys.
In spite of this, the principles of cast iron solidification are
understood from the binary iron carbon phase diagram, where the
eutectic point lies at 1154 °C and 4.3 wt% carbon. Because cast iron
has this composition, its melting temperature of 1150 to 1200 °C is
about 300 degrees less than the melting point of pure iron. Cast iron
tends to be brittle, though the name of particular alloy may suggest
opposite. The color of a fracture surface may be utilized to identify
an alloy; carbide impurities allow cracks to pass straight through
resulting in a smooth "white" surface, while graphic flakes deflect a
passing crack and initiate countless new cracks as the material breaks,
leading to a rough surface that looks grey with its low melting point,
good fluidity, castability, excellent machinability and wear rising
resistance, cast irons have become an engineering material with a wide
range of uses like pipes, machine and auto parts.
Products:
Cast iron is produced by remelting pig iron, normally with large
quantities of scrap iron and steel and initiating steps to remove
unwanted contaminants like phosphorus and sulfur. Depending on use
carbon and silicon content are lessened to the required levels which
may be anywhere from 2% to 3.5% and 1% 3% respectively. Other elements
are then added to the melt prior to the final form being made by
casting.
Iron is generally melted in a small blast furnace called cupola. After
melting is over the melted iron is ladled from the forehearth of blast
furnace. This system was developed by the Chinese whose innovative
ideas brought revolution in field of metallurgy. Before that iron was
melted in an air furnace, which is a type of reverberatory furnace.
Some advantages of cast iron in engineering uses:
a) A family of metals having capacity of being used for engineering and
production needs. b) You can have it in a wide range of mechanical and
physical properties.
c) Good strength to weight ratio. d) Generally cheaper than other
competing metals and lower financial cost per unit of strength compared
to other metals. e) Lesser density and higher thermal conductivity then
steels at comparable tensile strength levels. f) Easily mechniable,
allows high speeds and feeds and less energy due to free graphite being
presence. g) Many iron castings may be utilized without heat treatment
(as cast) but when required may be heat treated to increase overall
properties or local property like surface hardness. h) Very good
damping capability especially in grey irons. i) Chemical analysis may
be changed to give improved special properties like corrosion
resistance, oxidation and wear resistance.
j) Quickly changes from design to finished goods. k) Capable of having
highly complex sizes from ounces to 100 tons. l) Of flexible pattern
and capacity to improve appearance for sales appeal. m) You can make
intricate shapes as well as very thin to very thick sections. n)
Capable of redesigning and combining two or more parts from metals into
a single casting thereby lessening assembly cost and time. o) Capable
of being cast with inserts of other metals.
p) Many casting systems for low, medium or high production. Less
tendency toward residual stress and warpage than other competing
metals.
