US3321304A

US3321304A - Materials for and methods of treating molten ferrous metals to produce nodular iron

Info

Publication number: US3321304A
Application number: US332902A
Authority: US
Inventors: William E Snow
Original assignee: American Cast Iron Pipe Co
Current assignee: American Cast Iron Pipe Co
Priority date: 1963-12-23
Filing date: 1963-12-23
Publication date: 1967-05-23
Anticipated expiration: 1984-05-23
Also published as: ES307443A1; NL149854B; DK130080B; DE1433405A1; AT278885B; DE1433405B2; IL22434A; DK130080C; NL6414239A; BE657254A; GB1043759A; CH437391A

Description

United States Patent MATERIALS FUR AND METHGDS 0F TREATING M'QLTEN FERRGUS METALS T0 PRODUCE N 01)- ULAR HRON William E. Snow, Birmingham, Ala., assignor to American Cast Iron Pipe Company, Birmingham, Ala., a corporation of Georgia No Drawing. Filed Dec. 23, 1963, Ser. No. 332,902

21 Claims. (Cl. 75130) This invention relates generally to materials for and methods of treating molten metals and alloys, and more particularly to the use of low boiling point alkali and alkaline earth reactive metal agents for treating molten iron or iron alloys to produce nodular iron.

-Nodular iron, also known as spheroidal graphite iron or ductile iron, is a product having a high carbon and a high silicon content in which most of the carbon has been caused to coagulate into spheres by special processing. During processing, an ingredient such as magnesium is added, followed by other ingredients such as silicon, calcium or combination of these ingredients. The resulting product acquires the structure of steel peppered with spheres of graphite, and its properties make it useful for a great many engineering applications.

Iron or iron alloy melts often must be subjected to a refining treatment in the melting furnace, or in the ladle, before the metal can be cast. Examples of such treatment of the metal are deoxidation, disulfurization, denitrogenizing, dephosphorizing, deslagging, degasing and alloying. Other treatments may also be required by which the content of some undesirable substance in the melt is removed or decreased to a desired degree. Many of these treatments have been known since the beginning of the production process for steel or ferro-alloys, while others have been developed when the utilization of impure raw material has brought about the introduction of undesired impurities.

In order to decrease or remove impurities, new refining methods are being developed continually, and the introduction of magnesium and sodium into molten ferrous metals and alloys has, in recent years, gained considerable importance.

The effect of magnesium and sodium as deoxidizers and cleansing agents is attributed to their ability to reduce dissolved oxides of the iron group and finely dispersed silicates and, in turn, to form insoluble magnesium or sodium oxides and silicates. It is also well known that magnesium attacks the soluble sulfides of the iron group and forms an insoluble magnesium sulfide which will rise to the surface where it can be removed. Sodium introduced into a molten metal at a temperature above the boiling point of sodium acts in a similar manner.

Prior techniques have utilized the metals sodium and magnesium, which have boiling points of 1638 F. and 2030 F., respectively, both considerably lower than the temperature of molten steel or cast iron. However, due to their relatively low boiling points, the introduction into molten iron or steel of either of these two metals in a pure or nearly pure state produces a violent reaction due to the metallic vapor generated. The degree of violence in the reaction is a function of the size or mass of the sodium or magnesium introduced, and the temperature of the iron or steel being treated. The temperature factor is, of course, related to the vapor pressure of the magnesium or sodium.

Due to the desirability of magnesium and sodium as treating agents for molten metals and alloys, much effort has been expended towards minimizing the problems of reactivity and volatility, and curbing the reactive and volatile nature of the treating metal. These efforts have resulted in various methods of introducing the low meltice ing and boiling point metals into molten iron or steel, such as alloying, powder injection, mechanical injection and briquetting. All of these methods have certain disadvantages, the principal one being the high cost of the contained percentage of low boiling point metal as compared to its cost in ingot form.

In the alloying method, the reaction is controlled by dilution of the low boiling point metal with higher boiling point metals which do not produce a violent reaction. Alloys containing magnesium, such as magnesium-ferrosilicon, nickel-magnesium and copper-magnesium have been utilized where the total magnesium content by weight is on the order of 8 to 30%. This method requires the payment of a premium price for the magnesium content in the alloy because of the special furnaces and procedures required in its manufacture. Also, the ratio of magnesium to silicon is fixed for the various grades, and often results in either an excessive or a deficient amount of silicon in the treated metal.

In the powder injection method, a carrier gas, such as nitrogen, is utilized to force finely divided pellets or powder through injection tubes into the molten metal bath. The violence of the reaction in this case is controlled by reducing the mass of, and dispersing, the low boiling point metal. While this method has met with some success, the cost of preparation of magnesium in powder form, and the additional expense for the carrier gas and associated apparatus, serve to increase the cost of production of the iron considerably. In addition, the use of a carrier gas also presents problems related to the decrease in iron temperature during injection.

In the mechanical injection method, a wire or small diameter rod of the low boiling point metal is forced through a refractory tube into the molten metal bath, and the violence of the reaction is controlled by the small mass of the low boiling point metal which is in contact with the molten iron or steel at any one time. The mechanical difiiculties associated with the feeding of the low boiling point metal, the cost of the rolled or extruded rods or wires, and the problems related to upkeep of the equipment and delivery tubes all increase the cost of this method and reduce its desirability.

In the briquetting method, mechanical mixtures of low boiling point alloys and high melting point metals, metallic oxides and refractories are briquetted, and the briquettes are introduce into the molten iron or steel. Here, again, the cost of the contained percentage of low boiling point metal is excessive.

In view of the disadvantages of these prior procedures, it is a principal object of the present invention to provide an improved material embodying a low boiling point alkali or alkaline earth metal for treating molten metals and alloys which are more economical and more efiicient than any of treating agents heretofore known.

Another object is to provide a novel method of manufacturing an agent for treating molten metals and alloys of the iron group to effect desulfurization and the formation of nodular or spheroidal graphite iron.

A further object of the invention is to provide a unique composition of matter for treating molten iron or steel which permits the use of low boiling point metals in their most economical form, such as ingots, pigs, bo-rings or scrap.

A still further object is the provision of an improved treating agent for producing nodular or ductile iron which does not require the use of costly refractory tubes, carrier gas and reaction inhibitors, and enables effective control of the amount of low boiling point metal introduced into the molten metal.

While this specification concludes with claims particularly pointing out and distinctly claiming the invention,

' the subject matter defined in the claims will be more easily comprehended from the following detailed description of exemplary embodiments of the inventive concept.

In general, the present invention relates to a porous refractory, metal-impregnated material which is produced by immersing a piece of porous coke, carbon or graphite in a molten body of low boiling point reactive metal, such as magnesium, and holding it there until the pores of the refractory material are filled with the metal. The impregnated refractory material thus produced may then be used as a treating agent by plunging it into a molten bath of iron or steel, and holding it beneath the surface thereof while the latent heat of the bath melts or vaporizes the low boiling point metal so it can enter the iron or steel and effect the desired nodularization of the graphite therein.

Coke, porous graphite and carbon have been found to have several unique properties which make them desirable as a carrier for the addition of low boiling point metals into a molten metal such as steel or cast iron. For example, as the temperature of these carbonaceous materials is increased up to 4000 F., the strength thereof increases, a characteristic which is opposite that of most other materials. In addition, coke, carbon and graphite can be produced with controlled porosity with the pores making up to approximately 50% of the total volume. These materials are also relatively stable When submerged in molten cast iron, and to a slightly lesser degree when submerged in molten steel.

Several theories have been advanced in an attempt to explain why magnesium or a low boiling point alkali metal enters the small diameter pores of the porous refractory; however, the theoretical aspects are still not understood and cannot be explained with exactness. A paper entitled The Physical and Chemical Character of Graphite, by Tee and Tonge, which appeared in the Journal of Chemical Education, volume 40, No. 3, March, 1963, at pages 117 to 122, has set forth a theory explaining the phenomena of intercalation. It has been hypothesized that perhaps the coke, carbon or graphite may be impregnated through intercalation. This article further points out that all of the lower members of the alkali metal group will react in the same way as magnesium. This includes sodium, potassium, rubidium, and cesium, all of which are effective desulfurizers and can be used to produce nodular or ductile iron.

Although various methods and systems have been devised for impregnation of the porous refractory, in one embodiment a porous refractory body of a desired volume and configuration is first heated to a temperature hotter than, and is then immersed in, a body of molten low boiling point metal the surface of which is protected against contact with the atmosphere in any suitable manner as by a layer of flux or a blanket of inert gas. The low boiling point metal is selected from the group consisting of magnesium, sodium, potassium, rubidium and cesium, each of which is suitable for use in the production of nodular iron. However, since magnesium is the preferred metal, the following detailed description will refer to the use of magnesium.

When impregnated, the porous refractory body may contain several times the magnesium content required to treat an individual ladle of molten iron if all the magnesium were to be expelled. Since the magnesium is expelled at the surface and volatilization progresses toward the center of the body in direct proportion to the heat transfer from the molten iron to the porous refractory material, the amount of magnesium expelled is a function of the total time of immersion and the temperature of the molten iron being treated. Removal of the porous refractory material from the molten iron stops the heat transfer and the expulsion of magnesium. While the porous refractory material is still hot, it can be reimmersed in the molten magnesium and the magnesium which had been expelled may be replaced by reimpregnation. The porous refractory material is then ready for treatment of another ladle.

For example, a porous graphite member may be machined to a predetermined size or volume to cause impregnation with a sufiicient amount of magnesium to treat a given amount of molten iron. The reaction rate or time required for the latent heat of the molten iron to expel the magnesium is a function of the iron temperature and the total surface area of the impregnated porous graphite block. For example, the porous graphite member may be machined to provide a 5-inch diameter sphere which has been found to be the correct size when impregnated to treat 1000 pounds of molten iron. For ladles containing a greater amount of iron, a porous graphite member having a greater volume is required.

Other shapes may also be utilized, such as a porous graphite cylinder having its external surface shaped or grooved to provide the desired surface area. In addition, the surface area-volume ratio can be varied by adding vanes or holes. If a low surface area-volume ratio is desired, a large rectangular block may be utilized.

After the porous graphite member is heated and submerged in molten magnesium, whereby impregnation of the pores takes place, the impregnated graphite is withdrawn from the molten magnesium and submerged beneath the surface of the molten iron or steel to be treated. Since the temperature of the molten iron or steel is greater than the boiling point of the magnesium, the magnesium is driven out of or expelled from the pores as a vapor and enters the iron in a controlled manner without a violent reaction, the rate of expulsion being a function of the surface-volume ratio. After the magnesium has been driven out of the porous graphite member, the latter can be removed from the molten iron and resubmerged beneath the surface of the molten magnesium for reimpregnation. The process for treating the molten iron may then be repeated so as to permit recycling.

In the preferred, most economical form of the invention, metallurgical coke is utilized as the porous refractory material. Coke is approximately 50% porous, exhibits good mechanical strength at high temperature and dissolves very slowly in molten cast iron. The treatment method consists of placing a number of pieces or lumps of magnesium-impregnated coke, Whose total magnesium content is known, in a conventional basket treatment device and submerging the basket below the surface of the molten iron. After the magnesium has been driven off and the basket removed, the spent coke floats to the surface and can easily be skimmed off.

In producing nodular iron with a porous refractory material of coke, graphite or carbon, the porosity of the material and amount of impregnated magnesium is known. The porous refractory material may be attached to a heavy ladle lid with a refractory stem such as is conventionally used on treatment baskets, or in the case of impregnated lumps of coke, the lumps are placed in a conventional treatment basket. The magnesium-impregnated refractory material is then immersed below the surface of the molten iron until the magnesium volatilizes. Immediately after the reaction, the porous refractory material is removed from the molten iron and reimmersed below the surface of tthe molten magnesium where it is reimpregnated. The cycle may be repeated a number of times with the same piece of porous refractory material.

It has been found that in treating molten iron or steel in this manner, a recovery of 40% of the magnesium can be expected. Magnesium recovery may be expressed by the following formula:

Residual Magnesium In Iron (lbs.)l0.75 (S -S (lbs).

Total Magnesium Used (lbs) where S; is the initial sulfur content of the iron (lbs) and S is the sulfur content of the iron after treatment (lbs).

Recovery expresses the efficiency of the treatment :method and is influenced by several variables. These variables are: metal temperature, metal composition, type of treat- Recovery ment method, depth of iron over the treatment device, construction of the treatment ladle, and speed of the treatment. The efficiency of any treatment method or system also determines the over-all treatment cost since a definite 15 inch porous graphite cylinder having a 7 inch diameter was machined with external grooves on 2 inch centers. The porous graphite cylinder was attached to a ladle cover and grooved to increase the surface-to-volume ratio. This amount of residual magnesium is required in the iron to 5 provided a sufficient surface-volume ratio to absorb produce the nodularizing effect. The efliciency or recovenough magnesium to treat 4000 lbs. of molten iron. The ery therefore dictates the total amount of magnesium graphite cylinder was heated in a coke fire and immersed Which must be added in order to achieve the desired residin molten magnesium where its void spaces absorbed the ual level. magnesium. The magnesium impregnated graphite cylin- Experiments have indicated that a definite relation- 10 der was then withdrawn and immersed in a 4200 pound ship exists between the pore size of the refractory and ladle of molten iron whose temperature was 2600 F. It impregnation. Porous graphite and carbon of various remained submerged in the iron for 4 minutes, 27 secpore sizes up to an average pore diameter of .0047 inch onds. When the cylinder was removed from the iron, the have been impregnated successfully in accordance with cylinder was still ejecting magnesium. Thus, the cylinder the teachings of this invention. However, difiiculty has demonstrated the capability of use in foundries where the been experienced in impregnating the :more porous grades treatment time for the molten metal is relatively long and of coke wherein the average pore diameter is about .020 the impregnated porous block can be left in the molten inch or greater. It should also be noted that in all atiron for long periods of time. tempts to impregnate where the porous refractory ma- Exam [8 H terial was only partially submerged beneath the surface of p the molten magnesium, the impregnation was unsuccess- In a foundry such as .a pipe production foundry, where ful. Accordingly, in order to effect successful impregnaa 4000 lb. ladle of molten iron is treated with magnesium tion, the porous material must be completely submerged every 5 minutes, the addition of magnesium should not below the surface of the molten magnesium. This is take longer than 1 minute since the iron must be transtheorized to be caused by the molten magnesium reacting ported to the casting machine, skimmed and reladled into With the Oxygen and {Imogen in the Pefes e Creating a the casting machine ladles within the 5-minute period. vacuum which sucksun the molten magnesium when the A i 'npregnated porous graphite body machined to a refractory mateflal 1S completely submerged; howeyer, spherical shape is particularly adapted to this system due when only Partlany submefgedr more an 15 sucked mm to the large volume available to contact the molten iron. the porous refractory m l A 5 inch diameter sphere of graphite having 48% of g z gg gg g i xiii 2 83 5; 522%: its volume as voids was heated by a coke fire and impreglower than the temperature of the molten metal, the ladle Dated 2 magnesium lmltnersmg H m molten is designed to provide a maximum depth of penetration in f Th6 magnesmm'lplpregnaled Sphere, was the molten metal to provide maximum recovery. The 35 taken d rectly from this operation and immersed in the low boiling point metal is converted to a metal vapor l at temperature of 2600 f 'than upon immersion in the molten metal and immediately allowing the graphite sphere to cool after treating the starts to rise toward the surface thereof. The metal vapor iron, the graphlte Sphere Was recycled by again immersing reacts with undesirable elements in the molten metal to it n the molten m g i m o receive another charge of be treated and in some cases goes into solution as an 40 magnesium. This cycle between the iron and magnesium alloying agent. The further the metal vapor must travel to was repeated a total of four times. reach the surface, the greater are its chances of reacting The first cycle produced only 5% recovery, but after the With the undesirable elements 01 being retained, since it sphere was recharged with magnesium and plunged into usually Oxides immediately p reaching The Surface the molten iron, 40% residual magnesium was recovered. The Porous refractory material of the Present invention The low recovery of the first cycle was mostly due to the is such as to distribute the low boiling point metal so that temperature of the graphite sphere being too low prior the formation Vapors is as evenly as Posslble to going into the molten magnesium. The heat from the in the l Thls prevents excesslve turbulence and conmolten iron during the first cycle raised the temperature Centratlon P the of the sphere sufficiently for the second cycle. The third In practlce, nodular iron has been produced by tr and fourth cycles produced 33% d 30% recovery, rethe molten iron with a magnesium-impregnated porous s goth/61y graphite. cylinder provided with amen-m1 grooves Wltha It was noted that there was no damage to the graphite magnes1um-1mpregnated porous graphite sphere, and with Af h 1 1 h magnesiumdmpregnated metallurgical coke, without any Sphere after cofltmuous cyc I E f 6 cyc t e apparent difference in product quality. In the system hlolten magnesium e 10 e y Wlth the ep using impregnated coke, coke in lump form Was placed rte sphere submerged 111 it. After six days, the magnesium in a conventional dipping basket, and ladles of 1000 lbs. was remelted and the sphere removed and cooled while and 5500 lbs. of molten iron Were treated. In each case, com letely covered with sand to prevent the magnesium nodular iron was produced of good quality with the estifrom burning in the atmosphere. No damage to the mated magnesium feeevel'y being The following sphere was observed, and it was still impregnated with magexamples illustrate in greater detail various aspects of nesimm th iHVeIItiOIl- A summary of the operation and partial chemical analy- Example I sis of Example II are given in the following table wherein A 4200 lb. ladle of ductile base iron was treated by the Percentages Silicon, Ihahga-hese and magneslum are the magnesium-impregnated graphite method in which a percentages by welght of the iron product:

i l 3 1 1 5 I ib n .Si (percent) Mn (percent) Mg (percent) K194823151? Obs.) (min/see.) (min/sec.)

The magnesium content in Cycle No. 2 represents a total for Cycles 1 and 2 and the magnesium content in Cycle No. 4 represents the total for Cycles 3 and 4. Recovery is calculated for individual cycles.

Example III Magnesium was injected into molten iron by impregnating porous graphite with magnesium and plunging it into a ladle of molten iron. A 5 inch diameter graphite sphere having 48% of its volume as voids was heated to a temperature in excess of 2000 F. and plunged into molten magnesium for 1 minute, 30 seconds. It absorbed 2 pounds, 6 ounces of magnesium into its void spaces. The sphere was allowed to cool while it was completely covered with fine sand to prevent its exposure to the atmosphere.

The magnesium impregnated graphite sphere was attached to a ladle cover plate regularly used in the basket method of treating iron and plunged into 1025 pounds of molten iron. The sphere was under the iron for 2 minutes, 20 seconds. The temperature of the iron at the time if treatment was 2640 F. The reaction for the first 5 seconds was slightly violent due to the magnesium on the surface of the sphere, but thereafter only a small stream of white smoke was emitted from the ladle.

Analysis showed 0.097% residual magnesium in the iron after treatment. This calculates to be 41.9% recovery of the magnesium placed in the ladle.

Example IV A 5 inch diameter sphere of porous graphite was attached to a ladle lid, preheated in a coke fire, impregnated with magnesium and used to treat a 1000 lb. ladle of molten iron. The magnesium content in the molten iron after treatment was 0.097% by weight which is more than suflicient to produce nodular or ducile iron. The porous sphere was machined from a grade 25 graphite, commercially available from National Carbon Company, having a pore size of 0.0047 inch average diameter, and a porosity of 48%. 2 pounds, 6 ounces of magnesium was volatized into the iron and gave a recovery of 41.9%.

Example V A 5 inch diameter sphere of porous graphite was attached to a ladle lid and preheated by immersion in molten iron at a temperature of approximately 2500 F. The heated sphere was then immersed in molten magnesium for impregnation. This sphere was then used to treat three successive ladles of 1000 pounds each by immersing in the first ladle of molten iron until all of the magnesium was ejected, reimmersing the sphere in the molten magnesium until it was reimpregnated and repeating the process until the three ladles had been treated. The graphite sphere was machined from a grade 25 graphite, as in the prior example, having a pore size of 0.0047 inch average diameter and a porosity of 48%. The following table illustrates the results of this example, the percentage of residual magnesium being the percentage by weight of the iron product:

Example VI A block of porous graphite 14 inches by 1 4 inches by 6 inches, weighing about 46 pounds, was attached to a ladle lid and preheated by immersion in molten iron at a temperature of approximately 2600 F. The heated porous graphite block was then immersed in molten magnesium Where it was impregnated. This block was used to treat a 4200 pound ladle of molten iron. After treatment, the iron had a residual magnesium content of 0.139% which is at least twice that required to produce nodular or duetile iron.

After treatment of this ladle, the porous graphite block was permitted to cool and then was cut in half. Examination showed approximately 50% of the original magnesium had been ejected from the outer surface of the block. The porous block utilized was a grade 45 graphite, commeroially available from National Carbon Company, having a pore size of 0.0023 inch average diameter and a porosity of 48 In this example, the amount of magnesium picked up by the block was approximately 30 pounds as determined by the decrease in height of the molten magnesium in the magnesium melt pot, or about 40% of the total weight of the impregnated block. This amount of magnesium would be sufficient to treat a ladle containing 8000-9000 pounds of molten iron if the impregnated block had been left in the iron until all of the magnesium had been ejected.

Example VII Coke of approximately 10-12 cubic inches per lump was placed in a barrel and ignited with a gas-air torch. After the coke reached incandescent temperature, individual lumps were immersed and impregnated in molten magnesium. Density measurements made before and after impregnation showed an average magnesium content of of the original coke weight, or about 43% of the total weight of the impregnated product. After impregnation, the lumps were covered with sand to prevent burning until they cooled to ambient temperature. Several days later, 35 pounds of the impregnated lump coke was placed in a thin sheet met-a1 can and the can placed in a conventional treatment basket and used to treat 5500 pounds of molten iron. The residual magnesium content was 0.065%.

Example VIII Coke of approximately 10-12 cubic inches per lump was placed in a furnace and ignited with a gas-air torch and permitted to partially burn. 30 to 40 pounds of the hot incandescent coke was then placed in a frame fabricated from /2 inch steel rods. The frame and hot coke were submerged in molten magnesium for approximately one minute, and were then removed from the molten magnesium and dropped into a barrel of oil which quenched and cooled the impregnated coke lumps. The lumps of impregnated coke were removed from the frame and the cycle repeated until approximately 900 pounds of the impregnated lumps were produced. The impregnated coke was stored for approximately one week and then used to treat two separate batches of molten iron in two separate operations approximately one week apart. The first batch comprised four ladles of molten iron and the second batch two ladles, each ladle having approximately 4200 pounds of molten iron. In each case, the magnesium introduced was sufiicient to efiect the formation of nodular or ductile iron. The iron treated in this manner was used to pour six 24 inch diameter nodular iron pipes, 20 feet long, and six 20 inch diameter pipes, 20 feet long.

The treatment of these ladles was accomplished by placing 45-50 pounds of the magnesiurmimpregnated coke lumps in a steel can which was then placed in a conventional treatment basket and submerged below the surface of the molten iron until all of the magnesium had been ejected. Upon removal of the treatment basket, the spent coke floated on the surface and was removed prior to casting by conventional skimming methods prior to casting the iron.

The following table summarizes the analysis of metals after treatment of the six ladles, the percentages of magnesium, silicon and carbon being percentages by weight of the iron product:

In accordance with the principles of this invention, scrap magnesium alloy aircraft castings have been remelted and successfully used to impregnate coke. The coke was later used to treat a 4000 pound ladle of iron. This magnesium alloy contained approximately 9% aluminum, 0.5% zinc and 1% manganese. The magnesium in scrap form is approximately 25% cheaper than in pig or ingot form. The alloys in the scrap were found not to interfere with the impregnation, and later tests on nodular iron pipe produced from the treated metal showed that the alloys did not interfere with the nodularizing effects of the magnesium.

In the foregoing illustrative examples, the porous refractory material was heated prior to impregnation. However, it has also been found that coke, porous graphite or porous carbon at room temperature may be submerged below the surface of molten magnesium and be impregnated if the porous material is kept submerge-d until its temperature equalizes with that of the molten magnesium. The time required for impregnation may be decreased by increasing the temperature of the magnesium above its melting point, and by increasing the temperature of the porous material before it is submerged and impregnated.

While porous carbonaceous materials, particularly coke, are the preferred refractories usable in carrying out the present invention, satisfactory results have also been obtained with porous silicon carbide refractories, including vitreous bonded silicon carbide of the type commonly used for grinding wheels. Silicon carbide grains and a carbonaceous binder, such as coal tar electrode pitch, may also be blended and fired to produce refractory members of suitable porosity and strength which will be resistant to molten iron and to alkali metal vapors at the temperature of molten iron. Porous silicon carbide refractories of this type may 'be impregnated with an alkali or alkaline earth metal, such as magnesium, and used to treat molten iron metal, either with or without recycling, in the same manner as that described above with reference to the porous carbonaceous refractories.

Although several specific embodiments of the invention have been described, various modifications may be made which will now suggest themselves to those skilled in the art, and it is intended by the appended claims to cover all such modifications which fall within the inventive concept.

What is claimed is:

1. An agent for use in the treatment of molten metals and alloys of the iron group to effect the formation of nodular iron consisting solely of at least one piece of a porous carbonaceous refractory material selected from the group consisting of porous metallurgical coke in lump form and porous graphite in preshaped form having a porosity of approximately 50% and an average pore diameter of less than about .020 inch, the pores of said refractory material being filled with a reactive metal selected from the group consisting of magnesium, sodium, potassium, rubidium and cesium.

2. An agent for use in the treatment of molten metals and alloys of the iron group to effect the formation of nodular iron consisting solely of at least one piece of porous metallurgical coke in lump form having a porosity of approximately 50% and an average pore diameter of less than about .020 inch, and having the pores thereof filled with a reactive metal elected from the group consisting of magnesium, sodium, potassium, rubidium and cesium.

3. An agent for use in the treatment of molten metals and alloys of the iron group to effect the formation of nodular iron consisting solely of at least one piece of porous metallurgical coke in lump form having an average pore diameter of less than about .020 inch and having the pores thereof filled with about 40% by weight of magnesium.

4. An agent for use in the treatment of molten meals and alloys of the iron group to effect the formation of nodular iron consisting of a preshaped member of porous graphite having a porosity of from 40% to 50% and an average pore diameter of less than about .020 inch and having the pores thereof filled with magnesium.

5. A treating agent as claimed in claim 4 wherein said preshaped porous graphite member is in the form of a sphere having a diameter of approximately 5 inches.

6. A method of preparing an agent for the treatment of molten metals and alloys of the iron group to effect the formation of nodular iron which comprises the steps of heating a porous refractory material selected from the group consisting of porous metallurgical coke in lump form and porous graphite in preshaped form, said material having a porosity of approximately 50% and an average pore diameter of less than about .020 inch, immersing said heated material in a molten bath of a metal selected from the group consisting of magnesium, sodium, potassium, rubidium and cesium, the temperature of said material being higher than the melting point of said metal at the time of immersion, and maintaining said material completely submerged in said molten bath until the pores thereof are filled with said metal.

7. A method as claimed in claim 6 including the additional steps of withdrawing the impregnated porous refractory material from said molten bath, and cooling the impregnated material while preventing the access of air thereto.

8. A method of preparing an agent for the treatment of molten metals and alloys of the iron group to effect the formation of nodular iron which comprises the steps of immersing in a molten bath of magnesium body of porous metallurgical coke in lump form having a porosity of approximately 50% and an average pore diameter of less than about .020 inch, maintaining said coke completely submerged in said molten bath until the pores of said coke are filled with magnesium, withdrawing the impregnated coke from said molten bath, and quenching said impregnated coke by immersion in a cooling medium.

9. A method as claimed in claim 8 including the preliminary step of heating the coke to incandescent temperature prior to immersion thereof in the molten bath.

10. A method of preparing an agent for the treatment of molten metals and alloys of the iron group to effect the formation of nodular iron which comprises the steps of immersing in a molten bath of magnesium a preshaped member of porous graphite having a porosity of from 40% to 50% and an average pore diameter of less than about .020 inch, and maintaining said body completely submerged in said molten bath until the pores thereof are filled with magnesium.

11. A method as claimed in claim 10 including the preliminary step of heating the preshaped porous graphite member to a temperature in excess of 2000 F. prior to immersion thereof in the molten bath.

12. An agent for use in the treatment of molten metals and alloys of the iron group to effect the formation of nodular iron consisting of at least one piece of porous metallurgical coke in lump form having a porosity of approximately 50% and an average pore diameter of less than about .020 inch, and having the pores thereof filled with magnesium.

13. A method of preparing an agent for use in the treatment of molten metals and alloys of the iron group to effect the formation of nodular iron which comprises the steps of heating porous metallurgical coke in lump form having a porosity of approximately 50% and an average pore diameter of less than about .020 inch to a temperature not less than the melting point of magnesium, immersing the heated coke in a molten bath of magnesium, maintaining the coke completely submerged in said molten bath until the pores of said coke are filled with magnesium, withdrawing the impregnated coke from said molten bath, and cooling the impregnated coke while preventing the access of air thereto.

14. A method of treating molten metals and alloys of the iron group to effect the formation of nodular iron by submerging in a bath of the molten iron metal a body of refractory material containing a reactive metal selected from the group consisting of magnesium, sodium, potassium, rubidium and cesium, the temperature of the molten iron bath being greater than the boiling point of the re active metal, and maintaining said body submerged in the bath beneath the surface thereof while the latent heat of the molten iron metal vaporizes the reactive metal and causes the latter to enter the iron metal and produce nodularization of the graphite therein, wherein the improvement resides in the use of a body of refractory material which consists solely of porous metallurgical coke in lump form having a porosity of approximately 50% and an average pore diameter of less than .020 inch, the pores of said coke being filled with the reactive metal when the coke is initially submerged in the molten iron metal, whereupon the reactive metal is expelled from the pores of the coke as a vapor and enters the iron metal in a controlled manner without violent reaction, leaving the spent coke intact in porous lump form.

15. A method of treating molten metals and alloys of the iron group to effect the formation of nodular iron comprising the steps of: immersing porous metallurgical coke in lump form in a molten bath of magnesium, maintaining said coke immersed in said molten bath until the pores thereof are impregnated with magnesium, withdrawing the magnesium impregnated coke from said molten magnesium bath, submerging said coke in a bath of molten iron metal and maintaining said coke submerged therein beneath the surface thereof while the latent heat of the molten iron metal vaporizes the magnesium, removing the coke from the molten iron metal bath after at least some of the magnesium has been expelled from the pores of the coke in vapor form and has entered the iron metal to produce nodularization of the graphite therein, re-impregnating the coke by re-immersion in the molten magnesium bath, and re-immersing the re-impregnated coke in a second, untreated molten iron metal bath.

16. The method of treating molten metals and alloys of the iron group as set forth in claim 15 including the further steps of quenching the coke after withdrawal thereof from the molten magnesium bath, and storing the quenched coke for a predetermined time before submerging it in the molten iron metal bath.

17. The method of treating molten metal and alloys of the iron group as set forth in claim 15 including the further step of heating the coke to incandescent temperature before immersing it in the molten magnesium bath.

18. A method of treating molten metals and alloys of the iron group to effect the formation of nodular iron by submerging in a bath of molten iron metal a body of refractory material containing a reactive metal selected from the group consisting of magnesium, sodium, potassium, rubidium and cesium, the temperature of the molten iron bath being greater than the boiling point of the reactive metal, and maintaining said body submerged in the bath beneath the surface thereof While the latent heat of the molten iron metal vaporizes the reactive metal and causes the latter to enter the iron metal and produce nodularization of the graphite therein, wherein the improvement resides in the use of a body of refractory material which consists solely of at least one piece of porous carbonaceous refractory material selected from the group consisting of porous metallurgical coke in lump form and porous graphite in preshaped form having a porosity of approximately 50% and an average pore diameter of less than .020 inch, the pores of said refractory material being filled with the reactive metal when the material is initially submerged in the molten iron metal, whereupon the reactive metal is expelled from the pores of the refractory material as a vapor and enters the iron metal in a controlled manner Without violent reaction, leaving the refactory material intact in porous form.

19. The method of treating molten metals and alloys of the iron group as set forth in claim 18, including the steps of impregnating the refractory material with the reactive metal by immersing the refractory material in a molten bath of said reactive metal, and recycling the refractory material after submergence in the molten iron metal bath by re-impregnating the refractory material by re-immersion in the molten bath of reactive metal and re-submerging the re-impregnated refractory material in a second, untreated molten iron metal bath.

20. The method of treating molten metals and alloys of the iron group as set forth in claim 18 wherein the porous carbonaceous refractory material consists of a preshaped body of porous graphite having the pores thereof filled with magnesium.

21. The method of treating molten metals and alloys of the iron group as set forth in claim 18 wherein the porous carbonaceous refractory material consists of metallurgical coke in lump form having the pores thereof filled with magnesium.

References Cited by the Examiner UNITED STATES PATENTS 2,569,146 9/1951 Bolkcom -129 X 2,716,602 8/1955 Ensign 75-53 2,726,152 12/1955 Eash 75130 2,823,989 2/1958 Deyrup et a1 75130 X 2,881,068 4/1959 Bergh 75-130 X 2,988,444 6/1961 Hurum 7513O X 2,988,445 6/1961 Hurum 75129 X DAVID L. RECK, Primary Examiner.

H, W. TARRING, Assistant Examiner.

Claims

1. AN AGENT FOR USE IN THE TREATMENT OF MOLTEN METALS AND ALLOYS OF THE IRON GROUP TO EFFECT THE FORMATION OF MODULAR IRON CONSISTING SOLEY OF AT LEAST ONE PIECE OF A POROUS CARBONACEOUS REFRACTORY MATERIAL SELECTED FROM THE GROUP CONSISTING OF POROUS METALLURGICAL COKE IN LUMP FORM AND POROUS GRAPHITE IN PRESHAPED FORM HAVING A POROSITY OF APPROXIMATELY 50% AND IN AVERAGE PORE DIAMETER OF LESS THAN .020 INCH, THE PORES OF SAID REFRACTORY MATERIAL BEING FILLED WITH A REACTIVE METAL SELECTED FROM THE GROUP CONSISTING OF MAGNESIUM, SODIUM, POTASSIUM, RUBIDIUM AND CESIUM.

14. A METHOD OF TREATING MOLTEN METALS AND ALLOYS OF THE IRON GROUP TO EFFECT THE FORMATION OF NODULAR IRON BY SUBMERGING IN A BATH OF THE MOLTEN IRON METAL A BODY OF REFRACTGORY MATERIAL CONTAINING A REACTIVE METAL SELECTED FROM THE GROUP CONSISTING OF MAGNESIUM, SODIUM, POTASSIUM, RUBIDIUM, AND CESIUM, THE TEMPERATURE OF THE MOLTEN IRON BATH BEING GREATER THAN THE BOILING POINT OF THE REACTIVE METAL, AND MAINTAINING SAID BODY SUBMERGED IN THE BATH BENEATH THE SURFACE THEREOF WHILE THE LATENT HEAT OF THE MOLTEN IRON METAL VAPOROIZES THE REACTIVE METAL AND CAUSES THE LATTER TO ENTER THE IRON METAL AND PRODUCE NODULARIZATION OF THE GRAPHITE THEREIN, WHEREIN THE IMPROVEMENT RESIDES IN THE USE OF A BODY OF REFRACTORY MATERIAL WHICH CONSISTS SOLEY OF POROUS METALLURGICAL COKE IN LUMP FORM HAVING A POROSITY OF APPROXIMATELY 50% AND AN AVERAGE PORE DIAMETER OF LESS THAN .020 INCH, THE PORES OF SAID COKE BEING FILLED WITH THE REACTIVE METAL WHEN THE COKE IS INITIALLY SUBMERGED IN THE MOLTEN IORN METAL, WHEREUPON THE REACTIVE METAL IS EXPELLED FROM THE PORES OF THE COKE AS A VAPOR AND ENTERS THE IRON METAL IN A CONTROLLED MANNER WITHOUT VIOLENT REACTION, LEAVING THE SPENT COKE INTACT IN POROUS LUMP FORM.