US1777081A - Manufacture of steel - Google Patents

Description

'have knowledge, suc

1 the best nary routi e operation frequently results in Patented Sept. 30, 1930 UNITED STATES PATENT OFFICE EDIKTARI) H. GRAF, OF CLEVELAND, OHIO, ASSIGNOR TO THE LUSIFER PRODUCTS COM- PANY, OF CLEVELAND, OHIO, A CORPORATION OF OHIO MANUFACTURE OF STEEL No Drawing. Continuation of application Serial No.

November 23, 1928.

This invention relates to the manufacture of steel and includes among its objects and advantages a reduction in the finely divide-d non-metallic-particles or sonims in the solid product. It is applicable to all the steel makin processes of which I as Bessemer, open hearth, and electric furnace.

The production of steel from pig iron involves primarily a reduction in the carbon content by oxidation, and elimination of the,

extremely undesirable iron sulphide. The carbon may be reduced by an air blast or by adding ferric oxide to the melt, and the iron sulphide may be eliminated by adding manganese. The manganese is usually added in quantities far in excess of the .theoretical amount necessary to react with the iron sulphide, so that mass action will completely eliminate all trace of iron sulphide.

The steps referred to in the preceding paragraph are commonly designated by theinelusive term finishing. Finishing has to be done mostl by the guess-work of a melter with years- 0 experience, assisted by a few incomplete chemical analyses hastily made while the reactions are going on. If the job happens to be perfectly done and the metal happens to be tapped at just the right time, the resultant steelwill lie quietly in the.

ladle and in the ingot molds, and will neither swell by continued evolution of gases nor shrink to form a deep pipe. Unfortunately guess-work now available in ordidefective i just right.

In finished steel the sonims may be classified under the following five headings.

I. The products from theireactions of the manganese, silicon, and other additions, with the sulphides and oxides of the unfinished steel. Given suflicient time these would have gots because the finishing is not gone into the furnace slag. This is the prin-' cipal source-of sonims.

- II. The products from the oxidation of some ofthe finished steel ingredients by atmospheric oxygen during the'progress of the steel from the furnace to solidification in the molds.

quantity of 67,667, filed November 7, 1925. This application filed Serial No. 321,503.

III. Oxides from the unfinished steel.

, IV. Slag particles entrained by the intimate mixing caused' by pouring the charge into the ladle.

V. Particles of dirt and othernon-metallic matter, and detritus from the lining of the furnace, ladle, and mold.

' The sonims in unfinished-steel are mainly oxides, and in finished steel sulphides and silicates. They are insoluble in molten steel and those of the first two classes are distinguished by the high percentage of manganese they contain. All these sonims as they occur in the molten steel are in a state of extremely fine sub-division and the products of the reaction between them and the manganese likewise exist at first in extremely small particles, too small to be readily floated out of the liquid by gravity. The silicates are mostly fusible at steel-melting temperatures and hence are eliminated more readily. In all cases the thoroughness with which these impurities are eliminated depends upon the length of time which was afforded for their liberation and the condition of the surface. to which they are permitted to migrate.

An important feature of my invention is the provision of a new-and sim le mode of treatment wherebythe eliminat on of these sonims is rendered more thorough than heretofore, swelling and shrinking in the ingot mold is prevented or restrained, and ebullition isquieted without the formation of the added sonims heretofore produced under such conditions; and another important feature of myinvention is the fact that it can be performed on the spot, requires nochange in the preceding treatment of the steel, saves many heats which would otherwise be scrapped, and substantially increases the yield of a steel works.

I subject the steel, at some time after the completion of the ordinaryfurnace operations and prior to the final solidification in further," in ase no oth r l g i present. or-

form is so cheap, dense, and readily fusible,

and even the iron impurity is twice valuable in this connection, first because it renders the substance cheaper, and second because it renders it more fusible and easier to combine with the sonims. It should be understood that this iron impurity, when present, should be intimately incorporated with the alumina so that its tendency to react with the molten metal is restrained; and that the percentage of this impurity ought not to be over 20%. Also it should be understood that by alumina I mean any aluminous substance suitable for my purpose. In this connection I may add that so far I have been successful only with fused substances, also that in these the impurities apparently may be mixed with the alumina either physically or chemically.

This material is used either in the ladle or in the ingot mold. For example, a. quantity of the same is thrown into the ladle simultaneously with the beginning of teeming, say at the rate of about one pound per ton of la? dle capacity. The molten steel as it cascades into the ladle melts the material and mixes it thoroughly with the steel prior to the emergence of any of the furnace slag through the tap-hole. As a result there is a period of several minutes during which this material fluxes the steel at its period of greatest turbulence and with no other fiuxing material present. The resulting products collect at the top of the melt in the form of :1V slag which becomes incorporated with the furnace slag when the same is drawn into the ladle; but in cases where no furnace slag is tapped it is found that each pound of my material employed in this manner combines with sufficient impurities in the melt to produce about six poundsof slag, the entire additive part of which by previous processes is left in the metal.

The reactions which occur are very various and complicated. I do not assert that my material.itself acts as a deoxidizer or that it enters into any direct chemical reaction with elemental impurities. Apparently its function is principally to combine with the products of the actual deoxidizers and remove those products, either by assisting them to collect togetherinto masses of sufficient size to gravitate to the surface, or by producing therewith a substance of lower melting point, or by preventing reduction of some product already formed; it is also suggested that while it does not act directly as a deoxidiier it may assist the action of such deoxidizers as are already present by removing their waste products and thus preventing mass action from arresting the reaction. It is also known that the use of my material at the times and in the modes herein described reduces the fusing and combining temperaturesi so as to enable the collection into a slag of various sonims ,which would otherwise remain disseminated throughout the steel as injurious inclusions.

The results of this addition are both physical and chemical: physical in that the top of the ingot is kept hot and solidification is restrained for several minutes longer than otherwise thereby affording more time for eliniinationfand further in that a top layer is produced into which the sonims pass more completely and more readily than through a skin of the naked metal; and chemical in that the composition of this slag when finally removed is very different from what it was originally. In the following parallel columns I have shown analyses of the two slags taken from adjacent ingots of the same heat. sample 6780 being the final composition of the slag when a flux of my invention was employed:

The ingredients which I added to the last mentioned ingot consisted of (approximately) Alumina 80 Silica 4 F6303 16 Aluminum was added to the mold as in the usual practice, which accounts for the 7.11 aluminum oxide shown by the first sample.

The two ingots being of the same size and poured successively, a certain proportion of the aluminum in the second sample also came from the metal, but it is impossible to say how much since the total amounts of the respective slags were not reported. It is known, however. that the total amount of the second slag was a multiple of that of the first slag, probably 4 or 5 times as much.

It is obvious that a chemical change has occurred. For example the proportion of aluminum oxide has fallen from 80 to 31.39, or more than 60%, but this cannot be due merely to dilution by the sonims, though even thatwould be an evidence of Value by removing so great a quantity of impurity, for the other ingredients do not show a similar dilution. -Thus silica, which was another ingredient of the slag, has increased instead of Hit) Furthermore, by the addition of this material to the ingot the rising or sinking of the metal is almost instantaneously arrested, its wildness killed, and its sparking, sputtering, and burning on top arrested. Furthermore during cooling it often exhibits a small but marked peculiarity, namely, that as the upper end of the metal hardens a pipe of very small size is formed while the entire upper end of the ingot shrinks inwardly away from the mold whereas with the naked ingot the upper end of the ingot adheres closely to the mold and sinks correspondingly in the center formsentials can be dropped and other substances reticalconsiderations, I do not limit my ing a deep pipe which terminates at the bottom in a region of high segregation.

As the metal of such an ingot cools it hardens inwardly progressively from the walls and bottom, leaving a molten core of gradually decreasing size and depth, the

metal at the same time gradually freezing superficially at the top from the exterior inwardly which freezing tends to press the slag gradually inwardly. Just before solidification occurs this slag ordinarily is thrown out with a stick of wood and a steel lid or plate is ordinarily laid over the molten metal so as to become tightly welded thereto. It was in this way that the two samples of the above analyses were taken.

The composition which I prefer to employ is asfollows:

A1203 50 to 98% (82 i 85) F820;; 1 to 20 1s 1 sio; 1 to 30 3.5) -10 TiO o to 1.5 4 A (100 (100) The last two columnsshow the actual compositions of two mixtures which I am uslng with very great success; theadjacent column indicates that the percentage of the different ingredients can permissibly vary through quite a wide range.

It will be understood that I do not limit myself to these exact figures as the non-esadded, either as non-essential diluents or for some particular additional purpose. Also, while I have set forth in detail certain theoclaims. by or to such theories but rely upon the observed result of practical experience.

. Also I have found that the ingredients may be present in the composition either as such or in combination.

Under all these circumstances my invention obviously is not limited to any one substance, or any one source of the ingredients, but comprises all substances having the essential action; furthermore my invention is not rested upon any theory of operation, but upon observed results.

Without further elaboration the foregoing will so fully explain my invention, that those skilled in the art, whether by proceeding as herein specifically outlined, or by substituting such substances as may be found to be equivalents of the specific substances enumerated herein and otherwise applying knowledge current at the time of such application, may'readily use the same under such various conditions of service as may be encountered.

This application is a continuation of my earlier filed application, Serial No. 67,667, filed November 7, 1925.

I claim:

1. In the production of steel the steps of substantially completing the usual finishing reactions, such as reducing the carbon by adding iron oxide, and eliminating iron sulphide by forming manganese sulphide, and including the addition of aluminum to put an end to the evolution of gas, so that no further addition will be required of such a nature as to form additional sonims by chemical action, the molten material at this stage being charged with finely dispersed sonims;

subsequently mixing through the molten mass rially before solidification, finely divided sonims to build up new slag particles of minimum melting point below that of the steel and of relatively larger sizes, the sonims be ing chiefly alumina.

.3. In the production of steel the steps of substantially completing the usual finishing reactions, such as reducing the carbon by adding iron oxide, and eliminating iron sulphide by forming manganese sulphide, and including the addition of aluminum to put an end to the evolution of gas, so that no further addition will be required of such a nature as to form additional sonims by chemical action, the moltenmaterial at this stage being charged with finely dispersed sonims; subsequently mixing through the molten mass after removal of the main finishing slag but materially before solidification a finely divided charge of alumina containing a substantial contamination of silica and iron oxide, each in excess of four percent, and thereby formnig silicates and other compounds in particles of relativelv large size and lower melting i pnntllnnthatelllieitcelmmtetakeout of the molten mass :1 new slag far greater in amount than the charge added.

4. In the production of steel the steps of substantially completing the usual finishing reactions to a point where no further addition will be required of such a nature as to form additional sonims by chemical action; subsequently mixing through the molten mass after removal of the main finishing slag but materially before solidification a finely divided charge of alumina and thus taking out of the molten mass a new slag greater in amount than the charge added.

5. In the production of steel the steps of substantially completing the usual finishing reactions; subsequently mixing through the molten mass after removal of the main finishing slag but materially before solidification a finely divided charge of alumina containing a substantial contamination of silica and iron oxide and thus taking out of the molten mass a new slag greater in amount than the charge added.

6. In the production of steel the steps of substantially completing the usual finishing reactions; subsequently mixing through the 'molten mass after removal of the main finishing slag but materially before solidification a finely divided charge of alumina containing a substantial contammation of silica and iron oxide, each in excess of four percent, and thus taking out of the molten mass a new slag greater in amount than the charge added.

7. In the production of steel the steps of substantially completing the usual finishing reactions; subsequently mixing through the molten mass materially before solidification a finely divided charge of alumina containng a substantial contamination of silica and lron oxide, and thus taking out of the molten mass additional slag greater in amount than the charge added.

8. Ihe method of cleaning finished steel containing finely dispersed sonims with meltmg points not materially lower than the steel itself, which comprises washing through the molten mass a charge of additional material, principally alumina, that will not react with the steel but that will react with the finely dispersed sonims and form larger sonim particles with lower melting points.

9. The method of cleaning finished steel contammg finely dispersed sonims with meltng points not materially lower than the steel itself, which comprises washing through the molten mass a charge largely alumina with material admixture of silica and ferric oxide.

\ 10. A fiuxfor washing finished steel, large ly alumina.

ly alumina with a material contamination of silica not 111 excess of 30lper cent.

12. A flux for washing mshed steel, largely alumina with a material contamination of comprises performing the main steel making reaction, and thereafter washing through the steel, While molten and before final solidification, a charge of fused alumina.

In testimony whereof I hereunto aflix my signature.

EDWARD H. GRAF.

I 11. A flux for washing finished steel, large-