US2836488A - Metallurgical compositions - Google Patents

Description

United States Patent METALLURGICAL COMPOSITIONS George L. Martin, Webster Groves, and Allan D. Gott, St. Louis, Mo., assignors to Mallinckrodt Chemical Works, St. Louis, Mo., a corporation of Missouri No Drawing. Application July 21, 1955 Serial No. 523,630

4 Claims. (Cl. 75-27) This invention relates to metallurgical compositions and processes, and more particularly to exothermic compositions useful in metallurgy.

Briefly, the invention is directed to an exothermic metallurgical composition comprising an alkali metal ferrate and a reducing agent for said alkali metal ferrate. The invention also includes the method of preparing an alkali metal ferrate primer comprising heating a mixture of an ore consisting primarily of titanium and iron oxides and an alkali metal carbonate in an oxidizing atmosphere at a temperature of between approximately 700 C. and 1100 C.

Among the several objects of this invention may be noted the provision of exothermic metallurgical compositions which contain an improved primer; the provision of exothermic compositions which have a controlled reactivity; the provision of exothermic metallurgical compositions of this type which do, not form objectionable smoke and gaseous by-products .upon ignition; the pro vision of exothermic metallurgical compositions which upon ignition form products which resist the viscosityincreasing effect of refractory substances which may be absorbed from molten metal; the provision of exothermic metallurgical compositions which are useful to reduce the viscosity of the slag normally associated with molten metal; the provision of exothermic metallurgical compositions which when added to molten metal produce a fluid slag which is useful in absorbing or changing the physical nature of the nonmetallic inclusions in steel, other ferrous alloys and certain nonferrous alloys, in rolled, forged and cast form; the provision of exothermic compositions which are useful to improve the hot-workability of ferrous alloys; the provision of exothermic metallurgical compositions which are stable under ordinary conditions of storage and shipping; and the provision of methods for preparing an improved alkali metal ferrate primer. Other objects and features will be in part apparent and in part pointed out hereinafter.

The invention accordingly comprises the products and methods hereinafter described, the scope of the-invention being indicated in the following claims.

Exothermic compositions containing a reducible metallic oxide and a reducing agent are well-known in the metallurgy for use in refining molten metals and for adding alloying elements, but usefulness and effectiveness of such compositions has been limited heretofore by several factors. The reaction products formed upon ignition of the exothermic compositions previously employed contain refractory materials which reduce the efliciency of the exothermic reaction and the beneficial effect on the metal being treated. Also, it has been difiicult to control the reactivity of the exothermic compositions employed so that they are reactive enough to be useful but not too reactive so as to present hazards to safety. The reactivity of such exothermic compositions has customarily been controlled by the kind and amount of primer which is generally included in the composition. The primers most 2 commonly used heretofore have been oxidizing'agents such as the alkali metal nitrates and readily oxidizable metals such as aluminum and magnesium. However, these substances have certain disadvantages which renders their use as primers objectionable. The alkali metal ni-' trates form gaseous by-products which under practical working conditions are often incompletely reduced and therefore, have an undesirable effect on many metals;

Moreover, in escaping from the molten metal these gase ous by-products carry along colloidal oxides and form a dense smoke that is both a nuisance and a health hazard. While aluminum and magnesium do not form gaseous byproducts, they form refractory objectionable.

The deficiencies of the primers known and employed heretofore have limited the effectiveness of many potentially valuable exothermic compositions. Thus, for example, exothermic compositions containing titanium dioxide, rare earth oxides and a silicon-containing reducing agent have been found to be very useful in metallurgy, particularly for refining steel, but such compositions do not attain maximum effectiveness unless well primed. If sufiicient sodium nitrate is included to prime the reaction, a large amount of dense smoke is formed. If either aluminum or magnesium is employed as a primer, a corresponding amount of a fluxing agent must also be included for the refractory oxides formed from these metals, and the dilution of the composition by the fluxing agent tends to reduce its efliciency.

In accordance With the present invention, it has now been found that the above-noted difiiculties can be substantially overcome through the use of a novel exothermic composition comprising an alkali metal ferrate and a reducing agent therefor. The alkali metal ferrate component of these compositions is a surprisingly useful and effective primer and yet does not suffer from the disadvantages of the primers previously used. Upon ignition, the alkali metal ferrate is reduced by the reducing agent and forms metallic iron and an alkali metal oxide, a basic oxide which acts as a fluxing agent for titanium and silicon dioxides as Well as other refractory acidic oxides. The exothermic compositions of this invention do not form undesirable gaseous by-products or dense smoke upon ignition, and add no inert or deleterious substances to the molten metal being treated. Furthermore, while the alkali metal ferrate component of these compositions is sufiiciently reactive to act as an efficient and useful primer, it is not so reactive as to present safety hazards.

Also, these novel compositions are stable under ordinary conditions of storage and shipping.

As employed herein, the term ferrates" includes compounds, variously known as ferrates and perferrates, in which iron has a valence greater than three. While sodium ferrate is the preferred primer for use in the practice of the invention, the other alkali metal ferrates may also be employed.

Examplary of reducing agents which may be employed in the exothermic compositions of this invention are silicon metal, silicon-zirconium, calcium-silicon, magnesium-aluminum, calcium boride, ferro-silicon, magnesium metal, magnesium-containing alloys, aluminum metal, and mixtures thereof.

If it is desired to provide an alloying element upon ignition of the exothermic composition, a metallic oxide may be included for this purpose. Suitable metallic oxides for use in the exothermic compositions of the present invention may be selected from the oxides of metals such as iron, titanium, the rare earth metals, zirconium, vanadium, niobium, tantalum and hafnium.

It is preferred that a sufiicient quantity of reducing agent be included in the compositions of. the invention Patented- May .27, I958 oxides which are equally quate supply of air.

to reduce substantially all of the alkali metalferr'ate.

If a metallic oxide is included in the compositions, an

additional quantityofreducing agent suificient to reduce the metallic oxide to metal may be included.

' "When' em'plo'yed for the purpose of introducing various alloyingelements into steel an-dother metals, the exotherrmc metallurgical compositions ofthis invention are advantageous forthis purpose because, when they are added.toimoltenjmetal, they simultaneously produce a fluid slag which protects the alloying elements against oxidation but does not entrap them or otherwise interfere withfltheir addition to the metal.

These compositions may be used to provide all of .an alloying element requiredor supplement and facilitate the addition of the alloying element in other forms. V

"The exothermic metallurgical compositions of this inventionarejalso useful 'to improve certain physical properties of steel, other ferrous alloys, and'certain' nonferrous alloys; In-general, the effect of these compositions is to improve hot-workability, i. e., to reduce the cracking or tearing frequently encountered when metal of-saleable metal from the ingot. The compositions of this invention are also useful in beneficially"affecting the nature of the usualnonmetallic inclusions in steel, other ferrous alloys, and certain nonferrousalloys, .in rolled,

forged and cast form. Themost obvious benefit may positions of this-invention may be prepared by calcining iron oxide 'With an alkali metal carbonate in an oxidizing atmosphere at temperatures between approximately 700 C. and 1100 C. If the calcination is carried out slowly :at thes'e'temperatures, a substantialamount of the alkali InetaIQferIa te is formed. In carrying out this preparat on it is preferable to calcine theiron oxide with an alkah metal carbonate slowly, for if the mixture is heated too rapidly it fuses and calcination is incomplete.

the physical 'nature of the nonmetallic ingots are hot rolled of forged, thus increasing the yield aseaaes a lent to the iron content of the ore, theiron'oxide reacts with the alkali metal carbonate preferentially. .This, is particularly advantageous since it is ordinarily desirable to' avoid the formation of a substantial amountof alkali metal titanate in the primer. The calcined ilmenite primer so obtained may then be combined with suitable amounts of reducing agent and other metallic oxides and components if desired to providea highly satisfactory and usefulexothermic composition. It is preferable to. supplement the calcined ilmenite primer with a small proportion of sodium nitrate, :but substantially lesssodium' nitrate is required than is the casewhen it is used alone as a primer. g V a While the exothermic metallurgical compositions of the present invention may be used in various forms such as, for example, powders; they are particularly useful and convenient when used in the physical form of pellets or tablets, preferably compressed pellets or tablets. A suitable size for tablets,'for example, is a diameter of about /2 inch, but they maybe either largeror smaller. 1 We havefound that excellent tablets can be prepared using sodium silicate as a binder and that no organic binders or lubricants, which may interfere with the ignition of the pellets, are necessary. The powdered exothermic C0111? position is thoroughly mixed with a solution of sodium silicate, granulated by conventional methods, and dried to a suitable moisture content. Granulations of the exothermic compositions prepared in this manner can then be formed into tabletsusing ordinary tableting equip ment Such tablets are. sufliciently strong and hardto withstand normal handling without breaking'or disintewhen added to molten metal.

The product may then contain substantial amounts of unreacted carbonate, which is apparently entrapped in the mixture even after prolonged heating. In order to obr tain an alkali metal ferrate. primer having maximum efiiciency,' it is preferable to heat a mixture of equivalent amounts of iron'oxide and an alkali metal carbonate at v a temperature below the fusiontemperature of the alkali metal carbonate to remove most of the carbon dioxide, andthen gradually completing the calcination by increasing the temperature to a maximum of'approximately 1100 C If the temperature is allowed to rise above approximately 1100 0., some or all of the alkali metal ferrate may be decomposed.

In preparing the alkali metal ferrate rimer of this invention, adequate oxidizing conditions should be prometal ferrate primer is to be used is also to include titanium dioxide as the metallic oxide component, it is particularly convenient and economical to prepare the primer by calcining an ore consisting primarily of titanium and iron oxides such as ilmenite. In accordance withthe present invention, it'has been found that if such an ore is' calcined,under the conditions described above, with an amount of alkali metal carbonate that is equivagrating and at'the same time they arereadily ignited In some cases it is more convenient to partiallydry the granulation before tableting it and then remove the remaining moisture from the finished tablets. However, thisis not necessary, and satisfactory tablets can be'prepared from the fully dried granulated compositions. The use of the exothermic compositions of this invention in the form of pellets and tablets improves control and reproducibility of, the

exothermic reaction and increases the reduction of metallic oxide to alloying element.

In the manufacture of these compositions an intimate mixture ofthe components is necessary for maximum efiiciency of the reaction. 3

The amount of these exothermic compositions which is added to the molten metal is governed by the purpose for which theyare to be used. It may, forexample, vary from as little as 1 pound per ton of molten metal to more than 60 pounds per ton of molten metal.

The followingexamples illustrate the invention.

Example 1 gether with a small amount of sodium ferrite (NaFeO The presence of sodium ferrate .(Na FeO was confirmed by the following chemical tests. Treatment of a portion of the product with water yielded a strongly purple'color, and chlorine gas was evolved.

Example 2 I Calcined ilmeni te primer was" prepared as follows: An

intimate mixture of 75 parts (EeOIIiO and 25 parts by weight of soda ash (Na CO both ground to about 30 mesh, was calcined was no evidence of crystalline sodium titana te. The

sharpness of the X-ray diffraction pattern indicated the absence of sodium titanate as an amorphous phase.

Example 3 An intimate mixture of ilmenite (54 lbs.) and sodium carbonate (18 lbs.), both finely milled, was loaded in stainless steel pans (6" x 18" x 18") up to a depth of about three inches. The pans were placed in a preheated electric mufile furnace (approx. 22" wide x 19" high x 57" deep) recording 700 C., and the material calcined for four hours. Then the furnace temperature was raised to 815 .C., the calcination proceeding for four more hours. Finally, after the furnace temperature was raised to 1005 C., the calcination was completed in four additional hours, the product then being cooled to room temperature. The yield was sixty pounds of calcined ilmenite primer.

I Example 4 An exothermic metallurgical composition containing sodium ferrate primer was prepared by thoroughly mixing 75 parts by weight of milled sodium ferrate primer, prepared as described in Example 1, with 25 parts by weight of milled calcium-silicon. The softening point and absorption capacity of the product obtained upon ignition of this exothermic composition were determined as follows:

A portion of the above exothermic composition was heated in a crucible until the mixture ignited. The ensuing exothermic reaction proceeded rapidly but not violently. After the exothermic reaction was complete, the product of the exothermic reaction was cooled and the larger particles of the metallic reaction product were separated and removed. Tl e remainder of the. reaction product, which was composed substantially of acidic and basic oxides but which probably also contained finely dispersed metal, was ground. Removal of the metallic component of the reaction product would facilitate grinding but is not essential since the presence of metal does not significantly aifect the temperature at which the oxidic product melts. A portion of the ground mixture was then heated in a furnace provided with a calibrated thermocouple and the temperature was gradually raised until the mixture softened, as determined by touching the mixture with a steel rod. It was found that this mixture began to soften at approximately 2000 F., and it became watery at 2350 F.

To determine the absorption capacity of the mixture, further proportions were directly mixed with weighed amounts of titanium dioxide. These mixtures were then heated in the furnace to 2600 F. and the mixture was tested by thrusting a steel rod into the melt and then withdrawing it. A mixture was considered to be fluid if it was nearly water-like and pourable in consistency and did not form threads when the steel rod was withdrawn. By determining this temperature for a series of samples containing increasing amounts of titanium dixoide it was found that the oxidic product obtained upon ignition of the above exothermic composition absorbed more than 20% of its weight of titanium dioxide and still remained fluid at a temperature of 2600 F.

by weight of ilmenite An exothermic metallurgical composition similar to that described in Example 4 was prepared in pellet form by thoroughly mixing milled sodium ferrate primer (7.5 lbs.) and milled calcium-silicon (2.5 lbs.). The dry mixture was sprayed with a 50% solution of sodium silicate (0.68 lb.) and water (0.65 lb.) and again thoroughly mixed. This wet material was forced through a 12 mesh screen and dried until 0.33 lb. of water was lost from a weighed mass of 10 lbs. The partially dried but still moist mass was then sifted through a 12 mesh screen to form granules. The granules were compressed into tablets of approximately inch in diameter using a conventional tableting press. The tablets were then dried until 0.47 lb. of water had been lost per each 10 lbs. of

tablets.

Example 6 An exothermic metallurgical composition containing calcined ilmenite primer was prepared by thoroughly mixing 63.3 parts by weight of milled calcined ilmenite primer, as prepared in Example 2, 29.4 parts by weight calcium-silicon and 7.3 parts by weight sodium nitrate. The ignition time of this composition was comparable to that of the .composition described in Example 4. The

softening point of the oxidic product obtained upon ignition of the composition was approximately 2000 F., and it became watery at 2350 F. The oxidic product absorbed more than 20% of its weight of titanium dioxide as determined by the method described in Example 4 and still remained fluid at a temperature of 2600 F.

Compressed pellets of this composition, approximately inch in diameter were prepared by the method described in Example 5.

Example 7 An exothermic metallurgical composition containing calcined ilmenite primer was prepared by thoroughly mixing 633 parts by weight of milled calcined ilmenite primer, as prepared in Example 3, 29.4 parts by weight calcium-silicon and 7.3 parts by weight sodium nitrate. The ignition time of this composition was comparable to that of the composition described in Example 4.

An 800 pound ingot of type 314 stainless steel was cast as follows: Pellets of an exothermic metallurgical composition corresponding to that described in Example 5 (10 lbs.) were poured intothe mold before the teeming operation. The metal was teemed in the usual manner and allowed to solidify. Much less smoke evolved during the teeming operation than occurred in a similar trial using pellets of an exothermic metallurgical composition containing 43 parts by weight of ilmenite, 30 parts by weight of calcium-silicon and 27 parts by weight of sodium nitrate.

On removal'of the ingot from the mold during the stripping operation, it was observed that the surface of the ingot was substantially different from other ingots from the same heat which had not been treated with this composition. The surface of the treated ingot was considerably smoother than the surface of the untreated ingots and it was noticed that all sharp corners (such as produced by the corners of the ingot molds) had been eliminated. The entire surface of the treated ingot appeared to have been covered during the teeming, indicating that the internal wall of the ingot mold was coated during teeming with the glassy slag produced with this composition. The hot workability of this ingot was judged better than that for untreated ingots from the same heat, indicating that an important benefit resulted 'fromithe useiofthis composition. I

,Example was repeated using 10 pounds of pellets ofthe exothermic metallurgical composition described in Example 6. The condition of the finished ingot Was comparable to that'of the ingot which had been cast using an exothermic composition as described in Example 8. Only a small "amount of smoke, comparable to that in Example 8, -evolved during-the teeming operation.

Erample 10' :An. exothermic metallurgical composition containing calcined ilmenite was prepared by thoroughly mixing 53.5 parts by Weight of milled calcined ilmenite primer, 9.4

parts by weight of milled rare earth oxides, 29.7 parts by In view of the above, it will be seen that the severah objects of the invention are achieved and other advantageous results attained.

As various changes could be made in the above methods and products without departing from the scope of the invention, it is intended thatall matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.

We claim: 1. An exothermic metallurgical composition compris- I ingtitaniu'm dioxide, sodium ferrate and a reducing agent for sodium ferrate.

i 2. exothermic metallurgical composition comprising titanium dioxide, a mixture of rare earth oxides, sodium ferrate and calcium-silicon, said composition forming uponignition a product containing a basic oxide, said product remaining fluid at a temperatureof approxi-. .mately 2600" F. after absorbing at least approximately 15% of its weight of'titanium dioxide. V

3.,The method of preparing an alkali metal ferrate primer comprising heating a mixture of'ilmenite and an alkali metal carbonate under oxidizing conditions at a temperature below the fusion temperature of the alkali metal carbonate and then gradually increasing the temperatureto not more than 1100 C. to complete the calcination of the iron oxide portion of the ilmenite, the amount of alkali metal carbonate in saidmixture being equivalent to the iron content of said mixture. v

4. The method of preparing an alkali metal fer rate primer comprising heating a mixture of ilmenite and an alkali metal carbonate in an oxidizing'atmosphere at a temperature below' the fusion temperature of the alkali metal carbonate until substantially all of the carbon dioxide has been removed, and then gradually increasing the temperature to not more than 11.00 C. to complete the calcination of the iron oxide portion of the ilmenite,

the amount of alkali metal carbonate in said mixture being equivalent to the iron content of said mixture.

References Cited in the file of this patent UNITED STATES PATENTS Hansley June 14, 1955 FOREIGN PATENTS 7 17,335 Australia Apr. 27; 1934 152,514 Australia July 23,1953

Claims (1)

1. 3. THE METHOD OF PREPARING AN ALKALI METAL FERRATE PRIMER COMPRISING HEATING A MIXTURE OF ILMENITE AND AN ALKALI METAL CARBONATE UNDER OXIDIZING CONDITIONS AT A TEMPERATURE BELOW THE FUSION TEMPERATURE OF THE ALKALI METAL CARBONATE AND THEN GRADUALLY INCREASING THE TEMPERATURE TO NOT MORE THAT 1100*C. TO COMPLETE THE CALCINATION OF THE IRON OXIDE PORTION OF THE ILMENITE, THE AMOUNT OF ALKALI METAL CARBONATE IN SAID MIXTURE BEING EQUIVALENT TO THE IRON CONTENT OF SAID MIXTURE.