US3201226A - Steel purification vacuum method - Google Patents

Description

Aug., Il?, 1965 R. smwfm@ @115ML ymg@ STEEL PURIFICATION VACUUM METHOD Filed Aug. 6, 1962 5 Sheets-Sheet l Aug- 17, 1955 y R. sPoLDERs ETAL 3,201,226

STEEL PURIFICATION VACUUM METHOD Filed Aug. 6, 1962 5 Sheets-Sheet 2 Aug. 17, 1965 R. sPoLDERs ETAL STEEL PURIFICATION VACUUM METHOD 5 Sheets-Sheet 3 Filed Aug. 6, 1962 .inve/7M@ @MAJ f, ffff/Qf Aug 17 1955 R. sPoLDERs ETAL 3,201,226

STEEL PURIFICATION VACUUM METHOD Filed Aug. 6, 1962 5 Sheets-Sheet 4 .Im/@ninfa Hw@ lau/Yun,

ug- 17, l965 R. sPoLDERs ETAL 3,201,226

STEEL PURIFICATION VACUUM METHOD Filed Aug. 6, 1962 5 Sheets-Sheet 5 United States, Patent O 3,201,226 STEEL PURIFIQAHN VACUUM METHD Rudolf Spolders, Bochum, Wilhelm Breung, Hattingen, and Heinz Pieper, Bochum, Germany, assignors to Ruhrstahl Hiittenwerhe Aktiengesellschaft, Essen, Germany Filed Aug. 6 1962, Ser. No. 214,963 Claims priority, implication` Germany, Feb. 27, 1957, R 20,644; Mar. Z9, 1959, R 25,203, R 25,204 l Claims. (Cl. 75-49) This is a continuation-in-part of our application Serial No. 16,754 filed Mar. 22, 1960, and now US. Patent No. 3,060,015, granted Oct. 23, 1262, which application, in turn, is a continuation-in-part of our application Serial No. 717,756, filed Feb. 26, i958, and now abandoned.

The present invention relates to steel purification and more particularly, it relates to a method for purifying molten steel by means of gases.

It is well known that steel, as it comes from the furnace or converter, contains considerable quantities of occlusions `including gases which exert a harmful eifect and the passage of which through the bath of molten steel is rendered difiicult or prevented due to the ferrostatic pressure of the molten steel.

It has been attempted to facilitate the passage of undesirable gases through and out of the molten `steel by passing argon through the body of molten steel. The argon while not reacting with the steel serves to flush out desirable gases. However, the large quantities of argon required forthis purpose are frequently not available and, in any event, malte this process uneconomical.

It is therefore an object of the present invention to provide an effective and economical method for the removal of undesirable matter from molten steel.

It is another object of the present invention to provide a method whereby particularly hydrogen can be removed from molten steel in an economical and simple manner.

Gther objects and advantages of the present invention will become apparent from a further reading of the description and of the appended claims.

With the above and other objects in view, the present invention contemplates in a method of purifying steel, the steps of subjecting a mass of molten steel to a partial vacuum blowing a first oxidizing gas into the lower portion of the mass of molten steel, and simultaneously blowing a second non-oxidizing or reducing gas into the interior of the mass of molten steel at a point located above the lower portion of the mass of molten steel, while maintaining the partial vacuum.

According to a preferred embodiment of the present invention, the same comprises in a method of purifying molten steel, the steps of blowing hydrogen gas into the bottom portion of a mass of unkilled molten steel, and blowing into the interior of the mass of molten steel at a point located above the bottom portion thereof a second gas selected from the group consisting of `argon and carbon monoxide.

It has been found that a molten steel bath can be purged easily of a large proportion of undesirable gases by blowing through the molten steel either carbon dioxide or carbon monoxide or a mixture of these two gases. It may be assumed that the following reactions odour when carbon dioxide is blown through the molten steel:

lt is believed that the above assumption will facilitate the understanding of the present invention, however, the present invention is not based on or dependent on the accuracy of the reaction described above.

It has been found that frequently best results are obtained by using a quantity of 5 cubic meters of carbon dioxide calculated at atmospheric pressure per 1 metric ton of molten steel. When using 5 cubic meters of carbon dioxide for l metric ton of molten steel the decarbonization will amount to 0.1 kilogram per ton of steel.

When carbon monoxide is blown through the molten steel, decarbonization of the same does not take place but only a flushing or purging effect.

Due to the fact that the reaction of carbon dioxide within the molten steel is an endothermic reaction and since heat is also withdrawn by the blowing process itself, it has been found advantageous to preheat the gases, be it carbon dioxide or carbon monoxide or a mixture of the same, in per se known manner prior to introduction of the gases into the molten steel. In many cases it has been found particularly advantageous to burn Carbon monoxide with oxygen so as to transform all or part of the carbonmonoxide into carbon dioxide and to introduce the thus-formed hot reaction gas into the steel bath.

This latter method also affords the opportunity to introduce the gas into the steel bath at optimum temperature. The carbon monoxide used for this: purpose may be for instance produced in a coke generator operated with oxygen and carbon dioxide, such as is described in the copending patent application Serial No. 682,256, Div. 59, or the carbon monoxide may also be formed by decomposition of synthetic gas, or in any other suitable manner.

lt has been found particularly advantageous according to the present invention to combine `the gas treatment of the molten steel bath with a vacuum treatment of the same. Heat consuption in a vacuum chamber used for this purpose is considerable and it is therefore desirable to preheat the gas which is to be blown through the molten steel in the vacuum chamber. A further economy with respect to the heating of the vacuum chamber can be achieved by introducing within the chamber into the area adjacent to the upper surface of the liquid steel body a quantity of oxygen suihcient to burn carbon monoxide emanating at the surface of the molten steel so that the thereby formed combustion heat can be utilized for the heating of the vacuum chamben Per t0n of molten steel about l0 cubic meters of carbon monoxide calculated at atmospheric pressure will become available and consequently the heat provided by oxidation of carbon monoxide near the surface of the molten steel bath'will amount per ton of molten steel to about the following:

(5) Q (heat) :10X 302G=3020 .Kcal

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specic embodiments when read in connection with the accompanying drawings, in which:

FIG. 1 is au elevational View in cross section of an embodiment of the device of the present invention;

FIG. 2 is a cross section through the device illustrated in FIG. 1 taken along the line Il-II;

FIG. 3 is an elevational view in cross section of an other embodiment ofthe device of the present invention; FIG. 4 is an elevational view in cross section of yet another embodiment of the device according to the present invention;

FIG. 5 is an elevational View in cross section of a sa further embodiment of the device according to the present invention; and

FIG. 6 is an elevational view in cross section of a still another embodiment of the device according to the invention.

Referring now to the drawings, and particularly to FIGS. 1-3, container 1 adapted to receive molten steel is shown carrying in its bottom portion removable tuyere block 2 and laterally spaced therefrom stopper nozzle 3. Underneath container l, a blast box d of circular horizontal cross section is shown towards which burner 5 extends in a direction tangential to the inner circular wall lof the blast box d. Oxygen is introduced into burner 5 through conduit d, and carbon monoxide through conduit portion 7. Within the blast box d combustion of the carbon monoxide t-o carbon dioxide takes place. Thus, blast box 4 fulfills the function of a combustion chamber. Blast box i may also be additionally provided with a conduit for introducing carbon dioxide into the same. However, it is also possible to introduce carbon dioxide jointly with either the oxygen or the carbon monoxide, or to use an excess of carbon monoxide relative to the quantity of oxygen. The individual nozzles of the tuyere block preferably have a dia ieter of about l rnm. in order to prevent liquid steel after completion of the introduction of gas to pass through the nozzles into the combustion chamber or blast box. lf the diameter of the nozzle is chosen sufficient-ly small, steel will penetrate into the same only for a short distance and will then solidify. The tuyere blocl: is then to be removed after each treatment of a batch of molten steel and after the treated steel has been drawn oir".

As Will be explained in detail below, it is particularly advantageous to admix a gaseous halogen or halogen compound to the carbon monoxide or carbon dioxide gas prior to blowing the same through the molten steel. For in troduction of a halogen or a vaporized halogen compound, it is sometimes advantageous to provide an additional conduit communicating with blast box Il. Evaporation or gasification of suitable halogen compounds is known per se and can be achieved without diihculties.

As illustrated in FlG. 3, a hood 8 is superposed over container 1 so as to form a vacuum chamber. It is of course necessary that hood S and container ll are airtightly connected. Conduit 9 leads to a suitable vacuum pump provided with a cooling device, and lance llt? serves for introducing oxygen into the vicinity of the upper level of molten steel within container 1, i.e. into the area where carbon monoxide emanates from the molten steel. Thereby it is achieved that the carbon monoxide is ioxidized to carbon dioxide, freeing a considerable amount of heat and thus improving the heat economy of the entire process.

A preferred embodiment of the present invention will he best understood in connection with FG. 4 of the drawing. The purication of the steel bath is carried out according to FIG. 4 under vacuum and with introduction of two diiferent gases which are introduced vertically spaced from each other. This can be accomplished in a modilication of the apparatus illustrated in FG. 1, and including the following features.

A cover 8 is superposed upon container l closing the same. Cover S is formed with conduit 9 communicating with a means for producing a partial vacuum. Lance l@ extends into the container and terminates therein at a point upwardly spaced from the gas distributing means 2 located in the bottom of container ll.

Reference numeral 11 indicates a sight glass and reference numeral 12 a conventional arrangement for preventing splashing molten steel from entering into conduit 9 leading to the vacuum pump or the like.

With an apparatus such as illustrated in FIG. 4, and described above, it is possible to introduce at least two gases of different composition into the molten metal while simultaneously maintaining a partial Vacuum in the apparatus. Introduction of the two gases is carried tout at or in the vicinity of the bottom of the container and at a level which is substantially higher than the container bottom. In many cases, it has been found to be particularly advantageous to introduce into the molten steel through the bottom of the container an oxidizing gas, and through the lance at the higher level a deoxidizing `or neutral gas. On the other hand, particularly in the case of unkilled steel, a reducing gas such as hydrogen gas may be introduced through the bottom of the container and a substantially neutral gas such as argon or carbon monoxide through the lance at the higher level. The neutral gas which is introduced through a lance may also consist fully or in part of vaporized or gasiiied ha-logens or halogen compounds.

After treatment by introduction of anl oxidizing gas has been completed, it is sometimes desirable to introduce through the bottom distributing plate 2 a reducing gas without introducing a second gas through the lance during this last stage of the process.

The apparatus illustrated in FIGS. 5 and 6 is particu larly well suited for providing a partial Vacuum without requiring tight closing of the entire container top.

According to the embodiment of FIGS. 5 and 6, a hood is partially lowered into the container so that the lowermost preferably outwardly aring portion of the hood will be situated below the upper level of Vmolten metal in the container. This allows a convenient and flexible arrangement of the lance, as well as gas introduction and gas withdrawal towards the vacuum producing means, without requiring the placing of an air-tight cover member on the top of the container.

As shown in FIGS. 5 and 6, the lower portion of hood l2 extends downwardly below level lo of the molten steel in container 4. Due to the downwardly Haring coniiguration fof lower portion l1 ,of hood 12, gas losses will not occur to any appreciable extent. Gas will be withdrawn from the molten metal towards the partial vacuum maintained in hood 12. Due to the partial vacuum therein, the upper level 17 of molten metal within hood 12 will be higher than the upper level 16 of molten metal outside hood 12. Hood i2 is removably kept in the indicated position by conventional means not shown in the drawing. Conduit 1S connects the interior of hood 1.2 with vacuum-producing means such as a vacuum pump (not shown). Gas is introduced into the molten metal vrithin the container by means of lance 13.

The embodiment illustrated in FIG. 6 dilfers from what is shown in FlG. 5 by additionally providing means for introducing gas through the bottom of the container, similar to those shown in FIG. l; by including in Vhood 12 an arrangement l@ for preventing splashing metal from reaching vacuum conduit l5, and by arranging sight glass t7 in the upper portion of hood 12. Tuyere block 2 is replaceable and may be removed after hood 12 has been raised, the container has been tilted and the molten metal has been poured. In combustion chamber 4, a mixture of a combustible gas such as carbon monoxide (which is introduced through nozzle 7) and oxygen (introduced through conduit d) may be burnt and the thus formed hot combustion gas introduced into the container through distributor 2. ln this manner, Very hot carbon dioxide gas penetrates from the bottom of the container through the molten steel and passes into daring hood portion 1l, so that separate heating means for the steel bath will not be required. Additionally, a similar or different gas may be introduced through lance 13. lt is of course possible to introduce a great variety of gases through lance i3 and tuyere block 2 depending on the specific requirements of the melt. s Y

As stated above, it is possible to introduce jointly with the purging gas consisting of carbon monoxide or carbon dioxide or a mixture of carbon monoxide and carbon dioxide, a halogen or vaporized halogen compound into the molten metal bath. Thereby, it is achieved that due to the intermediary reactions between the halogen and the hydrogen gas contained in the steel bath, the gaseous hydrogen is removed from the steel bath to a very considerable extent. For practical purposes, chloride and fluorine are preferred as halogens for the present process, particularly in view of the higher costs of bromine and iodine.

A great number of halogen compounds can be advantageously used in accordance with the present invention. Particularly good results are obtained by using aluminum chloride or'aluminum fluoride as the halogen compound and it has also been found that carbon tetrachloride is particularly elfective since it is relatively easy to saturate the purging gas with any desired dosage of carbon tetrachloride and consequently optimum concentration of the carbon tetrachloride for any given operating conditions can easily be maintained. However, other halogenized hydrocarbons such as hexachlorobenzene have also been advantageously used. All of these` halogen-supplying gases or Vaporized substances can be used either alone or as a mixture of several of the same.

The following examples are given as illustrative of the process ofthe present invention, the invention however not being limited to the specific details of the examples.

Example II Steel Type: St 37 m Si Standard Analysis:

C, 0.10-0.14 Si, 0.15-0.30 Mn, 0.40-0.50 P upto 0.035 t S up to 0.035 Batch Analysis: C, 0.13 Si, 0.20

Mn, 0.4-8 P, 0.026

Temperatures Prior to treatment, 1620 C.

After treatment, 1590 C. Ti'eating Gas:` CO, 4.0 m.3/t. steel Treating Time: 12 minutes Gas Pressure: 2.2-2.4 atmospheres excess pressure Hydrogen Content:

Prior to treatment, 8.0 cm3/100 g. steel` After treatment, 4.8 cm/ 100 g. steel 6 Example III Steel Type: SII shipbuilding plate Standard Analysis:

C, 0.14-0.17 Si, O15-0.30 Mn, G50-0.60 P upto 0.045 S up to 0.045 Batch Analysis:

C, 0.17 Si, 0.22 Mn, 0.51 P, 0.038 S, 0.028 Temperatures 2 Prior to treatment, 1610a C. After treatment, 1585 C. Treating Gas: CO2-CCL, Gas Consumption:

CO2, 2.54- m.3/t. of steel CC14, 0.043 l./t. of steel Treating Time: l2 minutes Gas Pressure: 2.2-2.4 atmospheres excess pressure Hydrogen Content:

Prior to treatment, 8.3 cm.3/ g. steel After treatment, 3.6 cm/ 100 g. steel In all examples, gas volumes are given vat atmospheric pressure.

The puriiication obtained according to the present invention can be clearly seen by comparing the hydrogen content of the steel prior and after treatment. Hydrogen content in all cases was determined on steel. samples taken from the treating vessel. Furthermore, the viscosity of the treated steel was lower thus facilitating casting of the same.

This was true with the steel `as before mentioned with an oxide content of 0.04% and hydrogen content of 7-8 cm.3/\100 g. steel. After blowing of 1'80 m CO with 2% Cl the temperature was changed from 1600 C. to 1590 C., the oxide content was @O15-0.02% and hydrogen content 3.5 cm3/1100 g. steel.

The degree of vacuum applicable in the process of the invention may be varied within wide ranges. Although it is poss-ible to apply a vacuum, eg. of 50-0.1 mm. Hg and less, it may be preferred to apply a vacuum not far from atmospheric pressure (S0-400 mm. Hg under atmospheric pressure), i.e. the pressure within the vessel may be between about 700-300 mm. Hg.

The amount of halogen, e.g. chlorine, may range `from .about 2 to 5% of the gas or gas mixture applied. When using halogen compounds the amounts of said compounds may be calculated so that the `amount of halogen, e.g. chlorine, contained in said compounds would constitute about 2-5% of the gas or gas mixture. This is true also when 2 or more halogen or halogen compounds or mixturcs -ot halogen and halogen compound are used.

Besides, the proportions of CO and CO2 may be varied `as desirable for the special conditions. Itis preferred to burn off a part of CO to CO2 to raise the temperature of the gas mixture. So, e.g. a mixture with abou-t 50% CO and 50% CO2 with an 4addition of vaporized aluminum chloride (7 kg.) was very effective. A similar mixture was prepared with 45% CO and 55% CO2; with an addition of carbon tetrachloride (6 kg).

Introduction of suitably preheated gas will prevent any `appreciable drop of the temperature of the steel bath dur-ing the above described purification process.

Example I V Molten steel, ltreated and finished in conventional manner in an electric furnace, was introduced into container 1 of the apparatus shownin FIG. 4.` Container 1 had a capacity of 30 tons and the composition of the steel was as follows:

Percent C 0.35 Si 0.27 Mn 0.59 S 0.017 P 0.009

After introducing the steel into container 1, the container was closed by superposing thereon cover 8 holding lance 10 so that the free end of lance 10 was located about in the center of the bath of molten steel. In combustion chamber 4, a hot gas consisting of 90% carbon dioxide .and 10% carbon monoxide was produced by combustion of carbon -monoxide with oxygen. Production of this gas was so arranged that a total quant-ity of about 25 liters of hot gas were introduced into container for each ton of molten steel. Through the lance, hydrogen gas was blown into the molten steel in an amount of liters per ton of steel. Pressure reduction was carried out so that after about three minutes Ia residual pressure of 2 mm. mercury was reached and this residual pressure was then maintained during the entire treating period which lasted a total of fifteen minutes.

Thereafter, atmospheric pressure rwas restored, cover `and lance 10 were removed and it was found that the above-descri bed two-gas vacuum-treatment had resulted in `a reduction of the oxygen content of the steel by about 50%, the hydrogen content by about 45% and occlusion by about 55%. The bath temperature prior to treatment was 1620 C. and was found to be 1595 C. upon completion of treatment.

Example V The general method and apparatus as described in EX- `ample IV were used, however, with the modification that the steel was not killed during tapping from the electric furnace, so that the silicon content was only 0.07%. In this case, liters of hydrogen per ton of steel were introduced through tuyere block 2, as well as 10 liters of car-bon monoxide per ton of steel through lance 10. Degree of vacuum land length of treatment were the same -as described in Example IV.

Initial steel bath temperature was 1615 C. and the .temperature upon completion of treatment was 1595 C. It was found that the oxygen content of the steel had been reduced by about 65%, the hydrogen content by about 45% and the amount of occlusion by about 65% In Examples IV and V, determination of the oxygen content was carried out by the hot extraction method, determination of the hydrogen content by the tin fusing method and ldetermination of lthe occlusione by separation of the residue.

Example VI The method of the present invention was `carried lout in an apparatus .as illustrated in FIG. 5.

Liquid steel was treated and finished in an open hearth furnace in conventional manner. Eighty tons of the molten steel were introduced into container 1 of FIG. 5. The steel composition was as follows:

Percent C 0.30 Si 0.27 Mn 0.50 S 0.034 P 0.021

`of steel. Lance 13 was made ofceramic material andthe introduction of argon was evenly distributed over the entire treating period of about l16 minutes. The lance was placed in such position within container 1 that the free lower end of the lance was located about 30 cm. above the bot-tom of container 1.

After completion of the treatment, lance and hood were removed and the molten steel was cast into ingots.

Analysis of the thus treated steel in accordance with the methods described in connection with Example V, showed that the above treatment had reduced the oxygen content of the steel by about 25%, hydrogen content by about 30% and occlusions by about 30%. The initial bath temperature was 1620 C. and the temperature upon completion of treatment was 1590o C.

Example VII A process somewhat similar to what has been described in Example VI was carried out in the apparatus illustrated in FIG. 6.

Through tuyere block 2, a combustion gas consisting of 40% carbon monoxide and 60% carbon dioxide was introduced in a quantity `of 28 liters per ton of steel.r The temperature of the combustion gas entering container 1 was about 1450" C. Simultaneously, through lance 12, 15 liters of argon per ton of steel were introduced into the molten mass. Treatment was carried out for 12 minutes at a residual pressure of 2 mm.rmercury as described in Example VI.

Steel bath temperature prior to treatment was 1610 C. and upon completion of treatment 1600 C.

It was found, by using the analytical methods described in Example V, that the oxygen content of the steel had been reduced by about 35% the hydrogen content by about 40% and occlusions by about 40%.

Without further analysis, the foregoing will so fully reveal the gist of the present invention, that others can, by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention, and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. In a method of purifying molten steel, the steps of subjecting a mass of unkilled molten steel to a partial vacuum; blowing hydrogen gas into the bottom portion of said mass of unkilled molten steel; and simultaneously blowing into the interior of said mass of molten steel at a point located above said bottom portion thereof a second gas selected from the group consisting of argon and carbon monoxide while maintaining said partial vacuum.

2. In a method of purifying molten steel, the steps of subjecting a mass of molten steel to a partial vacuum; blowing first gas into the lower portion of said mass of molten steel; and simultaneously blowing into the interior of said mass of molten steel at a point located above said lower portion thereof a second gas, while maintaining said partial vacuum, one of said first and second gases being an oxidizing gas and the other being a non-oxidizing gas.

3. In a method of purifying molten steel, the steps of subjecting a mass of molten steel to a partial vacuum; blowing first gas into the lower portion of said mass of molten steel; and continuously blowing into the interior of said mass of molten steel at a point located above said lower portion thereof a second gas, while maintaining said partial vacuum, one of said first and second gases being an oxidizing gas and the other being a reducing gas.

e. In a method of purifying killed molten steel, the steps of subjecting a mass of molten steel to a partial vacuum; blowing a first oxidizing gas into the lower portion of said mass of molten steel; and simultaneously blowing into the interior of said mass of molten steel at a point located above said Ilower portion thereof a second reducing gas, while maintaining said partial vacuum.

5. In a method of purifying molten steel, the steps of subjecting a mass of molten steel to a partial vacuum;

blowing a first reducing gas into the lower portion of said mass of molten steel; and simultaneously blowing into the interior of said mass of molten steel at a point located above said lower portion thereof a second inert gas, while maintaining said partial vacuum.

6. In a method of purifying molten steel, the steps of subjecting a mass of molten steel to a partial vacuum; blowing a first reducing gas into the lower portion of said mass of molten steel; and simultaneously blowing into the interior of said mass of molten steel at a point located above said lower portion thereof a second gas, consisting at least partly of gasied halogen and halogen compounds, while maintaining said partial vacuum.

7. In a method of purifying molten steel, the steps of subjecting a mass of molten steel to a partial vacuum; blowing a first reducing gas into the lower portion of said mass of molten steel; and simultaneously blowing into the interior of said mass of molten steel at a point located above Said lower portion thereof a second gas consisting at least partly of chlorine, while maintaining said partial vacuum.

8. In a method of purifying molten steel, the steps of subjecting a mass of molten steel to a partial vacuum;

lowing a first reducing gas into the lower portion of said mass of molten steel; and simultaneously blowing into the interior of said mass of molten steel at a point located above said lower portion thereof a second gas consisting at least partly of fluorine, while maintaining said partial vacuum.

9. In a method of purifying molten steel, the steps of subjecting a mass of molten steel to a partial vacuum; blowing a first reducing gas into the lower portion of said mass of molten steel; and simultaneously blowing into the interior of said mass of molten steel at a point located above said lower portion thereof a second gas consisting at least partly of carbon tetrachloride, while maintaining said partial vacuum.

l0. In a method of purifying molten steel, the steps of subjecting a mass of molten steel to a partial vacuum; blowing a first reducing gas into the lower portion of said mass of molten steel; and simultaneously blowing into the interior of said mass of molten steel at a point located above said lower portion thereof a second gas consisting at least partly of aluminum chloride, while maintaining said partial vacuum.

Il. In a method of purifying molten steel, the steps of subjecting a mass of molten steel to a partial vacuum;

blowing a rst reducing gas into the lower portion of said mass of molten steel; and simultaneously blowing into the interior of said mass of molten steel at a point located above said lower portion thereof a second gas consisting at least partly of aluminum fluoride, while maintaining said partial vacuum.

12. In a method of purifying molten steel, the steps of subjecting a mass of molten steel to a partial vacuum; blowing a first oxidizing gas into the lower portion of said mass of molten steel; and simultaneously blowing through a lance into the interior of said mass of molten steel at a point located above said lower portion thereof a second reducing gas, while maintaining said partial vacuum.

I3. In a method of purifying molten. steel, the steps of subjecting a mass of molten steel to a partial vacuum; blowing a mixture of carbon dioxide and carbon monoxide into the lower portion of said mass of molten steel; and simultaneously blowing into the interior of said mass of molten steel at a point located above said lower portion thereof hydrogen gas, while maintaining said partial vacuum.

14. In a method of purifying molten steel, the steps of subjecting a mass of molten steel to a partial vacuum; blowing hydrogen gas into the lower portion of said mass of molten steel; and simultaneously blowing carbon monoxide into the interior of said mass of molten steel at a point located above said lower portion thereof, while maintaining said partial vacuum.

I5. In a method of purifying molten steel, the steps of subjecting a mass of molten steel to a partial vacuum; blowing a mixture of carbon dioxide and carbon monoxide into the lower portion of said mass of molten steel; and simultaneously blowing argon into the interior of said mass of molten steel at a point located above said lower portion thereof, while maintaining said partial vacuum. Y

References Cited by the Examiner UNITED STATES PATENTS 1,921,060 8/33 Williams 75-49 2,817,584 12/57 Iootz 75-60 2,871,008 l/59 Spire 75--59 FORElGN PATENTS 3 38,409 11/30 Great Britain.

OTHER REFERENCES Metal Progress, September i959, pp. lll-114.

DAVID L. RECK, Primary Examiner.

Claims (1)

1. IN A METHOD OF PURIFYING MOLTEN STEEL, THE STEPS OF SUBJECTING A MASS OF UNKILLED MOLTEN STEEL TO A PARTIAL VACUUM; BLOWING HYDROGEN GAS INTO THE BOTTOM PORTION OF SAID MASS OF UNKILLED MOLTEN STEEL; AND SIMULTANEOUSLY BLOWING INTO THE INTERIOR OF SAID MASS OF MOLTEN STEEL AT A POINT LOCATED ABOVE SAID BOTTOM PORTIONTHEREOF A SECOND GAS SELECTED FROM THE GROUP CONSISTING OF ARGON AND CARBON MONOXIDE WHILE MAINTAINING SAID PARTIAL VACUUM.

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