Ductile Nodular Cast Irons

It is recommended to use ductile (nodular) cast iron instead of gray cast iron (brittle). Ductile iron pipe with a cement mortar lining has given excellent performance. 

Alloys with other useful properties can be obtained by using yttrium as an additive. The metal can be used as a deoxidizer for vanadium and other nonferrous metals. The metal has a low cross section for nuclear capture. 90Y, one of the isotopes of yttrium, exists in equilibrium with its parent 90Sr, a product of nuclear explosions. Yttrium has been considered for use as a nodulizer for producing nodular cast iron, in which the graphite forms compact nodules instead of the usual flakes. Such iron has increased ductility. 

Gray cast irons do not have the abrupt ductile to brittle fraction transition down to -40°C as takes place in steels. Special austenitic nodular cast iron similar to the AUS 203 grade, but with a higher manganese content of about 4%, has been obtained for cryogenic purposes for temperatures down to -253°C. 

Nodular cast iron, also referred to as ductile cast iron, is manufactured by inoculating the molten metal with magnesium or cesium. 

Yttrium is also a deoxidizer of vanadium, and its addition improves the ductility of nodular cast iron. Yttrium oxides increase the resistance of ceramic materials to heating due to an increase in melting temperature. Yttrium hydrate is used as temperature stabilizer both to increase the stability of heating alloys and to moderate neutrons in nuclear reactors (Luckey and Venugopal 1978 Greinacher 1981 Jezowska-Trzebia-towska et al. 1990). 

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. 

Ductile cast iron Nodular cast iron Spheroidal graphite iron Sphemlitic graphite cast iron SG iron... 

Pearlitic blackheart malleable cast iron. Pearlitic blackheart malleable iron has a pearlitic rather than ferritic matrix, which provides higher strength but lower ductility than ferritic blackheart irons. It has good wear resistance and the highest strength of malleable irons. It can be hardened, and a wide range and combination of properties are possible by control of matrix microstructure. However, it is difficult to weld and requires longer heat-treatment cycle times compared with nodular cast iron. 

Antimony may be added to copper-base alloys such as naval brass. Admiralty Metal, and leaded Muntz metal in amounts of 0.02—0.10% to prevent dezincification. Additions of antimony to ductile iron in an amount of 50 ppm, preferably with some cerium, can make the graphite fliUy nodular to the center of thick castings and when added to gray cast iron in the amount of 0.05%, antimony acts as a powerflil carbide stabilizer with an improvement in both the wear resistance and thermal cycling properties (26) (see Carbides). 

The most common material used in cylinder construction is cast iron for the larger, low-pressure cylinders and steel for the smaller, high pressure cylinders. In some cases, nodular or ductile iron can be used in lieu of cast iron. For hydrocarbon service, steel is most desirable, although not universally available. 

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