of essential plus desired elements into a prospective table of composition for most standards is somewhat akin to a roll call of an appreciable segment of the periodic table.

The results of a survey conducted in 1950 by ASTM Committee E-2 on Emission Spectroscopy revealed that at that time 13 elements were required for inclusion in proposed cast iron spectrochemical standards. Also significant was the realization that eight individual standards would be required to cover the wide ranges of concentration for most of the desired elements. In 1955 the NBS, in cooperation with the cast iron industry, planned the chemical compositions for eight white cast iron spectrochemical standards. The final compositions adopted by NBS and accepted by industry are shown in table 1. As can be seen, the proposed standards were planned to contain a concentration range for 21 elements (and iron). iron). To provide for general application of the standards, five commercial cast iron compositions were chosen: piston ring, wear plate, die, brake drum, and mold. To these, three special compositions were added to provide for the required wide concentration ranges of the contained elements.

The balancing of the eight compositions to promote a white structure required careful study [2]. For example, the silicon content is the principal factor in controlling depth of chill. Chromium and vanadium are strong carbide formers and hence markedly promote the chilling properties.

Table 1. Planned Compositions of Eight Proposed
NBS White Cast Iron Spectrochemical Standards

Dashes indicate that no addition for this element was planned. For aluminum it was anticipated that a concentration range of about 0.01 to 0.1 percent would be obtained as a result of this element being present in several of the planned master alloy additions.

7

Phosphorus and nickel reduce the depth of chill.

Manganese

and sulfur usually form manganese sulfide, and if balanced with respect to each other in the proportions added, have little effect on the chill. In the absence of enough manganese, however, sulfur has a marked stabilizing action. on the cementite and promotes chill.

In the cast iron industry, the tendency to graphitize often is expressed as the "carbon equivalent", an empirical relationship of the total carbon, silicon, and phosphorus content expressed by the formula: CE = %TC +0.3 (%Si + %P).

Most gray iron foundries prefer to hold their CE within the range of 3.9 to 4.3. When the eight planned compositions are examined in the light of their carbon equivalents, as shown below, it is evident that on this basis, several of the

compositions have considerable tendency toward graphitizing. Admittedly, this crude calculation does not take into account the other elements present in the proposed standards; however, it appeared desirable to add the powerful carbide stabilizers, tellurium and bismuth, to ensure heavy chilling and also to provide a concentration range for these elements as well.

5. CASTING

Early attempts to prepare white cast iron standards included: centrifugally-cast pins (Research Laboratories of

the General Motors Corp.), machine-cast bolts and centrifugallycast large diameter pipe (American Cast Iron Pipe Co.), and unidirectionally solidified slabs cast on a copper plate (Watertown Arsenal). Although none of these were entirely successful, the results of studies at NBS on the cast slabs appeared promising; it was determined that (1) a suitable depth of chill for standards could be induced for most cast iron compositions; (2) homogeneity of both composition and structure were satisfactory, particularly near the chillcast surfaces; and (3) samples cut from the slabs were equally suitable to both optical emission and x-ray spectrochemical methods of analysis. Because of the extreme hard

was

ness (RC 60) of the white cast irons, however, cutting the slabs to samples was found not to be economically feasible. As a consequence of the work on the unidirectionally cast slabs, a massive water-cooled copper mold assembly designed and constructed at NBS for unidirectional casting of a large number of white cast iron samples simultaneously. The mold assembly, shown in figure 1, consists of a 5-ft square steel plate to the periphery of which was edgewelded a 5-in. wide steel strip to form a 5-ft annulus having a tangential outlet. Within this area another strip was edge welded to serve as a spiral baffle from center to periphery

Figure 1.

for water cooling. To the top of this structure was bolted a 5-ft square copper plate, 1-in. thick. The copper plate was made from oxygen-free, high conductivity (OFHC) copper. The bolts, 1 in. in diameter, also were made of OFHC copper and were threaded to extend into the copper plate about twothirds of the thickness. A lead gasket near the periphery sealed the entire assembly to prevent water leaks.