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Cast Iron

Cast iron is made from re-melting pig iron, usually with some quantities of scrap iron, scrap steel and some alloys, such as Cr, Ni, Mo and Cu according to the different requirements.

Depending on the specific application, iron foundries reduce the carbon and silicon content to the desired levels from 2 to 3.5% and 1 to 3% respectively. Other alloys and elements are also added during melting process according to the different requirements. With the different melting and inoculation processes, the different cast irons will be produced.

White Cast Iron

White cast iron is named after its white surface after fractured. With a lower silicon content and faster cooling, the cementite which precipitates from the melt forms as relatively large particles, where the other phase is austenite. These eutectic carbides are much too large to provide precipitation hardening. Rather, they increase the bulk hardness of the cast iron simply by virtue of their own very high hardness and their substantial volume fraction.

White iron is too brittle for use in many structural components, but with good hardness and abrasion resistance and relatively low cost, so the white iron castings could be used as the wear surfaces (impeller and volute) of slurry pumps, shell liners and lifter bars in ball mills and grinding mills, and the teeth of a backhoe's digging bucket.

Grey Cast Iron

Grey iron is characterized by its graphitic microstructure of flakes, which causes fractures of the material to have a grey appearance. Grey cast iron is named after its grey fractured surface.

Most of grey cast irons have a chemical composition of 2.5 to 4.0% carbon, 1 to 3% silicon, and the remainder is pure iron. Grey cast iron has less tensile strength and shock resistance than ductile iron or malleable iron, however its compressive strength is comparable to low and medium carbon steel.

For the low degrees of grey cast iron, they could be used to produce the casting parts with low requirements for tensile strength, but have good friction and wear properties, such as protective cover, cover, oil pan, hand wheels, frame, floor, hammer, small handle, machine base, frame, box, knife, bed, bearing seat, table, wheels, cover, pump, valve, pipe, flywheel, motor blocks, gas burner, stove grates etc.

For the medium and high degrees of grey cast iron, they have certain degree of tightness or corrosion resistance, so they could be used to produce more important castings such as cylinder, gear, automotive flywheels, cylinder block, cylinder liner, piston, gear box, brake wheel, coupling Plate, medium pressure valve, heavy machine tools, shears, presses, automatic lathe bed, high-pressure hydraulic parts, piston rings, force larger gear, bushings, large engine crankshaft, cylinder block, cylinder liner, cylinder head, etc

Malleable Cast Iron

Malleable iron starts as a white iron casting that is then heat treated at about 900 centigrade. Graphite separates out much more slowly in this case, so that surface tension has time to form it into cottony particles rather than flakes.

Due to their lower aspect ratio, spheroids are relatively short and far from one another. They also have blunt boundaries, as opposed to flakes, which alleviates the stress concentration problems faced by grey cast iron. In general, the properties of malleable cast iron are more like mild steel. There is a limit to how large a part can be cast in malleable iron, since it is made from white cast iron.

However, the malleable cast iron has been replaced by the developed ductile iron because of more good characters of ductile iron.

Ductile Cast Iron

After years development, there are nodular iron or called as ductile cast iron. Tiny amounts of magnesium or cerium added to these alloys slow down the growth of graphite precipitates by bonding to the edges of the graphite planes. Along with careful control of other elements and timing, this allows the carbon to separate as spherical particles as the material solidifies. The properties are similar to malleable iron, but parts can be cast with larger sections.

Ductile iron castings almost cover all major industrial sectors. They have been applied in these sectors that require high strength, ductility, toughness, wear resistance, resistance to severe thermal and mechanical shock, high temperature or low temperature, corrosion resistance and dimensional stability. To meet the conditions of use of these changes, many of the existing grade nodular iron, mechanical properties and provides a rational to a kiss a wide range.

History of Cast Iron

Cast Iron was first invented in China in the 4th century BC and poured into moulds to make ploughshares and pots as well as weapons and pagodas. In the west, where it did not become available till the late 14th century, its earliest uses included cannon and shot. Henry initiated the casting of cannon in England. Soon, English iron workers using blast furnaces developed the technique of producing cast iron cannons, which, while heavier than the prevailing bronze cannons, were much cheaper and enabled England to arm her navy better. The ironmasters of the Weald continued producing cast irons until the 1760s and armament was one of the main uses of irons after the Restoration.

With its relatively low melting point, good fluidity, casting ability, excellent machining ability, resistance to deformation and wear resistance, cast irons have become an engineering material with a wide range of applications and are used in pipes, machines and automotive industry parts.

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