US2815274A

US2815274A - Method of producing steel

Info

Publication number: US2815274A
Application number: US486608A
Authority: US
Inventors: Oelsen Willy; Rellermeyer Heinrich
Original assignee: August Thyssen Huette AG
Current assignee: Thyssen AG
Priority date: 1954-02-05
Filing date: 1955-02-07
Publication date: 1957-12-03
Anticipated expiration: 1974-12-03

Description

Dec. 3, 1957 W. OELSEN ETAL METHOD OF PRODUCING STEEL Filed Feb. 7, 1955 4 Sheets-Sheet 1 o k 2 p INVENTQRS Hgmrl'q, Rel/ermeger 4nd Q oelsen MM 5 firm Deg. 3, 1957 w. OELSEN ETAL 2,815,274

METHOD OF PRODUCING STEEL Filed Feb; 7, 1955 4 Sheets-Sheet 2 INVENTOR5= Heinrich fieuermeqer [@0195 vels en' SIS-Yuma. at

Dec. 3, 1957 w. OELSEN ET AL 2,815,274

METHOD OF PRODUCING STEEL Filed Feb. 7, 1955 4 Sheets-Sheet 5 $115. 5Q. E15. 5%.

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Dec. 3, 1957 w. OELSEN ET AL METHOD OF PRODUCING STEEL 4 Shets-Sheet 4 Filed Feb. 7, 1955 INVENTOR. Hginn'ch Bel/ermeqey BY and win Oels Mama; s wam/L Clai- METHOD OF PRODUCING STEEL Willy Oelsen, Clausthal-Zellerfeld, and Heinrich Rellerrneyer, Duisburg-Hamborn, Germany, assignors to August Ihysserr-Hiitte Aktiengesellschaft, Duisburg- Hamborn, Germany Application February 7, 1955, Serial No. 486,608

Claims priority, application Germany February 5, 1954 12 Claims. (CI. 75-52) The present invention relates to a method of producing steel, and more particularly to a method of blowing pig iron in a basic lined furnace to produce steel.

A great number of processes for producing steel by blowing with air or with air and oxygen have been proposed.

All known processes for blowing pig iron to produce steel, Whether these processes are discontinuous, or continuous and carried out with partitions in the apparatus, are dependent on the afiinity of the elements silicon manganese, carbon, phosphorous, and iron to oxygen, and the order of afiinities can hardly be overcome. As far as carbon and phosphorous are concerned, blowing from the top may result in dephosphorizing before decarbonizing even though the pig iron has a high initial phosphorous content when certain conditions, such as ample supply or ore, are present, but this result cannot be achieved with absolute certainty. When the blowing is carried out from the bottom and pig iron having a high phosphorous content, such as Thomas pig iron, is used, the phosphorous is eliminated only after the charge has been completely decarbonized.

It is one object of the present invention to overcome the disadvantages of the known processes of producing steel from pig iron, and to provide a process of blowing pig iron in which the sequence in which impurities are burned ofi is not determined by the afiinities of the impurities to oxygen.

It is another object of the present invention to provide a process of blowing pig iron in which the composition of the molten steel and of the slag is maintained constant during the process.

It is a further object of the present invention to provide a process of blowing pig iron in which the temperature is maintained substantially constant during the greater part of the process.

It is a still further object of the present invention to provide a process of blowing pig iron in which the nitrogen content of the produced steel is low as compared with the steel obtained by the known processes of blowing pig iron.

It is an important object of the present invention to provide a process of blowing pig iron in which the desired low percentage of impurities is obtained shortly after the start of the process, and maintained until the process is terminated.

Other objects of the present invention will become apparent as the description of the process of the present invention proceeds.

With the above objects in view, the present invention mainly consists in a method of producing steel, comprising the steps of continuously introducing a charge mass including pig iron into a furnace, and continuously blowing the introduced charge mass so as to continuously convert the pig iron contained in the charge mass into steel substantially as the charge mass is introduced into the furnace.

The term charge mass as used throughout the specification and claims is meant to denote a complete .charge which, however, according to the present invention is not States atent introduced as a unit but is introduced continuously over a prolonged period of time as compared to known processes. The term continuously as used throughout the specification and claims is meant also to include the consecutive introduction of portions of a charge mass wherein the portions are introduced so close to each other in time as to render the introduction of the portions continuous, the introduction of the entire charge mass being over a prolonged period of time as compared to the introduction of charges in the known processes.

According to the process of the present invention, the introduction of the charge mass is at such rate that the capacity of the furnace is not reached for at least six minutes, the pig iron of the charge being continuously converted to steel by blowing as the charge mass is introduced into the furnace. Preferably the rate of introduction is such that it requires from 6 to 20 minutes to reach the capacity of the furnace. As indicated later in the specification, it is not however necessary to reach the capacity of the furnace according to the process of the invention.

The method, according to the present invention, can be carried out with any kind of blowing apparatus for pig iron regardless of whether the gas is admitted from the top, from the bottom, or from the side of the vessel and regardless of whether air or oxygen or a mixture of air and oxygen is used.

According to one method of the present invention, the preheated blowing vessel is supplied with a certain portion of lime, for instance one-third of the total amount determined by the capacity of the vessel, and a certain portion of the pig iron, for instance one-tenth to one-third of the total amount, whereupon air, or oxygen, respectively, is blown into the vessel. After slag has been formed, and the respective amount of the pig iron has been almost completely converted into steel, pig iron and lime are continuously supplied in amounts corresponding to the amount of blown gas and the pig iron continuously blown as it is supplied, and in such manner that all impurities contained in the pig iron are uniformly burned off while the composition of the charge, and the composition of the slag remains substantially unchanged. The temperature of the charge remains unchanged or rises only very slightly during the blowing. The process is terminated when the vessel is completely filled to capacity and cannot receive .any further pig iron or lime. Obviously, a quantity smaller than the full capacity of the vessel can be processed.

In the process of the present invention, the sudden temperature rise after the conversion and the rapid change of the composition of the slag which are disadvantages of the conventional Thomas process are avoided. Such temperature rise after conversion in the known processes causes among other things the high nitrogen absorption of the charge in the Thomas process. In the process of the present invention, a much higher temperature prevails soon after the start of the process than in the conventional Thomas process, which has a favorable influence on .the dissolving of scrap additions and improves the blowing qualities of the converter when the blowing is carried out from below. The high temperature level at the beginning also assures brisk reaction of the carbon. The temperature maximum reached in the process of the present invention is not as high as in the conventional Thomas process which constitutes a particular advantage regarding the removal of phosphorous and the low nitrogen content of the steel.

In the event that the process is carried out on Thomas pig iron by blowing from the top, the phosphorous does not burn off before the carbon, but at the same time as the carbon.

Air, oxygen, or ,a mixture of air and oxygen may be used as blowing gas, to which CO or H O may be added. The blowing of a charge in the process of the present invention does not take any longer than the conventional blowing processes, which is self-evident since the required time is determined by the supplied amount of oxygen in the blowing gas.

In the process of the present invention slag may be removed several times during the process or may be continuously removed while the blowing proceeds. On the other hand, it is also possible to retain the slag in the converter until the process is terminated, and then to remove the entire slag.

A particular advantage of the present invention resides in that the composition of the burnt gases and the temperature of the same remains substantially constant during the entire blowing operation so that particularly the increase of the carbon monoxide content of the burnt off gases during the decarbonizing period occurring in the conventional processes is avoided. In the process of the present invention the carbon monoxide content of the burnt oif gases remains constant and is for each charge only substantially 60% of the carbon monoxide content of the burnt 01f gases produced in the conventional blowing processes. Thereby a substantial reduction of the temperature and of the radiated heat of the converter flame is obtained.

Due to the fact that the composition of the waste gases is uniform almost during the entire process and that the waste gas is combustible, the waste gas can be much better utilized for pre-heating lime and scrap, and even for burning olf limestone than waste gas having varying composition as is obtained by the conventional blowing process. Consequently, it is a self-evident further development of the processing of the present invention that suitable pre-heating devices are provided in connection with the blowing converter.

Since the temperatures of the charge and of the slag are high from the very beginning and uniformly and slightly increase as the process of the present invention proceeds, the amounts of cooling substances added to the charge, such as scrap, ore, and limestone can be determined easily by only estimating or determining the temperature.

The process of the present invention may be modified in several ways without departing from the spirit of the present invention. The supply of pig iron at the beginning of the process may be made greater than would be required by the amount of oxidizing gas, and a correspondingly greater amount of lime may be supplied. n the other hand, a smaller supply of pig iron may be preferred at the beginning of the process and a slagification of the iron and liquifying of the lime may be desired. It is also possible to continuously supply the pig iron and to supply the lime in portions.

According to a modified process of the present invention the type of supplied pig iron is changed during the process. For instance the process is started with a pig iron having a high phosphorous content and then continued with a pig iron having a low phosphorous content.

According to a further modified process of the present invention the process is started with pig iron having a low manganese content whereupon slag is removed, and the process is continued by supplying pig iron having a high manganese content.

As pointed out above, according to one method of the present invention, the process is started with a small amount of pig iron and lime which is blown to produce a high temperature which is maintained by further blowing as pig iron and lime are continuously added. Instead of removing the entire produced steel when the capacity of the vessel is reached, it is advantageous to retain a portion of the steel and a portion of the slag in the vessel when the first charge has been processed. Thereupon pig iron and lime are continuously supplied and blown until the capacity of the vessel is again reached.

The finished steel and the slag are then removed with the exception of a small amount which is left in the vessel to start the next charge.

This preferred process of the present invention has considerable advantages. After the major portion of the slag has been removed, the remaining amount of slag 1s solidified to such extent that the major portion of the molten steel can be poured into the ladle while the solidified slag remnant remains in the vessel.

In the event that the vessel would be completely emptied into the ladle, it could hardly be avoided that the last portion of the steel flows out together with the last portion of the slag. That would result in rephosphorizing, particularly when the slag has a high phosphorous content. In any event, the added deoxidation agent would be slagged in the form of ferromanganese. In killed charges, silicon and aluminum are similarly slagged. This, however, causes irregularity of the steel composition and is detrimental for the quality of the steel.

In accordance with the preferred process of the present invention, these disadvantages are avoided by removing a major portion of the slag, solidifying the remainder of the slag and emptying the blowing vessel only to such extent as steel flows out underneath the bridge consisting of solidified slag formed in the spout. No losses of deoxidation agents take place. The portion of the slag remaining in the converter is not lost but utilized when the next charge is processed. This is particularly important for slag having a high phosphorous content which is produced by the blowing of Thomas pig iron and are used as phosphate fertilizers.

The amount of steel remaining in the vessel after the blowing of one charge has been completed is not of particular importance. Since a great amount of steel remaining in the blowing vessel correspondingly reduces the capacity of the vessel available for the next charge, the retained amount of steel and slag is made as small as possible.

From the above discussion of methods according to the present invention it will become apparent that the essence of the present invention resides in the continuous supply of pig iron and lime to a converter and in the continuous blowing of the pig iron as it is supplied until the capacity of the vessel is reached. The initial portion of pig iron and lime as blown according to the present invention is mainly for the purpose of increasing the temperature to such level as is required for carrying out the process of the present invention. In the preferred method a retained steel portion is used to start the process, and it would be possible to carry out the process of the present inventionafter an initial small charge has been heated by means other than blowing to the temperature required for the process.

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. la is a diagram illustrating the burning of carbon, phosphorous, manganese and silicon during the process of the present invention applied to Thomas pig iron;

Fig. 1b is a diagram illustrating the temperature increase during the process illustrated in Fig. 1a:

Fig. 1c is a diagram illustrating the amount of metal in the vessel at various time periods during the process illustrated in Figs. 1a and 1b;

Fig. 1d is a diagram corresponding to Fig. 1a and illustrating a conventional blowing process applied to Thomas pig iron;

Fig. 1e is a diagram corresponding to Fig. lb and illustrating the temperature rise during the process illustrated in Fig. 1d;

.5 Fig. 1 is a diagram illustrating theam-ount of metal in the vessel during the conventional blowing process illustrated in Figs. 1d and 1e;

Fig. 2a is a schematic sectional view of a conventional converter blown from the bottom soon after the start of the process according to the present invention illustrated in Figs. la, 1b, and 1c;

Fig. 2b is a schematic sectional view corresponding to Fig. 2a illustrating the charge in the converter shortly before the end of the blowing;

Figs. 3a, 3b and 3c are diagrams corresponding, respectively, to the diagrams of Figs. 1a, 1b and 1c and illustrating the process of the present invention applied to Bessemer pig iron containing phosphorous;

Figs. 3d, 3e and 3 are diagrams corresponding to the diagrams of Figs. 1d, 1e and 1 and illustrate a conventional blowing process applied to Bessemer pig 1ron containing phosphorous; and

Figs. 4a and 4b are schematic sectional view of a vessel in which the process of Figs. 3a, 3b and 30 18 carried out and illustrating, respectively, the conditions soon after the start of the process and shortly before the ending of the blowing.

Referring now to the drawing, and more particularly to Fig. 2a, a quantity of pig iron and lime 3 is supplied to the vessel 1 and blown through tuyeres 2. This condition is illustrated in Fig. 1a which clearly shows that after 2 minutes the carbon, phosphorous, manganese and silicon of the first charge portion are burnt off. Thereupon, the pig iron 4 and lime are continuously supplied and the blowing is correspondingly continued so that the amounts of manganese and phosphorous remain substantially constant until the process is terminated aftenaltogether 12 minutes. The vessel filled to full capacity at the end of the process is illustrated in Fig. 2b. As shown in Fig. lb, the temperature rises to the desired level during the first 4 minutes in which the initial quantity is blown and remains substantially constant to the end of the process. The quantities of the charge in the converter are illustrated in Fig. 1c from which it will be apparent that an initial quantity is present during the first 4 minutes whereupon the quantity is continuously increased until the capacity of the vessel is reached after 12 minutes.

Figs. 10., 1e and 1 illustrate the process of the known art in which the vessel is filled to capacity at the beginning as illustrated in Fig. 1 The temperature rises continuously as illustrated in Fig. 1e, and the burning off takes place as illustrated in Fig. 1d. It will be apparent that it is much more diflicult to determine the end of the process in the conventional process illustrated in Fig. 1d as compared with the process of the present invention illustrated in Fig. 1a.

The following example is illustrative for the process of the present invention applied to Thomas pig iron and carried out in the manner graphically illustrated in Figs. 1a, 1b and 1c.

The converter has a capacity of 47 tons. Fifteen tons of pig iron containing 3.5% carbon, 2% phosphorous, 1.2% manganese, 0.35% silicon, and 0.05% sulphur are placed in the converter. At the same time 1.7 tons lime are placed into the converter. The converter is then moved to upright position and blown 4 minutes at which time the initial charge portion is fully processed as shown in Fig. 1a. The finished initial charge portion contains 0.02% carbon, 0.12% manganese, 0.030% phosphorous, 0.020% sulphur, and 0.008% nitrogen. The temperature is at that time 1,620 centigrade, and the slag contains 18.5% phosphoric acid, 12.0% iron oxide, 5.0% manganese oxide, 6.3% silicic acid, and 55.5% lime. From there on 4 tons pig iron per minute are continuously supplied through the top aperture while the blowing is continued. After another 8 minutes the converter has received 47 tons of pig iron and is filled to capacity. During the continuous supply of pig iron simultaneously small portions of lime are supplied at the rate of 250 kg. per min. so that after the additional 8 minutes, 3.6 tons of lime are supplied to the converter. The composition of the steel and of the slag as well as the temperature of the steel remains unchanged, or at least substantially unchanged, from the fourth minute of the process to the end of the process.

Referring now to Figs. 4a, and 4b, the illustrated vessel 5 is blown from the top through a nozzle 6 which is gradually retracted as the amount of the charge increases during the process. The lime 7 is supplied from a hopper 8 to a conveyor band 9 which drops the lime into the vessel 5. Fig. 4a illustrates the conditions after 5 minutes in which the first portion of the charge has been blown, and at the beginning of the continuous supply of Bessemer pig iron 10 and lime 7. Fig. 4b illustrates the conditions shortly before the end of the blowing in which the vessel 5 is filled to capacity by the charge 3. The slag is designated by the reference numeral 11.

The following example is illustrative of a process carried out in the arrangement illustrated in Figs. 4a and 4b in accordance with the diagram of Figs. 3a, 3b and 3c. The supplied Bessemer pig iron contains 3.8% carbon, 0.3% phosphorous, 1.0% silicon, and 2.5% manganese. At first 10 tons of the pig iron together with 700 kg. lime, constituting 7% of the pig iron, are placed in the vessel. Oxygen is blown into the vessel until the initial charge is decarbonized after 5 minutes. At that time the steel contains 0.05% carbon, 0.32% manganese, 0.025% phosphorous, and 0.004% nitrogen. The slag contains at that time 43.5% lime, 14.0% silicic acid, 7.3% phosphoric acid, 20.2% manganese oxide, and 13.1% iron oxide. After 5 minutes blowing the temperature of the steel is 1650 centigrade.

Thereupon, 1.33 tons pig iron per minute are continuously supplied as illustrated in Fig. 30 until the full capacity of the vessel is reached. At the same time, blowing is continued and the conveyor 9 supplies approximately kg. lime per minute continuously to the vessel. After 15 minutes the vessel contains 30 tons and is filled to capacity. The composition of the steel and of the slag is substantially the same as after the first 5 minutes of the process. During the entire blowing period, altogether 4.5 tons scrap constituting 15% of the pig iron, are supplied to the vessel in portions of 600 kg. and at time intervals of 2 minutes. The temperature at the end of the process is 1665 centigrade, that is slightly higher than after the first 5 minutes of the process.

Figs. 3d, 3c and 3 illustrate a conventional blowing process applied to Bessemer pig iron containing phosphorous and correspond, respectively, to Figs. 3a, 3b and 30 which illustrate the process of the present invention. It will be apparent from Fig. 3e that the temperature rises continuously in the process of the known art. Figs. 3a and 3d clearly show the advantage of the present invention over the known process, inasmuch as the amounts of phosphorous, carbon and manganese contained in the charge are substantially constant after 5 minutes in the process of the present invention, while the blowing process is completed in the known process at a time which cannot be exactly determined.

This is a considerable disadvantage of the prior art since due to the rapid sequence of reactions the concentrations change so rapidly in the charge that it is very difficult to determine the time at which the process should be terminated. This results in finished steel whose composition may not exactly correspond to the desired composition, and in greater variations of the composition than occur in steel obtained by the Siemens-Martin process, and similar processes.

The process of the present invention operates with continuously supplied pig iron so that the composition of the steel and of the slag is maintained uniform during the process, while the temperature is kept constant. Consequently, the process of the present invention is more accurate than any other known process, and even superior to the Siemens-Martin process which is very slow as compared with the process of the present invention.

The process of the present invention is economical since the charges are rapidly processed and permit a high output of each blowing vessel, as well as comparatively low heat losses.

Moreover, it has been found that in a blowing process carried out in a conventional converter blown from the bottom, the nitrogen content in the steel is lower and remains lower than in the conventional blowing processes, particularly as far as Thomas pig iron having a high phosphorous content is concerned. This is due to the fact that the process of the present invention does not require further additional blowing after decarbonizing, as is required in the known processes for pig iron having a high phosphorous content.

The method according to the present invention can be applied to any type of pig iron which can be converted to steel by a blowing operation. The same is true as regards the required additions to the charge. The amount of lime depends on the amounts of metalloid which have to be converted into slag by the lime and is just as high as in the conventional processes. Similarly, the required amount of cooling agents and the necessary blowing time are practically the same in the process of the present invention as in the conventional processes.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of methods of blowing steel differing from the types described above.

While the invention has been illustrated and described as embodied in a method of blowing pig iron in which pig iron and lime are continuously supplied and blown until the capacity of the converter is reached, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

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 the method of producing steel in which a predetermined quantity charge, including pig iron, is blown to steel in a furnace, the improvement which comprises initially blowing a portion of the charge filling a portion of the furnace, thereafter substantially continuously add- 8 ing the remainder of the charge over an extended period of time, while substantially continuously continuing said blowing during the addition, and thereafter discharging at least a substantial portion of the blown steel from the furnace.

2. Improvement according to claim 1, which includes after said discharging substantially continuously adding a further quantity of charge to the furnace while substantially continuously blowing the charge during its addition, and thereafter at least partially discharging the blown steel from the furnace.

3. Improvement according to claim 2, in which a substantial portion of the slag formed during said blowing is retained after said first discharging, and in which said adding of the further quantity of charge is effected in the presence of said retained slag.

4. Improvement according to claim 1, in which said blowing is effected in the presence of lime.

5. Improvement according to claim 4, in which lime is substantially continuously introduced into the furnace simultaneously with said charge.

6. Improvement according to claim 1, in which said charge is introduced into said furnace at a rate sufficient to substantially fill the same within 6 to 20 minutes.

7. Improvement according to claim 1, in which said initially blown portion of the charge fills said furnace between about A and /3 of its capacity and in which the total charge is an amount sufiicient to substantially fill said furnace.

8. Improvement according to claim 1, in which said initial blowing of the portion of the charge is effected for a period of time sufiicient to substantially convert this portion into steel prior to said addition of the remainder of the charge.

9. Improvement according to claim 8, in which said blowing of said remainder of the charge is substantially continuously effected with substantially the stoichiometric amount of oxygen required to convert the added charge to steel.

10. Improvement according to claim 1, which includes removing slag from the furnace during said blowing.

11. Improvement according to claim 10, in which the slag is substantially continuously removed during said blowing.

12. Improvement according to claim 11, which includes removing slag formed after the entire charge has been blown to steel.

References Cited in the file of this patent UNITED STATES PATENTS 714,450 Carson Nov. 25, 1902 1,080,606 Thiel Dec. 9, 1913 1,459,712 'Bauret June 26, 1923 2,502,284- Slottm-an Mar. 28, 1950 2,649,366 Jordan Aug. 18, 1953 2,741,555 .Cuscoleca et al. Apr. 10, 1956

Claims

1. IN THE METHOD OF PRODUCING STEEL IN WHICH A PREDETERMINED QUANTITY CHARGE, INCLUDING PIG IRON, IS BLOWN TO STEEL IN A FURNACE, THE IMPROVEMENT WHICH COMPRISES INITIALLY BLOWING A PORTION OF THE CHARGE FILLING A PORTION OF THE FURNACE, THEREAFTER SUBSTANTIALLY CONTINUOUSLY ADDING THE REMAINDER OF THE CHARGE OVER AN EXTENDED PERIOD OF TIME WHILE SUBSTANTIALLY CONTINUOUSLY CONTINUING SAID BLOWING DURING THE ADDITION AND THEREAFTER DISCHARGING AT LEAST A SUBSTANTIAL PORTION OF THE BLOWN STEEL FROM THE FURNACE.