US3666438A - Process for the production of manganese-silicon alloy - Google Patents

Abstract

A PROCESS FOR THE PRODUCTION OF A MANGANESE-SILICIDE ALLOY HAVING A LOW CARBON CONTENT INCLUDING SMELTING MANGANESE ORE, SILICON METAL AND MANGANESE-SILICON SLAG IN AN ELECTRIC FURNACE WITH SUFFICIENT CARBONACEOUS REDUCTANT TO PROVIDE A MELT OF MANGANESE-SILICIDE ALLOW A THROWAWAY SLAG, INTRODUCE THE MELT INTO A LADLE, AND THEN SEP ARATING REMOVING THE ALLOY AND THROW-AWAY SLAG FROM THE LADLE. THE CARBON IS USED AS AN EXCLUSIVE REDUCING AGENT AND THE SILICON IS USED ONLY FOR ALLOYING PURPOSES. IN THE INVENTION, THE THROW-AWAY SLAG CONTAINS MANGANESE VALUES AND IT RECYCLED, THUS MAKING POSSIBLE THE DIRECT USE OF MANGANESE ORE AS THE MANGANESE BEARING MATERIAL.

D R A W I N G

Description

y 1972 l. MADRQNIC ETAL 3,666,438

PROCESS FOR THE PRODUCTION OF MANGANESE-SILICON ALLOY Filed Nov. 16, 1970 I P 2 P l m ore ilia l Coal Mn d cow eniidte L 38 W 612 hi ng m I O lGCtT'IC Open Arc smelting Furnace Ladle With Bolt m SICLG Tapping H e l FtidAlltfoy Cast Iron -22 p Poured Pots For Slag 24 26 885 5 |8 Slag Dmnplng Slag Crush-L g Cooltmg waste 2 81 3O A a ggi i 2O Crushm o Recyc le or pp g To Process r Concentmti 32 S10 34 Plant was I 36 Mn 31 Concentrate w INVENTORS IVO MADRONIC ATTORNEYS United States Patent 3,666,438 PROCESS FOR THE PRODUCTION OF MANGANESE-SILICON ALLOY lvo Madronic, Marietta, Ohio, and Akgun Mertdogan, Homewood, Ill., assignors to Interlake, Inc., Chicago,

Filed Nov. 16, 1970, Ser. No. 89,904 Int. Cl. C2211 7/06 US. Cl. 75-10 9 Claims ABSTRACT OF THE DISCLOSURE A process for the production of a manganese-silicide alloy having a low carbon content including smelting manganese ore, silicon metal and a manganese-silicon slag in an electric furnace with suflicient carbonaceous reductant to provide a melt of manganese-silicide allow and a throwaway slag, introducing the melt into a ladle, and then separately removing the alloy and throw-away slag from the ladle. The carbon is used as an exclusive reducing agent and the silicon is used only for alloying purposes. In the invention, the throw-away slag contains manganese values and is recycled, thus making possible the direct use of manganese ore as the manganese bearing material.

BACKGROUND OF THE INVENTION This invention relates in general to a process for the production of manganese-silicon alloys and more particularly relates to the production of a manganese-silicide alloy having a low carbon content from manganese ores.

Generally, manganese-silicide alloys have high manganese and silicon contents and relatively low amounts of carbon and other elements therein. Such alloys are generally employed as additives, such as deoxidizers or the like, for the production of low carbon steels.

In the past, manganese-silicide alloys have generally been produced by smelting manganese ores, quartzite, reducing agents and fluxes in an electric furnace. Since the specification for manganese-silicide alloys requires a controlled silicon content and relatively low carbon, the operation and/or control of the electric furnace to achieve the desired selective reduction of the charge is of utmost importance and is, therefore, highly critical. Accordingly, variations in the charge material analysis, in the electric furnace operation, and in the weighing of the charge and/ or additions thereto, all act to eifect the quality and quantity of the ultimate alloy product produced. Moreover, in the prior art processes, difficulties have been encountered in maintaining such control conditions, particularly in that an extremely equilibrated composition, as well as careful regulation of the other operating conditions was required. Thus, where such conditions were not properly maintained, the silicon content in the alloy product varied in a relatively wide range, such as from 25% to 35%. As a result, the quantity of commercial first quality products having a controlled silicon content of 28% to 32% and a carbon content of .05% maximum was well below desired requirements.

In addition to the foregoing, such prior art processes Were not entirely satisfactory for a number of reasons. For example, the alloy was often subjected to overheating and/or certain amounts of the principal elements desired (i.e. silicon) were carried away and not used in the alloying. Furthermore, the production costs of such prior processes were high, and the average production time for producing a first quality alloy product were of relatively high duration oftentimes requiring excessive operating personnel and/or auxiliary equipment. Still further, in such prior processes there were oftentimes produced Patented May 30, 1972 SUMMARY OF THE INVENTION The present invention relates to a process for the production of a manganese-silicon alloy having a low carbon content comprising, smelting manganese ore and manganese-silicon materials having a substantial metallic silicon value with sufiicient carbonaceous reductant to provide a melt alloy containing high values of elemental manganese and silicon and a manganese slag, and then separating the melt alloy and slag from one another. Preferably, the process includes providing a charge comprising manganese ore, coal and slag from the same process and adding suflicient silicon in order to bring the final alloy to the desired silicon level, smelting the charge in a furnace to provide a melt of manganese-silicide alloy and a throw-away slag, introducing the melt into a ladle, and then separately removing the alloy and throw-away slag in.the ladle from one another. In the invention, the throw-away slag with a predetermined slag to alloy ratio (i.e. in the furnace) may be continuously recycled with a new charge for reduction in the furnace. In a modified form, predetermined amounts of the manganese ore, coal, silicon metal and manganese silicon slag from the same process may be blended with a manganese-silicon alloy for reduction in the furnace.

By the foregoing and following description, it will be seen that there is provided a novel process for the produc tion of manganese-silicon alloys which reduces the criticality required in furnace operation and in determining the composition and/or-weights of the materials in the furnace charge. The process ensures achieving the desired chemical analysis of the manganese-silicon alloy end product, and particularly a manganese-silicide alloy of low carbon content, such as .05% maximum, and results in the recovery of more of the principal elements, such as about an recovery of manganese and about recovery of silicon which indicates that all of the silicon introduced with the charge is employed for alloying purposes. Moreover, though the criticality of the furnace operation is substantially reduced, the production of a first quality product having a controlled silicon content of about 28% to 32% is achieved with a minimum of operating personnel, and without the need for auxiliary equipment.

Another advantage of the process includes improved recovery of manganese and silicon with a relatively low carbon content in the alloy, due, in part, to improved recovery of manganese from the ore and a suitable usage of high silicon containing material, such as silicon metal. Moreover, the process can be emplo'yed with manganese ore containing a very high percentage of fines, and yet which reduces gas blowings and eruptions to a minimum.

BRIEF DESCRIPTION OF THE DRAWINGS The figure is a schematic representative of the process for the production of manganese-silicon alloys, such as manganese-silicides, in accordance with the present invention.

DESCRJIPTION OF THE PREFERRED EMBODIMENTS In accordance with the preferred form of the present invention, the charge for introduction into the furnace includes a manganese ore having a predetermined manganese-to-iron ratio and a predetermined manganese-tophosphorus ratio, and a manganese-silicon material having a substantial metallic silicon value. The charge is introduced into the furnace with sufiicient carbonaceous reductant to provide a melt alloy containing high values of elemental manganese and silicon and a manganese slag. Preferably, the melt is introduced into a ladle and after a predetermined holding time the alloy and slag are separated from one another in the ladle. In the invention, the manganese-silicon materials preferably include metallic silicon, a manganese-silicon alloy and a manganese-silicon slag. In the invention, the slag is removed from the ladle and may be continuously recycled having predetermined slag to alloy ratio (i.e. in the furnace) for reduction in the furnace. The molten alloy and slag removed from the ladle may then be subjected to subsequent cooling, crushing and/or concentrating operations for storage, shipping and/or for recycling to the furnace, as will be more fully described hereinafter.

By the foregoing process, there is provided an end product having about 218% to 32% silicon, 60% to 67% manganese, .05% phosphorous maximum, .05 carbon maximum with the balance being substantially iron plus impurities. In addition, the process provides a throwaway slag having a controlled manganese content, such as 4% to 6% MnO, which may be continuously recycled for reduction with the charge in the furnace.

The manganese ore of the type preferred for use in the present process is one that has a high manganese content and a high ratio of manganese-to-iron and a still higher ratio of manganese-to-phosphorous. It has been found that a preferred ratio of manganese-to-iron in the ore is about 30:1 and the manganese-to-phosphorous is about 1000zl. Moreover, it will be understood that other types of manganese ore may be utilized dependant upon the manganese and phosphorous content in the ore, as aforesaid. The maximum content of the iron in the charge is dependent upon the final alloy specification. In the invention, since the manganese and silicon content of the alloy is about 95%, the iron content (plus other impurities) in the charge specifically would not exceed about 100 lbs/net ton of alloy.

Preferably, the neductant for the charge is in the form of a bulky, carbonaceous material which is employed to supply a substantial portion of the carbon reductant in the process. Preferably, a carbonaceous material, such as low volatiles coal, may be employed. It is to be understood, however, that other reductants which may be employed in the smelting operations may include metallurgical coke, and the like.

Now in accordance with the invention, a high silicon content material is employed with the charge for introduction into the furnace. Preferably, such material includes metallic silicon having a silicon content of about 90%. The iron content of the silicon metal tobe employed in the process will depend upon the iron content in the manganese ore. Preferably, the iron content is less than 10% by weight and has a size less than about 2 inches.

In the invention, if the slag constituents in the manganese ore are too low so as not to provide the proper slag/alloy volume ratio, it is preferred that a throw-away manganese-silicon slag be continuously recycled with the next batch to the furnach. For example, the slag produced from the first tap may be used in the preparation of the slag requirements of the second tap, third tap, etc. Preferably, the amount of slag in each batch should be suflicient to yield the desired slag to alloy ratio in the furnace.

In accordance with the invention, a suitable open-arc electrical furnace may be employed which employs a three-phase electrical power source with 35-inch prebatked carbon electrodes. The average spacing between the electrodes (face-to face) is about 41 inches, with the shell of the furnace being stationary and of a generally triangular, in top plan, construction. The inside diameter of the shell is about 23 feet and the distance from the top of the shell to the hearth is 72 inches. The furnace is preferably equipped with a 10,000 lrva. transformer and may employ a secondary voltage (phase-to-phase) of 135 volts for the smelting operation. In such case, the secondary current is 40,000 amperes with the calculated density of the electrodes being 41.5 amperes per square inch. The charge in the furnace is preferably heated to between about 2500 F. to 2800" F. for between about 1 to 2 hours, and preferably about 1 /2 hours. In the invention, though the operation has been illustrated as being carried out in an electric furnace, it will be understood that other types of furnaces, such as induction furnaces may be employed.

In the invention, a Chilean manganese ore may be employed in which the manganese is in the form of MnO,, and Mn O During the smelting operation, these higher oxides are decomposed to the lower oxide MnO. In order to obviate a violent decomposition of such higher oxides in the manganese ore and to prevent gas eruptions, the electrical power load may be lowered during the first half hour of smelting time.

In the invention, the furnace preferably includes a bottom-side tapping hole. After suflicient smelting time has elapsed, a slag is produced on the top of the alloy. The alloy and the slag are then tapped from the bottomside opening of the furnace at about 2600 F. into a suitable ladle. The alloy tapped from the bottom of the furnace contains manganese-silicide together with silicon carbide.

In order to provide for good separation of the silicon carbide from the molten alloy, the manganesesilicide and silicon carbide mixture and manganese silicide slag are tapped from the furnace and allowed to cooled for a predetermined time, such as 40 minutes to 60 minutes, in the ladle until good separation occurs. The silicon carbide, being lighter, rises to the top of the ladle, whereupon, the manganese-silicide alloy may then be removed from the ladle and bottom-side tapped into a second ladle. From the second ladle, the manganese-silicide alloy may then be top-poured into a suitable container, such as a mold, for casting to the desired shape. After the casting operation, the material may be cooled, then crushed and shipped and/or stored for shipment.

The slag remaining in the first ladle may then be poured off into a metal pot, such as cast iron. The slag may then be dumped from the pots, cooled and then subjected to a crushing operation. Certain portions of the dumped and cooled slag may be disposed of as waste slag while other large size portions of the crushed slag containing manganese values, may then be recycled to maintain a molten pool in the furnace. Certain other portions of the crushed slag may be delivered to a concentrating plan to recover manganese and silicon concentrates Which, in turn, may be recycled with the charge to the furnace. In addition, certain portions of the slag remaining after the concentrating operation may be discharged in the form of waste slag.

In the slagging operation, if the slag constituents in the initial manganese ore are to low in order to provide a proper slag/alloy volume ratio, some of the throw-away manganese-silicide slag from the crushing operation is preferably recycled with the charge to the furnace. It has been found that the recycling of a portion of the throwaway slag to the furnace renders the smelting conditions in the furnace smoother and prevents overheating of the alloy. Recycling of the manganese-silicon concentrates from the concentrating plant back to the furnace improves the manganese and silicon recoveries of the process.

The following examples show the chemical analysis of the charge, the size of the charge ingredients and the analysis of the alloy product produced in accordance with the present invention.

EXAMPLE I An open are electric furnace was charged with a mix having the following composition by weight:

Chilean manganese ore: 12,180 lbs., 50% Olga coal: 4,050 lbs., 17%

Silicon metal: 2,485 lbs., 10%

Mn, Si slag: 5,600 lbs., 23%

The analysis of the above raw materials was:

Chilean ore The size of the raw materials charged into the furnace was:

Chilean manganese ore 2" x D Olga coal 1" x D Silicon metal 1" x D Mn, Si slag 3" x D The furnace was of the kind described heretofore. A secondary voltage, phase-to-phase, of 135 volts was used with the secondary current of 40,000 amperes and a calculated current density in the electrodes of 41.5 A./sq. inch. The smelting time was about 2 hours. At a power load of 8,125 kw., a total of 15,600 kwh. was consumed.

The final alloy weighed 7,630 lbs. and had the following analysis:

Percent Mn 64.24 Si 30.69 C .040 P .045 Fe Balance The slag contained 6% MnO and 37% SiO The calculated recovery of manganese, disregarding any moisture content of the manganese ore, in the aforesaid alloy was 86.34%. The calculated recovery of silicon was 101.2%. The alloy was held in the ladle for about 45 minutes to separate it from the silicon carbide. The alloy was then removed by being bottom tapped into a second ladle from which it was top poured into a cast iron mold.

EXAMPLE II Test heats were run using the charge materials of Example I except that about 50% by weight of the manganese ore and 50% by weight of the silicon metal were replaced by an alloy containing about 66% manganese and 25% silicon.

In accordance with such modification, the mix charged to the electric furnace was as follows:

Chilean manganese ore: 5,000 lbs., 29%

Mn, Si alloy (66% Mn, 25% Si): 5,0001bs., 29% Olga coal: 1,650 lbs., Silicon metal: 1,350 lbs., 8%

Mn, Si throw-away slag: 4,000 lbs., 24%

The analyses and the size of the mix components were similar to those indicated in the first example. The furnace used and the operations performed were also identical to those in the first example.

The weight of the final alloy was 8,200 lbs. The analysls was as follows:

Percent Mn 63.53 Si 29.20 C .041 Fe Balance The final slag contained 6.3% MnO and 35.84% SiO' and the power consumption for the total heat was 13,500 kwh. The calculated manganese recovery, disregarding any moisture content of the manganese ore, was 92.52% and silicon recovery was 95.37%. The advantage of the variation of Example II is that higher production rates and lower consumption of silicon metal per unit of the final alloy were obtained.

In the invention, it is to be recognized that the carbon content of the alloy increases as the silicon content of the alloy decreases. Accordingly, the minimum tolerable silicon content of the alloy depends on the carbon specification of the alloy. For example, a carbon content of 0.05% maximum would require a silicon content of about 28%. If the silicon content of the alloy is too low, the carbon content would exceed the limits specified. If the silicon content is too high, any increase in silicon beyond 32% of the designated limit would decrease the manganese content, such as below a 63% minimum, for example. Further, it has been found that manganese silicide having an excess of 32% silicon tends to disintegrate. Moreover, in the invention the silicon content in the manganese silicide should be in the range between 28% to 32% with the preferred amount being about 30%.

Based on the weight of the manganese ore in the charge, the reductant is added in a weight ratio of about 1:3, the silicon metal about 1:5, and the manganese-silicon slag about 1:2 with the weight of the charge varying plus or minus about 5%. Where the manganese-silicon alloy is employed with the charge, the weight ratio of manganesesilicon alloy is about 1:1, the reductant about 1:3, silicon metal about 1:4, and the manganese-silicon slag about 0.8:1.

In the invention, the amount of recycled slag in each batch should be sufficient to yield a proper final slag to alloy ratio. In Example I, the recycled slag was 1468 pounds per net ton of alloy to yield a final slag to alloy ratio of 1.06:1; and in Example II, the amount of recycled slag was 976 pounds per net ton of alloy to yield a final slag to alloy ratio of 0.6:1. Perferably, the ratios 30; the final slag and alloy should be about 1:1 and In the invention, it has been found that a proper slag to alloy ratio in the furnace improves the heat transfer in the charged materials and makes the smelting conditions in the furnace smoother. In addition, the slag acts as a protective cover over the alloy, prevents overheating of the alloy and, minimizes the manganese loss as a vapor. By the use of the preferred embodiment, recovery of manganese in the final alloy is about and the recovery of silicon is about 100%. Thus, all the silicon introduced with silicon metal is being used for alloying.

OPERATION In a typical operation and with reference to the schematic illustration, there is illustrated a preferred form for carrying out the process of the present invention. As shown, a charge is provided containing manganese ore, as at 2, containing about 60% MnO; a high silicon bearing material, as at 4, having a silicon content of about and a manganese-silicon slag, as at 8. containing 5% MnO with a suitable reductant, as at 6, such as coal in an amount sufficient to provide a melt of manganesesilicide alloy and a throw-away slag containing about 4% to 6% MnO. After the proper proportions of the charge have been weighed, as at 10, they are mixed together and delivered to an electric open arc furnace, as at 12, for smelting for reduction of the manganese ore by the reaction with the carbon of the reductant. During the smelting operation, the manganese combines with the silicon metal to produce molten manganese-silicide. The melt may then be tapped into a ladle, as at 14, wherein it is allowed to cool for a time suflicient to enable the slag and silicon carbides to float to the top. The manganesesilicide is then removed by bottom-side tapping from the ladle 14 into a second ladle, as at 16, from which it is subsequently top-poured into a mold, as at 18, for casting to the desired shape. The casting may then be cooled and crushed for shipment and/or for storage and subsequent shipment, as at 20, as desired.

The slag materials produced in the first ladle, as at 14, may then be delivered to a pot, as at 22, of cast iron or the like. From the pot 22 the slag may then be dumped and cooled, as at 24. The cooled slag may be subjected to a crushing operation, as at 28, where the slag is reduced to 3-inch size and over for recycling, as at 30, back to the furnace to maintain a molten pool therein. Dependant upon the manganese content of the ore, about one-third of the total large size slag produced may be recycled to the furnace. The remaining oversize slag may then be sent to a concentrating plant, as at 32, where the slag is crushed to inch size and down. In the concentrating steps, the metallic portion of the manganese-silicon slag is mechanically separated and recycled, as at 36, back for use with the charge in the furnace, and the non-metallic portion delivered to waste, as at 34.

In the invention, and as illustrated in Example II, it has been found that certain portions of the manganese ore and silicon metal may be replaced and blended with a manganese-silicon alloy. For example, it has been found that about 50% of the manganese ore and 50% of the silicon metal may be replaced with an alloy containing manganese and silicon. For example, it has been found that an alloy containing about 64% to 68% manganese and about 25% silicon may be added to the charge with reduced amounts of ore and silicon metal. The advantages of this form are high production rates and lower consumption of silicon metal per unit of the final alloy. The manganese-silicon alloy may be prepared in the same furnace or in a different (i.e. submerged electrode) furnace, by smelting ore, quartzite and reductant and then remelted with the manganese ore and silicon metal in accordance with the present invention.

We claim:

1. A process for the production of an alloy of manganese silicide containing by weight about 60% to 67% manganese, about 28% to 32% silicon, a maximum of .05% carbon, a maximum of .05% phosphorus, and the balance essentially iron which comprises,

smelting in an open hearth electric furnace, a mixture of a manganese ore, a carbonaceous reducing agent, silicon metal and a manganese silicide slag containing 4' to 6% MnO by weight for a suificient length of time to form an alloy of molten manganese silicide and a manganese silicide slag montaining 4% to 6% MnO by weight, transferring the melt to a ladle, removing the molten alloy and the slag separately from the ladle, cooling and crushing the alloy, cooling and crushing the slag, and using a portion of the slag in a subsequent similar melting operation. 2. A process according to claim 1, wherein the manganese ore has a manganese to iron ratio of about 30 to 1. 3. A process according to claim 1, wherein the manganese ore has a manganese to phosphorus ratio of 1000 to l. 4. A process according to claim 1, wherein the silicon metal has about 90% silicon and is present in the charge in the ratio range between 1:4 to 1:5 based upon the weight of the manganese ore. 5. A process according to claim 1, wherein the alloy when tapped from the furnace is held in a ladle for a suilicient length of time to obtain a separation of silicon carbide from the alloy after which the alloy is bottom-side tapped into a second ladle from which the alloy is poured into a mold. 6. A process according to claim 1, wherein the ore is Chilean manganese ore, and wherein the carbonaceous reducing agent is Olga coal. 7. A process according to claim 1, wherein the ingredients of said mixture by weight comprise about 50% ore, about 17% reducing agent, about 10% silicon metal and about 23% slag. 8. A process according to claim 1, wherein about 50% by weight of the manganese ore and about 50% by weight of the silicon metal are replaced with an alloy containing about 64% to 68% by weight of manganese and about 23% to about 27% by weight of silicon. 9. A process according to claim 1, wherein the slag is present in the charge in the ratio range between about O.5:1 to about lzbased on the weight of said manganese ore.

References Cited UNITED STATES PATENTS 2,775,518 12/1956 Udy 11 3,083,092 3/1963 Kuhlmann 75l33.5 X 3,329,597 7/1967 Deadrick 7580 X 3,369,887 2/1968 Keyser et al. 75--l0 R 3,138,455 6/1964 Carosella et al. 75l33.5 3,395,011 7/1968 Dery et al. 7524 WINSTON A. DOUGLAS, Primary Examiner M. J. ANDREWS, Assistant Examiner US. Cl. X.R.

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