Nodular iron

Rare-Earth Silicides. Rare-earth sihcides, in the form of a ferroalloy that contain up to 33% rare earths, are used increasingly by the iron and steel industries. Whereas the term sihcides is no longer used for alloys of this type, it is stih in common usage for these materials. Eor nodular iron, addition... 

Casing materials are, in most cases, cast iron, nodular iron, or casi steel. Fabricated casings are generally made of carbon or alloy steel. Ca ... 

Nickel iron (55/45) Metal are l or high-strength gray and nodular irons Reasonable maehinability... 

Compressor cylinders [dry or water-cooled) of cast iron, nodular iron, or forged steel are engineered to suit required pressures and capacities. 

Figure 12-2Q. Cast or nodular iron cylinders for pressures to 1,500 psi. Note double distance-pieces (left, vented or purged, to prevent oil and process gas from leaking past the shaft and right-end fixed clearance pocket). (Used by permission Bui. 85084, 1992. Dresser-Rand Company.)...

Figure 12-2T. Medium- or high-pressure, double-acting cylinder with flanged liner. The liner is locked in place by a flange between head and cylinder barrel. A step on the liner O.D. permits easy insertion. The cylinder may be made of cast-iron, nodular iron, or cast steel, depending on operating pressure. Note Optional two-compartment distance piece (type D) designed to contain flammable, hazardous, or toxic gases is illustrated. (Used by permission Bui. 33640, June 1985. Dresser-Rand Company.)...

Iron/ carbon alloy, poured as a hot molten liquid into a mold. Usually produced as either gray iron (where flakes of graphite are embedded in an iron matrix) or nodular iron (spheroids of graphite in the matrix). 

Dual nickel, 9 820—821 Dual-pressure processes, in nitric acid production, 17 175, 177, 179 Dual-solvent fractional extraction, 10 760 Dual Ziegler catalysts, for LLDPE production, 20 191 Dubinin-Radushkevich adsorption isotherm, 1 626, 627 Dubnium (Db), l 492t Ductile (nodular) iron, 14 522 Ductile brittle transition temperature (DBTT), 13 487 Ductile cast iron, 22 518—519 Ductile fracture, as failure mechanism, 26 983 Ductile iron... 

The Role of the Rare Earth Elements in the Production of Nodular Iron... 

Before discussing, in any detail, the role of rare earths in the production of nodular iron, it is important to arrive at some basic understanding regarding the metallurgy of this material. It is also appropriate to discuss the rare earth materials being used commercially. 

Figure 5. Appearance of polished nodular iron microsample (200x) etched in 2 % nital. Matrix structure is pearlite.

The nodular iron industry was born. However, there was much work yet to be done. 

The rare earths play three roles in the production of nodular iron. These roles are as a nodulizing element (or as the growth modifier) as a means of enhancing the nodule count (or nucleation) and, finally as controllers of deleterious elements. The use of the rare earths for each of these purposes will be described in detail in the following sections. 

The modern foundry process for producing nodular iron can be oversimplified by describing it as the treatment of a base iron (3% to 4% carbon, 1% to 2% silicon) having low (0,005% to 0.05%) sulfur levels and containing little (<0,05%) phosphorus. The treatment is carried out by means of the introduction of the appropriate nodulizer into this base iron. Inadequate addition of nodulizer results in incomplete spheroidization. Excessive concentrations of nodulizers promote the formation of unwanted iron carbides. The nodulizing elements include the rare earths, magnesium, yttrium and calcium. The latter two elements find little or no use today because of economical and technical problems. 

One of today s basic requirements for economical nodular iron production is a base (or untreated) iron having between 0,004% and 0,05% sulfur. In most practices, the sulfur level is held at approximately 0,01% in order to minimize the necessary addition of nodulizing elements. On the other hand, a minimal sulfur level is evidently required in order to facilitate adequate nucleation (12). 

In view of the poor magnesium recoveries (and the associated pyrotechnics) and the present availability of desulfurized base iron, efforts have been made to establish the rare earths as the primary nodulizers (13). After all, Morrogh originally produced nodular iron by the use of mischmetal. The rare earths are more dense than the liquid base irons (p=6.6 gm/cm for cerium (14), whereas p 6.2 gm/cm for gray irons above the liquidus (15)). They also are liquid at iron founding temperatures. As a result, there is not a problem with pyrotechnics and alloy flotation can be minimized. Recoveries of the rare earths in the iron have been found to be high. 

These same researchers also explored the efficacy of the individual rare earths as nodulizers (17). They concluded, by their ability to produce nodular iron having adequate physical properties without excessive iron carbides present, that cerium was the most effective of the four rare earth elements (lanthanum-neodymium) evaluated as nodulizers. They reported that it required 1.5 times as much neodymiun or praseodymium and three times as much lanthanum as cerium to yield equivalent results. 

In nodular iron, the goal is a carbide-free matrix hence, a... 

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