US3026195A - Method of degasifying steel and other metals - Google Patents

Description

March 20, 1962 J. o. EDSTROM ETAL 3,026,195

METHOD OF DEGASIFYING STEEL AND OTHER METALS Filed March 25. 1958 F162 FIG.3

Patented Mar. 20, 1952 [ice 3,026,195 METHDD F DEGASIFYING STEEL AND OTHER METALS John Olaf Edstriim, Hantverkarbacken 38G, Sandviken, Sweden, and Gustaf Henrik Widmark, Enspannargatan 56, Stockholm-Vallingby, Sweden Filed Mar. 25, 1958, Ser. No. 723,744 Claims priority, application Sweden Mar. 26, 1957 3 Claims. (Cl. 75-49) The present invention relates to a method of degasifying a metal so as to remove dissolved gases, such as oxygen, hydrogen, nitrogen, carbon monoxide, carbon dioxide, water vapour and the like, without reaction products of these gases remaining in the metals and without using pumps for the removal of the gases.

For many years metallurgists have tried to manufacture steel and metal products with the lowest possible content of oxygen, nitrogen and hydrogen. Under normal circumstances it is not possible to free steel or other metals of gaseous or non-metallic inclusions causing a deterioration of the mechanical and physical properties of the steel or other metals.

In steel, oxygen is found atomically dissolved and is very easily removed in the form of carbon monoxide according to the reaction From this formula it becomes evident that it is possible to eliminate oxygen efiectively, if the carbon monoxide pressure can be reduced to low values. In the reaction formulas given in this specification, the substances dissolved in steel are indicated by underlining their chemical symbols. In order to eliminate oxygen according to the formula a pressure lower than mm. Hg is required.

Hydrogen and nitrogen can be eliminated by processes according to the formulas H 1/2H2 and N )1/2N2 respectively.

The difficulties in eliminating hydrogen and nitrogen are caused by the fact that the equilibrium contents decrease proportionally to the square root of the value of the gas pressure. In order to avoid the formation of flakes, the hydrogen content should be lower than 0.0003%, which corresponds to an equilibrium pressure of 10 mm. Hg. For the effective elimination of oxygen, nitrogen or hydrogen from steel or other metals, of course, the highest possible vacuum should be attained.

The vacuum treatment can be applied through the melting of steel or other metals in induction melting furnaces which, however, are of limited capacity and of complicated and expensive design. About 1940, a method was found which allowed the vacuum treatment of steel in large quantities. According to this method, steel in liquid state is treated in ladles or chills in a special chamber from which the gases can be evacuated by means of vacuum pumps. For 16 tons of steel in the ladles a vacuum treatment of about minutes is required.

According to another method, a ladle which can be emptied through the bottom, is placed above a vacuum chamber in which a chill is provided. When the steel is being tapped down into the vacuum chamber, the molten metal stream is made to explode due to the gas pressure,

and the oxygen, hydrogen and nitrogen contents decrease very rapidly. During the tapping of the steel from the ladle, the vacuum is maintained in the vacuum chamber by the exhaust of gas therefrom by suitable pumps. The pressure within the vacuum chamber is held at about 10 mm. Hg. This method is most suitably used for casting large-size ingots.

Another degasifying method has been worked out which allows the vacuum treatment of steel in large quantities in ladles. The ladle is placed on a platform above which a vacuum chamber, a so-called vacuum pipette, provided with pumping equipment is suspended on an overhead crane. With the only exception of a vertical, 1500 mm. long pipe leading into its bottom, the vacuum chamber is completely sealed. The chamber is lowered sufiiciently so that the pipe is immersed in the steel, and the vacuum chamber is then evacuated. Thus, a certain steel quantity is sucked up into the chamber and, after being degasified, is tapped down into the ladle. This cycle is repeated several times, with the entire treatment lasting about 30 minutes. While the oxygen as well as the hydrogen content is reduced by one third, the nitrogen content is not subject to a considerable decrease, particularly when the nitrogen content is about 0.004% at the beginning.

The abovementioned existing methods all seek to degasify the metals by means of a vacuum applied above the molten metals and created by evacuating the gas by means of pumps. At a high temperature and high vacuum, the gas volume evacuated is large in relation to the Weight evacuated, which necessarily requires a large capacity, and therefore expensive, pumping means. If, for example, steel is to be deoxidized at 1600 C., a gas volume of about 700 mfi/ton steel is obtained While the oxygen content is reduced by 0.01% and the pressure is held at 10 mm. Hg. Besides, equally large volumes of hydrogen and nitrogen are to be eliminated at the same time.

The present invention relates to a method of eliminating these large gas volumes in a rather compact state, namely in the form of solid or possibly liquid reaction products to be obtained through the absorption of the gases during a chemical or physical procedure.

A method embodying the present invention and usable for degasifying molten iron and steel will now be described. A representative example of the gas combination to be found above a molten steel surface under vacuum, is CO, 15% H and 5% N the normal gas quantity being 0.3 Nm. /ton steel [=03 m. at STP (60 F., 29.92 Hg) per ton of steel].

From this gas mixture CO is eliminated, for example, according to the following carbon deposition reaction At a temperature of, for instance, 400 C. the equilibrium pressure is 10- mm. Hg, the reaction speed being rather high. H can be eliminated, for example, according to the reaction formula for which reaction the equilibrium pressure is 10- mm. Hg at 400 C. The quantities of CaO and Fe O consumed are small. The binding of H requires only about 1 kg. Fe O and 0.11 kg. CaO, and the binding of CO 0.3 kg. CaO per ton of degasified steel. Owing to the fact that the materials are regenerated without cost, no material is in reality consumed.

N is eliminated, for example, through Al according to the reaction At a temperature as high as 1500 C., the equilibrium pressure is l0- mm. Hg, and at 400 C. it is only about 10- mm. Hg. 0.04 kg. Al is required per ton of steel to be degassed. The expenditures for all reactants are thus insignificant.

As shown by the reaction formulas and accompanying description given below, Al can also be used for eliminating CO, H In thi case Al is easily introduced into the evacuated chamber by injection thereof in molten, dispersed or powdered state, whereby a large reaction surface and, consequently, a high reaction speed is attained. Mg, Ca, Si, and other metals, possibly also a mixture of them, are favourably used in the same way. Beside metals in the pure state, it is so p ssi l to u alloys of metals and other compounds, as CaSi, CaAl, FeTi, AlTi, MgAl, and the like.

Generally, the elimination of gas can be achieved according to a plurality of reactions. As explained above, CO can be eliminated through the reaction with carbonate forming oxides (CaO, BaO, SrO, Na O, K 0, MgO, MnO, and the like) with the precipitation of free C in the presence of catalysts (for example iron or some iron compound), or by the reaction with oxides which are easy to deoxidize (possible superoxides) and carbonate formers.

Principal formulas are 2C0 +MeO- MeCO +C 'Co-i- MeO+M O MeCO +M O CO is also bound according to the reaction Me+CO MeO-|C for example with the metals Al, Si, Ca, Mg, Ba, Sr, Na, K, Fe, or Z, or by reactions with carbides according to the typical formula for example with Al-, Ca-, Mg-, Fe-, Cr-, Ti-, Zr-, or Si-carbides. Another principal formula for binding CO is As further examples, Me can be replaced by Ti, V, Cr, Zr, Si, Mo, B and other element with high atfinity to oxygen and carbon. H; can be eliminated according to the method exemplified above, i.e. through oxidation with an oxide which easy to deoxidize and the absorption of water formed as an hydroxide. Normally, water is also to be bound through usual absorption or adsorption means, such as CaCl MgClO silica gel, H 50 A1 0 and the like. Hydrogen can also be bound as hydride according to the formula in which Me, may be replaced for example, by Ca, Ba, Sr, Na, Li, Al, and the like. It is also possible to burn (possibly catalytically) H and CO to H 0 and CO through the injection of oxygen gas whereby H 0 and CO are absorbed according to the above method or alternatively condensed by cooling. The reactions are CO+ /2O +MeO- MeCO H /2O MeO Me(OH) N can be eliminated from a gaseous atmosphere through the reaction with metals, for example, Al, Ti, Zr, Ta, Mg, Cr, Mn, or Fe, or with silicon or boron, with the formation of nitride.

2Me+N 2MeN Effects are also produced by reactions with carbides (for example CaO A1 0 and others), for instance, according to the formulas MeC-FN MeCN Cir N can also be burned catalytically or oxidized in a difierent way, whereafter the oxidation products are, for example, condensed by cooling.

Also gases developed from metals other than CO, H N as for example, 0 CO H O, halogens, sulphur compounds, phosphorous compounds, and the like can be absorbed or adsorbed in a Way corresponding to the method described above.

Absorption methods can also be used for a selective elimination of gases usually found above the surface of metals. It is, for instance, possible to eliminate two of the gas components and to maintain only one gas, for example, N in contact with the surface of the metal.

Several examples of apparatus suitable for the practice of the methods embodying the present invention are hereinafter described in detail with reference to the accompanying drawing, wherein:

FIGS. 1 to 6, inclusive, are vertical sectional views of the respective apparatus.

In the several views of the drawing, the same reference numerals are used to identify the corresponding parts of the respective apparatus.

The absorption medium can be injected into the vacuum chamber either in portions which are fractions of the total amount required, or the latter can be injected all at one time. Further, the absorption medium can be introduced before the operation is started, or it may be added during operation. The vacuum obtained can be varied through varying the temperature or quantity of the reactants, so that the degasification intensity is thus easily controlled. This is especially easily done with the apparatus according to FIG. 5 which is hereinafter described in detail.

FIG. 1 shows the ladle 1 with steel 2 therein placed in a vacuum chamber 3 which completely surrounds the ladle 1 and is provided with a cover and a paclc'ng 5. The absorption medium is placed in a gas pervious section 6 of the cover. The chamber 3 is provided with a control valve 7. Since the absorption medium reacts with the gases within sealed chamber 3 to form liquid or solid reaction products, a vacuum is produced in chamber 3.

FIG. 2 shows a ladle 1 with steel 2 therein provided with a cover 8 sealed with the packing 5 so that the space Within cover 8 forms a vacuum chamber. The absorption medium is placed in the section 6 of the cover. The cover 8 is provided with a control valve 7.

FIG. 3 shows the tapping of steel 2 from the ladle 1 provided with a tapping valve 9 arranged for tapping through the bottom of ladle down into a chill 10 placed in a vacuum chamber 11. A packing 13 is provided between the ladle bottom and the chamber 11. The absorption medium is placed in a section 12 in chamber 11 or injected into the latter by means of the sprayer 14. The vacuum chamber 11 is provided with a control valve 7.

FIG. 4 shows the steel 2 sucked up from the ladle 1 into a vacuum pipette 15 through a depending pipe 16. The vacuum pipette can be lifted or lowered by means of an overhead crane, for which purpose the pipette is provided with an eye 17 for the hook of the crane. The absorption medium is placed in the section 18 within the pipette, and the latter is equipped with a control valve 7. The vacuum required for raising steel from the ladle 1 into the pipette 15 can be brought about possibly several times, through the absorption procedure which creates a vacuum in pipette 15 above the surface of the steel therein.

FIG. 5 shows a ladle 1 with steel 2 provided with a sealing cap 19 and with absorption medium being placed in a separate section 20 of the cap which is connected to the ladle 1 by means of pipes 21. Fractionated absorption can be performed, for instance, in the order CO, H; and N When the reaction has started, the gas is sucked from the steel to the absorption medium by the relatively low pressure created in section 20. The absorption section 20 is provided with a control valve 22.

FIG. 6 shows a vacuum chamber defining cover 8 with a sealing packing 5 placed above an induction furnace 23 with steel 2 in the latter. The absorption medium is placed in the gas pervious section 6 within the vacuum chamber defined by cover '8, and the latter is provided with a control valve 7.

While the above examples refer to molten steel, the method of degasifying all other types of molten metals is generally similar thereto.

Several of the reactions for degasitying molten metals, as proposed in this description, were previously performed in a metal bath, which caused the solidified metals to contain non-metallic inclusions as, for instance, oxidic slag. According to the method described, the oxygen, for example, is instead sucked up from the molten metal bath and allowed to form oxides at a place spaced from the metal bath. Thus, the solidified metals are free from slags and non-metallic inclusions in general.

What we claim is:

1. A method of eliminating at least one of the gaseous components dissolved in molten steel, comprising the steps of placing the molten steel in a closed vessel having a volume greater than that of the molten steel so as to provide a space above the free surface of the molten steel and disposing in said space remote from said free surface at least one substance in an amount of 0.04 to 1.1 kg./ ton of molten steel and selected from the group consisting of metals and metal alloys, oxides and carbides capable of selectively reacting With only certain of said gaseous components of the molten steel to produce nongaseous reaction products, thereby to create a vacuum of at least 10 mm. of Hg in said space, and evacuating the remainder of said gaseous substances by mechanical means from said space.

2. A method of eliminating at least one of the gaseous components dissolved in a metal, comprising the steps of placing the metal in a closed vessel having a volume greater than that of the metal so as to provide a space above the free surface of the metal, disposing in said space remote from said free surface at least one substance capable of reacting selectively with only certain of said gaseous components of the metal to produce nongaseous reaction products, thereby to create a vacuum of at least 10 mm. Hg in said space for promoting the further release of the gaseous components of the metal into said space for continuing the reaction with said substance, and evacuating the remainder of said gaseous substances by mechanical means from said space.

3. A method of eliminating at least one of the gaseous components dissolved in a metal, comprising the steps of placing the metal in a closed vessel having a volume greater than that of the metal so as to provide a space above the upper surface of the metal, and disposing in said space above the upper surface of the metal at least one substance capable of reacting selectively with only certain of said gaseous components of the metal to produce non-gaseous reaction products, thereby to create a vacuum of at least 10 mm. Hg in said space for promoting the further release of the gaseous components of the metal into said space for continuing the reaction with said substance, and evacuating the remainder of said gaseous substances from said space by mechanical means.

References Cited in the file of this patent UNITED STATES PATENTS 127,953 Bennett June 18, 1872 1,815,691 Wilson July 21, 1931 1,921,060 Williams Aug. 8, 1933 2,144,200 Rohn et a1 Jan. 17, 1939 2,253,421 De Mare Aug. 19, 1941 2,452,665 Kroll et al. Nov. 2, 1948 2,776,886 Kelly et al. Jan. 8, 1957 2,837,790 Rozian June 10, 1958 FOREIGN PATENTS 569,699 Germany Feb. 6, 1933 OTHER REFERENCES Gas Free Metals, The Metals Research StaflF, National Research Corporation, Cambridge 42, Mass, September 1947, page 1 relied on.

Claims (1)

1. A METHOD OF ELIMINATING AT LEAST ONE OF THE GASEOUS COMPONENTS DISSOLVED IN MOLTEN STEEL, COMPRISING THE STEPS OF PLACING THE MOLTEN STEEL IN A CLOSED VESSEL HAVING A VOLUME GREATER THAN THAT OF THE MOLTEN STEEL SO AS TO PROVIDE A SPACE ABOVE THE FREE SURFACE OF THE MOLTEN STEEL AND DISPOSING IN SAID SPACE REMOTE FROM SAID FREE SURFACE AT LEAST ONE SUBSTANCE IN AN AMOUNT OF 0.04 TO 1.1 KG/TON OF MOLTEN STEEL AND SELECTED FROM THE GROUP CON-

Images