US2749238A

US2749238A - Method for producing cast ferrous alloy

Info

Publication number: US2749238A
Application number: US115088A
Authority: US
Inventors: Millis Keith Dwight; Gagnebin Albert Paul; Pilling Norman Boden
Original assignee: International Nickel Co Inc
Current assignee: Huntington Alloys Corp
Priority date: 1949-09-10
Filing date: 1949-09-10
Publication date: 1956-06-05
Anticipated expiration: 1973-06-05

Description

June 5, 1956 K. D. MlLLlS El AL METHOD FOR PRODUCING CAST FERROUS ALLOY Filed Sept. l0 1949 2 Sheets-Sheet l June 5, 1956 K. D. MlLLls ETAL 2,749,238

METHOD Foa PRoDUcING CAST FERROUS ALLOY Filed Sept. lO, 1949 2 Sheets-Sheet 2 BY m ATTORNEY METHOD FR PRODUCING CAST FERROUS ALLOY Keith Dwight Millis, Rahway, Albert Paul Gagnebin, Red

Bank, and Norman Boden Pilling, Westfield, N. E., assignors to The International Nickel Company, Inc., New York, N. Y., a corporation of Belaware Application September 10, 1949, Serial No. 115,088

23 Claims. (Cl. 75-130) The present invention relates to a method for producing a unique ferrous alloy possessing advantageous features of gray cast iron and malleable iron, but devoid of defects and shortcomings thereof, and, more particularly, to a method for producing a new ferrous product having improved and unusual combinations of properties, especially an improved and unusual combination of founding properties and mechanical and physical properties.

Cast iron is a eutectiferous alloy comprised mainly of iron and containing carbon, and usually a substantial amount of silicon, the carbon being present in excess of the amount which can go into solid solution in austenite at the eutectic temperature of the alloy, whereas steel is an alloy which contains less than this amount of carbon and which does not exhibit a eutectic of iron and carbon. Cast irons are usually considered as being either white cast iron or gray cast iron. Sometimes a cast iron which possesses some of the characteristics or structural features of a White cast iron and some of the characteristics or structural features of a gray cast iron is termed a mottled cast iron, but for general purposes and for purposes of the present description, such a product is classified as either a white cast iron or a gray cast iron, depending upon which characteristics or structural features predominate. The kind of cast iron which has generally been most commonly used for centuries is gray cast iron, i. e., the soft and machinable kind in which the major part of the carbon not required to forni the matrix structure is present as graphite in the as-cast condition. It has been recognized that the graphitic carbon occurs as elongated particles, commonly called flake graphite, disseminated throughout the matrix. ln polished gray cast iron sections, the flake graphite appears under the microscope as a grayish, soft constituent. The weakening discontinuities produced by flake graphite are reflected in the greatly reduced tensile strength, fatigue resistance, toughness and ductility of gray cost iron compared to a product made up entirely of the matrix cornponent, e. g., a comparable steel. White cast iron is a harder, brittle cast iron in which the major part of the excess carbon not required to form the matrix is present as combined carbon, i. e., as carbide, in the as-cast condition. While some advances, considered notable at the time, have been made in ordinary foundry gray cast iron, no one has proposed prior to the present invention a satisfactory, generally applicable method for eliminating from ordinary foundry gray cast iron the detrimental effect of graphite due to its ake form in the as-cast condition. As a result, it has been necessary to resort to the use of ferritic or pearlitic malleable iron or even cast steel when higher properties or combinations of properties were required, although these engineering materials are considerably more expensive than gray cast iron and possess other disadvantages.

The present invention is based on the discovery of a method whereby carbon in a high-carbon as-cast ferrous alloy, i. e., in an as-cast ferrous alloy containing carbon within the cast iron range, can be made to appear aired States Patent 2,749,238 Patented June 5, 1956 consistently and reproducibly in the form of dispersed gray-colored, soft particles substantially spheroidal or spherical in shape and generally having a radial structure, thereby eliminating the deleterious effects of ilake graphite. In the ferrous alloy produced by the method embodying the present invention, this form of carbon can be obtained in the as-cast condition, i. e., without heat treatment, together with a combination of properties of an order entirely different from and higher than that obtained in gray cast iron.

It is among the objects of the present invention to provide methods or processes for consistently and reproducibly eliminating ake graphite substantially or entirely from high-carbon ferrous alloys, and to provide highcarbon as-cast ferrous alloys in which carbon occurs as substantially spheroidal or spherical, soft, gray-colored particles.

Other objects and advantages of the present invention will be apparent to those skilled in the art from the following description taken in conjunction with the drawings in which:

Figs. l and 2 are reproductions of photomicrographs taken at a magnification of 25 diameters and showing, in polished sections of representative alloys produced by the process contemplated by the present invention, the spheroidal form of carbon obtained inthe as-cast condition by the presence of a special element employed in the process contemplated by the present invention;

Fig. 3 is a reproduction of a photomicrograph taken at a magnification of 250 diameters and showing the etched structure in the as-cast condition of an alloy produced in accordance with the present invention and containing the spheroidal form of carbon in a pearlitic matrix;

Fig. 4 is a reproduction of a photomicrograph taken at 50 diameters showing the occurrence of the spheroidal form of carbon in the etched structure of an alloy in the as-cast condition and produced in accordance with the invention;

Fig. 5 is a reproduction of a photomicrograph taken at a magnification of 1000 diameters of an etched specimen and showing in more detail the structure of the spheroidal form of carbon obtained in alloys in the ascast condition produced by the process contemplated by the present invention;

Fig. 6 is a reproduction of a photomicrograph taken at a magnication of 1000 diameters on an etched specimen and showing in detail the structure of the spheroidal form of carbon obtained in alloys produced by the process contemplated by the present invention after having been given a treatment to ferritize the matrix;

Fig. 7 is a reproduction of a photomicrograph taken at a magnification of 250 diameters and showing the etched structure of a high-carbon ferrous alloy containing a special element employed in the process contemplated by the invention after a treatment to ferritize the matrix; and

Fig. 8 is a reproduction of a photograph of three bend-test specimens made of the alloy produced by the process contemplated by the present invention, one specimen having been tested in the as-cast condition and the other two specimens having been tested after different ferritizing treatments.

The present invention provides a novel method for producing a novel ferrous product containing at least about 50% iron and particularly at least about 87% iron, carbon and silicon within the cast iron range, the carbon in excess of that required to form the matrix being predominantly in the uncombined form, and containing a small but effective amount of magnesium to control the form of uncombined carbon. The invention provides a cast iron product characterized by a microstructure containing carbon in the form of randomly dispersed, soft, gray-colored, substantially spheroidal or spherical particles or agglomerates of such particles. In accordance with the present invention, the aforementioned microstructure of the product is obtained in the as-cast condition to provide a novel product characterized by an improved combination of properties and by a structure not reproducibly obtained prior to the present invention in cast irons in the as-cast condition. The product of the invention is preferably substantially devoid of flake graphite. Another distinguishing feature of the microstructure is that usually no sulfide particles are seen embedded in the matrix, whereas ordinary cast iron usually contains many easily recognized sulfide inclusions embedded in the matrix.

Generally speaking, the present invention contemplates the method for the production of a new cast ferrous alloy containing uncombined carbon in a spheroidal form in the as-cast condition which comprises establishing a molten ferrous alloy bath of such composition that if cast after inoculation it would be a gray cast iron, for example, if cast in a sand mold or in the type of mold to be employed in producing the final product shortly after a late inoculating addition such as conventionally employed in treating cast iron, incorporating magnesium into said bath in such amounts that a small but effective retained magnesium content (for example, about 0.035% or about 0.04% or more magnesium) up to about 0.4% or 0.5% is obtained to produce the spheroidal carbon form in the final castings and inoculating the bath at least once (preferably with a late addition of at least 0.2%, or more preferably at least 0.3%, of silicon as a silicon-containing metallic agent such as ferro-silicon), and casting the inoculated bath. Usually about 0.04% to about 0.4% magnesium, preferably at least about 0.05% to about 0.2% or about 0.06% to about 0.15% magnesium is retained in the bath and in the castings produced therefrom when using ordinary foundry irons. It is preferred that inoculation be employed in carrying out the process embodying the present invention. However, in some cases, where the graphitizing power of the magnesium-containing bath is very high, inoculation may not be necessary to insure that a sutiicient amount of the total carbon will be in the uncombined form in the soliditied casting, although it has been found that inoculation is always beneficial. The instances where inoculation would not be necessary are relatively exceptional. As those skilled in the foundry art know, the inoculation of ordinary cast iron has a graphitizing eiect and comprises a late addition of a strong graphitizer which is usually a silicon-containing agent such as ferro-silicon, calcium silicide, nickel silicide, etc., but may also be another strong graphitizer such as aluminum. By employing an agent containing both magnesium and the inoculating element, for example, a nickel-magnesium-silicon alloy containing about 30% or 50% or more silicon, it is possible to introduce the magnesium and the inoculant by means of a single addition agent and such practice is within the scope of the present invention but is not as preferred as inoculating after the magnesium introduction, as the latter procedure generally is more effective in assuring the presence of the soft, gray-colored spheroids or spheres with the required retained magnesium content in the as-cast product and produces higher properties. As indicated hereinbefore, the molten bath which is treated in accordance with the invention is one which would be a gray cast iron if cast after a graphitizing inoculation, e. g., in a sand mold or in the type of mold to be employed to produce the tinal product. Of course, a molten bath with suicient graphitizing power to produce a gray cast iron Without inoculation is within the scope of those that can be treated in accordance with the present invention because such a bath obviouslyl would still be a gray cast iron if cast after inoculation which merely further increases or insures graphitization in cast iron.

Under the microscope, the difference between the ascast product provided by the method embodying the present invention and gray cast iron is readily apparent. In polished sections of the as-cast novel product provided by the present invention, som-c or practically all of the spheroidal form of uncombined carbon appears as compact, soft, gray-colored, rounded particles, usually nearly circular. or as agglomerates or groups of such particles. The occurrence of the spheroidal form of carbon in polished (unetched) specimens of the magnesium-containing ferrous alloy in the as-cast condition is illustrated in Figs. l and 2. rfhe appearance of the spheroidal form of carbon in etched sections of the alloy in the as-cast condition illustrated in Fig. 3 wherein the spheroidal carbon occurs in a matrix of pearlite. When the composition is such that the matrix contains ferrite as well as pcarlite in the as-cast condition, the ferrite often tends occur around the spheroidal carbon particles, as illustrated in Fig. 4. in the tis-polished condition and particularly in the etched condition, the rounded particles of carbon seen in properly polished sections generally have a well-defined radiating structure. Fig. 5 shows the representative radiating or radial structure of the spheroidal or rounded particles which at a magnification of i000 diameters usually are about l to 21/2 inches in average diameter in cast sections of normal thicknesses. in polished sections of gray cast irons, the uncombined carbon has appeared entirely or almost entirely as elongated particles or iiakes which are very long in comparison to their Width. The spheroidal or rounded particle seen under the microscope in polished sections of thc magnesium-containing alloy generally has the appearance of a plurality of crystals radiating from approximately the center, i. e., a radiating and polycrystalline appearance. When viewed under reflected polarized light through a microscope, radiating portions or sectors of the rounded particle (which apparently produce the radiating or radial structure of the particle) extinguish at diiferent intervals as the stage of the microscope is revolved. In gray cast irons containing iiake graphite, the entire flake, which has been recognized to be a single crystal, usually extinguishes at one time during the stage rotation.

Retention of magnesium A feature of the present invention in obtaining the aforementioned product having a microstructure containing the spheroidal form of carbon is the introduction of magnesium into the molten bath and the retention of at least a critical minimum amount of magnesium in the nal product. It is not suicient merely to add magnesium to the molten bath. The presence of retained magnesium in the bath and in the aforementioned product is essential in order to obtain the spheroidal carbon structure therein. While the theory of the magnesium effect on the form of carbon and on the properties of the product provided by the present invention is not fully apparent, it has been found that the presence of retained magnesium 1s required in order to obtain the compacted spheroidal or spherical, soft, gray-colored form of carbon and to obtain the high combination of properties in the as-cast ferrous alloy of the present invention. if the final product contains no retained magnesium or too small an amount of retained magnesium, the results of the present invention as indicated by either the properties or thc carbon form are not obtained. As pointed out in the aforesaid U. S. Patent No. 2,485,760, it was recognized that magnesium determinations of the order involved herein were difficult to make, and the values given herein are based upon analyses by a chemical wet method and Were reproducible within about 0.005% or so. It was also pointed out in the aforesaid patent that the accuracy of the values of retained magnesium were complicated by the presence of other elements associated with `magnesium in the ferrous product. A striking characteristic which is usually exhibited by the product produced by the process contemplated by the invention, particularly in its preferred embodiment containing a major proportion of the uncombined carbon in the spheroidal form, is the Steely appearance of its fracture as compared to the gray fracture of gray cast iron. The minimum retained magnesium content, at which the spheroidal form of uncombined carbon is induced, generally increases slightly with the carbon content and/or silicon content of the alloy and with the section size of the casting to be produced. Thus, when a particular treated bath is to be cast in a large section, e. g., four inches, the retained magnesium content should be slightly increased as compared to the satisfactory minimum retained magnesium content that could be employed if the same treated bath were to be cast in a small section, e. g.,

yone inch.

If any undesirable elements which tend to combine with and/or counteract the effect of magnesium, for example, sulfur, etc. (including oxygen, if any be present in the molten cast iron bath as is believed possible by some metallurgists), are present in the bath or are subsequently added, the amount of magnesium introduced should be increased by the amount required to counteract the effect of the presence of these elements or impurities by removing the elements or by otherwise overcoming their effects. Obviously, if any undesirable elements are not present or are present in smaller amounts than usual, the amount of magnesium introduced could be decreased.. Sulfur is the magnesium-counteracting element which is most likely to be present. No other common elements in the usual amounts which occur in cast iron, with the possible exception of large amounts of copper, have been found to have any marked detrimental eifect in interfering with the desired function of magnesium. Certain subversive elements which are comparatively rare in cast iron and which should be avoided are discussed hereinafter. When sulfur is present in the molten bath before treatment, it is necessary to introduce into the bath an amount of magnesium which is suiiicient not only to produce the desired retained magnesium content but also to react with sulfur. In addition, the magnesium recovery under the particular conditions and with the particular addition agents employed must also be taken into consideration in determining the amount of magnesium to be added, as will be discussed in more detail hereinafter. It has been found that in all baths treated in accordance with the present invention, all the magnesium-containing agents which produced the spheroidal form of uncombined carbon obtained by the invention also introduced the magnesium in a form which combined with sulfur present in the bath with the result that the sulfur content was reduced to about 0.010% to 0.015%, e. g., 0.012%. The results also have clearly indicated that only the unconsumed excess of magnesium is then available to perform its function of controlling the form of the uncombined carbon and providing the required retained magnesium content. Since many baths that can be treated in accordance with the invention will usually contain sulfur in various amounts as high as even 0.3% or more, it is therefore necessary to add an amount of magnesium which is sufficient to introduce magnesium to combine with the sulfur and to provide an excess suficient to give the retained magnesium content required by the invention. In other words, the lower the content of sulfur, etc., the lower the amount of magnesium that need be introduced and retained. The introduction of about three parts by weight of magnesium is required to react with about four parts by weight of sulfur. In actual practice, it is preferred to introduce one part by weight of magnesium for each part by weight of sulfur to be removed. Thus, if the bath contains 0.155% sulfur and it is desired to obtain a retained magnesium content of 0.06%, then, since the sulfur content must first be re duced from 0.155% to about 0.015 about 0.14% mag nesium is introduced for this purpose and an additional 0.06% magnesium must be introduced to provide the desired retained magnesium content. A total of about 0.20% magnesium would therefore have to be introduced into the molten bath. The amount actually added to the bath would be even greater because in practically all cases, except when the more preferred magnesium addition agents described hereinafter such as the nickel-magnesium alloys containing 90% or more nickel and the nickelmagnesium-carbon alloys containing over nickel are employed, it is possible to obtain an introduction of only a small amount of the magnesium added to the bath. This is apparently due mainly to its high volatility at the temperatures involved and also due to its low solubility in iron.

Control of graphitizing factors An important consideration in carrying out the invention is the graphitizing power of the molten ferrous bath to be treated. Satisfactory baths or melts which may be treatedv in accordance with the invention to produce a product having high properties and the spheroidal form of gray-colored carbon in the as-cast condition are those which, before the introduction of magnesium, have sufficient graphitizing power to be clearly classified by those skilled in the art as gray cast irons if cast in sand molds or in the particular kind of mold to be employed if it is a different mold, at least after inoculation such as is conventionally employed in producing better grades of gray cast iron. The aforementioned satisfactory baths include those molten baths having such high graphitizing power that they would be gray cast ironswhen solidified regardless of whether or not they were inoculated. The bath should have such graphitizing power that, when cast as indicated hereinbefore after inoculation, it would be substantially entirely devoid of massive carbides such as occur in white cast irons. The graphitizing power of the bath is the summation of a number of possible variable factors. The carbon content is one factor, i. e., for a given set of conditions graphitizing power increases rapidly as the carbon content increases. The bath generally will contain over 1.7% carbon and may contain as much as 4.5% or even 5% of carbon. Preferably, the bath to be treated contains about 2% to 4.5% carbon. Baths and final compositions containing 2.5% to 4% carbon have given very satisfactory results. Silicon present in the initial melted charge and/or added prior to the magnesium introduction also imparts graphitizing power but not to the same extent as carbon or as a late inoculating addition after the magnesium introduction and just prior to casting. As a very rough rule for predicting the effect of carbon and silicon on graphitizing power, it can be said that silicon is about three-tenths or one-third as effective in increasing the graphitizing power as carbon, i. e., that an increase of 3% of silicon is equal to an increase of 1% of carbon. It must be understood that this is only an empirical approximation and is affected by a number of other factors including the entire composition of the bath, the type of charge employed and numerous other conditions well known by those skilled in the art to iniiuence graphitization during the cooling from casting temperatures. The aforementioned molten bath, before treatment in accordance with the invention to produce an improved as-cast product, will generally contain at least about 0.5% silicon, preferably at least about 0.8% silicon, and may contain as much as 5% or even 5.5% or 6% of silicon, although the occasions when such large amounts of silicon would be employed are rare in view of the fact that carbon is more eective in imparting graphitizing power and that silicon in large amounts at a given carbon level has a tendency to reduce the properties, especially the toughness, ductility and/or tensile strength. Silicon is a strong ferrite former, and for this reason, it might be desirable to employ large silicon contents where a matrix containing a large proportion of ferrite is desired in the as-cast condition. After the magnesium treatment and any required inoculation, the bath will generally contain at least about 1% silicon, preferably at least 1.3% silicon, and may contain as much as 5% or 5.5% or even 6% silicon. Satisfactory results have been obtained in as-cast products made from preferred baths which contained about 0.5% or 0.8% to 3% or 3.5% silicon before magnesium treatment and inoculation, and particularly with baths containing up to 2.25% silicon before treatment and inoculation, e. g., baths containing 1%, 1.25%,1.5%, 1.75%, 2%, and 2.25% silicon. After magnesium treatment and inoculation, which introduced additional silicon, these baths had final silicon contents when cast between about 1.0% and 4.5%, preferably at least 1.5% silicon. More preferably, the bath should have such a silicon content that, after any additional silicon incorporated during the treatment with magnesium or the inoculation, it will contain between about 1.5% and 2.5% or 3% silicon. Other elements which impart graphitizing power to the bath are well known to those skilled in the art and include such elements as nickel, aluminum, etc.

In addition to the composition, many other factors also affect the graphitizing behavior of the bath as is well known to those skilled in the art of cast iron. Thus, the

nature of the mold in which the iron is to be cast is a factor, as the rate at which it is able to extract heat affects the cooling rate which in turn influences the graphitization. Likewise, the graphitizing power or potential of a particular bath will operate less effectively when cast in small section sizes, e. g., one-half inch, than when cast in large section sizes, e. g., four inches or eight inches, even though the same kind of mold is employed. The temperature of the mold in which the bath is cast, the degree of superheat of the molten bath, the pouring temperature, the nature of the metallic raw materials employed in the charge used to produce the bath and numerous other factors will influence graphitization. The composition of the bath to be treated in accordance with the invention should be controlled in the light of the various factors well known by those skilled in the art to influence the amount of graphitization. A particularly responsive range of final bath compositions having sufficient graphitizing power to ave-id, under most practical foundry conditions, the occurrence of massive carbides or incidental chills in sections of a/s in thickness or greater, is defined by the carbon limits 2.5% to 4.5%, the silicon limits 1.0% to 4.0%, and the silicon content being so related to the carbon content that the sum of Si C' 3.1 4.5

is greater than 1.00. lt is desirable that within this range and especially toward the lower limits of carbon and silicon, the alloy product be substantially free from tellurium and bismuth in order to avoid vagaries in graphitizing power and irregular tendencies toward chilling.

Iizocnlation The inoculation which accompanies or follows the introduction of magnesium into the bath is another important aspect of the invention, except in certain rare cases when the bath has a Very high graphitizing power, for example, such an excessive amount of graphitizing power that after the magnesium treatment it will produce the gray-colored, spheroidal form of carbon in the casting regardless of whether or not inoculation is used along with or after the magnesium introduction. If the inoculation precedes the introduction of the magnesium, it may not produce the desired results in the as-cast product. This can be remedied by another inoculation along with but preferably after the magnesium introduction. Inoculation may be accomplished by a late addition of an inoculant such as silicon. 1t is preferred to employ silicon in amounts between about 0.3% and 2% or 2.5%, more preferably between about 0.4% and 1.2%, as the late addition to effect inoculation. lt has been found that if the treated bath is held too long after inoculation, the inoculating effect wears off and is lost. This can be compensated for by another inoculating addition which may incorporate a smaller amount of the inoculant, c. g., silicon. As little as about 0.1% or 0.15% of silicon can be introduced to re-inoculate the bath, although, of course, larger amounts may be employed. By periodically reinoculating the bath while maintaining the required retained magnesium content, it is possible to cast a large treated bath over a considerable period of time.

lt is preferred, in carrying out the present invention to produce a product having the higher order of properties and the spheroidal form of carbon in the as-cast condition, to introduce the magnesium into the bath and thereafter separately introduce the graphitizing inoculant which is preferably a silicon-containing inoculant, such as ferrosilicon. While ferro-silicon, e. g., an iron alloy containing a major proportion up to about or 95% silicon, gives satisfactory results as an inoculant, other metallic silicon-containing agents or alloys such as nickel-silicon alloys or nickel silicide, calcium-silicon alloys or calcium silicide, silicon metal, and various proprietary inoculating alloys commonly used for reducing dendriticism and reducing chill in foundry gray cast irons may be employed. .es those skilled in the art know, commercially available ferro-silicon and Various proprietary inoculants usually contain calcium, e. g., up to about 1% calcium. It is also known that ferro-silicon and various proprietary inoculants contain aluminum. In by far the greater number of cases, it is essential that inoculation be employed to produce the aforementioned product having the higher order of properties in the as-cast condition. As magnesium has been found to have by itself a very strong whitening effect, very few molten baths employed in actual practice can ce treated with magnesium in accordance with the invention and cast without inoculation to produce the novel product of the invention or to obtain the novel combination of properties provided by the invention. As an empirical approximation, which may be employed to estimate whether or not a particular bath has such high graphitizing power that inoculation will not be required, it can be said that when the carbon content of the bath plus one-third the silicon content of the bath at the time of the magnesium introduction is approximately 5% or more, then inoculation probably is not required but would still be advantageous. Although, as stated hereinbefore, it is preferred to inoculate the molten bath after the magnesium introduction, it has been found that certain baths having not quite as high graphitizing power apparently can be inoculated prior to the magnesium introduction. For example, a molten inoculated bath containing 4% carbon and 2% silicon (including 0.75% silicon introduced for inoculation) just prior to the magnesium introduction did not require another and subsequent inoculation although such an inoculation of part of the bath was benecial and raised the transverse properties of the product. However, a similar inoculated bath containing about 3% carbon and 2.3% silicon (including 0.75% silicon introduced for inoculation) just prior to the magnesium introduction solidified as a white cast iron when cast after the magnesium introduction without additional accompanying or subsequent inoculation. When a portion of this bath was inoculated after the magnesium introduction with 0.2% silicon and east shortly thereafter, the product of the present invention was obtained. As in predicting the initial graphitizing power of the molten bath to be treated, it must be borne in mind that other factors, well known by those skilled in the art to influence the graphitization of the bath when it is cast, should also be taken into consideration, e. g., the section size of the casting to be produced, the kind of mold to be employed, etc. As an illustrative eramole, a magnesium-treated molten bath containing about 3.5% carbon and about 5 o silicon will not ordinarily require inoculation although such treatment would be preferred. Those magnesium- 'amazes treated baths not requiring inoculation will, in general, contain over 3% carbon. The presence of hard, chilled corners or edges in a casting made from the magnesiumcontaining molten metal is an indication that the graphitizing power is low but near the borderline. This low graphitizing power ordinarily should be compensated for by employing inoculation if it had not been employed or by using more effective inoculation or by otherwise increasing the graphitizing power or graphitization. For some applications, it may be desirable to produce a product having a hard chilled surface portion or outer layer in which the carbon is in the combined form to provide Wear resistance or the like while also obtaining in the product a core or body portion having substantial amounts of uncombined carbon in the spheroidal form and having the improved properties provided by the invention. Such products may be made by controlling the known factors which affect the amount of graphitizaton that will take place in the various portions of the product. It has been found that the magnesium-containing molten composition has a somewhat greater chilling propensity than has a vsimilar magnesium-free gray cast iron composition but the chilling propensity is affected to a lesser extent by lchanges in the carbon content than is that of conventional gray cast iron. The treated inoculated metal can be cast in accordance with accepted foundry technique, bearing in mind that the shrinkage characteristics of the molten alloy are such that castings made from the alloy should be gated and risered more in conformity with the practice employed for steel than that employed for unalloyed or low-alloyed gray cast iron.

The molten composition employed in the present process may be free from alloying elements or may contain substantial amounts of alloying elements, e. g., nickel, molybdenum, chromium, manganese, etc. No common alloying elements in the usual amounts employed heretofore in gray cast iron, with the possible exception of large amounts of copper, have been found to prevent the results -of the invention from being obtained in the as-cast condition. As will be apparent to those skilled in the art, the 'whitening or carbide-stabilizing properties of some alloy- .ing elements must be borne in mind in view of the re- Iquirement that the final bath treated in accordance with .the invention must possess suicient graphitizing power when cast to produce a substantial amount of uncombined carbon in cooling from pouring temperatures. For this reason, it is preferred that the chromium content normally not exceed about 1%, more preferably not over about 0.5% or 0.6%. However, the amount of chromium that can be tolerated depends upon the composition of the final treated bath as a whole, and the maximum amount of chromium is that which will provide a treated bath having the required graphitizing power. Thus, satisfactory results were obtained in an as-cast austenitic ferrous product produced in accordance with the invention which contained about 2% chromium in addition to about 20% nickel, 1.2% manganese, 2.2% silicon, 2.6% `carbon and 0.075% magnesium. Manganese, a milder whitener or carbide-stabilizer can be tolerated in larger amounts, and the results of the invention have been obtained with as-cast compositions containing up to about 2.5% manganese. Larger amounts of manganese can be present when the iinal cast alloy has an austenitic composition or matrix. In general, manganese tends to lower certain mechanical properties, especially in those as-cast :alloys in which the iron is in the alpha form, and it is :preferred that the manganese content not exceed 0.8% tor 1%. Higher ductility and toughness are particularly :notable in such alloys when the manganese content does :not exceed about 0.3%. Aluminum decreases carbide stability and acts as a graphitizer. The term alloying eelements includes residual amounts of those elements :added as treating agents, degasiiiers, etc., and those ele- :ments introduced along with the magnesium as carrier i'elements for magnesium or introduced by master alloys 10 containing magnesium. Copper should not be employed in large amounts as it has been found that this element when present in large amounts interferes with the formation, in the as-cast condition, of the spheroidal or spherical form of carbon required by the present invention. For this reason, it is preferred that copper not be employed in amounts exceeding 3%, and more preferably not exceeding 2%, without first determining the effect of copper upon the carbon formation in the particular composition. Certain alloying elements such as nickel may in conjunction with copper increase the tolerance for the copper. It has been found that certain other elements not usually found in cast iron should be avoided or should be present only in traces or very small amounts because they interfere with the formation of the spheroidal form of carbon and/or the attainment of the high properties provided by the invention. These subversive elements include tin, lead, antimony, bismuth, arsenic, selenium, tellurium, etc. It may be possible to compensate for the presence of a small amount of these subversive elements, preferably less than about 0.1%, by increasing the amount of magnesium introduced into the bath and/or by the introduction of specific elements to form compounds of high stability with the subversive element. The presence or addition of tin has been found to be particularly detrimental, and the tin content should be kept below 0.1%, preferably below 0.05%. It is more preferred that the bath and final alloy be devoid of tin. Phosphorus (which does not interfere with the formation of spheroidal carbon) is usually considered an impurity but may be added sometimes to obtain specific effects. The phosphorus content may be as high as 0.5 or more, but preferably should not exceed approximately 0.25% and more preferably should not be more than about 0.15%. Where high properties, especially impact properties and/or ductility, are desired in the as-cast ferrous alloy, it is recommended that the phosphorus content not exceed 0.06%, for example, 0.02% to 0.06%. In the product produced by the process contemplated by the present invention, the sulfur content is low, usually not exceeding about 0.02%, and is commonly between about 0.007% or 0.010% and 0.015% unless the raw materials and/or the process employed in producing the product introduce less sulfur. Obviously, the lower the amount of subversive, detrimental or interfering elements, the lower the amount of magnesium that need be introduced and retained. The balance of the composition of the bath and of the magnesium-containing product is iron (including small amounts of impurities, preferably less than a total of about 0.5 In most eases, the magnesium-containing product will be unalloyed or lowalloyed and the iron content will be at least about or 87% by weight of the total composition. In the case of the more highly alloyed compositions, usually having an austenitic matrix, the iron content may be considerably lower than 87% but will be at least 50% or 55%. The process embodying the present invention contemplates the production of as-cast cast iron compositions having ferritic matrices, martensitic matrices (such as described in U. S. Patent No. 2,324,322), austenitic matrices (such as those containing 21% or 29% or 36% nickel, etc.), etc.

Introduction of magnesium The introduction of the essential amounts of magnesium required by the present invention can be accomplished in a number of Ways. However, the amount of magnesium to be added to the bath will depend upon the retained magnesium desired, the additional amount of magnesium required to overcome the presence of interfering elements such as sulfur, etc., the amount of magnesium lost by delaying the casting of the bath after the introduction of the magnesium and the proportion of magnesium recovered in the hath from the magnesium addition agent. The last factor involves the losses of magnesium incurred in attempting to introduce the magnesium into the molten bath. This last factor presents considerable ditiiculties, as it has been found that in many cases no magnesium can be recovered from the addition agent employed or only a small amount recovered, e. g. 3% of the amount added. The art has taught that magnesium docs not alloy with iron, and as a matter of fact, when it has been attempted to introduce metallic magnesium in elemental form into a molten bath of iron when the latter was at the ordinary elevated temperature required for satisfactory casting, a reaction of l such explosive violence took place that the molten iron was blown from the receptacle in which it was held. In addition, it is known that the temperatures of molten iron baths usually exceed the boiling temperature of magnesium. The fact that the introduction of elemental magnesium into molten iron baths produces a reaction of explosive violence has been well recognized in the art heretofore, and the introduction of magnesium into molten iron has been generally regarded as being irnpossible on a practical scale. Proposals have been made by the prior art to solve an analogous problem encountered in the introduction of various highly volatilizable elements into molten baths, for example, U. S. Patent No. 1,931,144 relating to the introduction of sodium as sodium vapors into a molten bath to purify the bath. lt has been found that magnesium in the form of a solid magnesiu11i-containing agent can be added in a number of ways to introduce into the molten bath magnesium in a form capable of acting as if it were introduced in elemental form, for example, in a form available to react with sulfur, such as the sulfur which is usually present in the molten carbon-containing ferrous bath being treated in accordance with the process of the invention. Metallic magnesium can be added with due caution in solid elemental form directly to the molten ferrous bath when the bath is cold, i. e., at a temperature not far above the liquidus temperature of the molten composition, e. g., about 2250 to 2400 F. The temperature should be only sufficiently high for the molten bath to be completely molten but viscous. Such an addition of elemental magnesium is accompanied by the burning of the magnesium on the surface of the molten bath with consequent brilliant flashing, evolution of large quantities of magnesium oxide smoke and the loss of by far the greater portion of the magnesium added. However, recovery of sutlcient retained magnesium to obtain the effect on carbon occurrence in the alloy contemplated by the invention can be accomplished by this method if a sufiiciently large amount of magnesium is added. It is important in using this method, however, that the temperature not be fi too high and/or that it not be endeavored to submerge completely and hold the magnesium below the surface of the melt, in order that the attendant reactions not be excessively violent. When this method is used, the

temperature of the melt after the magnesium introduction is then preferably quickly elevated to about 2500 F. or higher to increase the uidity of the bath, to enable it to reject non-metallics and to insure a sound casting when the bath is cast. After elevating the temperature of the bath, it is inoculated, e. g., with about 0.3% or more of silicon7 and then cast in an inoculated condition. Magesium may also be added in the form of briquettes with binders and the like to decrease the burning of the magnesium and to allow the magnesium to become incorporated more quietly and with greater recovery of the magnesium in the bath. Of course, briquettes may also be employed to introduce the magnesium in the other forms described herein, e. g., as magnesium-containing alloys.

It is preferred to add the magnesium as a metallic agent, such as an alloy, containing about 2% to about 4050 magnesium. Suitable alloys include those alloys which are sometimes referred to as intermetallic compounds, e. g., MgNiz, or mixtures of an intermetallic compound with a metal or with another intermetallic compound, e. g., MgNiz-l-Ni or MgNiz-l-MgzNi. It has been found desirable to introduce the magnesium as an alloy with one or more metals in which the magnesium is soluble in the molten condition, these metals in turn being soluble in iron in the molten condition. In carrying the invention into practice, nickel, copper and/or silicon are the preferred metals with which the magnesium is alloyed to form the addition agent. The usefulness of copper is somewhat limited due to the desirability of maintaining the copper content of the nal product relatively low as indicated hereinbefore, e. g., below approximately 2%. The copper concentration of the addition alloy should be such that it will not introduce excessive copper. Likewise, high silicon contents in the final product, e. g., 5% or 6%, or usually undesirable because of their adverse effect on the mechanical propcrties of the final product, and this restricts the usefulness of the high-silicon addition alloys although the final product will contain the required spheroidal form 0f carbon. In practice, very satisfactory results have been obtained with binary and more complex alloys of nickel and magnesium. Preferably, the magnesium should be introduced as an alloy which has a density approaching that of the molten bath or exceeding it, as it has been found that the greater the density the greater the proportion of the magnesium recovered in the molten bath under a given set of conditions. A series of alloys which have given satisfactory results are the nickel-magnesium alloys containing from about 4% to about 20% magnesium. It has been found that when the nickel-magnesium alloys also contain carbon, for example, up to the maximum amount that the alloys will take up, the addition characteristics of the alloys, especially those containing about 10% to 15% magnesium, are improved. Furthermore, by iirst producing a molten nickel-carbon alloy and then introducing magnesium therein, the manufacture of a nickel-magnesium addition alloy is facilitated. Nickel-magnesium-carbon alloys containing 10% to 15% magnesium and containing carbon within the range of about 1% to 4%, preferably about 2% to 4%, have given good results when used as addition agents.

In general, the higher the concentration of magnesium in the addition agent the lower the proportion of magnesium introduced into the molten bath. Various means may be employed to increase the proportion of magnesium introduced into the bath for any given composition, but the high reactivity of magnesium should always be borne in mind. The lower the temperature of the moldten bath at the time of the magnesium introduction, whether as an alloy or in another form, the higher will be the proportion of magnesium introduced from a given agent. Likewise, the proportion of magnesium introduced can be increased by blowing a pulverulent or powdered magnesium-containing alloy through a tube or the like into the molten bath below the surface thereof by means of a gas which is inert or non-oxidizing with respect to magnesium. The proportion of magnesium introduced into the molten bath from a given magnesium-containing alloy of lower density than the molten bath being treated can be increased by submerging the addition alloy below the surface of the bath, e. g., by adding crushed addition alloy to a molten stream of the metal bath being poured into a ladle. From the standpoint of ease of introduction of magnesium, the 96% nickel4% magnesium alloy is very satisfactory because this alloy has about the same density as the molten bath and tends to sink therein so that substantially no burning of magnesium occurs. Because of the high nickel concentration of this addition alloy, substantial amounts of nickel are also introduced in the molten bath and carried over into the nal product. As the magnesium concentration in the nickel-magnesium alloys is increased, the burning and loss of the magnesium is increased since the alloys become progressively less dense and are less immersed in the molten bath. Good, reasonably economic alloys suitable for introducing magnesium into the molten bath are (l) an alloy containing 13 Y t approximately magnesium and approximately 90% nickel and (2) an alloy containing about 12% to 15% magnesium, about 2% to 4% carbon and the balance essentially nickel. Of course, other magnesium-containing alloys can be employed. Thus, the nickel-magnesium alloys may also contain other elements such as silicon, manganese, copper, iron, etc., but it has been found that, in general, the proportion of magnesium introduced into the molten bath from the addition alloy increases as the nickel content of the addition alloy increases. For example, replacing part of the nickel by iron usually decreases the proportion of magnesium introduced from the addition alloy. The following Table I sets forth the approximate composition of some magnesium-containing alloys which can be employed as addition agents for the purpose of introducing magnesium into the molten bath inthe amounts required by the invention.

TABLE I Percent S1 Gu Per- Percent Percent Percent Percent C Mn Fe Others An unusual feature of the invention is that the magnesium treatment very effectively removes sulfur from the molten ferrous bath even when it is under the inuence of acidic conditions such as created by furnace 1inings, ladle linings, slags, etc., of a siliceous nature or other acidic nature as well as under neutral o1' basic conditions created by the furnace lining, the ladle lining, the slag, etc. Another unusual feature of the invention is that the removal of sulfur by the magnesium treatment does not require the presence of any slag and takes place regardless of Whether a slag is or is not present. For example, sulfur can be removed by the magnesium treatment from a molten ferrous bath while it is not covered by a slag and while it is being held in an acid-lined ladle or other acid-lined contained.

The essential features of the novel product produced by the invention are the presence of carbon, and usually silicon, in amounts within the cast iron range, the presence of a substantial amount of the carbon in the uncombined form, and the presence of a small but eifective amount of retained magnesium with the remainder essentially iron to provide an as-cast ferrous matrix in which the soft, gray-colored spheroids of uncombined carbon are dispersed. In other words, the novel product provided by the process embodying the present invention contains a small but effective amount of magnesium, for example, about 0.04% or more magnesium, with the balance of the alloy being a gray cast iron composition. All the carbon present in the product provided by the invention need not be uncombined carbon present in a spheroidal form. Thus, micro-constituents of the ferrous matrix (which may be pearlite, martensite, austenite, bainite, etc.) usually contain combined carbon. In general, less than half of the carbon present in excess of that required to produce the matrix structure will be combined carbon in the product produced by the invention. The uncombined carbon will be present as compacted particles, at least some of these particles and more preferably most or even all of the particles occurring in a substantially spheroidal or spherical, soft, gray-colored form. The occurrence of some of the carbon in the very compact substantially spheroidal or spherical form in the as-cast condition is accompanied by a compacting of the remaining uncombined carbon, but this compacting may be to a lesser extent. This compacting, including the presence of about 25% or more of the uncombined carbon as spheroids or spheres, indicates that a notably improved combination of properties will be obtained.

The product produced by the process embodying the present invention containing the spheroidal form of carbon in the as-cast condition has such a remarkable combination of properties, as compared to those of cast iron, cast steel and pearlitic malleable iron, that it can be classified as a completely new ascast ferrous alloy and provides the art with a new metallic engineering materi-al. The as-cast alloy has excellent founding properties, e. g., it can be readily cast into molds of intricate design, the molds being made of the usual materials employed in molds for casting cast iron. The molten alloy has better castability than steel and has a castability comparable to, or even better than, many grades of cast iron, especially the higher quality gray cast irons which, in order to develop high mechanical proper-ties, are limited to the lower carbon and silicon contents of the cast iron range. The as-cast alloy produced by the process embodying the invention has the desirable property of being strongly self-feeding in the mold, thus providing an automatic check on the quality of the castings made of the new alloy because improperly fed castings often will be misshapen and will exhibit depressed or shrunken regions on the surface. The product produced by the invention has an exceptionally high combination of strength and ductility in the as-cast condition and in this respect is far superior to any cast iron of comparable composition available heretofore. The new product possesses unique elastic properties not possessed by gray cast iron (for example, a straight-line proportionality of stress to strain over a wide range of stresses, a high proportional limit and a consistently high tensile modulus of elasticity of about 25,000,000 pounds per square inch or greater), resistance to the combined effects of oxidation and heat (e. g., growth resistance) superior to that of gray cast iron, and other improved or high properties. In general, the tensile strength of the as-cast product will be more than about 50% greater than would be obtained in the same composition not containing magnesium, and usually the improvement in tensile strength will be or much more, e. g., the tensile strength will be increased over that of the base composition by at least about 40,000 pounds per square inch or much more. In the pearlitic compositions, high tensile strengths on the order of 85,000 pounds to 120,000 pounds per square inch, or even more, are produced in combination with elongations as high as 5% or even more. The properties possessed by the product provided according to the invention are dis closed in detail in our aforesaid Patent No. 2,485,760.

The product provided by the method embodying the present invention may be produced from the usual ferrous raw materials employed in the production of gray cast iron. For example, the novel product can be made from a charge comprised of pig iron as the ferrous raw material. The usual furnaces employed in the production of gray cast iron or malleable iron can be employed in carrying out the process embodying the present invention. Thus, the cupola furnace commonly used in an ordinary foundry can be employed very advantageously in carrying out the invention although other furnaces, e. g., the -arc or induction electric furnace, ythe air furnace, etc.,

may be employed. Duplex melting operations may also be employed. As pointed out hereinbefore, the operations can be carried out under acidic, neutral or basic conditions created by furnace linings, ladle linings, the slags, etc.

Herzt treatment When it is desired to enhance certain particular properties or to modify the combination of properties possessed by the alloy provided according to the present invention, it may be subjected to known heat treatments, including induction hardening, flame hardening and similar surface treatments, to atect particular properties or combinations of properties of ferrous alloys. Thus, the alloy produced by the process embodying the invention can be subjected to heat treatments for stress relief, strengthening, hardening, toughening, etc. These heat treatments include so-called iso-thermal treatments or austempering treatments of ferrous alloys to transform austenite, including any retained austenite, to an acicular constituent at or near the temperatures corresponding to the nose of the S-curve or below said nose but above the martensite transformation temperature. Other illustrative heat treatments which may be employed to modify somewhat the properties of the as-cast alloy of the invention include quenching and drawing, normalizing and drawing, etc. For example, the product can be reheated above the critical transformation temperature, then cooled in air or quenched in oil or water, and then drawn at about 400 F. to about 1250 F. illustrative examples of various heat treating procedures and the properties resulting therefrom are set forth in our aforesaid Patent No. 2,435,760.

A special heat treatment has been found which produces markedly improved ductility in combination with high tensile strength in as-cast alloys having a pearlitic matrix. This heat treatment involves treating a pearl'itic cast alloy within a range of temperatures slightly below the lower critical temperature, generally for at least about one hour. In practice, it is preferred to employ temperaturcs not more than 75 F. below the critical transformation temperature of the composition being treated and more preferably not more than 50 F. below said critical temperature (often also referred to as the critical point or the A1 point, i. e., the lowest temperature where the alpha-gamma transformation takes place in the particular composition involved). It is also preferred that the heat treatment at an elevated temperature slightly below the critical temperature be conducted for at least about two hours. An advantage of this treatment at relatively low temperatures is that it can be carried out in comparatively short periods of time but there are no particular limitations on t'ne maximum time of treatment. Treating times up to fifteen or twenty hours have given satisfactory results, e. g., tive hours or ten hours.

It has been found that the aforementioned special l heat treatment of the magnesium-containing, as-cast ferrous alloy having a pearlitie matrix at atmospheric temperatures and containing the spheroidal form of carbon produces an improved combination of properties, especially an improved combination of ductility and tensile properties, as compared to the properties of malleable iron, e. g., standard or ferritic malleable iron. Because the aforementioned special heat treatment has a ferritizing ciiect on the matrix, this heat treatment has been referred to as a ferritizing treatment and the product as a ferritized product. After the ferritizing heat treatment of the present invention, the magnesium-containing product has a microstructure comprised predominantly or even substantially entirely of a ferrite matrix containing compacted and dense, randomly dispersed, substantially equiaxed particles of uncombined carbon, preferably spherulitoid, spheroidal or spherical in shape. The structure of the heat treated or ferritized product of the invention is preferably substantially free from flake graphite. Generally, no sulfide particles appear in the matrix, whereas ordinary gray cast irons, white cast irons, and malleable irons contain many easily recognized sulfide inclusions embedded in the matrix. The spherulitoid or spheroidal particles in the ferritized product of the invention are soft and gray-colored and are comprised of a large spheroidal or spherical body with a very thin irregular fringe, shell, edging or rim as shown in Fig. 6. Under high magnification, e. g., a magnificaof 1000 diameters at which the particles are usually about 1 to 21/2 inches in average diameter, the spherulitoid or spheroidal particles are generally characterized by a radiating or radial type of structure in the body portion, which is apparently composed of a plurality of crystals radiating from one or more points near the center of the particle. The fringe or edging, which is very thin, has a rougher and pebbly appearance. This edging or fringe does not necessarily appear around the entire circumference of the body portion of the carbon particle.

The ferritized alloy provided by the present invention usually contains over about 1.7% but less than 5% carbon, over 1% but less than 4% silicon, and magnesium usually within the range of about 0.04% to 0.25% or 0.3%. A feature of the composition is that it can have a high graphitizing power such as cannot be present in compositions employed to produce malleable iron. Compositions having such high graphitizinz power that the carbon content plus one-third the silicon content is over 3.5% or 3.7% can be employed to produce the ferritized alloy of the present invention as well as compositions having lower graphitizing power. Many as-cast compositions in which the carbon content plus one-third the silicon content was 4.2% or more have been treated very satisfactorily to produce the heat treated ferritized product of the present invention. in producing the ferritized alloy, it is preferred to maintain the carbon content within the range of 2% to 4.5%, to maintain the silicon content within the range of 1.3% to 3.5%, more preferably within the range of 1.5 /b to 3%, and to maintain the magnesium content within the range of 0.05% to 0.2%, especially within the range of 0.06% to 0.15%. The fact that silicon contents above 1.5% and/or carbon contents above 3% can be employed in part distinguishes the ferritized product of the present invention from high quality malleable iron which has been restricted to low silicon contents, usually not over 1.2% (e. g., 0.8% to 1.2%), and/or low carbon contents, usually not over 2.7% (e. g., 2.0% to 2.7%). Most of the carbon, and often essentially all the carbon, will be uncombined and will be present in the spherulitoid or spheroidal form of uncombined carbon in the ferritized alloy of the present invention. In some instances, for example, when the heat treatment has not been conducted for a sufliciently long time and/ or when the composition contains a substantial amount of carbide stabilizers such as chromium, manganese, etc., a minor proportion of combined carbon or carbides may be present in the final ferritized product. Retained magnesium in the amounts contemplated by the invention has been found to have a very strong whitening effect and to have a tendency to refine pearlite slightly. Although magnesium has a whitening effect, the ductile magnesiumcontaining ferritized product of the present invention can be obtained from the as-cast product of the invention with a considerably shorter heat treatment than is required to obtain ferritic malleable iron. The ferritized alloy may be free from alloying elements or may contain small amounts of alloying elements, particularly nickel. Thus, the alloy to be ferritized may contain the small amounts of nickel, molybdenum, chromium, manganese, etc., that permit obtaining a pearlitic matrix in the as-cast product. The nickel content is preferably less than 4%, e. g., 0.5% to 2.5% or 3%. Molybdenum stabilizes austenite and, in addition, tends to increase the heat treating time required. It is preferred that chromium be absent, although amounts of chromium not exceeding about 0.5% or 0.8% may be present. Manganese preferably does not exceed 0.8% or 1%. Manganese is an austenite stabilizer and, like chromium, interferes to some extent with the ferritizing heat treatment, usually by increasing the heat treating time required, and for this reason is more preferably maintained below 0.4% or 0.3%. It is preferred that copper not be present in large amounts, e. g., in amounts exceeding 2%. While phosphorus may 'be as high as 0.4% or 0.5%, it preferably should not exceed 0.25% and more preferably not more than about 0.06%, as it has been found that phosphorus tends to lower the properties of the ferritized product, especially the ductility and the tensile strength. Due to the presence of magnesium in the product, the sulfur content is low as pointed out hereinbefore. For the reasons set forth previously, the product should be substantially devoid of or should contain only very small amounts of the subversive elements referred to hereinbefore. The balance of the composition is iron except for small amounts of impurities. The iron content, in general, willbe at least about 87% and will usually be at least 90% of the total composition. The final heat treated ferritic product made in accordance with the invention and having the foregoing compositions will have the structure described hereinbefore. v Y

The ferritic product produced by the special heat treatment and having the aforementioned composition and microstructure is distinguished from ferritic malleable iron by an improved combination of founding properties, strength and ductility. Usually, the ferritized castings of the invention possess high ductility which is evidenced by `an elongation in tension of over 5% and as high as 20% or more. The high ductility is obtained in conjunction with higher strength than has been obtained in malleable iron and similar alloys. The high ductility combined with high strength can be obtained in compositions containing more carbon and/or silicon than has been employed in malleable iron. Another feature of the ferritized alloy is that it can be produced in large section sizes, e. g., up to 4 or 5 inches or even more, without unduly sacrificing properties or appreciably increasing the heat treating time required and is not limited to the small section sizes, e. g., up to 1 inch and on occasion up to about 2 inches, which restrict the pro duction of malleable iron products. For example, it has been recognized that increasing the section size up to about 2 inches considerably lowers the properties of malleable iron or increases the heat treating ltime required to produce the same. In addition, a'requirement of malleable iron is that it be made from a cast iron substantially devoid of uncombined carbon in the as-cast condition, i. e., a white cast iron free from lprimary graphite, whereas the ferritized product of the present invention is made from a magnesium-containing ferrous alloy having a substantial amount of thetotal carbon content present in the uncombined form in thev as-cast condition. In actual practice, particularly satisfactory results have been obtained in ferritized products containing about 2.8% to about 3.8% carbon, about 1.5% to about 2.7% silicon, about 0.06% to about 0.15% magnesium, about 0.5% to about 3% nickel, about 0.1% to about 1% manganese, and the balance essentially iron, particularly when the manganese content does not exceed about 0.3% and the phosphorus content does not exceed about 0.05%. Ferritized products having compositions within the aforesaid range, i. e., the most preferred range of compositions, will generally have the following average properties:

Yield strength 45,000-55,000 p. s. i. (0.2% offset) Tensile strength 63,00075,000 p. s. i.

Elongation.. 12 to 18% Hardness 150 to 190 Vickers number j Table'II sets forth data showing the new combination of properties that were obtained in alloy 29 (see Table III) after a ferritizing treatment (No. 4) for ve hours at l300 F. as compared to the properties possessed by the pearlitic product in the as-cast condition.

TABLE II Property As-cast Ferritized Percent Elongation (2 in.) 20. 5 Percent Reduction of area 6. 4 17. 6 Yield strength (0.2%), p. s. i. 60, 100 48, 500 Tensile strength, p. s. i.. 96, 300 66, 100 Vickers hardness 23 181 final heat treated product and compensates for possible variables of production in the initial casting. The higher temperature treatment is satisfactorily accomplished Vby subjecting the castings to one or more temperatures between about 1800 F. and the critical temperature, preferably for at least about one hour and more preferably for at least two hours. There is no particular'limitation upon the maximum time at temperature in this treatment, but generally satisfactory results are obtained in less than about 15 hours, e. g., in about 3 to 5 hours. A suitable treatment comprises subjecting the casting to temperatures between about 1750 F. and 1500o F. This higher temperature treatment which precedes the lower temperature treatment can be effected by holding the casting at one or more temperatures and then cooling at any convenient rate, or by gradually cooling the cast-` ing through the range of temperatures. Such a gradual cooling treatment is obtained by furnace cooling, pit cooling, or even cooling in the mold when the mass is sufficiently large to maintain a slow cooling rate. Average cooling rates of about to 200 F. per hour, e. g., about F. per hour, through the range of temperatures down to the critical temperature can be utilized as the vhigher temperature treatment to produce satisfactory results. The foregoing treatment can be accomplished in a number of ways. For example, in one method which utilizes the heat contained within the hot casting, these hot castings are stripped from their molds at red or black heats, transferred to a preheated pit at 1400 F. to 1800 F., e. g., 1500 F. to 1750 F., and allowedto cool slowly in the pit until the temperature is slightly below the critical temperature, at which point the cooling -is interrupted and the castings held at thatl temperaure for the required time. Alternatively, cold pearlitic castings can be placed in the preheated pit and held for the required time to raise the temperature to within the range of 1400 F. to 1800 F. and then treated in the same manner. Cold castings can also be transferred to a furnace or pit and held at a temperature between 1400 F. and 1800 F., e. g., 1550 F. or 1600 F. or 1700 F. or 1750 F., then air cooled or quenched, e. g., to room temperature or to just below the critical temperature, and then treated at a temperature or within the range of temperatures just below the critical temperature. In general, a temperature range (for treating just below the critical temperature) of about 1270 F. to 1310 F. has given satisfactory results in treating most compositions in accordance with the invention. Instead of holding the casting at one temperature or a plurality of temperatures just below the critical temperature and/ or instead of interrupting the cooling from above the critical temperature when a temperature just below the critical temperature is reached, satisfactory results can be obtained by slowly cooling the casting through the range of temperatures just below the critical temperature, e. g., furnace cooling, pit cooling, or even by cooling extremely slowly in a mold. Slow cooling rates of 50 F. per hour, more preferably 25 F. or 30 F. per hour, or slower, can be used in cooling through the range of temperatures slightly below the critical temperature without interrupting the cooling or Without holding the casting at one or more xed temperatures. The critical temperature is iniiuenced by many factors, as is well known to those skilled in the art. For example, each composition has its own critical temperature. The temperature range set forth hereinbefore is generally suitable for most compositions but may have to be adjusted under particular conditions. Thus, silicon usually raises the critical temperature while nickel lowers the critical temperature. Accordingly, if the nickel content is high, slightly lower temperatures should be employed, while if the silicon content is high, slightly higher temperatures should be employed. Nickel and/or silicon may occasionally be present in the composition in amounts which may require an adjustment in the treating temperature in order to maintain said treating temperature just below the critical temperature as described hereinbefore.

The inuence of the ferritizing treatment on the matrix of the magnesium-containing as-cast alloy produced by the process embodying the present invention is illustrated in Fig. 7. Fig. 7 shows the polished and etched structure at a magnication of 250 diameters of a cupolamelted, magnesium-treated, inoculated gray cast iron composition containing about 3.6% carbon, 2.3% silicon, and the required amount of retained magnesium to provide the spheroidal form of carbon in the as-cast condition after a ferritizing heat treatment comprising cooling slowly in a furnace from 1700 F. to 1280 F. and holding at 1280 F. for ve hours. As illustrated by the etched structure in Fig. 7, the pearlite in the matrix has been converted by the heat treatment to ferrite.

In order that those skilled in the art may have a better understanding of some of the preferred embodiments of the ferritizing heat treatment and of the properties that can be obtained in the ferritized product produced according to the process embodying the present invention, data have been set forth in Tables III, 1V, and V giving the composition (the balance being iron except for small amounts of impurities), the ferritizing heat treatment and the properties of ferritized products made in accordance with the invention from magnesiumcontaining ferrous alloy castings containing the spheroidal form of carbon in the as-cast condition.

TABLE IH Percent Percent Percent Percent Percent Percent Alloy No. Mg Mn P Ni 2. 4 2. 1 0. 067 0.07 0.02 l. 3 3. 3 2. 7 0. 058 0.8 0.02 1. 6 2.1 1. 9 0. 078 0.8 0. 01 1.9 2. 4 1. 0 0. 000 0. 07 0.02 1. 9 2. 6 2. 3 0. 072 0.9 0. 0T 1. 9 3.1 2.1 0. 031 0.8 0. 06 1. 9 3. 4 2. 0 0. 058 0.8 0. 02 1. 9 3. 4 2. l 0.079 0.13 0. 02 l. 9 3.5 2. 3 0. 074 0. 1-0. 2 x11. d. 2. 0 3. 5 2. 4 0. 066 0. 8 0.02 1. 9 3. (i 1.6 0. 001 0. 8 0.02 1. 9 3.6 2.1 0. 075 0. 09 0.02 1. 9 3. 7 1.1 O. 049 0. S 0.02 1. 9 3.8 1.4 0.050 0.8 0. 08 1.9 3.8 1.9 0.083 0.8 0.02 1.9 4.2 2. 3 0. 05% 0.5 0.03 2.3 3. 4 2. 4 0. 019 0. 18 0. 04 2. B 4. 2 2. 3 0.002 0. 5 0. 03 3.0 3. 4 2.1 0. 055 0. 8 0.02 3.1 3.6 2. 3 0.10 0.17 0. 04 3.6 3. 6 2. 3 0. 084 0. 73 0. 04 3. 6

1n. d.-Not determined, low.

TABLE IV No. Heat Treatment 5 0 .As cast (no heat treatment).

5 Cold castings heated t0 about l,750 F., held 5 hrs., furnace cooled to room temperature, reheated to about 1,300" F., held 5 hrs.

6 Cold castings heated to about 1,700 F., held 15 ruin., fur

nace or pit cooled to about 1,280" F., held 5 hrs.

7 Red hot castings (stripped from mold) furnace or pit cooled from about 1.700o F. to about 1,275 F., hc1d2 hrs.

8 Red hot castings (stripped from mold) furnace or pit cooled from about 1,700 F. to about 1,275 F., held 5 hrs.

9 Cold castings normalized by holdingfor 1 br. at about 1,550: F. and air cooling to room temperature. reheatcd Lo about 1.300 F.. held for 5 hrs.

.10 Cold castings heated to about 1,550 F. and held for 1 hr.,

quenched in oil, rehcated to about 1,300c F., held for 5 hrs.

TABLE V Treat- Alloy No ment No. El. R. A. VJIN Y. S. T. S

0 1. 5 336 33,500 96.500 5 14.0 14.0 190 52,500 a0, 200 6 12. 0 11. 4 137 54,500 73,100 5 19. 0 19. 6 195 54. 400 73. 300 0 1. 0 1. 1 347 34, 500 109, 500 5 16. 0 13.0 223 55,500 92, 000 0 0.5 321 70,000 94,500 5 s. 0 9 3 218 57,000 93, 400 6 8.5 9 3 139 52,000 72, 400 0 0. s 296 7B, 000 89, 200 5 s. 5 7. 1 201 47, 500 73, 100 6 8. 5 8. 2 210 57,000 75,300 18 9 7. 5 6. 7 222 63, 000 80, 900 10 6. 5 6. 0 222 63, 500 83, 200 0 1. a 2. 3 299 71,000 100. 300 6 7. 0 8. s 186 54,000 67. 300 9 13. 0 10. 9 197 5s, 500 75, 000 0 5. 0 4. 9 23s 62, 500 100,000 5 15. 0 14.6 137 4s, 000 70,000 6 13. 5 13. 0 192 40,000 72, 400 0 4.0 4.4 59,000 93,000 5 17.0 19. 6 155 45, 000 03, 800 0 7. 0 6. 4 23s 60. 100 90, 300 5 22. 5 21. 3 167 47, 400 04, 500 6 21. 5 21. 5 168 46. 300 64. 000 0 5. 0 8. 9 258 67,000 100,000 5 17. 5 15. 6 179 52, 000 72,000 6 16. 0 17.1 192 56,000 74,700 0 3. 0 2. 3 220 66, 000 110,000 5 13. 0 14. 5 175 43, 500 71,000 0 5.0 4.4 234 60,000 98,000 6 18. 5 15. 6 150 46, 500 63, 900 7 13. 0 9. 8 17s 49,500 6a, 500 0 1.0 1.1 303 64, 500 83,200 5 11. 0 10.2 180 41,000 72, 900 0 2. 5 2. 2 272 03, 500 95, 300 5 11.0 11.3 161 43,000 64,800 0 2. 5 2. 7 238 7s, 000 108, 200 5 12. 5 13. 0 167 49, 500 72, 300 5 10. 5 12. 5 51,000 67, 400 0 2.5 63,000 79,150 5 6.0 49,500 0,000 5 6.0 59,200 72,000 0 5 6.1 203 52,000 71,600 0 3.3 30s 91,000 121,500 5 10. 3 211 66, 500 S5. 500 6 14. 1 202 07,000 78,000 8 15. 6 197 53, 500 76,400 0 1. 7 340 100,000 128.100 5 8. 7 244 76,500 94. 700

R. A.=Percent reduction of area. See footnotes of Table VI for key to terms, etc.

The improvement in ductility obtained by the ferritizing heat treatment is illustrated in Fig. 8 which depicts photographs of originally straight bend-test specimens,

about 6 inches long, after said specimens had been subjected to a bend test to determine their ductility to the point of fracture. All three specimens were made of alloy 29. The top specimen shows the high ductility of the aS-cast alloy. The middle specimen shows the ductility of the alloy after having been given heat treatment 6.

The marked improvement in ductility over the as-cast ductility is shown by the greater amount of bend withstood by the specimen before cracking. The bottom specimen shows the ductility of the alloy after having been subjected to heat treatment 5.

By varying the ferritizing treatment, e. g., the temperatures, the time of treatment, etc., it is possible to obtain various diierent combinations of ductility and strength.

In general, as the ductility is increased, the strength propertiesv of the heat treated casting are decreased and v.vice versa. Thus, the ductility Will usually be higher the longer the treating time just below the critical temperature lof the composition. This effect of varying the treating time is illustrated in Table VI which shows the effect on the properties of alloy 32 of a heat treatment comprising heating cold castings made of said alloy to about l700 F., furnace cooling (e. g., cooling at an average rate of about 80 F. to 100 F. per hour) to about 1275 F., and holding at the latter temperature for the various periods of time indicated in Table VAI.

E1.=Percent elongation iu 2 inches.

R. A.=Percent reduction of area.

VHN=Vickers Hardness Number.

Y. S.=Yield strength (0.2% offset) in pounds per square inch. T. S.=Tensile strength in pounds per square inch.

As indicated by the foregoing data in Table VI and by the data in Tables IV and V, a high combination of properties, particularly-high ductility, can be obtained by a ferritizing heat treatment in which the total time of treatment required is short. The data presented herein illustrate the satisfactory results that can be obtained by the ferritizing heat treatment of the present invention in a total time, including a high temperature treatment, of about 5 to 16 hours. In many cases, particularly those in' which the more preferred maximum amounts of manganese, chromium and other stabilizing elements are not exceeded (and in which other carbide stabilizing factors are not dominant), a satisfactory combination of properties can be obtained by treating hot castings for about two hours at 1275 F. to 1300 F. When a partially pearlitic or spheroidized matrix structure is required, as, for example, where somewhat higher strength with a moderate increase in ductility is desired, the total time of treatment can be shortened. For practical purposes, the pit cooling treatment referred to hereinbefore, e. g., in T able IV, is a particularly satisfactory treatment because it can be carried out in the simplest equipment.

- It has been indicated hereinbefore that the phosphorus content of the ferritized casting is preferably maintained low, Increasing amounts of phosphorus have been found to lower the properties of the ferritized casting, particularly Ithe tensile strength and the ductility (which is indicated by elongation and/ or reduction of area).

It is also preferred that the manganese content of the ferritized product be low, e. g., not more than 0.3% or 0.4%. Manganese apparently stabilizes carbon in the form of carbides, for examplein the pearlite of the matrix, because as the manganese content increases, longer treating times below the critical temperature are required to obtain similar structures. Likewise, it is preferred that the silicon content of the ferritized product not be too high. It has been found that high silicon contents detrimentally affect the properties, particularly the ductility. Silicon in amounts from about 1% to about 3% does not appear to have any detrimental effect on the properties and, in fact, improves the properties as the silicon is increased above 1.5% within this range. A detrimental effect becomes evident at about 3% silicon and becomes quite pronounced when the silicon content exceeds about 3.5%.

It has been found that any free massive carbides existing,yas a` result of production variables, in the pearlitic castings can be removed by the treatment above the critical temperature. Magnesium-containing alloys which arecarbidic as cast but in which the excess'carbon is predominantly in the uncombined form and which contain uncombined carbon in `the spheroidal form, such as magnesium-containing alloys which have Vnot been very effectively inoculated, e. g., been held too long in the ladle after inoculation, can be heat treated to decompose the free carbides by means of the high temperature treatment above the critical temperature, whereby the amount of uncombined carbon in the form of spheroidal bodies increases without the development of graphite in flake form. When the magnesium-containing ferritic product is desired, this treatment is followed by treatment just below the critical temperature. The production of a ferritized product from such a carbidic casting by this method will usually require a longer time, particularly in the high temperature treatment, e. g., at least 2 hours in the high temperature treatment and at least 2 hours in the treatment just belowthe critical temperature.v

The ferritizing heat treatment provided by the present invention has been found to produce particularly satisfactory results when applied to the treatment of magnesium-containing castings having av matrix comprised of pearlite in the as-cast condition. The ferritizing heat treatment can also be applied to other matrices containing combined carbon and having the iron in the alpha form at atmospheric temperatures, for example, matrices containing martensite, bainite, etc. However, these nonpearlitic matrices are more diicult to treat and in general require longer treating times to ferritize the matrix, e. g., at least about 3 or 4 hours. Castings having such anonpearlitic matrix will usually contain larger amounts of alloying elements than Will be present in a pearlitic casting of an analogous composition. Thus, the presence of about 4% or more of nickel, e. g., 4.7% nickel, will usually result in a casting having a martensitic matrix and having a lower critical temperature than if made of a similar pearlitic composition containing less nickel.

It will be appreciated from the foregoing that carbides in the as-cast structure of the casting can be decomposed at a temperature at least as high'as about 75 F. below the critical temperature, e. g., over a range extending from the aforementioned temperature slightly below the critical temperature up to about 1800 F. When the carbides are massive primary carbides, the temperature employed to decompose the carbides should exceed the critical temperature, and when the carbides are a component of the matrix, the temperature should be within 75 F. below the critical temperature.

State of carbon form of carbon having the radiating structure with a polycrystalline appearance has not been conclusively established, but in all tests conducted thereon, the spheroidal form of carbon has exhibited the same behavior, color and individual properties as graphite. Thus, the spheroidal form of carbon has a gray color the same as or very closely similar to that possessed by graphite. Itis also soft like graphite. It behaves in the same manner as graphite under chemical tests. Thus, in the chemical analysis of the alloy provided by the invention for uncombined carbon, it is obtained as a residue after treatf ment with acids in the same manner as a graphite residue is obtained in the chemical analysis of gray cast iron and in the same proportion to the total carbon as if the spheroidal form of carbon were graphite. Like graphite, the spheroidal form ofV gray-colored carbon behaves anisotropically under polarized, reected light. It has a' greasy feel similar to that exhibited by graphite. No evidence has been found to indicate that the spheroidal form of carbon is not graphite. In describing the present` invention, the carbon in the spheroidal form has been referred to as uncombined carbon in View of its-close resemblance in behavior, color and properties to the uncombined carbon obtained as a residue after treatment with acids, as in the chemical analysis of grayl cast iron-,5 and in'v view of the fact that, like the graphite residue, it

is combustible to a gaseous'compound of carbon 'and oxygen. The term uncombined carbon is employed lixr the conventional metallurgical sense as applied to ferrous alloys such as gray cast iron and refers to the presence of the carbon in a substantially uncombincd condition. Thus, while the flake graphite of gray cast iron is conventionally referred to as uncombincd carbon, it is known that this flake graphite often contains small amounts of other elements, particularly iron.

M echa/:ism of invention While the mechanism involved in the present invention is not fully understood theoretically, the conditions which need to be met in the production of the as-cast product containing the spheroidal form of uncombincd carbon are believed to comprise (l) establishing a molten ferrous composition which strongly tends to freeze as a white cast iron, yet the carbides of which are at the same time relatively unstable; and 2) providing a graphitizing tendency opposing the whitening tendency of the molten composition, such as by providing high graphitizing power in the primitive melt or by effective inoculation whereby uncombincd carbon is stimulated to start crystallizing from the melt at a temperature sufficiently high to allow its free growth as spheroids or spheres, largely in liquid surroundings. ing tendencies may be approached variously, provided sufficient control is exercised. The metallurgical relations of magnesium to iron, including the power it possesses to whiten iron and its limited solubility in molten iron, provide a very practical means for the dependable accomplishment of this balance.

As described hereinbefore, the foregoing relationship between opposing tendencies can be realized in accordance with the present invention by melting a charge to establish a bath or melt of such composition, particularly carbon and silicon content, that if then cast, for example, in sand, would result in gray cast iron which contains ake graphite; adding thereto an agent having a strong whitening effect in cast iron in an amount to produce a whitening effect such that the melt if then cast would freeze as a white cast iron, yet the carbides of which are relatively unstable; graphitizing the bath or melt, for example, by adding a graphitizer to produce a graphitized bath or melt which when then cast into molds of the materials usually employed in casting cast iron, e. g., sand, etc., results in a casting of gray cast iron composition containing substantial amounts of uncombincd or free carbon in the spheroidal form and preferably substantially devoid of Hake graphite.

As noted hereinbefore, the metallurgical relations of magnesium to iron make magnesium the most preferable and a very practical means for the purpose of carrying out the process described herein. Magnesium has the required strong whitening effect in cast iron, and when incorporated in a molten gray cast iron in the required amounts results in a bath or melt which would freeze as a white cast iron, a term which herein includes mottled to all-white irons in which the white iron characteristics and structural features predominate, yet the carbides of which are at the same time relatively unstable or, in other words, are metastable carbides. The process disclosed herein thus uses an agent having a carbide metastabilizing effect to produce a metastabilized melt, i. e., uses a carbide metastabilizing or carbide metastabilizer agent. ln order to oppose the foregoing whitening effect which would produce relatively unstable or metastable carbides, a strong graphitizing agent, for example, a ferrosilicon inoculant, is added to the bath or melt to insure that a substantial amount of uncombincd carbon will be in castings made from the bath or melt upon cooling from pouring temperatures. The graphitized bath or melt is then cast to produce castings of gray cast iron composition containing uncombincd carbon or graphite in the desired spheroidal form described and illustrated herein, which form is sometimes also referred to by those skilled in the art as This delicate relationship between opposspherulitic, spheruliticnodular, nodular and spherulitio, etc. (see, for example, the article by H. Morrogh entitled Nodular Graphite Structures Produced in Gray Cast Irons published in American Foundryman, April i948, at pages 9l-l06, particularly pages 91 and 92). lt has been pointed out herein that the agent utilized to provide the required whitening (or carbide metastabilizing) elfect must also stimulate or induce the carbon, dissolved and dispersed in the bath or melt, to crystallize as the spheroidal form of uncombincd carbon; in other words, the agent must be of the type sometimes referred to as the spherulitic nodular-impelling type." As previously noted, the iron castings made in accordance with the present invention are preferably substantially devoid of flake graphite, i. e., substantially devoid of the type of graphite commonly found in gray cast iron which has sometimes been referred to as saucer-shaped or saucer-form flake graphite (see, for example, the American Society for Testing Materials (A. S. T. M.) Designation A247-41T, issued in 1941 and published, e. g., at page 300 in 1941 Supplement to A. S. T. M. Standards, Part I, Metals, November 1941).

Applications The present invention may be applied to the manufacture of a wide variety of ferrous products and articles which will be apparent to those skilled in the art from the properties and structure of the ferrous alloy provided by the invention. These products and articles include those made heretofore of ferrous alloys such as gray cast iron, pearlitic malleable iron, ferritic or standard malleable iron, and even certain grades of cast steels. Illustrative examples of such products and articles include engine crank shafts, dies, car wheels, beds for machine tools, understructures of large steel mill and railroad weighing scales, machinery parts such as roll mill housings and run-out tables for steel mill equipment, rolls such as paper machinery rolls and steel mill rolls, gyratory crusher housings and shells, castings for railroad equipment, for ships, for agricultural implements and machinery and for earth-moving and conveying machinery, pressure castings for valves and pumps such as are used in power stations, in the oil industry and in the mining industry, furnace parts, melting and heat treating pots, manifolds and other articles subjected to heat, composite products in which the material provided by the invention forms one or more components, e. g., steel mill rolls with machinable necks in combination with a non-machinable martensitic body, car wheels having a steel rim with the material provided by the invention forming the hub and web, composite rolls having roll shells made of the material provided by the invention, and centrifugally cast products having one metallic material in the outer portion and another metallic material in the inner portion. innumerable other applications utilizing the improved combination of properties provided by the product embodying the present invention will be apparent to those skilled in the art.

It is to be observed that the present invention provides a novel method for producing a novel gray cast iron product having a novel, unusual, and highly useful combination of founding properties and mechanical and physical properties, and that the novel process provided by the invention is applicable to cast iron compositions readily handled in the gray cast iron foundry. Thus, in carrying out the present process under practical foundry conditions in a conventional foundry, ordinary gray cast iron baths containing about 3.3% to about 3.6% carbon and about 1.7% to about 2% silicon are treated with magnesium and are inoculated to yield final gray cast iron compositions containing the aforesaid amounts of carbon, about 0.06% to about 0.1% magnesium and about 2.2% to about 2.7% silicon. The aforesaid baths of ordinary foundry irons are readily and economically handled in the usual foundry equipment, have excellent fluidity and castability, have low shrinkage in the mold, require little 25 feeding, etc., while the aforesaid products have very good c ombinations of properties.

This application is a continuation-impart of our copending U. S. application Serial No. 787,420, filed November 21, 1947, now Patent No. 2,485,760, granted October 25, 1949.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to Without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such variations and modifications apparent to those skilled in the art are considered to be Within the purview and scope of the invention and the appended claims.

We claim:

1. The method for producing a ductile cast iron having a microstructure containing in the as-cast condition uncombined carbon in a spheroidal form and characterized by a high combination of properties which comprises establishing a molten ferrous bath containing about 2% to about 4.5 carbon, about 0.5% to about 3.5% silicon, with the sum of the percentage of carbon plus one-third the percentage of silicon being not more than about 5, and the balance a gray cast iron composition when cast in an inoculated condition and having iron in the alpha form at atmospheric temperatures, introducing into said ferrous bath magnesium in an amount to provide about 0.06% to about 0.15% magnesium in castings made from said bath, thereafter inoculating the magnesium-containing bath with about 0.3% to about 2.5 silicon as a silicon-containing agent and casting the metal from said inoculated bath in an inoculted condition to produce a ferrous alloy casting containing the aforesaid amounts of retained magnesium to cause the occurrence of uncombined carbon in a spheroidal form in the as-cast condition and devoid of subversive amounts of elements materially interfering with the elfect of magnesium in causing the occurrence of uncombined carbon in said spheroidal form. 2. VThe method for producing a ductile cast iron having a microstructure containing in the as-cast condition uncombined carbon in a spheroidal form and characterized by a high combination of properties which comprises establishing a molten ferrous bath containing about 2.5% to about 4% carbon, about 0.5% to about 3.5% silicon, with the sum of the percentage of carbon plus one-third the percentage of silicon being not more than about 5, and the balance being a gray cast iron composition when cast in an inoculated condition and having iron in the alpha form at atmospheric temperatures', introducing'into'said ferrous bath magnesium' in an amount to provide about 0.05% to about 0.2% magnesium retained in castings made from said bath, thereafter inoculating the magnesium-containing bath with about 0.4% to aboutl 1.2% silicon'as ferrosilicon and casting the metal from said inoculated bath shortly after an inoculation to produce a ferrous alloy casting containing the aforesaid amounts of retained magnesium to cause the occurrence of uncombined carbon ina spheroidal form in the as-cast condition and devoid of subversive amounts of elements materially interfering with the effect of magnesium in promoting the occurrence of uncombined carbon in said spheroidal form.

3. The method for producing a ductile cast iron having a microstructure containing in the as-cast condition uncombined carbon in a spheroidal form and characterized by a high combination of properties which comprises establishing a molten ferrous bath containing about 1.7% to about 4.5% carbon, about 0.8% to about 5% silicon, with the sum of the percentage of carbon plus one-third the-percentage of silicon being not more than about 5, and the balance a gray cast iron composition when cast in fan inoculated condition and having iron in the alpha form'y at atmospheric temperatures, introducing into'said ferousbath magnesium in an amount to provide about 0.035% to about 0.4% magnesium retained in castings made from said bath, inoculating the ferrous bath with about 0.3% vto about 2.5 silicon as' a silicon-containing agent such that said inoculation does not precede said magnesium incorporation and casting the metal from said inoculated bath in an inoculated condition to produce a ferrous alloy casting containing the aforesaid amounts of retained magnesium to cause the occurrence of uncombined carbon in a spheroidal form in the as-cast condition and devoid of subversive amounts of elements materially interfering with the effect of magnesium in promoting the occurrence of uncombined carbon in said spheroidal form.

4. The method for producing a ductile cast iron having a microstructure containing in the as-cast condition uncombined carbon in a spheroidal form and characterized by a high combination of properties which comprises establishing a molten ferrous bath having such a composition as to be a gray cast iron when cast in an inoculated condition and containing carbon and silicon such that the sum of the percentage of carbon plus one-third the percentage of silicon does not exceed 5, introducing into said ferrous bath magnesium in an amount sucient to provide at least a small but effective amount up to about 0.5% magnesium retained in castings made from said bath, inoculating the ferrous bath with at least about 0.2% silicon as a siliconcontaining agent such that said inoculation does not precede said magnesium incorporation and casting the metal from said inoculated bath in an inoculated condition to produce a ferrous alloy casting having iron in the alpha form and containing the aforesaid amounts of retained magnesium to cause the occurrence of uncombined carbon in a spheroidal form in the as-cast condition and devoid of subversive amounts of elements materially interfering with the effect of magnesium in promoting the occurrence of uncombined carbon in said spheroidal form.

5. The method according to claim 4 wherein magnesium is incorporated into the molten ferrous bath in the form of an alloy containing about 4% magnesium with the balance essentially nickel.

6. The method of producing an improved gray cast iron having the free carbon thereof in spheroidalforrn comprising melting a charge of iron of such carbonand silicon content that if cast in an inoculated condition would result in a gray cast iron containing ake graphite, introducing magnesium into said melt in quantities suicient to produce a white cast iron if cast, and thereafter graphitizing the melt suflciently to produce a spheroidal graphite gray cast iron casting from the melt with substantially complete absence of ake graphite.

7. vThe method of producing cast iron comprising melting a chargel of such composition that if inoculated and cast in vsand would result in a gray cast iron containing flake graphite, introducing magnesium into the melt in such amount that the treated melt if cast in sand would result in a white iron, adding a graphitizing agent to the melt in such amount that the graphitized melt if cast in sand would result in gray iron, and finally pouring a casting from said melt.

8. The' method of producing graphitic cast iron having the free carbon thereof in nodular and spherulitic form comprising, melting a charge of iron of such carbon and silicon content that if cast in the absence of a carbidemetastabilizer agent of the spherulitic nodular-impelliug type would result in a gray cast iron containing saucerform flake graphite, and adding said carbide-metastabilizer agent to the melt in quantity sucient to produce a mottled to-all-white iron if cast, the metastabilizer agent dissolving and dispersing the carbon in the melt, andi thereafter graphitizing the melt sufdciently to produce a spherulitic modular-graphite gray cast iron casting from the melt with substantially complete absenceof saucerform flake graphite. v.

9. The method of producing cast iron comprising, melting a charge of such composition that if cast in sand would result in a gray cast iron containing flake graphite,v adding a carbide-metastabilizingagent tothe melt in 27 such amount that the treated melt if cast in sand would result in a substantially mottled to all-white iron, adding a graphitizing agent to the meta-stabilized melt in such amount that the graphitized melt if cast in sand would result in gray iron, and nally pouring a casting from said melt.

l0. The method of producing graphitic cast iron having the free carbon thereof in nodular and spherulitic form comprising, melting a charge of iron of such carbon and silicon content that if cast in the absence of a carbidemetastabilizer agent of the spherulitic nodular-impelling type would result in a gray cast iron containing saucerform flake graphite, and adding said carbide-metastabilizer Iagent to the melt in quantity sufficient to produce a mottled to all-white iron if cast, and thereafter graphitizing the melt sufficiently to produce a spherulitic nodulargraphite gray cast iron casting from the melt with substantially complete absence of saucer-form ake graphite.

l1. The method of producing graphitic cast iron having uncombined carbon in spheroidal form as cast comprising establishing a molten iron composition of such carbon and silicon content that if cast in an inoculated condition it would result in a gray cast iron containing flake graphite, introducing in said molten iron compositionmagnesium in an amount less than about 0.5% but sufficient to produce a cast iron which tends, if cast, to be white cast iron containing relatively unstable carbides and graphitizing the molten iron composition, and casting molten magnesium-containing iron to produce a spheroidal graphite cast iron.

12. A method of producing an improved graphitic cast iron having a microstructure containing uncombined carbon in the as-cast condition in spheroidal form in a matrix having iron in the alpha form which comprises establishing a melt of molten iron composition containing at least about 87% iron and an amount of magnesium sufficient in the absence of inoculation to cause the molten iron composition to possess higher chilling propensity than the molten iron composition Without magnesium, said melt being one which in the absence of magnesium would produce, when cast, gray cast iron having its uncombined carbon predominantly in the form of ake graphite; inoculating magnesium-containing iron from said melt with a graphitizing agent; and casting the inoculated magnesium-containing iron to obtain a graphitic cast iron containing at least about 87% iron and containing in the ascast condition uncombined carbon in a spheroidal form in a matrix having iron in the alpha form.

13. A method of producing an improved graphitic cast iron having a microstructure containing uncombined carbon in the as-cast condition in substantially spheroidal form in a matr-ix having iron in the alpha form comprising establishing a molten iron composition which if cast in an inoculated condition would be a gray cast iron containing tiake graphite in a matrix having iron in the alpha form, introducing in said molten iron composition an amount of magnesium suiiicient to cause the molten iron composition to tend to freeze as a white cast iron containing carbides which are relatively unstable, introducing an inoculant in the molten iron composition to provide a graphitizing effect to overcome the whitening tendency of the molten magnesium-containing iron composition, and casting the molten magnesium-containing iron composition in an inoculated condition and with less than about 0.02% sulfur to obtain a graphitic cast iron having iron in the alpha form and being substantially devoid of subversive amounts of elements materially interfering with the effect of magnesium in promoting the occurrence of uncombined carbon in a substantially spheroidal form in the graphitic cast iron in the as-cast condition.

14. A method of producing an improved graphitic cast iron having a microstructure containing uncombined carbon in the as-cast condition in spheroidal form in a matrix having iron in the alpha form which comprises introducing in a molten iron bath of such composition that, if

cast in an inoculated condition, it would be a gray cast iron having iron in the alpha form and containing ake graphite, an amount of magnesium suicient to provide a molten composition which strongly tends to freeze as a white cast iron containing carbides which are relatively unstable and containing less than about 0.02% sulfur, introducing a graphitizer in the molten iron composition to provide a graphitizing tendency overcoming the whitening tendency imparted by the magnesium to the molten iron composition, and casting the treated molten iron composition to obtain a graphitic cast iron having iron in the alpha form and substantially devoid of subversive amounts of elements materially interfering with the aforesaid occurrence of spheroidal uncombined carbon when cast.

l5. A method of producing a casting of an improved graphitic cast iron having a microstructure containing uncombined carbon in the as-cast condition in spheroidal form in a matrix having iron in the alpha form which comprises establishing a molten iron composition which, if cast in an inoculated condition, would be a gray cast iron containing at least about 87% iron and containing flake graphite in a matrix having iron in the alpha form, introducing in said molten iron composition magnesium in an amount less than about 0.2% suflicient in the absence of inoculation to cause the molten iron composition to tend to freeze as a white cast iron containing carbides which are relatively unstable and introducing a siliconcontaining inoculant to provide a graphitizing effect, and thereafter casting in an inoculated condition molten magnesium-containing iron with less than about 0.02% sulfur and substantially devoid of subversive amounts of elements materially interfering with the effect of magnesium in promoting the occurrence of spheroidal uncombined carbon into a casting of graphitic cast iron containing at least about 87% iron and having a microstructure containing uncombined carbon in the as-cast condition in spheroidal form in a matrix containing iron in the alpha form.

16. The method of making an improved graphitic cast iron which comprises producing a molten iron composition having such carbon and silicon content and such graphitizing power that if cast it would produce gray cast iron containing flake graphite in a matrix having iron in the alpha form; treating said molten iron composition to introduce therein magnesium in the presence of high graphitizing power and in an amount suicient to induce the occurrence of uncombined carbon in a substantially spheroidal form in the graphitic cast iron when cast; and thereafter casting the molten iron composition, while retained magnesium and graphitizing power are effective, to produce graphitic cast iron possessing, when cast, a microstructure containing uncombined carbon in a substantially spheroidal form in a matrix containing iron in the alpha form.

17. A method as set forth in claim 16 wherein a graphitizing inoculant is added to provide high graphitizing power.

18. In a method for producing graphitic cast iron, the improvement comprising establishing a molten iron composition having a cast iron composition containing at least about 87% iron, introducing magnesium in said molten iron composition in suicient amount to provide in the cast iron when cast a retained magnesium content less than about 0.5% and suicient to promote the occurrence of substantially spheroidal graphite in the graphitic cast iron when cast and adding a graphitizing inoculant to said molten iron composition in such manner that it does not substantially precede the magnesium introduction and in an amount adequate to produce graphitic cast iron when cast, whereby a casting of magnesium-containing graphitic cast iron can be produced having a structure in the as-cast condition containing graphite in a substantially spheroidal form.

19. A method of producing an improved graphitic cast iron having a microstructure containing uncombined carbon in the as-cast condition in substantially spheroidal form in a matrix having iron in the alpha form which comprises establishing a molten iron composition which, in the absence of magnesium, would produce gray cast iron having its uncombined carbon substantially in the form of flake graphite and which contains at least about 87% iron and magnesium less than about 0.5% effective to induce, when cast after inoculation, the occurrence of uncombined carbon in a substantially spheroidal form; subsequently inoculating said molten iron composition containing magnesium with a graphitizing agent; and casting said inoculated magnesium-containing iron composition to obtain a graphitic cast iron containing at least about 87% iron and containing in the `as-cast condition uncombined carbon in a substantially spheroidal form in a matrix having iron in the alpha form.

20. The method of producing an improved graphitic cast iron having a microstructure containing when cast uncombined carbon in a substantially spheroidal form which comprises establishing a molten iron composition which lif cast in an inoculated condition would be a gray cast iron containing ake graphite, introducing into said molten iron composition an amount of magnesium suilicient to retain less than about 0.5 magnesium therein effective to induce the occurrence of at least about 25% of the uncombined carbon in a substantially spheroidal form when cast and inoculating the molten iron composition with a silicon-containing graphitizer, and thereafter casting the inoculated magnesium-containing iron to obtain a graphitic cast iron having at least about 25% of the uncombined carbon therein in a substantially spheroidal form in the as-cast condition.

2l. A method for producing an improved graphitic cast iron having a structure in the as-cast condition containing uncombined carbon in substantially spheroidal form comprising establishing a molten iron composition which would be gray cast iron containing flake graphite if cast in an inoculated condition, introducing magnesium into said molten iron composition in suicient amount to provide in the graphitic cast iron when cast a retained magnesium content suiiicient to promote the occurrence of at least about 25% of the graphite in substantially spheroidal form in said graphitic cast iron when cast, adding a graphitizing inoculent to said molten iron composition in such manner that it does not substantially precede the magnesium introduction and in an amount suiicient to produce graphitic cast iron when cast, and thereafter casting said magnesiumcontaining, inoculated molten iron to obtain graphitic cast iron containing at least about 25% of the graphite in substantially spheroidal form.

22. A method for producing improved graphitic cast iron comprising establishing a molten iron bath having such a cast iron composition that, if cast after inoculation, it would have a gray cast iron structure and would contain about 1.7% to about 5% carbon, about 0.5% to about 6% silicon, and at least 87% iron; introducing magnesium in the molten iron composition in suiicient amount to provide in the graphitic cast iron when cast a retained magnesium content less than about 0.5 sufficient to promote the occurrence of substantially spheroidal graphite in said graphitic cast iron and providing a graphitizing inoculant in an amount adequate to produce graphitic cast iron, when cast; and thereafter casting the molten magnesium-containing iron composition in an inoculated condition and with low sulfur and oxygen to obtain a graphitic cast iron containing at least about 87% iron, having iron in the alpha form and containing uncombined carbon in a substantially spheroidal form in the as-cast condition.

23. The method of producing an improved graphitic cast iron having a microstructure containing when cast at least about 25% of the uncombined carbon in a substantially spheroidal form in a matrix having iron in the alpha form which comprises establishing a molten iron bath having such a composition that if cast in an inoculated condition it would be a gray cast iron containing at least about 87% iron and containing ake graphite in a matrix having iron in the alpha form, introducing into the molten iron composition an amount of magnesium sufcient to retain less than about 0.2% magnesium'therein effective to induce the occurrence of at least about 25 of the uncombined carbon in a substantially spheroidal form and inoculating the molten iron composition with a silicon-containing graphitizer, and casting inoculated magnesium-containing molten iron with a sulfur content less than about 0.02% to obtain a graphitic cast iron containing at least about 87% iron and having at least about 25% of the as-cast uncombined carbon therein in a substantially spheroidal form in a matrix having iron in the alpha form.

References Cited in the le of this patent UNITED STATES PATENTS 1,801,742 Hayes Apr. 21, 1931 2,467,406 Reece Apr. 19, 1949 2,485,760 Millis et al. Oct. 25, 1949 2,496,863 Deschamps et al Feb. 7, 1950 OTHER REFERENCES Cast Metals Handbook, 1944 edition, pages 523 to 526.

Claims

1. THE METHOD FOR PRODUCING A DUCTILE CAST IRON HAVING A MICROSTRUCTURE CONTAINING IN THE AS-CAST CONDITION UNCOMBINED CARBON IN A SPHEROIDAL FORM AND CHARACTERIZED BY A HIGH COMBINATION OF PROPERTIES WHICH COMPRISES ESTABLISHING A MOLTEN FERROUS BATH CONTAINING ABOUT 2% TO ABOUT 4.5% CARBON, ABOUT 0.5% TO ABOUT 3.5% SILICON, WITH THE SUM OF THE PERCENTAGE OF CARBON PLUS ONE-THIRD THE PERCENTAGE OF SILICON BEING NOT MORE THAN ABOUT 5, AND THE BALANCE A GRAY CAST IRON COMPOSITION WHEN CAST IN AN INOCULATED CONDITION AND HAVING IRON IN THE ALPHA FORM AT ATMOSPHERIC TEMPERATURES, INTRODUCING INTO SAID FERROUS BATH MAGNESIUM IN AN AMOUNT TO PROVIDE ABOUT 0.06% TO ABOUT 0.15% MAGNESIUM IN CASTINGS MADE FROM SAID BATH, THEREAFTER INOCULATING THE MAGNESIUM-CONTAINING BATH WITH ABOUT 0.3% TO ABOUT 2.5% SILICON AS A SILICON-CONTAINING AGENT AND CASTING THE METAL FROM SAID INOCULATED BATH IN AN INOCULTED CONDITION TO PRODUCE A FERROUS ALLOY CASTING CONTAINING THE AFORESAID AMOUNTS OF RETAINED MAGNESIUM TO CAUSE THE OCCURRENCE OF UNCOMBINED CARBON IN A SPHEROIDAL FORM IN THE AS-CAST CONDITION AND DEVOID OF SUBVERSIVE AMOUNTS OF ELEMENTS MATERIALLY INTERFERING WITH THE EFFECT OF MAGNESIUM IN CAUSING THE OCCURRENCE OF UNCOMBINED CARBON IN SAID SPHEROIDAL FORM.