US2079901A - Metallurgical addition agent and process - Google Patents

Description

Patented May 11, 1937 METALLURGICAL ADDITION AGENT AND PROCESS Arthur 0. Davidson, Canton, Conn., assignor of one-third to Burtner Fleeger, Tulsa, Okla.

No Drawing. Application July 5, 1934, Serial No. 733,859

Claims.

This invention relates to the art of metallurgy. In the treatment of ferrous and non-ferrous metals, and in the production of various metallic alloys. including plain and alloyed steels, it has 5 been the practice of the prior art to treat molten charges of these various metallic compositions for the purpose of removing sonims, metalloids, harmful gases and occluded oxidized particles, as well as to prevent blow-holes and formation of pipe in the product.

Various deoxidizing agents and scavengers have been used in the prior, art in an attempt to properly accomplish the above purposes, but the use of the known scavengers and deoxidizers are attended with secondary reactions which often leave free oxides in the bath and fail to completely deoxidize or scavenge the molten metal even under conditions where an excess of deoxidizer is used. The common deoxidizers are 90 those metals and metallic compositions which usually have a high affinity for oxygen, nitrogen and other deleterious substances with which they combine under the conditions of treatment in a reaction of an exothermic nature. For example, metallic aluminum when thrown into a bath of molten metal combines with any oxygen present to form A1203 with a molecular heat of formation of 392,600. Should the oxygen of the bath be in the combined state, an oxygen transfer occurs to the aluminum, provided the heat of formation of aluminum oxide. is greater than the heat of formation of the residual oxide. Besides various inter-related chemical reactions involved in ordinary deoxidation processes, and besides secondary reactions whereby slag forming constituents are increased or depleted in their acidic or basic relationship to the metal, there occurs in addition physical phenomena which have some important effect on the metal. These physical phenomena manifest themselves in the type of grain structure, of either the casting, ingot or worked product.

The present invention marks an advance over the known processes and products of the prior art by reason of the discovery that complete deoxidatlon and higher quality metal results from the utilization of a scavenging composition which will hereinafter be set forth in complete detail. My discovery provides a deoxidizing and scavenging composition which does not detract from the quality of the metal in which it is introduced and is suihciently powerful and rapid in its action, that instantaneous combination with oxides and sonims occurs in the bath without molten metal, whether ferrous or non-ferrous,

either in elemental or alloyed condition, with a composition comprising lime, silicon, aluminum, carbon, sodium bichromate and ammonia. The composition can be adjusted in its various ingredients to give less or more pronounced reactions, and is preferred within the following acceptable ranges:

Per cent Lime 10.00 to 50.00 Silicon 351-00 to 75.00 Aluminum .50 to 25.00 Carbon .50 to 10.00 Sodium bichromate .00001 to 10.00 Ammonia .00001 to 10.00 Iron maximum 5.00

An example of a composition for rapid action within the above ranges and including a suitable amount of sodium bichromate and ammonia is as follows:

Per cent Lime 50.00 Silicon 35.00 Aluminum 5.00 Carbon 10.00

A composition to give moderate action when in combination with ammonia and sodium bichromate is as follows:

Per cent Lime 10.00 Silicon 73.00 Aluminum"; 15.00 Carbon 2.00 Iron "maximum" 3.50

A composition to give less moderate action in combination with ammonia and sodium bichromate is as follows:

Per cent Lime i 35.00 Silicon 54.00 Aluminum 10.00 Carbon 1.00

Iron "maximum" 3.50

In preparing these compositions, I prefer to use the electric furnace. but any other suitable melting furnace may be used within the dictates of commercial practice. I prefer to charge the full amount of lime plus and to add thereto 2% of iron containing over 5% of carbon. When melted, the required amount of silicon is added, then the melting operation is continued and of white silica sand is added. This latter addition 10 of white silica is reduced to silicon during the melting process. In a separate furnace, the desired proportions of aluminum covered with sodium silicate as a protecting slag may be melted. The full amount of carbon is next added to the 15 lime mixture, and the molten lime mixture is then poured into a ladle from the electric furnace, simultaneously pouring the molten aluminum from the separate furnace into the lime mixture stream flowing into the ladle.

It should be borne in mind, however, that good results are obtainable without melting the aluminum in that such can be added separately in a solid state to the crushed or pulverized lime mix and in the proportions mentioned. For example, in commercial practice this has been accomplished by treating innumerable heats consisting, for illustrative purposes, of 5600 pound charges. The proportions of the mixture were as To the above the following was added:

1 pounds of aluminum metal /2 ounce sodium bichromate 3 to 4 c. c. ammonia in solution The resulting castings showed every indication of a super-deoxidized metal. The mechanical structure was of highest density. Though poured at various temperatures from 2825 F. to 3100" F., there was consistent absence of optical dendritic formation. Dendrites invariably form in steel of similar analysis when poured above 2900 F. and into cold molds. In this' connection, it is worthy of note that those metals of so-called phenomenal qualitiesare the result of a superdeoxidized melt occurring rarely in innumerable melts; however, metallurgists generally have been unable to discover the cause for such accidental perfection. The nearest approach to the solution is in an article of May 31, 1934, Iron Age, by

Mr. E. C. Bain on that part of the subject relating to perfect deoxidation. With the use of the teachings of the aforesaid invention, however, super 65 or complete deoxidation occurs constantly and as a uniform accomplishment. What seems fantastic appears to be an element not known or understood, namely, that by the very action which creates the ebullition and super-deoxidation, non- 7 metallic substances are eliminated or those remaining are so minutely subdivided into harmless particles, that a more complete metallic amalgamation must result. Y

The resulting product comprising the lime 75 mix is cast into pigs and. when cold, is crushed and pulverized -into powdered or comrninuted .form. Sodium bichromate dissolved in a solution of warm ammonia is mixed with the powder at any convenient time and preferably just before the mixture is actually used for its intended purpose. It is preferred not to add the sodium bichromate and ammonia until the mixture is to be used, since the ammonia may otherwise be lost by decomposition.

The best procedure for treating molten metal with the teachings of the above described invention can be illustrated. in connection with the manufacture of a steel containing carbon 28%, manganese 54%, and silicon 26%. In the making of this steel, ordinary silico-manganese is added to the molten bath to bring up the silicon and manganese to the proportions desired in the finished product and to remove the greater portion of free oxides and gases not in solution. After this preliminary treatment, a spoon test is taken, if the steel is dead or killed then one pound of the above deoxidizing and catalytic composition is added for each 1000 pounds of molten metal. If the spoon test does not show proper shrinkage of the metal approximating one-eighth inch after the preliminary addition of silico-manganese, then 1 to 2 pounds of the herein defined novel catalytic composition is added to each 1000 pounds of molten metal. This is accomplished by thrusting the same down to the bottom of the metal bath in the furnace by means of a rod at the end of which the-composition is securely attached. The method of purging metal baths with a rod and a container attached thereto is old in the art, and forms no part of the present invention, except as the novel catalytic composition hereinbefore defined may be used for the pur pose set forth.

The treatment with silico-manganese may be omitted, but in the making of compositions containing silicon and manganese in the final product, I find it preferable to use such as above explained. It will be understood, however, that the use of such a known treating agent or any other treating agent will not so far as applicant is informed, give the results accomplished by the present invention unless used in conjunction with my novel catalytic composition. It will be further understood that my catalytic composition may be used in the practice of the invention ad libitum without the use of any other aiding agent such as the -silico-manganese treatment described supra.

I do not wish to be limited to the theory of the reaction, but I believe that the silicon, lime, aluminum, and the carbon composition, when suddenly subjected to the high heat of the molten metal (for example in the case of steel making, about 2800 F.) instantly combine to form calcium-aluminum-carbide setting up rapid exothermic conditions in the bath of molten metal. Simultaneously, the ammonia gas and sodium bichromate instantly decompose and as a result of the ebullition, the entire mass of sonims and occluded oxides are rapidly swept from the metal intothe overlying Slag, thus effecting cleansing heretofore unknown or unaccomplished in the prior art. Possibly, at the high ,temperatures above 2000 F., the oxides either in free or suspended condition, are in somemanner decomposed by the sodium bichromate at those temperatures.

In the manufacture of a 5600 pound charge of steel, containing carbon .28%,'manganese 54% and silicon 26%, a metal resulted having physicals in the case condition not heat treated in any manner as follows:

Tensile strength pounds per square inch '71, 700

Elastic limits do 50, 400 Elongation percent 17. 5 Reduction of area do 21.0

My novel catalytic scavenging composition may be added to the metal in the furnace, in the ladle, or in the molds. The following pulverized mixture has been added to the first stream of metal discharged from the furnace going into the ladle in a loose cloth or paper bag:

Percent of weight In the treatment of non-ferrous metals, and for example, copper or copper mixtures, the usual copper phosphide scavenging agent may be omitted in most instances if approximately .15% of my catalytic composition is introduced under conditions of high temperatures such as 2000 F. By 15% is meant .15% catalyst of the charge to be treated and not 15% of the catalyst weight. It is well to give the composition suflicient time in the bath (at least five minutes) so that the action is completed. In the treatment of aluminum and aluminum alloys. the catalytic cmposition can be used in the same manner as described in connection with the treatment of copper.

Where the process is applied to alloy steels containing chromium or nickel-chromium, tungsten or molybdenum, the ordinary deoxidizers of the prior art should be used (ferro-silicon as an example) after the addition of the alloying elements, followed in to minutes with the treatment with my novel catalytic composition, re gardless of the physical condition of the test block taken as a result of a spoon test. If desired, the ordinary deoxidizers may be used first to kill the bath of steel, the alloying addition in the form of ferro-alloys may be then made, and this can be followed in one to five minutes with treatment by my novel catalytic composition. When this composition is left in a steel bath without removing the slag for over 3 minutes, it also causes a reduction in the sulfur and phosphorus content of the bath.

Steels treated by the above composition and process, whether plain or alloyed steels, are substantially non-dendritic. uniform in structure and dense in character in the cast condition. Such steels are also more amenable to standard heattreating processes for the production of satisfactory heat-treated products. These products include both hardened and annealed steels. From the above disclosure, it will be seen that .a composition of lime, silicon, aluminum and carbon has been provided as a base for incorporating therewith sodium bichromate and ammonia. The specific amounts or proportions of lime, silicon, aluminum and carbon are not critical in the practice of the invention and may be changed as desired or as commercial practice may dictate; however, the use of sodium bichromate in material amount up to 10% together with the use of ammonia is essential to the ends of the invention. Preferably .0001 to .002% of sodium bichromate and .0001% to ,001% of ammonia are added by weight to any desirable proportion of lime, silicon, aluminum and carbon in the mixture.

Various changes may be made in the embodiments of the invention herein specifically described without departing from or sacrificing any of the advantages of the invention as defined in the appended claims.

I claim:

1. The process of scavenging molten metal which comprises treating the same with a composition containing lime, silicon, aluminum, carbon, sodium bichromate and ammonia in suitable relative proportions to impart the desired reactions for removing sonims, metalloids, harmful gases and oxidized particles from the resulting product without harmfully combining therewith.

2. As an addition agent for molten metal, a deoxidizing and scavenging composition includ ing lime, silicon, aluminum, carbon, sodium bichromate and ammonia in suitable proportions to impart a sufilciently powerful and rapid reaction for efiecting instantaneous combination with the sonims and oxides in the molten metal without being included in any substantial amount in the resulting product.

3. The method of preparing a deoxidizing and cleansing composition for molten metal which comprises melting together lime, silicon and iron containing a suitable quantity of carbon; separately melting aluminum; simultaneously pouring both melts in a common stream to produce a composite product; cooling the product and mixing the same with sodium bichromate and ammonia.

4. An addition agent for treating molten metal comprising Percent Lime 10 to 50 Silicon 35 to '75 Aluminum .50 to 25.00 Carbon .50 to 10.00 Sodium bichromate .00001 to 10.00 Ammonia .00001 to 10.00 Iron maximum 5.00

5. A treating agent for cleansing and improving molten metal containing a pulverized mixture of approximately the following:

Percent by weight ARTHUR C. DAVIDSON.