US3604494A

US3604494A - Process for the production of composite ingots of magnesium containing prealloys

Info

Publication number: US3604494A
Application number: US672163A
Authority: US
Inventors: Heiner Trager; Albert Kaune; Horst Muhlberger; Karl Josef Reifferscheid; Ludwig Grimm; Gerhard Wagner; Heinrich Haslinger
Original assignee: Metallgesellschaft AG
Current assignee: GEA Group AG
Priority date: 1966-10-04
Filing date: 1967-10-02
Publication date: 1971-09-14
Anticipated expiration: 1988-09-14
Also published as: GB1194588A

Abstract

Compact, magnesium containing prealloy ingots are produced by casting a molten magnesium containing prealloy around prefabricated solid pieces of a prealloy having the same or similar composition as that of the molten prealloy. The resulting compact prealloy ingots are used in the production of cast iron with spheroidal graphite.

Description

United States Patent llelner Trager Neu Isenburg;

Inventors Albert Kaune, Frankfurt; Horst Muhlberger, Frankfurt; Karl J osei Reifierscheid, Petterweil; Ludwig Grimm, Hart (All); Gerhard Wagner, Unterneukirchen-I-lart; Heinrich I-Iaslinger, Garching (Alz), all of, Germany 672,163 Oct. 2, 1967 Sept. 14, 1971 Appl. No. Filed Patented Assignees Metallgesellschalt Aktlengesellschalt Frankfurt/Main, Germany; Suddeutsche Kalkstick-stoplwerke A.G.

Trostbert, Germany Priority Germany M 71156 and M 75554 PROCESS FOR THE PRODUCTION OF Oct. 4, 1966, Sept. 15, 1967 COMPOSITE INGOTS OF MAGNESIUM CONTAINING PREALLOYS 8 Claims, 1 Drawing Fig.

u.s. c1

Primary Examiner-R. Spencer Annear Attorney-Stephens, I-Iuettig and O'Connell ABSTRACT: Compact, magnesium containing prealloy ingots are produced by casting a molten magnesium containing prealloy around prefabricated solid pieces of a prealloy having the same or similar composition as that of the molten prealloy. The resulting compact prealloy ingots are used in the production of cast iron with spheroidal graphite.

PROCESS FOR THE PRODUCTION OF COMPOSITE INGOTS OF MAGNESIUM CONTAINING PREALLOYS BACKGROUND OF THE INVENTION Magnesium containing prealloys are used in the preparation of cast iron with spheroidal graphite for the deoxidation or desulfurization of cast iron in which the graphite which separates out upon the cooling of the molten iron is in spheroidal form. (See US. Pat. Nos. 3,328,164; 3,306,707; 3,030,205; 2,762,705 and co-owned and now abandoned US. Pat. application Ser. No. 653,661, filed July 17, 1967, in the names of Horst Muhlberger and Herbert Knahl.)

It is known to use the magnesium containing prealloys in socalled immersing bell jars or plunging cups and to treat cast iron melts therewith in dipping or immersing processes for the purpose of producing cast iron with spheroidal graphite (see US. Pat. No. 3,306,737, column 2, lines 61-69, and US. Pat. No. 3,030,205, column 2, lines 7-52). The magnesium containing prealloy is generally used, in such processes, in the form of solid pieces of the prealloy, which are first charged into a sheet metal container which is used as the bell jar or plunging cup. It is also known to, preferably, use the magnesium containing prealloy in the form of a cylindrical ingot for the production of cast iron with spheroidal graphite. A further known proposal provides for the use, for this purpose, of magnesium or magnesium alloys in the form of semicylindrical ingots or composite cylindrical ingots formed from a plurality of the semicylindrical ingots, formed from a plurality of the semicylindrical ingots, as disclosed in German Gebrauchsmuster Pat. No. 1,71 1,729.

The magnesium containing prealloys which are used for the production of cast iron with spheroidal graphite, however, because of their chemical composition, tend to separate into their component parts in the molten stage and it is often difficult to obtain, after solidification, an ingot having the most homogeneous composition possible with a constant, invariable chemical analysis throughout. In order to avoid the tendency of the molten magnesium prealloys from separating into their component elements during the solidification of the melt, relatively thin sheets of the prealloys were prepared in a conventional manner in order to attain a fast rate of cooling of the prealloy, as disclosed in German Pat. No. 1,142,444.

The casting of prealloys of the type discussed herein in the form, for example, of ingots, calls for the need, in accordance with conventional procedures, for a substantially slower cooling of the melt, and as a rule, results in the separation of the elements from the alloy composition during the solidification of the melt. The use of the magnesium prealloys, in the form of pieces which are prepared by breaking up relatively thin sheets of prealloy of the type disclosed in German Pat. No. 1,142,444, in the production of cast iron with spheroidal graphite, requires a) that large volumes of the necessary amounts of the prealloy additive be used, b) that a large immersing jar or plunging cap be used for a relatively small bulk weight of prealloy and c) that the cast iron melt to be treated with the prealloy provide a comparably large surface area to provide access thereto for the prealloy. The latter requirement results, however, in the often undesirable, rapid'liquefication of the magnesium prealloy during the prealloy immersion process and in undesirably violent reactions, particularly of the magnesium rich prealloy in the treating ladle. According to proposals already known to those in the art, and as disclosed for example in German Pat. No. 1,173,667, the conduct of the casting operation can be influenced by the magnesium prealloy by varying the chemical composition of the prealloy and with the aid of different components of the prealloy, which components, at times, must be used, with respect to each other, in established proportional amounts.

For the production of cast iron with spheroidal graphite there is, from a technical point of view, the need for the use of prealloys which contain as much magnesium as possible, and, at the same time, high operating temperatures. There can be thus obtained in a reliable and controllable casting operation a moreeffective utilization of the prealloy and an improvement in slag separation, so that with comparable sized prealloy charges larger amounts of cast iron can be treated therewith, or with comparable weight charges of the prealloy the cast iron treating process can be conducted with a decrease (a) in the amounts of prealloy needed, (b) in temperature losses, and in the size of the immersing jar or plunging cup needed.

Those in the art, therefore, have sought procedures and techniques whereby shortcomings in the use of 1 magnesium containing prealloys in the preparation of cast iron with spheroidal graphite could be overcome.

SUMMARY OF THE INVENTION The object of the present invention is to provide magnesium containing prealloys in such form as to enable them to be more effectively 'used in the production of cast iron with spheroidal graphite.

Another object of the present invention is to produce cast iron with spheroidal graphite using a novel form of magnesium containing prealloy.

The essence of the present invention lies in the preparation of solid, compact prealloy ingots having a high magnesium content. The ingots are used in such compact ingot form in the treatment of cast iron melts for the preparation of cast iron with spheroidal graphite. The compact ingots are formed by casting molten prealloy around solid, prefabricated pieces of prealloy, wherein the composition of the molten alloy and that of the alloy in piece form are the same or similar.

The FIG. depicts a magnesium containing ingot during the process of its preparation according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION INCLUDING PREFERRED EMBODIMENT For the solution of the problems facing those in the an as indicated above, the present invention provides a process for the production of ingots made from magnesium containing prealloys which are suitable for use as a large unitary mass in the treatment of cast iron melts, and which undergo no separation of the component elements therein when used as such compact ingots.

This process for the production of such compact ingots comprises the steps of a. preparing prefabricated, solid pieces of magnesium containing prealloy,

b. charging the solid pieces of the prealloy into a container or a permanent mold, which preferably has a cylindrical shape, with the densest packing of such pieces in such container as possible,

c. casting a molten magnesium containing prealloy into the hollow spaces existing between the densely packed solid pieces of alloy, and

d. fusing the edges of the solid pieces of prealloy with the molten prealloy so as to thereby embed the individual pieces in an integrally compact prealloy ingot upon the cooling of the composite article.

The molten magnesium containing prealloy which is used to prepare the composite ingot should preferably be one which has a chemical composition which is the same as, or similar to,

,that of the magnesium containing prealloy which is used in piece form.

In conducting the process of the present invention relative to the preparation of the compact ingots, it is expedient to use a casting mold of the type which is cylindrical in shape and open at one end. There can also be used for this purpose, a simple sheet metal sleeve which is placed on a casting support. The container walls. of a simple vessel of this type can be made, for example, of very thin, about 5 mm. sheet iron. In particular instances it my be expedient to quickly cool the walls of the container and thereby remove the heat of the molten alloy in order to prevent the hot melt from breaking through the thin walls of the container.

According to a particularly preferred embodiment of the process of the present invention relative to the preparation of the compact ingots, the process can be conducted with or without the need for additional cooling of the ingot mold by using single or multicompartment ingot molds of commercial quality and made of materials such as cast iron, copper, and other fireproof materials. Using such techniques, containerless prealloy ingots may be prepared which can be subsequently placed in containers which are more suitable for shipping and storage purposes, for example, in drums of metal, paper or plastic, and which protect the ingots against external factors.

In many instances it may also be expedient to insert a sheet metal sleeve in the ingot mold which would serve as an outer mantle for the prealloy ingot to be produced in the mold in order to, above all, prevent the possibility of breakage occurring when preparing ingots of relatively large weight. Finally, it is also advantageous, to cast into the prealloy ingot a hanger device, for example, an iron hook, which will facilitate the insertion and fastening of the prealloy ingot in the dipping bell or cup.

The production of the prealloy ingots according to the present invention is accomplished in the following manner. F Irst, pieces of a prefabricated magnesium containing prealloy are charged into the container or mold provided for this purpose. To this end it is expedient that the manner of charging or packing the pieces of prealloy into the mold be conducted in a particular way using a particular sequence of steps. The packing procedure can be illustrated with reference to the drawing accompanying this specification.

Referring to the drawing therefore the sequence of steps to be followed in charging the ingot mold is a. Three to four pieces of prealloy 1, each of which has about a 30-60 mm. average diameter are charged into the bottom of cylinder 6 which is positioned on casting support 5. Cylinder 6 is a sheet metal sleeve open at the top and bottom thereof. The bottom opening of cylinder 6 is completely sealed from atmosphere by casting support 6. Casting support and the cylinder 6 are made of fire resistant materials which are inert with respect to the prealloy to be charged into cylinder 6.

b. One or more pieces of prealloy 2, in the form of sheets are then placed on top of pieces 1 so as to form a pallet at the base of cylinder 6, the top or potential load bearing surface of which pallet occupies about three-fourths to four-fifths of the cross-sectional area of cylinder 6. The space in cylinder 6 between casting support 5 and the top of piece 2 represents about percent to percent of the total volume of cylinder 6.

c. Small sized pieces 3 of the prealloy, which have an average diameter of about l0-50 mm. are then charged into cylinder 6. They are supported by the pallet formed by piece(s) 1 and 2, and fill the cylinder to he extent that pieces 1, 2 and 3 occupy about percent to 75 percent of the total volume of cylinder 6.

d. The empty spaces remaining in cylinder 6 after all of pieces 1, 2 and 3 are charged therein are filled with molten prealloy 4.

Following this procedure one obtains a complete embedding of the packed pieces of prealloy as a result of the subsequent immersion thereof in the molten prealloy 4 and thus there is obtained a quasimonolithic cast ingot of uniform composition which is capable of being easily transported and stored.

The pieces 2 of the prealloy which are used to form the platform portion of the pallet thus form, in the entire prealloy ingot, a special type of core, which is surrounded by the other pieces of prealloy l and 3, as well as by the molten prealloy 4.

Suitable starting materials which may be used for the prealloys are alloys having the following composition:

20-60 percent magnesium l-l0 percent calcium 20 percent iron 0-12 percent rare earth metals l .5 percent impurities remainder silicon, which can be entirely or partially in the form of nickel and/or copper silicides. 7

It has also been found to be expedient to use, for the one or more core pieces 2 of the ingot, an alloy the composition of which is different from the composition of the molten prealloy. The difference in such compositions relates particularly to the presence in such core" pieces of certain alloy components which are used for the elimination or prevention of the undesirable influence which may be caused during the preparation of cast iron with spheroidal graphite by the presence of elements such as titanium, lead, antimony and bismuth in he cast iron melt. This latter group of elements interferes with the formation of the graphite in spheroidal form. The alloy used for the core pieces, therefore, differs from that used for the molten prealloy and the other pieces of prealloy with respect to the rare earth metal content thereof, that is, the molten prealloy and the other pieces of prealloy contain, in this instance, magnesium as the only element responsible for inducing the formation of spheroidal graphite and does not contain any, or only negligible quantities of, rare earth metals.

An alloy which is suitable for use in the formation of the core pieces of prealloy and which would contain rare earth metals has the following composition:

30.8 percent magnesium 4.4 percent calcium 5.9 percent iron 10.6 percent rare earth metal 1.5 percent impurities remainder silicon.

Using a magnesium containing ingot with he rare earth metal salts only in the interior thereof, in the preparation of cast iron with spheroidal graphite, provides the advantage that the rare earth metals are not used in a desulfurization process together with the magnesium during the initial portion of the treatment of the cast iron melt with the magnesium ingot. Rather, in essence, it is only the magnesium in the prealloy which is devoid of rare earth metals and which prealloy is present in preponderant quantities at this initial stage of the treatment of the cast iron melt that is available and is used for the desulfurization process. The magnesium sulfide slag, moreover, separates from the molten cast iron much easier than the sulfide slag formed with rare earth metals.

There may be, therefore a functional nucleus or core present in the prealloy ingot made according to the process of the present invention, which core has a different composition, with respect to specific reactive materials such as the rare earth metals, than that of the main body of the prealloy ingot which surrounds such core. It can also be expedient, on occasion to place, immediately on top of the load bearing piece(s) 2 in the center of the ingot, and before the packing of the smaller sized pieces 3 on top of piece(s) 2, an additional one or more pieces of prealloy having the same rare earth metal rich composition as piece(s) 2. Finally, there can be used individual pieces 3 of prealloy in the center of the ingot which have an alloy composition, which is different, with respect to the rare earth metal content thereof, than that of the prealloy pieces 1 and 2 and of the rest of the prealloy pieces 3 and that of the molten prealloy 4, that is, the compositions of all of the prealloys used in making the ingot is essentially the same except the core piece.

The amount of molten magnesium prealloy which is to be used as the embedding melt is, expediently, substantially less than the amount of magnesium prealloy which is to be used in piece form. After the fusing of the edge regions of the prealloy pieces the molten prealloy very quickly solidifies, since the readily available quantities of heat in the molten prealloy are quickly absorbed by the pieces of prealloy and, in time, by the walls of the ingot container or mold. Following this procedure, the separation of the component elements of the ingot is avoided and no separation of such elements occurs. If the molten and piece prealloy materials have the same chemical composition, then there is thus produced an alloy ingot which, in analytical and metallurgical respects, is completely homogeneous in composition.

The cast ingot made from magnesium containing prealloys according to the present invention is particularly suitable for use in the dipping process treatment of cast iron which is used for the production of cast iron with spheroidal graphite.

The process of'the present invention provides a number of advantages. For example, magnesium containing prealloys can be produced in the form of ingots of any desired technically useful size and with unusually good homogeneity of composition. A further advantage is to be noted in that ingot shaped and homogeneous prealloys with an unusually high magnesium content can be produced, which, inspite of this unusually high magnesium content and relatively low active surface area, assures a calm and safe sequence of reaction and handling operations with comparatively greater utilization of the magnesium content of such ingots in contrast to the use of a prealloy of the same composition in piece form in the treatment of cast iron.

in addition, a compact prealloy ingot can be produced ac cording to the present invention with a functional core for an economically advantageous treatment of molten cast iron. The active elements of such functional cores do not take part, to any practical extent, in the initially occurring desulfurization reaction phase of the treatment of the cast iron melt and are entirely available for use in the subsequent spheroidal graphite formation phase of the production of cast iron with spheroidal graphite.

A more general advantage of the process of the present invention is also to be noted in that the magnesium containing compact prealloy ingots made according toe present invention allow for the use of comparatively smaller dipping jars or cups. These smaller dipping jars are more stable and easy to handle and the use of these smaller dipping jars also provides lower amounts of heat loss during the dipping process.

The volume of the prealloy ingots produced according to the present invention is not only substantially less than the corresponding amount of prealloy in piece form, but in addition, the prealloy ingot can provide a higher magnesium content since the inherent and expected greater reactability of the prealloy, due to its high magnesium content, is compensated for by the reduction in the surface area of the ingot and thus a less violet running of the reaction is assured. By obtaining, in this way, an almost invariable utilization of the entire magnesium content of the ingot, there is also obtained a high utilization of all the components of the prealloy.

A greater advantage of the process of the present invention relative to the treatment of cast iron with the prealloy ingots can be also seen in that the use of the prealloy ingots prepared according to the present invention for this purpose allows for the use of treatment temperatures which are substantially higher than those which may be employed when using prealloys of the same composition in piece form, which latter process, again, gives rise to problems involved in the various relationships between prealloy volume and prealloy surface area.

The processes of the present invention are further explained in the following examples.

The following examples, however, are merely illustrative of the present invention and are not intended as a limitation upon the scope thereof.

EXAMPLE 1 A magnesium containing prealloy was produced in a conventional manner in a graphite crucible in an induction fur trace and was then cast in an open hearth into sheets which were 40-55 mm. thick. The prealloy had the following composition: llltlllclll-l Percent gig 50. 9 a 4. 8 SE* 0. 8 Fc "4. 6 Si Remainder After being cooled the prealloy sheets were broken up into pieces ranging size from that of walnutsto that of the palm of a hand. into a container made of sheet iron and open at the top, 2.7 kg. of the broken up pieces of the prealloy were densely packed. The container had a diameter of 250 mm. and its walls were 2.5 mm. thick. The broken pieces of alloy occupied about 35 percent of the volume in the container.

The remaining empty space in the container between the broken pieces of prealloy was filled up by pouring in molten magnesium prealloy which was slightly overheated. The molten magnesium prealloy was prepared by remelting a portion of the magnesium prealloy first described above in this example and it had, therefore, the same chemical composition as EXAMPLE 2 Cast iron with spheroidal graphite was produced in a foundry using the dipping process in two different experiments. In one of the experiments there 5 used a commercially available magnesium prealloy in piece form which had a magnesium content of 30.4 percent, and in the other experiment there was used the prealloy ingot produced in example 1 which had a magnesium content of 50.9 percent. A magnesium prealloy in piece form and having a high magnesium content comparable to that of the prealloy ingot made in example i does not lend itself to use in the intended process because of the danger of explosions.

Table I below gives a description of the compositions of the two prealloys used and table II gives data relative to the use of the two prealloys in the two experiments.

Prealloy used Commercial prealloy Example I prealloy Weight ofprealloy, kg. 6.2 Magnesium content, 30.4 50.9 Cast iron charge. kg. 1000 1000 Cast iron charge analysis, 71

5 (Milli ll.0l7

Fe remainder remainder Dipping temperature 1485 C. l500 C. Dipping time 50 seconds 55 seconds FeSi-QO-innoculation 5 kg. Si 5 kg. Si Analysis of cast iron at beginning of casting & after dipping process,

Table ll-Continued The FeSi90 alloy for innoculation, ofa grain sizes from 2-6 mm. had the composition 90.5

l A], balance Fe. It was added to the melt after the treatment with magnesium when typping the melt in the melt in the pouring ladle.

Based on the above noted analytical results it was determined that the yield", i.e., amount actually used, of magnesium and prealloy in each of the two experiments was as follows:

Experiment Commercial prealloy Treatment with Mg yield, 2 Prealloy yield, )2

Example I prealloy EXAMPLE 3 All the prealloy used in this Example, in piece or molten form, had the following composition:

31.4 percent Mg. 4.5 percent Ca 7.1 percent Fe l .5 percent impurities remainder silicon A cylindrical sleeve 180 mm. high with a diameter of 175 mm. and made of sheet iron about 2 mm. thick was stood on one of its ends on a cast iron plate. At the bottom of the sleeve a pallet like form was erected by first setting three pieces of prealloy at the base of the sleeve, resting on the cast iron plate. These three pieces of prealloy were 30-50 mm. in particle size. These three pieces of prealloy functioned as legs for the pallet and correspond to pieces 1 shown in the drawing. A platform forming piece of prealloy was then placed on top of the three previously positioned pieces of prealloy. The platform piece corresponded to piece 2 shown in the drawing. The platform piece occupied about three-fourths of the cross-sectional area of the inside of the cylinder and it was about 35 mm. thick. On top of the platform piece there was then poured pieces of prealloy which were to 50 mm. in particle size. The total weight of prealloy used in piece form in the cylinder was now 4.5 kg.

Molten prealloy was then poured into the cylinder, which had been charged with prealloy in piece form as described above, so as to fill the hollow areas between the pieces and to cover the top layer of pieces. After the molten prealloy had solidified a quasi-monolithic ingot had been thus prepared from the molten prealloy and piece form prealloy which had a total weight of 8 kgflOO g. The weight of the block was very accurately determined using a scale as disclosed above. The pieces of prealloy were bound into the ingot by the solidified molten prealloy. The molten prealloy solidified very quickly due to the cooling effect or heat absorbing action of the prealloy in piece form, so that the sheet metal cylinder did not melt away. The ingot was lifted off the cast iron plate and the base of the ingot was inspected. The inspection showed that the three pieces of prealloy that were first placed in the base of the cylinder as legs for the pallet were still plainly discernible. They were inclosed by the solidified molten prealloy, with only their surfaces, which were at the extreme base of the cylinder, being essentially free of any of the subsequently charged and solidified molten prealloy. The ingot had excellent strength and was capable of being readily transported.

EXAMPLE 4 A prealloy ingot which weighed 8 kg. was produced by the procedure described in example 3. The procedure of example 3, however, was deviated from in that the prealloy piece which was used as the platform forming piece of prealloy and which took up about three-fourths of the cross-sectional area of the cylinder weighed about 800 grams and was prepared from a prealloy having the following composition:

30.8 percent Mg.

4.4 percent Ca 5.9 percent Fe 10.6 percent SE* 1.5 percent impurities remainder Si *SE rare earth metal This prealloy composition differs from the prealloy composition used in example 3, in essence, only by virtue of a high rare earth metal content.

By using, as the molten prealloy for embedding the piece form prealloy in the resulting ingot, a prealloy having the composition as that used in example 3, the finished ingot has the following average composition:

30-32 percent Mg 4.2-4.6 percent Ca 8 percent Fe about 1 percent SE 1.5 percent impurities remainder silicon This is an alloy composition which is generally used in the treatment of cast iron in the dipping process.

By using magnesium containing ingots made according to the present invention in the treatment of cast iron, one is assured that, during the utilization of the ingot in the cast iron, melt being treated therewith, at first a prealloy devoid of rare earth metals reacts with the molten cast iron and then only later does prealloy containing such rare earth metal become available for use in the cast iron treating process. This leads to the result that the desulfurization phase of he treatment of the molten cast iron which takes place first, would only entail losses of the Mg content of the prealloy and would not entail any significant losses of the rare earth metal content of the prealloy.

A prealloy ingot made according to the present invention and as described in example 4 was used in the treatment of molten cast iron in the clipping process. The charge of molten cast iron weighed 1,000 kg. and had a sulfur content of 0.06 percent and a temperature of 1480 C. After the treatment, which lasted for about 1 minute, the molten cast iron was almost free of sulfur, i.e., it had a sulfur content of 0.006 percent, and the Mg content of the molten cast iron amounted to 0.068 percent. An adequate alloy content is thus assured to um containing prealloy comprising a. densely packing a substantial portion of the volume of a cope with some of the disturbing influences that the cast iron will encounter during itsperiod of use.

All percentages used in this application are in terms of perl. A process for the production of an ingot from a magnesimold with a plurality of solid pieces of a magnesium con taining prealloy,

b. filling the remaining void spaces in said mold with a molten magnesium containing prealloy so as to fuse the edges of said pieces, said pieces of prealloy and said molten prealloy being of essentially the same chemical composition, and

c. cooling sad molten prealloy and said solid pieces of prealloy to form a composite ingot wherein said pieces of prealloy are embedded in said molten prealloy.

2. A process in claim 1 in which said mold has an internal volume of about 0.05 to 3 cubic feet.

3. A process as in claim 2 in which said solid pieces occupy about 25 to 75 percent of the space in said mold.

4. A process as in claim 3 in which a) is accomplished by i. forming, in the bottom of said mold, with'a relatively small number of said pieces ofabout 30 to 60 mm. average diameter in size, a pallet having a load bearing surface equal to about three-fourths to four-fifths of the crosssectional area of said mold, and

loading the remainder of said pieces on said load-bearing surface, each of the remainder of said pieces having an average diameter of about 10 to 50 mm.

5. A process as in claim 4 in which all the prealloy used is of the type used in the treatment of cast iron melts for the production of cast iron with spheroidal graphite.

6. A process as in claim 5 in which all the prealloy has the composition 2060 percent magnesium 1-1 0 percent calcium 20 percent iron 0-12 percent rare earth metals 1.5 percent impurities remainder silicon containing materials selected from the group consisting of silicon and nickel and copper silicides.

7. A process as in claim 5 in which said ingot is formed with a core having a composition different from that of the remainder of said ingot by using for said core prealloy in piece form having the composition desired forsaid core.

8. A process as in claim 7 in which said core is formed from prealloy containing magnesium and rare earth metals.

Claims

2. A process in claim 1 in which said mold has an internal volume of about 0.05 to 3 cubic feet.
3. A process as in claim 2 in which said solid pieces occupy about 25 to 75 percent of the space in said mold.
4. A process as in claim 3 in which a) is accomplished by i. forming, in the bottom of said mold, with a relatively small number of said pieces of about 30 to 60 mm. average diameter in size, a pallet having a load bearing surface equal to about three-fourths to four-fifths of the cross-sectional area of said mold, and loading the remainder of said pieces on said load-bearing surface, each of the remainder of said pieces having an average diameter of about 10 to 50 mm.
5. A process as in claim 4 in which all the prealloy used is of the type used in the treatment of cast iron melts for the production of cast iron with spheroidal graphite.
6. A process as in claim 5 in which all the prealloy has the composition 20-60 percent magnesium 1-10 percent calcium <20 percent iron 0-12 percent rare earth metals <1.5 percent impurities remainder silicon containing materials selected from the group consisting of silicon and nickel and copper silicides.
7. A process as in claim 5 in which said ingot is formed with a core having a composition different from that of the remainder of said ingot by using for said core prealloy in piece form having the composition desired for said core.
8. A process as in claim 7 in which said core is formed from prealloy containing magnesium and rare earth metals.