What's in a Name.

What's in a Name.

First Edition: January, 2001

cvdv@home.nl

Original article "What's in a Name?"
Published in American Foundryman 1949, october pp. 34-38, november pp.44-46.

(October 1949) Shakespeare put it:" A rose by any other name etc." very nice. But what about this newest member of the cast ferrous alloys family? Already the metallurgists have divided themselves into several nomenclature camps on whether this newest type of cast iron should be called nodular, spheroidal, globular, lump, or something else...including nodulite.
What should the casting buyer (or, for that matter, the poor editor of a technical publication) do under these circumstances? The difficulty lies in the fact that the proponents of each name refer not only to an end product but equally to the technique employed, the alloying elements used and even to such touchy questions as patent and proprietary rights and precedence.
As a technical society, A.F.S. believes this question of nomenclature should be resolved soon, and accordingly is seeking the opinions of of all concerned - metallurgists, producers, buyers, et al. Two names in particular thus far have been most widely accepted in the industry-nodular and spheroidal- but it does not appear that they are safely (or perhaps metallurgically) interchangeable. What, then, is the answer?
Other industries have faced this problem, and have let the buying public make the rules. Consider camera (a generic term) and Kodak (a trade name); phonograph vs. Victrola; electric refrigerator vs. Frigidaire, etc. The list is long, the lesson well learned in the consumer industries.
Perhaps the producers' answer to the present dilemma lies, eventually, in adoption of individually copyrighted trade names. But that still does not solve the problem for a technical society or publication, or a specifications writer, who cannot in fairness to all use trade names.
Well, just what is in a name? What's your opinion-and reason? No "coined" name, it seems to us, will do. It must be a generic term that the industry is willing to adopt and use freely, and which a casting buyer can specify safely. After that (but not before), the merits of individual or specialized technique, practice, and application can be brought to bear full force. in the competitive market that seems bound to result from development of this truly revolutionary (even if now miscalled) product. Tell us what you think!
Editor

Historically the word "nodular" has been used for many years in the malleable iron industry to describe the irregular, roughly spherical masses of graphite in annealed malleable iron, to distinguish this form of precipitated graphite from the flake form present in gray cast iron, and the terminology was reasonable and satisfactory.
Morrogh, in describing his work on the production of graphite in the spherical or nodular form in nickel-carbon alloys, cobalt-carbon alloys, and later in iron-carbon alloys, in the as-cast state, used the term "nodule" to describe the ball-shape of the precipitated graphite, and the adjective "nodular" followed naturally.
This procedure was logical from Morrogh's view-point, since the spherical masses of graphite present in English whiteheart malleable are of the sme compact, uniform crystal structure as the nodules now produced in iron as-cast, and the extension of the term "nodule" to designate all spherical masses of graphite, however produced, followed.
In annealed blackheart malleable iron, the roughly spherical masses of graphite prent are composed of aggregates of tiny graphite flakes, as is well known, while the graphite present in whiteheart malleable iron or in magnesium- or cerium-treated cast irons is apparently a homogenous crystal, as shown in Fig.1.

Graphite nodule (left Fig.1) and the same nodule in polarized light (right Fig.2). X1500.
In Fig.2 is shown the same nodule in polarized light, and the uniformity of structure is inferred.
Graphite in blackheart malleable iron shows no such effect in polarized light. A second point of differentiation between the graphite in blackheart malleable iron and in magnesium- or cerium-treated iron is in the smoothness of outline, the latter usually approaching and frequently having perfect sphericalshape, while the former are usually quite irregular in outline.
Although the above described differences in structure of the graphite masses do exist, the terms "nodular,"spheroidal,""spherical," and "spherulitic," are all designations of external shape or form, and so can all be accurately applied to describe any ball-shaped masses of graphite, and have all been used in the literature of malleable iron.
The only question then would seem to be one of designating the particular type of graphite crystallization found in magnesium- or cerium-treated irons, to distinguish it from the flake-aggregate type in blackheart malleable. This cannot be done by the shape or form designation, and so the question of terminology of these new irons is not based on logic but on custom.
Any of the terms "nodular," "spheroidal," "spherical," or "spherulitic" should then be suitable, with the choice being based on the implied meaning. Since "nodule" and "nodular" are familiar words in connection with iron metallurgy, and through decades of use are familiar as designation of ball-shaped masses of graphite in iron, it would seem that these terms would be best applied to the newq cast irons, and indeed, already are the subconscious choise of most workers in the field.

J.E.Rehder, Foundry Engr.
Div. of Physical Metallurgy
Bureau of Mines
Ottawa, Ont.,Canada

Relative to the proper designation for iron containing graphite in rounded form in the as-cast condition, we find the following definitions in Webster's:
Spherulite-A spherical crystalline body made up of radiating crystal fibers often found in vitreous volcanic rocks, as obsidian and pearlite.
Spheroid-A figure like a sphere, but not spherical, esp., an elipsoid or revolution.
Spherical-Having the form of a sphere, or one of its segments.
Nodule-A rounded mass of irregular shape, a little lump.
Nodular-Pertaining to, characterized by, having, or in the form of, nodules, as nodular structure.
Globular-Having the form of a ball or sphere.
Ductile-Capable of being permanently drawn out or hammered thin; said specially of metals; capable of being molded or worked; specifically, capable of being drawn out into wire or thread.
When compared in its figurative sense with plastic, malleable, and tractable, ductile is stated as: That is ductile which is pliant, flexible, or capable of being drawn, conducted, or molded whether with or without effort.
It appears quite evident from these definitions that the terms "spheroid" or "spherical" as well as "globular" and in particular, "ductile" are terms which do not properly characterize this material. The best definition undoubtedly is "spherulitic" but this word is somewhat more cumbersome than "nodular" which latter, although it does not fully designate the conditions at hand, is so simple and already so widely adopted that it is our recommendation that it be used to designate this new type of iron.
Gosta Vennerhol, Met.
Ford Motor Co.
Dearborm, Misch.

The proper terminology for iron in which all the graphite is present as spherulites could be "cast iron with wholly spherulitic graphite in the as-cast condition". Such a periphrase is not at all practical, and we feel that foudrymen would not use it.
However, the proper designation will always be one employing a circumscription: in fact, it is not the iron but the largest amount of the contained graphite that is spherulitic and even the term given above is not exact as often, if not always, a small amount of non-spherulitic graphite will be present.
The above considerations, and especially the practical aspect of this question, incline us to suggest the simplest possible nomenclature for this new type of iron: thus we suggest "nodular iron" rather than "nodular graphite iron" or spherulitic graphite iron".
The first designation is international and corresponds to the French "fonte nodulaire," while the two following designations need a periphrase in French ("fonte a graphite nodulaire" or fonte a graphite spherulitique").
It further appears desirable to distinguish at least between the as-cast and the soft annealed or completely ferritized condition. Even in the as-cast condition one may produce two different types of nodular iron and, of course, the intermediates.

Figure 3 Pearlitic nodular iron, as-cast. X200.
The first type has a complete or nearly complete pearlitic matrix (Fig.3) and corresponds to very high strenght iron, for example, 120,000 psi. The elongation is rather low, 2-3 per cent( American A test bar).with almost no reduction of area. It does not appear desirable to designate such a material as "ductile". The second type has a complete or nearly complete ferritic matrix in the as-cast condition; although we have not yet been able to obtain the wholly ferritic matrix as-cast, it may be quite possible. The micrographs of Fig.4 correspond to the proposed ferritic nodular iron with over 90 per cent ferrite in the as-cast condition, tensile strength of about 80,000 psi, and elongation of 10-15 per cent ( American A test bar).

Figure 4-Ferritic nodular as-cast, magnification left X300, right X100.
The third type is the as-cast nodular iron (Type 1, Type 2, or intermediates) after complete ferritization by annealing (Fig.5). The designation "ferritized nodular iron" makes it evident that the iron was nodular as-cast.

Figure 5-Ferritized nodular iron, annealed. X300.
According to the properties (tensile strength, 75,000 psi, elongation, 20-25 per cent (American A test bar), reduction of area, 25-30 per cent, and Bhn, 150-160) that type of iron may also be called "nodular malleable iron" but, as the heat treatment is mainly ferritizing instead of nodulizing and ferritizing, we should prefer the designation "ferritized nodular iron."
The proposed nomenclature, being practical and presenting an international character, has a further advantage; as nodular iron responds to heat treatment, the nature of the matrix after treatment may impose the designation "austenitic, bainitic, or acicular nodular iron."
Prof.Albert De Sy,
University of Ghent, Belgium

Until a few years ago cast iron nomenclature was not a problem, but new offspring in the family of cast irons such as nodular graphite cast iron and acicular cast iron made the whole picture of cast iron designations confusing. The only possible solution appears to be the development of a completely new nomenclature on a systematic basis.
The nomenclature, at least in cast iron specifications, should be logical and based on structure since structure determines the specific properties of the irons. Also, most of the new cast irons have derived their names from some structural component. Since cast iron contains excess carbon as free graphite or carbide in a steel matrix, both the nature of the carbon and the matrix should be incorporated in the designations. Furthermore, the terms should lend themselves to international understanding; hence Latin roots should be used where new terms must be developed. The following designations are suggested for carbon:
Foliolitic graphite=flake graphite (from Latin folium=leaf)
Spheroidal graphite (or nodular graphite, which term however does not describe the shape of the graphite particles quite adequately and has been used earlier for certain types of temper carbon thst do not grow radially)
Floccular graphite= temper carbon (from latin floccus=flock)
Carbide.
By combining the carbon designation and the matrix designation any cast iron can be completely defined and distinguished from other irons. The system suggested has one drawback-the names become a little too long. However, it may be possible to develop suitable abbreviations.
The examples put together in the accompanying table give an idea about the system suggested.

FLAKE GRAPHITE	FERRITIC	FOLIO-GRAPHITO-FERRITIC
FLAKE GRAPHITE	PEARLITIC	FOLIO-GRAPHITO-PEARLITIC
FLAKE GRAPHITE	ACICULAR	FOLIO-GRAPHITO-ACICULAR
FLAKE GRAPHITE	MARTENSITIC	FOLIO-GRAPHITO-MARTENSITIC
NODULAR GRAPHITE	FERRITIC	SPHERO-GRAPHITO-FERRITIC
		(NODULO-GRAPHITO-FERRITIC)
NODULAR GRAPHITE	PEARLITIC	SPHERO-GRAPHITO-PEARLITIC
TEMPER CARBON	FERRITIC	FLOCCU-GRAPHITO-FERRITIC
TEMPER CARBON	PEARLITIC	FLOCCU-GRAPHITO-PEARLITIC
CARBIDE	PEARLITIC	CARBIDO-PEARLITIC

Erik O.Lissel, Res.Dir.
Sveriges Mekanforbund
Stockholm, Sweden

Nodular graphite is an old, well-known form of graphite in the United States, and the handbooks 1,2 describe it as temper carbon.According to the handbooks, temper carbon or nodular graphite, forms during annealing and is not present immediately after solidification. A typical nodule of temper carbon is shown in Fig.6, which demonstrates the well-known fact that it consists of an aggregate of fine flakes intermixed with iron.

Figure 6 Nodular graphite in malleable iron. X250.
The spheroidal graphite particles shown in Fig.7 represent the form of graphite obtained in the new magnesium-treated iron. This spheroidal graphite consists of polycrystalline-appearing, radial structured spheroids. Spheroidal graphite occurring in the new magnesium-treated iron differs markedly from nodular graphite in its mode of formation, appearance and structure.

Figure 7-Spheroidal graphite in magnesium-treated iron. X250.
Consequently, we are of the opinion that it would be an error to identify the spheroidal form of graphite with the same name as that applied to the nodular form of graphite.
Both Webster and Funk&Waagnall describe nodular as pertaining to "a rounded, irregular mass," which seems to us to be an accurate description of the graphite shown in Fig.6. A spheroid is defined as "a body having a form nearly like a sphere," and since this harmonizes with the general shape of the graphite particles shown in Fig.7, it has been our custom to refer to the graphite in magnesium-treated iron as "spheroidal graphite."
We feel that the new graphite form should be called "spheroidal" because this term describes its shape accurately. Furthermore, this graphite form should be distinguished from the old familiar types of graphite, such as flake and nodular.
A suitable name for the product presents different problems. Alloys are sometimes described in terms of their compositions, structures or properties. We have always preferred funtional names, i.e., names describing a use or property. We have applied this principle in connection with magnesium-treated iron and suggest "ductile cast iron" as a suitable name.
1.American Malleable Iron, 1944 edition: Glossary, p.248, "Temper Carbon-Carbon in Nodular Form;" photomicrograph shown on p.184, Fig.3
2.Cast metals Handbook, 1944 edition, American Foundrymen's Society.

A.P.Gagnebin, Met.
The International Nickel Co., Inc.
Bayonne, N.J.

We prefer the term "nodular graphite cast iron" for the following reasons:
1. The first public announcement of this material was made by H.Morrogh and co-workers in reporting work sponsored by the British Cast Iron Research Association. They used "nodular graphite cast iron " as the generic term for the irons produced by the cerium treatment. Magnesium treatment produces essentially the same graphite modification as the cerium treatment and certainly does not warrant different terminology. We feel stongly that the right of priority in nomenclature should be observed and the terminology used by Morrogh et al should be continued.
2. The term "nodular" to describe the graphite modification in either cerium or magnesium treated cast irons is quite accurately descriptive. "Nodule" is defined as "a small roundish lump of some mineral aggregate" (Webster's International Dictionary-Unabridged-2nd Ed.-1945).In other meanings there is definitely connoted in the word nodule the idea of a structure build up about a central nucleus.
Of course, there are nodules in these materials which mineralogically would be classed as spherulites, but at the same time there may be flake aggregate nodules. As an accurate description of the material under discussion, the generic term "nodular graphite cast iron" is exact and logical.
Charles K.Donoho, Chief Met.
American Cast iron pipe Co.
Birmingham, Ala.

We prefer the name "nodular iron castings" for the following reasons: 1.Graphitic carbon in this new type of casting is usually in the form of nodules. Quite often the carbon is in true "spheroidal" form, but not always. The following definitions, from Webster's dictionary, distinguish the various shapes: Node-A knot, a nob. A point at which subsidiary parts center; Nodule-A rounded mass of irregular shape; Nodular-Pertaining to, characterized by having, or in the form of nodules; Spheroid-A figure like a sphere, but not spherical.
It would seem that the term "nodular" covers quite accurately the shapes of the graphite in the new irons. A study of the micrographs in published articles would make Webster's definition especially applicable when one includes all the graphite forms in nodular castings, and not simply the forms which are "spheroidal".

Figure 8-Graphite forms in Mg-Cu treated iron. Unetched. X1000.
The micrograph (Fig.8) shows two adjacent forms of graphite in iron treated with magnesium-copper, which tested 109,000 psi as-cast. One might be called a "nodule", the other a "node", and the casting could properly be described as "nodular."
2. As "nodular iron" was introduced to the world by H.Morrogh in his many publications, there would seem to be justice in following Morrogh's "nodular" nomenclature, particularly as it describes the general graphite forms so well.
3. we prefer the term "nodular iron castings" to Morrogh's "nodular cast irons." The new product is quite distinct from cast iron and to our mind should not be coupled with cast iron in nomenclature.
E.K.Smith, Consulting met.
Los Angeles

The terminology introduced by H.Morrogh in his paper "The production of Nodular Graphite Structures In Cast iron," Journal, Iron and Steel Institute, vol. 158, March, 1948, pp.306-322 adequately describes and difines the various forms of carbon occurring in cast irons. Accordingly, the term "nodular graphite" signifies the occurrence of free carbon in spheroidal or spherulitic particles either in the annealed malleable iron or in specially treated (cerium, magnesium, etc.) cast irons.
To distinguish between "spheroidal" and "spherulitic" nodules, it is pointed out that spheroidal nodules are imperfectly formed (irregular or ragged appearing) spheres of graphite such are observed in annealed malleable iron when its sulpher content is predominantly in the form of MnS. The alternative term "graphite flake aggregate" type of nodule has also been used to designate this form of carbon.
On the other hand, "spherulitic nodules" are exemplfied by the more nearly perfectly spherical graphite particles occurring in annealed malleable iron when its sulphur content is predominantly in the form of FeS. in this connection it is pointed out that the nodular graphite occurring in cerium- and magnesium-treated irons is usually of the spherulitic variety. These particles are characterized by markedly smooth spherical outlines in contrast to the ragged appearance of temper carbon nodules in normal American blackheart malleable iron.
In view of these facts, the writer believes that the term "nodular cast iron" is more comprehensive and hence the best suited to the description of those specially treated (cerium,magnesium, etc.) irons whose carbon is predominantly in the form of spherulitic nodules as-cast.
Wm.W.Austin,Jr.,Met.
Southern research Institute
Birmingham,Ala.

(November 1949) The problem of naming the new material which in the as-cast condition contains graphite in a nodular or spheroidal form was outlined a month ago in American foundryman. We published the opinions of a number of foundrymen and metallurgists and include herewith additional ideas of workers in the field. Other communications will appear on the Letters to the Editor page as thewy are received.
Henceforth, where no other descriptive terminology is provided, American Foundryman will use the term nodular iron or nodular graphite cast iron for this new material.
Editor.

The terms "nodular graphite cast irons" or "nodular irons," have been applied to describe cast irons having nodular graphite structures in the as-cast state. Whether these terms are scientifically correct may be questioned, but a large number of metallurgists and foundrymen now understand what they mean. This must be borne in mind if considerations of terminology lead to changes in nomenclature.
It is important that others-engineers,designers,users-should understand the terms adopted.In this extrametallurgical field, terms referring to the properties of the material are frequently best appreciated.Unfortunately, nodular irons may be ductile or relatively non-ductile; hard or relatively soft; magnetic or non-magnetic; heat-resisting or not particularly heat-resisting; etc. In fact, all the physical and chemical properties of the material can vary between quite widely placed extremes. What, the, are the specific characteristics of nodular irons? They are the metallographic characteristics, coupled with the method of manufacture. They all should possess at least part of their graphite in the form of nodules in the as-cast state.
According to the dictionary, the term "nodular" means: having the form of, opr occurring in nodules; and a "nodule" is defined as: a small rounded lump of some mineral. In this sense the term "nodules" has been used quite satisfactorily to describe the graphite which characterizes malleable cast irons and much of the graphite in the newer materials. More specifically, the nodular graphite in malleable iron has been referred to as "temper carbon nodules." This implies, quite correctly, that the nodular graphite structures are produced by heat treatment. Strickly speaking, most of the conventional malleable cast irons are also nodular cast irons, although we believe they are never referred to as such.

Graphite Forms in Malleable iron
In malleable cast irons we have distinguished two forms of nodular graphite. The one form, which occurs when the sulphur present in the iron is in the form of manganese sulphide, we have termed "graphite flake aggregate temper carbon nodules." This nodular structure consists of an aggregate of small, apparently randomly oriented graphite particles. This structure is typical of American or blackheart malleable iron.
Another form of temper carbon nodule can occur, the spherulitic form, when the sulphur in the iron is predominantly in the form of iron sulphide. The spherulitic form of nodule has in the past been confined almost entirely to European whiteheart malleable cast iron, but this spherulitic structure is also that which characterizes the as-cast nodular cast irons.
It is important that the nature of the spherulitic structure be thouroughly understood. Considerable misuse of this term has occurredin the literature. "Spherulitic" is not synonymous with "spheroidal". Spherulites may have any shapes. It so happens that the spherulites of graphite in cast iron are usually approximately spheroidal in outline, but not always so. Each spherulite consists of a number of graphite crystallites radiating from a common center, the basal planes of each graphite crystallite being oriented so that they are approximately at right angles to the radii of the spheroid of which the spherulite can be considered to be com posed.
The important point about the term "spherulite" is that it refers to a specific arrangement of graphite crystallites inside each nodule. Instances of extreme departure from the spheroidal outline are shown in Fig.9 and 10.

Figure 9-Elongated graphite spherulite in a nickel-carbon alloy treated with strontium-magnesium. Unetched. X1500.
Figure 9 shows an elongated graphite spherulite in a nickel-carbon alloy treated with a strontium-magnesium alloy, and Fig.10 shows a similar structure in a sample of high sulphur whiteheart malleable cast iron.

Figure 10- Elongated graphite spherulite in a sample of whiteheart malleable iron having sulphur present as FeS. Etched, 4 per cent picral. X150.
Considering some of the terms which might be applied to the material, the following objections can be listed:
1.Spherulitic Cast Iron: This does not distinguish as-cast nodular cast irons and high sulphur European whiteheart malleable cast iron.
2.The term "nodular" does not differentiate, stricktly speaking, the as-cast materials from the whole range of malleable cast irons.
3."Spheroidal" does not differentiate as-cast materials from many malleable irons, and it is undesirably more specific than "nodular."
Although the terms "nodular cast iron," "nodular graphite cast iron" or "as-cast nodular cast iron" are somewhat vague in them selves, it does appear that metallurgists understand them to refer to the new material; in fact, in Great Britain it appears that "nodular cast iron" is quite adequate to convey the meaning. This being the case, we would favor the acceptance of the term "nodular iron" or nodular cast iron" to define the new product when all or a substantial part of the graphitic carbon is in the form of spherulitic nodules in the as-cast condition.
H.Morrogh, Research mgr.
British Cast Iron Research Assn.
Birmingham, England

Cast iron having the graphite in the form of spherulites or spheroids in the as-cast state is a new material and deserves a name which will distinguish it from gray cast iron and malleable iron. The term decided upon should be simple and readily acceptable and yet clearly distinguish this material from other cast ferrous products.Among the more widely used terms designating this new type of cast iron are: "spheroidal graphite cast iron," spherulitic cast iron,"ductile cast iron," and "nodular cast iron."
The graphite particles shown in Fig.11 were obtained by dissolving nodular cast iron in dilute acid and treating the residue with hydrofluoric acid to drive off the silica. Almost all of the graphite is in the form of spheres or balls and, since most of them are distorred, the term "spheroids" probably describes them more accurately.

Figure 11-Graphite particles in spherical form were obtained from nodular cast iron by dissolving the iron in dilute acid and treating the residue with hydrofluoric acid to drive off the silica. X100.
From the standpoint of accuracy, the term "spheroidal graphite cast iron" probably should be the first choice. The only valid objection to its use might be that it is rather cumbersome. If this objection could be overcome, the use of this term would result in less confusion than that of any other term. The term should also be applied to irons which have been cast white and annealed providing sufficient magnesium or other element is present to assure formation of spheroidal graphite rather than flake aggregates.
Although the use of the term "ductile cast iron" may be justified on the basis of appreciable ductility possessed by some of these irons, the term is not always applicable to this material. In some applications high strenght and hardness are much more important than ductility. An iron of this type either heat treated or alloyed to produce a tensile strength of over 125,000 psi would not be expected to possess appreciable ductility. Certain properly inoculated alloy irons having flake-type graphite have been known to show as much as 4 per cent elongation on a tensile test. Such an iron might be classed as "ductile" and yet not have the structure possessed by a properly treated iron with spheroidal graphite.
From the standpoint of simplicity and convenience, the term "nodular cast iron" or "nodular iron" is hard to improve upon. The term has the objection that it is not as accurate as "spheroidal graphite cast iron." Although the graphite found in malleable cast iron is of the flake aggregate type, the term "nodules" has often been used to designate such flake aggregates. By definition, the term is thus correctly used. Malleable iron has seldom if ever been referred to as "nodular iron," and it is not likely that its name will ever be changed.

Figure 12-Temper carbon in annealed malleable iron appearing as flake graphite. Etched, 2 per cent nital. X500.

Figure 13-Graphite formation in annealed ductile iron appearing as rounded masses with radial structure. Etched, 2 per cent nital. X500.
"Nodular cast iron" has been developed to the point where setting up specifications seems to be in order.It is suggested that the present ASTM system be extended through the use of appropriate suffixes. For example, an 80-N-5 iron might be one with 80,000 psi minimum tensile strength, nodular iron structure, and with minimum elongation of 5 per cent.
D.E.Krause, Exec.Dir.
Gray Iron Research Institute
Columbus, Ohio

The writer prefers to apply the term "ductile iron" to the newest cast ferrous material because it best describes the outstanding property of the material-ductility(with high tensile strength) as-cast.
The word "nodular" should not be used in connection with "ductile iron" because it is frequently associated with the form of graphite found in malleable iron and known as "temper carbon." The 1948 edition of ASM Metals Handbook in the section entitled "Definitions of Metallurgical Terms" defines temper carbon as "the free or graphitic carbon that comes out of solution, usually in the form of rounded equiaxed nodules in the structure, during the graphitizing or malleablizing of white cast iron."
Careful comparison of photomicrographs of malleable iron with those of ductile iron shows that the temper carbon in malleable iron and the graphite formation in ductile iron are entirely different.Figures 12 and 13 show the structures of malleable iron ans ductile iron. At X500 magnification it is evident that the temper carbon in malleable iron is in reality an aggregate of flakes, while the carbon in the ductile iron appears as solid rounded masses having a radial structure. The latter is an entirely new type of graphite formation.
In the writer's opinion, the words "nodular," "spheroidal," "and "spherulitic," regardless of definitions, are inapproppriate for describing the new iron as they refer to types of graphite formations, while the point in question is that of selecting the correct terminology for an iron and not for one of the microconstituents present in the iron.
W.W.Levi,Met.
Lynchburg Foundry Co.
Lynchburg,Va.

The dictionary defines the word "nodule" as a little knot or irregular round lump. Therefore, it would appear that the word "nodular" will fit both the uniformly rounded forms of graphite as well as the irregularly rounded forms of graphite which occur in the new type of iron in the as-cast condition. the accompanying photomicrograph of the structure shows both types of nodules. it has been our experience that in most cases the structure of this iron at X250 will show graphite in both forms (Fig.14).

Figure 14-Graphite types in as-cast structure. X250.
While the terms "spheroidal" and "spherulitic" may be more applicable to the round forms of graphite, they do not seem appropriate to the irregular forms.
It is true that malleable iron contains graphite in the form of nodules, but this concerns only after the malleablizing heat treatment and not in the as-cast condition. Generally speaking, the nodules in malleable iron are much smaller than those encountered in nodular graphitic cast iron.
For these reasons it seems to us that the term "nodular cast iron" is more appropriate for this material.
J.C.H.Stearns,Mgr.,Ingot Sale
The Dow Chemical Co.
Midland,Mich.

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