Cast iron (metallurgy) - SpeedyLook encyclopedia

The cast iron , in Iron and steel industry, is a rich Alliage of Fer from 1,7 to 6,67% of Carbone, below this percentage they are the Acier S and the Fer S industrialists.

Principal characteristics

The pig iron and cast iron all of alloys is intended for the foundry. The pig iron and cast iron is distinguished from other alloys by their excellent Coulabilité (this term gathers thermal inertia and the fluidity of alloy in fusion, it is measured in a way standardized by the test known as of the spiral).

The cast iron has a temperature of fusion going from 1135 °C to 1350 °C according to the percentage of Carbone and Silicium which it contains.

The cast iron is a precursor in the manufacture of the Acier starting from Minerai (Hématite) and of coke. It is the alloy which leaves the Haut-fourneau and which will be refined out of steel by heating (Décarburation). It is called then pig iron, to distinguish it from the worked out cast iron, generally resulting from a distinct fusion, composition determined, and intended for the production of castings.

History

The cast iron was discovered in China during the period of the Royaumes combatants (IVe century before Jesus Christ). In Europe, it is during the XIXe century that the cast iron took seat in the economy, via the " process indirect" (production of iron to the blast furnace with obtaining the cast iron in intermediate product).

The cast iron was produced in blast furnaces with Charcoal. Abraham Darby, which was roaster in the beginning, succeeds in producing cast iron using coke (the " coak" that one wrote more tardily: coke of English, to cook, to cook). In 1709, By using not very sulfur coal, it carried out first cast coke pig iron, in its factory of Coalbrookdale. But the product, famous of less good quality which the cast iron with wood, put fifty years before being essential and to become one of the major products of industrialization. Between 1777 and 1779, Abraham Darby III built the bridge of Ironbridge, in Coalbrookdale, the first bridge out of cast iron of the European history. The production of cast iron to wood persisted nevertheless, to some extent because of the protectionism practiced by the producer countries (France, Germany), partly because of quality allotted to this type of cast iron and of the reserves of certain ironmasters.

Compositions of the pig iron and cast iron

One distinguishes different the pig iron and cast iron by their percentage from Carbone:

hypoeutectic cast iron: from 2.11 to carbon 4,3%;
eutectic cast iron: carbon 4,3%

This cast iron at the lowest melting point to 1135 °C.

hypereutectic cast iron: from 4,3 to carbon 6,67%;

Steels crystallize in the diagram metastable iron-carbon: iron-cementite (represented below), whereas the pig iron and cast iron crystallizes in the diagram stable iron-carbon: iron-graphite. The difference between these 2 diagrams lies initially in the speed of cooling, which when it is rather slow, makes it possible to obtain graphite, and not of cementite.

Diagram of phase iron-carbon, allowing to visualize conditions of existence of the pig iron and cast iron

White pig iron

Solution of Pearlite and Cementite. Carbon is there in the form of Carbure Fer (Fe₃C). Having a good flow, and a white aspect shining, white pig iron is mainly used for the parts of aspect and the foundry of Article Très abrasion resistant to wear and, it is very with difficulty usinable.

Principal qualities of the pig iron and cast iron white are:

an excellent wear resistance and abrasion
a beautiful aspect
an excellent flow

The principal defects are:

with difficulty usinable

Grey iron

Family of the pig iron and cast iron where carbon is in the form of Graphite. The graphitic structure of carbon is obtained by a very slow cooling of the cast iron, or the addition of components graphitisants like the Silicium.

Cast iron GL (Lamellate Graphite)

It is most current of grey irons. Graphite is there in the form of plates. Principal qualities of pig iron and cast iron GL are:

Facilitated machining
Very good corrosion resistance and to the hot deformation.
Very good absorption of the vibrations
dimensional Stability (realization of Machine tool quiet and stable geometrically)
Excellent flow.
Price of metal relatively low.

Principal defects:

Relatively fragile compared with steels.

Principal uses:

All parts mechanics (different ranks from resistance)
Built machine tools, good resistance to the vibrations.
Pipes and drain (it is possible to run tubes of big size via the casting by centrifugation)

Cast iron GS (Spheroid Graphite, also called Ductile pig iron)

Cast iron in which graphite is in the form of nodules (spheroids). This particular microstructure is obtained by the magnesium addition in the cast iron little time before the moulding (if the cast iron is maintained in fusion, it loses specificities of pig iron and cast iron GS at the end of ten minutes). Magnesium evaporates but causes a fast crystallization of graphite in the form of nodules. This microstructure gives him mechanical characteristics close to steel.

Obtaining a cast iron GS

A cast iron GS is a cast iron with graphite in which the addition of a modifying agent prevents by mechanisms complex and not completely included/understood at present, the crystallization of the graphite which occurs normally in the form of plate. This delay with the solidifcation then causes the appearance of graphite in the form of more or less spherical nodules. The modifying agent currently used is the Magnésium. Because of its sulfur greed, one needs a basic cast iron forlow sulfur rate to avoid the formation of the Sulfure of magnesium: $Mg+S \rightarrow MgS$ . Paradoxically, a cast iron completely Désulfuré does not give a nodular cast iron. This is why after having desulphurized the cast iron, of sulfur is generally reintroduced in the form of pyrite (FeS) has height of 0.05%. The presence of Phosphore makes fall the characteristics of Ductilité and impact strength.

Structures of the pig iron and cast iron with spheroid graphite

The structure of the pig iron and cast iron depends on the elements on addition and the speed of cooling, these parameters strongly depend on the thickness of the parts. This structure strongly influences the mechanical characteristics.

One distinguishes:

pig iron and cast iron with ferritic matrix
pig iron and cast iron with perlitic matrix
pig iron and cast iron with austenitic matrix
pig iron and cast iron with bainitic matrix or ADI

Principal qualities of pig iron and cast iron GS:

resistant
ductile
good coulabilitée
weldability

Principal defects:

Principal uses:

Auto industry: Part of connection on the ground (ex: suspension arm)
Drains

Uses

The cast iron is used for any type of machine element. For their majority the parts are obtained by run molten metal in siliceous sand moulds. (see Moulding)

the cast iron, and particularly cast iron FGS, is very much used by auto industry for manufacture, moulding then partial machining, of the blocks Moteur, the discs of brakes, the brake drums or of the Stealing S engines, bodies of suspension, Camshaft, Vilebrequin etc
cast iron FGL is used for the manufacture of counterweight (Lifting truck), for the realization of elements of heating, particularly those of high-end.
cast iron FGL is impossible to circumvent for the realization of and the insert firebacks of chimney.
cast iron FGS is particularly used in elements of roadway system like the grids and glances of cleansing (grid of sewer)
Pig iron and cast iron FGS and FGL are used for the realization of urban furniture like the benches and worked rambardes (Metro entrances Guimard), and in ornamentation of buildings like the windowsills, the rosettes of gate, the peaks of grid. There, the FGS is appreciated for its weldability.
cast iron FGL is used for the manufacture of conduits and pipes. With exclusion, for a few years, of the conduits of Gas for domestic use because it has been too breakable with respect to the requests of the traffic of the heavy vehicles and particularly during the use of road rollers with vibration by the road works.
cast iron FGL is preferred for the realization of the frames of machine tools because it has a very good capacity for absorption of the vibrations.

Other use of the cast iron term

The cast iron term is sometimes used ill-advisedly, all these uses are incorrect but nevertheless current:

the term cast aluminum (of copper, zinc…) is sometimes used to indicate a part (alloy) manufactured by Moulage. For alloys aluminum to see Alloys of aluminum for foundry

the term cast iron of steel is sometimes used, in particular for the articles of gardening or the barbecues. It is an abuse language to strictly commercial vocation which indicates actually grey iron. A ferrous alloy not being able to be a cast iron and a steel, the reference to steel be-saying is made to avoid confusion with the aluminum pig iron and cast iron, but actually the reference to steel is commercially more developing that the denomination grey iron.

the term cast iron of stainless or stainless cast iron is sometimes used. Attention this term is voluntarily misleading because there does not exist of stainless cast iron step standardized (oxidation posing little problem to the cast iron). This name in general indicates an aluminum alloy, a plating or a treatment applied to aluminum, even sometimes another material. Be wary of the articles which use this denomination.

Simple: Cast iron

Random links: