ftsting bad a nkamestum plus cerium content of about o.05%. The thus-treated metal was inoculated with about 0.5% awcon as comniercial ferrosmeon and mt. The resulting casting. made in amrdance with the Invention, was a 5 gray cast iron containing substantially all the graphite as spheroids. 7be fracture of th6 casting wa3 steely and, when tested under the same conditions as ExamPle 1, the casting had a transverse suwigth of about 8770 pounds, an impact lo value greater than 120, 1 and a BrineU hardness of about 268. It is recognized tbat magnesium and cerium determinations of the order involved herein are difficult to make. The values given herein for is these elements am based upon ilnalyses which have been checked and are reproducible within about 0.005% and the values given for cerium are reproducible within about 10%. The present invention may be applied to the 20 manufacture of a wide variety of ferrous products and articles. Flor example, engine crankshafts, machinery parts such as roU mUl housings and run-out tables for steel mill equipment, ingot molds, railroad castings, marine castings, go castims for agricultural implements, automotive =tings, etc., can be made of the alloy provided by the lnvention. It is to be noted that the present invention is not to be confused with the teachings and dis- 30 closures of Mor.-ogh et al. (for example, in the article published in the March 1948 issue of the journal of the Iron and Steel Institute at pages 306 et seq., in the article published in the April 1948 lmue of American F'oundryman at pages 91 35 et seq., etc.) since the cerium treatment process disclosed by Morrogh et al. must be applied to a hypereutectic cast iron composition and is applied to low-sulfur content cast iron melts. Thus, at page 92 of the aforesaid American to Foundryman article, Morrogh et al. state that a compositional requirement for the treatmp-nt of cast irons by their process is that the iron - "must be of hypereutectic carbon content, that is, the carbon content should exceed the value 45 4.3-% (percent Si+pereent P)." The require- ment that the cast iron be of hypereutectic composition Is a serious limitation since hypereuteetic cast irons are not commonly used in co-mercial practice. The present process, on the other r)( hand, is applied specificAUy to the treatment of hypoeutectic cast iron melts more commonly employed in commercial practice and is not restricted to the treatment of cast Iron melts of very low sulfur content. fi-i Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the rpirit and scope of the inven- 60 tion as those skffled in the art wiU understand. Such modifications and variations are considered tp be within the purview and scope of the invention and,of the appended claims. We claim, 65 1. The improved process for producing hypoeutectic gray cast iron containing spheroidal graphite which comprises establishing an iron bath having such a composition as to be a hypoeutectic gray cast iron when inoculated and cast, 70 Incorporating in said bath sufficient magnesium to provide a retained magnesium content of at least about 0.0157o but less than about 0.04% and insumcient by ftself to control the occurrence of substantiauy spheroidal graphite in castings T& made from &aid bath and sufficient cerium to provide a retained cerium content of at least about 0.015% In castings made from said ))ath, Inoculating said bath with about 0.3% to about 2.5% silicon and casting the metal from the inoewated bath in an inoculated condition to obtain a hypoeutectic gray iron casting containing about 0.05% to about 0.075 % ma@nt%zium plus cerium and containing graphite in a substantiary spheroidall form. 2. 7be improved process for producing bypoeuteetic gray cast Iron containing spheroldal graphite which comprises establishing an Iron bath having such a composition as to be a hypoeutectic gray caat iron wheninoculated and cast, incorporating in said bath sufficient magnesium to provide a retained magnesium content of at least about 0.015% to about 0.035% 9@nd lmufficient by itself to control the oc6urrence of substantially spheroidai graphite in castings made' from said bath and sufficient cerium to provide a retained cerium content of at least about 0.015% in castings made from said bath, and casting the metal from the bath in an inocuiated condition to obtain a hypoeutectic Iron casting containing about, 0.035% to about 0.1% magnesium plus cerium and oontaining graphite in a substantially spheroidal form in the as-cast condition.. 3. The improved Process for producing hypoeutobtic gray cast iron contabitng spheroidal graphite,which comprises establishing a molten L cast iron bath having such a composition as to be a hypoeutectic gray cast iron bath when ca3t in an inoculated condition, incorporating In said bath an amount of magnesium sufneient to provide a retained magnesium content cif at least albout 0.015% but less than about 0.04% and insufficient by itself to control the occurrence of a substantial amount of graphite in a substantially spheroidal form in castings made from said bath and an amount of cerium sumcient to provide a retained cerium content of at least about 0.015% to about 0.1% in castings made from said bath, and casting metal from the thus-treated bath to obtain hypoeutectic. gray cast iron castings containing a substantial amount ot graphite In a substantially spheroidal form and characterlmd bY an iinproied combination of properties as compared to the properties of a sinjilar gray iron casting not containing both magnesium and cerium in the aforesaid amounts. 4. The Improved process for producing hypoeutecti@ gray cast iron containlng uncorabined carbon in a substantially spheroidal form which comprises incorporating in- a molten cast irgn bath having such a Composition as to be a hypoeutectic gray cast iron bath when cast 'in an inoculated conditidn an amount of magnesium sufficient to provide a retained magnesium content of at lea@t abgut 0.015 % but less than, about 0.04% and insufficient by itself to contiol the occurrence of a substantial amount of uncombined carbon in a spheroidal for-m in castings made from said bath and an amount of cerium sufficient to provide a retained cerium content of at least aboiit 0.0159o' but le@s th.an about 0.16% in castings made from said bath, and casting metal from said bath in an inoculated oondition to obtain hypoeutectic gray cast iron castings containing a substantial amount of the uncgmbined carbon in a substantiaby spheroidal form and characterized by an improved combination of properties as compared to the propa.

9 ties of a dninar gray km owding devdd ot mag. nesium. 5. The improved proem for producing bn*eutectic gray cast Iron containing substantial. ly spheroidal graphite which o=prim establishIng a molten iron bath having such a composi. tion as to be a hYPoeutectic cast iron when inoculated and cast, incorporating and retaining in said bath at least about 0.015% but less than about .0.04% magnesium and at least about 0.015% cerium, the igim of the retained mag- ' nesium and retained cerium contents being at least about 0.035%, and castbw metal from mdd bath containing the aforewld amounts of magresium and cerium In an Inoculated condition to obtain a hypoeutectic gray cast l.ron casting containing graphite In a substantially spheroidal form and having an Improved combination of properties as compared to a simil I casting de. void of magnesium. 6. The process for producing an improved hypoeutectic gray cast iron which comprlm establishing a bath of molten Iron of such a oom. position as to be a hypoeutectic gray cast iron when Inoculated and cast and dontaining over about 0.06% sulfur, reducing the awfur content to a value less than about 0.05%, incorporating into said bath an amount of magnesium suflicient to provide a retained magnesium content of at least about 0.015% to about 0.035% and insumclent by Itself to control the occurrence of graphite in a,spheroidal form In castings made from said bath, incqrporating Into said bath an amount of cerium sufficient to provide a retained cerium content of at least about 0.015% up to about 0.08% In castings made from said bath, Inoculating said bath with about 0.3% t,6 about 2.5 % silicon and casting metal from said bat]6 in an inoculated condition to obtain a hypoeutectic gray cast IrOn casti ng cOnWning graphite in a spheroidal form and contabihw at least about 0.035% magnesium plus cerium. 7. The process for producing an improved ductile hypoeutectic gmY cast lmn whlch comprises estabushing a bath of molten iron of such a composition as to be a hypoeutectic prmy cast Iron when cast in an inoculated condition-and containing more than about 0.06% sulfur, incorporating Jnto said bath an amount of magnesium sufficient to reduce the sulfur content thereof below about 0.03% and to provide a re7tained Magnesium content of at least about 0.015% up to about 0.04% in castings made from said bath, incorporating into said magnesiumtreated bath an amount of cerium sumcient to provide a retained cerium content of at least about 0.015 go' up to about 0.1 clo in castings made from said bath, and casting metal from said bath in an inoculated condition to obtain a hypoeutectic gray cast iron casting containing uncombined carbon In a spheroidal form, and containing at lelst about 0.04 % magnesium plus certurn. 8. An Iron casting containing about 2.5e/, to about 3.7% carbon with the excess carbon not required t,6 form th; matrix being predominantly uncombined, about 1.5% to about 3% silicon, up to about 0.5% PhosPhorus, the carbon, silicon Rnd PhOsPhorus contents being so reated that the sum of the carbon content plus one-third the siucon content plus one-third the phosphorus content Is less than 4.3. magnesium from about 0.015% to about 0.035go' and insilfficient by itself to control the occurrence of a substant'al amount Of gmphite in & $Pheroidal form, at least about 0-015% cerium, with the magnedum Plus ceri@m .10 content being about 0.05% to about 0.075% to control the occurrence of a substantial amount of the uncombined carbon in. a substantlauy spheroidal form, and the balance essentially Iron to provide a ferrous matrix In which the substan. tially spheroidal uncombined carbon particles are dispersed. 9. A hypoeutectic gray iron castft containing about 2.5% to about 3.7% carbon, about 1.5,y,, 10 to about 3% silicon, magnesium from about 0.015% to less than abdut 0.04% and lnsumelent by itself to control the occurrence of graphite in a spheroidal form in the casting, at least about 0.0159o cerium, with the total quant,ty of mag15 nestum plus cerium being about 0.04% to glbout 0.19o' to control the occurrence of graphite In a sphqroidal form, and the balance essentially Iron. 10. A gray iron casting containing about 1.7% to about 3.99o' carbon, with the excess carbon 20 not required to form the matrix being predominantly uncombined, about 1.29'o to about 7go' silicon, up to about 0.5% phosphorus, with the carbon, siucon and phosphorus contents being so related that the carbon content plus onethird 25 the ri'icon content plus one-third the phosphorus content is less than 4'3, up to about 10clo nickel, up to about 2% COPPer, at least about 0;015LYo but less than about 0.040/o magnesium, at least about 0.015% cerium, with the sum of the mag30 nesium and cerium contents being about 0.05% to about 0.075 %, and the balance essentially iron, said casting being characterlzed by uncombined carbon in a substantially spheroidal form and by an improved combination of properties as com35 pared to those of a simflar casting devoid of magnesium. 11. A gray iron casting contalnlng about 1.7tYo to about 3.9% carbon, with the excess carbon not requ!red to form the matrix being predomi-, 40 nantly uncombined, about 1.2,9o' to about 79,0 silicon, up to about 05% phosphorus, with the carbon, sibcon and ph@sphorus contents being so related that the carbon content plus one-third the silicon content plus one-third the phosph I orus 45 content Is less than 4.3, up io about 10% nickel, uP to about 2% copper, at least about 0.015% to about 0.04,1/o magnesium, at least about 0.015% cerium, with the sum of the magnesium and cerium contents being about 0.035% to about 0.1%, 50 and the balance essentially Iron, said casting being characterized by uncombined carbon in a substantially spheroidal form and by an improved combination of properties as compared to those of a similar casting'devoid of magnesium. 55 12. A gray Iron casting containing magnes4um from about 0.015% to about 0.035go' and insufficient bY itself to control the occurrence of graphite in a spheroidal form in the casting and at least about 0.015% cerium, with the total 60 quantity of magnesium plus cerium being about .0-035% to about 0.1% to@ control the occurrence of graphite In a substant4aUy spheroidal form, with the balance being a bypoeutectic cast iron composition. 65 13. An iron casting containing at least about 0.015% up to about 0.04% magnesium, at least about 0.015% and up to about 0.16clo cerium, with the total quantity of magnesium plus cerium being about 0.049,' tiD about 0.2%, and contain-ng 70 uncombined carbon In a substantially spheroidal fornl'with the balance being a hypoeutectic gray cast iron composition. 14. An improved gray iron casting containing the Carbon not required to form the matrix 75 PredOnlinalitlY in an uncoinbined form, at lewt

about 0.015% up to about.0.06% cerium, a was]' but effective amount up to about 0.035% of magnesium insumcient by Itself to control theoccurrence of uncombined carbon in a spheroidal form In mdd coating but effective IA combimtidn'with the aforesaid amounts of cerium to control the occurrenee of uncombined e*rbon In a spheroidal form In Wd casung, and. the b&l&nce a hypo-. eutectic cast iron composition devoid of subversive &mounts of elements which materi&Uy interfere la with the formation of uncombhied carbon in a spheroidal forml ALBERT PAUL GAGNEBIN. WARRELQ MCLELLAN SPZAI;L ',ENCEB CITZD The fohowing references an of rawrd in the fUe of this patent : UNr= STATzs pATzM Number Name DMe 2,485,760 Milli et &I Oct. 25, 1"9 2,"5.761 MJ"fs et aL Oct. 35, 1%9 2.488,512 MOrrOgh ---------- Nov. 15, IM

Patented Feb. 2% 1951 2rWv655 UNITED STATES PATENT OFFICE 21542,$U GRAY CAST EMON Albut Paul ==R,d Ba"k "a Wan,,m MoLdl= beth, N. I., audgum to The International Nickel Co3npany, Inc.' New York N. Y, a corporation of Ddavmft No Dmwim. AppUmtion geptmbw 17,190, Serial No. 116,421 14 Cbdnm (CL 75-123). 2 The present Invention relates to a novel method for the production of gmy cut Iron containing spheroidal graphite and to the novel hypoeutectic gray cast Iron product produced thereby. It is an object, of the present invention to Pro- 5 vide a novel method for the production of bypoeutect ic gray cast iron containing, graphite in a spheroidal form. Another object of the Invention is to Provide a novel bypoeutectic gray cast iron having a greatly 10 impr,ov ed combination of properties. The invention also contemplates providing a novel hypoeutectic gray cast Iron containing a special combination of elements to control the occurre nce of graphite in a spheroidal form. 15 Genera Uy speaking, the present invention contemplate s a novel process for producing hypoeutectic gray cast Iron containing uncombined carbon or graphite in a substantiauy spheroidal form in the as-east condition a,nd the product 20 produce d thereby. The novel process contemplated by the present invention comprises Incorporat ing in a molten iron bath having such a, composit4. on as to be a hypoeutectic gray cast. iron when inoculated and cast an amount of 25 mamsiu m sufficient to provide a retained magnesium content of at least about 0.015% but less than about 0.035% or 0.04% in castings made from said bath, an amount of cerium sumcient to provide a retained cerium content of at least 30 about 0.015% and up to about 0.16% in castings made from said bath with a total content of magnesi um and cerium in said castings being at least about 0.035% or 0.04% up to about 0.2% and casting metal from said treated bath in an 33 inoculat ed condition to produce castings of hypoeutectic cast Iron containing uncombined carbon or graphite In a spheroidal form in the ascast condition. Very satisfactory results are obtained when the retained content of magnesium 40 plus cerium is about 0.05% to about 0.075%, although retained contents of magnesium plus cerium of up to about 0.1% can be employed especia uy in compositions having high graphitizing power, e. g., those cast in heavy sections such 45 as about four inches. The cerium content is usuauy less than about 0.1%. e. g., up to 0.06% or 0.08 %. As those sklued in the art know, cast Irons are eutectite rous alloys whose principal constituents 50 are -iron and carbon aW hypoeutectic cast irons are those containing km carbon than the euteetic amount. The eutectic amount of carbon in anY particular composition varies depending upon the amounts of other elements in the composi'tion, e. g.. sircon. Hypoeutectic gray cast irons are those containing carbon, sflicon and phosPhorus in such amounts that the carbon content Plus one-third the swcon content plus one-third the phosphorus content is less than 4.3, e. g., 4.2 or less, with the carbon in excess of that required to form the matrix being predomin ntly in the uncombined form. in general, the gray cas*. iron compositions produced according to the present invention contain, in addition to the aforesaid amounts Of MLgnesium and cerium, about 1.7% to about 3.9% ewbon with the excess carbon not required to form the matrix being Predominantly uncombined, about 1.2% to about 7% silicon, about Q.05% to about 2% manganese, up to about 0.5% phosphorus, up to about 10% nlekel, e. g., about 0.05% to about 3% nickel, up to about 2% copper, e. g., about 0.05% to about 1.5% copper, and the balance essentiallv iron to provide a ferrous matrix. The iron content is usually at. least about 85% or 80% of the.total compositio@n and the iron is in the alpha form at atmospheric temperatures. The carbon content in castings produced in accordance with the Inventiori is controued such that it is always less than the value represented by the formula 4.3 minus Y3 (Si+P). Particularly satisfactory results are obtained when the carbon content is about 2.5 % to about 3.7 % and the silicon content is about 1.5 % to about 3 %. Such castings usuauy contain at least about 1.3% or 1.5% uncombined carbon or usuauy about 2% uncombined carbon in the as-cast condition. Within the ranges of composition set forth hereinbefore, the retained magnesium and cerium contents contemplated by the invention cooperate to produce a new result, i. e., theprgduction of a hypoeutectic gray cast Iron containing graphite or uncombined carbon in a spheroidal form although the retained magnesium content Is insufilcient by itself to control the occurrence of a large proportion of the graphite in a spheroidal form. This result is unexpected in view of the fact that cerium, in the absence of magnesium, is not effective by itself In hypoeutectic cast iron

2,542,655 3 composltions to Provide the rebmts obtained by the present invention but acts as a desulfurizer and carbide stabilizer or whitener even when Inoculation is employed after the introduction of cerium. g in the process contemplated by the invention for producing spheroidal graphite in a hypoeutectic gray cast iron composition, Inoculation Is an essentjal feature required to produce uncombined carbon or graphite in the;solldiflfd produdt 10 provided by the invention. Inoculation of the hypoeutectic cast hon bath is accomplished along with or subsequent to the incorporation therein of the amounts of magnesium and cerium contemplated by the invention. In6rulation Is 15 accomplished by a late addition of an inoculant, e. g., swcon. Preferably, the graphitizing iiioculation is carried out after the incorporation of magnesium and cerium Into the molten@hypoeutectic cast iron bath. Very satisfactory results 20 have been obtained using ferrosilicon, e. g., on iron alloy containing a major proportion up to about 95% silicon as t4e inoculating agent although other metallic siliconcontaining agents or alloys, such as nickel-sijicon alloys or riiekel 26 swcide, calcium-silicon alloys or calcium silicide, silicon metal and various propriet@ry inoculating alloys commonly used for reducing, dendriticism and reducing chill in@foundry gray cast irons may be employed. As those @kiued in the art know, 30 commerciauy available ferro-silicon and various proprietary inoculants WualIy contain calcium, e. g., up to about 1% or so, and the presence of this element has been recognized to increase the effectiveness of the inoculant in many instances. 35 It is also known th,,it ffrrosilicon and various proprietary inoculants often contain aluminum. It is preferred to employ suicon in amounts between about 0.3,lo and about 2% or 2.5%, more preferably between about 0.4% and about 1.2%, 40 as the late addition to effect inoculation. Since the aforesaid am6unts of silicon are added to effect inoculation in the process embodying the present inventiori, the initial silicon dontent of the hypoeutectic cast iron bath to be treated 45 In accordance with the present invention is usually about 0.8 % to about 2 %. Iii carr@ing out the process contemplated by the invention to produce hypoeutectic gray cast iron containing spheroidal carbon and having 50 high ductility, it is preferred that the manganese content be low as this element detrimentauy affects the ductility. Thus, it is preferred that the man-.anese content not exceed about 0.3% to provide good ductility. When high strength, 55 rigidity @and wear resistance are desired, a pearhtic matrix containing about 0.5% to about 0.6% manganese is employed. Phosphorus, which is usually considered an impurity but which in the usual amounts does not materially 60 interfere with the formation of spheroidal graphite, is also preferably maintained at a low level as phosphorus detrimentally affects the ductility. Although the phosphorus content may be as high as about 0.5% or more, phospho,.rus 63 preferably does not exceed approximately 0.25% and more preferably does not exceed about 0. I%. The sulfur content in hypoeutectic cast iron products produced in accordance with the inventioii is low, usually not exceeding about 0.02%, 70 e. g., about 0.01% to about 0.018%. Certain other elements not usually found in cast Iron should be avoided or should be present only in traces or in very small amounts because these elements interfere with the formation of sphe- 76 4 roidal grRPhite. These subversive elements include tin, lead, antin2ony, bismuth, arsenic, selenium, tellurium, etc. These elements preferably are not present in a total amount over about 0.05%. Other alloying elements which may be present In the composition to provide specific effects upon the matrix structure include up to about I-'/o chromium, up to about 1% molybdeniim, up to about 0.5% vanadium, etc. Magnesium can be introduced Into the molten hyi@oeutectic gray 'east iron, in me'tallic form provided Proper precautions are observed or it can be introduced in the form of an alloy. Nickel, copper and/or silicon are the preferred metals with which magnesium is alloyed to form addition agent.-., Very satisfactory aroys include nickel-magiiesium alloys containing about 4%'to about 20% magnesium; nickel-magnesium-carbou alloys containing about 10% to about, 15% magnesium, and about 1.5% to about 3% carbon; nickel-magnesium-silicon aroys containing about 13% to about 20% magnesium and about 20% to about 30% silicon; and iron-magnesium-silicon alloys containing about 129'o to about 16% magnesium and about 30% to about 60% silicon. Cerium is added to the 'molten cast iron in the form of cerium metal or as an alloy or a mixture, e. g., mischmetal. In carrying out the process contemplated by the lnventibn, particularly when the sulfur content of the ',Iiypoeutectic cast iron bath to be treated is about 0.05% or 0.06% to 0.15% or more, e. g.. up to about 0.3% sulfur, magnesium in an amount sufficient to reduce the sulfur content of the bath, e. g., to a value beiow about O.OS% or 0.02%, and to i@rovide the required retained magnesium content in castings made from the bath is incorporated in the bath; thereafter the required amounts of cerium are incorporated in the bath, the bath is inorulated at least once and metal from this treated inoculated bath is cast to obtain hypoeutectic gray cast iron containing spheroidal graphite. Alternatively, other means may be used to reduce the sulfur below about 0.05% or even below about 0.02% prior to the introduction of magnesium and/or cerium, e. g., by means of a basic slag, etc., and this practice is beneficial and advantageous. When the sulfur content of the hypoeutectic cast Iron bath is low, e. g., below about 0.05%, the cerium addition can be made simultaneously with the magnesium addition, or even prior thereto. Magnesium is a very powerful desulfurizer in cast iron baths, even baths which are hold under acid conditions, as in an acid-lined ladle etc. About one part by weight of magnest@i@ is introduced into the cast iron bath for each part by weight of sulfur to be removed and the magnesium consumed in removing sulfur is not effective to promote the formation of graphite in a spheroidal form. Of course,.sufficlent magnesium must be added not only to compensate for the losses of magnesium encountered In removing sulfur from the bast ir6ii bath, In the addition reactioris. in holding the bath after the Incorporation of magnesium, etc., but also to incorporate the required amounts of magnesium in the bath to provide the required retained magnesium content in the final casting. Moreover, losses are similarly encountered In introducing and retaining cerium in the cast iron melt, and these losses also mil t be compensated for In incorporating the requirfd amounts of cerium in th-m. cast iron bath to provide the re-

quired retained cerium content In the nnal cast. Ing. In the novel gray cast iron product provided by the invention in the as-east condition, some or practicauy all, of thel uncombined carbon or graphite appears as compact, soft, gmy-colored, rounded tarticles or spheroids, or as agglomerates dr groups of such particles. These rounded particles or sipheroids of =combined carbon or graphite visible in properly polished and etched sections have awell-deflned radial or radiating structure. The particle has the appearance of a plurality of crystals radiating from approximately the center, 1. e., a radiating and polycrystalline appearance. At least some, e. g-, usually about 25 or more, of,the uncombined carbon or graphite is in a spheroidal form in the novel gray cast iron provided by the invention. When some of the uncombined carbon or graphite is in the spheroidal form, the use of a slightly higher amount of retained magnesium and/or cerium, e. g., about 0.01% or 0.02% additional retained magnesium and/or cerium, is sufficient in most cases to cause the uncoinbined carbon or graphite to appear predominantly in a substantially spheroidal form. The novel product provided by the Invention containing spheroidal graphite in the aseast condition possesses a very remarkable combination of properties and characteristics. - In general, the tensfle strength of the as-cast product will be 50 % or more. greater than would be obtained in the same composition devoid of magnesium, and usuary the improvement in tensile strength will be 100,Vo or much more. Tensile strengths on the order of 85,000 pounds per square inch or more aife obtained in the pearlitie L (I. e., generauy preferred) compositions.. The high tensile strengths are obtained in combination with iinproved ductility, e. g., elongations in tension as high as 5 % or more, L in compositions having pearlitic matrices. The novel as-east product is characterized by a consistently high tensile modulus ofelasticity of about 25,000,000 pounds per square inch and other improved or high properties. Castings made of the novel ma.@. terial have a light-colored or steely fracture as compared to the gray fracture of gray cast iron and have the unexpected characteristic that when struck with or against a hard object they en2it a definite steel-Uke ring rather than the duller sound emitted by gray cast iron. A highly useful property possessed by castings manufactured in accordance with the invention is that the hardness within -a particular casting Is very uniform even though the section size of, the casting varies considerably. As indicated hereinbefore the genemby preferred matrix structure in 4;e- as-east product provided by the invention is a pearlitic matrix. However, the spheroidal form of uncombined carbon or graphite which characterizes the novel aspast product provided by the invention can be obtained in any matrix obtainable in gray cast irons of simuar composition. Thus, the ferrous matrix may be pearlite, ferrite, martensite, an acicular constituent (e. g., bainite or other transformation products of austenite explained by the Scurve), etc., or the known combinations thereof. When it is desired to enhance certain properties or to modify the combination of properties, the as-cast alloy may be subjected.to known heat treatments, surface treatments, etc., for stress relief, hardening, strengthening, toughening, etc. and dmwing, normalizing mid drawing, austeniPert=, annealing at tempemtures both above and/or below the critical temperature, slow cooling from the casting temperature, etc. 5 F or the Purpose of giving those skibed in -the art a better understanding of t4e i I uvention, the followi ng iUustrat.1ve e3mmples are given: - 7=inj)le I 10 A hypoeutectic cast iron bath containing about 2.8% carbon, about 1.5% silicon, about 0.06c/, mang anese, and about 0.07% phosphorus was establi shed. To one portion of the bath, sufllcient magn esium was incorporated to provide a rp-- 15 , tained. magnesium content of about 0.016 c/o, and suMci ent cerium Was incorporated to provide a retain ed cerium content of about 0.031% in @.he final casting. The treated metal was inoculated With about 0.5% swcon as ferrosilicon and cast. 20 This casting, made In accordance with the present Invention, was a gray cast iron, had graphite. in a,$Pheroidal form atid had a transverse load in a 1.2-inch arbitration bar tested over 12-inch CenterS of about 9300 pounds, an iinpact value of 25 78, and a BrineU hardness of 269. The fracture of. this casting was steely. To another portion of the said bath 0.069,o cerium (but nomagnesium) was incorporated. The portion was inoculated with about 0.5% silicon as commercial ferrosilicon and cast. This casting, not made ac30 cording to the invention, was a white cast iron and had a tmnsverse load of 5700 pounds, an jinpact value of 24, and a Brinell hardness of 430. The fracture of this casting was white. 35 Example 2 A hypoeutectic cast iron melt containing about 3.3% carbon, about 1.8% silicon, about 0.6% manganese, about 0.05% phosphorus, aiid about 40 0.03% sulfur was established. To one portion of the bath sufllcient magnesium was incorporated to provi@e a retained mamesium content of 0.014%. and sufficient cerium was incorporated tO PrOVide a ftnal retained cerium content of 45 about 0.016% in the flnal casting, i. e., the final casting had a magnesium plus cerium content of about 0.03%. The treated metal was inoculated with about 0.5% silicon as commercial ferrosilicon and cast. 7his casting, not made according 50 to the invention, had a gray fracture and, when tested under the same conditions as in Example 1, had a tmnsverse load of about 3480 pounds, impact value of about 29, and a Brinell hardness of about 179. Into another portion of the afore55 said bath, suffleient cerium to provide a final retained cerium content of about 0.019% and sufficient magnesium to provide a fin il retal-ied magnesium content of about 0.016% were incorporated, i. e., the final casting had a magneGo sium plus cerium content of about 0.035%. This portion was likewise inoculated with about 0.5% silicon as commercial ferrosilicon and cast. This casting, made in accordance with the invention, was a gray cast iron containhig a substantial (15 portion of the graphite as spheroids. The fracture of this c"ting was steely, and, when tested under the same conditions as in Example 1, the casting had a transverse 109,d of about 6770 pounds an impact value of 70, and a Brinell 70 hardii;6 of about 215. To another portion of the aforesaid bath, sufficient magnesium was incorporated to provide a ftnal magnesium content of about 0.017% in the final casting and sufficient cerium was incorporated to provide a final ceMu.strative heat treatments include quenching la rium content of about 0.033% therein, i. e., the