IL22434A - Materials for treating molten ferrous metals to produce nodular iron - Google Patents

Description

This Invention relates generally to materials, for treating molten metals and lloys, and more particu-larly to low boiling point alkali metal agents for treating molten iron or iron alloys to produce nodular Iron.

Nodular iron, also known as speroidal 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 pro-oessing. 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 melt are deoxidatlon, desulfuriza-tion, denltrogenizing, dephosphorizing, deslagglng, degassing 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 to molten . ferrous metals and alloys has, In recent years, gained considerable Importance· The effect of magnesium and sodium as deoxi-dlzers 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* P., 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 oourse, 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 toward minimizing the problems of reectivity and volatility, and curbing the reactive and volatile nature of the aiiewti metal. These efforts have resulted in various methods of introducing the low melting 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 con* trolled 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 magneslum-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 o 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 pel-lets 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 difficulties 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 briquet ing method, mechanical mixtures of low boiling point alloys and high meltejpoint metals, metallic oxides and refractories are briquetted, and the briquettes are introduced 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 metal for treating molten metals and alloys.

In general, the present invention relates to a porous refractory, a¾caH-metal-Impregnated material which is produced by immersing a piece of porous coke, carbon or graphite in a molten body of low boiling point alkali metal, such as magnesium, and holding it there until the pores of the refractory material are filled with thejBAtesAi 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 nodularlzatlon 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 a^l boiling point alkali metal enters the small diameter pores of the porpus 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 magncoium, 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 deeired volume and configuration is first heated to a temperature hotter than, and is then immersed in, a body of molten low boiling point alkali 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 al a me a 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 relmmersed in the molten magnesium and the magnesium which had been expelled may be replaced by re?* impregnation. 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 sufficient amount of magnesium to treat a given amount of molten iron. The reaction rate or time re-quired 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- olume ratio. A er 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 reoycling.

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 relmmersed below the surface of the 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 0 of the magnesium can be expected. Magnesium recovery may be expressed by the following formula: Recovery (#) <* Residual Magnesium In Iron (lbs,) + 0,75 (S^-Sp) (lbs.) Total Magnesium Used (lbs* where is the Initial sulfur content of the iron (lbs.) and Sp 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 treatment 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 amount of residual magnesium is required in the iron to produce the nodularizing effect. The efficiency or recovery therefore dictates the total amount of magnesium which must be added in order to achieve the desired residual level.

Experiments have indicated that a definite relationship exists between the pore size of the refractory and Impregnation. Porous graphite and carbon of various pore sizes up to an average pore diameter of .0047 Inch have been impregnated successfully In accordance with the teachings of this invention. However, difficulty has ¾een experienced in impregnating the more porous grades of coke wherein the average pore diameter is about .020 inch or greater* It should also be noted that in all attempts to Impregnate where the porous refractory material was only partially submerged beneath the surface of the molten magnesium, the Impregnation was unsuccessful* Accordingly, in order to effect successful impregnation, the porous material must be com-pletely submerged below the surface of the molten magnesium* This is theorized to be caused by the molten magnesium reacting with the oxygen and nitrogen in the pores and creating a vacuum which sucks in the molten magnesium when the refractory material is completely submerged; however, when only partially submerged, more air is sucked into the porous refractory material* When introducing one metal into another molten metal where the boiling point of the metal being introduced is lower than the temperature of the molten metal, the ladle is designed to provide a maximum depth of penetration in the molten metal to provide maximum recovery* The low boiling point metal is converted to a metal vapor upon immersion in the molten metal and immediately starts to rise toward the surface thereof* The metal vapor reacts with undesirable elements in the molten metal to be treated and In some cases goes into solution as an alloying agent* The further the metal vapor must travel to reach the surface, the greater are its chances of reacting with the undesirable elements or being retained, since it usually oxidizes ime-diately upon reaching the surface* The porouB refractory material of the present invention is such as to distribute the low boiling point metal so that the formation of vapors is spread as evenly as possible in the ladle, This prevents excessive turbulence and concentration of the vapors.

The use of magnesium-impregnated coke in the production of nodular or ductile iron in accordance with the present invention provides a further beneficial side effect in that it may increase the carbon content of the treated iron due to the solubility of the coke. Increases of up to 0.15$ in carbon content have been obtained in practicing the invention, the specific amount of carbon increase apparently being a function of both the time that the magnesium-Impregnated coke remains immersed in the iron and the original carbon content of the base iron. The immersion time is a factor because, during the first two or three minutes following immersion of the magnesium-impregnated coke, the magnesium vapor expelled from the coke lumps actually protects the coke against dissolving. On the other hand, if the coke remains submerged until most or all of the magnesium is expelled, the iron directly contacts the coke and some of the carbon goes into solution in the iron. The original carbon content of the base iron affects the amount of carbon Increase because any iron of a specific silica content has a definite saturation point for carbon beyond which no further carbon will go into solution.

Consequently, the higher the silicon and carbon content of the base iron, the lower will be the carbon pick-up from, the coke.

The Increased carbon content due to pick-up from magnesium-impregnated coke is advantageous in some cases, first, because an increase in carbon content increases fluidity of the iron which is beneficial in pouring castings of thin section or which require good surface finish, and, second, because carbon which goes Into solution in the iron just prior to casting acts as an in^oculant which beneficially changes the structure and physical properties of the iron and thereby saves the expense involved in adding the usual ferro-silicon In practice, nodular iron has been produced by treating the molten iron with a magnesium-Impregnated porous graphite cylinder provided with external grooves, with a magnesium-Impregnated porous graphite sphere, and with magnesium-impregnated metallurgical coke, without any apparent difference in product quality. In the system using impregnated coke, coke in lump form was placed in a conventional dipping basket, and ladles of 1000 pounds and 5500 pounds of molten iron were treated. In each case, nodular iron was produced of good quality with the estimated magnesium recovery being 0#. The following examples illustrate in greater detail various aspects of the invention.

EXAMPLE I A 4200 pound ladle of ductile base iron was treated by the magnesium-impregnated graphite method in which a 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 provided a sufficient surface-volume ratio to absorb enough magnesium to treat 4000 pounds of molten iron. The graphite cylinder was heated in a coke fire and immersed in molten magnesium where its void spaces absorbed the magnesium. The magnesium impregnated graphite cylinder was then withdrawn and immersed in a 4200 pound ladle of molten iron having a temperature of 2β00β P, It remained submerged in the iron for 4 minutes,, 27 seconds. When the cylinder was removed from the iron, the cylinder was still ejecting magnesium. Thus, the cylinder demonstrated the capability of use in foundries where the treatment time for the molten metal is relatively long and the impregnated porous block can be left in the molten iron for long periods of time.

EXAMPLE II In a foundry such as a pipe production foundry, where a 4000 pound ladle of molten iron is treated with magnesium every minutes, the addition of magnesium should not take longer than 1 minute since the iron must be transported to the casting machine, skimmed and reladled into the casting machine ladles within the 5-niinute period. An impregnated porous graphite body machined to a spherical shape is particularly adapted to this system due to the large volume available to contact the molten iron.

A 5 inch diameter sphere of graphite having 48$ of its volume as voids was heated by a coke fire and impregnated with magnesium by immersing it in the molten magnesium. The magnesium-impregnated sphere was taken directly from this operation and immersed In the molten iron at a temperature of 2600° F. Instead of allowing the graphite sphere to cool after treating the iron, the graphite sphere was recycled by again immersing it in the molten magnesium to receive another charge of magnesium. This cycle between the iron and magnesium was repeated a total of four times.

The first cycle produced only 5$ recovery, hut after the sphere was recharged with magnesium and plunged into the molten iron, 40# residual magnesium was recovered.

The low recovery of the first cycle was mostly due to the temperature of the graphite sphere being too low prior to going into the molten magnesium. The heat from the molten iron during the first cycle raised the temperature of the sphere sufficiently for the second cycle. The third and fourth cycles produced 33# and 30$ recovery, respectively.

It was noted that there was no damage to the graphite sphere after continuous cycling. After the last cycle, the molten magnesium was allowed to solidify with the graphite sphere submerged in it. After six days, the magnesium was remelted and the sphere removed and cooled while completely covered with sand to prevent the magnesium from burning in the atmosphere. No damage to the sphere was observed, and it was still impregnated with mageslum.

A summary of the operation and partial chemical analysis of Example II are given in the following table: Weight Time In Time In Cycle of Iron Magnesium Iron Si Mh Mg Recovery No. (lbs.) (Min.) ,(M >); ( ) (%) { ) % 1 1000 2 : 30 1 :22 2«30 0.27 0.010 5 2 1000 2:00 3 :00 2.88 0,29 0.090 40 3 1000 25 :00 2 :15 2.30 0.30 0.066 33 4 1000 1 :45 2 :30 2.75 0.33 0.126 30 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 lmpreg-natlng porous graphite with magnesium and plunging it into a ladle of molten iron. A 5-1/2 inch diameter graphite sphere having 8$ of its volume as voids was heated to a temperature in excess of 2000° P. 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 of treatment was 2640° P. 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 1.9$ recovery of the magnesium placed in the ladle.

EXAMPLE IV A 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 pound ladle of molten iron. The magnesium content in the molten iron after treatment was 0.097$ by weight which is more than sufficient to produce nodular or ductile 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 8$. 2 pounds, 6 ounces of magnesium was volatilized into the iron and gave a recovery of 1.9$· 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° P. The heated sphere was then immersed in molten magnesium for Impregnation. This sphere was then used to treat three successive ir ladles of 1000 pounds each by immersingfin the first ladle of molten iron until all of the magnesium was ejected, re-immersing the sphere in the molten magnesium until it was relmpregnated 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$, The following table illustrates the results of this example : Cycle Time In Mag. Time in Iron Residual Mag. Recovery No. (Mln.) (Min.) (≠) (*) 1 2.0 3.0 0.080 40 2 25.0 2.25 0.066 33 3 1.75 2.50 0.060 30 EXAMPLE VI A block of porous graphite 14 Inches by 14 inches by 6 inches, weighing about 46 pounds, was attached to a ladle lid and preheated by immersion in molten iron at a temperature of approximately 2600* Ρ· The heated porous graphite block was then immersed in molten magnesium where it was impregnated. This block was used to treat a 4200 pound ladle of molten iron. After treatment, the iron had a residual magnesium content of 0,139$ which is at least twice that required to produce nodular or ductile 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, commercially 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 80# of the original coke weight, or about 43$ of the total weight of the impreg-nated 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 metal 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 bum. 30 to 0 pounds of the hot incandescent coke was then placed in a frame fabricated from 1/2 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 the 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 sufficient to effect 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 magnesium-impregnated 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 by conventional skimming methods prior to casting the Iron, The following table summarizes the analysis of metals after treatment of the six ladles: 1 0.077 2.17 3.19 2 0.066 2.33 3.20 3 0.134 3.19 3.50 4 0.116 2.71 3.43 0.072 2.35 3.44 6 0.134 2.54 3.50 In accordance with the principles of this invent tion, 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 refraotory 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 submerged 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 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.

Claims (20)

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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 of a porous carbonaceous refractory material having the pores thereof impregnated with an «aliaH metal selected from the group consisting of magnesium, sodium, potassium, rubidium and cesium,

2. An agent according to claim 1, wherein the refractory material is selected from the group consisting of coke, graphite and carbon.

3. « An agent according to claim 2, wherein the refractory material is coke in lump form having a porosity of approximately 50$.

4. · An agent according to claim 3, wherein each lump of coke has a volume of from about 10 to about 12 cubic inches.

5. An agent according to claim 3 or , wherein the coke has ashore diameter of less than about «020 inch.

6. An agent according to claim 2, wherein the refractory material is a pre-shaped member of porous graphite having a porosity of from 0 to 50$.

7. An agent according to claim 6, wherein the graphite member is in the form of a sphere approximately five inches in diameter.

8. An agent according to any preceding claim, wherein the alkali metal is magnesium.

9. An agent according to claim 8, wherein the magnesium amounts to about O0 by weight of the Impregnated material ·

10. 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, comprising the steps of immersing a porous/refractory material in a molten bath of an ttikali metal selected from the group consisting of magnesium, sodium, potassium, rubidium and cesium, and maintaining the said material completely submerged in the bath SeueC until the pores thereof are impregnated with the alkali metal.

11. The method according to claim 10, wherein the refractory material is selected from the group consisting of coke, graphite and carbon, and has a porosity of from 0$ to 50#.

12. The method according to claim 10 or 11, including the step of heating the refractory material prior to its immersion in the molten bath, the temperature of the material at the time of immersion being higher than the melting point of the alkali metal.

13. · The method according to any of claims 10 to 12, Including the additional steps of withdrawing the impregnated porous refractory material from the molten bath, and cooling the Impregnated material while preventing the access of air thereto.

14. The method according to claim 13, wherein the impregnated material is cooled by immersion in a liquid quenching medium.

15. The method according to any of claims 10 to 14, wherein the refractory material used is porous coke in lump form and the alfeaii metal Is magnesium.

16. The method according to claims 12 and 15, wherein the coke is heated to Incandescent temperature prior to its immersion in the molten bath.

17. · The method according to any of claims 10 to 14, wherein the refractory material is a pre-shaped member of porous graphite having a porosity of from 40$ to 50$, and the aikali metal is magnesium.

18. The method according to claims 12 and 17* wherein the graphite member is heated to a temperature in excess of 2000* P. prior to its immersion in the molten bath.

19. An agent for use in the treatment of molten metals and alloys of the iron group, substantially as described hereinabove.

20. A method of preparing an agent for use in the treatment of molten metals and alloys of the iron group, substantially as described hereinabove. ο*τβ© THIS 1!ttt OAT W Novewaan, 1964 OR TUB APPM0ANT8, OR. ftSttmOLO COHN ft 00.