EP0166868B1 - Method of and installation for metallurgical after-treatment of premelted steel - Google Patents

Method of and installation for metallurgical after-treatment of premelted steel Download PDF

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Publication number
EP0166868B1
EP0166868B1 EP85103726A EP85103726A EP0166868B1 EP 0166868 B1 EP0166868 B1 EP 0166868B1 EP 85103726 A EP85103726 A EP 85103726A EP 85103726 A EP85103726 A EP 85103726A EP 0166868 B1 EP0166868 B1 EP 0166868B1
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EP
European Patent Office
Prior art keywords
electrodes
steel
melt
carbon
premelted
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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
EP85103726A
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German (de)
French (fr)
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EP0166868A2 (en
EP0166868A3 (en
Inventor
Karl-Heinz Dipl.-Ing. Heinen
Wolfgang Dr.-Ing. Glitscher
Heinz Dipl.-Ing. Zörcher
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Krupp Hoesch Stahl AG
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Krupp Stahl AG
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Publication date
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Publication of EP0166868A2 publication Critical patent/EP0166868A2/en
Publication of EP0166868A3 publication Critical patent/EP0166868A3/en
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Publication of EP0166868B1 publication Critical patent/EP0166868B1/en
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D1/00—Treatment of fused masses in the ladle or the supply runners before casting
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/10—Supplying or treating molten metal
    • B22D11/11—Treating the molten metal
    • 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
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/0075—Treating in a ladle furnace, e.g. up-/reheating of molten steel within the ladle

Definitions

  • the invention relates to a device for the metallurgical aftertreatment of premelted steel according to the preamble of claim 1 and to a method according to the preamble of claim 6.
  • the aftertreatment pan is provided with a pan heating device, usually in the form of an arc heater.
  • a pan heating device usually in the form of an arc heater.
  • the molten steel can be heated via the resulting electric arc via one or more electrodes (usually operated with alternating current) which are suspended on support arms and guided through the cover in electrode guides.
  • the electric arc heating can take place both under atmospheric pressure - a sealing of the pan against the lid is not necessary - and under vacuum, the pan being sealed in a vacuum-tight manner from the atmosphere and the electrodes being led through the lid via vacuum seals.
  • Round graphite electrodes are used as electrodes according to the prior art, which can be loaded with high currents and generate an easily controllable arc. Depending on the pan size and the desired heating output, they have a diameter of 300 to 500 mm.
  • the electrodes are consumed by oxidation with the atmosphere during operation.
  • the electrode consumption is approx. 0.5 kg / t of treated steel.
  • - DM / kg electrode this corresponds to costs of approx. 150,000, - DM with a monthly post-treatment of approx. 50,000 tons of steel.
  • the present invention therefore proposes to provide a device for metallurgical aftertreatment of the type mentioned at the beginning with electrodes made from steel strands.
  • the electrodes advantageously consist of billets cast in the strand, which have a composition corresponding to the analysis of the molten metal intended for aftertreatment.
  • the casting structure of these continuous casting billets - in particular of steel billets with a dendritic solidification structure in the core - permits high current loads on such a metal electrode with a high current density, but without the electrodes melting quickly.
  • the burn-off of an electrode made of a continuous cast billet of steel quality 42 Cr Mo 4 with a square cross section of 175 x 175 mm at a load of 40,000 amps and 250 volts for a period of 10 minutes is only approx. 0.5 m, corresponding to a melting weight of 120 kg.
  • a total of 360 kg which is added to the weight of the steel melt to be treated as additional metal.
  • the melted material of the continuous cast billet electrode is therefore not lost, but rather increases the output of the post-treated steel melt. Because of the very low electrode burn-up in relation to the total weight of the molten steel, there is generally no need to consider a different steel quality between the electrode and the melt, since the possibilities of analysis deviations are negligible.
  • the electrodes choose a steel composition that corresponds to the analysis of the post-treated metal.
  • Remnants of continuous casting billets or remnants of continuous casting base material are preferably used as metal electrodes. If these remaining pieces are not of sufficient length for clamping as an electrode, they can easily be welded together to form a longer piece before being used as an electrode.
  • the invention is particularly suitable for the production of low-carbon steels or for the production of steel grades with a narrowly defined carbon content.
  • the inventive method according to claim 6 is advantageously carried out with electrodes made of continuously cast steel billets.
  • Fig. 1 a pan aftertreatment system is shown schematically.
  • the pan 1 consists of a cylindrical pan 1, which contains liquid metal 2.
  • the molten metal is stirred over a bottom blowing stone 3.
  • the pan 1 is closed with a lid 4 through which three electrodes 51, 52 and 53 are passed. The electrode tips reach close to the surface of the molten metal and heat the molten metal there via the electric arc.
  • the electrodes consist of steel strands, preferably of continuous casting billets or round casting material, which have a composition corresponding to the analysis of the molten metal.

Description

Die Erfindung bezieht sich auf eine Vorrichtung zur metallurgischen Nachbehandlung von vorgeschmolzenem Stahl gemäß dem Oberbegriff des Anspruchs 1 und auf ein Verfahren gemäß dem Oberbegriff des Patentanspruchs 6.The invention relates to a device for the metallurgical aftertreatment of premelted steel according to the preamble of claim 1 and to a method according to the preamble of claim 6.

Vorrichtungen dieser Art gehören seit langem zum Stand der Technik (so z. B. GB-Z Steel Times, Febr. 1978, Seiten 205-211).Devices of this type have long been state of the art (e.g. GB-Z Steel Times, Feb. 1978, pages 205-211).

Sie sind aus dem Wunsch heraus entwickelt worden, beim Schmelzen von Metallen weitgehend alle metallurgische Arbeit aus dem eigentlichen Schmelzaggregat in ein nachgeschaltetes Behandlungsgefäß zu verlagern. Im Schmelzaggregat soll nur noch eingeschmolzen werden. Dadurch erzielt man insbesondere bei Elektrostahlwerken zum Schmelzen von Stahl beträchtliche Ofenzeitverkürzungen und damit eine erhöhte Leistung.They were developed out of the desire to transfer all metallurgical work from the actual melting unit into a downstream treatment vessel when melting metals. The melting unit should only be melted down. As a result, considerable furnace time reductions and thus increased performance are achieved, in particular in electrical steelworks for melting steel.

Dies führt zu der sog. Pfannenmetallurgie, im angelsächsischen Schrifttum als secondary steelmaking bezeichnet, bei der das Metall aus dem Vorschmelzaggregat in eine Pfanne abgestochen und in dieser nachbehandelt wird.This leads to the so-called ladle metallurgy, referred to in the Anglo-Saxon literature as secondary steelmaking, in which the metal is tapped from the premelting unit into a pan and aftertreated in it.

Bei der Erzeugung von Stahl sind Hauptaufgaben der Nachbehandlung

  • - Auflegieren des Stahles
  • - Einstellung exakter Analysen
  • - Analysen- und Temperaturhomogenität in der Pfanne.
The main tasks in post-treatment are the production of steel
  • - alloying of the steel
  • - Setting exact analyzes
  • - Analysis and temperature homogeneity in the pan.

Um die während der Behandlung unvermeidlichen Temperaturverluste in der Pfanne - inbesondere bedingt durch die Zugabe fester Legierungsmetalle und das Spülen der Stahlschmelze mittels über Bodenblassteine eingeleiteter Inertgase - zu kompensieren, ist die Nachbehandlungspfanne mit einer Pfannenaufheizeinrichtung versehen, meistens in Form einer Lichtbogenheizung. Bei einer derartigen Heizung befindet sich über der Pfanne ein Deckel ähnlich dem eines Lichtbogenofens. Über ein oder mehrere an Tragarmen aufgehängte und in Elektrodenführungen durch den Deckel geführte Elektroden (meist wechselstrombetrieben) kann die Stahlschmelze über den entstehenden elektrischen Lichtbogen aufgeheizt werden. Das elektrische Lichtbogenheizen kann sowohl unter Atmosphärendruck - wobei eine Abdichtung der Pfanne gegen den Deckel nicht erforderlich ist - als auch unter Vakuum stattfinden, wobei die Pfanne gegenüber der Atmosphäre vakuumdicht verschlossen ist und die Elektroden über Vakuumdichtungen durch den Deckel geführt sind.In order to compensate for the temperature losses in the pan that are unavoidable during the treatment - in particular due to the addition of solid alloy metals and the purging of the molten steel using inert gases introduced via bottom blowing stones - the aftertreatment pan is provided with a pan heating device, usually in the form of an arc heater. With such a heater, there is a lid over the pan similar to that of an electric arc furnace. The molten steel can be heated via the resulting electric arc via one or more electrodes (usually operated with alternating current) which are suspended on support arms and guided through the cover in electrode guides. The electric arc heating can take place both under atmospheric pressure - a sealing of the pan against the lid is not necessary - and under vacuum, the pan being sealed in a vacuum-tight manner from the atmosphere and the electrodes being led through the lid via vacuum seals.

Als Elektroden nach dem Stand der Technik werden runde Grafitelektroden verwendet, die mit hohen Stromstärken belastet werden können und einen gut regelbaren Lichtbogen erzeugen. Je nach Pfannengröße und gewünschter Heizleistung weisen sie einen Durchmesser von 300 bis 500 mm auf.Round graphite electrodes are used as electrodes according to the prior art, which can be loaded with high currents and generate an easily controllable arc. Depending on the pan size and the desired heating output, they have a diameter of 300 to 500 mm.

Die Elektroden verbrauchen sich jedoch während des Betriebes durch Oxydation mit der Atmosphäre. So liegt bei einer mit drei wechselstrombetriebenen 450 mm-Elektroden bestückten Pfannenheizanlage der Elektrodenverbrauch bei ca. 0,5 kg/to behandelten Stahles. Dies entspricht bei einem Preis von ca. 6, - DM/kg Elektrode Kosten von ca. 150.000, - DM bei einer monatlichen Nachbehandlung von ca. 50.000 to Stahl.However, the electrodes are consumed by oxidation with the atmosphere during operation. In a ladle heating system equipped with three AC-operated 450 mm electrodes, the electrode consumption is approx. 0.5 kg / t of treated steel. At a price of approx. 6, - DM / kg electrode, this corresponds to costs of approx. 150,000, - DM with a monthly post-treatment of approx. 50,000 tons of steel.

Abgesehen von diesen Kosten ist der Einsatz von Grafitelektroden bei der Nachbehandlung von Stählen mit niedrigsten Kohlenstoffgehalten (0,02 % C) bzw. von Stählen mit einem engen, den Kohlenstoffgehalt betreffenden Analysenbereich nicht möglich.Apart from these costs, it is not possible to use graphite electrodes in the aftertreatment of steels with the lowest carbon content (0.02% C) or steels with a narrow analysis range that affects the carbon content.

Das zur Homogenisierung der Stahlschmelze - insbesondere nach einer Legierungszugabe - durch Bodenblassteine in die Schmelze eingeleitete inerte Spülgas bringt die Schmelze derart in Wallung, daß die normalerweise dicht über der Schmelzoberfläche « brennenden » Elektroden mit der Schmelze in Berührung kommen und aus dem Grafitmaterial der Elektroden derartig viel Kohlenstoff in die Schmelze gelangt, daß die vorgeschriebenen niedrigen bzw. eng bestimmten Kohlenstoffgehalte überschritten werden und der Stahl somit für den vorgesehenen Verwendungszweck nicht mehr brauchbar ist. Zur Vermeidung der oben angeführten Nachteile schlägt die vorliegende Erfindung daher vor, eine Vorrichtung zur metallurgischen Nachbehandlung der eingangs genannten Art mit Elektroden aus Stahlsträngen zu versehen. Vorteilhafterweise bestehen die Elektroden dabei aus im Strang gegossenen Knüppeln, die eine der Analyse der zur Nachbehandlung vorgesehenen Metallschmelze entsprechende Zusammensetzung aufweisen. Das Gußgefüge dieser Stranggußknüppel - insbesondere von Knüppeln aus Stahl mit im Kern dendritischen Erstarrungsgefüge - erlaubt hohe Strombelastungen einer solchen Metallelektrode bei hoher Stromdichte, ohne daß jedoch die Elektroden schnell abschmelzen.The inert purging gas introduced into the melt by bottom blowing stones to homogenize the steel melt - especially after adding an alloy - sets the melt in such a way that the electrodes, which normally "burn" closely above the melt surface, come into contact with the melt and from the graphite material of the electrodes in such a way Much carbon gets into the melt that the prescribed low or narrowly determined carbon contents are exceeded and the steel is therefore no longer usable for the intended use. To avoid the disadvantages mentioned above, the present invention therefore proposes to provide a device for metallurgical aftertreatment of the type mentioned at the beginning with electrodes made from steel strands. The electrodes advantageously consist of billets cast in the strand, which have a composition corresponding to the analysis of the molten metal intended for aftertreatment. The casting structure of these continuous casting billets - in particular of steel billets with a dendritic solidification structure in the core - permits high current loads on such a metal electrode with a high current density, but without the electrodes melting quickly.

So beträgt der Abbrand bei einer Elektrode aus einem Stranggußknüppel der Stahlqualität 42 Cr Mo 4 mit einem quadratischen Querschnitt von 175 x 175 mm bei einer Belastung von 40 000 Amp und 250 Volt während einer Zeit von 10 Min. nur ca. 0,5 m, entsprechend einem Abschmelzgewicht von 120 kg. Bei drei Elektroden, angeschlossen an 3-Phasen-Wechselstrom, somit insgesamt 360 kg, die als zusätzliches Metall in das Gewicht der nachzubehandelnden Stahlschmelze eingehen. Das abgeschmolzene Material der Stranggußknüppel-Elektrode ist somit nicht verloren, sondern erhöht das Ausbringen der nachbehandelten Stahlschmelze. Wegen des im Verhältnis zum Gesamtgewicht der Stahlschmelze nur sehr geringen Elektrodenabbrandes braucht im allgemeinen auf eine unterschiedliche Stahlqualität Elektrode/ Schmelze keine Rücksicht genommen werden, da die Möglichkeiten von Analysenabweichungen verschwindend gering sind.For example, the burn-off of an electrode made of a continuous cast billet of steel quality 42 Cr Mo 4 with a square cross section of 175 x 175 mm at a load of 40,000 amps and 250 volts for a period of 10 minutes is only approx. 0.5 m, corresponding to a melting weight of 120 kg. With three electrodes, connected to 3-phase alternating current, a total of 360 kg, which is added to the weight of the steel melt to be treated as additional metal. The melted material of the continuous cast billet electrode is therefore not lost, but rather increases the output of the post-treated steel melt. Because of the very low electrode burn-up in relation to the total weight of the molten steel, there is generally no need to consider a different steel quality between the electrode and the melt, since the possibilities of analysis deviations are negligible.

Bei Qualitäten mit höchster Analysengenauigkeit empfiehlt es sich jedoch, für die Elektroden eine Stahlzusammensetzung zu wählen, die der Analyse des nachbehandelten Metalls entspricht.For qualities with the highest analysis accuracy, however, it is recommended for the electrodes choose a steel composition that corresponds to the analysis of the post-treated metal.

Als Metallelektroden werden vorzugsweise Reste von Stranggußknüppeln bzw. Reste von Stranggußrundmaterial eingesetzt. Sofern diese Reststücke eine für die Einspannung als Elektrode nicht ausreichende Länge aufweisen, können sie vor Einsatz als Elektrode leicht zu einem längeren Stück zusammengeschweißt werden.Remnants of continuous casting billets or remnants of continuous casting base material are preferably used as metal electrodes. If these remaining pieces are not of sufficient length for clamping as an electrode, they can easily be welded together to form a longer piece before being used as an electrode.

Die Erfindung eignet sich besonders zur Herstellung kohlenstoffarmer Stähle bzw. zur Herstellung von Stahlqualitäten mit eng definiertem Kohlenstoffgehalt. Das erfindungsgemäße Verfahren nach Patentanspruch 6 wird vorteilhaft mit Elektroden aus stranggegossenen Stahlknüppeln durchgeführt.The invention is particularly suitable for the production of low-carbon steels or for the production of steel grades with a narrowly defined carbon content. The inventive method according to claim 6 is advantageously carried out with electrodes made of continuously cast steel billets.

Es ist nicht in jedem Fall erforderlich, auf niedrige Kohlenstoffgehalte in den Elektroden zu achten, sie sollten aber unter 0,5 % Kohlenstoff, vorzugsweise unter 0,2% Kohlenstoff liegen. Die Abschmelzrate ist nämlich überraschend gering, wie Versuche gezeigt haben.It is not always necessary to pay attention to low carbon contents in the electrodes, but they should be below 0.5% carbon, preferably below 0.2% carbon. The melting rate is surprisingly low, as tests have shown.

In Fig. 1 ist schematisch eine Pfannennachbehandlungsanlage dargestellt.In Fig. 1 a pan aftertreatment system is shown schematically.

Sie besteht aus einer zylindrischen Pfanne 1, die flüssiges Metall 2 enthält. Über einen Bodenblasstein 3 wird die Metallschmelze umgerührt. Die Pfanne 1 ist mit einem Deckel 4 verschlossen, durch den drei Elektroden 51, 52, und 53, hindurchgeführt sind. Die Elektrodenspitzen reichen bis nahe an die Oberfläche der Metallschmelze und heizen dort über den elektrischen Lichtbogen die Metallschmelze auf.It consists of a cylindrical pan 1, which contains liquid metal 2. The molten metal is stirred over a bottom blowing stone 3. The pan 1 is closed with a lid 4 through which three electrodes 51, 52 and 53 are passed. The electrode tips reach close to the surface of the molten metal and heat the molten metal there via the electric arc.

Die Elektroden bestehen erfindungsgemäß aus Stahlsträngen, vorzugsweise aus Stranggußknüppein bzw. Stranggußrundmaterial, die eine der Analyse der Metallschmelze entsprechende Zusammensetzung aufweisen.According to the invention, the electrodes consist of steel strands, preferably of continuous casting billets or round casting material, which have a composition corresponding to the analysis of the molten metal.

Claims (6)

1. Apparatus for the metallurgical after-treatment of premelted steel, consisting of a cylindrical ladle accomodating the melt and closed by the lid and one or more electrodes passing through said lid for reheating the melt by an electric arc, characterised in that the electrodes (51, 52, 53) consist of steel castings.
2. Apparatus according to Claim 1, characterised in that the electrodes (51, 52, 53) consist of continuously cast steel billets.
3. Apparatus according to one of Claims 1 and 2, characterised in that such electrodes are employed which have a composition corresponding to that of the metallic melt.
4. Apparatus according to one of Claims 1 to 3, characterised in that the electrodes (51, 52, 53) have a square cross-section of 120 to 200 mm lateral length.
5. Apparatus according to one of Claims 1 to 3, characterised in that the electrodes (51, 52, 53) have a circular cross-section with diamaters of 120 to 200 mm.
6. Process for producing steels with carbon contents below 0.02 % or steels having narrow carbon tolerances, in which the steel is premelted in a smelting unit and is subsequently alloyed, stirred and homogenised in a secondary treatment unit, said melt being reheated by electric arcs between the melt and electrodes, characterised in that the predetermined carbon content is established within the smelting unit and is maintained in the secondary treatment unit by employing electrodes consisting of low-carbon steel for generating the said electric arcs.
EP85103726A 1984-07-04 1985-03-28 Method of and installation for metallurgical after-treatment of premelted steel Expired EP0166868B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE3424510 1984-07-04
DE19843424510 DE3424510A1 (en) 1984-07-04 1984-07-04 DEVICE AND METHOD FOR METALLURGICAL TREATMENT OF PRE-MELTED METALS

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EP0166868A2 EP0166868A2 (en) 1986-01-08
EP0166868A3 EP0166868A3 (en) 1986-10-08
EP0166868B1 true EP0166868B1 (en) 1988-03-02

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EP85103726A Expired EP0166868B1 (en) 1984-07-04 1985-03-28 Method of and installation for metallurgical after-treatment of premelted steel

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US (1) US4604135A (en)
EP (1) EP0166868B1 (en)
JP (1) JPS6119722A (en)
DE (2) DE3424510A1 (en)

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3612174A1 (en) * 1986-04-11 1987-10-15 Krupp Stahl Ag Method and apparatus for lengthening steel heating electrodes of an aftertreatment plant for molten steel
US6751986B2 (en) 2000-12-22 2004-06-22 The Bog Group, Inc. Structured packing
JP7139876B2 (en) * 2018-10-25 2022-09-21 日本製鉄株式会社 Ladle refining method for molten steel
JP7139878B2 (en) * 2018-10-26 2022-09-21 日本製鉄株式会社 Ladle refining method for molten steel
JP7139877B2 (en) * 2018-10-26 2022-09-21 日本製鉄株式会社 Ladle refining method for molten steel
DE102020005129A1 (en) 2020-08-21 2022-02-24 Technische Universität Bergakademie Freiberg, Körperschaft des öffentlichen Rechts Low-carbon and carbon-free electrodes for use in steel metallurgy

Family Cites Families (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AT295060B (en) * 1969-07-21 1971-12-27 Boehler & Co Ag Geb Device for electroslag remelting of metals, in particular steels
US3826646A (en) * 1969-10-13 1974-07-30 G Karlsson Method for treating melts and means for carrying out this treatment
US4090054A (en) * 1976-10-12 1978-05-16 Brown Boveri Corporation Electrical preheating apparatus
JPS5611133A (en) * 1979-07-11 1981-02-04 Kawasaki Steel Corp Arc-type heating apparatus for molten steel contained in ladle
BG35678A1 (en) * 1981-12-01 1984-06-15 Savov Method and device for treating and refining liquid alloys
LU84133A1 (en) * 1982-05-07 1984-03-07 Arbed METHOD AND DEVICE FOR METALLURGIC TREATING OF LIQUID METALS

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Publication number Publication date
DE3424510A1 (en) 1986-01-09
JPH0142322B2 (en) 1989-09-12
DE3561690D1 (en) 1988-04-07
EP0166868A2 (en) 1986-01-08
EP0166868A3 (en) 1986-10-08
JPS6119722A (en) 1986-01-28
US4604135A (en) 1986-08-05

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