Nodular graphite castings

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). 

Use of magnesium instead of mischmetal for production of nodular graphite castings. 

Alloyed Iron. Tin-alloyed flake and nodular cast irons are widely used throughout the world. Estimated 1980 consumption was ca 1,200 t. As little as 0.1% tin when added to flake and spheroidal graphite cast irons in the pouring ladle gives the iron a structure that is completely pearlitic. Tin-inoculated iron has a uniformity of hardness, improved machinability, wear resistance, and better retention of shape on heating. Where pearlitic and heat-resistant cast irons are required, such as for engine blocks, transmissions, and automotive parts, tin additions may provide a suitable material. 

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

Spheroidal-graphite cast iron combines the strength, toughness and ductility of steel with the ease of casting of grey cast iron. Usually abbreviated to SG iron, it is also known as ductile or nodular iron. 

Ductile cast iron (SG) (nodular or spheroidal graphite cast iron)... 

Table 11.5 Designations, Minimum Mechanical Properties, Approximate Compositions, and Typical Applications for Various Gray, Nodular, Malleable, and Compacted Graphite Cast Irons... 

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. 

In metallurgical practice, sodium uses include preparation of powdered metals removal of antimony, tin, and sulfur from lead modification of the stmcture of siHcon—aluminum alloys appHcation of diffusion alloy coatings to substrate metals (162,163) cleaning and desulfurizing alloy steels via NaH (164) nodularization of graphite in cast iron deoxidation of molten metals heat treatment and the coating of steel using aluminum or zinc. 

Another form of microstructural galvanic corrosion, graphitic corrosion, is unique to gray and nodular cast irons. It may be encountered in cast iron pumps and other cast iron components. It is a homogeneous form of galvanic corrosion, not requiring connection to a different metal. 

Graphitic corrosion has two distinct features that are useful in distinguishing it from other forms of corrosion. First, it affects an unusually limited number of metals the only metals commonly affected are gray cast iron and nodular cast iron. Second, metal that has experienced graphitic corrosion may retain its original appearance and dimensions. Consequently, graphitic corrosion frequently escapes detection. 

The occurrence of graphitic corrosion is not location specific, other than that it may occur wherever gray or nodular cast iron is exposed to sufficiently aggressive aqueous environments. This includes, and is common to, subterranean cast iron pipe, especially in moist soil (Case History 17.1). Cast iron pump impellers and casings are also frequent targets of graphitic corrosion (Case Histories 17.2 through 17.5). 

Austenitic cast irons (either flake graphite irons or nodular graphite irons) are produced by mixing in nickel from 13-30%, chromium from 1-5% and copper from 0.5-7.5 (to lower nickel-containing grades to augment the corrosion resistance at lower cost). 

Selective form of iron corrosion, primarily in gray cast iron but also less commonly in nodular cast iron, whereby the (anodic) iron matrix converts to iron oxide while the (cathodic) graphite remains intact. The casting retains it shape but loses all strength and can be cut with a knife. 

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