WO2004042090A1

WO2004042090A1 - Inmould process for the spheroidization and inoculation treatment of cast sg iron

Info

Publication number: WO2004042090A1
Application number: PCT/US2003/034740
Authority: WO
Inventors: Leonard S. Aubrey; Donald B. Craig
Original assignee: Porvair Plc
Priority date: 2002-10-30
Filing date: 2003-10-30
Publication date: 2004-05-21
Also published as: AU2003290560A1

Abstract

A system for treating molten iron comprising a sprue (6) for collecting molten iron. A spheroidizing chamber (8) receives molten iron from the sprue. A first filter (3) is received in the spheroidizing chamber. A spheroidizing pellet (2) is attached to the first filter. An inoculating chamber (9) receives molten metal from the spheroidizing chamber. A second filter (5) is received by the inoculating chamber. An inoculating pellet (4) is attached to the second filter.

Description

TITLE

INMOULD PROCESS FOR THE SPHEROIDIZATION AND INOCULATION TREATMENT OF CAST SG IRON

TECHNICAL FIELD

[0001] The present invention is related to an improved method for treating and inoculating iron. More particularly, the present invention relates to an improved method for treating iron with a spheroidizing agent prior to inoculation.

BACKGROUND OF THE INVENTION [0002] Cast iron is an extremely versatile engineered material comprising iron- carbon-silicon alloys that have been used in many commercial applications including the manufacture of mechanical parts. The versatility of cast iron has led to the utilization of this material in many structural applications where the homogeneity and consistency of the iron will have a critical impact on the components performance. The casting of clean homogenous iron is an essential step in the production of high quality engineered castings. Due to the critical applications of these cast components, it is imperative that iron be consistently cast with uniform morphology, with minimum included impurities and with properties that are reproducible. [0003] Cast iron has an unusual metallurgical structure. Most metals form a metallic crystalline structure during solidification. Cast iron, however, has a far more complex morphology during solidification. The crystalline phases that form during solidification of cast iron are dependent on the rate of solidification. Most engineered castings desire the formation of graphite within the iron matrix during solidification. If the cast iron solidifies too rapidly primary iron carbides can crystallize within the casting. Primary iron carbide is a hard brittle phase that makes the iron very difficult to machine and changes the physical and mechanical properties of the primary cast iron. Primary iron carbides are commonly referred to as "chill". Carbon contained as iron carbide is generally considered to be detrimental in most iron castings. , Carbon present as graphite improves the physical and mechanical properties of cast iron. [0004] Carbon can crystallize as either iron carbide or graphite during solidification.

The formation of either phase is driven by the rate of solidification and the degree of nucleation contained within the liquid iron. The rate of solidification is constrained by the geometry of the casting, the rate of heat extraction of the mold material and the amount of superheat the iron contained when the metal entered the mold. The degree of nucleation is constrained by the metallurgical history of the molten iron. Carbon present as graphite is an advantageous form and persuading carbon to crystallize as graphite is an ongoing goal of standard foundry operations.

[0005] Graphite can be present in several morphological forms including spherical, as is the case with ductile iron, and flake-like, which is the case with gray iron. The present invention is most preferably directed to the formation of ductile iron and more specifically with the formation of spheroidal graphite for casting ductile iron. [0006] To obtain a spheroidal graphite structure requires that the base iron, which normally would have a flake graphite structure, be treated with a spheroidizing agent prior to the inoculation step. Typically pre-treatment to obtain the spheroidal graphite structure requires the addition of a strong oxide and sulfide former, such as magnesium, typically 0.02 to 0.06 wt.%, to a low sulfur base iron. Treatment tends to fade with time and it is therefore desirable to treat molten metal as late in the pour as possible. Previously, this has been difficult to achieve. Magnesium can be introduced as pure magnesium metal, a specially prepared magnesium ferrosilicon alloy (FeSiMg) or a nickel-magnesium alloy. The most common method is to utilize a FeSiMg alloying addition followed by a ferrosilicon final inoculant addition. The most common methods or processes used to introduce magnesium, or magnesium alloys, are the sandwich process, the inmold process and pure magnesium treatment. [0007] The sandwich process involves the addition of a FeSiMg alloy typically containing between about 3 to about 10%, by weight, Mg and about 0.5 to about 2%, by weight, rare earths. The FeSiMg alloy is introduced at the bottom of a specially designed treatment ladle. The molten base iron is then tapped into from the holding furnace. Typically magnesium recovery is low. While the metal is being transferred into the final inoculation ladle, or being poured into the mold, the magnesium level drops or fades with time. The decrease in magnesium results in deterioration of the spheroidal graphite structure. Another disadvantage is that during holding of the treated iron the amount of magnesia-rich dross inclusion material increases. The addition of the FeSiMg alloy results in a significant elemental silicon pickup in the iron. The silicon pickup can limit the amount of returns or in-house scrap that can be put back into the process.

[0008] The inmold process involves placement of a special FeSiMg alloy into a specially designed chamber in the runner system of the mold. By introducing FeSiMg alloy into the runner system the problem of magnesium fade is minimized. This method tends to generate a lot of dross inclusion within the mold cavity and has the further problem of silicon pick-up. A significant problem with the in-mold process is handling the FeSiMg alloy. FeSiMg alloy is typically a loose granular material that has to be added into the specially designed chamber. The loose granular material needs to weighed or controlled volumetrically. Loose granular material also poses a special problem in molding systems that utilize a vertical or complex parting system. In addition, the loose granular FeSiMg alloy not consumed in the treatment process can cause a contamination problem in the molding sand.

[0009] The pure magnesium treatment uses magnesium metal that is placed within a special chamber in a pressurized converter vessel. While the problem of silicon pickup is solved, there is an issue of magnesium fade. Metal temperature loss is also a problem since the treated iron requires transfer into a final pouring ladle.

[0010] In addition to spheroidization, standard foundry metallurgical practice includes inoculation. During inoculation the nucleation and growth of graphite is encouraged at the expense of iron carbide formation. Preferential nucleation greatly enhances the mechanical and physical properties of the finished casting. Inoculation is typically done by addition of an inoculating agent to either the pouring ladle, the metal stream or within the mold. The inoculating agent is typically added to the pouring ladle by pouring the granulated inoculating agent into the ladle when the ladle is filled with liquid iron, whereas the inoculant is added to the metal stream by injecting or spraying a finely divided powder of the inoculating agent in the molten metal stream as the molten metal enters the mold. It is typically desirable to add the inoculating agent to the molten metal as late as possible to minimize fading. Insufficient or improper inoculation is constantly at the forefront of quality based losses in a foundry operation. [0011] The inoculation treatment is therefore very important. It is in fact well known that inoculation, whatever the inoculants used, has on the liquid cast iron an effectiveness which reduces with time and which, generally, has already reduced by 50% after a few minutes. To obtain maximum effectiveness one skilled in the art generally practices progressive inoculation. Progressive inoculation involves applying several additions of inoculants at different stages of the development of the cast iron. The final addition may be made "in mould" as the moulds are fed. Alternatively, the final addition is made in the feed conduits of the moulds by placing in the path of the liquid cast iron inserts constituted by an inoculant material. These inserts are generally used associated with a filter; in this case they generally have a perfectly defined shape in order to be able to be fixed in the filter, most often in an adapted cavity. SUMMARY OF THE INVENTION

[0012] It is an object of the present invention to provide an improved method for treating and inoculating molten metal.

[0013] It is another object of the present invention to provide a process wherein molten metal can be treated, preferably with a spheroidizing agent, and inoculated in line by incorporation of the spheroidizing agent and inoculating agent into filter elements.

[0014] A particular feature of the present invention is the ability to incorporate filtration with treatment. Even more particularly the present invention allows filtration and treatment to be accomplished with a single filter element.

[0015] These and other advantages, as will be realized, are provided in a process for the production of ductile iron. The process comprising the steps of: passing molten iron through a spheroidizing filter assembly to form a treated molten metal. The spheroidizing filter assembly comprises a filter and a spheroidizing pellet associated therewith. The treated molten metal is then passed through an inoculating filter assembly to form an inoculated treated molten metal. The inoculating filter assembly comprises a filter and an inoculating pellet associated therewith. The inoculated treated molten metal is then cooled. [0016] Yet another advantage is provided in a system for treating molten iron comprising a first filter, and spheroidizing pellet associated therewith, and a second filter with an inoculating filter associated therewith.

[0017] Yet another embodiment of the present invention is provided in a filter element comprising a open cell ceramic filter and a pellet comprising a spheroidizing element. [0018] Yet another embodiment is provided in a system for treating molten iron comprising a sprue for collecting molten iron. A spheroidizing reservoir receives molten iron from the sprue. A first filter is received in the spheroidizing reservoir. A spheroidizing pellet is attached to the first filter. An inoculating reservoir receives molten metal from the spheroidizing reservoir. A second filter is received by the inoculating reservoir. An inoculating pellet is attached to the second filter.

BRIEF DESCRIPTION OF DRAWINGS [0019] Fig. 1 is a schematic representation of a runner system incorporating filter elements for treatment and inoculation. [0020] Fig. 2. is a top schematic representation of the embodiment of Fig. 1. DETAILED DESCRIPTION

[0021] The present invention relates to an improved method for the formation of ductile iron comprising the use of a two-stage reaction/filtration system. The first stage preferably incorporates a spheroidization agent such as magnesium, magnesium containing alloys or rare earth suicides, into a flowing iron stream to form spheroidal graphite. The spheroidizing agent incorporation is concurrent with the filtration of the flowing iron stream. The second stage inoculates and filters the molten iron stream to prohibit formation of iron carbide and to encourage formation of the graphite phase. [0022] The invention will be described with reference to the figures which form a part of the specification. Fig. 1 is a side cross-sectional representation of an embodiment of the present invention. Fig. 2 is a representation of the embodiment of Fig. 1 as viewed from the top.

[0023] Fig. 1 shows an inventive two-step process where two sequentially placed tablet-filter assemblies are located in a runner system, 1. The first filter-tablet assembly comprises a spheroidizing tablet, 2, containing a spheriodizing agent, in integral relationship with a first filter, 3. The spheriodizing tablet, 2, and first filter, 3, represent a spheroidizing filter assembly. The spheroidizing filter assembly, comprising the spheroidizing tablet, 2, and first filter, 3, are preferably contained in a spheroidizing chamber, 8. [0024] The second filter-tablet assembly contains an inoculant tablet, 4, containing an inoculant, in integral relationship with a second filter, 5. The inoculant and second filter represent an inoculant filter assembly. The inoculating pellet, 4, and second filter, 5, are preferably contained in an inoculating chamber, 9. [0025] Molten iron is introduced into a sprue, 6, which is sized and proportioned to control the rate of flow of the molten iron through the runner, 1. The molten metal enters a sprue well, 10, with overflow from the reservoir being directed by a channel, 7, to the spheroidizing chamber, 8. As molten metal contacts the spheroidizing tablet, 2, the spheroidizing elements are incorporated into the molten metal by dissolution. The spheroidizing treated molten iron is then filtered as it passes through the first filter, 3. A second channel, 7, directs the treated molten metal to the inoculation chamber, 9. As the treated molten metal contacts the inoculation pellet, 4, inoculating agents are incorporated into the treated molten iron by dissolution to form treated inoculated molten iron. The treated inoculated molten iron is then filtered as it transits through the second filter, 5. A third channel, 7, transports the treated inoculated molten iron into the casting cavity of the mold.

[0026] The spheriodizing tablet is preferably a solid material, preferably monolithic solid material, comprising magnesium, magnesium containing alloy or a rare earth suicide. It is more preferred that the spheriodizing tablet comprise either a FeSiMg alloy, magnesium metal, magnesium suicide, MgCeSi or rare earth suicide. Even more preferably the spheriodizing tablet comprises FeSiMg, magnesium or rare earth suicide.

Magnesium metal is the preferred spheriodizing agent with rare earth suicide being equally preferred. [0027] Rare earth suicides may comprise the rare earth, particularly lanthanides, in the naturally occurring ratios. Alternatively, the rare earth suicides may have certain rare earths enriched, or depleted, relative to the naturally occurring ratios.

[0028] The spheroidization tablet can be either a compressed bonded particle compact or a solid cast insert. [0029] The advantages of the inventive process includes minimum silicon pickup, consistent magnesium recovery, avoidance of dross buildup in the pouring ladle, minimal magnesium fume, and avoidance of loose granular treatment material into the recycled molding sand where it is a contaminant.

[0030] Although the embodiment in Figs. 1 and 2 show a horizontally parted mold, the proposed method could just as easily be used in a vertically parted mold. In addition the filters could be oriented horizontally with the metal flowing either downwards or upwards through the filter.

[0031] In one embodiment one filter assembly could be oriented vertically and the other filter assembly oriented horizontally with the metal flow direction either upwards or downwards.

[0032] One skilled in the art who practices inoculation at the different stages of the development of the cast iron uses products which are all the finer the later the inoculant is added in the process. The logic is that upstream the products have all the time necessary to dissolve and that when they reach the inlet of the molds they have only a few seconds left before solidification.

[0033] Controlling the dissolution rate to allow for a wide range of flow rates, or approach velocities, now allows for predictable inoculation without regard for approach velocities within a working range of 1-60 cm/sec measured at 30.25 cm² flow cross- section. [0034] The effective inoculation component of one embodiment of the present invention comprises a ferrosilicon carrier and at least one active element. The ferrosilicon carrier is a non-active element which dissolves in molten iron without forming seed nuclei. The active element is an element, or combination of elements, which dissolve in molten iron and react with elements in the molten iron to form seed nuclei upon which graphite preferentially crystallizes.

[0035] The effective component of one embodiment of the inoculant pellet preferably comprises 40-99.5%, by weight, carrier and 0.5-60%, by weight active element. Particularly preferred carriers are prepared from ferrosilicon comprising non- reactive impurities. Ferrosilicon is available commercially from a variety of sources. Ferrosilicon is typically provided as 75% ferrosilicon which indicates, by nomenclature in the art, that the material comprises approximately 75%, by weight, silicon and 25%, by weight, iron. Ferrosilicon is widely available as 50% ferrosilicon which indicates that the material comprises approximately 50%, by weight, silicon and 50%, by weight, iron. For the purposes of the present invention the binder includes all non-inoculating elements. It is most preferred that the carrier comprise at least about 30%, by weight ferrosilicon. It is preferable to add a binder to the effective components prior to forming a pellet. The binder, such as sodium silicate, is well known in the art to assist in pellitization of a powder. [0036] The active inoculant elements of the present invention include at least one inoculating agent chosen from the group consisting of cerium, strontium, zirconium, calcium, manganese, barium, bismuth, magnesium, titanium, aluminum, silicon and lanthanum and alloys, particularly iron alloys, of these inoculating agents. Particularly preferred inoculating agents include at least one element chosen from the group consisting of strontium, aluminum, barium, zirconium and calcium. The inoculant preferably comprises about 0.5-60%, by weight inoculating agent. More preferably, the inoculant comprises about 0.5-40%, by weight, active inoculating agent. Most preferably, the inoculant comprises about 1-20%, by weight, active inoculating agent. Effective inoculation is described in U.S. Pat. Appl. Nos. 10/043,644 filed 1/10/2002 and 60/398,268 filed 7/24/2002 which are included herein by reference thereto.

[0037] In one embodiment the inoculant tablet contains concentrated amounts of sulfide and oxide forming elements. The tablet preferably contains enough inoculating elements to effectively inoculate molten iron as the metal flows through the gating system during mold filling. The concentrated levels of inoculating elements gives an improved microstructure and chill reduction and dissolves rapidly without the use of auxiliary binders or energy consuming sintering.

[0038] The silicon levels in one embodiment of the tablet are preferably maintained at above 15% so as to provide exotheπnicity or a positive heat of solution and to assist other slower dissolving additions so as to improve the dissolution rate of the inoculant.

Various levels of oxy-sulfide forming elements, may be added to the base alloy blend to enhance properties for specific applications.

[0039] In one embodiment the inoculant tablet has a specific gravity in the range of about 2.2 to about 2.5 grams/cc. The tablet preferably has a high solubility in cast iron with temperatures as low as 2250°F. The blend of ingredients used for tablet fabrication, but without the iron powder, can also be used in the granular form and have provided similar property improvement.

[0040] It is most preferred that the pellets be prepared from powders with a particle size of less than 1 mm and having a particular internal particle size distribution defined in the following way: passing to 1 mm: 100 %; fraction between 50μ and 250μ: 30% to

60%, and preferentially 40% to 50%; fraction below 50μ: less than 25% and preferentially less than 20%.

[0041] A powder of this type agglomerates easily which makes it possible to operate with lower proportions of binding agent. Thus with sodium silicate, which is a well- known binding agent, doses of 0.3cm for lOOg of powder to 3cm for lOOg of powder are sufficient according to the pressures employed which may vary from 50 to 500MPa; since the mechanical performance of the pellet is easily acquired, the pressure and binding agent percentage parameters may be used to control the dissolution speed of the pellet and not its mechanical performance. [0042] The preparation of powder with this particle size distribution is preferably prepared by a dosing of size fractions prepared in isolation.

[0043] The filter associated with the inoculating pellet, or spheroidizing pellet, is preferably a ceramic filter comprising continuous or semi-continuous voids or passageways which the metal passes and in which any included particles larger than 10 microns and preferentially 3 microns become lodged.

[0044] The dissolution rate of the inoculant is defined as the amount of inoculating agent introduced as a function of time. The analysis of certain inoculants is difficult therefore the dissolution rate is based on the analysis of a determinant element, either an inoculant or marker. The weight ratio of the determinant element to other inoculating agents is assumed to be the same in the cast iron as the weight ratio in the original pellet. For the purposes of the present invention zirconium is used as an inoculating determinate element. Therefore, the total inoculant in the cast iron is determined as the amount of zirconium plus other inoculants in the iron. For example, if an inoculant has 1 part zirconium, by weight, to 1 part calcium, by weight, and the amount of zirconium in the iron is 20 ppm then the amount of calcium will also be 20 ppm for a total inoculant of 40 ppm. The grams of zirconium plus calcium, which is present in an amount of 40 ppm, divided by the pour time is the inoculant dissolution rate. [0045] An inoculant dissolution rate of at least approximately 0.02 g/sec. is necessary to have sufficient inoculation for approach velocities of 1-60 cm/sec. Below 0.02 g/sec. an insufficient inoculation rate is observed, particularly early in the pour, to insure minimum or no chill and to substantially eliminate the formation of iron carbide. Alternatively, the approach velocity must be lowered to a level which is impractical with an inoculant dissolution rate below approximately 0.02 g/sec. More preferably, the inoculant dissolution rate is no less than 0.03 g/sec. An inoculant dissolution rate of no more than approximately 0.32 g/sec. is required to insure that the rate of dissolution is sufficiently slow to insure that pellet remains throughout the entire pour at approach velocities of 1-60 cm/sec. Above approximately 0.32 g/sec. the pellet may dissolve prematurely thereby failing to inoculate the late portions of the pour. Alternatively, the approach velocity must be increased to a level which is impractical. More preferably, the inoculant dissolution rate is no more than approximately 0.25 g/sec. Most preferably, the inoculant dissolution rate is no more than approximately 0.20 g/sec. [0046] The present invention illustrates that a ferrosilicon based inoculant can be prepared which, when prepared to a narrow range of dissolution rate, can be utilized as an inoculant pellet and the resulting cast iron has a low level of chill. Furthermore, the proper dissolution rate allows for superior inoculation with minimal inoculating agent. This substantially decreases the cost of inoculation and increases the predictability. Yet another advantage offered by the teachings herein is the ability to determine the proper amount of inoculant pellet to achieve a proper level of inoculation. [0047] A dissolution rate of approximately 0.02 to approximately 0.32 g/sec. allows for the same pellet to by used at approach velocities of 1-60 cm/sec. without fade or under inoculation in any portion of the pour. More preferably, the dissolution rate is approximately 0.02 to approximately 0.32 g/sec. at approach velocities of approximately 1 to approximately 40 cm/sec. Even more preferably, approach velocities of 10 to 30 cm/sec. can be utilized and most preferably an approach velocity of 15-25 c /sec. can be utilized with the preferred pellet dissolution rate of 0.05 to 0.25 g/sec. A particularly preferred pellet dissolution rate is 0.05 to 0.15 g/sec.

[0048] In a particularly preferred embodiment the dissolution rate of the pellet is determined at an approach velocity of 15 cm/sec. measured at a cross-sectional area of 30.25 cm². At an approach velocity of 15cm/sec. the pellet preferably has a dissolution rate of at least approximately 0.05 g/sec. to no more than approximately 0.3 g/sec. More preferably, measured at an approach velocity of 15 cm/sec. the pellet has a preferred dissolution rate of at least approximately 0.05 g/sec. to no more than approximately 0.20 g/sec.

[0049] The filtration rate of the filter can be adjusted between 0.01 lcg/(s cm²) and 0.5 kg/(s'cm²). More preferably between 0.04 kg/(s'cm²) and 0.24 kg/(s'cm²) according to the application. [0050] Due to the inoculation rate generally required which is between 0.05% and 0.15% and due to the filtration capacity of the filter of the invention, which is between 1 and 1.5 kg of liquid iron per cm , the filter inoculant package is preferably sized with a ratio (pellet mass in g/filter surface in cm²) between 0.75 and 1.5. For instance, a filter inoculant package made of a 25 g pellet and a 30 cm² filter would be a convenient sizing. [0051] Approach velocity is a practical measure, well lαiown. in the industry, to indicate the volume of metal flowing to, and through, a filter. As would be apparent to one of ordinary skill in the art the approach velocity is determined at a fixed cross- sectional flow area. For the purposes of the present invention all approach velocities are calculated at a cross-sectional area of 30.25 cm² unless otherwise stated. It would be readily apparent to one of ordinary skill in the art that different cross-sectional areas would generate different approach velocities, however, the approach velocity could be easily compared to those cited herein by simple conversion as known in the art. [0052] The dissolution rate of the pellet is controlled by composition and packing density. As the packing density increases the dissolution rate decreases. For the purposes of the present invention a ferrosilicon binder compressed to achieve a density of approximately 2.3 g/cc to approximately 2.6 g/cc is suitable to obtain the dissolution range required for the invention. Such a result can be obtained by adjusting the density of a pellet which can be obtained between 60% and 80% of the true density of the inoculant alloy the pellet is made of, depending on the pressure used for agglomerating which can vary from 50 to 500 MPa. Filter inoculant packages according to the invention, may be sized for the treatment of molten iron flow rates between 1 and 10 kg/s.

[0053] Ceramic filter elements are porous members comprising continuous or semi- continuous voids or passageways through which the metal passes and in which any included particles become lodged. The porous ceramic filter elements are preferably prepared by the manner described in U.S. Patent No. 4,056,586, which is incorporated herein by reference. Further elaboration on methods for manufacturing ceramic filter elements is provided in U.S. Patent Nos. 5,673,902 and 5,456,833, both of which are included herein by reference.

[0054] The form of the inoculant agent in one embodiment can be either a very dense pellet or a mixture of the same elements in loose or granular powder form. The range of chemistries available using this approach are much broader and allows the incorporation of concentrated levels of the critical elements needed for the inoculation process compared to traditional inoculating alloys which are produced by a smelting and casting process.

[0055] In one embodiment of inoculant tablets, the product is produced on a high pressure press and which utilizes iron powder as the primary 'carrier' and densification agent. The iron powder provides improved specific gravity and heat transfer for improved alloy dissolution. The iron powder provides a source of "mechanical particle interlocking" that assists in the consolidation of the alloy ingredients into a tablet which possesses outstanding green handling properties. Use of iron as the "carrier" agent essentially eliminates the need for ferrosilicon based inoculating alloys. [0056] In one embodiment the inoculating pellet, or loose granular powder, comprises at least one element chosen from the group consisting of silicon, calcium sulfur, magnesium and aluminum.

[0057] In one embodiment an inoculating pellet or loose granular powder is made with varying blends of oxy-sulfide forming elements blended to form a mixture consisting essentially of 1.) 15-49% silicon, 7 to 22% calcium, 3 to 10% sulfur, 2 to 4% oxygen, 2.5 to 7.5% magnesium and 0.50 to 5.0% aluminum, the balance being iron and incidental impurities.

[0058] A preferred form of one embodiment of the inoculating insert or tablet consists of essentially about 15% silicon, 7.0%) calcium, 3.0% sulfur, 4.5% aluminum, 2.0% oxygen, 5.0% magnesium, the balance being iron and incidental impurities. The preferred granulated inoculant consists of 49%) silicon, 22%) calcium, 2.7% magnesium, 2.8%) sulfur, 2.8% oxygen, 1.5% rare earths, and 3.5% aluminum. [0059] In one embodiment the microstructure has 98%> nodularity and is carbide free. [0060] The pellet, either spheriodization or inoculation, is preferably secured to the filter by pressing the pellet into a partial bore in the filter. The bore is preferably sized to accommodate the pellet in a friction fit relationship. The pellet can be secured to the surface by a suitable adhesive. The invention has been described with particular emphasis on the preferred embodiments. It would be apparent to one of ordinary skill in the art that alternate embodiments could be realized without departing from the scope of the invention which is set forth in the appended claims.

Claims

Claimed is:

1. A system for the production of ductile iron comprising the steps of: passing molten iron through a spheroidizing filter assembly to form a treated molten metal wherein said spheroidizing filter assembly comprises a filter and a spheroidizing pellet associated therewith; passing said treated molten metal through an inoculating filter assembly to form an inoculated treated molten metal wherein said inoculating filter assembly comprises a filter and an inoculating pellet associated therewith; and cooling said inoculated treated molten metal.

2. A system for treating molten iron comprising: a first filter and spheroidizing pellet associated therewith; and a second filter and inoculating pellet associated therewith.

3. A filter element comprising: an open cell ceramic filter; and a pellet comprising a spheroidizing element.

4. The filter element of claim 3 wherein said spheroidizing element comprises either FeSiMg alloy, magnesium metal, magnesium suicide, MgCeSi or rare earth suicide.

5. The filter element of claim 4 wherein said spheroidizing element comprises either FeSiMg or magnesium.

6. The filter element of claim 4 wherein said spheroidizing element comprises said rare earth suicide.

7. The filter element of claim 5 wherein said spheroidizing element comprises magnesium metal.

8. The filter element of claim 7 wherein said spheroidizing element consists essentially of magnesium.

9. The filter element of claim 3 wherein said filter element further comprises an inoculation filter element comprising a second filter and an inoculation pellet in contact therewith.

10. The filter element of claim 9 wherein said inoculation pellet comprises at least one element selected from the group consisting of cerium, strontium, zirconium, calcium, manganese, barium, bismuth, magnesium, titanium, aluminum, silicon and lanthanum.

11. The filter element of claim 3 wherein said filter further comprises a bore and said pellet is received in said bore.

12. A system for treating molten iron comprising: a sprue for collecting molten iron; a spheroidizing reservoir for receiving said molten iron from said sprue; a first filter received in said spheroidizing reservoir; a spheroidizing pellet attached to said first filter; an inoculating reservoir for receiving molten metal from said spheroidizing reservoir; a second filter received by said inoculating reservoir; and an inoculating pellet attached to said second filter.

13. Iron formed by the system of any of claims 1 , 2 or 12.

14. The system of any of claims 1, 2 or 12 wherein said spheroidizing pellet comprises one of FeSiMg alloy, magnesium metal, magnesium silicide, MgCeSi or rare earth silicide.

15. The system of claim 14 wherein said spheroidizing pellet comprises either FeSiMg or magnesium.

16. The system of claim 14 wherein said spheroidizing pellet comprises said rare earth silicide.

17. The system of claim 15 wherein said spheroidizing pellet consists essentially of magnesium.

18. The system of claim 12 wherein said inoculating pellet comprises at least one element selected from the group consisting of cerium, strontium, zirconium, calcium, manganese, barium, bismuth, magnesium, titanium, aluminum, silicon and lanthanum.