Mechanical Property Ductile Irons

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. 

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. 

A more recent development that is attracting considerable attention is the use of lanthanum in high-temperature iron-base alloys. One such alloy manufactured in the U.S.A. (5) combines excellent oxidation resistance to llOO C with good ductility and ease of fabrication. By comparison with other alloys possessing similar mechanical properties, the manufacturers attribute the alloys superior oxidation resistance to what they describe as a small (200 ppm) but effective addition of lanthanum. 

Aluminium alloys well with up to about 3-5 per cent, of tantalum, which has no effect, however, on the mechanical strength, ductility, and working properties of aluminium.3 Reduction of tantalum pentoxide by the thermite process yields hard, brittle alloys.1 A substance the composition of which corresponds with the formula TaAls has been obtained by reducing potassium tantalum fluoride, K2TaF7, with aluminium filings at a high temperature. It is described as an iron-grey crystalline powder, of density 7-02, which is scarcely attacked by acids.5... 

Steels are alloys of iron and up to 1.7% carbon, although steels are not usually found with more than 1.2% carbon. The importance of steels is that their mechanical properties are greatly influenced by their carbon content. As the carbon increases in the steel, the ductility goes down while the hardness and tensile strength go up. A further important consideration is that the hardness of steels can be dramatically increased to even higher levels by a process of heating to above 800°C and quenching in water or some other fluid such as urine... 

Nodular cast iron is obtained by the addition of Mg, either pure or as a FeSiMg or NiMg alloy, to the molten metal. Prior to this, a desulphurisation treatment may be necessary to guarantee successful nodularisation. The presence of Mg in the melt provokes a solidification of the graphite phase in the sh e of microscopic spheres. This gives rise to higher mechanical properties, such as strength and ductility. 

Machining of Spheroidal Ductile Iron, Fig. 3 Relationship between microstructure and mechanical properties for EN-GJS grades according to CLASS GUSS (www.clasguss.de)... 

In [ 1991 Par] the cast iron containing small contents of Cu and Mo was studied aiming to improve mechanical properties. Phase transformations during heat treatment and flieir influence on strengfli, ductility and fracture toughness were established. 

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