US3421886A - Cast iron with at least 50% of the graphite in vermicular form and a process for making same - Google Patents

Description

Jan. 14, 1969 SCHELLENG 3,421,886

CAST IRON WITH AT LEAST 50% OF THE GRAPHITE IN VERMICULAR FORM AND A PROCESS FOR MAKING SAME Filed March 13. 1968 Sheet I Of 5 F l G l mvsmoa ROBERT DOUGLAS SCHELLENG 'IM-QPMZI ATTORNEY OWXH QOOQXQ 0.o/2%M ,o.0o4z0 00/676 17 0.006 %a 00227611, awaxca 1969 R. D. SCHELLENG 3,421,886

CAST IRON WITH AT LEAST 50 OF THE GRAPHITE IN VERMIGULAR FORM AND A PROCESS FOR MAKING SAME Filed March 13, 1968 Sheet 2 7.5.3.2 l3. 0035701 0 .Ge.

Ti EA.

INVENTOR ROBERT DOUGLAS SCHELL NG ATTORNEY Jan. 14, 1969 R. m. SCHELLENG 3,421,386

- CAST IRON WITH AT LEAST 50/o OF THE GRAPHITE IN VERMICULAR FORM AND A PROCESS FOR MAKING SAME Filed March 13, 1968 Sheet 3 of 5 INVENTOR ROBERT DOUGLAS SCHELLENG ATTORNEY United States Patent 7 Claims ABSTRACT OF THE DISCLOSURE A graphitic cast iron consisting essentially of about 2% to about 4% carbon, about 1.5% to about 3.5% silicon, up to about 36% nickel, about 0.005% to about 0.06% magnesium, about 0.001% to about 0.015% of a metal from Group IIIB of the periodic table, about 0.15% to about 0.5% titanium, with said magnesium, Group IIIB metal and titanium contents being eifective to control the occurrence of graphite in said cast iron predominantly in the vermicular form and the balance of said cast iron being essentially iron with other elements and impurities in small amounts which do not materially interfere with the occurrence of graphite in said vermicular form. A process for making said cast iron is also claimed,

The present application is a con-tinuation-in-part of my copending U.S. application Ser. No. 453,223 filed May 4, 1965, now abandoned.

The present invention is directed to improved graphitic cast iron and, more particularly, to an improved stronger cast iron having a controlled vermicular graphite structure and having essentially the foundry characteristics of flake graphite cast iron.

Since the advent of ductile iron, i.e., cast iron containing graphite in a spheroidal form, as described in U.S. Patent No. 2,485,760, the foundry industry has undergone a revolution in regard to the ability of the industry to provide castings having very high strength and useful levels of ductility as compared to gray cast iron containing graphite in the flake form. Ductile iron is now well established as a foundry product and the use of this material in the form of castings in industry is expanding each year. The increased tonnage of ductile iron which is sold each year may properly be taken as an indication of the acceptance which castings made of the material have secured in industry. As is Well known, however, ductile iron exhibits inferior foundry characteristics as compared with gray cast iron, and for that reason has not found favor in those applications Where good foundry characteristics are of paramount importance. The expression good foundry characteristics is used in the industry to include such factors as fluidity, improved resistance to the formation of shrinkage cavities in sections which are diflicult to feed, freedom from dross defects, low chilling tendency, etc. It is considered in the foundry industry that flake graphite gray cast iron has good foundry characteristics. With particular reference to the problem of shrinkage in castings, it is unquestionable that the shrink properties of gray cast iron castings are more favorable than is the case in "ice the higher strength ductile iron castings. As used in this application, the expression gray cast iron is used to denote cast iron having its uncombined carbon in the form of ordinary, unmodified flakes. A demand accordingly exists for a cast iron having greater strength and ductility than gray cast iron, but also having better foundry characteristics than ductile iron. For example, the automotive engine block has traditionally been produced as a gray iron casting. In recent times, foundries producing engine block castings have been required to produce lighter and lighter castings having thinner and thinner wall sections in response to demands of automotive designers for lighter engines having higher power-to-weight ratios and in response to a powerful competitive thrust from die cast aluminum engine blocks. In order to supply the demand for such castings, it would be desirable to employ ductile iron therein so that the markedly higher strength and modulus of elasticity of this material as compared to gray iron could be used with advantage. However, the foundry characteristics of ductile iron are such that it is difficult to produce sound and leak-proof thin-Walled castings of complicated configuration in the material on a production basis. The high strength of ductile iron as compared to gray iron would also appear to be useful in other castings such as lightweight brake drums and ingot molds. However, it has been found from experience that the thermal conductivity of ductile iron is lower than that of gray iron and this undesirable characteristic has inhibited the adoption of ductile iron in such applications and in other applications requiring high thermal conductivity and resistance to thermal shock.

A cast iron material having its uncombined carbon in the vermicular form is capable of satisfying this demand. On the one hand, because its graphite is in vermicular rather than flake form such a material possesses substantially greater strength and ductility than gray cast iron of the same composition, and, on the other hand, because the form of its graphite is more nearly flake-like than nodular such a material possesses substantially better foundry characteristics than ductile iron. The term vermicular graphite is used in this application to denote the type of graphite identified by that name and depicted in the paper by Donoho published in Modern Castings for July, 1961 at pages -71, inclusive.

Vermicular graphite structures have sporadically and on rare occasions been observed in connection with unsuccessful attempts to produce ductile iron in which insuflicient or incorrect nodularizing treatments were employed. Such structures have, however, been of unpredictable occurrence and unknown cause. Being thus uncontrollable and unreproducible, vermicular structures have not heretofore been regarded by the foundry industry as being of any practical utility. The vermicular graphite form has, rather, been looked upon as a manifestation of failure in the production of ductile iron.

I have now discovered a new cast iron composition and a method for producing the same, which material has a controlled vermicular graphite structure and is characterized by strength properties intermediate between gray cast iron and ductile iron of essentially the same base composition and which is further characterized by improved foundry characteristics, improved thermal conductivity, and improved thermal shock resistance as compared to ductile iron.

It is an object of the present invention to provide gray iron castings containing vermicular graphite.

It is a further object of the invention to provide castings having a gray iron composition which are characterized by vermicular graphite and by a strength intermediate between gray cast iron and ductile iron having essentially the same base composition.

Still another object of the invention is to provide a gray cast iron product having improved strength while having improved thermal conductivity and thermal shock resistance as compared to a ductile iron of the same base composition.

A further object of the invention is to provide a casting having the basic composition of gray cast iron, having improved strength as compared to gray cast iron of the same base composition and having improved foundry characteristics as compared to ductile iron of the same base composition.

It is a further object of the invention to provide a process for consistently and reliably producing vermicular graphite structures in cast iron.

Other objects and advantages of the invention will become apparent from the following description and the accompanying drawing in which:

FIGURE 1 is a reproduction of a photomicrograph taken at 100 diameters depicting the vermicular graphite microstructure which it is the object of the invention to produce;

FIGURES 2A, 2B, 2C and 2D are reproductions of photomicrographs taken at 100 diameters depicting vermicular graphite structure in cast iron produced in accordance with the invention over a range of magnesium contents;

FIGURES 3A, 3B and 3C are reproductions of photomicrographs taken at 100 diameters depicting the production of spheroidal graphite structures when an element essential to the present invention is omitted from the cast iron composition;

FIGURE 4 is a reproduction of a photograph taken at three-fourths actual size depicting the longitudinal section of a poorly fed complicated valve body casting demonstrating, in comparison to FIGURE 5, that improved soundness is obtained in castings produced in accordance with the invention; and

FIGURE 5 is a reproduction of a photograph taken at three-fourths actual size depicting the longitudinal section of a similar casting to that shown in FIGURE 4 to illustrate the foundry characteristics of ductile iron under the same conditions.

I have found, first, that the addition of cerium to a cast iron containing slightly less magnesium than will produce spheroidal graphite therein changes the form of the graphite from flake to vermicular. Thus, FIG. 1 shows the structure of cast iron containing about 0.01% magnesium which was converted from Type A flake graphite to vermicular graphite by the addition of about 0.005 cerium.

However, in order for this phenomenon to occur, the retained magnesium content of the cast iron must be maintained within a very narrow range lying just below the spheroid-producing amount for the particular composition being treated. Increasing the magnesium content above this range results almost immediately in a predominantly or fully spheroidal structure. Because of the extreme difliculty of maintaining the magnesium content within the requisite limits, the inevitable variabilty of the composition of cast iron from heat to heat, and for other reasons as well, vermicular structures cannot be obtained through the use of magnesium-cerium treatments alone on other than an uncontrollable, hit-and-miss basis.

I have also found, however, that the addition of titanium to the cast iron suppresses the formation of spheroidal graphite therein while in no way interfering with or suppressing the vermicular-inducing efiect of the magnesium and cerium. Thus, titanium, if added in suflicient quantity;

enables the production of predominantly vermicular graphite structure in cerium-magnesium treated irons over a relatively wide range of magnesium content. Thus, for example, at a low titanium level such as is normally considered tolerable in the manufacture of ductile iron, a spheroidal graphite structure was obtained with 0.025% retained magnesium and a small amount of cerium. With 0.3% titanium in the base iron, however, the iron contained a large proportion of vermicular graphite at this and even higher magnesium contents. The addition of titanium thus provides a means whereby the desired vermicular graphite can be obtained safely, reliably and reproducibly.

Broadly stated, the present invention comprises a graphitic cast product having the graphite predominantly in a vermicular form and containing about 0.005% or about 0.01% to about 0.06% magnesium, about 0.15% to about 0.5% titanium, about 0.001% to about 0.01% or 0.015% of a metal, e.g., cerium, from Group III-B of the periodic table, not more than about 0.02% or 0.025% sulfur, and the balance a gray cast iron composition. In the special cast material provided in accordance with the invention, the carbon content is about 2% to about 4%, the manganese content is about 0.1% to about 2.5%, or more when nickel is high enough to make the alloy austenitic, and the silicon content is about 1.5% to about 3.5%, more advantageously, not exceeding 3%. The product may contain up to about 1.0% chromium, up to about 2% molybdenum, up to about 0.5% vanadium, up to about 0.2% phosphorus, up to about 0.2% zirconium, up to about 0.05% aluminum, etc. The nickel content of the alloy may optionally be as high as about 36% as, for example, in castings having an austenitic matrix and containing about 20% or more nickel. In the presence of nickel in amounts sufficient to render the matrix austenitic, the contents of carbide-forming elements such as chromium, molybdenum, vanadium and manganese may be higher than those set forth hereinbefore. Thus, for example, austenitic castings may contain about 2% of chromium. The elements copper, tin, lead, antimony and bismuth are undesirable impurities in the special cast material provided in accordance with the invention since these elements interfere with the controlled production of vermicular graphite in castings contemplated by the invention in that they undesirably increase the tendency to form spheroidal graphite. Thus, the copper content should not exceed about 0.5% and the tin content should not exceed about 0.03% when the magnesium content is about 0.04% or higher. As the magnesium content is decreased below 0.04%, the tolerance for copper and tin are increased until at a magnesium content of about 0.02% a copper content up to about 2% and a tin content up to about 0.15% may be permitted without an undesirable formation of spheroidal graphite being encountered. In all cases, the lead content should not exceed about 0.01% and the antimony and bismuth contents should not exceed about 0.01% each. While aluminum opposes the spheroid-inducing effect of magnesium in a manner similar to titanium, this element is detrimental to foundry characteristics in that it produces a sticky, slaggy melt of decreased fluidity and yields a drossy casting having a poor surface, particularly on the cope side. Castings in accordance with the invention accordingly contain less than about 0.05% aluminum. Boron is another undesirable element in castings produced in accordance with the invention since it strongly tends to form massive cementities and/or other undesirable carbidic forms which are diflicult to remove by annealing the castings. Accordingly, this element is not present in amounts exceeding about 0.002%. Zirconium appears to act in the same manner as titanium in the special cast iron of the invention, but only about 0.05% of this element can be introduced with the cast iron under usual conditions.

More advantageously, the special cast material provided in accordance with the invention contains 3% to 3.6%

carbon, about 2% to 2.6% silicon, about 0.2% to about 0.7% manganese, about 0.2% to about 0.5% titanium, about 0.01% to about 0.04% magnesium, not more than about 0.01% or 0.02% or 0.025% sulfur, and about 0.001% to about 0.01% cerium or other element from Group III-B of the periodic table. Castings produced within the more advantageous ranges of composition exhibit freedom from shrinkage porosity and low chilling tendency in combination with moderately high strength.

Nickel is an important alloying element in the special cast material since it provides an improvement in matrix properties, particularly strength, and does not detrimentally affect the graphite structure. Thus, at nickel contents up to about 5%, each additional percent of nickel will provide an increase in tensile strength of the castings of about 6,000 pounds per square inch (p.s.i.). The carbide-forming elements chromium, molybdenum and vanadium do not appear to affect the formation of the desired vermicular graphite structure but do increase the chilling propensity of castings containing these elements. Accordingly, in any application in which chill control is a factor, the use of these elements generally is avoided.

The special cast material provided in accordance with the invention may have any matrix structure characterizing corresponding alloyed and unalloyed gray cast irons in the as-cast and/or heat treated conditons. Thus, the as-cast matrix microstructure may be ferritic, pearlitic, austenitic, martensitic, acicular, etc.

The three elements magnesium, titanium and cerium or other Group III-B element employed in combination within the ranges set forth hereinbefore cause and control the occurence of graphite to the vermicular form and each of these elements is maintained within ranges given to secure the special control of graphite structure contemplated in accordance with the invention. Thus, with magnesium contents less than about 0.005%, the graphite is no longer in the predominantly vermicular form but instead assumes the flake form and the strength of the alloy is reduced. On the other hand, when more than about 0.06% magnesium is present, unduly increased amounts of spheroidal graphite occur in the structure with an accompanying undesirable increase in chilling propensity and in solidification shrinkage together with an increased tendency to form dross inclusions which cause surface defects. More advantageously, the magnesium does not exceed about 0.04%, since in such irons occurrence of undesired graphite forms such as spheroids with the resulting occurrence of undesirable solidification shrinkage is avoided and increased chilling propensity is minimized. When less than 0.15% titanium is present, the control of graphite predominantly in the vermicular form becomes difficult and uncertain to the point of impracticability. More advantageously, the titanium content is at least about 0.2%. On the other hand, when the titanium content exceeds about 0.5%, oxide films form on the surface of the liquid iron which tend to cause surface defects on the castings produced. When cerium is absent, flake graphite forms and the strength of the iron is low. On the other hand, when the cerium content exceeds approximately 0.01%, e. g., about 0.012% or 0.015%, control of the occurrence of graphite predominantly in the vermicular form again becomes difficult and uncertain. Occurrence of excessive spheroidal graphite in the structure is encountered and the shrinkage of the resulting castings is undesirably increased. In such irons, the chilling propensity is markedly increased even in moderately thick castings. The graphite structure of castings containing only magnesium and titanium exhibit only flake graphite or mixtures of flake graphite and spheroidal graphite, while irons containing only cerium and titanium or only magnesium and cerium tend to transform abruptly from the flake form to the spheroidal form as either magnesium or cerium is increased above a critical value. The formation of vermicular graphite in the absence of the required amount of titanium is a matter of difficulty characterized by a higher tensile strength as compared to that of gray cast iron having the same base composition. In addition, the castings have a true modulus on the order of about 20 to about 22x10 psi. and have a useful ductility. The castings have improved fatigue resistance as compared to gray cast iron castings 'of the same base composition. As indicated, other elements from Group IIIB of the periodic table, such as yttrium, lanthanum or other element of the lanthanide or rare earth metal series may be employed in the place of cerium. Mischmetal, e.g., an alloy containing about 50% cerium and about 25% lanthanum with the remainder being comprised of other rare earth elements, is a satisfactory cerium-containing addition material for the production of castings in accordance with the invention. It is found in practice that, 'when such a mischmetal alloy is added to molten cast iron, lanthanum recovery is only about one-half as great as is the cerium recovery. Those skilled in the art will appreciate that cerium or other Group III-B metal can be added to the molten cast iron both in metallic form or in the form of a compound, e.g., oxides, etc., which are reducible to metal in the bath.

In order to give those skilled in the art a better understanding of the invention, the compositions of a number of castings produced in accordance with the invention are set forth in the following Table I and the tensile properties determined from 1-inch keel bar castings in the ascast condition are set forth in the following Table II. 'In each case, the melts were inoculated with 0.5%, by weight, of a calcium-bearing grade of ferrosilicon containing about silicon.

TABLE I [Percent] Si Mn Mg Ti Ce S Other 2. 53 0.23 0. 013 0. 15 0.004 0. 003 2. 59 0.24 0.023 0.23 0.006 0.002 2. 56 0.25 (0.007) 0.28 0.009 0.004 0.002 Pb 2.57 0.25 0.016 0.27 0. 006 0.007 0.002 Pb 2. 61 0.25 0.023 0.27 0. 005 0.005 0.002 Pb 2. 57 0.24 0. 013 0.28 0.006 0.003 (0.005) Pb 2. 54 0. 25 0. 011 0. 29 0. 005 0. 002 .005) Pl) 2. 54 0. 25 0.019 0.28 0.007 0.001 (0.005) Pb 2. 20 0. 14 0. 042 0.20 0. 007 0. 018 2. 10 0. 13 0. 015 0. 22 0. 005 0. 003 2. 26 0. 31 0. 013 0.31 0.005 0. 015 2. 33 0.29 0. 014 0.27 0. 005 0. 017 0.78 Ni 2. 41 0.29 0.019 0. 24 0.005 0.015 1.58 Ni 2. 28 0. 43 0.015 0. 34 *0. 007 0. 019 2. 40 0. 63 0.017 0.29 0. 0055 0.015 2. 31 0. 29 0. 016 0. 30 0.005 0. 019 0.12 C1 2. 36 0. 29 0.017 0.25 (0. 006) 0.018 0.15 Mo (2. 3) (0. 3) 0. 023 0. 33 *0. 006 0. 009 1. 73 0.65 0.017 0.35 (0.003) 0. 019 1. 89 0. 33 0. 017 0. 34 (0. 003) 0. 022 2. 28 0.41 0.013 0.35 (0.006) 0.005 (2.3) (0. 3) (0.008) 0. 23 0.006 0.007

*Single analysis, all others are the average of two analyses.

No'rE.-The melts set forth in the above table were produced using a mischmetal alloy containing about 50% cerium and about 25% lanthanum and contained cerium and lanthanum in a ratio of about 4 to 1. Numbers in parentheses are estimated.

TABLE II TABLE v Alloy Tensile Yield Elongw Modulus, A IiUlCOllt No. strength, strength, tion, p.s.i. BIIN Structure Section Tensile Yield Elonga- Yernnck.s.i. '.s.i. percent Alloy Size, Strength, Strength, tioii, BIIN nlar v No. inches k.s.i. k.s.i. Percent (but. 1 47.4 38.1 5.5 207x10 137 80%\, 5 splicbal. S. roidal) 2 40.4 30.0 0.5 200x10 140 %V,

1151. s; n 08.0 48.3 3.0 104 00 40.2 38.3 4 200x110 143 00% V, 00.5 43.4 4.0 137 75 bal. 1 54.5 40.4 3.0 108 50.1 40.8 5.5 20.0 143 80%; 2 40.2 37.3 3.0 140 00 a 5.. 51.2 41.3 75 201x10 140 70%V, 10 24 14 00.1 03.0 3.0 222 00 Del. 8. 73. 2 53.2 5. 0 207 00 42.3 34.8 4.5 101x10 131 00% V, 1 01.0 47.0 2.5 100 70 D01. 8; 2 5s. 3 44.0 3. 0 170 80 45.4 30.5 5.5 230x10 131 70%V,

48.0 30.5 5.5 name 137 00% V, 47.3 38.8 0 210x10 130 00%;, The data in Table V also demonstrate that the properties 21. '1 4H 36.0 6 207x10, 90% V of the spec al cast product are not affected by variations 49 1 4 2 2 1 r 1V6 in section size to any greater extent than are the proper- 0 z f ties of common gray cast irons. 53.0 45.0 1.8 225x10 103 00%, V, no In order further to illustrate the effect of titanium ac- 587 5M L5 2113x100 157 90% 0 cording to the invention in broadening the magnesium 54 3 439 1 8 200 w m a kcompositional range over which vermicular graphite is X i g obtained in the coprescnce of cerium, substantially iden- -0 -0 X 179 233;. tical melts were produced containing about 3.5% carbon, 51,1 L8 21 6X100 179 :0 05 about 2.3% silicon, about 0.3% manganese and the hal- 17 m 1 44 O 9 0 2,) 106 108 i l ance essentially iron. The melts were desulfurized to about f 0.005% sulfur by calcium carbide injection. Titanium was 13 143 Y/5 introduced into one series of melts in an amount of about 19 53,8 4 g 5 17s v, 0.32% to 0.34% while the titanium content of the other eri w l5 r 'n an sium 20 51.1 4M m 163 95% V, 5 es as about 00 A; Va ious a iounts of ma e m 3, and cerium were employed The treated metal in each case 21 47.4 44.0 1.0 170 1007 V. v n H 5&7 43.9 m n no Soc/270V, was noculatedwith about 0.5% by w ei ht of calcium bat bearing ferrosilicon containing about 85 /a silicon and cast into various castings including step bars and l-inch keel V=vermicular. $=splie1oidal. NOTE.-Structures were observed in 2-inch section castings and tensile blocks. The micro-structure obtained in the 2-inch section and hardness properties were determined on l-iiich keel block castings. f the Step bars was examined and h structure for the titanium-bearing series are shown in FIGURES 2A, 2B, 2C and 2D of the drawing while the structures for the essentially titanium'free series are shown in FIGURES The special cast material provided in accordance with 40 l f l 3C of 6 S Z -f keel l d l the invention is characterized by improved thermal cong O1 3 i COO e to ductivity and damping capacity as compared to ductile 1e Ours an t COO to 611N193? iron and data demonstrating the foregoin are set forth in mfamx i b F Propemesh e proport lons the following Table 0 yertnicu ar grap nte in t e structures, t magnesium, cerium and titanium analyses and the tensile properties are shown in the following Table VI.

TABLE VI TABLE III 7 Percent Graph- Tensile properties EL, Thermal Conductivity, Re a vo Alloy ite Sti-uc- Fig. Icr- BIIN Materia c -/c -/scc-/cm-/C- D pi N0. Mg Ce Llli'c* No. U.I.S., Yield, cent Capacity k.s.i. k.s.i.

Iron of this invention About 0.11 0.6 Titanium 0.320.34% Gray iron About 0.12 1.0 Ductile iron About 0.08 0.34 +95%V 2. 1 48.2 40.0 0.5 142 00% V 28 48.0 11.4 0.0 144 Nora-Damping capacities were detennined by applying to SDCCmlCHs 80%V 2C 402 42.2 0.0 143 of the test materials a vibrational stress initially varying between 4,003 50% V 2]) 50, 0 4g, 0 g 5 151 p.s.i. in compression and 1,000 psi. in compression and measuring tn relative rates at which the amplitude of vibration decreased initially '11tnni 0 015% when the imposed vibration was shut oti.

50%V 311 52.5 30.3 8.5 143 30% V 313 57.4 41.0 12.5 148 15% V 30 03 0 43.2 10 140 Balance spheroidal graphite.

The vermicular graphite structure of the special cast product produced in accordance with the invention is not materially affected by variations in section size over the range from about /4 inch up to about 4 inches as illustrated by data set forth in the following Tables IV and V.

The data in Table VI and the structures shown in FIG- URES 2A, 2B, 2C and 2D of the drawing demonstrate clearly that the graphite structure of castings produced in accordance with the invention are caused to appear in the predominantly vermicular form due to the required presence of titanium even though magnesium is increased substantially. On the other hand, in the essential absence of titanium, the graphite structure rapidly is converted to spheroids as magnesium increases only slightly as is shown in FIGURES 3A, 3B and 3C. The high elongation figures obtained in the tensile tests conducted from alloys 30 and 31 as shown in Table VI confirm that these alloys contained a large proportion of graphite in spheriodal form.

The chilling propensity of the special cast material is lower than that of a ductile iron casting and is approximately proportional to the magnesium content, in the absence of other carbide-forming elements. It is accordingly advantageous in applications in which chilling propensity is to be minimized, as, for example, in thin-sectioned castings having wall thicknessess on the order of inch or less, to operate at magnesium contents in the lower end of the range set forth hereinbefore. In such instances, it may also be advantageous to desulfurize the molten iron to a level not exceeding about 0.02% prior to treatment with magnesium, titanium and cerium or other Group IIIB element. It will also be appreciated than when the magnesium content is low, e.g., on the order of about 0.01%, precautions must be taken to insure that at least an effective magnesium content not combined with sulfur as MgS is present in the iron.

In order to demonstrate the improved feeding characteristics which characterize the special cast product of the invention as compared to ductile iron, valve body test castings of complicated configuration were made using the two materials in identical molds designed to provide poor feeding conditions. The special casting of the invention contained 3.73% carbon, 2.21% silicon, 0.18% manganese, 0.010% magnesium, 0.25% titanium, 0.009% cerium and had graphite in the vermicular form. The ductile iron casting was made in the same base iron, contained about 0.05% magnesium and had spheroidal graphite. The castings were sectioned longitudinally and were photographed with the casting in accordance with the invention being depicted in FIGURE 4 and the ductile iron casting being depicted in FIGURE 5. As shown in FIG- URE 4, the casting according to the invention was almost completely sound while the ductile iron casting was characterized by severe shrinkage cavities in the poorly fed areas.

In producing castings in accordance with the invention, melt of gray cast iron composition is established, i.e., a cast iron melt having such graphitizing power that is cast, at least after a graphitizing inoculation, it would be a gray cast iron substantially devoid of massive carbides such as occur in white cast iron. If the sulfur content of the meltexceeds about 0.02%, it is advantageous to reduce the sulfur content of the melt to about 0.02% or lower by means of common desulfurizing techniques, including the use of magnesium. Any of the common furnaces employed in the production of foundry gray cast iron can be employed to produce the special cast material provided in accordance with the invention. The melt is brought to a proper temperature for casting, e.g., a temperature in the range of about 2600 F. to about 2800 F. Additions of cerium or other Group IIIB element, magnesium and titanium are then made to provide residual contents of these elements within the ranges set forth hereinbefore. Titanium in small amounts less than required by the invention is commonly found in cast iron whereas magnesium, cerium and other Group IIIB elements are not. The amount of titanium contained in the molten cast iron should be ascertained and only the amount of titanium required to adjust the bath titanium content to the required final level should be incorporated in the bath. Shortly befort casting, an addition of a graphitizing inoculant such as ferrosilicon, e.g., an alloy containing 85% silicon, about 0.5% calcium, and the balance essentially iron, in an amount sufiicient to introduce about 0.5% silicon, e.g., about 0.3% to about 0.7% silicon, is made to the treated melt and the melt is then cast. In instances wherein thin-section castings are to be made, for example, castings as thin as one-eighth inch or less, the instant inoculation procedure, wherein a few grams of powdered inoculating alloy, e.g., ferrosilicon, is introduced into the feeder gate prior to pouring the casting, advantageously may be employed. Usual heat treating procedures employed in the art to decompose carbides and/or pearlite may also be applied to the castings produced in accordance with the invention.

It is to be understood that the expression predominantly is used herein in conjunction With the description of the vermicular graphite structure produced in accordance with the invention to mean that at least 50% of the graphite particles in the structure are in the vermicular form. The remainder of the graphite particles may be spheroids. The presence of flake graphite in the structure is to be avoided as low strength properties are then encountered. It is further to be understood that references to the periodic table herein are made to the Periodic Chart of the Elements set forth at pages 56 and 57 of Handbook of Chemistry, compiled and edited by Norbert Adolf Lange, Tenth Edition, McGraw-Hill Book Company, 1961.

Applications in which the special cast material provided in accordance with the invention may be employed with advantage include ingot molds, brake drums, particularly brake drums cast integrally with the hub, pumps and valves, cam shafts, gears, gear boxes and gear carriers, engine blocks and heads, piston rings, sealing rings, heattreating pots, paper mill rolls, machine beds and frames, transmission cases, etc.

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 spirit and scope of the invention as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

I claim:

1. A graphitic cast iron consisting essentially of about 2% to about 4% carbon, about 1.5% to about 3.5% silicon, up to about 36% nickel, about 0.005% to about 0.06% magnesium, about 0.001% to about 0.015% of a metal from Group IIIB of the periodic table, about 0.15% to about 0.5% titanium, with said magnesium, Group IIIB metal and titanium contents being effective to control the occurrence of graphite in said cast iron so that at least 50% is in the vermicular form and the balance of said cast iron being essentially iron with other elements and impurities in small amounts which do not materially interfere with the occurrence of graphite in said vermicular form.

2. A graphitic cast iron according to claim 1 wherein the Group III-B metal is cerium.

3. A graphitic cast iron according to claim 2 containing about 3% to about 3.6% carbon, about 2% to about 2.6% silicon, about 0.2% to about 0.7% manganese, about 0.01% to about 0.04% magnesium, about 0.2% to about 0.5 titanium and about 0.001% to about 0.01% cerium.

4. A graphitic cast iron according to claim 1 containing about 0.01% to about 0.04% magnesium and about 0.2% to about 0.5 titanium.

5. A process for producing graphitic cast iron having at least 50% of the graphite in the vermicular form which comprises establishing a bath of gray cast iron containing about 2% to about 4% carbon, and up to about36% nickel, adjusting the titanium content of said bath to about 0.15% to about 0.5 incorporating about 0.005 to about 0.06% magnesium and about 0.001% to about 0.015 of a Group III-B metal into said bath the contents of titanium, magnesium, and the Group IIIB metal being eifective to control the occurrence of graphite in said cast iron so that at least about 50% is in the vermicular form in the finishing casting, and casting metal from the resulting bath in an inoculated condition to provide a casting consisting essentially of about 2% to about 4% carbon, up to about 36% nickel, about 1.5 to about 3.5% silicon, about 0.005 to about 0.06% magnesium, about 0.001% to about 0.015% of Group III-B metal and about 0.15% to about 0.5% titanium, not more than 2,749,238 6/1956 Millis 75-123 XR about 0.025% sulfur, and with the balance except for 2,841,488 7/1958 Morrogh. small amounts of incidental elements and impurities being 2,841,489 7/1958 Morrogh.

essentially iron. 2,841,490 7/1958 Steven.

6. The process according to claim 5 wherein the Group 5 2,867,555 1/1959 Curry 75-123 III-B metal is cerium. 2,873,188 2/1959 Bieniosck 75-130 7. The process according to claim 6 wherein the casting 2,877,111 3/1959 Barnes 75-130 contains about 0.01% to about 0.04% magnesium, about OTHER REFERENCES 0.2% to about 0.5% titanium, about 0.001% to about 0.01% cerium, and not more than ab0ut0.02% sulfur. Physical & Engineering Properties of Cast Iron 10 Angus, 1962, pages 121, 230, 231, 241,287, 307, and 308.

References Cited UNITED STATES PATENTS 2,485,761 10/1949 Millis 75-123 15 2,488,511 11/1949 Morrogh. U.S. Cl. X.R. 2,542,655 2/1951 Gagnebin. 75-130; 148-35 L. DEWAYNE RUTLEDGE, Primary Examiner.

PAUL WEINSTEIN, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,421,886 January 14, 1969 Robert Douglas Schelleng It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, line 31 "iron" should read irons Column 4, lines 66 and 67, "cementities" should read cementites Column 7, in the footnote to TABLE III, line 2 the indistinct number should read 4,000 same footnote, line 3, "th should read the Column 8, line 74, "from should read upon Column 9, line 15, "than" should read that line 39, after "invention, insert a line 44, "melt" should read melt Column 10, lines 43 and 60, after "least", each occurrence, insert about line 70, "finishing" should read finished Signed and sealed this 7th day of April 1970.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

Commissioner of Patents Edward M. Fletcher, Jr.

Attesting ()fficer

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