US2970902A

US2970902A - Ductile iron

Info

Publication number: US2970902A
Application number: US559574A
Authority: US
Inventors: Adolph P Alexander; Jr Arthur F Spengler
Original assignee: International Harverster Corp
Current assignee: Navistar Inc
Priority date: 1956-01-17
Filing date: 1956-01-17
Publication date: 1961-02-07
Anticipated expiration: 1978-02-07

Description

Feb. 7, 1961 A. P. ALEXANDER ETAL 2,970,902

DUCTILE IRON Filed Jan. 17. 1956 2 Sheets-Sheet 1 250 X Nital & Picral Etch Ifig. 1. Regular Nodular lron 302 brinell.

2 0x Nital & Picfal Etch P 19. 2. Lanthanum treated nodular iron -l97 brinell.

25OX Picral 8. Nital Etch Fig. 3. Hard nodular iron 363 brinell.

INVENTORS.

ADOLPH P. ALEXANDER ARTHUR SPENGLERJL Feb. 7, 1961 Filed Jan. 17, 1956 Fig. 5.

A. P. ALEXANDER ETAL DUCTILE IRON 2 Sheets-Sheet 2 250 X Picral 8. Nital Etch Fig. 4. Same hard nodular iron as Fig. 3, with 0.010% Lanthanum added 321 brinell.

Picral 8- Nital Etch Typical structure of beneficiated iron produced by adding percentages of Lanthanum and Magnesium too low for complete nodulization.

nvvmmxs AIIOLPH P. ALEXANDER ARTHUR F. SPENGLERJn .Br MQ' ATTK United States Pat m 2,910,902 nocrnn IRON Adolph P. Alexander and Arthur F. Spengler, In, Memphrs, Tenn., assignors to International Harvester Company, a corporation of New Jersey Filed Jan. 17, 1956, Ser. No. 559,574

9 Claims (Cl. 75-123) This invention relates to a new and novel ferrous alloy which may be made from any normal base mix composition of gray iron within commonly known specifica tions as well as a base mix of gray iron that is not necessarilywithin the usual range ofsuchspecifications. The resulting ferrous alloy, according to this invention, in the .ascast condition is soft, ductile, readily machineable and possesses distinct properties of high tensile strength, high elongation and impact strength and thereby produces castings which may be machined without the necessity of a further :thermal treatment.

It is well known that castings made from a normal gray iron mix possess free carbon in the form of flaked graphite which is more or less uniformly distributed throughout the matrix resulting in a casting having a low tensile strength in the rage of-30,000 to 50,000 pounds per square inch. It is also well known that if magnesium in amounts necessary to introduce from the casting or alternatively cerium inamounts necessary to introduce 0.02 to about 0.050 percent in the casting,

about 0.02 to 0.04 percent in I or a combination of these two elements, the grap'hitic carbon tends to coalesce or agglomerate to form particles which are neither flake-like or spherulitic in shapebut instead are irregularly shaped in whatmay be said 'to be a transition stage between the "flake shape on theone one hand and spheroidal or spherulitic on the other hand.

The particles therefore appear in some portions to reseinble an approach to a flake shape and other portions approach that of spheroidalorspherulitic shape. Such an iron is generally termed beneficiated. in that the resulting castings may possess up to and even exceeding 80,000 pounds per square inch in tensile strength depending upon the percentage of magnesium or cerium, or a combination of both elements, is present in the casting.

However, as is well known, when sufiicient. amounts of magnesium (i.e. 0.04 to 0.5 percent) or cerium (i.e. 0.05 to 0.5 percent) are added to the molten base gray iron mix resulting in a casting having, a percent of magnesium or cerium exceeding the maximum percentages specified above for beneficiated iron, 'the graphite will essentially coalesce or agglomerate to form nodules of carbon or graphite substantially spheroidal orspherulitic in shape which nodules are more or less disposed uniformly in the matrix in the casting. Such iron is gener- "ally termed nodular iron and castings made therefrom usually possess a tensile strength in the range of90,000

to 120,000 pounds per square inch or higher.

It should be mentioned here that the sulphur content {of the base gray iron mix used for making beneficiated iron ornodular iron, as above described, must be sufficiently low so that the resulting castings contains a sul- Well known equation adequately ,defines the aforemen tioned terms:

pesos herein it will be understood that the following may be further 2,970,902 Patented Feb. 7, 1961..

where TC represents the percent total carbon present in present and Si represents the percent silicon present. When CE equals 4.30 the iron is said to be of eutectic composition; when CE exceeds 4.30 the iron is said to be of hyper-eutectic composition; and when CE is less than 4.30 the iron is said to be of hypo-eutectic composition.

Gray irons with nodular graphite made as described above from normal base irons that conforms with the requirements of the Society for Automotive Engineers specifications are usually hard and have a Brinell -hardness number (3000 kilogram load-10 millimeter ball) above 250 in standard 1 inch thick Y-lBlock test castings illustrated in Military Specification M1L-l- 17166A (SHIPS). Castings from these irons in sections of inch thickness or less are too hard for routine machining operations. In addition these light section castings have suflicient free Or massive iron carbides in the matrix of the cast structure to cause the casting to be brittle with little or noductility. Such castings have a low shock resistance and require thermal treatment for satisfactory engineering use. 7,

Soft as-cast nodular irons can be produced with great difiiculty from a cupola with either magnesium or cerium including suitable alloys thereof only if special precautions are taken. One method is to make a base iron having an extremely low silicon content, less than 0.10 percent phosphorus and less than 0.40 percent manganese. Castings made from such base iron would be unsuitable for machining operations. base iron mix is added magnesium or cerium in combination with a high amount of silicon and thereafter a further large addition of a silicon alloy is made, a resulting casting may contain from 2.00 to 4.00 percent silicon which would be relatively soft and readily machineable.

For the above reasons it is usualin the foundry industry to use premium priced pig iron of carefully selected expensive steel scrap to use for the production of nodular irons. These requirements for soft as-cast nodular iron make it impractical to economically make gray iron from the same base mix. The only other heretofore known alternative is to make the hard and brittle type nodular iron castings and subsequently subjecting the resulting castings, to a relatively expensive thermal treatment prior to machining operations. It is therefore a prime object of this invention to provide beneficiated and nodular irons which in the as-cast condition are soft and ductile, having high strength and shock resistant properties, and may bemade from normal molten base gra'y iron compositions. 1

It is a further object of this inyention to provide beneficiated and nodular irons which in the as-cast condition are softand ductile, having high strength and shock resistant properties, and may be made from base gray iron molten mixes having compositions outside the limits of normal gray iron specifications.

A still further object of this'invention is to provide beneficiated and nodular irons according to thepreceding objects the properties of the castings madetherefrom enhanced by a subsequent thermal treat: ment. g

These and other desirablexobjects inherent in and encompassed by the invention will be more readily understood from the ensuing description, the appended claims and the annexed reproductions of photomicrographs wherein: H .1 y

"Figure 1 is a photomicrograph of apolished and etched surfaceillustrating hard nodular iron madefrom a northat base gray iron, the microstructure being enlargedjby 250 diameters.

Figure 2 is a photomicmgmph of a Polished and e ged However, if in such a molten surface illustratingsoft nodular iron made in accordance with thisinvention using the same base gray iron of Fig'-' ure 1, the microstructure being enlarged by 250 diameters.

Figure 3 is a photo'micrograph of a" polished and etched surface illustrating a very hard nodular iron made by the gray iron beneficiat'ed by the addition of smaller amounts of magnesium and softened in accordance with this invention; the microstructure being enlarged by' 250 dimeters.

The aforementioned military specification indicates that nodular iron having a silicon content above 2.50 percent is undesirable. It is unusually'difficult to produce nodular iron in accordance with the aforesaid military specifica'non which is soft in the as-cast condition from a cupola base iron that is also suitable for pouring gray iron castings conforming to standard engineering specifications because the base iron silicon content must be kept very low to permit a large late addition of ferrosiliconfor so ftening the" resulting castings. From this it may be" readily appreciated that the production of beneficiat'ed or nodular gray iron castings. made from normal base" gray iron meeting commonly known engineering specifications wduld be of exceedingly great value to mercenar industry. Such production would enable a'ifo'undry to pour asil inachineable castings hay- P be accomplished by" taking" a ladle of moltennormal base gray iron, castings of which would have a tensile strength of 30,000 to 50,000 pounds per square inch, and making a. simple inexpensive ladle addition of special alloyshereinafte'r"discussed which converts the normal base gray iron to beneficiated or nodular iron of which castiiigs made therefrom. will be soft, ductile" and of very high tensile strength. a We. have discovered that a molten normal base gray iron of .hypoeu tectic" or hyper eut ectic c'o rnpo'si tidn, the addition thereto' of amixtu're' of magnesium fer'rd-silicoii (8.5% Mg 46.0%" .Si)'- plus lanthanum, or, magnesium ferro silicon plus a m ner-ear rare earth: metals containing a minimum of 30% lanthanum will'fres'ult in beneficiate'd or nodularigraphi'te iron depending upon the amountsadded. Thereafter the molten mix isihoculated with a late addition 'of' a. graphitizer such as ferro-silicon up to 0.40 percent, and the castings made therefrom assert and machineable and of high strength properti'e's. .Bythis means we have produced castings'having' a Brinell hardnessnumber. of about 200' on a standard lr'ensiie strength up to and excee in 90",00q pou-qus squa e" inch. According to our invention this may 7 While that shown in Figure 2'wasonly 19'7; A. c'om' 4 I I v The above described results are exceedingly unusual for nodular graphite irons because castings made from the same base irons mentioned above but in accordance with previously known methods or compositions would result in castings havinga-Brinnell hardness of over 250 in test bars andlight or thin section castings could be machined only with 'great'difiiculty if at all.

Referring now to Figures- 1 and'-2- the'se photorn'icro graphs illustrate the structures" of nodular irons made from the same gray i'ronbase mix with the addition of magnesium which formed the sphe'rulitic' or nodular graphite particles. Howeverin thecase of Figure 2 the molten iron was in further addition treated with lanthanum in accordance with our invention. The Brinell hardness of the casting illustrated in Figure 1. was" 302 parison' of the two microstructures indicatesthatcon; siderable more graphite carbon was freed to form nod-*- ule's when lanthanum was present resultingin a casting having'far more ferrite in the matrix. Thus it seeiris that the lanthanum reduces the dissolved carbon or combined carbon to form additional graphite nodules thereby resulting in a softerv casting.

1" Y-Block test bar, with'atensile strength from 80,000

to 100,000 pounds per square inch and dep ending upon the slicon content, an elongationof 3 to 10 percent or over, 7

Nodular graphite iron castings made with lanthanum as outlined above have a hardness range of from only l. I

rrbm' .110. 01122 as described in ASTM. Designation,

59-49T which covcrsgray irons having tensilelstr engt liv in the range frdfn20i000 645,000 pouneg'perisqua're inch.

As a specific example of the above described results we present a comparison of nodular iron; made by a well known procedure, with nodular iron made in accordance with this invention. Four hundred pounds of basic cupola normal gray base iron was used. To the first lot of two hundred poundswas added 2.25 percent magnesium ferro silicon (8 .5% Mg, 46.0% Si) containing 0.50 percent cerium plus gramsof a high cerium rare earth alloy (Misch-mctalg'see. Table 1'). Then the fir'st l'ot'wa's in oculated with 0.35% ferro-silicon (75% Si) and'pbured into castings. 'The second lotwasmade identicallythe same as the first lot? exceptinstead of the high cerium rare earth alloy 75" grams offhigli'lanthan'um rare earth alloy" (see Table I) was substituted. Analysis of the.

castings of the first lot indicated about 0:003- percent lanthanum present while that of the second lot showed about 0.010 percent lanthanum present.

TABLE 1 Htgh Cerium 1 .High (Misch-Metal), Lanthanum percent 45 45-50%. 25 30% (Mini). 15 r 0. v V 20-24%; Fe. 5' 1.0% (Mair.)

Did. Groupof rare earths having atomic numbers 59 to 7l'inclnsive and 39in varvinz amounts; A. g i V v "castingsmade from the above mentioned lots were tested for hardness andthe results are shown inTable 2. v p v I TABLE 2 Standard 1", "Y-Blo'c'lc hardfzess of high cerium and high] la'nth zn'um no dula'riiz as-ca'st' condition First Lot" Second Lot 7 High Cerium High Lantha- Rare'Ea'rth numRareEmth 1 B rinoll hardness 110. (3,000 kg. Lea -rommwbniy.-

'The'Brinell hardness test results of the first lot shown in Table 2 are typical and are in conformance with the results reported by others. However, theBrinell hardness test results of the second lot are unusually low and llustrates the effect offour invention in softening or -ductilizing the resulting nodular iron. The same type striking results arelobtained in the case of beneficiated "-11'01'15 too. In the case of the castings from the second flot the microstructures thereof again showed that far more ferrite (approximately 80% was present than that of the castings from the first lot. Furthermore the Brinell hardness of the nodular graphite iron made with the magnesium without the addition ofrareearth ma- "terial was over 250. Thus' it can be seen that increas- 1 ing amounts of magnesium or ceriumin the castings results inprogressive hardening or, "in other words, the presence of cerium or magnesium in iron castings will result in a harder and more brittle product.

The above discussed first example was concerned primarily with a comparison of hardness characteristics of nodular iron made in accordance with previous known concepts with that of the addition of lanthanum according to our invention.

Table 3 illustrates, in a series of nodular irons made,

from normal base gray irons, the effect of composition on certain physical properties of the resulting castings made therefrom. It may be noted that the elongation property decreases as the silicon content increases wh'le the tensile strength remains fairly constant at from.

I 92,000 to 95,000

pounds per square inch after 2.75% silicon is reached. i

TABLE 3 of high lanthanum rare earths and magnesium Heat N0. 1 2 3 4 5 6 SiL, percent 2. 47 2. 51 2. 74 2. 81 3.21 3. 56 percent 3. 44 3. 51 3. 53 3. 21 3. 21 2. 82 Mn, percent. 0.41 0.39 0.45 0. 44 0.47 0.45 P, percent 0.05 0.04 0. 04 0.05 0.06 0.08 S, percent. 0.02 0.02 0.02 0.02 0.02 0.02 Ni, percent 0.12 0.15 0. 31 0. 23 0. 27 0.18 Cr, percent... 0.07 0.10 0.13 0.16 0.11 0.17 Mg, percent 0. 045 0.055 0. 043 0.047 0. 053 0. 065 Ce, percent" 0.021 u. 026 0.015 0.019 0.022 0. 019 7 La, percent. 0.009 0.011 0. 007 0.008 0.009 0.009 ,BHN -1 197 197 200 207. 197 229 Tensile (p. s.1.). 79,500 84,500 92,000 95,000 91,900 92,000 Yield (n.s.1.)-..- 61, 200 63,600 81,250 76, 500 66. 450 79, 600 Elongation, percent. 10 11 8. 5 7. 0 7.0 3. 0 Unnotched Charpy Impact, Ft. lbs.: 70 F 21.8 19.0 11.0 4.5 40 F 8.3 5.5 5.5 3.0

.1 Broke outside gauge marks.

'A rise in tensile strength to about 80,000 to 95,000

\ pounds'per square inch at constant hardness is rather unusual in nodular iron and even in steel. This unusual result seems tobe associated with the effect of the presence of lanthanum according to this invention which will be discussed later. It should also be noted from Table 3 that the silicon and carbon contents of the several heats vary considerably but the softening eifect of the lanthanum appears to control the hardness at a low constant. In respect of hardness we have also no ed a rather amazing phenomena in lanthanum softened nodular iron. We find that light section castings as thick as 04 are softer as cast thanthe standard 1" thick Y-Block corresponding test bar. As an example we found that using the same iron a Y Block 1" thick eithibited a hardness of 241 Brinell while a thick 'casting of the'same iron composition showed only 217 Brinelll Impact strengthof lanthanum treated nodular irons are also of :a higher order than that of previously known" A s-cast properties of nodular iron produced by additions:

nodular irons. As shown in Table 5 the enhanced impact strength of nodular irons made in accordance with our invention appears to be independent of the base composition of the iron or, in other words, the softening effect of the lanthanum and its elfect on raising impact strength of nodular iron is, at least to an appreciable extent, independent of the composition of the base iron which may be of either hypo-eutectic or hyper-eutectic composition.

In nodular or beneficiated graphite iron the elongation properties vary inversely with the phosphorus content.

, Therefore the phosphoruscontent should be kept below 0.1 percent toobtain good elongation properties. It is also preferable to keep the percentage content of certain other elements such as silicon, manganese, nickel, etc., low in the iron for maximum ductility of the iresulting casting. However, if special characteristics such as high strength or wear resistance are required, the

nodular or beneficiated iron may be deliberately alloyed in a well known manner. In these cases the incorporation of lanthanum of this invention will soften the iron and will increase the impact resistance.

The eiIect of thermal treatment" on lanthanum containing nodular iron castings made according to this invention is illustrated in Table 4 for heat Nos. 3 to '6 of Table No.13.

TABLE 4 Heat treated properties of nodular iron produced by additions of high lanthanum rare earth; and magnesium as in Table 2 i Heat No 3 4 5 6 Treatment:

Short Cycle Anneal, 1,700

E. 2% I-Ir.-1,400 F., 2% Hr., Air Coo1 60. 8 12. 5 36. 5 r 34. 0 -40 F 15. 8 6.0 11. 0 5. 5 Oil Quench and Temper,

1,725 F., 2% Hrs; Ten1- per, 1,l00 F., 2% Hrs.-

Tensile 151, 000 149, 000 152, 500 122, 000 Yield 119, 000 122, 000 110, 500 Elong., 2" 2 5 3.0 3.5 4.0 Hardness, BHN 363 g 363 241 Charpy Impact F 17. 5 28.0 17.5 40 F 14.0 11.5 16.0 10. 5 Normalize, l,700 F., 2% 1 Hrs. Air Oool-- Tensile 114, 500 111, 800 114, 000 109, 250 i :1 90,000 91, 750 92,500 85, 250 gm, 2 4.5 3.0 3. 5 5.0 Hardness. BHN 269 302 285 269 Charpy Impact:

70 F 16. 5 10.0 14. 5 16. 5 40 F 9. 5 9. 0 S. 5 8. 5

The above results from thermal treatment appear to be well in line with that which might be reasonably expected.

Although Charpy impact test results apparently do not establish iron toughness as a criterion which ismore thoroughly discussed in Designation E23-47T of the American Society for Testing Materials, nevertheless we tested some of the nodular iron castings of this invention for comparison with nodular irons of the well known type. These impact test results are shown in Table 35.

7 TABLE-5 flmpdctfresillts'on slanda rd 'n'odular iron' and nodular iron treated with lanthanum 1 Gray Iron base treated with magnesium; and silicon alloy. I 3 Similarbase iron treated with magnesium and silicon alloy plus high lanthanum rare earth alloy. 1

3 Gharpy'unnotched impact as per A.S.T.M. E23-47T. I i 2% hrs, 1700 F.2%hrs. 140 O'1*., air cooled total time, shrs. (standard production cycle). a

As might be expected the impact test results in Table 5 are quite scattered, Thesingle extremely high result for standard nodular iron is not accounted for nor was it duplicated. Disregarding this extremely high result it appears that the lanthanum treated nodular iron made "in accordance with this invention may have an average impact strength of somewhat higher order than that possessed by nodular iron--made-in accordance with previously known methods.

As a further demonstration of the softening effect in' the as-cast condition of'=nodulargraphite iron'by' high lanthanum rare-earthscontaining a minimum 'of 30' percent lanthanum, standard nodular iron was first made by the well known addition of magnesium alloys. The hardness =of-"a standard" 1'' thick Y-Block test bar -casting was 302 'Bn'n'ell. To a 200 pound quantity of the same melt an amount of high lanthanum rare earths was added to incorporate one-fourth ounce of lanthanumand the resulting hardness of a 1" thick Y-Block' casting was only 250 Brinell. Then in another similartyp'e'test a very hard type ofnodular iron was made which resulted i in castings having a Brjinell hardness ofi363 (Figure 3).

Then to 200 pounds of'the iron'melt was added only 8 grams 'of elemental lanthanum. --The resulting castings had but 0.010 percent lan'Eihanum'and the Brinell hardness dropped to 321 (Figure 14).

Comparing the microstructuresof the two irons made "in the'last described test as shown-in Figures '3 and 4,

it will again be noted that the lanthanum containing iron (Figure 4) shows more-carbon in the .form of graphite nodules than-that shown in the". untreatediron of Figure 3. Again itappears' that the lanthanum te'ndsto free *more carbon 'to' form nodules"antlTcorrespondingly in- {creasing the amount or percentage-of ferrite present in the matrix. The underlying causes'and-reasonsfor the formation of nodular graphite instead of"flake" graphite in iron is not yet thoroughly understood. Also the reason for the softening eifect'by lanthanum is not completely clear. As stated previously there is some evidence that lantha-' num frees an additional amount of carbon to form more graphite nodules and thereby increase the amount of ferrite present in the matrix through reduction of carbides. It is also suspected that lanthanum softens the iron by 1 combining with gases-such as; hydrogen, oxygen and nitrogen which are well known potent iron hardeners.

It has been mentioned previously that the presence of ceriumor magnesium will result in a harder gray iron in the as-cast condition. "It should also be noted that under certaincircumstanceslanthanum may be a hardener for gray iron. lt hasb'een found" during the course of our inv'efstigation that if the amount'of lanthanum in the iron exceeds 0.020 percent the' 'resiilting'iron will prograssiveiy {become harderflas lthe pe centa e of lanthanum further ases. Therefore only minute pereefirages offlanthanum-should be used to soften grayiron, namely; the range of 0.004 to 0.020 percent lanthanum, .to soften either-beneficiated or nodular iron.

As the percentage of magnesium is.lowere'd-:to below 5 about 0.03 or 0.04 percent and the lanthanumbelow 0.004 percentcomplete spheroidization of the graphite is not achieved and the resulting product is -of-the beneficiated iron type. previously discussed. Figure 5 represents :a typical structure of beneficiatediron which in 10 l this illustration has but relatively'few nodules, the bulk of the free carbon being coalesced to a transitional stage 'between fiakeform and nodular form. S'uch beneficiated iron is soft having 'a tensile strength in the order of 00,000 pounds per'square inchrand may haVe -an elongation of up to and even exceeding six percent, For example a beneficiated iron-made in accordance with the above and shown in Figure 5 possessed, in the as-cast condition, a tensile strength of 81,000 pounds per square inch with ayield strength of 61 ,000pounds per-square 20, inch and an elongation of 4 percent. Such ironmay be used' in numerous applications without the necessity of supplemental thermal treatments.

Having thus described our invention including several specific examples thereof it can now be seenthat the objects of the invention have been fully achieved and it must be understood that changes andmodifications -might be made which do not depart from the spirit of the invention; as 'disclosed nor from the scope thereof as defined in the appended claims. a Weclaimr; j j k 1. A ductile iron casting having improved machinability characteristics containing in the matrix thereof particles of carbon substantially in' agglomerated form, said castingcontaining from 3.00to 3.' 70% total carbon frorn 1.80 to 2.80% 'licon from 0.50 t9 -1.00% maiigianelsejfrom 0.10 w02s% phosphorus'fnot more than 0.03% sulfur,

a carbon agglomerant retained 1n anamountsuflicientto agglomerate substantially said carbon particles in the ab- -sence of effective amounts of retained residual. elements 40 subversive to said'carbon agglomerant, and a-ductilizing agent consisting of metalliolanthanum retained in-an amount of 0.004 to 0.020 percent to impart said improved niachinability characteristics to said casting inthe as-cast condition. 1

2. A ductile iron casting having improved machinability characteristics containing in the matrix thereof particles of carbon agglomerated substantially in spheroidal form, said casting containing fr0m'.3.00 to 3.70%

total'carbon, from 1.80 to 2.80% silicon, from 0.50: to

1.00% manganese, from 0.10 to 0.25% phosphorusynot more than 0.03% sulfunacarbon agglomerant retained in an amount from 0.0 2 to 0.50% selected from the group of metals consisting of cerium and magnesium in the absence of eiiective amounts of retained residual elehients subversive to saidcarbon agglomerant, and a ducparticles of carbon agglomerated substantially in sphe-m roidal form,said casting containing from 3.00 to 3.70% total. carbon,.from 1.80 to 12.80% silicon,.from 0.50 to 1.00% manganese, from 0.10 to 0.25%'phosphorus, not

more than 0.03% sufur, aretained carboniagglomerantselected from the group of metals consisting of'rnagnesium in an amount from 0.04 to 0.5% and cerium in an amount from 0.05 to 0.50% inthe absence of eiiective amounts 0 of retained residual element's subversive to saidcaibon agglomerant, and a ductilizing agent consisting of 'metal! lic lanthanum retained in an" amount from 0.004 to0l020 percent to impart said improved machinability characters 'istics' tosaid casting in theas-cast condition. as *4. A ductile iron"casting-having im roved-memoir.

was

ty characteristics containing in the matrix thereof particles of agglomerated graphite shaped irregularly in a transition stage between flake form and spheru'itic form, said casting containing from 3.00 to 3.70% total carbon, from 1.80 to 2.80% silicon, from 0.50 to 1.00% manganese, from 0.10 to 0.25% phosphorus, not more than 0.03% sulfur, a retained graphite agglomerant selected from the group of metals consisting of magnesium in an amount from 0.02 to 0.04% and cerium in an amount from 0.02 to 0.05% in the absence of effective amounts of retained residual elements subversive to said graphite agglomerant, and a ductilizing agent consisting of metallic lanthanum retained in an amount from 0.004 to 0.020 percent to impart said improved machinability characteristics to said casting in the as-cast condition.

5. A ductile iron casting having improved machinability characteristics containing in the matrix thereof partieles of carbon substantially in agglomerated form, said casting containing from 2.82 to 3.53% total carbon, from 2.47 to 3.56% silicon, not more than 0.1% phosphorus, not more than 0.03% sulfur, a carbon agglomerant retained in an amount sufficient to agglomerate substantially said carbon particles in the absence of effective amounts of retained residual elements subversive to said carbon agg omerant, and a ductilizing agent consisting of metallic lanthanum retained in an amount of 0.004 to 0.020 percent to impart said improved machinability characteristics to said casting in the as-cast condition.

6. A ductile iron casting having improved machinability characteristics containing in the matrix thereof particles of carbon agglomerated substantially in spheroidal form, said casting containing from 2.82 to 3.53% total carbon, from 2.47 to 3.56% silicon, not more than 0.1% phosphorus, not more than 0.03% sulfur, a carbon agglomerant retained in an amount from 0.02 to 0.50% selected from the group of metals consisting of cerium and magnesium in the absence of effective amounts of retained residual elements subversive to said carbon agglomerant, and a ductilizing agent consisting of metallic lanthanum retained in an amount of 0.004 to 0.020% to impart said improved machinability characteristics to said casting in the as-cast condition.

7. A ductile iron casting having improved machinability characteristics containing in the matrix thereof particles of carbon agglomerated substantially in spheroidal form, said casting containing from 2.82 to 3.53% total carbon, from 2.47 to 3.56% silicon, not more than 0.1% phosphorus, not more than 0.03% sulfur, a retained carbon agglomerant selected from the group of metals consisting of magnesium in an amount from 0.04 to 0.50% and cerium in an amount from 0.05 to 0.50% in the absence of effective amounts of retained residual elements subversive to said carbon agglomerant, and a ductilizing agent consisting of metallic lanthanum retained in an amount from 0.004 to 0.020 percent to impart said improved machinability characteristics to said casitng in the as-cast condition.

8. A ductile iron casting having improved machinabiity characteristics containing in the matrix thereof particles'of agglomerated graphite shaped irregularly in a transition stage between flake form and spherulitic form, said casting containing from 2.82 to 3.53% total carbon, from 2.47 to 3.56% silicon, not more than 0.1% phosphorus, not more than 0.03% sulfur, a' retained graphite agglomerant selected from the group of metals consisting of magnesium in an amount from 0.02 to 0.04 and cerium in an amount from 0.02 to 0.05% in the absence of efiective amounts of retained residual elements subversive to said graphite agglomerant, and a ductilizing agent consisting of meta lic lanthanum retained in an amount from 0.004 to 0.020 percent to impart said improved machinability characteristics to said casting in the as-cast condition.

9. A ductile iron casting having improved machinability characteristics containing in the matrix thereof particles of carbon agglomerated substantially in spheroidal form, said casting containing from 2.82 to 3.53% total carbon, from 2.47 to 3.56% silicon, not more than 0.1% phosphorus, not more than 0.03% sulfur, a retained carbon agglomerant selected from the group of metals consisting of magnesium in an amount from 0.04 to 0.50% and cerium in an amount from 0.05 to 0.50% in the absence of effective amounts of retained residual elements subversive to said carbon agglomerant, and a ductilizing agent consisting of metallic lanthanum retained in an amount from 0.007 to 0.011% to impart said improved machinability characteristics to said casting in the as-cast condition.

References Cited in the file of this patent UNITED STATES PATENTS 2,622,022 CrOme Dec. 16, 1952 2,841,490 Stevens et a1. July 1, 1958 FOREIGN PATENTS 721,717 Great Britain Jan. 12, 1955 730,712 Great Britain May 25, 1955 1,070,939 France Aug. 19, 1954

Claims

2. A DUCTILE IRON CASTING HAVING IMPROVED MACHINABILITY CHARACTERISTICS CONTAINING IN THE MATRIX THEREOF PARTICLES OF CARBON AGGLOMERATED SUBSTANTIALLY IN SPHEROIDAL FORM, SAID CASTING CONTAINING FROM 3.00 TO 3.70% TOTAL CARBON, FROM 1.80 TO 2.80% SILICON, FROM 0.50 TO 1.00% MANGANESE, FROM 0.10 TO 0.25% PHOSPHORUS, NOT MORE THAN 0.03% SULFUR, A CARBON AGGLOMERANT RETAINED IN AN AMOUNT FROM 0.02 TO 0.50% SELECTED FROM THE GROUP OF METALS CONSISTING OF CERIUM AND MAGNESIUM IN THE ABSENCE OF EFFECTIVE AMOUNTS OF RETAINED RESIDUAL ELEMENTS SUBVERSIVE TO SAID CARBON AGGLOMERANT, AND A DUCTILIZING AGENT CONSISTING OF METALLIC LANTHANUM RETAINED IN AN AMOUNT OF 0.004 TO 0.020 PERCENT TO IMPART SAID IMPROVED MACHINABILITY CHARACTERISTICS TO SAID CASTING IN THE AS-CAST CONDITION.