US3672871A - Metallurgical material and processes for treating steel therewith - Google Patents

Abstract

COARSE (-3/8 INCH) METALLURGICAL-GRADE SILICON CARBIDE HAS 6-15 WEIGHT PERCENT OF SODIUM CARBONATE ADDED TO IT, AND THIS IS USED AS A TREATMENT AGENT FOR RECARBUIRIZING, RESILICONIZING, OR DEOXIDIZING STEEL AND INSURING ITS CLEANLINESS. THIS MAKES IT POSSIBLE TO USE A COARSER MATERIAL, WHILE IMPROVING THE QUALITY OF THE STEEL AND THE EFFICIENCY OF THE UTILIZATION OF THE SILICON CONTAINED IN THE SILICON CARBIDE. COMPARED WITH DEOXIDIZING WITH FERROSILICON OF 50% SILICON CONTENT OR WITH ALUMINUM, COST SAVINGS ARE ALSO EFFECTED.

Description

June 27, 1972 w. A. BROWN ETAL 3,672,871

METALLURGICAL MATERIAL AND PROCESSES FOR TREATING STEEL THEREWITH Filed Jan. 12', 1970 United States Patent Office 3,672,871 Patented June 27, 1972 3,672,871 METALLURGICAL MATERIAL AND PROCESSES FOR TREATING STEEL THEREWITH William A. Brown, Rector, and John F. Drenning, Monroeville, Pa., assignors to Miller and Company, Chicago, Ill.

Continuation-impart of application Ser. No. 645,557, May 11, 1967, which is a substitute for application Ser. No. 172,614, Feb. 12, 1962. This application Jan. 12, 1970,

Ser. No. 2,202

Int. Cl. C21c 7/04 US. C]. 75-58 2 Claims ABSTRACT OF THE DISCLOSURE Coarse inch) metallurgical-grade silicon carbide has 6-15 weight percent of sodium carbonate added to it, and this is used as a treatment agent for recarburizing, resiliconizing, or deoxidizing steel and insuring its cleanliness. This makes it possible to use a coarser material, while improving the quality of the steel and the efliciency of the utilization of the silicon contained in the silicon carbide. Compared with deoxidizing with ferrosilicon of 50% silicon content or with aluminum, cost savings are also effected.

CROSS-REFERENCES TO RELATED APPLICATIONS This application is a continuation in part of our earlier-filed copending application Ser. No. 645,557, filed May 11, 1967, now abandoned which, in turn, is a substitute of our earlier-filed application Ser. No. 172,614, filed Feb. 12, 1962, which became abandoned Mar. 19, 1964.

BACKGROUND OF THE INVENTION (1) Field of the invention This invention relates to a composition of matter consisting principally of metallurgical-grade silicon carbide and about 6-15 weight percent of soda ash, and to methods of treating steel that utilize such composition.

(2) Description of the prior art A great variety of methods are known for making steel, such as the open-hearth process, the basic oxygen process, the Bessemer process, the electric furnace process, etc. Within the above-mentioned processes, there are a multiplicity of particular practices that are used to make steels of particular kindssrnall or substantial amounts of various elements such as carbon, silicon, aluminum, vanadium, molybdenum, etc. are purposely added to the steel, in the furnace or in the ladle, with a view to achieving a desired combination of properties. The steelmaking processes mentioned above have in common, however, that they ordinarily begin with a substantial amount of blast-furnace hot metal that contains, for example, about 4% plus carbon and up to 2% plus silicon, and they finish with a steel that contains less than about 1.5% carbon and usually less than 1% of silicon. In the main, the making of steel comprises removing carbon, silicon, sulfur, and phosphorus from blast-furnace hot metal, and then appropriately adjusting the chemical composition of the metal, if necessary to bring it within desired limits. The foregoing statements are generalities that have a number of obvious and important exceptions. The open-hearth process may be operated with an all-scrape charge, and when this is done, hot metal from the blast-furnace is not required, and the amount of carbon removal that must be done is generally not great. In a number of electrical steels, silicon is purposely added in amounts up to 5%. In the acid openhearth process, sulfur and phosphorus are not removed. The processes do have in common, however, that it is desirable to produce steel that is clean, rather than dirty. A dirty steel contains segregations or inclusions of alumina, silicon dioxide of the like. The vincity, in a piece of steel, of such an inclusion or segregation is a point of weakness. It is especially important in tools or in pieces of steel subjected to high stresses to avoid, to the greatest extent possible, the occurrence of such segregations or inclusions.

Considerable is known about the likelihood of the occurrence of segregations or inclusions of the kind that render a steel dirty. If a steel has a high silicon content, or if it is made under a relatively basic or viscous slag, it is more likely to be dirty. Steel made in an acid open-hearth furnace, under a relatively fluid acidic slag, is more likely to be clean than a steel made in a basic open-hearth furnace. Ladle additions are more likely to make a steel dirty than furnace additions.

Another factor having a considerable influence upon the tendency of a steel to be dirty rather than clean is its dissolved-oxygen content. The removal from a molten ferrous melt of carbon or silicon is customarily conducted by causing the melt to be brought into contact with air or oxygen; when this happens, the molten ferrous melt becomes, in most instances, as nearly saturated with oxygen as is possible, considering the carbon and silicon content of the ferrous melt. The dissolved-oxygen content of a ferrous melt is very importantly influenced by the carbon content of the melt. In most instances, when the carbon content of the melt is above about 0.50%, relatively little oxygen remains dissolved in the ferrous melt, but when the carbon content of the ferrous melt is less than that, increasing amounts of oxygen remain dissolved in the molten steel. Of course, these amounts of oxygen have a strong tendency to leave the steel or react with a silicon and/or aluminum therein as it cools and solidifies.

It is known to kill steel. When a steel is killed, there is added to it a substance (such as aluminum, silicon metal, ferrosilicon, or silicon carbide) that tends strongly to react with oxygen dissolved in the steel. After a steel has been killed, there are no dissolved gases remaining in it to counteract its natural tendency, upon solidification, to form a hollow or cavity, called pipe, in the center of the ingot. Dead-killed steels are usually hot-topped to minimize pipe, but hot topping adds to the cost of making the steel.

As indicated above, the dissolved-oxygen content increases as the carbon content decreases. There are, accordingly, a number of steels with carbon contents on the order of 0.04-0.10% that are sufliciently high in dissolved-oxygen content that they may be characterized as capping or rimming. In each case, use is made of the removal by eifervescence of the dissolved oxygen from the steel, upon solidification, to avoid the development of unwanted pipe. Those skilled in the art will understand that it is important, in adding materials to steels that are intended to be rimming or capping, to avoid adding so much that the desired rimming or capping action will be lost, with the steel behaving like a dead-killed steel.

The art of making additions to steel in a ladle, as it is being withdrawn from a furnace, whether it be an openhearth furnace, an electric furnace, or a basic oxygen furnace, includes various practices, among which is the addition to the steel of a suitable amount of ferrosilicon having a. silicon content of between 50-98%. An addition of silicon will increase the strength of the steel, but will also increase, to some extent, the chances of its being dirty, especially if the dissolved-oxygen content of the steel is high and the slag is viscous. When, however, the

desired strength cannot be economically obtained unless silicon is used, it is usual to add ferro-silicon, taking the risk that the steel will become dirty.

It is also known to add to steel some silicon carbide, especially where it appears that it would be advisable to increase both the silicon content and the carbon content of the steel. For this purpose, it has been customary to use a metallurgical-grade silicon carbide, i.e., one containing about 85-92% of silicon carbide. Moreover, the teachings, of the prior art are such that when this is done, it is customary to require that the silicon carbide used in a 50 mesh size condition, or finer, or in any event, not coarser than 36 mesh. The prior-art practice includes putting the metallurgical-grade silicon carbide of 50 mesh size into one or more paper bags and addingit to the ladle into which a furnace is tapped, shortly after the traping has begun, so that there is on the bottom of the ladle about 6-18 inches of molten steel. It is known that when this is done, the carbon and silicon content of the steel may or may not be increases and that the steel becomes, at least to some substantial extent, lower in dissolved-oxygen content than it had been before.

Attempts had been made to use a coarser silicon carbide to treat steel, but these attempts had, in general, been unsuccessful. The silicon carbide tends to float to the surface and remain gathered in the slag, rather than having its desired effect upon the steel.

Another factor to be considered is the temperature of the molten steel to which the silicon carbide is added. In the earlier days of the use of silicon carbide of metallurgical grade as an additive to treat steel, it did not often occur that the steel was tapped in large quantities or at such a temperature as to be possessed of substantial superheat. Accordingly, it was essential that the silicon carbide be present in a finely divided form, so that it could be caused to react as rapidly as possible with the molten steel. In view of the unsatisfactory results ordinarily obtained when silicon carbide of metallurgical grade, but used in the form of material coarser than 50 mesh, was utilized, the prior art has looked away from the use of such coarser silicon for the treatment of steel. Although in modern times it has become much more usual to Work with larger or'better-heated quantities of steel, the attempts that have been made, prior to the present invention, at the use of such coarser silicon carbide have yielded disappointing results.

It is known, of course, that sodium salts have a catalytic action with silica. This is basic to the chemistry of making glass. There would not, however, from this fact be any basis for concluding that it would be reasonable to expect the addition of, for example, 9 weight percent of sodium carbonate to a metallurgical-grade silicon carbide would so increase its effectiveness as a treating agent for steel, by reason of the fluxing and/or catalytic action if silicon formed on the surfaces of particles of the silicon carbide, as to improve the quality of the steel produced to the extent indicated hereinbelow in the disclosure of the present invention, or to render possible the use of coarse 4 metallurgical-grade silicon carbide. The fluxing and/or catalytic effect of sodium carbonate speeds the dissociation of silicon carbide in liquid steel.

It is known, moreover, to deoxidize cast iron with the use of briquettes of silicon carbide that have been modified with sodium carbonate. The cast irons are remarkably different from the steels in their dissolved-oxygen content. The cast irons contain over 1.7% of carbon, and perhaps A as much dissolved oxygen as a steelof 0.50% carbon content, or about li as much dissolved oxygen as a steel of 0.10% carbon content. There would, accordingly, be nothing seen by persons of ordinary skill in the art in a patent relating to the deoxidation of cast iron with the use of a briquette of silicon carbide modified with sodium carbonate that would lead such person of ordinary skill in the art to believe that, despite the remarkably greater oxygen content of steels, the same or a similar composition may well be used for the effective deoxidation of and promotion of cleanliness in such steels.

SUMMARY OF THE INVENTION Molten steel is treated with metallurgical-grade silicon carbide (about -92% pure) to which 6-15 weight percent of sodium carbonate (soda ash) has been added. The material is used coarse inch by 0), being supplied to the ladle into which the steel is tapped in paper bags containing about 25-50 pounds of material, at a time shortly after the beginning of tapping of the furnace in which the steel is made. The amount of material used ranges between 4 pound and 7 pounds per ton of steel. The soda ash fluxes the silicon that forms on the surfaces of the particles of silicon carbide, making it possible to use silicon carbide that is coarser. This yields a cost saving, and at the same time, the cleanliness of steel produced is improved, as well as the efiiciency of utilization of contained silicon carbide.

DESCRIPTION OF THE DRAWINGS A complete understanding of the invention may be had from the foregoing and following description thereof, taken together with the appended drawings, in which:

FIGS. 1 and 2 are photomicrographs of steel specimens, FIG. 1 illustrating a microstructure obtained by casting steel in accordance with the prior art and FIG. 2 illustrating the microstructure obtained in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The metallurgical material of this invention is made by mixing metallurgical-grade silicon carbide, i.e., a material containing about 85-92% pure silicon carbide, in a size range of preferably inch, but possibly as coarse as inch, with between 6 and 15 weight percent of sodium carbonate (soda ash). Between 6 and 9 percent of soda ash is optimal for most purposes.

Concerning the metallurgical-grade silicon carbide, it should be understood that silicon carbide is commercially made by packing a furnace generally in the form of a long cylinder, with an exterior surrounding of a mixture of silica sand, sawdust and salt and an interior core of graphite, with an electrode at each end of the furnace in contact with the graphite. The electrical power is passed through the electrodes for a relatively short period of time through the electrodes for a relatively short period of time, a few hours, and then the reaction between the graphite and the silica sand continues for a substantial further period of time, on the order of several hours. There is thus obtained in the furnace a processed charge that ranges, near the center of the furnace, from near-pure silicon carbide (such as the material 97-99% pure that is used for polishing or for refractories), to less pure silicon carbide (about 50% pure) near the exterior of the processed charge. Moreover, as it comes from the furnace where it is produced, the silicon carbide tends to be in the form of massive crystalline structures at the center to finer crystals at the exterior of the furnace. If a fine size is specified, such as 50 mesh, it is necessary to crush the larger crystals to below 50 mesh, which is expensive because of the extreme hardness of silicon carbide. This means that inch of metallurgical-grade silicon carbide is substantially less costly to produce than 50 mesh metallurgical-grade silicon carbide because the crushing operation does not take so much time for a given amount of each size.

Although it has long been appreciated that metallurgical-grade silicon carbide might be made available at lower cost in the form of inch material, those skilled in the art of treating steel with various additives, including metallurgical-grade silicon carbide, have not been led prior to the present invention, to use inch metallurgical-grade silicon carbide. Past experience with coarser fractions of metallurgical-grade silicon carbide has been unsatisfactory because the larger particles float upward through the steel and into the slag without reacting with impurities in the steel or becoming dissolved in the steel to an appreciable extent, indicative of a reasonably good efficiency of utilization of the contained silicon carbide, such as about 90% or greater. Past experience indicates that the relatively more costly 50 mesh material was required. In making it possible to use the coarser metallurgical-grade silicon carbide, containing a substantial amount of material quite coarse, about 30% or more of it being in the size range between 20 mesh and inch, the present invention represents a substantial step forward in the art of treating steel.

The amount of soda ash or sodium carbonate that is to be used varies, as indicated above, between 6 and 15 percent by weight. With less than 6%, the soda ash is not present in the quantity large enough to have its desired effect of promoting the catalytic action and/or removal of silica that tends to form on the surfaces of the larger particles while they are in contact with the molten steel. On the other hand, there is in most cases little or no observable benefit obtained when the proportion of soda ash used is greater than 9%, and as the proportion of soda ash used is taken in higher, the material loses its content of carbon and silicon values. The upper limit of 15% is set with these considerataions in mind, representing the greatest soda ash content that can generally be tolerated while keeping the carbon and silicon values sufiiciently high to be generally useful.

There is no requirement that any particular effort be made to obtain an especially homogeneous mixture of the inch metallurgical-grade silicon carbide and the soda ash. If the two materials are merely fed simultaneously from their respective supply hoppers through suitable automatic weigh feeders into a bag or other container, satisfactory results are obtained.

Although it is known that sodium salts will flux silica, and on that basis, the selection of sodium carbonate might seem obvious, we have found that this is not the only consideration involved. For example, we have tried sodium chloride in place of sodium carbonate and found, that although it will flux the silica from the surfaces of the larger particles of silicon carbide, it also has a strong tendency to form fumes that make its use undesirable.

Moreover, it was somewhat surprising to discover that the fluxing and or catalytic action of 6 weight percent of soda ash was so strong as to yield the results and advantages that characterize our invention.

The manner of using the above-indicated mixture of soda ash and inch metallurgical-grade silicon carbide is similar to the manner of using the 50 mesh material, namely, by placing it in bags holding a suitable quantity thereof, such as about 25 pounds or about 50 pounds, and then, after the bottom of the ladle into which the furnace in which the steel is made is tapped has been covered with a suitable layer of molten steel, namely, one of about 6-18 inches deep, placing a suitable number of bags of such material into the ladle. The reason for placing a layer of steel on the bottom of the ladle before adding the bags of metallurgical material is that silicon carbide is very refractory, and if the bags were placed into an empty ladle, the material would tend to ball-up, thus slowing down the rate of reaction between the silicon and carbon and the FeO in the steel. Eventually, the silicon carbide would go into solution, but it would be too late to do the prime function of deoxidation, and an area rich in carbon and silicon would result in the ladle. The reason for using the bags is to retard to a minor eX- tent the loss of the fines in the material through the convection currents in the ladle as the molten steel is tapped from the furnace into the ladle. This improves to some extent the efliciency of its action.

The number of bags of material to be used will depend upon the kind of steel being treated, the quantity of steel being treated, and the intended purpose of the treatment. In general, however, there will be required between A pound and 7 pounds of our novel metallurgical material per ton of steel being treated. When treating the rimming and capping steels, which have a carbon content of about 0.040.10% and are relatively rich in dissolved oxygen, it is important not to use so much of our novel metallurgical material as to destroy the desired rimming action. If, for example, we were to add as much as 4 pounds per ton of our material to such steel, it would become deadkilled and develop pipe when cast as an ingot. In treating such steels, we prefer to use about 4 pound to 1 pound of our novel material per ton of steel being treated, with the greater amounts being used with the ones of such steels that are lower in carbon and therefore somewhat richer in dissolved oxygen.

When used in this manner, the novel metallurgical material of our invention may be used to replace aluminum, pound for pound. The aluminum is more expensive than our material, and has the further drawback that when it reacts with the dissolved oxygen, its product of oxidation (alumina) is one that is rather undesirable to have in contact with molten steel if it is especially desired that a clean steel be produced. When the material of our invention is used, the products of oxidation are silica and carbon dioxide, a gas which tends to flush out the silica and other inclusions. The excess soda ash forms a large low-melting-point inclusion which tends to rise through the molten steel in the ladle and entrap other inclusions, which then rise to the slag in the ladle.

The novel material of our invention has advantages over ferrosilicon of 50% silicon content as a deoxidant for molten steel. We find that we can replace approximately 5 pounds of 50% ferrosilicon with 3 pounds of our novel material, but our novel material is less costly to start with. Moreover, the steeel so made is cleaner, because with our material it contians less silicon and one of the by-products of deoxidation is a gas; therefore, less silica is formed and has a better chance of being flushed out of the ladle. Moreover, our novel material, like aluminuc, is exothermic in its effect, whereas 50% ferrosilicon is not. There are ferrosilicons of greater silicon content, such as 75%, and these are exothermic, but they are considerably more costly than the 50% ferrosilicon.

Silicon carbide is not always added to steel for the purpose of deoxidation. There are times, for example, in the making of a rail steel containing 0.85% carbon and 0.20% silicon, that it becomes necessary to adjust the composition of the steel that has been made in the openhearth or other steelmaking furnace. It may happen, for example, that while refining the steel in the steelmaking furnace so as to achieve adequate removal of the surfur and phosphorus in the steel, the refining has been carried to a point where the carbon content is brought down to 0.65% and the silicon is close to nil. In order to make, then, a rail steel having the composition indicated above, it is necessary to introduce a substantial amount of carbon and silicon into the steel. Moreover, since the amount of carbon to be added is so great, it is not desirable because of quality requirements to use coke alone for restoring the carbon content. Therefore, although part of the carbon can be restored by adding coke, the rest is put in the form silicon carbide, which has a substantial exothermic effect as a result of its heat of solution. In comparison with the prior practice of using influxed 50 mesh silicon carbide, the use of the material of our invention provides cost savings (because of its tolerance of coarser materials) and a cleaner steel (because of the presence of flux).

It should be understood from the explanation given above, our invention thus provides advantages in cost and cleanliness of steel produced in both of the kinds of use hitherto made of 50 mesh silicon carbide, namely, the deoxidant use and the carbon-silicon-restoral use. It should also be understood, however, that the invention is not foreshadowed or made obvious by prior art teachings concerning the production of briquettes that contain silicon carbide and sodium carbonate. Such briquettes are taught in US. Pat. No. 3,051,564. They have the disadvantage, in comparison with the present invention, that they are necessarily more costly than the metallurgicalgrade silicon carbide from which they are made because of the expense of providing a suitable binder and the operation of the briquetting equipment. Silicon carbide is a very hard, abrasive substance, and the wear on the dies of a press used to briquette it is very high. Moreover, the suitable binders used in making such briquettes are either materials such as pitch or tar that contain sulfur and would be deleterious to the composition of the steel, or inorganic binders of basic nature, such as Portland cement, that would add to the viscosity of the slag and increase the likelihood of the occurrence of undesired non-metallic inclusions, i.e., the production of dirty steel.

The present invention is also to be understood as being distinct from the practice disclosed in British Pat. No. 643,692 and in the corresponding US. Pat. No. 2,444,424. The practice involves placing 36 mesh (or finer) metallurgical-grade silicon carbide in bags, adding them to a ladle of steel to be treated, filling the ladle and holding for a substantial period of time. These patents do not suggest our discovery that by adding sodium carbonate, we can obtain a cleaner steel while using material of greater coarseness and while avoiding the necessity of the above-indicated holding period.

The invention described and explained above is illustrated by the following specific examples.

EXAMPLE I There was made in an acid open-hearth furnace 50 tons of a forging-grade steel having a final composition of 0.32 carbon, 0.66% manganese, 0.034% phosphorus, 0.035% sulfur, 0.37% silicon, balance substantially iron. The usual practice in making this grade was to utilize a furnace addition of about 400 pounds of. metallurgicalgrade silicon carbide, at least as fine as 36 mesh and usually 50 mesh. In this example of the invention, however, the practice was changed slightly. There was prepared a metallurgical material in accordance with our invention, made by mixing 425 pounds of metallurgicalgrade silicon car-bide (88% pure, '20 mesh) with 42.5 pounds of soda ash. Three-hundred fifty pounds of this novel metallurgical material were added to the furnace with the charge. After the furnacing was complete, steel was tapped from the furnace into a ladle of 50-ton capacity to a depth of 1 foot, and there were added to the ladle three 25-pound bags of novel metallurgical material. The ladle was then filled with steel from the furnace, and the steel was poured into ingots. Metallographic specimens were prepared of the steel in such ingots. The attached FIG. 2 is a representation at magnification of 250 diameters of a photomicrograph obtained from a typical one of said metallographic specimens. For comparison, FIG. 1 is a similar photomicrograph, taken from an earher heat from the same furnace, with the furnace being used to make the same grade of steel in accordance with the above-indicated prior practice of using a 400-pound furnace addition of 36 mesh of silicon carbide. The photomicrograph of FIG. 1 is typical of those obtained with specimens of steel produced according to such prior practices.

The cleanliness of the steel in FIG. 2 is especially noteworthy when it is considered that the steel in FIG. 1 was made in an acid open-hearth furnace and with the avoidance of a ladle addition, both of which are circumstances favoring the production of a clean steel, whereas the steel of FIG. 2 was produced with the use of a ladle addition.

EXAMPLE II In an acid-lined electric furnace, 5000 pounds of steel were made, having the composition of 0.25% carbon, 0.45% manganese, 0.50% silicon, balance iron and impurities. The 5000 pounds of steel were made, starting with 4700 pounds of plate steel and 300 pounds of pig iron. Fifty-five minutes after the furnace pilot was turned on, there were added an addition of 400 pounds of pig iron, 65 pounds of ferromanganese, and 3 pounds of 50% ferrosilicon. Heating of the steel in the acid-lined electric furnace was continued with the steel reaching a tapping temperature of about 3050 F. The steel was tapped into a ladle of 5000-pound capacity, with about 60 pounds of Grade 1 1 bar aluminum being added to the ladle. Steel was then poured from that ladle into a ladle of 400-pound capacity, with there being added to the 400-pound ladle, after its bottom was covered to a depth of approximately 6 inches, 915 grams of material comprising metallurgical-grade silicon carbide (85% pure, -20 mesh) and 6% by weight of sodium carbonate, thereby providing the equivalent of 511 grams of pure silicon. The 400-pound ladle was then filled to its capacity with steel of the same heat. Upon pouring of steel from the ladle and the formation of an ingot therefrom, steel- Was obtained that was of noticeably improved cleanliness, in comparison with steel of the same kind prepared in accordance with prior art practices, including the use of the more expensive, more finely divided silicon carbide, added in the furnace rather than to the ladle.

EXAMPLE III Example II was repeated, except that the material added to the 400-pound ladle comprised 944 grams (the same amount of metallurgical-grade silicon carbide, but sufficient sodium carbonate to amount to 9 weight percent of the mixture). The results were the same.

EXAMPLE IV Example III was repeated, but a 12% by weight addition of sodium carbonate was made, to provide a ladle addition of 975 grams. Again, the results were the same, indicating that the function of the sodium carbonate is achieved adequately by providing amounts not greater than 9% by weight of the addition.

EXAMPLE V Example IV was repeated, but 15% by weight of sodium carbonate was added to the silicon carbide, to provide a ladle addition of 1001 grams, again containing the same amount of metallurgical-grade silicon carbide. The results were the same.

In the above working examples illustrating the invention, the material used was -20 mesh because this was the coarsest material readily available at the time that the tests involved were conducted. -It is our teaching, however, that satisfactory results are otbained with inch material, or in some circumstances (larger heats containing ample superheat) with inch material.

In view of the savings in cost and improvement in cleanliness of the treated steel, it is submitted that we have provided a substantial advance in the art of treating steel with silicon carbide.

We claim as our invention:

1. The method of making steel of good cleanliness at low cost comprising the steps of mixing a metallurgical additive material consisting essentially of from about 6 to 15 weight percent of sodium carbonate and the balance being silicon carbide (8292% pure), except for incidental impurities, of which material at least 30 weight percent of the silicon carbide is coarser than 36 mesh, tapping into a ladle about 6-18 inches of steel to be treated, adding to said ladle %7 pounds of said additive material per ton of steel being treated, and substantially filling said ladle with steel to be treated.

2. A method as defined in claim 1, characterized in that said steel to be treated contains about 0.04-0.10% carbon and in that the quantity of said additive material 10 utilized is %-1 pound of said additive material per ton of steel being treated.

References Cited UNITED STATES PATENTS 2,527,829 10/1950 Leittcn 75-57 X 3,051,564 8/ 1962 Drenning 75-53 FOREIGN PATENTS 643,692 9/ 1950 Great Britain 75-57 L. DEWAYN E RUTLEDGE, Primary Examiner J. E. LEGRU, Assistant Examiner -"U.S. Cl. X.-R. 75-129

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