Cast iron mechanical properties

This type of cast iron is made by high-temperature heat treatment of white iron castings. The mechanical properties of malleable cast irons are given in Table 3.1 usually they are applied to the fabrication of conveyor chain links, pipe fittings and gears. 

Carbon is the cheapest and most effective alloying element for hardening iron. We have already seen in Chapter 1 (Table 1.1) that carbon is added to iron in quantities ranging from 0.04 to 4 wt% to make low, medium and high carbon steels, and cast iron. The mechanical properties are strongly dependent on both the carbon content and on the type of heat treatment. Steels and cast iron can therefore be used in a very wide range of applications (see Table 1.1). 

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. 

The cast irons do not possess ductility. They cannot be pressed or forged even while heated however, their machining properties are considered good. Typical mechanical properties of various types of cast iron are given in Table 3.1. 

Table 3.1. Typical Mechanical Properties of Various Types of Cast Iron [1]...

The main advantages of austenitic cast irons are corrosion and heat resistance. For corrosion resistance, the flake and nodular are similar, but the mechanical properties of nodular cast irons are superior. Some of the commercially available austenitic cast irons are given in the Tables 3.4 and 3.5. 

Typical mechanical properties of various types of cast iron. 55... 

Cast irons are iron with high levels of carbon. Heat treatments and alloying element additions produce gray cast iron, malleable iron, ductile iron, spheroidal cast iron and other grades. The mechanical properties vary significantly. Nickel-containing cast irons have improved hardness and corrosion resistance. Copper or molybdenum additions improve strength. 

The figures quoted in Table 3.41, while not authoritative in indicating upper and lower limits, give some idea of the range of analysis to be expected for each type of iron. Because of this variation in composition, cast irons are usually specified in terms of their mechanical properties rather than on an analytical basis. 

The addition of about 20% nickel to cast iron produces materials with a stable austenitic structure these materials are sometimes known as austenitic cast irons but are more often referred to commercially as Ni-Resist cast irons. The austenitic matrix of these irons gives rise to very different mechanical and physical properties to those obtained with the nickel-free grey cast irons. The austenitic matrix is more noble than the matrix of unalloyed grey irons and it was shown in the early work of Vanick and Merica that the corrosion resistance of cast iron increases with increasing nickel content up to about 20% (Fig. 3.42). 

The austenitic irons show excellent casting properties and good machin-ability, which, in combination with the good mechanical properties and good corrosion resistance, ensures wide use of these materials in many applications. 

In view of the poor mechanical properties of the high-silicon irons, the development of any stresses in the castings during solidification is very dangerous, since they may cause the casting to crack in subsequent service. To overcome this risk, it is often desirable to strip the castings from the moulds while they are still red hot and to anneal them at 850°C for 4-5 h, followed by slow cooling ... 

In addition to nickel alloys, nickel also forms an important alloying element in stainless steels and in cast irons, in both of which it confers additional corrosion resistance and improved mechanical and engineering properties, and in Fe-Ni alloys for obtaining controlled physical and magnetic properties (see Chapter 3). With non-ferrous metals nickel also forms important types of alloys, especially with copper, i.e. cupro-nickels and nickel silvers these are dealt with in Section 4.2. 

Cast iron may be used under similar circumstances, but has inferior mechanical properties. It has been used, although not in current practice, for internal cathodic protection, where it has been demonstrated that the presence of ferrous ions in water is of benefit in reducing sulphide-induced attack on Cu alloy tube plate and tubesWater treatment has now been found to be a more practical method. 

Physical and Mechanical Properties of Aluminum, Iron/Steel, and Cast Iron... 

Ferrous Alloys. Many ancient objects allegedly made of iron actually consist not of the pure metal but of alloys of iron and carbon known by the generic name ferrous alloys. These can be broadly classified into two classes steel and cast iron. Steel is the common name for iron-carbon alloys in which the relative amount of carbon ranges between 0.03% and 2%. If the relative amount of carbon in the alloy exceeds 2%, the alloy is known as cast iron (see Table 33) (Angus 1976 Wertime 1961). Steel is outstanding because of the mechanical properties that it acquires when subjected to heat treatment, which causes changes in its structure and physical properties (see Textbox... 

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