US2980531A - Production of nodular iron - Google Patents

Description

V 1C6 Patented Apr. 18, 1961 PRODUCTION OF N ODULAR IRON Lester C. Creme, West Alexandria, Ohio, assignor to The Dayton Malleable Iron Company, Dayton, 'Ohio, a cor- K This invention relates to the production of nodular iron (as this term is presently understood as including an as-cast iron product of an originally essentially gray iron mix in which the graphitic carbon content thereof is precipitated in the form of nodules or spherulites instead of in the form of flake graphite) and, more particularly, to the production of such nodular iron castings by a process including a special chilling addition step, in addition to treatment of the mix with a nodularizing agent and/or a preconditioning slag, for controlling and enhancing the graphitizing potential of the molten mix and the immediate readiness and responsiveness of the and the carbon component thereof to precipitate into the desired nodular form upon pouring and cooling the casting in the mold.

It will be understood that, with molten iron mixes of the character to which this invention relates, the carbon content may be considered as dissolved and as precipitating from solution during cooling of the casting, and that it is this precipitation of graphitic carbon which it is desired to control into the nodular or spherulitic form in making nodular'iron to achieve the enhanced physical properties of the casting attributable to the nodular microstructure thereof when cooled. Also, particularly in the commercial production of nodular iron castings, it may be desired to add to the molten mix being treated a minimal amount of nodularizing agent, if only for cost or economy reasons, for controlling the precipitation of the graphitic carbon into the nodular form instead of the flake form. Similarly, particularly in large commercial casting production where a plurality of castings are to be poured from a single ladle of iron, it is important to have some assurance that the desired nodular microstructure will be obtained in all (not merely most) of the castings poured from the ladle since it may be quite inexpedient to test each casting (usually by demolishing the casting) to determine whether or not, in fact, the desired nodular microstructure was obtained.

If it is attempted to control and correlate these various factors by, for example, merely increasing the amount of carbon in the iron mix (or the so-called carbon equivalen as reflected by .the combined carbon and silicon contents of the mix), in order to increase the so-called graphitizing potentia of the mix by having available a more concentrated solution of carbon from which precipitation thereof may more readily occur upon initial cooling of the mix, it may be discovered that an excessive amount of carbon actually precipitates. That is, since the carbon, as precipitated in the cooling metal, has a tendency to float upwardly through the cooling iron in the mold, too great a carbon content may result ina concentration of carbon in the top portion of the casting, and even to such an extent that the physical properties of the iron matrix at such top portion of the casting may be less than desired. On the other hand, utilizing lower carbon contents, as with hypoeutectic mixes, may lead to a situation where the carbon content is sufliciently dilute that there may be difiiculty in obtaining the desired immediate and rapid and uniform precipitation of the carbon into agglomerated nodules, even when an undesirably large addition of nodularizing agent is utilized.

According to this invention, however, a system is provided whereby a molten iron mix is heated to a sufficiently high temperature for handling in the foundry and for insuring that all the carbon present is actually in solution, and then suddenly chilled, while still molten, for increasing the responsiveness of the mix at the time of nodularizing agent addition for precipitation of carbon as controlled by the nodularizing agent into the desired nodular microstructure, as, for example, by adding to the molten mix in the ladle or just prior to treatment with the nodularizing agent a substantial quantity of solid metal to achieve some sudden chilling of the molten mix as the added metal is melted by the residual heat in the mix.

One object of this invention is to provide a system for the production of nodular castings of the character described in which the molten iron mix to be treated with a nodularizing agent is suddenly chilled a substantial amount just prior to the addition of the nodularizing agent for increasing the graphitizing potential of the mix and enhancing the responsiveness or readiness with which carbon dissolved in the molten iron will precipitate in the cooling casting into the desired nodular form.

1 Another object of this invention is to provide, in a nodularizing iron producing process of the character described, a chilling step particularly useful with iron mixes in the hypoeutectic range of carbon compositions whereby the responsiveness of the mix to nodular graphite precipitation is enhanced immediately prior to the addition of a nodularizing agent and pouring of the castings into the molds.

A further object of this invention is to provide a nodular iron process of the character described whereby a substantial amount of cold metal is added to the molten iron mix in the ladle and prior to a nodularizing addition for enhancing the susceptibility of the mix to ready graphite precipitation therefrom during cooling and influencing thereof into a nodular microstructure.

A still further object of this invention is to provide a nodular iron process of the character described whereby a substantial amount of cold metal is added to the molten iron mix in the ladle and prior to a nodularizing addition for enhancing the susceptibility of the mix to ready graphite precipitation therefrom during cooling and infiuencing thereof into a nodular microstructure, and also including the steps of adding silicon after the chilling step for further enhancing the graphitizing potential of the mix.

Still another object of this invetnion is to provide a process for the production of nodular iron castings in which an essentially hypoeutectic iron mix is prepared for a ladle addition of nodularizing agent and at a temperature sufiiciently high for insuring that all carbon is in solution and for maintaining the fluidity of the mix as acquired by the handling and pouring procedures of the foundry, and then chilling the mix a substantial amount by the addition thereto of cold metal for melting therein prior to the addition of the nodularizing agent for enhancing the responsiveness and readiness with which the graphitic carbon in the mix will precipitate in the cooling metal in the mold into the desired nodular microstructure uniformly dispersed throughout the casting and as influenced by the nodularizing agent.

Other objects and advantages of this invention will be apparent from the following description and the appended claims.

There may be many instances where it is desired to utilize an essentially hypoeutectic molten iron mix for the production therefrom of nodular iron castings, and particularly in instances where it may be found that higher carbon contents produce in the finished casting a flotation of excess carbon in the upperportion of the casting as it stands in the mold with concomitantly reduced physical properties in such high carbon areas of the casting. In some situations, also, the carbon equivalent (as well understood in this art as meaning the weight percent of-carbon content plus one-third of the Weight percent of silicon) may be increased during the nodularizing process as by a desirable late addition of silicon in the ladle to increase the graphitizing potential of the mix and/or the inclusion of such substances as calcium silicide in or along with the added nodularizing agent.

It may also be found that the completeness with which a nodular microstructure is assured in a plurality of castings poured from a single ladle may increase with higher carbon equivalents, perhaps because of the increased graphitizing potential resulting from such higher carbon equivalents. For example, even though a carbon equivalent of 4.0 be considered a hypoeutectic iron prior to adding the nodularizing agent, this may be high enough to as sure virtually 100% production of nodular microstructures with usual or conventional nodularizing additions. Nevertheless, such a carbon equivalent may, indeed, produce, with certain section sizes in the casting and/or as a result of an increased carbon equivalent picked up from the nodularizing addition, an undesirable excess flotation of carbon in the upper portion of the casting. If, on the other hand, the carbon equivalent of the molten mixprior to nodularizing or late silicon treatment be held to a value substantially less than 3.5, the desired graphitizing may not be obtained.

Particularly with commercial production of a large number of castings on a production basis, the routine possibility that some (however few) of the castings produced from any one melting may not achieve the desired nodular microstructure and/ or physical properties specifications is a matter of substantial disadvantage and one which may, indeed, transcend the normal inspection or spot checking techniques in production foundry .practices. To the foregoing, also, should be added the thought that, with production foundry techniques, the molten mix is advantageously heated in the first instance to a temperature suificiently high for ensuring that the carbon will initially be dissolved in the molten iron and, also, to ensure that there will be enough residual heat in the mix after tapping from the furnace into the ladle to assure fluidity sufiicient, upon pouring, for the metal to run or fiow'into all the various interstices or cavities of the casting mold prior .to solidification.

If the readiness or responsiveness of the molten mix to graphite precipitation be considered as, at least in part, a function of the concentration of carbon dissolved in the iron solution, it might be considered possible to enhance the precipitation by maintaining the molten mix at a temperature not substantially higher than that at which the carbon would be expected to precipitate. Yet, particularly in production foundry practices for mass producing hundreds or thousands of identical small castings (as compared to custom founding of a single part for a single made-to-order machine), the standard production foundry handling techniques may require heating the metal initially to a substantially higher temperature so that a desirable degree of fluidity of the molten metal will be maintained notwithstanding a substantial time period as the metal is tapped from .the furnace and while it is being handled in the ladle and poured into the molds, etc.

Similarly, treating the routine and repeated accomplishment of satisfactory nodular iron results as,-at least in part, a function of graphitizing potential, or, otherwise stated, the actual tendency of the dissolved carbon to precipitate out of solution in the iron according to Well understood solution mechanics, one might consider instigating or nucleating the desired precipitation of even low carbon contents 'by the sudden or late addition of additional carbon or silicon to the molten mix. As noted above, however, the advantages expected from such a treatment may well be outweighed by the disadvantages stemming from increasing the carbon content (or the silicon content) by such nucleating treatment and particularly in cases Where a substantial additional carbon or silicon component is added to the molten iron for other purposes as by a pretreatment slag or by the extra addition of a silicide as part of the nodularizing agent.

Satisfactory results according to this invention, however, are achieved by preparing a molten gray iron mix of a composition as may be desired for the final casting and for nodularizing treatment of the mix with any particular nodularizing agent desired and/or for handling according to whatever foundry techniques and practices are desired, and then adding to themolten mix, preferably upon tapping from the furnace into the ladle, a substantial quantity (at least approximately 3% by weight and preferably about 5% or more) of cold or solid metal for providing a sudden chilling temperature reduction in the molten mix of the order of F. and preferably F. or more at the time of making the ladle addition of nodularizing agent and/or providing a new source of undissolved carbon to serve as a nucleating agent to encourage precipitation of dissolved carbon.

Whereas the mechanics of the effect of such treatment may not now, with certainty, be completely understood, it is believed that such sudden chilling, resulting from utilization of residual heat in the molten mix to melt the solid metal added thereto, provides a ready instigation of graphite precipitation more or less uniformly throughout the mix, and may also provide some actual or mechanical interjection into the mix of undissolved carbon as a source of nuclei on which the precipitating dissolved carbon can agglomerate, under the influence of the nodularizing agent, into the desired uniformly dispersed nodules or spherulites in the cooling metal in the mold, although the ultimate advantages of this invention may not be achieved merely by adding a nodularizing agent without the chilling. It is also preferred, according to this invention, to include a late addition of silicon, after the addition of cold metal to the mix and after the nodularizing agent addition, as giving further enhanced results, perhaps because of creating localized hypereutectic effects, even in an essentially hypoeutectic mix, as a further inducement to nucleation of the precipitating graphite into the desired nodular microstructure. Such added silicon, also as will be understood, provides a further increase of the carbon equivalent in the final composition.

Although the advantages of this invention are applicable to a wide variety of iron mix compositions as treated with a wide variety of nodularizing agents, the results are, perhaps, most emphatic with mass production foundry techniques utilizing hypoeutectic mixes having carbon equivalents of no more than 3.5 prior to treatment according to this invention and, particularly, when the desired nodularizing process may include treatment of the molten mix with a carbon-containing slag prior to nodularizing and/or when the nodularizing agent may include a silicide or be accompanied by a late silicon addition desirable for other purposes, all of which would, as well understood, increase the carbon equivalent in the cooling metal in the mold.

It may also be desired, for a number of reasons, to handle the molten metal as close as practicable to the desired pouring temperature thereof and, of course, not to go to the expense of heating the initial mix to any higher temperature than is required for the founding operation. Nevertheless, in order to get all the carbon into solution in the first place in the mix and adequately blend and treat the various components or raw materials from which the molten mix is originally made up, it

may be necessary, as a practical matter,.to heat the original melt to a temperature of, perhaps 2850 F. according to standard production foundry practices.

As noted above, it is desired that the chilling effect of adding solid metal to the molten mix produce a sudden reduction of temperature of the order of 100 to 160 F.

or more. As also will be understood, from conventional experience in the founding of nodular iron castings, a pouring temperature of at least about 2700 F. may be found necessary for pouring small and thin section castings, in order to achieve the required amount of fluidity of the molten metal when poured into the mold, although pouring temperatures as low as about 2300 F. are practicable for larger section castings. Similarly, also, the desired final carbon and silicon content of the finished casting can be adjusted according to this invention and more or.less independently of the effects to be expected from carbon or silicon additions to the finished casting resulting from slag treatments of the molten mix and/or silicon additions with or as a part of the nodularizing agent, since the desired propensity for graphitizing is enhanced by the chilling step also more or less independently of the graphitizing potential inherent in the molten mix tapped from the furnace. As will be noted, the advantages obtained by this invention are also more or less independent of the particular nodularizing agent used (whether or not a further addition of carbon or silicon to the iron being treated is made after tapping), although it appears to be more significantly useful commercially with the rare earth type of agent than with, for example, magnesium.

In connection with the foregoing and the temperatures mentioned it should be noted that satisfactory results have been attained according to this invention in producing finished castings having tensile strengths of at least the order of 60,000 pounds per square inch and elongations of the order of 10% (both as tested by standard methods) when the carbon equivalent in the finished casting was less than 4.5, and that of the melt prior to they nodularizing addition less than 4 and preferably less than 3.5 and still with reasonable assurance in production foundry techniques of obtaining the desired nodular microstruoture routinely and repeatedly.

Whereas the carbon or silicon content of the cold metal added during the chilling step accordihg to this invention may have its effect on the ultimate composition of the finished casting, it is believed that the primary effect according to this invention is one of sudden chilling.

For example, satisfactory results have been achieved in producing the enhanced readiness for precipitation of the carbon by adding, in the chilling steps, such diverse materials as copper, nickel, pig iron, a relatively pure iron such as Arrnco iron, low carbon steels, and nodular iron scrap. Thus, it will be noted that the addition of the cold metal to the molten mix in the ladle need not alter particularly the composition of the molten mix, unless desired, and particularly is this true when it is realized that, in mass production foundry techniques, as much as 50% of the heat may be routinely made up of scrap and sprue from previous runs.

It will also be noted that, except for specific temperature adjustment and whatever adjustment may be necessary in the composition of the mix depending upon the type of nodularizing or other ladle addition, the practicing of the process embodying this invention does not require specific control or alteration of either the composition of the mix or the particular nodularizing agent desired, nor need the practicing of this invention fundamentally alter the desired nodularizing foundry practices, although it does provide enhanced assurance of successful results, particularly with irons having a low hypoeutectic carbon equivalent as disclosed.

As illustrative of satisfactory results achieved according to this invention, one may note data regarding various castings made in accordance with this invention from an initial molten charge or mix includng approximately 50% remelted nodular iron, 20% pig iron, and 30% steel scrap. After the starting materials were molten, they were treated with a slag comprising high-calcium lime, fluorspar, and coke in the ratio of 16%, 5%, and 6% respectively, of the foregoing slag components on the melt, for the purpose, as will be understood, of enhancing the susceptibility or responsiveness of the mix to nodularization. After being held for about 1020 minutes at temperature with the slag, various portions of the mix were tapped off, subjected to an addition of cold metal in accordance'with this invention, subjected to an addition of nodularizing agent, cast, and tested, in accordance with standard procedures, to produce the data noted in the following tables.

In the various particular instances noted below, the nodularizing agent or additive was a 4-1 combination of calcium silicide and rare earth fluorides followed by a late silicon addition from 75% ferrosilicon (according to, for example, the nodularizing process disclosed in my copending application S.N. 779,544, filed December 11, 1958). It is to be understood that comparably enhanced results according to this invention are achieved with the use of other nodularizing agents or additives (e.g., magnesium, misch metal, alloys thereof, etc.).

Table 1 Mins. Percent Percent Percent Heat with Cold metal cold nodularlate Si slag added metal izing agent 10 Nodular Swap. 3 70 1.0 20 do 5 .48 1.0 10 .50 1. 0 3 .61 1.0 5 70 5 10 .50 1. 0 3 70 1.0 5 .70 1.0 8 .50 1.0 10 .46 1. 0 3 .70 .6 3 70 5 Representative castings of the foregoing runs or heats and which produce the data of Table I disclosed, upon analysis and testing by standard methods, characteristics as indicated in the following table:

1 Table II Percent Percent Tensile Elonga- Heat 0 Si O Equiv. Brinell Strength, tion,

p.s.i. Percent The percentage figures in the above tables are weight percents of the molten mix as analyzed after cold metal addition but before the nodular addition, and the physical properties data relate to the finished castings. The above data and runs or heats or castings are set forth, as noted, merely as illustrative of satisfactory results and operations according to this invention, although, as will be understood by men skilled in this art, comparable or equivalent enhanced results with other starting mixes, other nodularizing additives, etc.

While the methods, compositions and products described herein constitute' preferred embodiments of the invention, it is to be understood that the invention is not limited to these precise methods, compositions and products, and that changes may be made therein without departing from the scope of the invention which is defined in the appended claims.

What is claimed is:

1. In a process of the character described for the production of nodular iron castings from a molten gray iron mix, the steps Which comprise forming in a melting furnace a hypoeutectic molten gray iron rnix having a low carbon content, heating said mix in said melting furnace to a high founding and pouring temperature of at least about 2.850 F. for dissolving in said iron substantially all the carbon present in said mix, withdrawing said thus melted mix from said furnace, adding to said withdrawn molten mix solid metal effecting a sudden chilling of about 100 Fjof said molten mix by the addition of said solid metal thereto, thereafter treating said mix with a nodularizing agent, and pouring said thus treated mix into a mold to form said nodular iron casting.

2. In a process of the character described for the production of nodular iron castings from a molten gray iron mix, the steps which comprise forming in a melting furnace a hypoeutectic molten gray iron mix having a low carbon equivalent of less than about 4, heating said mix in said melting furnace to a high temperature of at least about 2850 F. and substantially above a pouring temperature for said mix for dissolving in said iron sub stantially all the carbon present in said mix, Withdrawing said thus melted mix from said furnace, adding to said withdrawn mix a substantial portion of solid metal effecting a sudden chilling of about 100 F. of said molten mix by the addition of said solid metal thereto and extra addition to said molten mix of undissolved carbon in said solid metal, thereafter treating said mix with a nodu larizing agent, and pouring said thus treated mix into a mold to form said nodular iron casting.

3. In a process of the character described for the production of nodular iron castings from a molten gray iron mix, the steps which comprise forming in a melting furnace a hypoeutectic molten gray iron mix having a low carbon equivalent of no more than about 3.5, heating said mix in said melting furnace to a high temperature of at least about 2850 F. substantially above a minimal pouring temperature for said mix for dissolving in said iron substantially all the carbon present in said mix, withdrawing said thus melted mix from said furnace, adding to said Withdrawn mix a substantial portion of solid metal effecting a sudden chilling of at least about 100 F. of said molten mix by the addition of said solid metal thereto and extra addition to said molten mix of undissolved carbon in said solid metal, thereafter treating said mix with a nodularizing agent, and pouring said thus treated mix into a mold to form said nodular iron casting.

4. In a process of the character described for the production of nodular iron castings from a molten gray iron mix, the steps which comprise forming in a melting furnaoe a hypoeuteclic molten gray iron mix having a low carbon equivalent of less than about 4, heating said mix in said melting furnace to a temperature of at least about 2850 F. for dissolving in said iron substantially all the carbon present in said mix, tapping said thus melted mix from said furnace, adding to said tapped molten mix about 3% by weight solid metal. effecting a sudden chilling of said molten mix by the addition of said solid metal thereto to enhance precipitation of dissolved carbon dur ing final cooling of said mix, thereafter treating said mix with a nodularizing agent, and pouring said thus treated mix into a mold to form said nodular iron casting.

5. In a process of the character described for the production of nodular iron castings from a molten gray iron mix, the steps which comprise forming in a melting furnace a hypoeutectic molten gray iron mix having a low carbon equivalent of less than about 3.5, heating said mix in said melting furnace to a temperature of at least about 2850 F. for dissolving in said iron substantially all the carbon present in said mix, tapping said thus melted mix from said furnace, adding to said tapped molten mix about 3% by weight solid metal effecting a sudden chilling of said molten mix by the addition of said solid metal thereto to enhance precipitation of dissolved carbon during final cooling of said mix, thereafter treating said mix with a nodularizing agent, and pouring said thus treated mix into a mold to form said nodular iron casting.

6. In a process of the character described for the production of nodular iron castings from a molten gray iron mix, the steps which comprise forming in a melting furnace a hypoeutectic molten gray iron mix having a low carbon equivalent of less than about 4, heating said mix in said melting furnace to a temperature of about 2850 F. and substantially above a minimal pouring temperature for said mix for dissolving in said iron substantially all the carbon present in said mix, tapping said thus melted mix from said furnace, adding to said tapped molten mix about 5% by weight solid metal effecting a sudden chilling of said molten mix by the addition of said solid metal thereto to enhance precipitation of dissolved carbon during final cooling of said mix, thereafter treating said mix with a nodularizing agent, and pouring said thus treated mix into a mold to form said nodular iron casting.

7. In a process of the character described for the production of nodular iron castings from a molten gray iron mix, the steps which comprise forming in a melting furnace a hypoeutectic molten gray iron mix having a low carbon equivalent of less than about 3.5, heating said mix in said melting furnace to a temperature of about 2850 F. for dissolving in said iron substantially all the carbon present in said mix, tapping said thus melted mix from said furnace, addin to said tapped molten mix about 5% by weight solid metal effecting a sudden chilling of said molten mix by the addition of said solid metal thereto to enhance precipitation of dissolved carbon during final cooling of said mix, thereafter treating said mix with a nodularizing agent, and pouring said thus treated mix into a mold to form said nodular iron casting.

8. In a process of the character described for the production of nodular iron castings from a molten gray iron mix, the steps which comp-rise forming in a melting furnace a hypoeutectic molten gray iron mix having a low carbon content, heating said mix in said meltingfurnace to a high founding temperature of at least 2850" F. and substantially above a minimal pouring temperature for said mix for dissolving in said iron substantially all the carbon present in said mix, tapping said thus melted mix from said furnace, adding to said tapped molten mix a substantial proportion of solid metal selected from the group consisting of copper, nickel, pig iron, cast iron, steel, and iron effecting a sudden chilling of at least about F. of said molten mix by the addition of said solid metal thereto to enhance precipitation of dissolved carbon during final cooling of said mix, thereafter treating said mix with a nodularizing agent, and pouring said thus treated mix into a mold to form said nodular iron casting.

9. In a process of the character described for the production of nodular iron castings from a molten gray iron mix, the steps which comprise forming in a melting furnace a hypoeutectic molten gray iron mix having a low carbon equivalent of less than about 4, heating said mix in said melting furnace to a temperature of at least about r 285=0 F. for dissolving in said iron substantially all the carbon present in said mix, tapping said thus melted mix from said furnace, adding to said tapped molten mix at least about 3% by weight solid metal selected from the group consisting of copper, nickel, pig iron, cast iron, steel, and iron effecting a sudden chilling of said molten mix by the addition of said solid metal thereto to enhance precipitation of carbon during cooling of said mix, thereafter treating said mix with a nodularizing agent, and pouring said thus treated mix into a mold to form said nodular iron casting,

10. In a process of the character described for the production of nodular iron castings from a molten gray iron mix, the steps which comprise forming in a melting furnace a hypoeutectic molten gray iron mix having a low carbon equivalent of less than about 3.5, heating said mix in said melting furnace to a temperature of at least about 2850 F. for dissolving in said iron substantially all the carbon present in said mix, tapping said thus melted mix from said furnace, adding to said tapped molten mix at least about 3% by weight solid metal selected from the group consisting of copper, nickel, pig iron, cast iron, steel, and iron effecting a sudden chilling of said molten mix by the addition of said solid metal thereto to enhance precipitation of carbon during cooling of said mix, thereafter treating said mix with a nodularizing agent, and pouring said thus treated mix into a mold to form said nodular iron casting.

11. In a process of the character described for the production of nodular iron castings from a molten gray iron mix, the steps which comprise forming in a melting furnace a hypoeutectic molten gray iron mix having a low carbon equivalent of less than about 4, heating said mix in said melting furnace to a temperature of at least about 2850 F. for dissolving in said iron substantially all the carbon present in said mix, tapping said thus melted mix from said furnace, adding to said tapped molten mix at least about 5% by weight solid metal selected from the group consisting of copper, nickel, pig iron, cast iron, steel, and iron effecting a sudden chilling 10 of said molten mix by the addition of said solid metal thereto to enhance precipitation of carbon during cooling of said mix, thereafter treating said mix with a nodularizing agent, and pouring said thus treated mix into a mold thus melted mix from said furnace, adding to said tapped molten mix at least about 5% by weight solid metal selected from the group consisting of copper, nickel, pig iron, cast iron, steel, and iron effecting a sudden chilling of said molten mix by the addition of said solid metal thereto to enhance precipitation of carbon during cooling of said mix, thereafter treating said mix with a nodulariz ing agent, and pouring said thus treated mix into a mold to form said nodular iron casting.

References Cited in the file of this patent UNITED STATES PATENTS Eyt et al. Feb. 19, 1952 Moore May 21, 1957

Claims (1)

1. IN A PROCESS OF THE CHARACTER DESCRIBED FOR THE PRODUCTION OF NODULAR IRON CASTINGS FROM A MOLTEN GRAY IRON MIX, THE STEPS WHICH COMPRISE FORMING IN A MELTING FURNACE A HYPOEUTECTIC MOLTEN GRAY IRON MIX HAVING A LOW CARBON CONTENT, HEATING SAID MIX IN SAID MELTING FURNACE TO A HIGH FOUNDING AND POURING TEMPERATURE OF AT LEAST ABOUT 2850*F. FOR DISSOLVING IN SAID IRON SUBSTANTIALLY ALL THE CARBON PRESENT IN SAID MIX, WITHDRAWING SAID THUS MELTED MIX FROM SAID FURNACE, ADDING TO SAID WITHDRAWN MOLTEN MIX SOLID METAL EFFECTING A SUDDEN CHILLING OF ABOUT 100*F. OF SAID MOLTEN MIX BY THE ADDITION OF SAID SOLID METAL THERETO, THEREAFTER TREATING SAID MIX WITH A NODULARIZING AGENT, AND POURING SAID THUS TREATED MIX INTO A MOLD TO FORM SAID NODULAR IRON CASTING.