CA1081968A - Method for melting steel - Google Patents

Method for melting steel

Info

Publication number
CA1081968A
CA1081968A CA223,556A CA223556A CA1081968A CA 1081968 A CA1081968 A CA 1081968A CA 223556 A CA223556 A CA 223556A CA 1081968 A CA1081968 A CA 1081968A
Authority
CA
Canada
Prior art keywords
furnace
slag
electrodes
vessel
steel
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
CA223,556A
Other languages
French (fr)
Inventor
Haye Roth
Gero Rath
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Mannesmann Demag AG
Original Assignee
Demag AG
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Demag AG filed Critical Demag AG
Application granted granted Critical
Publication of CA1081968A publication Critical patent/CA1081968A/en
Expired legal-status Critical Current

Links

Classifications

    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21CPROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C5/00Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
    • C21C5/52Manufacture of steel in electric furnaces
    • C21C5/5211Manufacture of steel in electric furnaces in an alternating current [AC] electric arc furnace
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21BMANUFACTURE OF IRON OR STEEL
    • C21B13/00Making spongy iron or liquid steel, by direct processes
    • C21B13/0046Making spongy iron or liquid steel, by direct processes making metallised agglomerates or iron oxide
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21BMANUFACTURE OF IRON OR STEEL
    • C21B13/00Making spongy iron or liquid steel, by direct processes
    • C21B13/12Making spongy iron or liquid steel, by direct processes in electric furnaces
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21CPROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C1/00Refining of pig-iron; Cast iron
    • C21C1/02Dephosphorising or desulfurising
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27FURNACES; KILNS; OVENS; RETORTS
    • F27BFURNACES, KILNS, OVENS, OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
    • F27B3/00Hearth-type furnaces, e.g. of reverberatory type; Tank furnaces
    • F27B3/02Hearth-type furnaces, e.g. of reverberatory type; Tank furnaces of single-chamber fixed-hearth type
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27FURNACES; KILNS; OVENS; RETORTS
    • F27BFURNACES, KILNS, OVENS, OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
    • F27B3/00Hearth-type furnaces, e.g. of reverberatory type; Tank furnaces
    • F27B3/08Hearth-type furnaces, e.g. of reverberatory type; Tank furnaces heated electrically, with or without any other source of heat
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27FURNACES; KILNS; OVENS; RETORTS
    • F27BFURNACES, KILNS, OVENS, OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
    • F27B3/00Hearth-type furnaces, e.g. of reverberatory type; Tank furnaces
    • F27B3/08Hearth-type furnaces, e.g. of reverberatory type; Tank furnaces heated electrically, with or without any other source of heat
    • F27B3/085Arc furnaces
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02PCLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00Technologies related to metal processing
    • Y02P10/20Recycling

Landscapes

  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Refinement Of Pig-Iron, Manufacture Of Cast Iron, And Steel Manufacture Other Than In Revolving Furnaces (AREA)
  • Vertical, Hearth, Or Arc Furnaces (AREA)
  • Treatment Of Steel In Its Molten State (AREA)

Abstract

ABSTRACT
It is known to melt steel in a closed electrical-resistance furnace, a layer of slag being used to cover the molten metal. In this invention, an oxidizing burden having a refining action is charged into the furnace, a deep bath of the molten steel is maintained in the furnace, the volume of the molten metal corresponding to between 5 hours and 2 days production, and a thick cover of slag is maintained covering the molten steel, the slag having a decarburizing, dephosphorizing, and desulphurizing effect, the thickness of the slag cover being between 250 and 1500 mm or corresponding to 1 to 10 days production. These measures permit the melting process to be carried out continuously, and the furnace can be heated con-tinuously by electrodes immersed in the slag.

Description

~8~g~ :
~he invention relates to a method for melting steel in a closed electrical-resistance furnace, a layer of slag being used to cover the molten metal.
~ow tnat the production of sponge iron has been develop-ed to the extent that large-scale production is possible, it is possible to make steel in an electrical-resistance furnace.
Because of its content of slag-forming substances, and its high porosity, sponge iron has a high electrical resistance. This makes it possible to use large amounts of electrical power in the ~urnace and, at the same time, to obtain satisfactory distribution of power.
In steel production, metallurgical treatments are being carried out to an increasing degree outside the furnace. These traatments are carried out on the steel upon tapping and in the ladle which accepts the steel emerging from the furnace, it being possible to subject the ladle to vacuum for the purpose of obtain-ing specific qualities in the steel. It is also desirable, or :
necessary, in many cases to carry out further processing in other furnace groups, e.g. in an induction channel-urnace.
If, however, the electrical-resistance furnace is batch-operated, the analysis of the steel is subject to certain fluc-tuations from one batch to the next, since the composition of the burden also alters unavoidably. In batch-operation, therefore, the course of the metallurgical process, which is largely dependent upon the carbon, sulphur, and phosphorus content of the burden, undergoes corresponding fluctuations.
It is thérefore the purpose of the invention to provide an improved method for melting steel in a closed electrical-resistance furnace. It is also sought to provide for the furnace ~08~9~
operation to be continuous, so that the s-teel produced is of substantially constant quality.
According to the present invention, in a method of continuously producing steel in a closed electrical-resistance furnace, in which an iron-bearing oxidizing burden having a refining action is charged into the furnace, a deep bath of the molten steel is maintained in the furnace, the volume of the molten metal corresponding to between 5 hours and 2 days production, and a thick cover of slag is maintained covering the molten steel, the slag having a decarburizing, dephosphoriæing, and desulphurizing effect, the thickness of the slag cover being between 250 and 1500 mm or corresponding to 1 to 10 days production, the furnace being heated continuously by electrodes immersed in the slag to bring said slag to a temperature in excess of the temperature at which the molten steel in the furnace is tapped.
The above-mentioned measures make it possible to operate an electrical-resistance furnace continuously, The FeO content in the slag required for decarburizing is obtained, when sponge iron is used, by adding iron ores to the charge or, if pre-reduced ores or agglomerates are used, by adjusting the degree of pre-reduction. This also produces steel of a constant composition, since differences in the composition of the burden charged into the furnace are compensated for by maintaining a thick covering of slag and ;
a large bath of metal. Continuous operation, as made possible ~ ;
by the method according to the invention, results in a substantially longer life for the furnace lining, in comparison with intermittent operation, since it eliminates the alternating heat stresses occurring, during intermittent operation, between the melting and charging operations. Continuous operation also eliminates sharp fluctuations in the load on the power supply.
- 2 -: ., -: , . ,. .-: . : , ' '" ' ': ~ :' ~1819~;~

Environmental pollution, as compared with smelting steel in an arc furnace, is reduced because vapourization of metal on so-calle~ ~Iburning areas~ is largely eliminated, and this results in a sharp decrease in the volume of stack gas.
One particular advantage of the method according to the invention is that or approximately the same investment costs per ton/year, there is a sharp reduction in furnace-lining costs, as compared with batch operation, since the high thermal stresses on the roof and walls of the furnace, arising during conventional furnace operation, are subRtantially reduced as a result of the reduction in radiation from the electrodes which are immersed in the layer of slag and covered by the burden lying on the bath of metal. Destruction of the brickwork by temperature fluctuations, which is unavoidable in batch-operation, is eliminated by the substantially uni~orm temperature obtaining in the furnace. Since radiation losses during the melting period are eliminated by immersing the electrodes in the ~hick layer of slag, and since radiation losses during the unavoidable dead periods arising in batch-operation are also eliminated, the power consumed by the method according to the invention per ton o~ Einished product is less than that consumed by existing methods. According to a conservative eskimate, the power consumption, which has hitherto ;
been 600 kWh/t of steel, would appear to drop to about 540 kWh/t of steel, i.e. by about l~/o.
Since continuous operatio~ resulks in a more uniform ~ ~
load on the source o-f power, it is possible in most cases to ;
obtain electric power at a lower price, where power is obtained from the outside. Experience shows that rates for an electrical-resistance furnace may be up to 3~/O lower than ~or an arc furnace.
- 3 -10819~

The reason for this is that there are no peak loads, high utiliza-tion gives continuous power consumption, and the operation of the Eurnace is better adapted to the power supply.
Continuous operation also has a favourable effect on subsequent processing equipment, such as -Eor example a continuous casting unit, since the operation o-f such a unit is no longer dependent upon the intermittent operation of a conventional urnace.
As a result of the thick layer o slag covering the bath of metal, the steel picks up less nitrogen from the air, and this is another advantage of the method according to the invention.
The method according to the invention also makes it possible to use pellets of an inferior quality than heretofore, since the necessary slag work can be carried out even when a large amount of slag is present.
Advantageously in the method of the invention, cooling of the furnace is increased in the vicinity of the slag level.
This results in a considerable decrease in slag attack on the brickwork in this particularly highly-stressed area of the furnace, since the said brickwork is protected by the cooled slag.
The method according to the invention also makes it possible to charge some of the burden into the furnace through ;
hollow electrodes and, if necessary, to feed in an oxygen-contain-ing gas or, under certain circumstances, pure oxygen, thus influencing the refining effect.
In producing tonnage steel, the method according to the ;
invention makes it possible to add the alloying substances outside the furnace, in a ladle. In producing special steels, use may be made of separate refining and alloying units.
The invention also relates to a device for carrying out :
..

10~
the method explained above, provision being made, in the case of a closed electrical-resistance furnace, for the said furnace to be equipped wi-th at least one tap for liquid metal and one tap for slag, with the said taps being located at different levels, and for the said furnace to be equipped, in the vicinity of the slag level, with a device providing increased cooling in that area, as compared with other areas.
The accompanying drawings shows a diagrammatic representation of a furnace for carrying out the method according to the invention.
In the drawing, a vessel 1 of an electrical-resistance furnace has a furnace cover 2. Soderberg electrodes 3a, 3b extend into the furnace vessel 1. As compared with the graphite electrodes used in arc furnaces, which for production and load-carrying reasons cannot be more than 600 - 700 mm in diameter at the most, Soderberg electrodes are less expensive and, since they are not limited as to diameter, may have a diameter of 2000 mm. Arranged between the said electrodes are charging pipes 4a, b, c and 5a, b, c communicating with bunkers 7 located above the furn~ce. A crude-gas line 6 is also provided. A retaining device 8 for electrodes 3a, b is arranged on a supporting structure 9 above the furnace.
The burden within the furnace is marked 10.12 is the molten steel at the bottom of furnace vessel 1, the molten metal being covered by a thick layer 11 of slag. The depth of the bath of molten steel will depend upon the diameter of the vessel 1, typically ranging from 200 mm in the case of a small furnace to 1500 mm in the case of a large furnace. ~ ~`
The volume of molten steel will generally correspond to between 5 hours and 2 days production, while the volume of slag will correspond to between 1 and 10 days production.
The said furnace vessel is provided with additional cooling in the vicinity of the slag level as indicated at 20, it also _ 5 _ )~ ~

9~8 has two tap-holes 13, 14 arranged one above the other, upper hole 13 being intended for slag and lower hole 14 for steel.
When the measures according to the invention are used, refining is achieved by means of a burden which ensures a constant ................................................

' ~

?

, ~ ,;

' - 5a - :

i8 FeO content oE between 15 and l~/o in the slag~ This is in accord-ance with standard slagging practice in electric-steel plants.
~ he layer of slag, which is maintained at all times and in which the electrodes are immersed without touching the bath of metal, has two purposes. Firstly~ heat is transferred by convection from the slag to the bath of metal. The thick layer of slag, which is maintained by arranging the slag tap-hole 13 at an appropriate height above the steel tap-hole 14, ensures not only a large heat potential, but also satisfactory heat distribution. Secondly, the thick layer o slag produces satisfactory desulphurizing and de- `
phosphorizing, since, in addition to the normal boundary-surface reaction between the bath of metal and the layer of slag, pre-dephosphorizing and pre-desulphurizing occurs as molten droplets of iron on the layer of slag, and the pellets initially floating thereon, descend through the layer of slag. The refining reaction is improved accordingly.
The large specific surace of the metal droplets produces - -an extremely satisfactory reaction. Since heat is transferred from the slag, which is heated by the immersed electrodes, to the bath 20 of metal, and takes place entirely by convection, the temperature of the slag must be slightly higher than the tapping temperature ~ ~
of the metal. For instance, if a steel tapping temperature of 1650 -is required (with subsequent argon flushing), the slag temperature must be 1670C. To this end, slags with a melting temperature of about 1620& are required, and these are superheated by about 50C.
The composition o a slag of this kind may be, for example, 15%
Feo, 2~/o sio2, and 65% CaO.
The large bath of metal equalizes the analyses, which otherwise tend to fluctuate, especially as regards the phosphorus and sulphur contents.

Claims (8)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS.
1. A method for continuously producing steel in a closed electrical-resistance furnace, in which an iron-bearing oxidizing burden having a refining action is charged into the furnace, wherein a deep bath of the molten steel is maintained in the furnace, the volume of the molten metal corresponding to between 5 hours and 2 days production, and a thick cover of slag is maintained covering the molten steel, the slag having a decarburizing, dephosphorizing, and desulphurizing effect, the thickness of the slag cover being between 250 and 1500 mm or corresponding to 1 to 10 days production, the furnace being heated continuously by electrodes immersed in the slag to bring said slag to a temperature in excess of the temperature at which the molten steel in the furnace is tapped.
2. A method according to claim 1 wherein the oxidizing burden comprises sponge iron and iron ore, pre-reduced iron ore or iron ore agglomerates.
3. A method according to claim 1 in which the furnace is cooled adjacent the slag level to a greater extent as compared with other areas of the furnace.
4. A method according to claim 1, in which the electrodes are hollow and an oxygen-containing gas or oxygen is fed in through the hollow electrodes.
5. A method according to claim 4, in which part of the burden is fed in through the hollow electrodes.
6. A furnace for carrying out the method of claim 1 comprising a closed furnace vessel, electrodes within said vessel for electrical resistance heating of material within the vessel, at least one tap-hole in the vessel for liquid metal and one tap-hole for slag, the said tap-holes being arranged at different levels;

and the vessel being provided adjacent the slag level with a device providing increased cooling, as compared with other areas of the vessel.
7. A furnace according to claim 6, in which the electrodes are hollow.
8. A furnace according to claim 7, in which the hollow electrodes are connected to a device which supplies oxygen or an oxygen-containing gas.
CA223,556A 1974-04-02 1975-04-01 Method for melting steel Expired CA1081968A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE2415967A DE2415967A1 (en) 1974-04-02 1974-04-02 METHOD OF MELTING STEEL
DEP2415967.9 1974-04-02

Publications (1)

Publication Number Publication Date
CA1081968A true CA1081968A (en) 1980-07-22

Family

ID=5911947

Family Applications (1)

Application Number Title Priority Date Filing Date
CA223,556A Expired CA1081968A (en) 1974-04-02 1975-04-01 Method for melting steel

Country Status (9)

Country Link
JP (1) JPS50134912A (en)
CA (1) CA1081968A (en)
DE (1) DE2415967A1 (en)
ES (1) ES436098A1 (en)
FR (1) FR2265864B3 (en)
GB (1) GB1502992A (en)
IT (1) IT1034650B (en)
NO (1) NO751095L (en)
ZA (1) ZA752046B (en)

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2608320C2 (en) * 1976-02-28 1978-12-07 Demag Ag METHOD FOR CONTINUOUSLY MELTING STEEL WITH A HIGH Purity
ZA935072B (en) * 1992-08-11 1994-02-07 Mintek The production of high titania slag from ilmenite
WO2002070760A1 (en) * 2001-03-05 2002-09-12 Anglo Operations Limited A furnace and a method of controlling a furnace
US6689182B2 (en) * 2001-10-01 2004-02-10 Kobe Steel, Ltd. Method and device for producing molten iron
JP5166805B2 (en) 2007-09-19 2013-03-21 株式会社神戸製鋼所 Method for producing molten iron by arc heating

Also Published As

Publication number Publication date
ES436098A1 (en) 1977-01-01
ZA752046B (en) 1976-03-31
DE2415967A1 (en) 1975-10-09
GB1502992A (en) 1978-03-08
FR2265864B3 (en) 1977-12-16
IT1034650B (en) 1979-10-10
NO751095L (en) 1975-10-03
JPS50134912A (en) 1975-10-25
FR2265864A1 (en) 1975-10-24

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