US3396011A

US3396011A - Process and apparatus for the continuous refining of ferrous metal and particularly pig iron

Info

Publication number: US3396011A
Application number: US493330A
Authority: US
Inventors: Trentini Bernard
Original assignee: Institut de Recherches de la Siderurgie Francaise IRSID
Current assignee: Institut de Recherches de la Siderurgie Francaise IRSID
Priority date: 1964-10-12
Filing date: 1965-10-06
Publication date: 1968-08-06
Anticipated expiration: 1985-08-06
Also published as: GB1114961A; OA01832A; BE670486A; DE1458877A1; ES318388A1; NL6512950A; AT274868B; FR1418925A

Description

ug. 6, 1968 B, TRENTlNl 3,396,011

PROCESS AND APPARATUS FOR TRE CONTINUOUS REFINING OF FERROUs METAL AND PARTIOULARLY PIG IRON Filed 001". 6, 1965 United States Patent O 3,396,011 PROCESS AND APPARATUS FOR THE CONTINU- OUS REFINING OF FERROUS METAL AND PAR- TICULARLY PIG IRON Bernard Trentini, Metz, France, assignor to Institut de Recherches de la Siderurgie Francaise, Saint Germainen-Laye, Yvelines, France Filed Oct. 6, 1965, Ser. No. 493,330 Claims priority, application France, Oct. 12, 1964,

991,1 Claims. (Cl. 75-60) ABSTRACT OF THE DISCLOSURE Ferrous, carbon-containing metal, such as pig iron, is `refined by introducing a stream of the ferrous metal which is to be refined into a bath of at least partially refined ferrous metal which has a lower carbon content than the ferrous metal which is to be refined, intimately mixing the introduced stream of the ferrous metal with the partially refined bath so as to for-m a molten ferrous mixture having an average carbon content lower than that of the -ferrous metal which is to be refined, blowing a stream of oxidizing gas into the thus-formed mixture without directly contacting as yet unmixed portions of the introduced stream of ferrous metal so that the oxidizing gas will not come in direct contact with ferrous metal of the initial relatively high `carbon content and will cause oxidizing refining of the ferrous mixture which has a carbon content lower than that of the initially introduced pig iron or the like.

The present invention relates to a process and apparatus for the continuous refining of metal, particularly ferrous metal, and more particularly, pig iron.

Various continuous refining processes for pig iron utilizing oxidizing gas have been proposed. However, generally, these processes are fraught with serious difficulties due to the formation of large quantities Kof red fumes, particularly when the oxygen content of the refining gas is high. On the other hand, if the oxygen content of the gas is low, the formation of red fumes will be reduced, however, the thermal balance of the process becomes progressively :more unfavorable, to an unacceptable degree las the oxygen content of the refining gas is reduced.

It is therefore an object of the present invention to overcome the difficulties and disadvantages shown by prior art refining processes based on the blowing of oxygen or oxygen-containing gas into the molten metal, particularly ferrous metal such as pig iron, which is to be refined.

It is Ianother object of the present invention to provide a method and an apparatus for refining ferrous metal, such as pig iron, by means of oxygen containing gas which process and apparatus permit carrying out the refining of the ferrous metal in a simple and economical manner, and without forming substantial quantities of red fumes.

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 includes a process for refining ferrous metal containing carbon, comprising the steps of introducing a stream of said ferrous metal to be refined into a bath of at leas-t partially refined ferrous metal having a carbon content which is lower than the Icarbon content of the ferrous metal to be refined, intimately mixing the thus introduced stream of ferrous metal with said at least partially refined bath so as to form a molten ferrous mixture having an average carbon content lower than the carbon content of the ferorus metal to be refined, blowing a ICC stream of oxidizing gas consisting at least partially of oxygen into the molten ferrous mixture Without contacting the ferrous metal to be refined at a location where the mixing has already been effected, so as to subject the molten ferrous mixture to oxidizing refining thereby reducing Ithe carbon content thereof, and withdrawing thus formed refined ferrous mixture of reduced carbon content from the bath at a point spaced from the point of introduction of the stream of ferrous metal. g

The present invention also contemplates in a device for refining metal, in combination, an elongated vessel adapted to hold a bath of molten metal, the vessel having a bottom wall and two opposite end portions, introducing means for introducing into the vessel in the region of one of the opposite end portions a stream of molten refinable metal, withdrawal means for withdrawing from the vessel in the region of the other end portion thereof a stream of molten refined metal, and blowing means at least partly located in the bottom wall of the vessel in a region closer to the other than to the one of the opposite end portions, for blowing an oxidizing gas through the bottom wall into the vessel.

Thus, according to the present invention, the continuous refining of the ferrous metal is carried out by introducing a stream of gas of relatively high oxygen content into the same, in such a manne-r that a stream of ferrous molten metal, such as pig iron which is to be refined, is poured into a bath of ferrous metal which has been at least partially refined and which has a carbon content which is significantly lower than the carbon content of the ferrous metal which is to be refined. The stream of molten ferrous metal which is to be refined is mixed with the bath of at least partially refined molten ferrous metal and a refining gas containing oxygen is blown into the thusformed mixture at a point where, due to forming of the mixture of ferrous metal to be refined and ferrous metal which has already been partially refined, the carbon content is lower than in the stream of ferrous metal prior to or at its introduction into the bath. Care is taken that the oxygen-containing gas will not directly contact the stream of ferrous metal, such as pig iron, but will come in contact only with ferrous metal of reduced carbon content. From the bath which thus has been treated with oxygencontaining gas, a stream of refined ferrous metal of reduced carbon content is withdrawn in a continuous manner, corresponding to the continuous introduction of unrefined ferrous metal into the bath.

The process of the present invention, according to preferred embodiments thereof, furthermore will include one or more of the following features:

(a) The average carbon content of the bath may not exceed 0.5%.

(b) The carbon content of the bath of ferrous metal at the point of contact with the oxygen-containing gas may not exceed 0.5% and preferably will be up to only 0.2%.

(c) The weight of the partially refined bath into which the stream of ferrous metal which is to be refined is introduced, will at all times equal at least between five and six times the weight of the stream of ferrous metal which is introduced into the bath within a period of one minute, and preferably the bath will consist of an amount of molten metal equal to the amount of unrefined ferrous metal which is introduced into the bath during a period of between about 10` and l2 minutes.

(d) The stream of ferrous metal which is to be -refined, is poured into the bath of partially refined ferrous metal at a peripheral portion thereof, and the refining gas, i.e., the oxygen-containing gas is introduced into the bath beneath the upper level of the same, at a point which is not only vertically but also horizontally spaced from the point of introduction of the stream of ferrous metal to be refined. Preferably, the bath is contained in an elongated vessel having two opposite end portions and the stream of ferrous metal which is to be refined is poured into the bath in the vicinity of one of the opposite end portions, and the oxygen-containing gas is introduced through the bottom of the vessel in the vicinity of the ther of the Opposite end portions of the vessel. In this manner, circulating currents will be formed in the bath which will cause quick and intimate mixing of the introduced stream of molten ferrous metal with the at least partially refined molten ferrous metal of the bath.

(e) In order to enhance the mixing of the introduced stream of ferrous metal with the contents of the bath, a mixing gas which is free of oxygen or is less oxidizing than the above-mentioned oxygen-containing gas is blown onto the surface of vthe bath of molten ferrous metal in the vicinity of the point of introduction of the stream of ferrous metal into the same.

(f) Solid materials, for instance slag forming materials, which are required or desirable for the refining process are introduced into the bath from above, preferably as a pulverulent suspension in a stream of auxiliary or carrier gas which may or may not be oxidizing and which also may be the above-mentioned mixing gas.

(g) Refined metal is drawn off from the bath and may be subjected to a complementary refining process, preferably by being introduced into a second bath and by being treated therein substantially in the same manner as the initial unrefined ferrous metal is treated in the above described first refining bath.

For carrying out the abovedescribed process, the present invention contemplates an apparatus which comprises an elongated metallurgical vessel adapted to hold a molten bath of ferrous metal, having two opposite ends cooperating with means for introducing a stream of ferrous metal such as molten pig iron to be refined in the vessel at one of the opposite ends thereof, and with means for withdrawing a stream of molten rened metal from the vessel at the other of the opposite ends thereof. Blowing means for blowing oxidizing gas into the vessel are arranged in the bottom of the vessel in a region located nearer to the end through which the refined metal is withdrawn from the vessel than to the end at which unrefined ferrous metal is introduced into the same.

The arrangement according to the present invention may also include a second vessel constructed substantially like the above-described vessel, for receiving the stream of metal withdrawn or iiowing from the above-described vessel, in which the metal which has been refined in the above-described first vessel is subjected to a substantially similar complementary refining process in order to arrive at the desired final composition of the ferrous metal. It is of course also within the scope of the present invention to arrange in sequence not only two but a greater number of such refining vessels.

According to a preferred embodiment of the present invention, the apparatus for carrying out the refining of ferrous metal comprises a single elongated metallurgical vessel which is divided into a plurality of compartments by means of at least one partition wall of refractory material having an opening in its lower portion for the passage of metal from one compartment to the next. The stream of ferrous metal which is to be refined is received by the first compartment which substantially represents the first vessel described hereinabove, while the next following compartment lrepresents the second vessel, and a third compartment may be arranged including the end portion of the vessel which is opposite to the portion thereof which forms the first compartment and into which the unrefined ferrous metal is poured. The third compartment will be formed with an opening in its end wall or a wall portion of lesser height for the removal of refined metal by overow at such lesser height which will thcn determine the upper level of the metal bath in all of the communicating compartments.

According to preferred embodiments of the present invention, the apparatus described above may also include one or more of the following features:

(a) The means for blowing oxidizing gas through the bottom of the vessel into the same may include as an essential element a porous refractory element inserted into the bottom wall of the vessel.

(b) The porous refractory elements may be arranged and located in the bottom of the vessel, or in the bottom of the first compartment thereof if the vessel is compartmentalized, in such a manner that the shortest distance which separates the porous element from the lateral end wall of the vessel or the compartment wall, through which the molten metal is withdrawn, will be equal to between 0.1 and 0.7 times the shortest distance which separates the opposie end portion of the vessel, in the vicinity of which the stream of ferrous metal to be refined is introduced, from the porous stone.

(c) The lateral side walls of the vessel or compartients may be formed with openings located above the upper level of the metal bath for the continnous removal of slag from the surface of the metal bath.

(d) lf two vessels are arranged adjacent to each other so that the refined ferrous metal from the first vessel flows into the second vessel for further refining, then the partition wall between the two vessels may be formed with an opening or a depressed portion above the level of the metal -bath to permit passage of slag from the first to the second vessel.

The process of the present invention will avoid formation of obnoxious quantities of red fumes which are a frequently unavoidable annoyance in carrying out the conventional processes of refining ferrous metal such as pig iron with technically pure oxygen as the refining gas.

It has been found that red fumes are formed only if oxygen gas comes in direct contact with ferrous metal of relatively high carbon content. This is the reason why the blowing of pure oxygen onto or into pig iron will produce undesirable quantities of red fumes. If the proportion of carbon in the metal which is exposed to oxygen is reduced, it will be found that the amount of red fumes will diminish, until at a carbon content of between about 0.2 and 0.1% only insignificant amounts of red fumes are formed, and that the formation of red fumes will cease completely upon reduction of the carbon content of the ferrous meal to about 0.05%. These numerical values, however, are not precise limitations but only an indication of the order of magnitude of carbon content of the ferrous metal which will cause or will not cause formation of red fumes upon contact of the ferrous metal with oxygen gas. To a certain extent, these figures vary, depending on the other conditions of the refining process.

Without intending to limit the present invention to any particular theory, it may be assumed that the red fumes are primarily formed -by vaporization of iron with subsequent oxidation of the condensed vapors. The presence of carbon in the bath of ferrous metal will, upon Contact with oxygen, produce a higher temperature and thus a higher degree of vaporization of iron. However, at lesser carbon contents of the ferrous metal which is subjected to oxygen treatment, the temperature reached upon reaction between the ferrous metal and the oxygen will be considerably lower and hardly any iron will be vaporized.

According to the present invention, the stream of ferrous metal such as pig iron which is to be refined is diluted in a bath of ferrous metal of lower carbon content, in such a manner that the refining oxygen will at no time come in contact with ferrous metal having a sufficiently high carbon content to cause substantial formation of annoying red fumes. Thus, the delivery of oxygen which is -blown into the bath is controlled in such a manner that the removal of carbon from the bath by oxidation and with the stream of refined metal leaving the refining vessel will compensate exactly for the amount of carbon which is introduced into the bath with the stream of ferrous metal which is to be refined, so that the average carbon content of the bath will remain constant.

1t is therefore important that the introduced stream of ferrous metal to be refined is mixed well with the bath of partially refined ferrous metal of lower carbon content, prior to being contacted with oxygen gas. For this purpose it is desirable to form in the bath carefully arranged circulating currents. Such currents are produced by arranging the porous element through which oxygen is introduced into the bottom of the Vessel in a certain position relative to the point of introduction of ferrous metal into the bath and relative to the point of withdrawal of at least partially lrefined ferrous metal from the bath. The porous element or elements are located, preferably in the bottom of the vessel, relatively close to the end portion of the vessel which is opposite to that end portion at which the stream of ferrous metal which is to be refined is introduced into the Vessel. The carbon monoxide gas which is formed by contact between the introduced oxygen gas and the carbon-containing ferrous metal will cause an intensive mixing action in `the bath above the porous element and will create circulating currents which will dilute the introduced stream of ferrous metal, i.e. the carbon content thereof, and will cause flow of the introduced stream towards the porous element.

However, the speed of circulation of the molten metal in the bath must -be sufficiently slow so as to allow formation in the vessel, of an intimate mixture of the metal bath contained in the Ivessel with the introduced stream of ferrous metal. Thus, a certain minimum capacity of the refining vessel, or a minimum bath volume or weight is required in relation to the lrate of introduction of the stream of ferrous metal which is to be refined. For practical purposes, the capacity of the refining vessel preferably should be such that the volume or weight of the bath which may be contained therein is at least equal to ten times the amount of molten ferrous metal which is introduced per minute into the bath; in any case, the miniumu capacity of the vessel should be at least equal to five or six times the rate of introduction per minute of ferrous metal into the bath.

Preferably, the refined metal is withdrawn from, or leaves, the refining vessel at a lower portion of the same, in the vicinity of the means for introducing oxygen into the vessel. This is important in order to obtain a uniform refined product because it assures that the metal will be withdrawn while still being subjected to the refining action of the oxygen gas. It also permits, depending on the specific arrangement of the vessel, to withdraw a refined metal having a content of various elements such as carbon, silicon, phosphorus, manganese, etc., which is lower than the average content of such metals in the molten bath.

The mixing of the introduced stream of ferrous metal with the molten metal of the bath can be accelerated and intensified by utilizing mixing means known per se in the art for causing circulating currents, or complementary agitation. For instance, electromagnetic stirring arrangements may be utilized. It is also possible and within the scope of the present invention to blow in the vicinity of the point of contact between the stream of a ferrous metal to be refined and the molten bath onto the surface of the bath a mixing gas which may be a nonoxidizing gas such as nitrogen or an only slightly oxidizing gas such as air. Such mixing or stirring gas may also be utilized for introducing, as a suspension therein, pulverulent materials which are required for the refining of the molten bath, for instance for slag formation. Thus, an auxiliary lance may be placed above the refining Vessel having an orifice pointed from above towards the portion of the surface of the metal bath which is contacted by the stream of ferrous metal which is introduced into the bath. The thus-introduced suspension will cause effective stirring of the bath in the zone of introduction of the ferrous metal which is to be refined.

The novel features which are considered as characteristlc 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 speci-fic embodiments when read in connection with the accompanying drawings, in which the figure is a somewhat schematic elevational cross sectional view of a refining arrangement according to the present invention.

Describing now a preferred embodiment of the apparatus and process of the present invention with reference to the drawing, a vessel 1 is shown, including a conventional basic refractory lining, and divided into three compartments indicated by

reference numerals

2, 3 and 4. These compartments are separated from each other by

partition walls

5 and 6.

The molten metal or stream of pig iron which is to be refined is introduced through channel 7 into compartment 2. Compartment 2 contains molten metal which already has been partially refined and the composition of which will be described further below. The stream of pig iron 8 which is to be refined is introduced into compartment 2 through channel 7 at the rate of 500 kg./min. The level of molten metal in the three compartments of the vessel is determined by the height of spout 9 located at the far end of compartment 4, i.e., of the compartment which is farthest distant from compartment 2. From spout 9, the refined molten metal flows into a receptacle 10 for further use, for instance for introduction into an arrangement for continuous casting of the thus-refined metal, which arrangement is not shown in the drawing. However, it is also possible to withdraw refined molten metal from vessel 1 for introduction into a somewhat similar vessel in which further refining of the molten metal can be carried out in a manner more or less similar to that which is now being described with respect to the vessel illustrated in the drawing. The molten metal passes from compartment 2 to compartment 3 through opening 5a and from compartment 3 to compartment 4 through opening 6a which openings are respectively formed in the lower portions of

partition walls

5 and 6. The bottom of vessel 1 is slightly inclined downwardly in the direction from compartment 4 towards compartment 2 and refractory plug 11 closes the opening of a nozzle 12 inserted into the lowermost portion of the bottom of vessel 1, in order to permit by removing plug 11 complete withdrawal of molten metal from vessel 1 when the refining process is to be interrupted or stopped.

Compartment 2 contains about 6000 kg. of metal, or about l2 times the amount of molten metal which is introduced per minute into compartment 2 through channel 7. The average carbon content of the metal in compartment 2 equals between 0.1 and 0.15%. Preferably, the average carbon content of the molten metal in the main refining compartment or refining vessel should not exceed 0.5%.

`Oxygen -gas is :blown into the bath in the form of technically pure oxygen through porous refractory element 13 forming part of the bottom of vessel 1 and having a surface area of 4000 cm.2. rI`he oxygen-containing gas reaches porous element 13 through conduit 13b and a gastight wind box 13a interposed between the bottom of vessel 1 and conduit 13b. The solid materials which are required for the refining process are introduced in pulverulent form from above through two

lances

14 and 15. Through lance 14, lime is blown directly above porous element 13 in such a manner that slag formation will start immediately. The thus introduced lime will contact the circulating current formed in the metal bath by the introduction of -gas through porous element 13 and by the formation of carbon monoxide gas in the bath in the vicinity of porous element 13. The circulating current is indicated by arrow 16. Through lance 15, cooling agents may be blown into the bath in the form of ore, or pulverulent prereduced ore. 'I'he pulverulent materials supplied through both lances are suspended in gas streams which may lbe nonoxidizing or only slightly oxidizing, for instance in streams of nitrogen gas. The particulate suspension in the gaseous medium blown through lance will contact the surface of the molten metal bath in vessel 1 at the point at which the stream of the ferrous metal or pig iron 8 also contacts the surface of the molten metal baths, and thus, the suspension blown through lance 15 will cause additional mixing between the molten metal of the bath and the molten metal of stream 8. Preferably, the material which is blown onto the surface of the molten metal will be a relatively dense suspension of solid particles in the carrier gas, i.e., a relatively large amount by weight of pulverulent material will be suspended in a relatively small volume of carrier gas. Nitrogen gas or air may be used as the carrier gas, air having the advantage of being less expensive and having only a small oxidizing effect. Thus, air may be used particularly for blowing through lance 14, since the suspension yblown from lance 14 will contact the molten metal at a point of the bat-h where the carton content already has been lowered.

The subdivided particles or even the molecules of the pig iron which contact the molten bath of metal in vessel 1 are thus subjected to a plurality of different forces, namely the kinetic energy of the stream of molten ferrous metal indicated by arrow 17 which tends to carry the .pig iron directly towards porous element 13 and the forces of the circulating current and of the suspension blown from lance 15 indicated by arrows 18 and 19. The combined forces result in a circulating movement of the molten metal along the walls of vessel 1 as indicated by arrow 20 causing formation of an intimate mixture between the contents of the bath in vessel 1 and the continuously introduced stream 8 of molten ferrous metal.

Oxygen gas is introduced through porous element 13 at a rate of about 24 standard cubic meters per minute, and is controlled relative to the amount of carbon and other oxidizable elements introduced into the bath by stream 8 of ferrous metal, in such a manner that the average composition of the bath remains constant.

In addition, to nearly completely eliminating the formation of red fumes, the present method has the further advantage of achieving a very great degree of homogeneity and uniformity of the final product, i.e., of the rened ferrous metal. This homogeneity can be shown by the uniformity of the bath temperature within compartment 2. Temperature measurements carried out with thermocouples immersed in the molten bath in compartment 2 show that at a -bath temperature in the vicinity of 1600 C., temperature variations within the various portions of the bath do not exceed 20 C. By carrying out the refining of similar ferrous metal in conventional arrangement similar to the overflow 22 of compartment 2. On the other hand, when pig iron of very high phosphorus content is to be relned, then all of the slag which is formed in compartment 2 is withdrawn through overow 22 and a new slag is formed in compartment 3 by introduction of fresh lime into the same.

The metal leaving compartment 2 passes through. opening 5a at the bottom of vessel 1 into compartment 3. Opening 5a is located in the vicinity of porous element 13, so that all portions of the metal bath in compartment 2 will be forced to pass above and relatively close to porous element 13 prior to reaching compartment 3, thereby assuring intimate contact 'between oxygen gas supplied through porous element 13 and the portion of the metal bath leaving compartment 2. The arrangement of opening 5a in the vicinity of porous element 13 combined with the associated forces applied to the molecules of pig iron further assures the uniformity of the relined product.

In compartment 3, the molten metal is further refined by means of oxygen gas blown through porous element 24. Oxygen is fed to porous element 24 by way of wind box 24a and conduit 24h. The surface area of porous element 24 equals 1500 cm?, and oxygen gas is introduced therethrough at a rate of about 1 standard cubic meter per minute. Porous element 24 is located in the vicinity of opening 5a in order to force in the molten metal in compartment 3 a circulation as indicated by arrow 25 which will bring the introduced molten metal in contact with the slag on the surface of the metal bath in compartment 3. There is only very little temperature difference between the molten metal baths in the various compartments.

Finally, the molten metal passes into the last compartment 4, free of slag, in order to be withdrawn through spout 9, If desired, a porous element 26 having a square area of 50 cm.2 and supplied with oxygen by way of wind box 26a and conduit 26h permits completion of the refining process so as to obtain an extra soft steel having a carbon content of 0.05% or less. The rate of introduction of oxygen gas through porous element 26 is controlled so as to obtain the desired steel composition and generally will be less than 0.25 standard cubic meter per minute.

As described, the three porous elements are supplied with oxygen through their

respective conduits

13b, 24h and 26b, which may be connected to a single oxygen source, not shown in the drawing, with interposed control elements such as valves, also not shown, which permit separate control of the oxygen supply to each of the porous elements.

Following the process as described above, the following compositions are obtained:

1 Traces.

manner by blowing oxygen from above into the molten bath, temperature variations of about 100 C. are found in the upper portion of the bath.

The slag which is formed in the relining process is removed through openings 21 in the lateral or side walls of vessel 1 and spout 22. A small channel 23 formed in partition 5 permits passage of slag from compartment 2 into compartment 3 so that slag .formation with respect to certain elements, particularly phosphorus, silicon and manganese may be completed in compartment 3. When retining certain types of pig iron of low phosphorus and sulfur content, it is frequently desirable to pass the entire slag through channel 23 into compartment 3 and then to withdraw the slag from compartment 3 through an overflow 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 continuous process for refining ferrous metal having an initial carbon content corresponding to that of pig iron and exceeding a predetermined maximum carbon content at which upon contact of said ferrous metal with oxygen substantially no red fumes will be formed, comprising the steps of introducing a stream of said ferrous metal to be refined in such an amount into a bath of at least partially refined ferrous metal having a carbon content which is lower than said predetermined maximum carbon content that the average carbon content of said introduced ferrous metal and said bath does not exceed 0.5%; intimately mixing the thus introduced stream of ferrous metal with said at least partially refined bath so as to form a molten ferrous mixture having said average carbon content so that the carbon content of at least a portion of said mixture does not exceed said predetermined maximum carbon content; blowing a stream of oxidizing gas consisting at least partially of oxygen into said portion of said molten ferrous mixture having a carbon content not exceeding said predetermined maximum carbon content so as to subject said molten ferrous mixture to oxidizing refining without directly contacting ferrous metal having a carbon content exceeding said preydetermined maximum carbon content with said oxidizing gas and thus substantially without formation of red fumes, thereby reducing the carbon content of said molten ferrous mixture; and withdrawing thus formed refined ferrous mixture of reduced carbon content from said bath at a point spaced from the point of introduction of said stream of ferrous metal.

2. A continuous process for refining pig iron, comprising the steps of continuously introducing a stream of pig iron having an initial carbon content exceeding a predetermined maximum carbon content at which upon contacting of said pig iron with oxygen substantially no red fumes will be formed, into a predetermined portion of a bath of at least partially refined pig iron having an average carbon content not exceeding 0.5 continuously blowing a stream of oxidizing gas consisting at least partly of oxygen into a portion of said bath spaced from said predetermined portion and having a carbon content lower than the carbon content of said predetermined portion without directly contacting with said stream of gas pig iron having a carbon content exceeding said predetermined maximum carbon content, so as to cause due to introduction of said stream of pig iron and blowing of said stream of gas intimate mixing of said stream of pig iron with said bath thereby forming a molten ferrous mixture having a carbon content not exceeding said predetermined maximum carbon content, and to subject the thus formed molten ferrous mixture to oxidizing refining thereby reducing the carbon content thereof; and continuously withdrawing thus formed refined ferrous mixture of reduced carbon content from said bath at a point spaced from said predetermined and said latter portion thereof.

3. A process as defined in claim 1, wherein said ferrous metal having an initial carbon content exceeding a predetermined maximum carbon content is molten pig iron.

4. A process as defined in claim 1, wherein said stream of oxidizing gas is blown into a portion of said molten ferrous mixture having a carbon content not exceeding 0.2%.

5. A process as defined in claim 2, wherein the weight of said bath of at least partially refined pig iron is maintained at at least 5 times the weight of pig iron introduced per minute into the same.

6. A process as defined in claim 5, wherein the weight of said bath of at least partially refined pig iron is maintained at between about 5 and 6 times the weight of pig iron introduced per minute into said bath.

7. A process as defined in claim 2, wherein said stream of oxidizing gas is blown from above into an end portionof said bath and said stream of pig iron is introduced into said bath at the opposite end portion thereof.

8. A process as defined in claim 2, and including the step of blowing a mixing gas having a lesser oxygen content than said oxidizing gas onto the surface of said bath in the vicinity of the point of introduction of said stream of pig iron and spaced from the point of introduction of said stream of oxidizing gas.

9. A process as defined in claim 2, and including the step of blowing onto the surface of said bath of at least partially refined pig iron a stream consisting of a gaseous suspension of pulverulent refining agents.

10. A process as defined in claim 9, wherein said refining agents are slag-forming agents.

References Cited UNITED STATES PATENTS 2,959,479 11/ 1960 Graef 75-60 3,169,055 2/ 1965 Josefsson 75-52 2,962,277 11/ 1960 Morrill 75-60 2,975,047 3/ 1961 Leroy et al 75-60 3,079,249 2/ 1963 Moustier 75-60 3,259,484 7/1966 Leroy et al. 75-60 3,275,432 9/ 1966 Alexandrovsky 75-60 FOREIGN PATENTS 514,352 1939 Great Britain.

HYLAND BIZOT, Primary Examiner.