US2593505A - Metal refining process - Google Patents

Metal refining process Download PDF

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US2593505A
US2593505A US20202A US2020248A US2593505A US 2593505 A US2593505 A US 2593505A US 20202 A US20202 A US 20202A US 2020248 A US2020248 A US 2020248A US 2593505 A US2593505 A US 2593505A
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iron
carbon content
oxygen
molten
bath
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James B Wagstaff
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Hydrocarbon Research Inc
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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
    • C21C5/04—Manufacture of hearth-furnace steel, e.g. Siemens-Martin steel

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  • This invention relates to the refiriing of metal compositions. More particularly, it perta'ins to a process wherein oxygen is introduced into a bath of molten crude iron to effect decarburization.
  • Oxygen is advantageously used in the elimination of carbon from molten iron preparatory to the manufacture of steel.
  • a stream of thegas may be introduced at a substantially constant rate into a bath of the metal including, for example, pig and scrap irons in an open hearth furnace and the process continued until the carbon content of the metal bath is decreased to ⁇ a predetermined amount as dictated by the type of steel which is to be produced.
  • a primary object of .the present invention is to increase the efiiciency in the refining of crude iron by contact with oxygen in concentratecl form.
  • Another important object is to accelerate the de'carburization of molten crude iron after its carbon content h'as been decreased to the critical value.
  • the aforesaid disadvantages are substantially minimized by adding continuously or periodically, iron oxide to the metal bath after the carbon content thereof has been lowered to the critical Value by blowing oxygen in concentrated form through the molten iron.
  • the added iron oxide appears to block or at least materially diminish the reaction between the oxygen and the molten iron so that as the introduction of oxygen is continued when the carbon content of the metal is below the critical value a smaller proportion of the oxygen is wasted in the undesirable side reaction than is the case When iron oxide is not added to the. bath.
  • the iron oxide is preferably and conveniently introduced below the surface of the molten metal bath by suspension in the oxygen stream injected thereinto.
  • Any desired iron oxide such as ferrous oxide, magnette, hematite, mill scale or the like may be used for the purposes of this invention but it ispreferred to select the more highly oxidized forms of iron like hematite.
  • the iron oxide is added to the bath in finely comminuted or powdered form and is rapidly dispersed under the agitation caused by the oxygen injected into the moltenbath. The added oxide tends to collect in the slag layer.
  • the entrainment of the iron oxide in the oxygen stream is :thought advisable since in this way the iron oxide is in the immediate presence of the oxygen introduced into the metal bath. Also, a some- What improved distributon of the iron oxide is accomplished by introducing this agent directly into the' molten bath along with the' oxygen.
  • I have shown for illustrative purposes, my invention as applied to the rening of crude iron in an open hearth furnace.
  • the numeral I& indicates an open hearth furnace of well-known type having a refractory base l I on which the bath of molten metal l2 rests, this bath as usual having an upper slag layer l'3.
  • the top l4 of this furnace is formed with an opening
  • Figure 2 is a graphic representation of a typical heat.
  • the carbon content of the molten iron and the iron oxide content of the slag layer are both plotted against the time of the refining heat.
  • the crude iron has a high carbon content at the start of the heat, usually in the range of about 2 to 4% by weight.
  • Oxygen say about 95% pure, is injected through the lance into the molten bath and its carbon content decreases because of the reaction With oxygen.
  • the rate at which the carbon is eliminated from the iron is fairly constant until the carbon content of the metal falls below 1% by' weight.
  • the rate of carbon elimination becomes appreciably smaller in many instances when the carbon content has dropped down to about 015% and more generally when the carbon content has fallen to about 031% and lower.
  • the carbon content at which an appreciably lower rate of carbon elimination is noted hasbeen referred to hereinbefore as the critical carbon content. If the injection of oxygen is continued at a uniform rate, the carbon content of the iron is slowly brought down to the desired value, say 0.06% by weight, in time T. Thus, under normal circumstances, the length of the heat period is time T.
  • the critical carbon content oi' the iron when the critical carbon content oi' the iron has been reached, say at time Te, iron oxide is introduced into the molten bath as well as the oxygen stream.
  • the slag layer shows an increasing content of iron oxide which content is made higher (see dotted line) than that normally noted in the absence of added iron oxide.
  • the added oxide promotes more rapid elimination of carbon (see dotted line) so that by the end of time Tz the carbon content of the iron is down to the value attained in the absence of added oxide in the longer time T.
  • the added oxide appears to accelerate the rate of carbon elimination so that if the introduction of iron oxide and oxygen were continued to time T, the carbon content of the iron would then be well below the desired ultimate content.
  • An open hearth furnace contains a molten bath comprising tons of pig iron and 40 tons of scrap iron.
  • the carbon content of the molten iron is 313% by weight at the start of the rening heat.
  • the furnace is maintained at a temperature of about 2900 F.
  • Oxygen (96% by Volume purity) is injected into the molten iron at a uniform rate of about 250 cu. ft. (standard conditions) per ton of iron per hour.
  • the injected oxygen not only eliminates carbon from the molten iron but also oxidizes other impurities such as silicon, phosphorus and m'anganese.
  • comminuted mill scale is added to the bath at the uniform rate of 'l tons per hour while the injection of oxygen is continued at the aforesaid rate.
  • the charging of the mill scale into the molten bath is preferably accomplished with apparatus of the type shown in Figure 1 wherein the mill scale is fed from hopper 22 into the mixing chamber 59 and thence conveyed by the oxygen stream through lance ll into the molten bath.
  • the desired ultimate carbon content of the iron is ⁇ 0.05% by weight and this carbon content is reached in about 1 hour from the time when the addition of mill scale is started. At this point the refining heat is terminated and the refined iron withdrawn from the furnace.
  • the desired ultimate carbon content of &05% by weight can be reached without the addition of the mill scale used in the example or any other iron oxide if the rening period is lengthened by about 1 hour. It is obvious that the additional hour required to reach the desired ultimate carbon content without the addition of iron oxide will consume an additional 50,000 cu. ft. (standard conditions) of oxygen for the specified refining heat.
  • the process of refinng crude iron having a oarbon content of about 2 to 4% by weight to yield a rened iron having a carbon content of the order of not more than 005% by Weight which comprises decreasing the carbon content of said crude iron to a carbon content of about 0.4 to 1% by weight solely by injecting concentrated oxygen of at least 80% by Volume purity into a molten bath of said crude iron, and thereafter further decreasing the carbon content of the iron in said molten bath to a carbon content of the order of not more than 005% by Weight by simultaneously injecting concentrated oxygen of at least 80% by 'Volume purity and iron oxide into said molten bath.

Description

Patented Apr. 22, 1952 UNITED STATES PATENT OFFICE James B. Wagstaff, Ridgewood, NMT., assignor to Hydroca'bon Research, Inc., New York, N. Y., a cor'poration of New Jersey Application April '10, 1948, semi N. 20202 l This invention relates to the refiriing of metal compositions. More particularly, it perta'ins to a process wherein oxygen is introduced into a bath of molten crude iron to effect decarburization.
Oxygen is advantageously used in the elimination of carbon from molten iron preparatory to the manufacture of steel. A stream of thegas may be introduced at a substantially constant rate into a bath of the metal including, for example, pig and scrap irons in an open hearth furnace and the process continued until the carbon content of the metal bath is decreased to` a predetermined amount as dictated by the type of steel which is to be produced. t
It has been found in practice that when the carbon content of the molten iron is decreasedby this process to below a certain figure, which, incidentally, is substantially above the desired ultimate content, increasingly greater amountspf oxygen are required to be introduced into the i metal bath to avoid a substantial diminution in the rate of carbon elimination. This figure appears to vary with several factors including the compositions of the metal bath and the slag layer. stated in another way, after the carbon content of the iron bath has been decreased to that certain figure (hereinafter for convenience called the critical carbon content), a constant rate of oxygen introduction into the molten metal yields a decreasingly smaller rate of decarburiz a tion or carbon elimination; `In mostcases the critical carbon content is of the order of by weight. When the carbon content approaches this Value, an equilibrium condition is apparently created involving the iron oxide in the slag layer and the residual carbon in the molten metal. This equilibrium indicates that, as the oxygen input continues after the critical carbon content has been reached, some of the oxygen is consumed in the formation of iron oxide and thus is not available for further decreasing the carbon content of the molten iron. M After the carbon content has been brought down to the critical value by the introduction of oxygen into the molten iron, further decrease in the carbon content of the molten iron can be effected by continuing the introduction of oxygen at substantially the same rate over a relatively long period or by increasing the rate of oxygen introduction and thus decreasing thecarbon con: tent of the molten iron to the ultimate desired value in a shorter period. In either case, it is clear that a greater Volume of oxygen is consumed per unit weight of carbon eliminated from the molten iron after the critical carbon content` has been passed than was consumed before this value was 2 ciaims. (o. 75 51) re'a'ched. Furthermore, some of the iron reacts with the oxygen to `form iron oxide after the carbon content of the molten bath has been decreased to below the critical value. Thus, a portion of the iron,'which would otherwise be recoverecl as a useful and valuable product, is undesirably converted ,to iron oxide as a by-product of the refining operation.
A primary object of .the present invention is to increase the efiiciency in the refining of crude iron by contact with oxygen in concentratecl form. i
Another important object is to accelerate the de'carburization of molten crude iron after its carbon content h'as been decreased to the critical value.
Other objects and advantages of the invention will become apparent from the following description considered in connection with the drawings illustrative of the applications of the inventicn.
In accordance With the present invention, it has been found that the aforesaid disadvantages are substantially minimized by adding continuously or periodically, iron oxide to the metal bath after the carbon content thereof has been lowered to the critical Value by blowing oxygen in concentrated form through the molten iron. The added iron oxide appears to block or at least materially diminish the reaction between the oxygen and the molten iron so that as the introduction of oxygen is continued when the carbon content of the metal is below the critical value a smaller proportion of the oxygen is wasted in the undesirable side reaction than is the case When iron oxide is not added to the. bath.
The iron oxide .is preferably and conveniently introduced below the surface of the molten metal bath by suspension in the oxygen stream injected thereinto. Any desired iron oxide such as ferrous oxide, magnette, hematite, mill scale or the like may be used for the purposes of this invention but it ispreferred to select the more highly oxidized forms of iron like hematite. The iron oxide is added to the bath in finely comminuted or powdered form and is rapidly dispersed under the agitation caused by the oxygen injected into the moltenbath. The added oxide tends to collect in the slag layer.
The entrainment of the iron oxide in the oxygen stream is :thought advisable since in this way the iron oxide is in the immediate presence of the oxygen introduced into the metal bath. Also, a some- What improved distributon of the iron oxide is accomplished by introducing this agent directly into the' molten bath along with the' oxygen.
Referring to the diagrammatc drawing of Figure 1, I have shown for illustrative purposes, my invention as applied to the rening of crude iron in an open hearth furnace. The numeral I& indicates an open hearth furnace of well-known type having a refractory base l I on which the bath of molten metal l2 rests, this bath as usual having an upper slag layer l'3. The top l4 of this furnace is formed with an opening |5 through which extends the leading end of a metal Conduit IT, the lower portion of which is provided with refractory sheath elements 18 for protection of the metal pipe from the deteriorating eflect of the molten metal. This lance comprising pipe H and refractory elements 18 is fully described and claimed in my copending application, Serial No. 3,726, filed January 22, 1948. The lower portion l of the conduit l'l dips into the metal bath well below the slag layer !3. The oxygen is introduced into a mixing chamber |`9 where it becomes intimately mixed with powdered or comminuted iron oxide introduced into the mixing chamber by a screw conveyor 20 driven by a motor 21. The iron oxide is passed to the screw conveyor from a hopper 22 through a valve 23 and thence into the mixing chamber !9. Thus, the comminuted iron oxide is Suspended in the oxygen stream flowing through chamber !9 and carried thereby through the lance into the molten metal bath. i
Figure 2 is a graphic representation of a typical heat. The carbon content of the molten iron and the iron oxide content of the slag layer are both plotted against the time of the refining heat. As shown, the crude iron has a high carbon content at the start of the heat, usually in the range of about 2 to 4% by weight. Oxygen, say about 95% pure, is injected through the lance into the molten bath and its carbon content decreases because of the reaction With oxygen. The rate at which the carbon is eliminated from the iron is fairly constant until the carbon content of the metal falls below 1% by' weight. Depending on the composition of the iron bath under treatment, the rate of carbon elimination becomes appreciably smaller in many instances when the carbon content has dropped down to about 015% and more generally when the carbon content has fallen to about 031% and lower. The carbon content at which an appreciably lower rate of carbon elimination is noted hasbeen referred to hereinbefore as the critical carbon content. If the injection of oxygen is continued at a uniform rate, the carbon content of the iron is slowly brought down to the desired value, say 0.06% by weight, in time T. Thus, under normal circumstances, the length of the heat period is time T. Durin this heat, it is noticed that the iron oxide content of the slag layer over the molten iron is fairly constant until the carbon content of the iron has fallen below about 1% by weight; in the vicinity of the critical carbon content of the iron, the slag shows an increasing content of iron oxide and this oxide content appears to keep rising rapidly to the end of the heat. I believe that the increase of iron oxide in the slag layer is attributable to a competitive reaction between the molten iron and its carbon content for the oxygenblown into the bath and that this competition for oxygen seriously afiects the rate of carbon elimination only after the carbon content of the molten metal has been decreased to a relatively low value, say 0.6 by weight. References herein to the critical carbon content of the molten iron are more readily understood in the light of this theory.
In accordance with my invention, when the critical carbon content oi' the iron has been reached, say at time Te, iron oxide is introduced into the molten bath as well as the oxygen stream. Assuming a substantially uniform rate of addition of iron oxide from time Te to time T2, the slag layer shows an increasing content of iron oxide which content is made higher (see dotted line) than that normally noted in the absence of added iron oxide. The added oxide, however, promotes more rapid elimination of carbon (see dotted line) so that by the end of time Tz the carbon content of the iron is down to the value attained in the absence of added oxide in the longer time T. stated in another way, the added oxide appears to accelerate the rate of carbon elimination so that if the introduction of iron oxide and oxygen were continued to time T, the carbon content of the iron would then be well below the desired ultimate content.
As graphically represented in Figure 2, my invention of adding an iron oxide to iron undergoing refining by oxygen after the carbon content has been lowered to the point (critical carbon content) where the rate of carbon elimination is appreciably curtailed results in a shortening of the heat period by an amount equal to the difference between times T and T2. If the operation of my invention is carried on to time T, the carbon content of the finished iron is lower than it would otherwise be. In any instance, it is evident that the addition of iron oxide to the bath after the critical carbon content has been reached results in an economy of valuable oxygen. The added iron oxide also minimizes the amount of iron converted to oxide during the refining treatment.
For further Clarification of the invention, a specific example is now presented. An open hearth furnace contains a molten bath comprising tons of pig iron and 40 tons of scrap iron. The carbon content of the molten iron is 313% by weight at the start of the rening heat. The furnace is maintained at a temperature of about 2900 F. Oxygen (96% by Volume purity) is injected into the molten iron at a uniform rate of about 250 cu. ft. (standard conditions) per ton of iron per hour. The injected oxygen not only eliminates carbon from the molten iron but also oxidizes other impurities such as silicon, phosphorus and m'anganese. When the carbon content of the molten iron has been decreased to a value of about 0.4% by weight, comminuted mill scale is added to the bath at the uniform rate of 'l tons per hour while the injection of oxygen is continued at the aforesaid rate. The charging of the mill scale into the molten bath is preferably accomplished with apparatus of the type shown in Figure 1 wherein the mill scale is fed from hopper 22 into the mixing chamber 59 and thence conveyed by the oxygen stream through lance ll into the molten bath. The desired ultimate carbon content of the iron is `0.05% by weight and this carbon content is reached in about 1 hour from the time when the addition of mill scale is started. At this point the refining heat is terminated and the refined iron withdrawn from the furnace.
In contrast to the results obtained when the refining process is conducted in accordance with the principles of this invention, the desired ultimate carbon content of &05% by weight can be reached without the addition of the mill scale used in the example or any other iron oxide if the rening period is lengthened by about 1 hour. It is obvious that the additional hour required to reach the desired ultimate carbon content without the addition of iron oxide will consume an additional 50,000 cu. ft. (standard conditions) of oxygen for the specified refining heat.
In refining crude iron by injcting concentrated oxygen into a molte n bath of the iron, I find it advisable to use oxygen of at least 80% by Volume purity and preferably of at least 90% by Volume purity. Recent developments in the field of oxygen production have eventuated in prccesses which yield oxygen of about 95% by Volume purity at costs permitting the large-scale use of such oxygen in processes of the type contemplated by this invention.
Various modications of the invention will occur to those skilled in the` art upon consideration of the foregoing disclosure without departing from the spirit and scope thereof. Accordingly, only such limitatons should be imposed as are indicated by the appended claims.
I claim:
1. The process of refinng crude iron having a oarbon content of about 2 to 4% by weight to yield a rened iron having a carbon content of the order of not more than 005% by Weight, which comprises decreasing the carbon content of said crude iron to a carbon content of about 0.4 to 1% by weight solely by injecting concentrated oxygen of at least 80% by Volume purity into a molten bath of said crude iron, and thereafter further decreasing the carbon content of the iron in said molten bath to a carbon content of the order of not more than 005% by Weight by simultaneously injecting concentrated oxygen of at least 80% by 'Volume purity and iron oxide into said molten bath.
2. The process of refining crude iron having a carbon content of about 2 to 4% by weight to yield a refined iron having a carbon'content of the order of not more than' 005% by weight, which comprises decreasing the carbon content of said crude iron to a carbon content of about 0.4 to 06% by weight solelyby injecting concentrated oxygen of at least 80% by Volume purity into a molten bath of said crude iron, and
thereafter further decreasing the carbon content of the iron in said molten bath to a carbon content of the order of not more than 005% by weight by simultaneously injecting concentrated oxygen of at least by Volume purity and iron oxide into said nolten bath.
JAMES B. WAGSTAFF.
REFEREN CES CITED The following references are of record in the file of this patent:
UNITED STATES PATENTS OTHER REFERENCES U. S. Bureau of Mines Report of Investigations, No. 2502, pages 31, 32 and 33, Published in July 1923.
Basic Open Hearth Steel Making, pages 36 to 38. Published in 1944 by the A. I. M. New York, N. Y.
Open Hearth Proceedings, 1947 edition, pages 14 to 32. Published by the A. I. M. E. New York, N. Y.
The, Iron Age, Feb. 20, 1947, pages 42 to 45. Published by the Chilton Co., Philadelphia.
Metal Progress, December 1947, pages 966 and 967. Published by the American Society for Metals, Cleveland, Ohio.
Year Book of the Amer. Iron and Steel Inst. 1947, pages 234 and 262. Published by the Amer. Iron and Steel Inst., New York, N. Y.

Claims (1)

1. THE PROCESS OF REFINING CRUDE IRON HAVING A CARBON CONTENT OF ABOUT 2 TO 4% BY WEIGHT TO YIELD A REFINED IRON HAVING A CARBON CONTENT OF THE ORDER OF NOT MORE THAN 0.05% BY WEIGHT, WHICH COMPRISES DECREASING THE CARBON CONTENT OF SAID CRUDE IRON TO A CARBON CONTENT OF ABOUT 0.4 TO 1% BY WEIGHT SOLELY BY INKECTING CONCENTRATED OXYGEN OF AT LEAST 80% BY VOLUME
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Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2878115A (en) * 1956-09-14 1959-03-17 United States Steel Corp Open-hearth steelmaking process
US2923615A (en) * 1957-03-28 1960-02-02 Pan American Petroleum Corp Process for obtaining metals from their ores
US3079452A (en) * 1958-07-07 1963-02-26 Electro Refractaire Manufacture of electrically-melted refractory products containing mineral oxides
US3157489A (en) * 1961-03-09 1964-11-17 Pullman Inc Method for reducing metal oxides
US3157490A (en) * 1961-10-23 1964-11-17 Pullman Inc Method for refining of metals
US3194539A (en) * 1960-02-11 1965-07-13 Eugene Goffart & Cie Mixing apparatus
US3212880A (en) * 1959-12-24 1965-10-19 Bot Brassert Oxygen Techik A G Method of carrying out metallurgical processes
US3859078A (en) * 1972-10-30 1975-01-07 Sydney Steel Corp Method of operating a basic open hearth furnace
US3898078A (en) * 1973-03-29 1975-08-05 Youngstown Sheet And Tube Co Method and apparatus for injecting refining oxygen in steelmaking processes
US3942978A (en) * 1973-11-28 1976-03-09 Uddeholms Aktiebolag Metallurgical method
US3960547A (en) * 1972-12-18 1976-06-01 Youngstown Sheet And Tube Company Steelmaking process
US4009023A (en) * 1973-02-15 1977-02-22 Uddeholms Aktiebolag Method for the refining of molten metal

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US193551A (en) * 1877-07-24 Improvement in the manufacture of iron and steel
US586047A (en) * 1897-07-06 Frank bernard last
US1541778A (en) * 1923-11-17 1925-06-16 Karl A Agricola Apparatus for refining metal
US1949731A (en) * 1930-11-29 1934-03-06 Soldatoff Vassily Vassily Agitating and heating device for steel melting processes
US2226967A (en) * 1939-08-11 1940-12-31 Edward J Chellus Production of stainless steels
US2291221A (en) * 1941-06-04 1942-07-28 Robert M Gibson Refining of metal
US2502259A (en) * 1946-12-12 1950-03-28 Air Reduction Method of eliminating carbon from and controlling the temperature of molten steel

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US193551A (en) * 1877-07-24 Improvement in the manufacture of iron and steel
US586047A (en) * 1897-07-06 Frank bernard last
US1541778A (en) * 1923-11-17 1925-06-16 Karl A Agricola Apparatus for refining metal
US1949731A (en) * 1930-11-29 1934-03-06 Soldatoff Vassily Vassily Agitating and heating device for steel melting processes
US2226967A (en) * 1939-08-11 1940-12-31 Edward J Chellus Production of stainless steels
US2291221A (en) * 1941-06-04 1942-07-28 Robert M Gibson Refining of metal
US2502259A (en) * 1946-12-12 1950-03-28 Air Reduction Method of eliminating carbon from and controlling the temperature of molten steel

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2878115A (en) * 1956-09-14 1959-03-17 United States Steel Corp Open-hearth steelmaking process
US2923615A (en) * 1957-03-28 1960-02-02 Pan American Petroleum Corp Process for obtaining metals from their ores
US3079452A (en) * 1958-07-07 1963-02-26 Electro Refractaire Manufacture of electrically-melted refractory products containing mineral oxides
US3212880A (en) * 1959-12-24 1965-10-19 Bot Brassert Oxygen Techik A G Method of carrying out metallurgical processes
US3194539A (en) * 1960-02-11 1965-07-13 Eugene Goffart & Cie Mixing apparatus
US3157489A (en) * 1961-03-09 1964-11-17 Pullman Inc Method for reducing metal oxides
US3157490A (en) * 1961-10-23 1964-11-17 Pullman Inc Method for refining of metals
US3859078A (en) * 1972-10-30 1975-01-07 Sydney Steel Corp Method of operating a basic open hearth furnace
US3960547A (en) * 1972-12-18 1976-06-01 Youngstown Sheet And Tube Company Steelmaking process
US4009023A (en) * 1973-02-15 1977-02-22 Uddeholms Aktiebolag Method for the refining of molten metal
US3898078A (en) * 1973-03-29 1975-08-05 Youngstown Sheet And Tube Co Method and apparatus for injecting refining oxygen in steelmaking processes
US3942978A (en) * 1973-11-28 1976-03-09 Uddeholms Aktiebolag Metallurgical method

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