for design calculations, the designer must request the foundry to produce test castings which will cool at approximately the same rate as the product casting. Mechanical tests on these test castings will yield the most accurate prediction of the properties in the product casting.

The presence or absence of carbides and the type of matrix obtained in any given section can be controlled by alloying or heat treatment. They need not be discussed here as long as the effects are recognized by the designer. The size of the spheroidal graphite, on the other hand, can be influenced by, amongst other things, the cooling rate of the casting which in turn can be determined by the shape or design of the casting. These effects should be considered in design calculations.

Providing the shape of the graphite is approximately spheroidal, there is negligible deterioration of chemical, physical and technological properties. However, published data vary over a very wide range. Some tenative information on the mechanical properties to expect in carbide-free Ductile Iron of different section sizes is given above. If more precise knowledge of these or other properties is essential

Courtesy: Cleaver-Brooks Company
Division of Aqua-Chem, Inc., USA

This manufacturer specified Ductile Iron pressure vessel sections over gray iron for its new line of cast iron boilers. Ductile Iron to ASTM specification A 395-80 (60-40-18) was selected for its superior tensile, yield and thermal fatigue strengths. For boiler applications these properties are important since they provide improved resistance to pressure vessel failures caused by thermal shock or other stresses. Ductile Iron's excellent corrosion and wear resistance was another factor in Cleaver-Brooks material selection.