US2068322A - Metallurgy - Google Patents

Description

Patented Jan. 19, 1937 METALLURQY Charles Hardy, Pelham Manor, N. Y., assignor, by mesne assignments, to Charles Hardy, Inc., New York, N. Y., a corporation of New York No Drawing.

Application December 54, 1935,

Serial No. 52,828

12 Claims.

melting point into molten baths'of base metals.

Thus it often is difficult to melt solid chromium, vanadium, tungsten, molybdenum, or combinations of these metals, with iron, by introducing them in the solid state into molten baths of iron or steel, because these metals and their ferrous derivatives have melting points considerably higher than the melting point of iron.

This difliculty may be aggravated, and freezing of the whole mass may occur, if it is desired to add these metals in a solid state to molten iron or steel contained in a ladle remote from a source of heat, as is frequently the case when tool steels, etc. are made.

In many cases it has been necessary to raise the temperature of a base metal bath considerably above its melting point in order to melt and incorporate an alloy ingredient of relatively high melting point, and this represents a waste of heat. Even when the base metal, for' example lead, has a relatively low melting point this waste of heat may be considerable. For example, if it is desired to introduce antimony in the solid state into a molten bath of lead, it is necessary to heat the entire bath above its melting point (327 C.) and in fact, substantially to the melting point of antimony (630 0.).

Many base metals used in alloy manufacture contain impurities, such as carbon, sulphur, phosphorus, or oxygen, which are undesirable constituents of the final alloy into which they are made. In other instances a small amount of carbon, oxygen, etc. may be tolerated in the final alloy, but in amounts below the quantity present in the base metal. Again, many alloy ingredients, such as unrefined ferrochrome, contain impurities, such as carbon, in amounts that will affect deleteriously the alloys into which they are incorporated. It is, therefore, necessary in many instances to remove some or all of such impurities at some stage in the operations.

The removal of carbon from the alloy or the alloy ingredient often presents extreme difliculties. Thus, in ferrous metallurgy, it is often desirable to remove all or part of the carbon contained in molten bath without deleteriously affecting the residual metal. Prior practices in which the carbon is removed as an oxide do not permit such a result, because the oxygen introduced into the bath (either in the elemental state or combined as an oxide) usually possesses a greater aflinity for a metal in the bath than for carbon. Consequently, in such decarbonization processes substantial quantities of metal may be oxidized and thus lost, at least temporarily.

The removal of oxygen in metal baths may also present difficulty. Thus, oxygen can be removed from ferrous metal baths by the addition of silicon, but silicon tends to alloy with the metal almost as readily as it tends to combine with-oxygen, and it does not volatilize readily. Consequently, processes in which silicon is used as a deoxidizing agent often result in a contamination of the final alloy with silicon, especially when an excess is used to insure complete deoxidation. Because silicon is generally respon- 2o sible for an increased brittleness of an alloy, its presence may be objectionable.

As a result of my investigations, I have found that non-metallic impurities, such as carbon, sulphur, phosphorus, oxygen,' etc., may be re-' moved from baths of base metal and from difllcultly fusible alloy ingredients at the same time that the difllcultlyfusible alloy ingredients are added to the bath, and with a minimum consumption of heat. Calcium tends to react exothermically with most non-metallic impurities present in metal baths or in solid metal ingredients which may be added thereto. An exact measurement of this exothermic effect is dim-- cult when the reaction proceeds in molten metal baths at high temperatures, due to the fact that thermo-couples do not withstand the high temperatures usually involved, and because observations with optical pyrometers are often vitiated by the presence of an intense calcium light. My observations indicate, however, that both the exothermic heat of reactions involving calcium, and the positive heat of solution of calcium in a metal bath, increase as the temperature of the bath increases.

Even when the materials involved contain no non-metallic impurities which will react with calcium,- this metal may be employed to facilitate the fusion of diflicultly fusible ingredients, by employing the heat of solution of calcium in another metal. D

Accordingly, my invention contemplates the utilization of the exothermic reaction heat of calcium, or the positive heat or solution of calcium, or both, to melt solid metal ingredients which have a higher melting point than the base metal of the bath into which the solid metal ingredients are to be incorporated. I accomplish this result by intimately associating calcium with an'alloy ingredient of relatively high melting point (i. e. higher than. the base metal into which it is to be alloyed) in a mass. I then introduce the mass into the molten bath of base metal, and maintain contact between the molten bath and the mass until the calcium has been consumed or dissolved and the accompanying alloy ingredient has been melted and incorporated into the bath. The calcium employed may function in any or all of the following ways:

(1) The calcium may react exothermically with an impurity accompanying the base metal (for example, sulphur in iron) thus converting the impurity into a separable form (for example, calcium sulfide) and at the same time generating heat to aid 'in the fusion of the alloy ingredient (for example, chromium).

(2) The calcium may react exothermically with an impurity accompanying the alloy ingredient (for example, carbon in ferrochrome) thus converting the impurity into separable form and-generating intense heat in a small zone adjacent the mass of ferrochrome and calcium, in which zone of intense heat the ferrochrome is quickly melted.

(3) The calcium may dissolve in the base metal (lead, for instance) with the generation of a positive heat of solution, which heat-concentrated in a small space, enablesthe alloy ingredient accompanying the calcium (for example, antimony) to be quickly melted, without necessarily raising the temperature of the whole bath.

In one of the aspects of my invention I employ calcium in amount sufficient to combine with-the non-metallic impurities present in a bath of molten iron and also to combine with the non-metallic impurities, such as carbon, present in ferrochrome which in the solid state is to be added to the molten iron bath. I agglomerate finely divided calcium in amount sufllcient for this purpose with the ferrochrome in finely divided form, by mixing the two together and compressing them into a briquette. (I have found that a porous briquette is somewhat more effective than a solid one in most instances.) The briquette is submerged in the bath of molten iron and kept there until it has been consumed.

The reaction between the calcium and the nonmetallic impurities proceeds with great rapidity and heat is generated at a rate greater than the rate at which it is dissipated into the surrounding molten bath. Consequently, a very high temperature is attained in a small zone. This zone roughly approximates the space occupied by the original briquette within the bath. As a result, the solid metal is rapidly melted, and thus changed to a condition in which it is quickly assimilated into the bath- Due to the tendency of the calcium to volatilize, the hot zone is violently agitated, and. in this way the melted alloy ingredient tends to become mixed with the molten iron originally present.

This practice of my invention results in an economy of heat, because it permits an alloy ingredient of high melting point to be rendered molten without heating the whole bath up to a temperature at which the alloy ingredient will go into solution. Inasmuch as the amount of alloy ingredient to be added is usually relatively small in amount as compared to the-amount of the bath, the economy is considerable.

During, the period in which the calcium is being consumed or dissolved, the bath should be kept substantially free of exterior oxidizing influences, either by covering it with a protective layer of slag, or by conducting the operation in an inert or reducing atmosphere, for example, of nitrogen, or air from which the oxygen content has been exhausted. In this way, the calcium is prevented from forming useless combination with oxygen from the atmosphere, etc., and it is usefully consumed in the removal of impurities from themetals. At the same time .the undesired oxidation of metallic constituents calcium and metal alloy ingredient present in the mass, and by regulating the size of the par- 7 ticles of calcium or of the alloy ingredient which are consolidated to form the coherent mass. In general, the smaller the particle size, the greater will be the amount of reactive surface, and the faster will be the reaction.

Although carbon or-other non-metallic impurities can be completely removed in the practice of my invention by employing calcium in excess of the chemical equivalent of the carbon present in the bath, it is frequently desirableto leave a predetermined residue of carbon in the bath. In such case, calcium in amount sufiicient to remove only the desired proportion of carbon from the bath is agglomerated with an amount of alloy metal ingredient suflicient to impart the desired percentage'of this alloy ingredient in the finished alloy. Because it is generally impossible to prevent the escape of a small amount of calcium from the bath as a vapor, (even when the bath is covered with a slag) it is desirable to employ an amount of calcium slightly in excess of the chemical equivalent of the carbon to be removed. The amount of such excess will depend upon the depth to which the reacting mass is submerged,

the particle size of the materials forming the agglomerate, the porosity of the agglomerate, and the viscosity and thickness of the slag overlying the bath, but in general calcium should be used in an amount at least 1.1 times the chemical equivalent of the carbon or other non-metallic.

impurity to be removed.

The calcium-containing mass may be prepared in several ways. One of the most convenient is to melt the calcium under a protective cover, and

then stir into the calcium the alloy ingredient in proper porosity. In general, pressures of about 5 tons per square inch will produce a mass having the desireddegree of porosity with material of the aforementioned particle size.

Lastly, when a particularly fast reaction is not desired, the calcium may be enclosed in a container of any convenient shape, together with the alloy metal ingredient. The container should be closed and is preferably constructed out of the base metal or from the alloy ingredient itself.

The following example will serve to illustrate the practice of my invention:

Iron is available containing 2% carbon, and it is desired to reduce this carbon content to 0.2 at the same time increasing the chromium content by 10% so as to produce a finished alloy. Ferrochrome is available containing chromium, but it also contains about 5% carbon.

To 100 pounds of the iron in the form of a molten bath it is necessary. to add about 25 pounds of ferrochrome. Calcium necessary to reduce the carbon content of the original iron from 2% to 0.2% is 3.0 pounds, or say 3.3 pounds (allowing for the 10% excess). Carbon to be removed from the ferrochrome is equal to 1.25 pounds, which will require 2.1 (or say 2.3 pounds of calcium, allowing for losses). Total calcium per 100 pounds of base metal is therefore 5.6 pounds, which is intimately associated with the 25 pounds of ferrochrome, as by briquetting.

, The briquette is added'to the molten iron in the ladle following a preliminary melting or smelting operation. The iron is kept covered by a protective slag, and the briquette is held sub- .merged until reaction and solution are complete.

Intense heat is generated in the neighborhood of the briquette, and assimilation of the ferrochrome is rapid.

Almost any of the usual alloy ingredients of steels may be incorporated in accordance with the method of my invention. Thus, elements which have a lower melting point than iron, for example, manganese, and cobalt, may be briquetted with calcium or other alkali or alkaline earth metal and incorporated into a molten bath of iron or steel with great rapidity simultaneously with the removal of non-metallic impurities from the bath or from the alloy ingredient. My invention is even more useful when alloy ingredients having a melting point higher than iron are to be added. Thus, titanium, tungsten, chromium, vanadium, and even molybdenum, may be incorporated into an alloy in accordance with the practice of my invention.

My invention possesses an outstanding advantage in that purification and the addition of alloy ingredients are accomplished simultaneously. A great economy of operation results and a fin-- ished alloy can be produced in a single step.

I attribute the results of the aforementioned practice of my invention to the extremely exothermic character of the reactions between calcium and other elements, such as oxygen sulphur, phosphorus and carbon, and to the fact that the specific heat and the latent heat of fusion of iron and its customary alloy ingredients are relatively low. I have reason'to believe that-the aforementioned heat of reaction between calcium and non-metallic impurities is greater at the high temperatures of metal baths than it is when the reaction is allowed toproceed at lower temperatures (as is the case in the laboratory determination of most reaction heats). In any case the heat generated in the consumption of a given weight of calcium is more than suflicient to supply the sensible heat and the heat of fusion for an equal amount of alloy ingredient.

My invention may be employed even when there are no impurities present in the base'metal or in the alloy ingredient which will react exothermically with calcium, providing that calcium 'has a positive heat of solution in the metal of the bath. The heat of solution of calcium in other metals is generally positive and of considerable magnitude. For example, the solution of 2.5 pounds of solid calcium in pounds of molten lead results in raising the temperature of the resulting calcium-lead alloy approximately 555 C. Similar effects are noted when calcium is dissolved'in molten copper. ance with the practice of my invention, this great heat of solution of calcium in lead or copper is used to fuse other alloy ingredients to be introduced into lead, copper, etc. Thus, calcium and copper or antimony are intimately associated in a briquette, which is then submerged in molten lead. The calcium goes into solution in the lead almost immediately, forming a relatively small hot zone within the mass in which the copper or antimony is quickly melted. A lead-calciumeopper alloy or a lead-calcium-antimony alloy is formed in this way. Similarly, a nickel-coppercalcium alloy may be formed.

The positive heat of solution of calcium in other metals may be utilized in like manner.

I claim:

1. A process for melting a difficultly fusible alloy ingredient containing carbon and for incorporating it into a molten bath of base metal having a lower melting point than the alloy ingredient which comprises submerging in the molten bath a solid mass containing the alloy ingredient, the carbon and metallic calcium, and maintaining the solid mass in contact with the molten bath until the calcium has reacted with the carbon to form substantially insolubie cal cium carbide, whereby a zone of intense heat is created adjacent the solid mass and the melting thereof is facilitated.

2. A process for incorporating into lead an alloy ingredient having a higher melting point than lead which comprises introducing a solid coherent mass of the alloy ingredient admixed with calcium into a molten bath of lead and -maintaining the mass in contact with the molten lead until the alloy ingredient and the calcium have been dissolved, whereby the exothermic heat of solution of calcium in lead creates a zone of intense heat in which the melting of the alloy ingredient is facilitated.

3. A process for incorporating into iron or steel forming. a coherent solid mass of the resultingmixture, submrging the coherent solid mass into a bath of molten iron or steel and maintaining the mass in contact with the molten iron or steel until the calcium has reacted with the excess carbon in the ferrochrome, whereby a zone of intense heat is created adjacent the ferrochrome and the melting thereof is facilitated.

4. A process for incorporating into a molten bath of iron or steel having an excessive carbon content an alloy ingredient having a higher melting point than iron which comprises admixing the finely divided alloy ingredient with finely divided metallic calcium, forming the .resulting mixture into a solid coherent mass, submerging the solid coherent mass into the molten bath,v

In accord is raised to facilitate the fusion of the alloy ingreclient.

5. A process for incorporating into amolten bath of iron or steel having an excessive carbon content an alloy ingredient having a higher melting point than iron which comprises admixing the finely divided alloy ingredient with finely divided metallic calcium in amount about 1.1 times the chemical equivalent of the carbon to be'removed from the iron or steel, forming the resultant mixture into a solid coherent mass, submerging the solid coherent mass into the molten bath and maintaining the mass in confinely divided metallic calcium in amount substantially equal 1.1 times the chemical equivalent of the carbon to be removed from the iron or steel, forming the resultant mixture into a solid coherent mass, covering the molten bath of iron or steel with a slag to protect it from oxidizing influences, submerging a solid coherent mass into the covered molten bath and maintaining the mass in contact with the molten bath until the calcium has reacted with the excessive carbon to form a substantially insoluble calcium carbide, whereby the excess carbon is removed from the bath and the temperature of the bath is raised to facilitate the fusion of the alloy inedient.

'7. A process for incorporating into a molten bath of iron or steel an alloy ingredient having a higher melting point than ironand an excessive carbon content which comprises admixing the alloy ingredient containing the excessive carbon with finely divided calcium, compressing the resulting mixture to form a/solid coherent mass, submerging the solid coherent mass in the molten bath while the molten bath is protected against exterior oxidizing influences, maintaining the mass in contact with the protected molten bath until the calcium has reacted with the excessive carbon content of the alloy ingredient to form substantially insoluble calcium carbide, whereby a zone of intense heat is created adjacent the mass and the fusion of the alloy ingredient is facilitated.

8. A process for incorporating into a molten bath of iron or steel having an excessive carbon content an alloy ingredient selected from the roup consisting in chromium, vanadium, tungsten, molybdenum and the combinations of these metals with iron which comprises combining a finely divided metal selected from the group with metallic calcium to form a heterogeneous coherent mass, covering the bath with a protective slag, introducing the coherent mass into the protected bath, maintaining the coherent mass in contact with the protected bath until the carbon content of the bath has reacted with the calcium to form an insoluble carbide, and separating the carbide thus formed from the molten bath, whereby the fusion of the metal selected from the group and the incorporation thereof into the molten bath are facilitated.

9. A process for removing carbon from baths of iron and steel and simultaneously introducing thereinto an alloy ingredient having a higher melting point than iron which comprises mixing the finely divided alloy ingredient with an amount of calcium in excess of the chemical equivalent of the carbon present in the bath and forming therefrom a heterogeneous coherent mass, submerging the coherent mass in the bath, and maintaining the'mass in contact with the bath until the carbon has been completely changed to the carbide and the excess calcium has been volatilized, whereby the iron or steel-is completely decarburized and the alloy ingredient is incorporated into the iron or steel with a, minimum consumption of externally applied heat.

10. A process for melting a diflicultly fusible alloy ingredient and incorporating it into a molten bath of base metal having a lower melting point than the alloy ingredient which comprises introducing into a molten bath of the base metal a solid mass containing the alloy ingredient together with metallic calcium in amount sufiicient to generate heat faster than said heat can be dissipated in the molten bath, so that a zone of intense heat is set up. in the molten bath adjacent" the solid alloy ingredient and the melting of the alloy ingredient is facilitated, and maintaining the mass of alloy ingredient and calcium in contact with the molten bath until the alloy ingredient is melted.

11. A process for melting a relatively infusible alloy ingredient and incorporating it into a base metal having a melting point below that of the alloy ingredient which comprises introducing into 'a' molten bath of the base metal a solid mass containing the alloy ingredient together with metallic calcium in amount suflicient to generate heat faster than said heat is dissipated in the molten bath, reacting the metallic calcium exothermically with another substance within the molten bath so that a zone of I intense heat is set up in the molten bath adjacent the solid alloy ingredient and the melting of they solid alloy ingredient is facilitated, and maintaining the mass of alloy ingredient and calcium in contact with the molten bath until the alloy ingredient is melted and the exothermic reaction has ceased.

12. A process for melting a relativelyinfusible alloy ingredient and incorporating it into a base metal having a melting point below that of the alloy ingredient and in which calcium has a positive heat of solution which comprises introducing into a molten bath of the base metal a solid mass containing the alloy ingredient together with metallic calcium in amount sufli cient to generate solution heat faster than it is dissipated in the molten bath, and maintaining the'mass in contact with the molten base metal until the calcium has dissolved therein with the liberation of heat, whereby a zone of intense heat is created adjacent the mass and the melting of the alloyingredient is facilitated.

CHARLES HARDY.