EP1816219A1 - Process for the heat treatment of metal strips by direct flame impingement - Google Patents

Process for the heat treatment of metal strips by direct flame impingement Download PDF

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Publication number
EP1816219A1
EP1816219A1 EP06007147A EP06007147A EP1816219A1 EP 1816219 A1 EP1816219 A1 EP 1816219A1 EP 06007147 A EP06007147 A EP 06007147A EP 06007147 A EP06007147 A EP 06007147A EP 1816219 A1 EP1816219 A1 EP 1816219A1
Authority
EP
European Patent Office
Prior art keywords
product
temperature
booster
zone
burner
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.)
Withdrawn
Application number
EP06007147A
Other languages
German (de)
French (fr)
Inventor
Herbert Eichelkrauth
Hans-Joachim Heiler
Werner Högner
Fred Jindra
Reinhard Paul
Ola Ritzén
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.)
Linde GmbH
ThyssenKrupp Steel Europe AG
Original Assignee
Linde GmbH
ThyssenKrupp Steel 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 Linde GmbH, ThyssenKrupp Steel AG filed Critical Linde GmbH
Priority to BRPI0707378-0A priority Critical patent/BRPI0707378B1/en
Priority to US12/162,641 priority patent/US9322598B2/en
Priority to CA2637847A priority patent/CA2637847C/en
Priority to JP2008552706A priority patent/JP5268650B2/en
Priority to EP07702696A priority patent/EP1979495B1/en
Priority to PL07702696T priority patent/PL1979495T3/en
Priority to PCT/EP2007/000219 priority patent/WO2007087973A2/en
Priority to RU2008135237/02A priority patent/RU2435869C2/en
Priority to CN200780004421XA priority patent/CN101448963B/en
Priority to KR1020087020692A priority patent/KR20080109737A/en
Priority to AT07702696T priority patent/ATE516372T1/en
Publication of EP1816219A1 publication Critical patent/EP1816219A1/en
Withdrawn legal-status Critical Current

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS, OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
    • F27D19/00—Arrangements of controlling devices
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/34—Methods of heating
    • C21D1/52—Methods of heating with flames
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D11/00—Process control or regulation for heat treatments
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
    • C21D9/54—Furnaces for treating strips or wire
    • C21D9/56—Continuous furnaces for strip or wire
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
    • C21D9/54—Furnaces for treating strips or wire
    • C21D9/56—Continuous furnaces for strip or wire
    • C21D9/561—Continuous furnaces for strip or wire with a controlled atmosphere or vacuum
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27B—FURNACES, KILNS, OVENS, OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
    • F27B9/00—Furnaces through which the charge is moved mechanically, e.g. of tunnel type; Similar furnaces in which the charge moves by gravity
    • F27B9/12—Furnaces through which the charge is moved mechanically, e.g. of tunnel type; Similar furnaces in which the charge moves by gravity with special arrangements for preheating or cooling the charge
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27B—FURNACES, KILNS, OVENS, OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
    • F27B9/00—Furnaces through which the charge is moved mechanically, e.g. of tunnel type; Similar furnaces in which the charge moves by gravity
    • F27B9/30—Details, accessories, or equipment peculiar to furnaces of these types
    • F27B9/36—Arrangements of heating devices
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
    • C21D9/54—Furnaces for treating strips or wire
    • C21D9/56—Continuous furnaces for strip or wire
    • C21D9/63—Continuous furnaces for strip or wire the strip being supported by a cushion of gas
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS, OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
    • F27D19/00—Arrangements of controlling devices
    • F27D2019/0028—Regulation
    • F27D2019/0034—Regulation through control of a heating quantity such as fuel, oxidant or intensity of current
    • F27D2019/004—Fuel quantity
    • F27D2019/0043—Amount of air or O2 to the burner
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS, OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
    • F27D99/00—Subject matter not provided for in other groups of this subclass
    • F27D99/0001—Heating elements or systems
    • F27D99/0033—Heating elements or systems using burners

Definitions

  • the invention relates to a method for the heat treatment of products made of steel, in particular steel bands or sheets, wherein the product is brought in a booster zone with at least one burner from an initial temperature to a target temperature, wherein the burner or burners with a fuel, in particular a fuel gas, and an oxygen-containing gas, wherein the oxygen-containing gas contains more than 21% oxygen, and wherein the product comes into direct contact with the flame (s) generated by the burner (s).
  • the strips to be coated are first cleaned, heated in a continuous furnace, and then annealed in a reducing atmosphere to the desired material properties. Thereafter, the actual coating is carried out in a suitable molten bath or with a corresponding method.
  • the steel In the heating phase in the continuous furnace, the steel should be heated under defined conditions in order to be able to better adjust the required properties in the following process steps. Depending on the type of steel used, it may be advantageous to minimize the oxidation, or to bring about a certain degree of oxidation targeted.
  • the heating of the steel strips is currently in continuous furnaces, the steel strips pass through a convection zone and a heating zone.
  • the bands are heated with burners and heated in the convection zone in front of the hot exhaust gases of the burner of the heating zone.
  • the degree of oxidation is difficult to control, since the temperature profile in this zone depends inter alia on the length of the convection zone and the temperature and amount of the exhaust gases.
  • the composition of the exhaust gases in the convection zone is determined by the operation of the burners and, if necessary, by passing through the continuous furnace false air. This means that the heating conditions in the convection zone are determined essentially by the requirements of the burners in the heating zone. For these reasons, a targeted adjustment of the temperature profile in the convection zone is not possible.
  • Object of the present invention is therefore to develop a method for heat treatment of steel products, which allows a targeted adjustment of the heating conditions.
  • This object is achieved by a method for the heat treatment of products made of steel, in particular bands or sheets of steel, wherein the product are brought in a booster zone with at least one burner from an initial temperature to a target temperature, wherein the burner or burners with a fuel , in particular a fuel gas, and an oxygen-containing gas, wherein the oxygen-containing gas contains more than 21% oxygen and wherein the product comes into direct contact with the flame (s) generated by the burner (s), and characterized is that within the flame, the air ratio ⁇ is set depending on the output temperature and / or the target temperature.
  • booster zone is meant a heat treatment furnace or a zone of a heat treatment furnace in which at least one burner is provided which is operated with a fuel gas and an oxygen-containing gas, the oxygen-containing gas containing more than 21% oxygen.
  • the burner is arranged or operated so that the product to be treated comes into direct contact with the flame of the burner.
  • the air ratio ⁇ indicates the ratio of the amount of oxygen supplied during the combustion to the amount of oxygen necessary for a stoichiometric conversion of the fuel used.
  • ⁇ the ratio of the amount of oxygen supplied during the combustion to the amount of oxygen necessary for a stoichiometric conversion of the fuel used.
  • excess oxygen ⁇ > 1
  • a hypostoichiometric reaction in the absence of oxygen is characterized by ⁇ ⁇ 1.
  • starting temperature and target temperature respectively refer to the surface temperature or, depending on the material thickness, the core temperature of the steel product before or after the treatment with the burner or the burners of the booster zone.
  • the surface temperature and the core temperature are very close together.
  • the surface temperature or the core temperature are selected as the starting and target tempera tures depending on the application.
  • the target temperature does not necessarily have to be greater than the starting temperature. It is also within the scope of the present invention to maintain the temperature of the product in the booster zone at a constant level. In this case, the initial and target temperatures are the same. It is even conceivable that the target temperature is below the starting temperature, for example, if the steel product is cooled in another way and serve the booster or burners of the booster zone to avoid excessive cooling or to control the degree of cooling.
  • the oxidizing agent used is oxygen-enriched air or technically pure oxygen.
  • the oxygen content of the oxidizing agent is preferably more than 50%, particularly preferably more than 75%, very particularly preferably more than 90%.
  • the steel product according to the invention is directly exposed to the flame of the burner, that is, the steel product or a part of the steel product comes into direct contact with the flame of the burner.
  • Such burners which are operated with a fuel and an oxygen-containing gas with more than 21% oxygen content and whose flame is oriented so that the steel product in direct contact with the flame, are also referred to below as a booster burner.
  • the booster burners can basically be used at any point within the heat treatment process.
  • the conventional heating of steel strips in continuous furnaces is carried out with burners, which are arranged above and / or below the steel strip and whose flames are directed to the surrounding furnace masonry.
  • the masonry then radiates again the heat energy to the current through the oven belt.
  • the flame therefore does not act directly on the steel strip, but only indirectly via the radiation of the brickwork heated by the flame.
  • the heat treatment conditions can be set in a defined manner.
  • the stoichiometry of the combustion ie the air ratio ⁇ , is selected within the flame as a function of the starting temperature and / or the target temperature.
  • the dependence of the ⁇ value on the temperature of the steel product shown in FIG. 1 has proved to be advantageous.
  • a ⁇ value of 1.12 is preferably selected, at 1.07 at 200 ° C, at 1.00 at 400 ° C, and at 0.95 at 600 ° C.
  • the heat treatment also shows positive results within a tolerance range with regard to the ⁇ value of ⁇ 0.05.
  • the dependence of the ⁇ value on the temperature can deviate from the curve shown in FIG.
  • the ⁇ value within the flame is set as a function of the starting temperature of the steel product.
  • the target temperature is also possible to use the target temperature as a parameter for the selection of the ⁇ value.
  • the target temperature in the case of relatively rapid heating, in which the target temperature deviates significantly from the starting temperature, it has proven to be favorable to use both temperatures, the starting temperature and the target temperature, to be considered when choosing the ⁇ value.
  • the booster zone it is advantageous to provide at least one further treatment zone in which the product is brought from an initial temperature to a target temperature, preferably also in the additional treatment zone the ⁇ value as a function of the respective starting temperature and / or the respective target temperature is set.
  • a defined heat treatment can also be carried out in the additional treatment zone (s).
  • At least one of the additional treatment zones is likewise designed as a booster zone.
  • at least two booster zones are thus provided, in which the steel product is heated with at least one booster burner, that is to say with a burner operated with oxygen or with oxygen-enriched air and with a fuel, the flame of which acts directly on the steel product.
  • the ⁇ value is advantageously set as a function of the starting and / or target temperature of the respective booster zone.
  • the exhaust gas produced during operation of the booster burners is preferably post-combusted in dependence on its CO content in the exhaust gas duct.
  • the product in a transport direction through the booster zone, wherein the flame the product over its entire Surrounding circumference transversely to the transport direction.
  • the steel product for example a steel strip
  • the flame of at least one booster burner acts on the steel product, the flame completely surrounding the steel product, that is, at the treatment site, the cross section of the steel product is completely within the flame.
  • the flame envelops the steel product in the direction perpendicular to the transport direction. In this way, a uniform and, as the stoichiometry is set in the flame according to the invention, defined heating of the steel product over its entire cross section is achieved.
  • the flame of the booster burner or the booster burner is expediently not used, as stated above, as an envelope flame, but is defined in specific areas, for example only the edge regions, of the steel product.
  • the direct effect of the flame of the booster burner on the steel product also makes it possible to specifically influence the target temperature in the booster zone by varying the geometry of the flame.
  • the invention is particularly suitable for the heat treatment of steel products, in particular steel strips or steel sheets, which are to be subjected to a subsequent finishing / coating in a molten bath or another suitable process.
  • the products to be galvanized are advantageously heat-treated according to the invention before hot-dip galvanizing.
  • FIG. 2 shows two booster burners 1, 2 which are used for heating a steel strip 3 according to the invention from an initial temperature to a target temperature.
  • the belt 3 is transported by a continuous furnace, not shown, in a direction perpendicular to the plane of the drawing.
  • the burners 1, 2 are arranged perpendicular to the transport direction and perpendicular to the strip surface 4.
  • the flames 5 generated by the booster burners 1, 2 envelop the entire cross section of the steel strip 3. Within the flame 5, the stoichiometry is set defined depending on the starting temperature and the target temperature.
  • the enveloping flames 5 according to the invention thus ensure a uniform and defined heating and treatment of the steel strip 3.
  • the inventive method is preferably used for cleaning and / or heating of strip-shaped steel products in continuous furnaces.
  • FIGS. 3 to 7 show various possibilities of arranging one or more booster zones in a continuous furnace, in particular in a continuous furnace, in which the work steps which are usually preceded by hot-dip galvanizing are carried out.
  • FIG 3 the use of booster zones for cleaning and preheating steel strips is shown schematically.
  • a manufactured by cold rolling / hot rolling Steel strip is to be heat treated for a following eg hot dip galvanizing.
  • the steel strip located at room temperature is fed to a first booster zone 6, in which the strip is substantially cleaned and preheated in a first stage.
  • a relatively high ⁇ value of 1.3 is selected in this zone and the steel strip is heated up to 400 ° C. under these superstoichiometric conditions.
  • booster zones 7, 8 For further heating of the steel strip two booster zones 7, 8 are provided, in which the strip is first heated from 400 ° C to 600 ° C and then to the desired final temperature of 650 ° C.
  • the steel strip is heated in both booster zones 7, 8, as well as in booster zone 6, each with a plurality of oxygen-enriched air and a fuel gas burners, the flames of the burner act directly on the steel strip.
  • the arrangement of the burners is preferably such that the steel strip, as shown in Figure 2, is completely enveloped by the flames of the burner over the cross section.
  • the ⁇ value in the burner flames in booster zone 7 is set to a value of 0.96 and that of the burner flames in booster zone 8 to a value of 0.90.
  • FIG 4 is shown for another heat treatment furnace, the course of the temperature of a steel strip to be heated and the ⁇ value within the steel strip heating flames over the furnace length.
  • the furnace is in this case divided over its length L into several booster zones, wherein the ⁇ value in each booster zone is gradually lowered in accordance with the respective starting temperature of this booster zone. In this way, an optimal adaptation of the heat treatment conditions to the current temperature conditions is achieved.
  • FIG. 5 shows an embodiment of the invention in which the booster burner (s) is used to clean a steel sheet contaminated with hot rolled or cold rolled steel.
  • a booster zone 10 is established on the first 2.5 m furnace length.
  • the steel strip is heated from 20 ° C to 300 ° C and existing rolling residues are burned.
  • the ⁇ value is set in this zone 10 to a value between 1.1 and 1.6, that is, it provides over-stoichiometric combustion conditions.
  • the booster zone 10 is followed by a 40 m long preheating zone 11, in which the steel strip is brought to the desired target temperature, for example 650 ° C.
  • the heating in the preheating zone 11 takes place substoichiometrically with a ⁇ -value of 0.96, before the steel strip is transported into a reduction furnace 12.
  • FIG. 6 shows the temperature of the steel strip as a function of its position in a continuous furnace according to FIG.
  • the dotted line shows the temperature profile when using a classic burner arrangement in the booster zone 10, that is, without the booster burner according to the invention.
  • the temperature of the belt increases only slowly, in the first zone 10, only an imperceptible increase in temperature is observed.
  • the solid line shows the temperature profile when using booster burners in the booster zone 10, as described with reference to FIG. Already on the first 2.5m furnace length - in the booster zone 10 - a temperature rise to over 300 ° C is achieved. In this way, the capacity of the oven can be increased by 25%.
  • the solid line shows the temperature profile at a production of 85 tons per hour, while the dot-dash line shows the temperature profile with an increase in production to 105 tons per hour.
  • FIG. 7 shows a variant of the invention in which the booster zone 14 is arranged directly in front of the reduction zone 15 of the heat treatment furnace.
  • the steel product is heated from ambient to 550 ° C in a conventional preheat zone.
  • a booster zone 14 in which a heating to 650 ° C takes place.
  • the booster burners are driven more than stoichiometrically with a ⁇ value of 1.1 in order to oxidise the steel strip in the booster zone 14 in a targeted manner.
  • booster zone or booster zones may also be positioned at other locations within the heat treatment process. Basically, a booster zone always useful where the steel product should be heat treated as quickly as possible in a defined atmosphere.
  • the steel product has also proved favorable to subject the steel product to a heat treatment according to the invention in a booster zone after a reducing heat treatment.
  • the temperature of the steel product is only slightly increased or maintained at the same temperature level.
  • the booster zone serves to selectively influence the material by means of a defined atmosphere, that is to set the surface, the properties or the microstructure of the steel product in the desired manner.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Thermal Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • General Engineering & Computer Science (AREA)
  • Heat Treatment Of Strip Materials And Filament Materials (AREA)
  • Coating With Molten Metal (AREA)
  • Heat Treatments In General, Especially Conveying And Cooling (AREA)

Abstract

Method for heat treating steel products, especially strips or sheets, comprises adjusting the air ratio within the flame produced by a burner depending on the starting temperature and/or the target temperature.

Description

Die Erfindung betrifft ein Verfahren zur Wärmebehandlung von Produkten aus Stahl, insbesondere von Bändern oder Blechen aus Stahl, wobei das Produkt.in einer Boosterzone mit mindestens einem Brenner von einer Ausgangstemperatur auf eine Zieltemperatur gebracht wird, wobei der oder die Brenner mit einem Brennstoff, insbesondere einem Brenngas, und einem sauerstoffhaltigen Gas betrieben werden, wobei das sauerstoffhaltige Gas mehr als 21 % Sauerstoff enthält und wobei das Produkt in unmittelbaren Kontakt mit der von dem oder den Brenner(n) erzeugten Flamme(n) kommt.The invention relates to a method for the heat treatment of products made of steel, in particular steel bands or sheets, wherein the product is brought in a booster zone with at least one burner from an initial temperature to a target temperature, wherein the burner or burners with a fuel, in particular a fuel gas, and an oxygen-containing gas, wherein the oxygen-containing gas contains more than 21% oxygen, and wherein the product comes into direct contact with the flame (s) generated by the burner (s).

Zur Herstellung beschichteter (z.B.feuerverzinkter) Stahlbänder werden die zu beschichtenden Bänder zunächst gereinigt, in einem Durchlaufofen erwärmt und anschließend in einer reduzierenden Atmosphäre auf die gewünschten Materialeigenschaften geglüht. Danach erfolgt die eigentliche Beschichtung in einem geeigneten Schmelzbad oder mit einem entsprechenden Verfahren.To produce coated (e.g., hot-dip galvanized) steel strips, the strips to be coated are first cleaned, heated in a continuous furnace, and then annealed in a reducing atmosphere to the desired material properties. Thereafter, the actual coating is carried out in a suitable molten bath or with a corresponding method.

In der Erwärmungsphase in dem Durchlaufofen soll der Stahl unter definierten Bedingungen erwärmt werden, um in den folgenden Verfahrensschritten die geforderten Eigenschaften besser einstellen zu können. Je nach Art des verwendeten Stahls kann es günstig sein, die Oxidation möglichst gering zu halten, oder auch einen gewissen Oxidationsgrad gezielt herbeizuführen.In the heating phase in the continuous furnace, the steel should be heated under defined conditions in order to be able to better adjust the required properties in the following process steps. Depending on the type of steel used, it may be advantageous to minimize the oxidation, or to bring about a certain degree of oxidation targeted.

Die Erwärmung der Stahlbänder erfolgt bisher in Durchlauföfen, wobei die Stahlbänder eine Konvektionszone und eine Aufheizzone durchlaufen. In der Aufheizzone werden die Bänder mit Brennern beheizt und in der davor geschalteten Konvektionszone von den heißen Abgasen der Brenner der Aufheizzone erwärmt. Insbesondere in der Konvektionszone ist der Oxidationsgrad nur schwer steuerbar, da das Temperaturprofil in dieser Zone unter anderem von der Länge der Konvektionszone und der Temperatur und Menge der Abgase abhängt.The heating of the steel strips is currently in continuous furnaces, the steel strips pass through a convection zone and a heating zone. In the heating zone, the bands are heated with burners and heated in the convection zone in front of the hot exhaust gases of the burner of the heating zone. In particular, in the convection zone, the degree of oxidation is difficult to control, since the temperature profile in this zone depends inter alia on the length of the convection zone and the temperature and amount of the exhaust gases.

Die Zusammensetzung der Abgase in der Konvektionszone wird durch die Betriebsweise der Brenner und gegebenenfalls durch in den Durchlaufofen eindringende Falschluft bestimmt. Das bedeutet, dass die Erwärmungsbedingungen in der Konvektionszone im Wesentlichen durch die Anforderungen an die Brenner in der Aufheizzone bestimmt werden. Aus diesen Gründen ist eine gezielte Anpassung des Temperaturprofils in der Konvektionszone bisher nicht möglich.The composition of the exhaust gases in the convection zone is determined by the operation of the burners and, if necessary, by passing through the continuous furnace false air. This means that the heating conditions in the convection zone are determined essentially by the requirements of the burners in the heating zone. For these reasons, a targeted adjustment of the temperature profile in the convection zone is not possible.

Aufgabe vorliegender Erfindung ist es daher, ein Verfahren zur Wärmebehandlung von Produkten aus Stahl zu entwickeln, welches eine gezielte Einstellung der Erwärmungsbedingungen erlaubt.Object of the present invention is therefore to develop a method for heat treatment of steel products, which allows a targeted adjustment of the heating conditions.

Diese Aufgabe wird durch ein Verfahren zur Wärmebehandlung von Produkten aus Stahl, insbesondere von Bändern oder Blechen aus Stahl, gelöst, wobei das Produkt in einer Boosterzone mit mindestens einem Brenner von einer Ausgangstemperatur auf eine Zieltemperatur gebracht werden, wobei der oder die Brenner mit einem Brennstoff, insbesondere einem Brenngas, und einem sauerstoffhaltigen Gas betrieben werden, wobei das sauerstoffhaltige Gas mehr als 21% Sauerstoff enthält und wobei das Produkt in unmittelbaren Kontakt mit der von dem oder den Brenner(n) erzeugten Flamme(n) kommt, und welches dadurch gekennzeichnet ist, dass innerhalb der Flamme die Luftzahl λ in Abhängigkeit von der Ausgangstemperatur und / oder der Zieltemperatur eingestellt wird.This object is achieved by a method for the heat treatment of products made of steel, in particular bands or sheets of steel, wherein the product are brought in a booster zone with at least one burner from an initial temperature to a target temperature, wherein the burner or burners with a fuel , in particular a fuel gas, and an oxygen-containing gas, wherein the oxygen-containing gas contains more than 21% oxygen and wherein the product comes into direct contact with the flame (s) generated by the burner (s), and characterized is that within the flame, the air ratio λ is set depending on the output temperature and / or the target temperature.

Mit dem Begriff "Boosterzone" soll ein Wärmebehandlungsofen oder eine Zone eines Wärmebehandlungsofens bezeichnet werden, in der mindestens ein Brenner vorgesehen ist, der mit einem Brenngas und einem sauerstoffhaltigen Gas betrieben wird, wobei das sauerstoffhaltige Gas mehr als 21% Sauerstoff enthält. Der Brenner wird dabei so angeordnet beziehungsweise betrieben, dass das zu behandelnde Produkt in unmittelbaren Kontakt mit der Flamme des Brenners kommt.By the term "booster zone" is meant a heat treatment furnace or a zone of a heat treatment furnace in which at least one burner is provided which is operated with a fuel gas and an oxygen-containing gas, the oxygen-containing gas containing more than 21% oxygen. The burner is arranged or operated so that the product to be treated comes into direct contact with the flame of the burner.

Die Luftzahl λ gibt das Verhältnis der bei der Verbrennung zugeführten Sauerstoffmenge zu der für einen stöchiometrischen Umsatz des verwendeten Brennstoffs notwendigen Sauerstoffmenge an. Bei Sauerstoffüberschuss ist λ > 1, d.h. die Verbrennung erfolgt überstöchiometrisch. Entsprechend ist eine unterstöchiometrische Reaktion bei Sauerstoffmangel durch λ < 1 gekennzeichnet.The air ratio λ indicates the ratio of the amount of oxygen supplied during the combustion to the amount of oxygen necessary for a stoichiometric conversion of the fuel used. In the case of excess oxygen, λ> 1, ie the combustion takes place more than stoichiometrically. Accordingly, a hypostoichiometric reaction in the absence of oxygen is characterized by λ <1.

Mit den Begriffen Ausgangstemperatur und Zieltemperatur wird jeweils die Oberflächentemperatur oder, in Abhängigkeit von der Materialdicke, die Kerntemperatur des Stahlprodukts vor beziehungsweise nach der Behandlung mit dem Brenner oder den Brennern der Boosterzone bezeichnet. Bei dünnen Blechen mit einer Stärke bis 5 mm liegen die Oberflächentemperatur und die Kerntemperatur sehr nahe zusammen. Bei dickeren Werkstücken können diese jedoch beträchtlich voneinander abweichen. In letzterem Fall werden als Ausgangs- und Zieltemperafurje nach Anwendungsfall entweder die Oberflächentemperatur oder die Kerntemperatur gewählt.The terms starting temperature and target temperature respectively refer to the surface temperature or, depending on the material thickness, the core temperature of the steel product before or after the treatment with the burner or the burners of the booster zone. For thin sheets with a thickness of up to 5 mm, the surface temperature and the core temperature are very close together. For thicker workpieces, however, these may differ considerably. In the latter case, either the surface temperature or the core temperature are selected as the starting and target tempera tures depending on the application.

Hierbei muss die Zieltemperatur nicht unbedingt größer als die Ausgangstemperatur sein. Es liegt ebenso im Rahmen der vorliegenden Erfindung, die Temperatur des Produkts in der Boosterzone auf einem gleich bleibenden Wert zu halten. In diesem Fall sind Ausgangs- und Zieltemperatur gleich. Es ist sogar denkbar, dass die Zieltemperatur unterhalb der Ausgangstemperatur liegt, wenn zum Beispiel das Stahlprodukt auf andere Weise gekühlt wird und der oder die Brenner der Boosterzone dazu dienen, eine zu starke Abkühlung zu vermeiden oder den Abkühlungsgrad zu steuern.In this case, the target temperature does not necessarily have to be greater than the starting temperature. It is also within the scope of the present invention to maintain the temperature of the product in the booster zone at a constant level. In this case, the initial and target temperatures are the same. It is even conceivable that the target temperature is below the starting temperature, for example, if the steel product is cooled in another way and serve the booster or burners of the booster zone to avoid excessive cooling or to control the degree of cooling.

Erfindungsgemäß erfolgt also die Wärmebehandlung der Stahlprodukte in einer Boosterzone mit einem Brenner, der mit einem Brennstoff, insbesondere einem Brenngas, und mehr als 21 % Sauerstoff betrieben wird. Als Oxidationsmittel kommt sauerstoffangereicherte Luft oder technisch reiner Sauerstoff zum Einsatz. Bevorzugt beträgt der Sauerstoffgehalt des Oxidationsmittels mehr als 50 %, besonders bevorzugt mehr als 75 %, ganz besonders bevorzugt mehr als 90%According to the invention, therefore, the heat treatment of the steel products in a booster zone with a burner which is operated with a fuel, in particular a fuel gas, and more than 21% oxygen. The oxidizing agent used is oxygen-enriched air or technically pure oxygen. The oxygen content of the oxidizing agent is preferably more than 50%, particularly preferably more than 75%, very particularly preferably more than 90%.

Durch die Sauerstoffanreicherung wird zum einen eine höhere Flammentemperatur und damit ein schnelleres Aufheizen des Stahlprodukts erreicht, zum anderen wird das Oxidationsverhalten verbessert.By the oxygen enrichment on the one hand a higher flame temperature and thus a faster heating of the steel product is achieved, on the other hand, the oxidation behavior is improved.

Das Stahlprodukt wird erfindungsgemäß unmittelbar der Flamme des Brenners ausgesetzt, das heißt das Stahlprodukt beziehungsweise ein Teil des Stahlprodukts kommt in unmittelbaren Kontakt mit der Flamme des Brenners. Solche Brenner, die mit einem Brennstoff und einem sauerstoffhaltigen Gas mit mehr als 21% Sauerstoffanteil betrieben werden und deren Flamme so ausgerichtet ist, dass das Stahlprodukt in direkten Kontakt mit der Flamme kommt, werden im Folgenden auch als Boosterbrenner bezeichnet. Die Boosterbrenner können grundsätzlich an beliebiger Stelle innerhalb des Wärmebehandlungsverfahrens eingesetzt werden.The steel product according to the invention is directly exposed to the flame of the burner, that is, the steel product or a part of the steel product comes into direct contact with the flame of the burner. Such burners, which are operated with a fuel and an oxygen-containing gas with more than 21% oxygen content and whose flame is oriented so that the steel product in direct contact with the flame, are also referred to below as a booster burner. The booster burners can basically be used at any point within the heat treatment process.

Die herkömmliche Erwärmung von Stahlbändern in Durchlauföfen erfolgt mit Brennern, die oberhalb und / oder unterhalb des Stahlbandes angeordnet sind und deren Flammen auf das umgebende Ofenmauerwerk gerichtet sind. Das Mauerwerk strahlt dann wiederum die Wärmeenergie auf das durch den Ofen laufende Band ab. Die Flamme wirkt also nicht direkt auf das Stahlband ein, sondern nur indirekt über die Abstrahlung des von der Flamme erwärmten Mauerwerks.The conventional heating of steel strips in continuous furnaces is carried out with burners, which are arranged above and / or below the steel strip and whose flames are directed to the surrounding furnace masonry. The masonry then radiates again the heat energy to the current through the oven belt. The flame therefore does not act directly on the steel strip, but only indirectly via the radiation of the brickwork heated by the flame.

Über die erfindungsgemäße direkte Einwirkung der Flamme auf das Stahlprodukt können die Wärmebehandlungsbedingungen definiert eingestellt werden. Erfindungsgemäß wird innerhalb der Flamme die Stöchiometrie der Verbrennung, das heißt die Luftzahl λ, in Abhängigkeit von der Ausgangstemperatur und / oder der Zieltemperatur gewählt.By means of the direct action of the flame on the steel product according to the invention, the heat treatment conditions can be set in a defined manner. According to the invention, the stoichiometry of the combustion, ie the air ratio λ, is selected within the flame as a function of the starting temperature and / or the target temperature.

In der Erfindung vorausgehenden Untersuchungen hat sich gezeigt, dass es günstig ist, mit steigender Temperatur des Stahlprodukts die Stöchiometrie innerhalb der Flamme des Boosterbrenners in Richtung niedrigeren Sauerstoffgehalts zu verschieben, um optimale Wärmebehandlungsergebnisse zu erzielen.Previous investigations in the invention have shown that it is beneficial to shift the stoichiometry within the flame of the booster burner towards lower oxygen content as the temperature of the steel product increases in order to achieve optimum heat treatment results.

Für Standardstähle hat sich beispielsweise die in Figur 1 gezeigte Abhängigkeit des λ-Wertes von der Temperatur des Stahlprodukts als vorteilhaft erwiesen. So wird beispielsweise bei 100°C vorzugsweise ein λ-Wert von 1,12 gewählt, bei 200 °C von 1,07, bei 400 °C von 1,00 und bei 600°C von 0,95. Die Wärmebehandlung zeigt aber auch innerhalb eines Toleranzbereiches hinsichtlich des λ-Wertes von ±0,05 positive Ergebnisse. Die Abhängigkeit des λ-Wertes von der Temperatur kann je nach Stahlart von der in Figur 1 dargestellten Kurve abweichen.For standard steels, for example, the dependence of the λ value on the temperature of the steel product shown in FIG. 1 has proved to be advantageous. For example, at 100 ° C, a λ value of 1.12 is preferably selected, at 1.07 at 200 ° C, at 1.00 at 400 ° C, and at 0.95 at 600 ° C. However, the heat treatment also shows positive results within a tolerance range with regard to the λ value of ± 0.05. Depending on the type of steel, the dependence of the λ value on the temperature can deviate from the curve shown in FIG.

Von Vorteil wird der λ-Wert innerhalb der Flamme in Abhängigkeit von der Ausgangstemperatur des Stahlprodukts eingestellt. Es ist aber ebenso möglich, die Zieltemperatur als Parameter für die Wahl des λ-Wertes zu nutzen. Insbesondere bei relativ schnellen Erwärmungen, bei denen die Zieltemperatur deutlich von der Ausgangstemperatur abweicht, hat es sich als günstig erwiesen, beide Temperaturen, die Ausgangstemperatur und die Zieltemperatur, bei der Wahl des λ-Wertes zu berücksichtigen.Advantageously, the λ value within the flame is set as a function of the starting temperature of the steel product. But it is also possible to use the target temperature as a parameter for the selection of the λ value. In particular, in the case of relatively rapid heating, in which the target temperature deviates significantly from the starting temperature, it has proven to be favorable to use both temperatures, the starting temperature and the target temperature, to be considered when choosing the λ value.

Von Vorteil ist neben der erfindungsgemäßen Boosterzone mindestens eine weitere Behandlungszone vorgesehen, in der das Produkt von einer Ausgangstemperatur auf eine Zieltemperatur gebracht wird, wobei vorzugsweise auch in der zusätzlichen, Behandlungszone der λ-Wert in Abhängigkeit von der jeweiligen Ausgangstemperatur und / oder der jeweiligen Zieltemperatur eingestellt wird. Außer in der Boosterzone lässt sich dadurch auch in der oder den zusätzlichen Behandlungszone(n) eine definierte Wärmebehandlung durchführen.In addition to the booster zone according to the invention, it is advantageous to provide at least one further treatment zone in which the product is brought from an initial temperature to a target temperature, preferably also in the additional treatment zone the λ value as a function of the respective starting temperature and / or the respective target temperature is set. In addition to the booster zone, a defined heat treatment can also be carried out in the additional treatment zone (s).

Besonders günstig ist es, wenn mindestens eine der zusätzlichen Behandlungszonen ebenfalls als Boosterzone ausgeführt ist. Bei dieser Verfahrensvariante sind damit mindestens zwei Boosterzonen vorgesehen, in denen das Stahlprodukt mit jeweils mindestens einem Boosterbrenner erwärmt wird, das heißt, mit einem mit Sauerstoff oder mit sauerstoffangereicherter Luft und mit einem Brennstoff betriebenen Brenner, dessen Flamme direkt auf das Stahlprodukt einwirkt. In jeder der Boosterzonen wird von Vorteil der λ-Wert in Abhängigkeit von der Ausgangs- und / oder Zieltemperatur der jeweiligen Boosterzone eingestellt.It is particularly favorable if at least one of the additional treatment zones is likewise designed as a booster zone. In this process variant, at least two booster zones are thus provided, in which the steel product is heated with at least one booster burner, that is to say with a burner operated with oxygen or with oxygen-enriched air and with a fuel, the flame of which acts directly on the steel product. In each of the booster zones, the λ value is advantageously set as a function of the starting and / or target temperature of the respective booster zone.

Das beim Betrieb der Boosterbrenner entstehende Abgas wird vorzugsweise in Abhängigkeit von dessen CO-Gehalt im Abgaskanal nachverbrannt.The exhaust gas produced during operation of the booster burners is preferably post-combusted in dependence on its CO content in the exhaust gas duct.

Es hat sich als vorteilhaft herausgestellt, das Produkt in der Boosterzone mit einer Wärmestromdichte von 300 bis 1000 kW/m2 zu beaufschlagen. Mit anderen Worten: Die von den Boosterbrennern pro Quadratmeter Oberfläche auf das Stahlprodukt übertragene Wärmeleistung beträgt 300 bis 1000 kW. Erst die erfindungsgemäße Verwendung von sauerstoffangereicherter Luft bis hin zum Einsatz von technischem Sauerstoff mit mehr als 80% Sauerstoffanteil ermöglicht, solch einen hohen Wärmeübertrag. Dadurch können die Stahlprodukte auf einer kürzeren Strecke schneller erwärmt werden, wodurch entweder die Länge der Durchlauföfen deutlich reduziert oder deren Durchsatz erhöht werden kann.It has proven to be advantageous to pressurize the product in the booster zone with a heat flux density of 300 to 1000 kW / m 2 . In other words, the heat output transferred by the booster burners per square meter of surface area to the steel product is 300 to 1000 kW. Only the inventive use of oxygen-enriched air up to the use of technical oxygen with more than 80% oxygen content allows such a high heat transfer. As a result, the steel products can be heated faster over a shorter distance, which can either significantly reduce the length of the furnaces or their throughput can be increased.

Besonders günstig ist es, das Produkt in einer Transportrichtung durch die Boosterzone zu bewegen, wobei die Flamme das Produkt über dessen gesamten Umfang quer zur Transportrichtung umgibt. Das Stahlprodukt, beispielsweise ein Stahlband, wird entlang einer Transportrichtung durch den Ofen transportiert. Quer zu dieser Transportrichtung wirkt die Flamme mindestens eines Boosterbrenners auf das Stahlprodukt ein, wobei die Flamme das Stahlprodukt völlig umgibt, das heißt an der Behandlungsstelle befindet sich der Querschnitt des Stahlprodukts vollständig innerhalb der Flamme. Die Flamme hüllt damit das Stahlprodukt in der Richtung senkrecht zur Transportrichtung ein. Auf diese Weise wird eine gleichmäßige und, da die Stöchiometrie in der Flamme erfindungsgemäß eingestellt wird, definierte Erwärmung des Stahlprodukts über dessen gesamten Querschnitt erreicht.It is particularly advantageous to move the product in a transport direction through the booster zone, wherein the flame the product over its entire Surrounding circumference transversely to the transport direction. The steel product, for example a steel strip, is transported along the transport direction through the furnace. Transverse to this direction of transport, the flame of at least one booster burner acts on the steel product, the flame completely surrounding the steel product, that is, at the treatment site, the cross section of the steel product is completely within the flame. The flame envelops the steel product in the direction perpendicular to the transport direction. In this way, a uniform and, as the stoichiometry is set in the flame according to the invention, defined heating of the steel product over its entire cross section is achieved.

Je nachdem, welche Form und Geometrie das zu behandelnde Stahlprodukt aufweist, kann es nötig sein, die Randbereiche und den Kernbereich des Stahlprodukts unterschiedlich stark zu erwärmen. In diesem Fall wird zweckmäßigerweise die Flamme des Boosterbrenners oder der Boosterbrenner nicht, wie oben ausgeführt als Hüllflamme verwendet, sondern definiert auf bestimmte Bereiche, beispielsweise nur die Randbereiche, des Stahlprodukts gerichtet.Depending on the shape and geometry of the steel product to be treated, it may be necessary to heat the edge regions and the core region of the steel product to different degrees. In this case, the flame of the booster burner or the booster burner is expediently not used, as stated above, as an envelope flame, but is defined in specific areas, for example only the edge regions, of the steel product.

Die direkte Einwirkung der Flamme des Boosterbrenners auf das Stahlprodukt erlaubt es weiterhin, die Zieltemperatur in der Boosterzone durch Variation der Geometrie der Flamme gezielt zu beeinflussen.The direct effect of the flame of the booster burner on the steel product also makes it possible to specifically influence the target temperature in the booster zone by varying the geometry of the flame.

Die Erfindung eignet sich insbesondere zur Wärmebehandlung von Stahlprodukten, insbesondere Stahlbändern oder Stahlblechen, die einer anschließenden Veredelung / Beschichtung in einem Schmelzbad oder einem anderen geeigneten Verfahren unterzogen werden sollen. So werden beispielsweise mit Vorteil vor dem Feuerverzinken die zu verzinkenden Produkte erfindungsgemäß wärmebehandelt.The invention is particularly suitable for the heat treatment of steel products, in particular steel strips or steel sheets, which are to be subjected to a subsequent finishing / coating in a molten bath or another suitable process. Thus, for example, the products to be galvanized are advantageously heat-treated according to the invention before hot-dip galvanizing.

Die Erfindung sowie weitere Einzelheiten der Erfindung werden im Folgenden anhand von in den Zeichnungen dargestellten Ausführungsbeispielen näher erläutert. Hierbei zeigen:

Figur 1
die Abhängigkeit des λ-Wertes von der Temperatur des zu behandelnden Produktes,
Figur 2
die Anordnung der Boosterbrenner zur Erzeugung einer Hüllflamme,
Figur 3
die Anordnung von drei Boosterzonen zur Vorwärmung eines Stahlbandes in einem Durchlaufofen,
Figur 4
den Verlauf des λ-Wertes und der Temperatur des Stahlproduktes bei einer speziellen Ausführung der Erfindung,
Figur 5
den Einsatz einer Boosterzone zur Reinigung des Stahlproduktes,
Figur 6
die Abhängigkeit der Stahltemperatur von der Ofenlänge bei einer Anordnung gemäß Figur 5 und
Figur 7
den Einsatz einer Boosterzone nach einer konventionellen Vorwärmzone.
The invention and further details of the invention are explained in more detail below with reference to exemplary embodiments illustrated in the drawings. Hereby show:
FIG. 1
the dependence of the λ-value on the temperature of the product to be treated,
FIG. 2
the arrangement of the booster burners for generating an envelope flame,
FIG. 3
the arrangement of three booster zones for preheating a steel strip in a continuous furnace,
FIG. 4
the course of the λ value and the temperature of the steel product in a specific embodiment of the invention,
FIG. 5
the use of a booster zone for cleaning the steel product,
FIG. 6
the dependence of the steel temperature of the furnace length in an arrangement according to Figure 5 and
FIG. 7
the use of a booster zone after a conventional preheating zone.

In Figur 2 sind zwei Boosterbrenner 1, 2 gezeigt, die zur erfindungsgemäßen Erwärmung eines Stahlbandes 3 von einer Ausgangstemperatur auf eine Zieltemperatur eingesetzt werden. Das Band 3 wird durch einen nicht dargestellten Durchlaufofen in einer Richtung senkrecht zur Zeichenebene transportiert. Die Brenner 1, 2 sind senkrecht zur Transportrichtung und senkrecht zur Bandoberfläche 4 angeordnet. Die von den Boosterbrennern 1, 2 erzeugten Flammen 5 hüllen den gesamten Querschnitt des Stahlbandes 3 ein. Innerhalb der Flammen 5 wird die Stöchiometrie in Abhängigkeit von der Ausgangstemperatur und der Zieltemperatur definiert eingestellt. Durch die erfindungsgemäßen Hüllflammen 5 wird so eine gleichmäßige und definierte Erwärmung und Behandlung des Stahlbandes 3 sichergestellt.FIG. 2 shows two booster burners 1, 2 which are used for heating a steel strip 3 according to the invention from an initial temperature to a target temperature. The belt 3 is transported by a continuous furnace, not shown, in a direction perpendicular to the plane of the drawing. The burners 1, 2 are arranged perpendicular to the transport direction and perpendicular to the strip surface 4. The flames 5 generated by the booster burners 1, 2 envelop the entire cross section of the steel strip 3. Within the flame 5, the stoichiometry is set defined depending on the starting temperature and the target temperature. The enveloping flames 5 according to the invention thus ensure a uniform and defined heating and treatment of the steel strip 3.

Das erfindungsgemäße Verfahren wird bevorzugt zur Reinigung und/oder Erwärmung von bandförmigen Stahlprodukten in Durchlauföfen eingesetzt. Besondere Vorteile bringt die Erfindung bei der Erwärmung beziehungsweise Vorbehandlung von Stahlprodukten vor einer folgenden Beschichtung/Feuerverzinkung. Die folgenden Figuren 3 bis 7 zeigen verschiedene Möglichkeiten der Anordnung einer oder mehrerer Boosterzonen in einem Durchlaufofen, insbesondere in einem Durchlaufofen, in dem die üblicherweise einer Feuerverzinkung vorausgehenden Arbeitsschritte durchgeführt werden.The inventive method is preferably used for cleaning and / or heating of strip-shaped steel products in continuous furnaces. Particular advantages of the invention in the heating or pretreatment of steel products before a subsequent coating / hot dip galvanizing. The following FIGS. 3 to 7 show various possibilities of arranging one or more booster zones in a continuous furnace, in particular in a continuous furnace, in which the work steps which are usually preceded by hot-dip galvanizing are carried out.

In Figur 3 ist der Einsatz von Boosterzonen zur Reinigung und Vorerwärmung von Stahlbändern schematisch dargestellt. Ein durch Kaltwalzen/Warmwalzen hergestelltes Stahlband soll für eine folgende z.B. Feuerverzinkung wärmebehandelt werden. Hierzu wird das auf Raumtemperatur befindliche Stahlband einer ersten Boosterzone 6 zugeführt, in der das Band im Wesentlichen gereinigt und in einer ersten Stufe vorgewärmt wird. Entsprechend der niedrigen Ausgangstemperatur des Bandes wird in dieser Zone ein relativ hoher λ-Wert von 1,3 gewählt und das Stahlband unter diesen überstöchiometrischen Bedingungen bis auf 400 °C erwärmt.In Figure 3, the use of booster zones for cleaning and preheating steel strips is shown schematically. A manufactured by cold rolling / hot rolling Steel strip is to be heat treated for a following eg hot dip galvanizing. For this purpose, the steel strip located at room temperature is fed to a first booster zone 6, in which the strip is substantially cleaned and preheated in a first stage. Corresponding to the low starting temperature of the strip, a relatively high λ value of 1.3 is selected in this zone and the steel strip is heated up to 400 ° C. under these superstoichiometric conditions.

Zur weiteren Erwärmung des Stahlbandes sind zwei Boosterzonen 7, 8 vorgesehen, in denen das Band zunächst von 400°C auf 600 °C und anschließend auf die gewünschte Endtemperatur von 650°C erwärmt wird. Hierzu wird das Stahlband in beiden Boosterzonen 7, 8 , ebenso wie in Boosterzone 6, jeweils mit mehreren mit Sauerstoff angereicherter Luft und einem Brenngas betriebenen Brennern erhitzt, wobei die Flammen der Brenner direkt auf das Stahlband einwirken. Die Anordnung der Brenner erfolgt vorzugsweise so, dass das Stahlband, wie in Figur 2 gezeigt, von den Flammen der Brenner über dessen Querschnitt vollständig eingehüllt ist. Der λ-Wert in den Brennerflammen in Boosterzone 7 wird hierbei auf einen Wert von 0,96 und derjenige der Brennerflammen in Boosterzone 8 auf einen Wert von 0,90 eingestellt. Nach Durchlaufen der Boosterzonen 6, 7, 8 wird das Stahlband in einem Ofenabschnitt 9 einer reduzierenden Atmosphäre ausgesetzt.For further heating of the steel strip two booster zones 7, 8 are provided, in which the strip is first heated from 400 ° C to 600 ° C and then to the desired final temperature of 650 ° C. For this purpose, the steel strip is heated in both booster zones 7, 8, as well as in booster zone 6, each with a plurality of oxygen-enriched air and a fuel gas burners, the flames of the burner act directly on the steel strip. The arrangement of the burners is preferably such that the steel strip, as shown in Figure 2, is completely enveloped by the flames of the burner over the cross section. The λ value in the burner flames in booster zone 7 is set to a value of 0.96 and that of the burner flames in booster zone 8 to a value of 0.90. After passing through the booster zones 6, 7, 8, the steel strip is exposed in a furnace section 9 of a reducing atmosphere.

In Figur 4 ist für einen anderen Wärmebehandlungsofen der Verlauf der Temperatur eines zu erwärmenden Stahlbandes und der λ-Wert innerhalb der das Stahlband aufheizenden Flammen über der Ofenlänge dargestellt. Der Ofen ist hierbei über seine Länge L in mehrere Boosterzonen eingeteilt, wobei der λ-Wert in jeder Boosterzone entsprechend der jeweiligen Ausgangstemperatur dieser Boosterzone schrittweise abgesenkt wird. Auf diese Weise wird eine optimale Anpassung der Wärmebehandlungsverhältnisse an die momentanen Temperaturbedingungen erzielt.In Figure 4 is shown for another heat treatment furnace, the course of the temperature of a steel strip to be heated and the λ value within the steel strip heating flames over the furnace length. The furnace is in this case divided over its length L into several booster zones, wherein the λ value in each booster zone is gradually lowered in accordance with the respective starting temperature of this booster zone. In this way, an optimal adaptation of the heat treatment conditions to the current temperature conditions is achieved.

Figur 5 zeigt eine Ausführungsform der Erfindung, bei der der oder die Boosterbrenner zur Reinigung eines nach dem Warm- bzw. Kaltwalzen mit Walzrückständen verunreinigten Stahlbleches verwendet wird. Auf den ersten 2,5 m Ofenlänge wird eine Boosterzone 10 eingerichtet. In dieser kurzen Zone 10 wird das Stahlband von 20°C auf 300 °C erwärmt und vorhandene Walzrückstände werden verbrannt. Der λ-Wert wird in dieser Zone 10 auf einen Wert zwischen 1,1 und 1,6 eingestellt, das heißt, es werden überstöchiometrische Verbrennungsbedingungen geschaffen.FIG. 5 shows an embodiment of the invention in which the booster burner (s) is used to clean a steel sheet contaminated with hot rolled or cold rolled steel. On the first 2.5 m furnace length, a booster zone 10 is established. In this short zone 10, the steel strip is heated from 20 ° C to 300 ° C and existing rolling residues are burned. The λ value is set in this zone 10 to a value between 1.1 and 1.6, that is, it provides over-stoichiometric combustion conditions.

An die Boosterzone 10 schließt sich eine 40 m lange Vorwärmzone 11 an, in der das Stahlband auf die gewünschte Zieltemperatur von beispielsweise 650 °C gebracht wird. Die Erwärmung in der Vorwärmzone 11 erfolgt unterstöchiometrisch mit einem λ-Wert von 0,96, bevor das Stahlband in einen Reduktionsofen 12 transportiert wird.The booster zone 10 is followed by a 40 m long preheating zone 11, in which the steel strip is brought to the desired target temperature, for example 650 ° C. The heating in the preheating zone 11 takes place substoichiometrically with a λ-value of 0.96, before the steel strip is transported into a reduction furnace 12.

In Figur 6 ist die Temperatur des Stahlbandes in Abhängigkeit von dessen Position in einem Durchlaufofen gemäß Figur 5 dargestellt. Die gepunktete Linie zeigt den Temperaturverlauf beim Einsatz einer klassischen Brenneranordnung in der Boosterzone 10, das heißt, ohne die erfindungsgemäßen Boosterbrenner. Die Temperatur des Bandes steigt nur langsam an, in der ersten Zone 10 ist nur eine unmerkliche Temperaturzunahme festzustellen.FIG. 6 shows the temperature of the steel strip as a function of its position in a continuous furnace according to FIG. The dotted line shows the temperature profile when using a classic burner arrangement in the booster zone 10, that is, without the booster burner according to the invention. The temperature of the belt increases only slowly, in the first zone 10, only an imperceptible increase in temperature is observed.

Die durchgezogene Linie zeigt dagegen den Temperaturverlauf bei Verwendung von Boosterbrennern in der Boosterzone 10, wie dies anhand von Figur 5 beschrieben wurde. Bereits auf den ersten 2,5m Ofenlänge - in der Boosterzone 10 - wird ein Temperaturanstieg auf über 300 °C erzielt. Auf diese Weise kann die Kapazität des Ofens um 25% gesteigert werden. Die durchgezogene Linie zeigt den Temperaturverlauf bei einer Produktion von 85 Tonnen pro Stunde, während die strichpunktierte Linie den Temperaturverlauf bei einer Erhöhung der Produktion auf 105 Tonnen pro Stunde wiedergibt.The solid line, however, shows the temperature profile when using booster burners in the booster zone 10, as described with reference to FIG. Already on the first 2.5m furnace length - in the booster zone 10 - a temperature rise to over 300 ° C is achieved. In this way, the capacity of the oven can be increased by 25%. The solid line shows the temperature profile at a production of 85 tons per hour, while the dot-dash line shows the temperature profile with an increase in production to 105 tons per hour.

Schließlich ist in Figur 7 eine Erfindungsvariante zu sehen, bei der die Boosterzone 14 unmittelbar vor der Reduktionszone 15 des Wärmebehandlungsofens angeordnet ist. Zunächst wird das Stahlprodukt in einer konventionellen Vorwärmzone von Umgebungstemperatur auf 550°C erhitzt. Hieran schließt sich eine Boosterzone 14 an, in der eine Erwärmung auf 650 °C erfolgt. In diesem speziellen Fall werden die Boosterbrenner überstöchiometrisch mit einem λ-Wert von 1,1 gefahren, um das Stahlband in der Boosterzone 14 gezielt zu oxidieren.Finally, FIG. 7 shows a variant of the invention in which the booster zone 14 is arranged directly in front of the reduction zone 15 of the heat treatment furnace. First, the steel product is heated from ambient to 550 ° C in a conventional preheat zone. This is followed by a booster zone 14, in which a heating to 650 ° C takes place. In this special case, the booster burners are driven more than stoichiometrically with a λ value of 1.1 in order to oxidise the steel strip in the booster zone 14 in a targeted manner.

Neben den in den Figuren gezeigten Anordnungen kann die Boosterzone oder können die Boosterzonen auch an anderen Stellen innerhalb des Wärmebehandlungsverfahrens positioniert werden. Grundsätzlich ist eine Boosterzone immer dort sinnvoll einsetzbar, wo das Stahlprodukt möglichst schnell in einer definierten Atmosphäre wärmebehandelt werden soll.In addition to the arrangements shown in the figures, the booster zone or booster zones may also be positioned at other locations within the heat treatment process. Basically, a booster zone always useful where the steel product should be heat treated as quickly as possible in a defined atmosphere.

Insbesondere hat es sich auch als günstig erwiesen, das Stahlprodukt nach einer reduzierenden Wärmebehandlung noch einer erfindungsgemäßen Wärmebehandlung in einer Boosterzone zu unterziehen. Vorzugsweise wird in dieser Boosterzone die Temperatur des Stahlprodukts nur noch geringfügig erhöht oder auf dem gleichen Temperaturniveau gehalten. Die Boosterzone dient in diesem Fall dazu, durch eine definierte Atmosphäre das Material gezielt zu beeinflussen, das heißt die Oberfläche, die Eigenschaften oder das Gefüge des Stahlproduktes in gewünschter Weise einzustellen.In particular, it has also proved favorable to subject the steel product to a heat treatment according to the invention in a booster zone after a reducing heat treatment. Preferably, in this booster zone, the temperature of the steel product is only slightly increased or maintained at the same temperature level. In this case, the booster zone serves to selectively influence the material by means of a defined atmosphere, that is to set the surface, the properties or the microstructure of the steel product in the desired manner.

Claims (10)

1. Verfahren zur Wärmebehandlung von Produkten (3) aus Stahl, insbesondere von Bändern oder Blechen aus Stahl, wobei das Produkt (3) in einer Boosterzone (6, 7, 8, 10, 14) mit mindestens einem Brenner (1, 2) von einer Ausgangstemperatur auf eine Zieltemperatur gebracht wird, wobei der oder die Brenner (1, 2) mit einem Brennstoff, insbesondere einem Brenngas, und einem sauerstoffhaltigen Gas betrieben werden, wobei das sauerstoffhaltige Gas mehr als 21 % Sauerstoff enthält und wobei das Produkt (3) in unmittelbaren Kontakt mit der von dem oder den Brenner(n) (1, 2) erzeugten Flamme(n) (5) kommt, dadurch gekennzeichnet, dass innerhalb der Flamme (5) die Luftzahl λ, in Abhängigkeit von der Ausgangstemperatur und / oder der Zieltemperatur eingestellt wird. 1. A method for heat treatment of products (3) made of steel, in particular strips or sheets made of steel, wherein the product (3) in a booster zone (6, 7, 8, 10, 14) with at least one burner (1, 2) is brought from a starting temperature to a target temperature, wherein the burner or burners (1, 2) are operated with a fuel, in particular a fuel gas, and an oxygen-containing gas, wherein the oxygen-containing gas contains more than 21% oxygen and wherein the product (3 ) comes into direct contact with the flame (s) (5) produced by the burner (s) (1, 2), characterized in that within the flame (5) the air ratio λ, as a function of the starting temperature and / or the target temperature is set. 2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, dass zusätzliche Behandlungszonen (9, 11, 12, 13, 15) vorgesehen sind, in denen das Produkt (3) jeweils von einer Ausgangstemperatur auf eine Zieltemperatur gebracht wird, wobei in jeder der Behandlungszonen (9, 11, 12, 13, 15) die Luftzahl λ in Abhängigkeit von der jeweiligen Ausgangstemperatur und / oder der jeweiligen Zieltemperatur eingestellt wird. 2. The method according to claim 1, characterized in that additional treatment zones (9, 11, 12, 13, 15) are provided, in which the product (3) is brought in each case from an initial temperature to a target temperature, wherein in each of the treatment zones ( 9, 11, 12, 13, 15) the air ratio λ is set as a function of the respective outlet temperature and / or the respective target temperature. 3. Verfahren nach Anspruch 2, dadurch gekennzeichnet, dass mehrere Boosterzonen (6, 7, 8) vorgesehen sind, die jeweils mit mindestens einem mit Brennstoff, insbesondere einem Brenngas, und einem mehr als 21 % Sauerstoff enthaltenden Gas betriebenen Brenner (1, 2) beheizt werden, wobei das Produkt (3) in unmittelbaren Kontakt mit der von dem oder den Brenner(n) (1, 2) erzeugten Flamme(n) (5) kommt. 3. The method according to claim 2, characterized in that a plurality of booster zones (6, 7, 8) are provided, each with at least one with fuel, in particular a fuel gas, and a more than 21% oxygen-containing gas operated burner (1, 2 ), the product (3) coming into direct contact with the flame (s) (5) produced by the burner (s) (1, 2). 5. Verfahren nach einem der Ansprüche 1 bis 4, dadurch gekennzeichnet, dass das Produkt (3) in der Boosterzone (6, 7, 8, 10, 14) mit einer Wärmestromdichte von 300 bis 1000 kW/m2 beaufschlagt wird. 5. The method according to any one of claims 1 to 4, characterized in that the product (3) in the booster zone (6, 7, 8, 10, 14) is acted upon with a heat flux density of 300 to 1000 kW / m 2 . 6. Verfahren nach einem der Ansprüche 1 bis 5, dadurch gekennzeichnet, dass das Produkt (3) in einer Transportrichtung durch die Boosterzone (6, 7, 8, 10, 14) bewegt wird und dass die Flamme (5) das Produkt (3) über dessen gesamten Umfang quer zur Transportrichtung umgibt. 6. The method according to any one of claims 1 to 5, characterized in that the product (3) in a transport direction by the booster zone (6, 7, 8, 10, 14) is moved and that the flame (5) the product (3 ) surrounds over its entire circumference transversely to the transport direction. 7. Verfahren nach einem der Ansprüche 1 bis 6, dadurch gekennzeichnet, dass die Zieltemperatur in einer Boosterzone (6, 7, 8, 10, 14) über die Flammengeometrie des oder der Brenner (1, 2) beeinflusst wird. 7. The method according to any one of claims 1 to 6, characterized in that the target temperature in a booster zone (6, 7, 8, 10, 14) on the flame geometry of the burner or (1, 2) is influenced. 8. Verfahren nach einem der Ansprüche 1 bis 7, dadurch gekennzeichnet, dass das Verfahren folgende Schritte umfasst: - Erwärmen des Produkts (3) in der Boosterzone (6, 10) auf eine erste Zieltemperatur von 300 bis 400 °C, - Erwärmen des Produkts (3) in mindestens einer weiteren Behandlungszone (7, 8, 11) von der ersten Zieltemperatur auf eine Temperatur von 600 bis 900 °C. 8. The method according to any one of claims 1 to 7, characterized in that the method comprises the following steps: Heating the product (3) in the booster zone (6, 10) to a first target temperature of 300 to 400 ° C, - Heating the product (3) in at least one further treatment zone (7, 8, 11) from the first target temperature to a temperature of 600 to 900 ° C. 9. Verfahren nach einem der Ansprüche 1 bis 7, dadurch gekennzeichnet, dass das Verfahren folgende Schritte umfasst: - Erwärmen des Produkts (3) in einer ersten Behandlungszone (13) auf eine erste Zieltemperatur von 500 bis 600 °C, - Erwärmen des Produkts (3) in der Boosterzone (14) von der ersten Zieltemperatur auf eine Temperatur von 600 bis 900 °C. 9. The method according to any one of claims 1 to 7, characterized in that the method comprises the following steps: Heating the product (3) in a first treatment zone (13) to a first target temperature of 500 to 600 ° C, Heating the product (3) in the booster zone (14) from the first target temperature to a temperature of 600 to 900 ° C. 10. Verfahren nach einem der Ansprüche 1 bis 9, dadurch gekennzeichnet, dass das Produkt (3) einem Beschichtungs-Nerzinkungsprozess unterzogen wird. 10. The method according to any one of claims 1 to 9, characterized in that the product (3) is subjected to a coating Nerzinkungsprozess. 11. Verfahren nach einem der Ansprüche 1 bis 10, dadurch gekennzeichnet, dass das Produkt (3) einer reduzierenden Atmosphäre ausgesetzt wird und anschließend in der Boosterzone auf die Zieltemperatur gebracht wird. 11. The method according to any one of claims 1 to 10, characterized in that the product (3) is exposed to a reducing atmosphere and then brought to the target temperature in the booster zone.
EP06007147A 2006-02-03 2006-04-04 Process for the heat treatment of metal strips by direct flame impingement Withdrawn EP1816219A1 (en)

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BRPI0707378-0A BRPI0707378B1 (en) 2006-02-03 2007-01-11 PROCESS FOR THERMAL TREATMENT OF STEEL PRODUCTS, IN PARTICULAR STEEL STRIPS OR SHEETS
US12/162,641 US9322598B2 (en) 2006-02-03 2007-01-11 Process for the heat treatment of steel strips
CA2637847A CA2637847C (en) 2006-02-03 2007-01-11 Process for the heat treatment of steel strips
JP2008552706A JP5268650B2 (en) 2006-02-03 2007-01-11 Heat treatment method for steel strip in a continuous heat treatment furnace equipped with an oxy-fuel burner
EP07702696A EP1979495B1 (en) 2006-02-03 2007-01-11 Process for the heat treatment of steel strips
PL07702696T PL1979495T3 (en) 2006-02-03 2007-01-11 Process for the heat treatment of steel strips
PCT/EP2007/000219 WO2007087973A2 (en) 2006-02-03 2007-01-11 Process for the heat treatment of steel strips in a continuous furnace with oxy-fuel burners
RU2008135237/02A RU2435869C2 (en) 2006-02-03 2007-01-11 Procedure for heat treatment of strip steel in continuous furnace with oxygen-fuel burners
CN200780004421XA CN101448963B (en) 2006-02-03 2007-01-11 Process for the heat treatment of steel strips in a continuous furnace with oxy-fuel burners
KR1020087020692A KR20080109737A (en) 2006-02-03 2007-01-11 Process for the heat treatment of steel strips in a continuous furnace with oxy-fuel burners
AT07702696T ATE516372T1 (en) 2006-02-03 2007-01-11 METHOD FOR HEAT TREATMENT OF STEEL STRIP

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BRPI0707378A2 (en) 2011-05-03
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US20090188591A1 (en) 2009-07-30
EP1979495A2 (en) 2008-10-15
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CA2637847A1 (en) 2007-08-09
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WO2007087973A8 (en) 2008-08-14
RU2008135237A (en) 2010-03-10

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