Properties of Cast Irons

Three main factors that determine the properties of cast iron are  

Most commercial cast irons contain 2.5-4% carbon, and it is the occurrence of some of this carbon as free graphite in the matrix that is the characteristic feature of thin material. About 0.8-0.9% carbon is in a bound form as cementite (iron carbide). 

The cast irons usually have a ferrite-pearlite structure, which determines its mechanical properties. The ferrite content determines the cast iron s viscosity, while the pearlite content determines its rigidity and strength. 

Because cast iron has a carbon content approximately equivalent to its eutectic composition, it can be cast at lower temperatures than steel and flows more readily than steel because of its much narrower temperature solidification range. The presence of the graphite flakes in cast iron decreases its shrinkage on solidification much less than that of steel. These factors contribute to the fabrication of cast iron as sound castings in complex shapes and with accurate dimensions at low cost. 

The physical properties of cast irons are characterized by the following data  

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ASTM. Report on Properties of Cast Iron at Elevated Temperatures, ASTM Special Report N248 (1959). 

Since buried pipes for water, sewage and gas are a major use of cast iron, the corrosion of buried iron structures needs special consideration in any study of the corrosion properties of cast iron. It is also a very complex topic that is not fully understood. 

The peritectic transformation generally has little effect on the structure, properties or corrosion resistance of steels at room temperature an exception to this occurs in the welding of certain steels, when 6-ferrite can be retained at room temperature and can affect corrosion resistance. Furthermore, since most steels contain less than about 1 -0 oC (and by far the greatest tonnage contains less than about 0-3%C) the eutectic reaction is of relevance only in relation to the structure and properties of cast irons, which generally contain 2-4%C. This discussion, therefore, will be limited to the eutectoid reaction that occurs when homogeneous austenite is cooled. 

Properties of cast iron, wrought iron, and steel. 

By mixing different grades of metal in the cupola, different makers produce cast-iron vessels which resist the action of special chemicals particularly well. The manipulation of cast-iron in the cupola to produce castings which have specific resisting properties in relation to different chemicals is a matter which has not yet received the attention it deserves. That the properties of cast-iron are largely influenced by admixtures with other elements is well established and it is possible that when our knowledge has become more complete, we shall be able to use iron vessels in operations for which at present they are not suitable. It may be generally said that cast-iron will withstand the action of alkalies when they are in solution and... 

Three main factors that determine the properties of cast iron are the chemical composition of the cast iron, the rate of cooling of the casting in the mold, and the type of graphite formed. 

Table 3.1 -82 Mechanical properties of cast irons, cont.

Element s5anbol, Ce rare earth/lanthanlde Z 58 A(r) 140.12 density (at 20°C), 6.77 g/cm m.p., 799°C named for the asteroid Ceres discovered 1803 used in alloys to improve properties of cast iron and magnesium alloys. Compxjunds used in ceramic coatings. 

Siiry, P. Hiltbrunner, K. Untersuchungen zum Einflul des Nickelgehaltes auf die Korrosionseigenschaften von Gu eisen (Tests on the influence of the Nickel content on the corrosions properties of cast iron) (in German)... 

Table 1 Material characteristics and properties of cast-iron drainpipes [19]...

Cast iron is an alloy of iron, carhon, silicon, and manganese. Carhon is in the range of 2 to 4%. The cooUng rate after casting of cast iron and subsequent heat treatment determine its mechanical properties. Carhon is very important to the properties of cast iron. 

Mechanical Properties of Cast Irons Due to the multitude of as-cast structures as a function of alloy corr5>osition, melt treatment, cooling rate (as influenced by the cooling conditions and the cross section of the work piece), and subsequent heat treatment, there is a wide range of mechanical properties which can be achieved according to the requirements of the application. Table 3.1-82 gives a survey in terms of characteristic examples. 

Cast irons have carbon content between 2 and 4%, and often significant amounts of carbon and smaller amounts of other elements. The following factors determine the properties of cast iron ... 

It is also known as ductile iron in USA and is produced by treating a high carbon equivalent liquid iron with manganese or cerium to prevent the formation of graphite flakes. The structure at room temperature comprises a graphite spheres in a matrix of ferrite. Ductility is increased by heating to 900°C followed by a slow quench. Typical properties of cast irons are given in Table 9.12. 

Cast irons can be cast into intricate shapes because of their excellent fluidity and relatively low melting points and can be alloyed for improvement of corrosion resistance and strength. With proper alloying, the corrosion resistance of cast irons can equal or exceed that of stainless steels and nickel-base alloys. The wide spectrum of properties of cast iron is controlled by three main factors the chemical composition of the iron, the rate of cooling of the casting in the mold, and the type of carbide or graphite formed. 

Still other annealing treatments are possible. For example, glasses are annealed, as outlined in Section 13.10, to remove residual internal stresses that render the material excessively weak. In addition, microstructural alterations and the attendant modification of mechanical properties of cast irons, as discussed in Section 11.2, result from what are, in a sense, annealing treatments. 

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