US3208117A

US3208117A - Casting method

Info

Publication number: US3208117A
Application number: US268224A
Authority: US
Inventors: Goedecke Fritz; Opel Paul; Olfe Eberhard; Martin Werner
Original assignee: Stahl- und Rohrenwerk Reisholz GmbH
Current assignee: Stahl- und Rohrenwerk Reisholz GmbH
Priority date: 1962-03-28
Filing date: 1963-03-27
Publication date: 1965-09-28
Anticipated expiration: 1982-09-28
Also published as: GB1025974A; DE1219183B

Description

Sept. 28, 1965 F. GOEDECKE ETAL 3,208,117

CASTING METHOD 2 SheetsSheet 1 Filed March 27, 1965 INVENTORS .H-lz Gueclec'ke Hm! O Je/ ibgrhq m1 OU'Q [Denver Him Z111 MICHAEL S1 STE/KER United States Patent 3,208,117 CASTING METHOD Fritz Goedecke, Dusseldorf-Benrath, Paul ()pel, Langenfeld-Richrath, and Eberhard ()lfe and Werner Martin, Dusseldorf, Germany, assiguors to Stahlund Rohrenwerk Reisholz G.m.b.H., Dusseidorf-Reisholz, German Filed Mar. 27, 1963, Ser. No. 268,224 Claims priority, application Germany, Mar. 28, 1962, St 19,020 9 Claims. (Cl. 22-214) Cast metal ingots, particularly steel ingots, frequently are formed with small faults or defective portions, particularly in the interior or core portion of the ingot block, while the remainder of the ingot is of faultless quality. These defects consist of impurities of non-metallic or oxidic nature located in or near blow holes or secondary pipings which form in the interior of the ingot. Such occlusions may prevent disappearance of the thus contaminated blow holes during subsequent forging of the ingot.

The above difficulties are particularly apparent in the case of large ingots and also in connection with highly alloyed steels, and are capable of greatly reducing the usefulness of the ingot or even to render the same unusable.

Subsequent elimination of these faults, i.e., after solidification of the ingot, usually is not possible. Considering the high value of large forgings and the great amount of time and work involved in processing the same, it becomes apparent that to prevent occurrence of the above described faults in cast ingots is a task of great economic importance.

Several methods have been suggested to avoid or to reduce the above described faults, particularly in large steel ingots. It has been attempted to so control the smelting process and the de-oxidation during the same, as well as the speed of pouring the molten metal into the ingot mold as to reduce formation of such occlusions of impurities during pouring of the molten metal. It also has been suggested to use ingot molds which are relatively wide and short so that the height of the ingot mold should be more or less equal to the diameter of the same. However, these suggestions did not lead to a reliable prevention of the occurrence of such faults in the core portion of cast ingots.

It is therefore an object of the present invention to overcome the above-discussed diiiiculties.

It is another object of the present invention to provide a method of casting metal ingots, particularly large steel ingots and to purify the steel or the like during the casting of the same, which will substantially prevent the formation of occluded oxidic impurities and the like in the ingot, particularly in the core portion thereof, and which method can be carried out in a simple and economical manner.

Other 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 a method of purifying metal during casting of the same, comprising the steps of pouring a mass of molten metal into a mold, treating the mass of molten metal in the mold prior to solidification thereof 'ice with a finely subdivided non-oxidizing gas, the gas rising through the mass of molten metal to the upper surface thereof carrying along and thus removing impurities from the interior of the mass of molten metal, and allowing the mass of molten metal to solidify in the mold.

The occlusions which are to be removed from the molten metal in the mold consist primarily of de-oxidation products, in other words, of oxides of the reducing agent which has been previously introduced in order to reduce the molten steel or the like.

The de-oxidation, generally, is not fully completed prior or during the pouring of the molten metal into the ingot mold. When then, during cooling and starting solidification of the metal in the ingot mold, the continuing de-oxidizing reaction is interrupted or retarded due to the lowering of the temperature of the initially molten and now solidifying metal, then the complete precipitation of the de-oxidation products will only take place shortly prior to solidification of the respective portion of the molten metal in the mold and this will be too late to permit rising of the de-oxidation products to the surface of the solidifying metal block. If at the same time cavities such as blow holes or secondary pipings are formed in the solidifying mass of molten metal, then the formation of the blow holes and the like will counteract the retardation of the formation of tie-oxidation products and thus, in the immediate vicinity of such blow holes, an increased precipitation of these impurities, i.e., the de-oxidation products will occur.

The present invention prevents the formation of macroscopic and microscopic precipitations or occlusions of these deoxidation products by counteracting the retardation of the formation thereof which is caused by the cooling of the metal during its solidification in the mold.

The speed of the de-oxidation reaction, i.e. the oxida tion of a reducing metal under simultaneous reduction of the steel or the like, is a function of the temperature of the molten metal and the speed of this reaction will be reduced concurrently with a reduction in the temperature of the molten metal. At the solidus point of the molten metal such as steel, the speed of the de-oxidation reaction will be very low. To the extent to which the de-oxidation reaction is not completed in the pan or ladle, during tapping or prior to pouring into the mold, the de-oxidation reaction and the formation of impurities consisting of oxidized reducing agent will slowly continue during the solidification of the molten metal at progressively lower temperatures. Due to the reduced speed of the tie-oxidation reaction and the retardation of this reaction which is experienced at lower temperatures, an over-saturation of the molten or solidifying steel with the de-oxidation products, i.e. with the oxidized reducing agent will take place and this will then lead to the precipitation of the oxidation products in the vicinity of cavities such as blow holes or the like, at a time at which solidification has progressed to such an extent that the thus precipitated de-oxidation products can no longer rise in the ingot mold to the surface of the mass of molten steel or the like but will form occlusions in the vicinity of such cavities.

However, by treating the mass of molten metal in the mold with a finely subdivided non-oxidizing gas which will rise through the molten metal in the mold to the upper surface of the mass of molten metal, the retarding influences with respect to formation of the de-oxidation prodnets are counteracted, the oxidation products will form more quickly and these impurities will rise to the surface of the mass of molten metal, together with the gas which has been introduced into or formed in the mass of molten metal, in accordance with the present invention.

Thus according to the present invention, faults and defects in the core portion of cast ingots, particularly of steel ingots are prevented by treating the liquid mass of steel or the like in the ingot mold while the mass of steel in the mold is still in sufliciently liquid condition to permit gas bubbles to rise to the surface of the mass of steel, with a neutral reducing gas of a type which is sub stantially insoluble in the steel. Noble gases, particularly argon, however also the other noble gases as well as carbon monoxide or nitrogen are suitable for this purpose. With respect to using nitrogen gas in accordance with the present invention, it must be noted that nitrogen gas should be employed only if a somewhat increased nitrogen content in the solidified ingot will be desirable either as a constituent of the alloyed metal, or in order to improve the creep resistance of the metal at high temperatures. On the other hand, if the intended end use of the steel makes a certain degree of brittleness undesirable then nitrogen gas should not be used.

In addition, it is also possible to use for the purpose of the present invention other gaseous compounds provided that under the conditions prevailing in the liquid steel, particularly at the temperature of the liquid steel, these gaseous compounds will have reducing characteristics and their solubility in the-molten steel will not be such as to deleteriously affect the quality of the subsequently solidified steel.

In order to achieve the desired result, it is important that the gas which is introduced into the mass of molten steel located in the ingot mold will be introduced or formed in finely subdivided form so that a relatively very large gaseous surface area will be in contact with the liquid steel. In other Words, the gas should form a great number of relatively small bubbles which will rise through the mass of molten steel. Thus, it is possible, for instance, to introduce the gas into the ingot mold by means of a lance extending downwardly at least into the center portion of the ingot mold, whereby the lance should be protected by a sleeve of refractory material. However, preferably the gas is introduced through the bottom of the ingot mold, either through a porous stone or through a suitable nozzle arrangement known, per se, in the art.

It is important that the gas bubbles passing through the molten steel will withdraw heat from the latter and thus will exert a localized cooling effect.

Such localized cooling will cause a spontaneous and quick precipitation of the de-oxidation products. Due to the limited space, i.e. only the immediate vicinity of the individual gas bubbles, in which this cooling effect takes place, it has little influence on the cooling or drop in temperature of the entire mass of liquid steel. However, the oxidation products which are formed and precipitated in the localized cooled areas will easily rise, together with or occluded in the gas bubbles. The local cooling or even super-cooling of the molten steel which is contacted by the gas bubbles will eliminate the retardation phenomena with respect to precipitation of the oxidation products which otherwise would occur during the slow cooling of the steel in the ingot mold.

Thus, the impurities or de-oxidation products which due to the gas treatment of the present invention are formed at an earlier point in time during the cooling or solidification of steel in the mold and which are formed in a more complete manner than in a mass of steel which is poured into the mold and allowed to solidify, without passage of the gas therethrough as required in accordance with the present invention, will not only be formed but also removed by being carried to the surface of the mass of molten and solidifying steel by the upwardly rising gas bubbles.

Furthermore, the solidification in the interior of the molten metal mass is improved particularly due to strong seed formation throughout the entire mass of molten steel which will cause formation of a more finely grained solidified structure and will reduce the formation of blow holes or secondary pipings. The time required for solidification of the steel or the like in the mold will be reduced. In addition, metal blocks formed in ingot molds in accordance with the present invention generally have a lesser oxygen content and are of higher purity than similar ingots which however were not treated according to the present invention. By starting the gas treatment simultaneously with the start of pouring the molten metal into the mold, the further advantage will be achieved that the gas escaping at the surface of the liquid steel will act as a protective gas and will prevent oxidation of the steel in the mold by contact with the oxygen of the air. The point in time when introduction of the gas is to start and the length of time for which gas is to be passed through the mass of metal in the mold may be adjusted to suit individual requirements and may vary within wide ranges. As indicated above, there is a particular advantage gained by starting the passage of gas through the molten metal into the mold simultaneously with starting the pouring of molten metal into the same.

However, it is also possible to start introduction of the gas after pouring has been completed and after a more or less thick layer of solid steel has been formed at the walls of the ingot mold. The later the gas treatment is started, the smaller will be the total amount of gas required per unit of weight of the steel or the like.

Preferably, introduction or blowing of the treating gas into the mass or body of molten metal will commence at a relatively high rate or speed, and the rate or speed of introduction of the treating gas will be reduced, for instance in a stepwise manner, as the gas treatment proceeds towards its termination.

In place of the above described gases, or admixed thereto and carried by the gas, it is also possible to introduce into the metal bath solid, preferably pulverulent, materials which will evaporate or melt at the temperature of the molten metal bath and/or will react with the same under formation of gaseous products.

Such suitable solid additions to the metal bath, in accordance with the present invention, include lithium, carbon, magnesium, aluminum, silicon, calcium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, niobium, molybdenum, caseium, cerium and cerium compounds, tantalum and tungsten.

Those of the above-mentioned solid materials which will evaporate in the liquid steel, such as calcium, lithium and magnesium, will also be capable of reacting in their vapor phase with the oxygen of the metal bath and thus a further removal of oxygen and improvement of the purity of the metal bath will result.

All of the above-mentioned elements which may be introduced, preferably distributed in a carrier gas, i.e., either a neutral or a reducing gas, possess a higher specific heat than the carrier gas and thus will increase the local undercooling of the molten metal and thereby the precipitation of the de-oxidation products.

Solid matrials which will dissolve in the molten steel include carbon, aluminum, silicon, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, niobium, molybdenum, cerium and cerium compounds, tantalum and tungsten.

Lithium, carbon, magnesium, aluminum, silicon, cerium and cerium compounds, and caesium will react with react with constituents of the molten metal bath such as a mass of molten steel. The elements which will evaporate in the metal bath, such as lithium, magnesium and calcium, will primarily react with the oxygen of the bath of liquid steel, while the pulverulent materials which will be dissolved only, without reacting with the liquid steel, will withdraw heat at localized points of the metal bath (namely the heat required for melting of the pulverulent particles) and simultaneously will have an effect similar to that of crystallization nuclei, so that upon solidification the steel will be of finer grain structure.

It is also within the scope of the present invention to introduce into the molten metal in the ingot mold pulverulent materials which will serve for de-oxidation desulphurization, or as alloying constituents of the molten metal such as steel, whereby lime, sodium carbonate and other alkali metal compounds may serve as de-sulphurization agents.

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 specific embodiments when read in connection with the accompanying drawings, in which:

FIG. 1 is a schematic elevational cross-sectional view of an apparatus for carrying out the process of the present invention;

FIG. 2 is a schematic elevational cross-sectional view of another device for carrying out the process of the present invention; and

FIG. 3 is a schematic elevational cross-sectional view of a further arrangement for carrying out the above-described process.

Referring now to the drawings and particularly to FIG. 1, it will be seen that the molten metal is poured from pan or ladle 9 into the mold arrangement which comprises ingot mold 2, head portion 1 and ingot mold base 3. While a stream 8 of molten metal is poured from ladle 9 into the ingot mold, finely subdivided gas is introduced into the molten metal in ingot mold 2 through the orifices of nozzle 4. The gas flows to nozzle 4 through flexible conduit 7, connected to rigid conduit 5 by flange arrangement 6.

In the embodiment illustrated in FIG. 2, the gas introduced is introduced into

ingot mold

21, 22, 23 through a lance consisting of a portion of rigid conduit 25 which is surrounded by a sleeve 24 or refractory material. Coupling 26 connects rigid conduit 25 to flexible conduit 27.

According to the embodiment illustrated in FIG. 3, in which only the base or foot portion 32 of the ingot mold is shown, the gas is introduced into nozzle 31 through conduit 33, while simultaneously pulverulent material is pneumatically conveyed through conduit 34 into the portion of conduit 33 which is adjacent to nozzle 31.

The following examples are given as illustrative only of the present invention without, however, limiting the invention to the specific details of the examples.

Example I Molten steel having a temperature of 1,540 C. and containing 0.20% carbon, 0.35% silicon, 0.55% manganese, 12.00% chromium, 1.00% molybdenum, 0.55% nickel and 0.30% vanadium, was poured into an ingot mold to form therein an ingot weighing 40,000 kg. Pouring was carried out at a maximum speed of 2,500 kg. per minute and was completed within 18 minutes.

Argon was blown into the mold through a porous stone located in the bottom of the mold, starting simultaneously with the pouring of the molten steel and terminating after 15 minutes, at the rate of about 130 standard liters per minute, and the rate of gas introduction was progressively reduced so as to be down to standard liters per minute at the time introduction of the gas was discontinued. The total amount of gas introduced in this manner was equal to about 1,200 standard liters, corresponding to 30 standard liters per 1,000 kg. of molten steel.

6 Example 11 Steel analysis: 0.22% carbon, 0.25% silicon, 0.70% manganese. Gas introduction through nozzle in bottom of ingot mold.

Gas: argon having during part of the blowing time pulverulent aluminum distributed therethrough.

Steel temperature prior to pouring: 1,550 C.

Ingot weight: 80,000 kg.

Speed of pouring: 3,500 kg. per minute.

Total pouring time: 27 minutes.

Gas blowing started simultaneously with pouring.

Rate of gas introduction: starting with 350 standard liters per minute, continuing at that rate for 15 minutes, and containing during this time a total of 8 kg. pulverulent aluminum, thereafter reduction of the blowing rate down to 20 standard liters per minute after 20 minutes. Total aluminum introduced with the gas corresponds to about 0.1 kg. per 1,000 kg. of molten steel.

Total blowing time: between 20 and 25 minutes.

Total gas consumption: between 5,500 and 6,000 standard liters corresponding to between and standard liters per 1,000 kg. of steel.

Example III Steel analysis: 0.22% carbon, 0.25% silicon, 0.70% manganese.

Gas introduction through lance from above.

Gas: argon, having during part of the blowing time pulverulent aluminum distributed therethrough.

Steel temperature prior to pouring: 1,555 C.

Ingot weight: 30,000 kg.

Speed of pouring: 2,000 kg. per minute.

Total pouring time: 17 minutes.

Gas blowing starts 2.5 minutes after the start of pouring of the steel.

Rate of gas introduction: about 200 standard liters per minute. The gas carried pulverulent aluminum during the period starting 3 minutes and ending 15 minutes after the start of pouring of the steel. Total amount of aluminum introduced with gas: 9 kg., corresponding to about 0.3 kg. per 1,000 kg. of steel. After 15 minutes, rate of gas introduction is reduced so that upon termination of pouring 20 standard liters per minute are intro duced through the lance into the steel bath. Thereafter, gas blowing in continued under further reduction of rate of gas introduction and raising of the lance to reduce depth of immersion thereof until about 22 minutes after start of pouring, so that the total blowing time is about 19 minutes.

Total gas consumption: about 2,400 standard liters, corresponding to standard liters per 1,000 kg. of steel.

Example IV Steel analysis: 0.25% carbon, 0.25% silicon, 0.65% manganese, 1.1% chromium, 0.25 molybdenum.

Gas introduction through lance from above.

Gas: nitrogen.

Steel temperature prior to pouring: 1,545 C.

Ingot weight: 60,000 kg.

Speed of pouring: 3,000 kg. per minute.

Total pouring time, 23 minutes.

Gas blowing starts after completion of pouring.

Rate of gas introduction; starting with about 70 standard liters per minute. Gas introduced for period of 30 minutes during which the rate of introduction is progressively reduced to 10 standard liters per minute.

Total gas consumption: about 1,200 standard liters, corresponding to 20 standard liters per 1,000 kg. of steel.

Example V Steel analysis: 0.30% carbon, 025% silicon, 0.60% manganeses, 1.30 chromium, 0.40% molybdenum, 1.85% nickel.

Gas introduction through nozzle or porous stone in bottom of ingot mold.

Gas: carbon monoxide.

Steel temperature prior to pouring 1,540 C.

Ingot weight: 100,000 kg.

Speed of pouring: 4,000 kg. per minute.

Total pouring time: 30 minutes.

Gas blowing start and ends simultaneously with pouring.

Rate of gas introduction: for the first 15 minutes 100 standard liters per minute, for the next 3 minutes 60 standard liters per minute, for the next 4 minutes 40 standard liters per minute and for the final 8 minutes 20 standard liters per minute.

Total gas consumption: about 2,000 standard liters, corresponding to 20 standard liters per 1,000 kg. of steel.

Example VI Steel analysis: 0.20% carbon, 0.35% silicon, 0.55% manganese, 12.00% chromium, 1.00% molybdenum,

Example VII Steel analysis: 0.22% carbon, 0.25% silicon, 0.70% manganese.

Gas introduction through porous stone in bottom of ingot mold.

Gas: carbon monoxide.

Steel temperature prior to pouring: between 1,540 and 1,560 C.

Ingot weight: 80,000 kg.

Speed of pouring: 3,500 kg. per minute.

Total pouring time: 27 minutes.

Gas blowing starts simultaneously with pouring of steel and ends after between 20 and 25 minutes.

Rate of gas introduction during the first 15 minutes equals 350 standard liters per minute and is then reduced to a final rate of 20 standard liters per minute.

Total gas consumption: between 5,500 and 6,000 standard liters, corresponding to between 70 and 75 standard liters per 1,000 kg. of steel.

Example VIll Steel analysis: 0.22% carbon, 0.25% silicon, 0.70% manganese.

Gas introduction through nozzle in bottom of ingot mold.

Gas: argon having during part of the blowing time pulverulent vanadium incorporated therein.

Steel temperature prior to pouring: between 1,540 and 1,560 C.

Ingot weight: 80,000 kg.

Speed of pouring: 3,500 kg. per minute.

Total pouring time: 27 minutes.

Rate of gas introduction: during the first 15 minutes equals 350 standard liters per minute and during the first 15 minutes 8 kg. of pulverulent vanadium, corresponding to 0.1 kg. pe rthousand kg. of steel are introduced with the gas.

After 15 minutes vanadium introduction is terminated and rate of gas introduction is reduced down to 20 standard liters of gas per minute at the end of 20 minutes.

Total gas consumption: between 5,500 and 6,000 standard liters, corresponding to between 70 and standard liters per 1,000 kg. of steel.

Example IX Steel analysis: 0.22% carbon, 0.25% silicon, 0.70% manganese.

Gas introduction: downwardly through a lance, for instance as illustrated in FIG. 2.

Gas: argon having during part of the blowing time pulverulent nickel incorporated therein.

Steel temperature prior to pouring: between 1,545 and 1,560 C.

Ingot weight: 30,000 kg.

Speed of pouring: 2,000 kg. per minute.

Total pouring time: 17 minutes.

Gas blowing starts 2.5 minutes after start of pouring of the molten steel and continues for between 19 and 20 minutes.

Rate of gas introduction: starting with 200 standard liters per minute, with addition of nickel from the third to fifteenth minute of pouring. The total amount of nickel powder introduced thereby being equal to 9 kg, corresponding to 0.3 kg. per 1,000 kg. of steel. The rate of gas introduction is progressively reduced after 15 minutes of pouring so that upon completion of pouring 20 standard liters per minute are blown into the molten steel. Thereafter, the depth of immersion of the lance in the molten steel is reduced and the rate of gas blowing is also further reduced until, 22 minutes after the start of the pouring of steel into the ingot mold, the introduction of gas is terminated.

Total gas consumption: 2,400 standard liters, corresponding to standard liters per 1,000 kg. of steel.

Example X Steel analysis: 0.22% carbon, 0.25% silicon, 0.70% manganese.

Gas introduction: through nozzle in bottom of ingot mold, for instance as illustrated in FIG. 3.

Gas: argon having during part of the blowing time pulverulent sodium carbonate distributed therethrough.

Steel temperature prior to pouring: between 1,540 and 1,560 C.

Ingot weight: 80,000 kg.

Speed of pouring: 3,500 kg. per minute.

Total pouring time: 27 minutes.

Gas blowing starts simultaneously with pouring of molten steel and ends after between 20 and 25 minutes.

Rate of gas introduction: starting with 350 standard liters per minute and including a total addition of 8 kg. of pulverulent sodium carbonate during the first 15 minutes of blowing. Thereafter, the rate of gas introduction is progressively reduced to reach 20 standard liters per minute after 20 minutes.

Example XI Steel analysis: 0.22% carbon, 0.25% silicon, 0.70% manganese.

Gas introduction: through lance from above.

Gas: argon having during part of the blowing time pulverulent lime distributed therethrough.

Steel temperature prior to pour-ing: between 1,545 and 1,560 C.

Ingot weight: 30,000 kg.

Speed of pouring: 2,000 kg. per minute.

.Total pouring time: 17 minutes.

Gas blowing star-ts 2.5 minutes after starting of the pouring of steel and is continued for between 19 and 20 minutes.

Rate of gas introduction: starting with 200 standard 'liters per minute and including during the period from the third to fifteenth minute after the beginning of the pouring of steel a total of 9 kg. of pulverulent lime. minutes after the beginning of the pouring of steel, the rate of gas introduction is reduced so that upon completion of the pouring of steel gas is introduced at a rate of standard liters per minute. Thereafter, gas blowing is continued at a further reduced rate and under reduction of the depth of immersion of the lance until 22 minutes after the start of pouring of molten steel.

The speed of pouring is indicated in the examples excluding the formation of the nozzle or feed head and for this reason the total pouring time is longer than would correspond to the indicated speed of pouring.

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. A method of purifying metal during casting of the same, comprising the steps of pouring a mass of molten metal into a mold; introducing through the center portion of the bottom of said mold into said mass of molten metal in said mold prior to solidification thereof a finely subdivided non-oxidizing gas which is substantially insoluble in the molten metal and selected from the group consisting of rare gases, nitrogen and carbon monoxide, said gas rising in fine bubbles through said mass of molten metal to the upper surface thereof carrying along and thus removing impurities from the interior of said mass of molten metal; and allowing said mass of molten metal to solidify in said mold.

2. A method of purifying steel during casting of the same, comprising the steps of pouring a mass of molten steel into an ingot mold; introducing through the center portion of the bottom of said mold into said mass of molten steel in said mold prior to solidification thereof a finely subdivided non-oxidizing gas which is substantially insoluble in the molten metal and selected from the group consisting of rare gases, nitrogen and carbon monoxide, said gas rising in fine bubbles through said mass of molten steel to the upper surface thereof carrying along and thus removing impurities from the interior of said mass of molten steel; and allowing said mass of molten steel to solidify in said mold.

3. A method of removing de-oxidation products from metal during casting of the same, comprising the steps of pouring a mass of molten metal into a mold; introducing through the center portion of the bottom of said mold into said mass of molten metal in said mold during the pouring thereof a finely subdivided non-oxidizing gas which is substantially insoluble in the molten metal and selected from the group consisting of rare gases, nitrogen and carbon monoxide, said gas rising in fine bubbles through said mass of molten metal to the upper surface thereof carrying along and thus removing impurities from the interior of said mass of molten metal; and allowing said mass of molten metal to solidify in said mold.

4. A method of purifying steel during casting of the same, comprising the steps of pouring a mass of molten steel into an ingot mold; introducing through the center portion of the bottom of said mold into said mass of molten steel in said mold prior to solidification thereof a finely subdivided rare gas, said gas rising in fine bubbles through said mass of molten steel to the upper surface thereof carrying along and thus removing impurities from the interior of said mass of molten steel; and allowing said mass of molten steel to solidify in said mold.

5. A method of purifying metal during casting of the same, comprising the steps of pouring a mass of molten metal into a mold; introducing through the center portion of the bottom of said mold into said mass of molten metal in said mold prior to solidification thereof finely subdivided argon, said argon rising in fine bubbles through said mass of molten metal to the upper surface thereof carrying along and thus removing impurities from the interior of said mass of molten metal; and allowing said mass of molten metal to solidify in said mold.

6. A method of purifying metal during casting of the same, comprising the steps of pouring a mass of molten metal into a mold; introducing through the center portion of the bottom of said mold into said mass of molten metal in said mold prior to solidification thereof a finely subdivided non-oXid-izing gas which is substantially insoluble in the molten metal and selected from the group consisting of rare gases, nitrogen and carbon monoxide having a pulverulent treating agent for said molten metal distributed therethrough, said gas rising in fine bubbles through said mass of molten metal to the upper surface thereof carrying along and thus removing impurities from the interior of said mass of molten metal; and allowing said mass of molten metal to solidify in said mold.

7. A method of purifying metal during casting of the same, comprising the steps of pouring a mass of, molten metal into a mold; introducing through the center portion of the bottom of said mold into said mass of molten metal in said mold prior to solidification thereof a finely subdivided non-oxidizing gas which is substantially insoluble in the molten metal and selected from the group consisting of rare gases, nitrogen and carbon monoxide having a pulverulent de-oxidizing agent for said molten metal distributed therethrough, said gas rising in fine bubbles through said mass of molten metal to the upper surface thereof carrying along and thus removing impurities from the interior of said mass of molten metal; and alloying said mass of molten metal to solidify in said mo 8. A method of purifying metal during casting of the same, comprising the steps of pouring a mass of molten metal into a mold; introducing through the center portion of the bottom of said mold into said mass of molten metal in said mold prior to solidification thereof .a finely subdivided non-oxidizing gas which is substantially insoluble in the molten metal and selected from the group consisting of rare gases, nitrogen and carbon monoxide having a pulverulent desulfurizing agent for said molten metal distributed therethrough, said gas rising in fine bubbles through said mass of molten metal to the upper surface thereof carrying along and thus removing impurities from the interior of said mass of molten metal; and allowing said mass of molten metal to solidify in said mold.

9. A method of purifying steel during casting of the same, comprising the steps of pouring a mass of molten steel lnto an ingot mold; introducing through the center portion of the bottom of said mold into said mass of molten steel in said mold prior to solidification thereof a finely subdivided non-oxidizing gas which is substantially insoluble in the molten metal and selected from the group consisting of rare gases, nitrogen and carbon monoxide having a pulverulent alloying metal for said molten steel distributed therethrough, said gas rising in fine bubbles through said mass of molten steel to the upper surface thereof carrying along and thus removing impurities from the interior of said mass of molten steel; and allowing said mass of molten steel to solidify in said mold (References on following page) References Cited by the Examiner UNITED STATES PATENTS Reese 7559 Kinzel 22214 Hu-hne 75-93 ,Gi'lcrest et a1 7559 Schreiber 7593 Hachiya et a1 22215 Dunn 2273 Spire 7559 Ruhenbeck et .al. 7559 Walml 7559 XR 12 Le Roy et a1 75-59 Spence 75-93 Allard 75-59 Muller et a1. 7593 XR Nelson et a1 7559 Booth et a1 7593 XR Finkl 22215 XR Finkl 22214 XR 10 I. SPENCER OVERHOLSER, Primary Examiner.

MARCUS U. LYONS, Examiner.