US2750284A - Process for producing nodular graphite iron - Google Patents

Description

June 12, 1956 Filed Dec. 22, 1951 H. K. IHRIG PROCESS FOR PRODUCING NODULAR GRAPHITE IRON 10 Sheets-Sheet l FERROUS METAL CONTAINING GRAPHITE YIELDING CARBON 2500 F EaT T MELT UNLESS ALREADY MEIJ'ED HALIDE 0F NODULARIZING ELEMENT u, m, Mg, s, Bu, Rb, c

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June. 12, I956- H. K. lHRlG 2,750,284

PROCESS FOR PRODUCING NODULAR GRAPHITE IRON Filed Dec. 22, 1951 10 Sheets-Sheet 2 Q/vw M/v MAM 9i. SW

June 12, I956 H. K. lHRlG PROCESS FOR PRODUCING NODULAR GRAPHITE IRON Filed Dec. 22, 1951 10 Sheets-Sheet 3 mow/mg June 12, 1956 H. K. IHRIG PROCESS FOR PRODUCING NODULAR GRAPHITE IRON Filed Dec.

10 Sheets-Sheet 4 v June 12, 1956 H. K. IHRIG PROCESS FOR PRODUCING NODULAR GRAPHITE IRON Filed Dec. 22, 195! 10 Sheets-Sheet 5 June 12, 1956 K. lHRlG PROCESS FOR PRODUCING NODULAR GRAPHITE IRON 10 Sheets-Sheet 6 Filed Dec. 22, 1951 June 12, 1956 K. IHRIG PROCESS FOR PRODUCING NODULAR GRAPHITE IRON 10 Sheets-Sheet 7 Filed Dec. 22, 1951 June 12, 1956 H. K. [HRIG 2,750,284

PROCESS FOR PRODUCING MODULAR GRAPHITE IRON Filed Dec, 22', 1951 1.0 Sheets-Sheet 8 B W M M. m m

June 12, 1956 H. K. IHRIG PROCESS FOR PRODUCING NODULAR GRAPHITE IRON 10 Sheets-Sheet 10 Filed Dec. 22, 1951 BRINELL HARDNESS ELONGATION IN 2 IN.

PHYSICAL PROPERTIES (u a YIELD TENSILE 050W HEAT United States Patent PROCESS FOR PRODUCING NODULAR GRAPHITE IRON Harry K. Ihrig, Milwaukee, Wis., assignor to Allis- Chalmers Manufacturing Company, Milwaukee, Wis.

Application December 22, 1951, Serial No. 262,957

8 Claims. (Cl. 75-430) This invention relates generally to ferrous metal alloys and to processes for making them and specifically to the production of an as-cast ferrous metal containing spherular granule of graphite. The invention is also useful in providing a novel, simple and economical process for introducing into ferrous metal certain metals which have an influence upon the configuration of carbon inclusions in the ferrous metal but which metals are ordinarily dimcult to introduce because of their volatility, chemical activity and other properties.

A ferrous metal which is high in carbon, and has its carbon inclusions in the form of graphite flakes is commonly termed cast iron. It is known that the physical properties of such ferrous metal, particularly the tensile strength, yield point and percent elongation, are im proved by (l) reducing the size of the graphite flakes, (2) distributing the flakes more uniformly throughout the metallic matrix, and (3) inducing a specialized pattern of distribution of the graphite flakes. Because the flakes have flat leaf-like configurations which introduce major discontinuities into the metallic matrix, there is a limit to the improvement of physical properties, particularly ductility, which can be achieved by any of the foregoing methods.

It has long been known that the physical properties of ferrous metal high in carbon, particularly the ductility, can be markedly improved by inducing the graphite inclusions to assume compacted shapes, sometimes in a form aptly described as nodular or spheroidal. When the graphite inclusions are compacted, the metallic matrix is substantially continuous and free of the major discontinuities inherent in matrices having flake or flake-like inclusions of graphite. The recognized superior physical properties of so-called malleable cast iron (a kind of iron made by a lengthy heat treating of white iron which has almost all its carbon in combined form) are attributable directly to the compacted form of the graphite inclusions although such inclusions (called temper carbon) are not strictly nodular or spheroidal in shape, as the terms are used herein.

Cast ferrous metal, containing graphite-yielding carbon, which exhibits a microstructure characterized to a substantial degree by compacted graphite inclusions which are spherular has come to be known as nodular iron and, because it has superior physical properties, it is deemed a highly desirable material for many structural purposes. Nodular irons advantage over gray cast or malleable cast iron lies not only in its improved physical properties, but also in the fact that nodular iron can be cast directly from the melt and does not require heat treatment after casting. Whereas malleable cast iron, which has physical properties superior to gray cast iron but generally inferior to nodular iron, can only be made from white cast iron which has been subjected to a costly, time consuming and relatively complicated heat treatment.

The production of nodular iron, therefore, has drawn the attention of investigator, with the result that several methods for its production have heretofore been proposed.

Patented June 12, 1956 The majority of these methods call for introducing into molten iron containing graphite-yielding carbon one or more substances capable of inducing the formation of spheroidal graphite and then casting the molten metal to obtain nodular iron.

Among the substances heretofore mentioned for addition to molten iron containing graphite-yielding carbon to induce the formation of spheroidal graphite without subsequent heat treatment after casting are magnesium, calcium, strontium, barium, tellurium, cerium and zirconium. It has heretofore been proposed to introduce one or more of these substances into the molten iron by bringing into contact with the molten iron either (1) the substance in elemental form, (2) an alloy of the substance, (3) a mixture of the substance with inert ingredients, or (4) a chemical compound of the substance with oxygen.

There are certain disadvantages to introducing these substances into the molten iron in any of the aforementioned forms.

For example, introducing magnesium in elemental form is impracticable as well as hazardous because magnesium has a boiling point below the melting point of a eutectic iron carbon solution and will vaporize when brought into contact with the melt. The flashing of magnesium metal to vapor under such circumstances occurs with enough explosive violence to blow portions of molten iron from the melt.

Since the temperature of a ferrous metal melt previous to pouring is generally maintained around 1500 C., the same disadvantage accompanies the introduction of calcium, barium, tellurium, and cerium in elemental form since the respective boiling points of these elements in degrees centigrade are 1170, 1140, 1390 and 1400.

Introducing the spheroidal graphite inducing substances alloyed with metals or nonmetals or mixed with inert materials, into the molten iron has the disadvantage of not only introducing unwanted ingredients into the iron, but in many cases of requiring the use of ingredients which are costly or difficult to obtain. For example, it has heretofore been proposed to use magnesium metal alloyed with one or more of the following: silicon, nickel, aluminum, chromium, titanium, vanadium, molybdenum, manganese and copper.

The addition of magnesium alloyed with certain metals such as nickel or copper is particularly undesirable when there is likelihood that the cast iron may later be used as scrap, since nickel and copper cannot economically be removed from the scrap metal. In some cases the alloying material may produce when added to the molten metal an elfect opposite to the graphitizing effect of the spheroidal graphite inducing substance. Vanadium, for example, is one such material. Vanadium is a powerful carbide forming element and when added to gray iron will restrain graphitization. Moreover, the majority of the alloying metals proposed are strategic metals and in war times or in times of national emergency may be so strictly allocated as to be virtually unobtainable.

Bringing molten iron into contact with a compound consisting of an oxide of a spheroidal graphite inducing substance has heretofore been mentioned as another method for producing nodular iron. For example, it has been proposed to bring molten iron containing graphiteyielding carbon into contact with magnesia (magnesium oxide), with silicon or ferrosilicon and perhaps small proportions of halides such as magnesium chloride, calcium fluoride or magnesium fluoride present, at temperatures above 1100 C. However, this particular prior art process has not been effective in producing nodular iron within temperature ranges ordinarily found in foundry practice; namely, 1100 C. to 1650 C.

Still another method heretofore proposed for making nodular iron consists of bringing magnesia (magnesium oxide) into contact with molten iron at temperatures above 1650" C. Temperatures above 1650 C. are not normally met with in iron foundry practice. For example, the normal temperature range in the melt Zone of a cupola in an iron foundry lies between 1370 and 165 C. Temperatures above this range can only be attained by increasing the normal rate of fuel consumption. Such increase means not only higher fuel costs but also higher maintenance costs because temperatures in the melt zone in excess of 1650 C. require special refractory linings which cost more than linings suitable for lower temperatures. Furthermore, the higher the temperature the shorter the life of the refractory lining and the more lining replacements necessary per ton of iron output.

7 The primary object of the present invention is to avoid the disadvantages of the prior art through the provision of an improved method for effecting the formation of spherular granules of graphite in cast ferrous metal containing carbon.

Another object of the invention is to provide an im proved method of adding to molten ferrous metal containing carbon the agents which induce the formation of spherular granules of graphite in the ferrous metal as the ferrous metal cools to the solid state.

Another object of the invention is to provide an improved method for effecting a reduction in the proportion of flake graphite to spherular graphite in cast ferrous metal containing carbon.

Another object of the invention is to provide an improved method for introducing into molten ferrous metal certain alloying metals which would ordinarily be volatile at the temperature of the molten ferrous metal.

Another object of the invention is to provide an improved method for avoiding an explosive condition when introducing into molten ferrous metal an alloying agent containing a metal which would ordinarily be volatile at a temperature below the temperature of the molten ferrous metal.

Another object of the invention is to provide an improved method for increasing the tensile strength, yield point, ductility and modulus of elasticity of ferrous metal containing carbon.

Another object of the invention is to provide an improved method of introducing into molten ferrous metal nodularizing metals selected from the group consisting of lithium, sodium, magnesium, strontium, barium, rubidium and cerium.

Another object of the invention is to provide an improved method for producing a nodular graphite cast ferrous metal which is substantially free from nickel or copper in the as-cast state.

Another object of the invention is to provide an irnproved process for the manufacture of nodular graphite ferrous metal which avoids the introduction of nickelmagnesium and copper-magnesium alloys into the ferrous metal.

Another object of the invention is to provide an improved method for making nodular graphite cast ferrous metal in which the nodularizing reagent is distributed throughout the ferrous metal.

Another object of the invention is to provide an improved method of manufacturing a cast ferrous metal containing carbon, having at least a portion of the free graphite distributed throughout the as-cast ferrous metal in the form of substantially spherular granules, wherein heat treatment of the ferrous metal after casting is avoided.

Another object of the invention is to provide an improved method for making nodular graphite cast ferrous metal, which method is economical and simple to perform.

Another object of the invention is to provide an 1mproved cast ferrous metal containng carbon which has physical properties in the as-cast condition supenor to the physical properties of ordinary gray cast iron in the as-cast condition.

Another object of the invention is to provide an improved cast ferrous metal containing carbon which has a tefnsile 1strength, yield point and ductility similar to that o stee.

Another object of the invention is to provide an improved cast ferrous metal containing carbon which has a modulus of elasticity substantially equal to or greater than that of malleable iron.

Another object of the invention is to provide an improved cast ferrous metal containing carbon but substantially free from nickel and copper, which cast ferrous metal exhibits physical properties substantially equal or superior to prior art cast irons containing nickel or copper.

Another object of the invention is to provide an improved method for adding to molten ferrous metal containing carbon certain substances capable of inducing the formation of spherular granules of graphite in the ferrous metal as the metal solidifies without introducing oxygen into the metal.

The present invention proposes to achieve the aforesaid objects by bringing together molten ferrous metal containing graphite-yielding carbon, a sufficient quantity of a halide of a spherular graphite inducing element selected from the group consisting of lithium, sodium, magnesium, strontium, barium, rubidium and cerium to induce nodularization when reduced, and a reducing agent capable of reducing the halide, and then solidifying the molten metal While the inducing element is effective in promoting the formation of spherular graphite.

Other objects and advantages will be apparent from the specification and the accompanying drawings.

In the drawings:

Fig. 1 is a flow sheet generally illustrating the process of the invention, a detailed explanation of which is to be found hereinafter in the specification;

Fig. 2 is a photomicrograph (X) of a section of a sample of nodular iron made by the process of the present invention in which magnesium chloride is used as the source of the spherular graphite inducing substance;

Fig. 3 is a photomicrograph (X100) of a section of a sample of nodular iron made by the process of the present invention in which sodium chloride is used as the source of the spherular graphite inducing substance;

Fig. 4 is a photomicrograph (X100) of a section of a sample of nodular iron made by the process of the present invention in which magnesium chloride and sodium chloride are the source of the spherular graphite inducing substances;

Fig. 5 is a photomicrograph (X100) of a section of a sample of nodular iron made by the process of the present invention in which lithium chloride is the source of the spherular graphite inducing substance;

Fig. 6 is a photomicrograph (X100) of a section of a sample of nodular iron made by the process of the present invention in which barium chloride is the source of the spherular graphite inducing substance;

Fig. 7 is a photomicrograph (X100) of a section of a sample of nodular iron made by the process of the present invention in which strontium chloride is the source of the spherular graphite inducing substance;

Fig. 8 is a photomicrograph (X100) of a section of a sample of nodular iron made by the process of the present invention in which misch metal chloride (approximately 50% cerium chloride) is the source of the spherular graphite inducing substance;

Fig. 9 is a photomicrograph (X100) of a section of a sample of nodular iron made by the process of the present invention in which rubidium chloride is the source of the spherular graphite inducing substance;

Fig. 10 is a photomicrograph (X100) of a sectlon of a sample of nodular iron made by the process of the present invention in which sodium bromide is the source of the spherular graphite inducing substance;

Fig. 11 is a photomicrograph (X100) of a section of a sample of nodular iron made by the process of the present invention in which sodium iodide is the source of the spherular graphite inducing substance;

Fig. 12 is a photomicrograph (X100) of a section of a sample of nodular iron made by the process of the present invention in which sodium fluoride is the source of the spherular graphite inducing substance;

Fig. 13 is a photomicrograph (X100) of a section of a sample of nodular iron made by the process of the present invention in which magnesium fluoride is the source of spherular graphite inducing substance;

Fig. 14 is a photomicrograph (X500) of a section of a sample of nodular iron made by the process of the present invention illustrating in more detail the structural form of the spherular granules of graphite obtained in the ascast iron;

Fig. 15 is a table giving specific examples of the approximate percentages by weight of certain ingredients (the ingredients being identified by their chemical symbols), and the values of certain quantities involved, in the practice of this invention; and

Fig. 16 is a table giving the physical properties of the iron made according to the process of the invention using the percent ingredients specified in the table of Fig. 15.

The present invention comprehends a process for making a ferrous metal characterized to a substantial degree by a matrix containing spherular granules of graphite as exemplified in the photomicrographs shown in Figs. 2 to 14. The invention utilizes the spherular graphite inducing effect of certain metallic elements when introduced into a molten ferrous metal containing graphite-yielding carbon, but instead. of introducing the element in uncomn bined form as a free chemical element, or as an element alloyed or mixed with other materials, or as a metallic oxide, this invention contemplates bringing the element in the form of a halide of the element into contact with the molten bath of ferrous metal in the presence of a suitable reducing agent consisting essentially of an element selected from the group consisting of calcium, potassium, and barium. In this way the spherular graphite inducing element can be introduced into the metal (1) without the explosive effects incident to introduction in elemental form, (2) without introducing unwanted or undesirable substances into the metal, and (3) without introducing a spherular graphite inhibitor such as oxygen.

Elements which have shown themselves to be satisfactory spherular graphite inducers when brought together in the form of halides with a bath of molten ferrous metal containing graphite-yielding carbon are lithium, sodium, magnesium, strontium, barium, rubidium and cerium. The halides of the foregoing elements will at times hereinafter be referred to as nodularizing halide compounds. Each of the elements mentioned, when introduced otherwise than as a halide, have recognized nodularizing effects, except for sodium Whose nodularizing action has not heretofore been known. The discovery that sodium halides are excellent nodularizing halide compounds is an important aspect of this invention particularly in view of the cheapness and ready availability of sodium chloride (common salt).

The reducing agent employed in conjunction with the nodularizing halide compound must be one active at the temperature of the molten metal bath to cause the nodularizing element to be released to perform its intended function. One reducing agent having the properties desired is metallic calcium which may be conveniently supplied as calcium silicide (an intermetallic composition containing about calcium). The calcium appears to combine with the halogen radical to render the nodularizing element available for performing its nodularizing function. The calcium halide thus formed (and-the silicon oxides formed from silicon which does not enter the metallic bath) appear as a floating slag.

Other reducing agents which may be employed are potassium and barium, the latter being conveniently supplied as barium silicide. Potassium has been found useful in causing the nodularizing element magnesium to be released from its chloride to perform its nodularizing function. Barium has been found useful in causing both the nodularizing elements magnesium and sodium to be released from their chlorides for the same purpose.

The nodularizing halide compound may be mixed with the reducing agent and molten metal containing carbon poured over the mixture which has previously been placed in a ladle, or the mixture may be added to the stream of molten metal as it is poured. In the table of Fig. 15, the column headed Pouring Temperature gives the temperature of the molten ferrous metal (base metal) at the instant it is brought into contact with the halide and reducing agent.

After the slag forms it is usually separated from the melt before obtaining the nodular iron casting. In a cupola or other furnace this separation may be accomplished according to the usual practice without actually removing slag from the melt, by tapping the melt below the slag level. If the nodular iron is made in a ladle, a teapot or bottom pour ladle may be employed to separate the slag from the molten metal at the time of pouring.

Soon after the halide has been reduced the melt should be poured so as not to lose the nodularizing effect of the inducing element since the nodularizing elfect is found to decrease as the time between reduction and pouring is extended. The length of interval between treatment and pouring, in which interval the nodularizing effect will not appreciably diminish, appears dependent upon the quantity of nodularizing halide compound and reducing agent introduced into the molten metal. It has been found, for example, with a 400 pound heat of pig iron (base iron containing carbon 3.35%, silicon 0.84%, phosphorus 0.055%, sulfur 0.028% and manganese 0.017%, and the remainder iron) that when the melt Was poured eight minutes after treatment (the percentage additions by weight being magnesium chloride 1.05%, sodium chloride 1.05% and calcium silicide 4.70%), the iron as cast was approximately ninety-five percent nodular, the remaining five percent showing modified flakes. When poured eleven minutes after treatment the iron as cast was approximately fifty to sixty percent nodular. Pouring fourteen minutes after treatment gave an iron, as cast, approximately fifteen to twenty percent nodular, and waiting an additional half minute resulted in an iron only approximately ten percent nodular.

Iron produced by this process has physical properties of a modulus of elasticity much superior to the base iron. As an example of the greatly improved physical properties that can be realized with this process, a gray iron having a tensile strength of 12,300 p. s'. i., a yield point of 7,000 p. s. i., and an elongation of 1% was treated according to this process to produce an iron, as cast, having a tensile strength of 78,200 p. s. i., yield point of 43,000 p. s. i. and an elongation of 12.5%. The modulus of elasticity before treatment was approximately 15,000,000 p. s. i., Whereas after treatment the modulus of elasticity was approximately 27,000,000 p. s. i., a figure comparable to malleable iron.

Tensile strengths exceeding 105,000 p. s. i. have been measured for materials made in accordance with this invention, although the average of tensile strengths for the specific examples listed in Fig. 16 is well over 70,000 p. s. 1.

The halides of the spherular graphite inducing elements include the chlorides, bromides, iodides and fluorides. Sodium chloride, sodium bromide, sodium iodide and sodium fluoride when introduced into molten iron containing carbon and reduced by calcium silicide produced iron characterized by the presence of sperular granules of carbon, as shown in the photornicrographs of .Figs. 2,

10, 11 and 12 respectively. Sodium .chloride, which is ordinary .table salt, .is inexpensive and easily obtained regardless of war times or national emergency. Ma nesium chloride is likewise inexpensive and readily available. For these reasons the chlorides of magnesium and sodium are preferred to the bromides, iodides and fluorides of these elements and to the halides of lithium, barium, strontium, cerium and rubidium.

It has been found that calcium alone will not produce nodular iron unless an inordinate proportion (50 percent or more) of nickel is present. The ostensible function of calcium in the process of the invention is to combine with the halogen to free the nodularizing element.

Mixing two halides such as sodium chloride and magnesium chloride and introducing the mixture into the molten metal for reduction by calcium silicide has been found as eflicacious in producing nodular graphite as introducing one or the other of the halides alone and eifecting the single reduction.

The process of this invention may be illustrated by a flow sheet or flow diagram, as shown in Fig. 1. The flow diagram presupposes operation conforming to ordinary foundry practices and equipment, and indicates that the ferrous metal containing graphite-yielding carbon is usually melted as a first step. Metal already moiten, as from a blast furnance, cupola, or the like, may, of course, be used as well. The diagram further assumes that treatments not indicated, such as adjustments of carbon or silicon content, elimination of oxygen, reduction of sulfur or phosphorus content, addition of alloying agents, employment of chill techniques in casting or others may or may not be performed at appropriate stages of the process without alteration of its main character and pupose.

'The process of making nodular iron according to this invention by bringing together molten ferrous metal containing graphite-yielding carbon, the halide of a spherular graphite inducing element, and a suitable reducing agent is illustrated by the following examples:

Example N0. 1

A charge of pig iron (base iron) containing carbon 4.03%, silicon 0.85%, phosphorus 0.050%, sulfur 0.023%

and manganese 0.15% was melted in the furnace at A sample machined from the final nodular casting had the following physical properties as cast:

Tensile strength p. s. i 65,600 Yield point p. s. i 41,500 Elongation in 2 inches percent 16.5

'Brinell hardness 159 A comparison of the physical properties of the iron before and after treatment according to the process of this invention, as exemplified by the preceding example, shows an increase after treatment in both tensile strength and yield point of almost 600%, and an increase in ductility to 16.5% from a ductility of zero percent for untreated material.

Example N0. 3

A charge of pig iron (base iron) containing by weight, as a percentage of the charge, carbon 4.34%, silicon 0.73%, phosphorus 0.045%, sulfur 0.023% and manganese 0.10% was melted in an induction furnance. To the molten iron in the furnace was added 0.7% calcium silicide .to .deoxydize the iron. However, the addition of calcium silicide is not essential :if the iron does' not need deoxydizing. The molten metal was then poured at 2675 F. over a mixture of 3.5% magnesium chloride, which was essentially anhydrous, and 3.5% calcium silicide previously placed in the bottom of a heated laddle. After the reaction had taken place the slag was removed and the molten metal cast into a mold.

A sample of the base iron before treatment had a tensile strength of about 12,000 ,p. s. i., yield point of about 7,500 p. s. i. and zero percent elongation.

A sample machined from the casting showed the following physical properties, as cast:

photomicrograph of Fig. 2, has all of the graphite in nodular form and has a matrix of about 50% ferrite and 50% pearlite.

Example N0. 3

A charge of pig iron (base iron) containing by weight, as a percentage of the charge, carbon 4.20%, silicon 0.75%, phosphorus 0.35%, sulfur 0.039% and manganese 0.10% was melted and to the charge was added 0.69% calcium silicide to deoxydize the iron. The molten metal was poured at a temperature of 2800 F. over a mixture of 4.41% of sodium chloride (which was essentially anhydrous) and 6.63% calcium silicide in a heated ladle. After removing the slag the contents of the ladle were cast into a mold.

A sample of the base iron before treatment had a tensile strength of about 12,000 p. s. i., yield point of about 7,500 p. s. i. and zero percent elongation.

A sample machined from the casting had the following physical properties, as cast:

Tensile strength p. s. i 90,200 Yield point p. s. i 85,000 Elongation in 2 inches -percent 3 Brinell hardness 207 Example N0. 4

A charge of pig iron (base iron) containing by weight, as a percentage of the charge, carbon 3.84%, silicon 0.66%, phosphorus 0.060%, sulfur 0.026% and manganese 0.13% was melted and to the melt was added 0.70% calcium silicide to deoxydize the iron. The molten metal was then poured at a temperature of .2700" F. over a mixture of 3.99% sodium chloride, 0.22% magnesium chloride and 5.26% calcium silicide. (Both the sodium chloride and the magnesium chloride were essentially anhydrous.) After removing the slag from the metal the contents of the ladle were cast into a mold.

A sample of the base iron before treatment had a tensile strength of about 12,000 p. s. i., yield point of about 7,500 p. s. i. and zero percent elongation.

A sample machined from the casting had the following physical properties, as cast:

Brinell hardness 163 The microstructure of this sample, as shown in the photomicrograph of Fig. 4, is approximately nodular. The matrix is ferrite.

Example N0.

A charge of pig iron (base iron) containing carbon 3.88%, silicon 0.67%, phosphorus 0.025%, sulfur 0.029% and manganese 0.11% was melted and to the charge was added 0.70% calcium silicide to deoxydize the iron. The molten metal was poured at a temperature of 2700 F. over a mixture of 3.25% anhydrous lithium chloride and 6.36% calcium silicide in a heated ladle. After removing the slag the molten metal was cast into a mold.

A sample of the base iron before treatment had a tensile strength of about 12,000 p. s. i. and zero elongation.

A sample machined from the casting had the following physical properties, as cast:

Tensile strength p. s. i 95,600 Elongation in 2 inches .percent Brinell hardness The microstructure of this sample, as shown in the microphotograph of Fig. 5, is predominantly nodular.

The matrix is almost entirly ferrite.

Example N0. 6

A charge of base iron containing by weight, as a percentage of the charge carbon 1.09%, silicon 0.16%, phosphorus 0.06%, sulfur 0.008% and manganese 0.35% was melted, and to the charge was added calcium silicide 0.66% to deoxydize the iron. The molten metal was poured at a temperature of 2900 F. over a mixture of anhydrous magnesium chloride 1.05%, anhydrous sodium chloride 1.05% and calcium silicide 4.00% in a heated ladle. After removing the slag the contents of the ladle were cast into a mold.

A sample machined from the casting contained spherular granules of graphite and had the following physical properties, as cast:

Brinell hardness The process of this invention may be practiced variously with the several nodularizing halide compounds and reducing agents identified in the table of Fig. 15, to give the improved physical properties shown in the table of Fig. 16. Each heat in the table represents base materials which initially had tensile strengths around 12,000 p. s. i., yield points around 7,500 p. s. i., and elongations from 0 to 1% before treatment, and which were treated in accordance with this invention generally following the practices described in the foregoing detailed examples. The physical properties listed were those ascertained by actual measurements.

The amounts and percentages given in the foregoing examples and in the examples in the table of Fig. 15 may be varied considerably without departing from the scope of the invention so long as the amounts and percentages are sufficient to produce a ferrous metal, as cast, having a microstructure characterized by a matrix containing spherular granules of graphite.

The term as cast, as used herein, represents the condition of a metal mass which has been brought from a liquid state above its melting point to a cold solidified state by cooling at a rate typical of the rate of cooling of castings in normal foundry practice.

The term ferrous metal containing graphite-yielding carbon, as used herein, defines a ferrous alloy which has suflicient carbon to form, upon solidification of the metal from the liquid state and upon cooling, a matrix microstructure characterized by free carbon inclusions in the cold metal. This ferrous metal is the metal referred to as Base metal in the table of Fig. 15.

The range of carbon content which complies with the foregoing definition is dependent upon substances in the alloy other than iron and carbon. For example, presence of silicon and certain other substances has an important bearing upon the readiness with which c'ementite of the ferrous metal will decompose to yield ferrite and free carbon. Such substances, termed graphitizing agents, act to extend the lower end of the range of carbon content within which this invention is usefully operative well down into if not throughout the range of the so-called hyper-eutectoid steels.

The upper end of the range of carbon content of ferrous metal high in carbon is set by convenience in melting and utility of the material produced, and reaches up to and beyond the upper limits of carbon content of high carbon pig iron. In the absence of substantial proportions of substances such as sulfur, phophorus, oxygen, and the like, and special alloying agents, this range will extend approximately from 0.8% carbon to 6.7% carbon but the limits of usefulness of the invention may extend outside of this range, as for example, when a substantial proportion of nickel, chromium, manganese or other alloying agents is present.

So-called high sulfur iron may be converted into nodular iron by the process of this invention, provided the iron has sufficient graphite-yielding carbon, if the iron is first desulfurized by any well known method such as adding sodium carbonate or calcium oxide to the melt.

It will be evident that by the aforementioned process a number of nodular iron alloys may be made which have a microstructure characterized by a matrix containing spherular granules of graphite and that these alloys may retain in the as-cast condition one or more of the following elements, lithium, sodium, magnesium, strontium, rubidium, barium and cerium.

Since the examples of the processes given are illustrative only, the invention is not to be limited thereto but may include equivalents, modifications and variations coming within the scope of the appended claims.

It is claimed and desired to secure by Letters Patent;

1. The process for obtaining from a molten ferrous metal containing graphite yielding carbon a ferrous metal characterized in the solid state by the presence of spherular granules of graphite therein, comprising: bringing together said molten ferrous metal, a halide of a spherular graphite inducing element selected from the group consisting of lithium, sodium, magnesium, strontium, barium, rubidium and cerium, and an agent capable of reducing said halide in said molten ferrous metal, said agent consisting essentially of an element selected from the group consisting of calcium, barium, and potassium; and solidifying said molten ferrous metal while said spherular graphite inducing element is effective in inducing the formation of spherular graphite.

2. The process for obtaining from a molten ferrous metal containing graphite yielding carbon at ferrous metal characterized in the solid state by the presence of spherular granules of graphite therein, comprising: bringing together said molten ferrous metal, magnesium chloride, and a reducing agent consisting of potassium, said reducing agent being capable in said molten ferrous metal of reducing said halide; and solidifying said molten ferrous metal while said magnesium is effective in inducing the formation of spherular graphite.

3. The process for obtaining from a molten ferrous metal containing graphite-yielding carbon a ferrous metal characterized in the solid state by the presence of spherular granules of graphite therein, comprising: bringing together said molten ferrous metal, lithium chloride, and a reducing agent capable in said molten ferrous metal of reducing said chloride, said reducing agent consisting of a compound of calcium and silicon; and solidifying said molten ferrous metal while said lithium is effective in inducing the formation of spherular graphite.

4. The process for obtaining from a molten ferrous metal containing graphite-yielding carbon a ferrous metal characterized in the solid state by the presence of spherular granules of graphite therein, comprising: bringing together said molten ferrous metal, barium chloride, and a reducing agent capable in said molten ferrous metal of reducing said barium chloride,,said reducing agent consisting of a compound of calcium and silicon; and solidifying said molten ferrous metal while said barium is effective in inducing the formation of spherular graphite.

5. The process for obtaining from a molten ferrous metal containing graphite-yielding carbon 2. ferrous metal characterized in the solid state by the presence of spherular granules of graphite therein, comprising: bringing together said molten ferrous metal, cerium chloride, and a reducing agent capable in said molten ferrous metal of reducing said cerium chloride, said reducing agent consisting of a compound of calcium and silicon; and solidifying said molten ferrous metal while said cerium is effective in inducing the formation of spherular graphite.

6. The process for obtaining from a molten ferrous metal containing graphite-yielding carbon a ferrous metal characterized in the solid state by the presence of spherular granules of graphite therein, comprising: bringing together said molten ferrous metal, magnesium chloride, and a reducing agent consisting of an intermetallic compound of calcium and silicon, said reducing agent being capable in said molten ferrous metal of reducing said magnesium chloride; and solidifying said molten ferrous metal while said magnesium is effective in inducing the formation of spherular graphite.

7. The process for obtaining from a molten ferrous metal containing graphite-yielding carbon a ferrous metal characterized in the solid state by the presence of spherular granules of graphite therein, comprising: bringing together said molten ferrous metal, sodium chloride, and a re- I12 ducing agent consisting of an intermetallic compound of calcium and silicon, said reducing agent being capable in said molten ferrous metal of reducing said sodium chloride; and solidifying said molten ferrous metal while said sodium is effective in inducing the formation of spherular graphite.

8. The process for obtaining from a molten ferrous metal containing graphite-yielding carbon a ferrous metal characterized in the solid state by the presence of spherular granules of graphite therein, comprising: bringing together said molten ferrous metal, chlorides of spherular graphite inducing elements consisting of magnesium and sodium, and a reducing agent consisting of a compound of calcium, said reducing agent being capable in said molten ferrous metal of respectively reducing said magnesium chloride and said sodium chloride; and solidifying said molten ferrous metal While said magnesium and sodium are effective in inducing the formation of spherular graphite.

References Cited in the file of this patent UNITED STATES PATENTS 906,009 Goldschmidt Dec. 8, 1908 2,036,576 Hardy Apr. 7, 1936 2,154,613 Guthrie Apr. 18, 1939 2,485,760 Millis et al. Oct. 25, 1949 2,488,511 Morrogh Nov. 15, 1949 2,527,037 Smalley Oct. 24, 1950 2,552,204 Morrogh May 8, 1951 2,662,820 Crome Dec. 15, 1953

Claims (1)

1. THE PROCESS FOR OBTAINING FROM A MOLTEN FERROUS METAL CONTAINING GRAPHITE YIELDING CARBON A FERROUS METAL CHARACTERIZED IN THE SOLID STATE BY THE PRESENCE OF SPHERULAR GRANULES OF GRAPHITE THEREIN, COMPRISING: BRINGING TOGETHER SAID MOLTEN FERROUS METAL, A HALIDE OF A SPHERULAR GRAPHITE INDUCING ELEMENT SELECTED FROM THE GROUP CONSISTING OF LITHIUM, SODIUM, MAGNESIUM, STRONTIUM, BARIUM, RUBIDIUM AND CERIUM, AND AN AGENT CAPABLE OF REDUCING SAID HALIDE IN SAID MOLTEN FERROUS METAL, SAID AGENT CONSISTING ESSENTIALLY OF AN ELEMENT SELECTED FROM THE GROUP CONSISTING OF CALCIUM, BARIUM, AND POTASSIUM; AND SOLIDIFYING SAID MOLTEN FERROUS METAL WHILE SAID SPHERULAR GRAPHITE INDUCING ELEMENT IS EFFECTIVE IN INDUCING THE FORMATION OF SPHERULAR GRAPHITE.

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