EP2179066A1 - Method for producing a surface-decarbonized hot-rolled strip - Google Patents

Method for producing a surface-decarbonized hot-rolled strip

Info

Publication number
EP2179066A1
EP2179066A1 EP08786978A EP08786978A EP2179066A1 EP 2179066 A1 EP2179066 A1 EP 2179066A1 EP 08786978 A EP08786978 A EP 08786978A EP 08786978 A EP08786978 A EP 08786978A EP 2179066 A1 EP2179066 A1 EP 2179066A1
Authority
EP
European Patent Office
Prior art keywords
steel strip
steel
temperature
decarburization
atmosphere
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.)
Granted
Application number
EP08786978A
Other languages
German (de)
French (fr)
Other versions
EP2179066B1 (en
Inventor
Jian Bian
Axel Grafen
Giovanni Sabatino
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.)
ThyssenKrupp Steel Europe AG
Original Assignee
ThyssenKrupp Steel Europe AG
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Publication date
Application filed by ThyssenKrupp Steel Europe AG filed Critical ThyssenKrupp Steel Europe AG
Priority to PL08786978T priority Critical patent/PL2179066T3/en
Publication of EP2179066A1 publication Critical patent/EP2179066A1/en
Application granted granted Critical
Publication of EP2179066B1 publication Critical patent/EP2179066B1/en
Active legal-status Critical Current
Anticipated expiration legal-status Critical

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Classifications

    • 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
    • C21D3/00—Diffusion processes for extraction of non-metals; Furnaces therefor
    • C21D3/02—Extraction of non-metals
    • C21D3/04—Decarburising
    • 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
    • C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
    • 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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0257—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment with diffusion of elements, e.g. decarburising, nitriding
    • 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
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • C21D9/48—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals deep-drawing sheets
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel

Definitions

  • the invention relates to a method for producing a decarburized hot strip, which is produced from a quenching steel containing at least 0.4 wt .-% carbon.
  • Hot rolled strips produced from steels of this type have a high hardness and are therefore particularly suitable for the production of articles which are exposed to high localized loads during use. This is the case, for example, in the case of punching blades or comparable cutting tools in which both the cutting edge and the blade body carrying the cutting edge have to absorb high forces during the cutting operation in practical use.
  • a hot strip is hot rolled from a slab at a final rolling temperature of 850-950 0 C.
  • the resulting hot strip is then coiled at a reel temperature of 600 0 C and then cold rolled to the desired final thickness.
  • the cold strip is wound according to the known method into an "open coil” and decarburizing annealed as an open coil.
  • an open-coil is so loosely wound that its individual winding layers are separated by open spaces.
  • the reaction gas can flow through the intermediate spaces between the individual layers of the coil, so that with optimized gas flow guidance, each surface of the coil is swept in the same way by the gas.
  • a steel containing 0.04 wt.% C must first be heated to the required decarburization annealing temperature under a substantially dry atmosphere for 8 to 12 hours. Subsequently, water vapor in the ratio 200: 1 is then added to the furnace atmosphere to initiate the decarburization process. Then decarburization annealing is continued for a further 10 hours under the reducing atmosphere so formed until the desired reduction in carbon content is achieved.
  • the invention was based on the object to provide a method that allows the production of steel strip, in which high hardness on the one hand and good formability on the other hand are optimally combined with each other.
  • a steel strip is first produced in known manner from a quenching steel containing at least 0.4% by weight of carbon.
  • This steel strip can be a cold or a hot strip, the procedure according to the invention being particularly suitable for the treatment of hot strip which is to be processed with a specific thickness lying above the thickness of cold strip.
  • the steel strip is wound according to the invention to an open coil and heated as an open coil over a sufficiently long period of time to a decarburization annealing temperature.
  • a decarburization annealing temperature This may be up to 20 0 C, in particular up to 10 0 C, below the A cl temperature of the respective tempering steel and must not exceed the A c3 temperature of the respective tempering steel.
  • the decarburizing annealing of the steel strip in the open coil is then carried out under a decarburizing atmosphere for a decarburization annealing time of at least 90 minutes.
  • the decarburizing gas forming the decarburizing atmosphere flows through the gaps existing between the winding layers of the open coil.
  • the advantage of the decarburization annealing according to the invention in wound to an open coil steel strip is that can be achieved in this way time-saving uniform temperature distribution over the length and width of each processed steel strip.
  • the annealing conditions are chosen according to the invention so that there is a uniformly distributed structure state over the entire strip. So is by the invention given range of the annealing temperature ensures that in each processed band still sufficient amounts of ferrite are present in order to allow rapid diffusion of the carbon. This is up to a hundredfold faster in ferrite than in austenite.
  • the decarburization annealing temperature according to the invention is preferably set in a range which is lower by 10 to 20 0 C than the A Ci temperature. This setting of the decarburization annealing temperature ensures that the tempering steel of the respective processed steel strip has a ferritic structure, so that an optimum diffusion rate of the carbon is achieved.
  • the open coil is accelerated cooled to prevent any undesirable and, in terms of its extent, insecure subsequent diffusion of carbon into the previously deliberately decarburized surface layer as a result of the coil's inherent heat.
  • the accelerated cooling should take place as soon as possible, as soon as possible after the end of the decarburization annealing time and at a cooling rate of at least 1 ° C / min.
  • steel sheet is one starting from the respective Decarburized surface layer measured measured surface of the steel strip whose depth is in each case smaller than a quarter of the thickness of the steel strip, so that only near-surface areas are included in the decarburization according to the invention.
  • the parameters of the method according to the invention are preferably chosen so that decarburization depths of a maximum of 120 ⁇ m, in particular 30-120 ⁇ m, are achieved.
  • the steel strip obtained by the procedure according to the invention is consequently characterized in that it has a high bend formability in the region of a near-surface layer as a result of the decarburization treatment.
  • the strip treated according to the invention has a high core hardness.
  • heat-treated steel strip as a result of WeichglühClouds has a relation to the initial state lowered strength, which has a favorable effect on the possibilities of further processing.
  • the inventive method can be carried out particularly cost effective and efficient.
  • steel sheet produced according to the invention can be used particularly well, for example, for the production of punching knives or similar objects which, if necessary, must be bent sharply in order to obtain their intended shape.
  • the production of a semifinished product made of sheet steel according to the invention may include separation operations, such as stamping or cutting, as well as forming operations, such as deep drawing or bending. If necessary, the semifinished products thus produced can also undergo a final tempering treatment.
  • the decarburization time selected in each case when carrying out the process according to the invention depends on the respectively required decarburization depth. It is typically at least 90 minutes. According to experience, the decarburization depth of at least 30 ⁇ m can be achieved in this time, for example in the case of tempered steels having a C content of 0.55% by weight, under the operating parameters prescribed by the invention.
  • the duration over which the decarburization treatment according to the invention has to be carried out in order to achieve a specific decarburization depth can be determined for a given decarburization temperature, given decarburization depth and given dew point of the decarburisation atmosphere on the basis of the carbon content and the coil weight of the steel strip to be treated. Should the decarburization depth be a maximum of 120 ⁇ m can be limited, it can be seen from experience, the decarburization annealing limited to a maximum of 120 minutes.
  • a gas mixture of nitrogen, hydrogen and steam is also used in the implementation of the decarburization according to the invention as decarburization gas.
  • decarburization gas typically, such a decarburizing atmosphere at a between 20 - 28 0 C, in particular 20
  • the heating to the decarburization temperature also takes place in the process according to the invention initially under a protective gas atmosphere.
  • the decarburization temperature is reached, the steel strip in the open coil is exposed to the decarburizing atmosphere.
  • the inert gas atmosphere maintained during the heating can be 85-97% by volume of nitrogen and 3
  • the amount of water required for the decarburization reaction in the furnace can be regulated as a function of the dew point.
  • the dew point of the decarburization atmosphere over the entire Decarburization annealing time are detected.
  • the water vapor content of the decarburizing atmosphere is then adjusted so that the dew point of the atmosphere is maintained in the range of 20-26%.
  • the steel strip In order to remove possibly existing oxide layers and lubricant residues on the processed steel strip, the steel strip should be pickled before winding to the open coil.
  • the method according to the invention can be carried out in a particularly simple manner when the heating and decarburization annealing of the open coil takes place in a hood annealing furnace.
  • a tempering steel suitable for the production of steel sheets processed according to the invention typically has the following composition (in% by weight):
  • One consisting of an addition of iron and unavoidable impurities (in% by weight) 0.5% C, 0.2% Si, 0.75% Mn, ⁇ 0.12% P, ⁇ 0.003% S, 0.02% Al and 0.1% Cr containing tempering steel has been cast in conventional continuous casting to a starting material, such as a slab or thin slab.
  • the slab has been hot rolled in a conventional manner to a steel strip.
  • the final temperature of the hot rolling was in the range of 850-950 0 C, wherein the specifically selected here Kaltwal zendtemperatur 900 0 C.
  • the temper rolled steel strip was then wound in a conventional manner to an open coil.
  • the winding layers of the steel strip have been held by inserting a wire or other suitable means at a distance, that between each two adjacent layers, a gas-permeable space is formed.
  • the steel strip is then placed as an open coil in a bell annealing furnace and heated for a heating time of 10 hours under a 93 vol .-% N and 7 vol .-% H 2 containing protective gas atmosphere until the entire coil the 700 0 C amount decarburization annealing temperature had.
  • the open coil was kept under this atmosphere for a decarburization annealing time of 90 minutes.
  • the dew point of the decarburization atmosphere prevailing in the hood furnace has been recorded continuously and adjusted to a desired value.
  • the open coil has been cooled in the hood furnace under a protective gas atmosphere at a cooling rate of 1 ° C / min.
  • the surface-decarburized steel strip thus obtained had decarburized surface layers adjacent to its surfaces, 40 ⁇ m thick, while its inner core region adjacent to the decarburized surface layers still had the carbon content of the starting steel.
  • the respectively achieved decarburization depth ⁇ t is in a range of 30-120 ⁇ m.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Sheet Steel (AREA)
  • Heat Treatment Of Strip Materials And Filament Materials (AREA)

Abstract

The invention relates to a method for generating steel strip optimally combining high hardness and good deformability. To this end, the following process steps are taken in producing a surface-decarbonized steel strip from a heat-treatable steel having at least 0.4 weight % carbon: - producing the steel strip from the heat-treatable steel; - heating the steel strip that has been wound into an open coil to a decarbonizing tempering temperature that can be up to 20 °C below the Ac1 temperature of the heat-treatable steel and does not exceed the Ac3 temperature of the heat-treatable steel; - tempering the steel strip in an open coil in a decarbonizing atmosphere for a decarbonizing tempering period of at least 90 minutes, the decarbonizing gas forming the decarbonizing atmosphere flowing through the intermediate spaces between the winding layers of the open coil; - accelerated cooling of the steel strip such that the measured depth (At) of decarbonization, starting from the surface of the steel strip, is limited to a range that is less than one-quarter of the thickness of the steel strip.

Description

Verfahren zum Herstellen eines oberflächenentkohlten Method for producing a surface-decarburized
Warmbandshot strip
Die Erfindung betrifft ein Verfahren zum Herstellen eines entkohlten Warmbands, das aus einem mindestens 0,4 Gew.-% Kohlenstoff enthaltenden Vergütungsstahl erzeugt ist. Aus Stählen dieser Art hergestellte Warmbänder weisen eine hohe Härte auf und sind daher insbesondere für die Herstellung von Gegenständen geeignet, die im Einsatz hohen lokal begrenzten Belastungen ausgesetzt sind. Dies ist zum Beispiel bei Stanzmessern oder vergleichbaren schneidenden Werkzeugen der Fall, bei denen im praktischen Einsatz sowohl die Schneidkante als auch der die Schneidkante tragende Messerkörper während des Schneidvorgangs hohe Kräfte aufnehmen müssen.The invention relates to a method for producing a decarburized hot strip, which is produced from a quenching steel containing at least 0.4 wt .-% carbon. Hot rolled strips produced from steels of this type have a high hardness and are therefore particularly suitable for the production of articles which are exposed to high localized loads during use. This is the case, for example, in the case of punching blades or comparable cutting tools in which both the cutting edge and the blade body carrying the cutting edge have to absorb high forces during the cutting operation in practical use.
Den Vorteilen einer Verwendung von Vergütungsstählen mit vergleichbar hohen Kohlenstoff-Gehalten steht der Nachteil gegenüber, dass derartige Stähle aufgrund ihrer großen Härte nur vergleichbar schwer verformt werden können. Dies führt dazu, dass es beispielsweise bei einer Verformung dünner, aus Vergütungsstahl mit hoher Härte hergestellten Blechen zur Bildung von Rissen an der Blechoberfläche kommt, von denen unter Belastung dann ein Bruch des aus dem jeweiligen Blech hergestellten Bauteils ausgehen kann. Grundsätzlich ist es bekannt, dass die Verformbarkeit von Stählen durch Entkohlungsglühen verbessert werden kann. So werden beispielsweise für eine Tiefziehverformung bestimmte, aus weichen Stählen gefertigte Stähle einer Entkohlungsglühung unterzogen. Ziel ist dabei, eine möglichst gleichmäßige Reduzierung des Kohlenstoff- Gehalts über den gesamten Blechquerschnitt zu erhalten, um ein möglichst gleichmäßiges Verformungsverhalten sicherzustellen.The advantages of using heat-treated steels with comparably high carbon contents is offset by the disadvantage that such steels can only be deformed with comparable difficulty due to their high hardness. As a result, for example, in the case of deformation of thin sheets made of high-hardness tempered steel, the formation of cracks on the sheet surface occurs, under which stress a break of the component produced from the respective sheet can result. Basically, it is known that the ductility of steels can be improved by decarburization annealing. For example, for deep-drawing deformation, certain steels made of soft steels are subjected to decarburization annealing. The aim is to obtain as even as possible a reduction in the carbon content over the entire sheet metal cross section, in order to ensure the most uniform possible deformation behavior.
Ein Beispiel für ein Entkohlungsglühen eines Kaltbands, das für eine Tiefzieh-Verarbeitung bestimmt und aus einem Stahl mit geringen, typischerweise deutlich weniger als 0,03 Gew.-% betragenden Kohlenstoffgehalten erzeugt ist, ist in der GB 1,189,464 beschrieben. Bei diesem bekannten Verfahren wird aus einer Bramme ein Warmband bei einer Endwalztemperatur von 850 - 950 0C warmgewalzt. Das erhaltene Warmband wird dann bei einer Haspeltemperatur von 600 0C gehaspelt und anschließend auf die gewünschte Enddicke kaltgewalzt.An example of a decarburization anneal of a cold strip intended for deep draw processing and made from a steel having low, typically significantly less than 0.03 wt% carbon levels is described in GB 1,189,464. In this known method, a hot strip is hot rolled from a slab at a final rolling temperature of 850-950 0 C. The resulting hot strip is then coiled at a reel temperature of 600 0 C and then cold rolled to the desired final thickness.
Nach dem Kaltwalzen wird das Kaltband gemäß dem bekannten Verfahren zu einem "Open-Coil" gewickelt und als Open- Coil entkohlend geglüht. Ein solches Open-Coil ist so locker gewickelt, dass seine einzelnen Wickellagen durch Freiräume voneinander getrennt sind. Auf diese Weise kann das Reaktionsgas durch die zwischen den einzelnen Lagen des Coils vorhandenen Zwischenräume hindurch strömen, so dass bei optimierter Gasstromführung jede Oberfläche des Coils in gleicher Weise von dem Gas überstrichen wird.After cold rolling, the cold strip is wound according to the known method into an "open coil" and decarburizing annealed as an open coil. Such an open-coil is so loosely wound that its individual winding layers are separated by open spaces. In this way, the reaction gas can flow through the intermediate spaces between the individual layers of the coil, so that with optimized gas flow guidance, each surface of the coil is swept in the same way by the gas.
Um den gemäß der GB 1,189,464 geforderten Grad der Entkohlung zu erreichen, sind lange Glühzeiten erforderlich. So muss ein 0,04 Gew.-% C enthaltender Stahl gemäß der GB 1,189,464 zunächst 8 bis 12 Stunden unter einer im Wesentlichen trockenen Atmosphäre auf die geforderte Entkohlungsglühtemperatur erwärmt werden. Anschließend wird dann Wasserdampf im Verhältnis 200:1 in die Ofenatmosphäre gegeben, um den Entkohlungsprozess in Gang zu bringen. Dann wird die Entkohlungsglühung für weitere 10 Stunden unter der so gebildeten reduzierenden Atmosphäre fortgesetzt, bis die gewünschte Reduzierung des Kohlenstoff -Gehaltes erreicht ist.In order to achieve the degree of decarburization required by GB 1,189,464, long annealing times are required required. Thus, according to GB 1,189,464, a steel containing 0.04 wt.% C must first be heated to the required decarburization annealing temperature under a substantially dry atmosphere for 8 to 12 hours. Subsequently, water vapor in the ratio 200: 1 is then added to the furnace atmosphere to initiate the decarburization process. Then decarburization annealing is continued for a further 10 hours under the reducing atmosphere so formed until the desired reduction in carbon content is achieved.
Eine andere Möglichkeit des Entkohlungsglühens eines für Tiefziehzwecke bestimmten, 0,03 - 0,06 Gew.-% Kohlenstoff enthaltenden Kaltbands ist in der DE-OS 2 105 218 beschrieben. Bei diesem Verfahren wird das Kaltband im Durchlauf durch einen Ofen geleitet, in der bei einer weniger als 780 0C betragenden Glühtemperatur eine reduzierende Atmosphäre aufrecht erhalten wird. Die Durchlaufzeit des Bandes durch den Glühofen wird dabei so eingestellt, dass sein Kohlenstoff-Gehalt beim Austritt aus dem Glühofen weniger als 0,01 Gew.-% beträgt.Another possibility of the decarburization annealing of a thermoforming purposes, 0.03 - 0.06 wt .-% carbon-containing cold strip is described in DE-OS 2,105,218. In this method, the cold strip in a continuous is passed through an oven in the draw forming in a less than 780 0 C annealing temperature, a reducing atmosphere is maintained. The cycle time of the strip through the annealing furnace is adjusted so that its carbon content at the exit from the annealing furnace is less than 0.01 wt .-%.
Vor diesem Hintergrund lag der Erfindung die Aufgabe zu Grunde, ein Verfahren zu schaffen, dass die Erzeugung von Stahlband erlaubt, bei dem hohe Härte einerseits und gute Verformbarkeit andererseits miteinander optimal kombiniert sind.Against this background, the invention was based on the object to provide a method that allows the production of steel strip, in which high hardness on the one hand and good formability on the other hand are optimally combined with each other.
Diese Aufgabe ist erfindungsgemäß durch das in Anspruch 1 angegebene Verfahren gelöst worden. Vorteilhafte Ausgestaltungen dieses Verfahrens sind in den auf Anspruch 1 rückbezogenen Ansprüchen angegeben. Gemäß der Erfindung wird zunächst in bekannter Weise aus einem mindestens 0,4 Gew.-% Kohlenstoff enthaltenden Vergütungsstahl ein Stahlband erzeugt . Bei diesem Stahlband kann es sich um ein Kalt- oder ein Warmband handeln, wobei sich die erfindungsgemäße Vorgehensweise insbesondere für die Behandlung von Warmband eignet, das mit einer bestimmten, über der Dicke von Kaltband liegenden Dicke verarbeitet werden soll..This object has been achieved by the method specified in claim 1. Advantageous embodiments of this method are specified in the dependent claims on claim 1. According to the invention, a steel strip is first produced in known manner from a quenching steel containing at least 0.4% by weight of carbon. This steel strip can be a cold or a hot strip, the procedure according to the invention being particularly suitable for the treatment of hot strip which is to be processed with a specific thickness lying above the thickness of cold strip.
Das Stahlband wird erfindungsgemäß zu einem Open-Coil gewickelt und als Open-Coil über eine ausreichend lange Zeitspanne auf eine Entkohlungsglühtemperatur erwärmt . Diese kann bis zu 20 0C, insbesondere bis zu 10 0C, unterhalb der Acl-Temperatur des jeweiligen Vergütungsstahls liegen und darf die Ac3 -Temperatur des jeweiligen Vergütungsstahls nicht überschreiten.The steel strip is wound according to the invention to an open coil and heated as an open coil over a sufficiently long period of time to a decarburization annealing temperature. This may be up to 20 0 C, in particular up to 10 0 C, below the A cl temperature of the respective tempering steel and must not exceed the A c3 temperature of the respective tempering steel.
Anschließend erfolgt das entkohlende Glühen des Stahlbands im Open-Coil unter einer entkohlenden Atmosphäre für eine Entkohlungsglühzeit von mindestens 90 Minuten. Während der Entkohlungsglühzeit strömt das die entkohlende Atmosphäre bildende Entkohlungsgas durch die zwischen den Wickellagen des Open-Coils vorhandenen Zwischenräume .The decarburizing annealing of the steel strip in the open coil is then carried out under a decarburizing atmosphere for a decarburization annealing time of at least 90 minutes. During the decarburization annealing time, the decarburizing gas forming the decarburizing atmosphere flows through the gaps existing between the winding layers of the open coil.
Der Vorteil des erfindungsgemäßen Entkohlungsglühens bei zu einem Open-Coil gewickelten Stahlband besteht darin, dass sich auf diese Weise zeitsparend eine gleichmäßige Temperaturverteilung über die Länge und Breite des jeweils verarbeiteten Stahlbands erreichen lässt. Die Glühbedingungen sind dabei erfindungsgemäß so gewählt, dass über das gesamte Band ein gleichmäßig verteilter Gefügezustand vorliegt. So ist durch den erfindungsgemäß vorgegebenen Bereich der Glühtemperatur gewährleistet, dass im jeweils verarbeiteten Band noch ausreichende Mengen an Ferrit vorhanden sind, um eine schnelle Diffusion des Kohlenstoffs zu ermöglichen. Diese ist im Ferrit um bis zu hundertfach schneller als im Austenit.The advantage of the decarburization annealing according to the invention in wound to an open coil steel strip is that can be achieved in this way time-saving uniform temperature distribution over the length and width of each processed steel strip. The annealing conditions are chosen according to the invention so that there is a uniformly distributed structure state over the entire strip. So is by the invention given range of the annealing temperature ensures that in each processed band still sufficient amounts of ferrite are present in order to allow rapid diffusion of the carbon. This is up to a hundredfold faster in ferrite than in austenite.
Um möglichst kurze Glühzeiten zu erreichen, wird die Entkohlungsglühtemperatur erfindungsgemäß bevorzugt in einen Bereich eingestellt, der um 10 - 20 0C niedriger ist als die ACi-Temperatur . Bei dieser Einstellung der Entkohlungsglühtemperatur ist sichergestellt, dass der Vergütungsstahl des jeweils verarbeiteten Stahlbands ein ferritisches Gefüge besitzt, so dass eine optimale Diffusionsgeschwindigkeit des Kohlenstoffs erreicht wird.In order to achieve the shortest possible annealing times, the decarburization annealing temperature according to the invention is preferably set in a range which is lower by 10 to 20 0 C than the A Ci temperature. This setting of the decarburization annealing temperature ensures that the tempering steel of the respective processed steel strip has a ferritic structure, so that an optimum diffusion rate of the carbon is achieved.
Im Anschluss an das Entkohlungsglühen wird das Open-Coil beschleunigt abgekühlt, um eine in Folge der Eigenhitze des Coils eventuell eintretende, unerwünschte und in ihrem Umfang unsichere Nachdiffusion von Kohlenstoff in die zuvor gezielt entkohlte Oberflächenschicht zu verhindern. Die beschleunigte Abkühlung sollte dabei so schnell wie möglich, möglichst sofort, nach dem Ende der Entkohlungsglühzeit einsetzen und mit einer Abkühlgeschwindigkeit von mindestens 1 °C/min erfolgen.Following the decarburization annealing, the open coil is accelerated cooled to prevent any undesirable and, in terms of its extent, insecure subsequent diffusion of carbon into the previously deliberately decarburized surface layer as a result of the coil's inherent heat. The accelerated cooling should take place as soon as possible, as soon as possible after the end of the decarburization annealing time and at a cooling rate of at least 1 ° C / min.
Auch ist es günstig, wenn die beschleunigte Abkühlung unter Schutzgas durchgeführt wird. Diese Maßnahme dient ebenfalls dazu, eine unkontrollierte Entkohlung des Stahlbands während der Abkühlung weitestgehend zu verhindern.It is also advantageous if the accelerated cooling is carried out under protective gas. This measure also serves to prevent uncontrolled decarburization of the steel strip during cooling as much as possible.
Bei einem so in erfindungsgemäßer Weise behandelten Stahlblech ist eine ausgehend von der jeweiligen Oberfläche des Stahlbands gemessene entkohlte Oberflächenschicht vorhanden, deren Tiefe jeweils kleiner als ein Viertel der Dicke des Stahlbands ist, so dass nur oberflächennahe Bereiche in die erfindungsgemäße Entkohlung einbezogen sind. In der Praxis werden die Parameter des erfindungsgemäßen Verfahrens bevorzugt so gewählt, dass Entkohlungstiefen von maximal 120 μm, insbesondere 30 - 120 μm, erreicht werden.In a thus treated in accordance with the invention steel sheet is one starting from the respective Decarburized surface layer measured measured surface of the steel strip whose depth is in each case smaller than a quarter of the thickness of the steel strip, so that only near-surface areas are included in the decarburization according to the invention. In practice, the parameters of the method according to the invention are preferably chosen so that decarburization depths of a maximum of 120 μm, in particular 30-120 μm, are achieved.
Das bei erfindungsgemäßer Vorgehensweise erhaltene Stahlband ist folglich dadurch gekennzeichnet, dass es in Folge der Entkohlungsbehandlung eine hohe Biegeumformbarkeit im Bereich einer oberflächennahen Schicht besitzt. Gleichzeitig weist das erfindungsgemäß behandelte Band aufgrund des Umstandes, dass im Kernbereich des fertig entkohlten Stahlbands noch der hohe Anfangskohlenstoff-Gehalt erhalten ist, eine hohe Kernhärte auf .The steel strip obtained by the procedure according to the invention is consequently characterized in that it has a high bend formability in the region of a near-surface layer as a result of the decarburization treatment. At the same time, due to the fact that the high initial carbon content is still obtained in the core region of the finished decarburized steel strip, the strip treated according to the invention has a high core hardness.
Insgesamt weist erfindungsgemäß wärmebehandeltes Stahlband in Folge des Weichglühzustands (keine Perlitbildung nach der Glühung) eine gegenüber dem Ausgangszustand abgesenkte Festigkeit auf, die sich günstig auf die Möglichkeiten der Weiterverarbeitung auswirkt .Overall, according to the invention heat-treated steel strip as a result of Weichglühzustands (no perlite formation after annealing) has a relation to the initial state lowered strength, which has a favorable effect on the possibilities of further processing.
Aufgrund der vergleichbar niedrigenBecause of the comparably low
Entkohlungsglühtemperaturen und der kurzen Glühzeiten lässt sich das erfindungsgemäße Verfahren besonders kostengünstig und effizient durchführen.Decarburization annealing temperatures and the short annealing times, the inventive method can be carried out particularly cost effective and efficient.
Die besondere Eigenschaftskombination eines erfindungsgemäß behandelten, aus einem Vergütungsstahl erzeugten Stahlblechs erlaubt es, solches Stahlband ohne die Gefahr von Rissbildung zu verformen. Als solches lässt sich erfindungsgemäß hergestelltes Stahlblech beispielsweise besonders gut für die Herstellung von Stanzmessern oder ähnlichen Gegenständen verwenden, die erforderlichenfalls stark gebogen werden müssen, um die ihnen zugedachte Form zu erhalten.The special combination of properties of a treated according to the invention, from a tempering steel produced steel sheet allows to deform such steel strip without the risk of cracking. As such, steel sheet produced according to the invention can be used particularly well, for example, for the production of punching knives or similar objects which, if necessary, must be bent sharply in order to obtain their intended shape.
Dabei kann die Fertigung eines Halbzeugs aus erfindungsgemäß hergestelltem Stahlblech Trennoperationen, wie Stanzen oder Schneiden, sowie Umformoperationen, wie Tiefziehen oder Biegen, umfassen. Erforderlichenfalls können die derart gefertigten Halbzeuge auch eine abschließende Vergütungsbehandlung durchlaufen .In this case, the production of a semifinished product made of sheet steel according to the invention may include separation operations, such as stamping or cutting, as well as forming operations, such as deep drawing or bending. If necessary, the semifinished products thus produced can also undergo a final tempering treatment.
Die bei der Durchführung des erfindungsgemäßen Verfahrens jeweils gewählte Entkohlungszeit richtet sich nach der jeweils geforderten Entkohlungstiefe . Typischerweise beträgt sie mindestens 90 Minuten. Unter den durch die Erfindung vorgegebenen Betriebsparametern lässt sich in dieser Zeit erfahrungsgemäß beispielsweise bei Vergütungsstählen mit einem C-Gehalt von 0,55 Gew.-% eine Entkohlungstiefe von mindestens 30 μm erreichen.The decarburization time selected in each case when carrying out the process according to the invention depends on the respectively required decarburization depth. It is typically at least 90 minutes. According to experience, the decarburization depth of at least 30 μm can be achieved in this time, for example in the case of tempered steels having a C content of 0.55% by weight, under the operating parameters prescribed by the invention.
Grundsätzlich lässt sich die Dauer, über die die erfindungsgemäße Entkohlungsbehandlung durchgeführt werden muss, um eine bestimmte Entkohlungstiefe zu erreichen, bei gegebener Entkohlungstemperatur, vorgegebener Entkohlungstiefe und vorgegebenem Taupunkt der Entkohlungsatmosphäre anhand des Kohlenstoffgehaltes und des Coilgewichtes des zu behandelnden Stahlbands bestimmen. Soll die Entkohlungstiefe auf maximal 120 μm beschränkt werden, so kann dazu erfahrungsgemäß die Entkohlungsglühzeit auf maximal 120 Minuten beschränkt werden.In principle, the duration over which the decarburization treatment according to the invention has to be carried out in order to achieve a specific decarburization depth can be determined for a given decarburization temperature, given decarburization depth and given dew point of the decarburisation atmosphere on the basis of the carbon content and the coil weight of the steel strip to be treated. Should the decarburization depth be a maximum of 120 μm can be limited, it can be seen from experience, the decarburization annealing limited to a maximum of 120 minutes.
In an sich bekannter Weise wird auch bei der Durchführung der erfindungsgemäßen Entkohlung als Entkohlungsgas ein Gasgemisch aus Stickstoff, Wasserstoff und Wasserdampf verwendet. Typischerweise enthält eine solche entkohlende Atmosphäre bei einem zwischen 20 - 28 0C, insbesondere 20In a manner known per se, a gas mixture of nitrogen, hydrogen and steam is also used in the implementation of the decarburization according to the invention as decarburization gas. Typically, such a decarburizing atmosphere at a between 20 - 28 0 C, in particular 20
- 26 0C, liegenden Taupunkt 85 - 97 Vol.-% Stickstoff und 3 - 15 % 7 Vol.-% Wasserstoff, wobei eine in der Praxis verwendete Atmosphäre typischerweise 93 Vol.-% Stickstoff und 7 Vol.-% Wasserstoff enthält.- 26 0 C, lying dew point 85 - 97 vol .-% nitrogen and 3 - 15% 7 vol .-% hydrogen, wherein an atmosphere used in practice typically contains 93 vol .-% nitrogen and 7 vol .-% hydrogen.
Zweckmäßigerweise erfolgt die Erwärmung auf die Entkohlungstemperatur auch beim erfindungsgemäßen Verfahren zunächst unter einer Schutzgasatmosphäre. Ist dann die Entkohlungstemperatur erreicht, wird das Stahlband im Open-Coil der entkohlenden Atmosphäre ausgesetzt. Die während der Erwärmung aufrechterhaltene Schutzgasatmosphäre kann 85 - 97 Vol.-% Stickstoff und 3Expediently, the heating to the decarburization temperature also takes place in the process according to the invention initially under a protective gas atmosphere. When the decarburization temperature is reached, the steel strip in the open coil is exposed to the decarburizing atmosphere. The inert gas atmosphere maintained during the heating can be 85-97% by volume of nitrogen and 3
- 15 Vol.-% Wasserstoff enthalten, wobei eine in der Praxis eingesetzte Schutzgasatmosphäre typischerweise 93 Vol.-% Stickstoff und 7 % Wasserstoff aufweist. Nach Erreichen der Entkohlungsglühtemperatur wird dieser Atmosphäre dann Wasserdampf zugeführt, um die reduzierende Entkohlungsatmosphäre zu schaffen, unter der die Entkohlungsreaktion C+H2O -> CO+H2 einsetzt.- contain 15 vol .-% hydrogen, wherein a protective gas used in practice typically 93 vol .-% nitrogen and 7% hydrogen. Upon reaching the decarburization annealing temperature, steam is then added to this atmosphere to provide the reducing decarburization atmosphere under which the decarburization reaction starts C + H 2 O -> CO + H 2 .
Die für die Entkohlungsreaktion im Ofen erforderliche Wassermenge kann in Abhängigkeit vom Taupunkt geregelt werden. Zu diesem Zweck kann der Taupunkt der Entkohlungsatmosphäre über die gesamte Entkohlungsglühzeit erfasst werden. In Abhängigkeit vom Ergebnis eines Soll-/Ist-Abgleichs wird dann der Wasserdampfanteil der entkohlenden Atmosphäre so eingestellt, dass der Taupunkt der Atmosphäre im Bereich von 20 - 26 % gehalten wird.The amount of water required for the decarburization reaction in the furnace can be regulated as a function of the dew point. For this purpose, the dew point of the decarburization atmosphere over the entire Decarburization annealing time are detected. Depending on the result of a target / actual adjustment, the water vapor content of the decarburizing atmosphere is then adjusted so that the dew point of the atmosphere is maintained in the range of 20-26%.
Um auf dem jeweils verarbeiteten Stahlband eventuell vorhandene Oxidschichten und Schmierstoffrückstände zu entfernen, sollte das Stahlband vor dem Wickeln zu dem Open-Coil gebeizt werden.In order to remove possibly existing oxide layers and lubricant residues on the processed steel strip, the steel strip should be pickled before winding to the open coil.
Im Hinblick auf die Maßhaltigkeit, insbesondere die Planheit, des erhaltenen Stahlbands kann es darüber hinaus günstig sein, das Stahlband nach dem Beizen und vor dem Wickeln zu dem Open-Coil dressierzuwalzen.In view of the dimensional stability, in particular the flatness, of the resulting steel strip, it may also be advantageous to roll-strip the steel strip after pickling and before winding to the open coil.
Besonders einfach lässt sich das erfindungsgemäße Verfahren dann durchführen, wenn die Erwärmung und Entkohlungsglühung des Open-Coils in einem Haubenglühofen stattfindet .The method according to the invention can be carried out in a particularly simple manner when the heating and decarburization annealing of the open coil takes place in a hood annealing furnace.
Praktische Untersuchungen haben ergeben, dass sich mit dem erfindungsgemäßen Verfahren besonders gute Herstellungsergebnisse erzielen lassen, wenn die Entkohlungsglühtemperatur 680 - 780 0C beträgt, wobei es sich insbesondere günstig auswirkt, wenn die Glühtemperatur nahe der Ad-Temperatur gewählt wird.Practical tests have shown that is possible to achieve particularly good production results with the inventive method, when the decarburization annealing temperature 680 - is 780 0 C, whereby it affects particularly low when the annealing temperature near the A d -Temperature is selected.
Ein für die Herstellung erfindungsgemäß verarbeiteter Stahlbleche geeigneter Vergütungsstahl weist typischerweise folgende Zusammensetzung auf (in Gew.-%) :A tempering steel suitable for the production of steel sheets processed according to the invention typically has the following composition (in% by weight):
C: 0,4 - 1,0 % Si: 0, 1 - 0, 5 %C: 0.4 - 1.0% Si: 0, 1 - 0, 5%
Mn: 0,3 - 1,2 %Mn: 0.3 - 1.2%
P: < 0, 02 %P: <0, 02%
S: < 0, 008 %S: <0, 008%
Al : 0, 01 - 0, 05 %Al: 0, 01 - 0, 05%
Cr: 0, 1 - 0, 5 %Cr: 0, 1 - 0, 5%
Ni: 0, 1 - 0,4 %Ni: 0, 1 - 0.4%
Mo: < 0, 1 %Mo: <0, 1%
Rest Eisen und unvermeidbare Verunreinigungen.Remaining iron and unavoidable impurities.
Nachfolgend wird die Erfindung anhand eines Ausführungsbeispiels näher erläutert.The invention will be explained in more detail with reference to an embodiment.
Ein aus einem neben Eisen und unvermeidbaren Verunreinigungen (in Gew.-%) 0,5 % C, 0,2 % Si, 0,75 % Mn, < 0,12 % P, < 0,003 % S, 0,02 % Al und 0,1 % Cr enthaltender Vergütungsstahl ist in konventionellem Strangguss zu einem Vormaterial, wie einer Bramme oder Dünnbramme, vergossen worden.One consisting of an addition of iron and unavoidable impurities (in% by weight) 0.5% C, 0.2% Si, 0.75% Mn, <0.12% P, <0.003% S, 0.02% Al and 0.1% Cr containing tempering steel has been cast in conventional continuous casting to a starting material, such as a slab or thin slab.
Anschließend ist die Bramme in an sich bekannter Weise zu einem Stahlband warmgewalzt worden. Die Endtemperatur des Warmwalzens lag dabei im Bereich von 850 - 950 0C, wobei die hier konkret gewählte Warmwal zendtemperatur 900 0C betrug.Subsequently, the slab has been hot rolled in a conventional manner to a steel strip. The final temperature of the hot rolling was in the range of 850-950 0 C, wherein the specifically selected here Kaltwal zendtemperatur 900 0 C.
Das mit dieser Warmwalzendtemperatur als Warmband aus der Fertigwalzstaffel austretende Stahlband ist auf eine Haspeltemperatur von 600 - 620 0C abgekühlt und zu einem konventionellen Coil mit dicht aufeinander liegenden Lagen gewickelt worden. Konkret betrug die gewählte Haspeltemperatur 620 0C. Nach dem Haspeln ist das Stahlband abgehapselt und in an sich ebenfalls bekannter Weise gebeizt und unmittelbar darauf folgend dressiergewalzt worden.The hot-rolling of this hot-rolled strip from the finishing roll line exiting steel strip to a coiling temperature 600-620 0 C cooled and been wound to a conventional coil having located close to each other layers. Specifically, the selected coiler temperature was 620 0 C. After the reeling, the steel strip is isolated and pickled in a manner which is also known per se and immediately thereafter temper rolling.
Das dressiergewalzte Stahlband ist dann in an sich bekannter Weise zu einem Open-Coil gewickelt worden. Dabei sind die Wickellagen des Stahlbands durch Einlegen eines Drahts oder eines anderen geeigneten Mittels so auf Abstand gehalten worden, dass zwischen jeweils zwei benachbarten Lagen ein von Gas durchströmbarer Freiraum gebildet ist.The temper rolled steel strip was then wound in a conventional manner to an open coil. In this case, the winding layers of the steel strip have been held by inserting a wire or other suitable means at a distance, that between each two adjacent layers, a gas-permeable space is formed.
Das Stahlband ist daraufhin als Open-Coil in einen Haubenglühofen gesetzt und über eine Erwärmungszeit von 10 Stunden unter einer 93 Vol.-% N und 7 Vol.-% H2 enthaltenden Schutzgasatmosphäre erwärmt worden, bis das gesamte Coil die 700 0C betragende Entkohlungsglühtemperatur aufwies .The steel strip is then placed as an open coil in a bell annealing furnace and heated for a heating time of 10 hours under a 93 vol .-% N and 7 vol .-% H 2 containing protective gas atmosphere until the entire coil the 700 0 C amount decarburization annealing temperature had.
Nach Erreichen der Entkohlungsglühtemperatur ist Wasserdampf in die Schutzgasatmosphäre geleitet worden, um die Entkohlungsreaktion zu starten. Die zugeführte Wasserdampfmenge ist dabei so bemessen worden, dass der Taupunkt der Atmosphäre während der Entkohlung konstant bei 26 0C lag.After reaching the decarburization annealing temperature, steam was introduced into the inert gas atmosphere to start the decarburization reaction. The supplied amount of water vapor has been so dimensioned that the dew point of the atmosphere was constant at 26 0 C during decarburization.
Das Open-Coil ist für eine Entkohlungsglühzeit von 90 Minuten unter dieser Atmosphäre gehalten worden. Während der Entkohlungsglühzeit ist der Taupunkt der im Haubenofen herrschenden Entkohlungsatmosphäre laufend erfasst und mit einem Sollwert abgeglichen worden. Abhängig vom Ergebnis dieses Vergleichs ist die Zusammensetzung der Entkohlungsatmosphäre, insbesondere ihr Wasserdampfgehalt, so eingestellt worden, dass ihr Taupunkt im Wesentlichen konstant bei 260C gehalten worden ist .The open coil was kept under this atmosphere for a decarburization annealing time of 90 minutes. During the decarburization annealing time, the dew point of the decarburization atmosphere prevailing in the hood furnace has been recorded continuously and adjusted to a desired value. Depending on the result of this comparison, the composition of the decarburization atmosphere, in particular their water vapor content, adjusted so that their dew point has been kept substantially constant at 26 0 C.
Unmittelbar nach Ablauf der Entkohlungsglühzeit ist das Open-Coil noch im Haubenofen unter einer Schutzgasatmosphäre mit einer Abkühlgeschwindigkeit von 1 °C/min abgekühlt worden.Immediately after the end of the decarburization annealing time, the open coil has been cooled in the hood furnace under a protective gas atmosphere at a cooling rate of 1 ° C / min.
Das so erhaltene oberflächenentkohlte Stahlband wies an seinen Oberflächen angrenzende, 40 μm dicke entkohlte Oberflächenschichten auf, während ihr an die entkohlten Oberflächenschichten angrenzender innerer Kernbereich noch den Kohlenstoffgehalt des Ausgangstahls besaß.The surface-decarburized steel strip thus obtained had decarburized surface layers adjacent to its surfaces, 40 μm thick, while its inner core region adjacent to the decarburized surface layers still had the carbon content of the starting steel.
In Fig. 1 ist schematisch für das in der voranstehend beschriebenen Weise entkohlungsgeglühte Stahlband der Kohlenstoffgehalt %C in Gew.-% über den Abstand A zur Oberfläche (Abstand A = O μm) des Stahlbands aufgezeichnet. Typischerweise liegt dabei die jeweils erreichte Entkohlungstiefe At in einem Bereich von 30 - 120 μm. In Fig. 1, the carbon content% C in% by weight over the distance A to the surface (distance A = O μm) of the steel strip is schematically plotted for the decarburization annealed steel strip as described above. Typically, the respectively achieved decarburization depth Δt is in a range of 30-120 μm.

Claims

P A T E N T A N S P R Ü C H E PATENT APPLICATIONS
1. Verfahren zum Herstellen eines aus einem mindestens 0,4 Gew.-% Kohlenstoff enthaltenden Vergütungsstahl erzeugten, oberflächenentkohlten Stahlbands, umfassend folgende Arbeitsschritte:1. A method for producing a surface-decarburized steel strip produced from a quench steel containing at least 0.4% by weight of carbon, comprising the following steps:
- Erzeugen des Stahlbands aus dem Vergütungsstahl;- producing the steel strip from the tempering steel;
- Erwärmen des zu dem Open-Coil gewickelten Stahlbands auf eine Entkohlungsglühtemperatur , die bis zu 20 0C unterhalb der Aci-Temperatur des jeweiligen Vergütungsstahls liegen kann und die Ac3-Temperatur des jeweiligen Vergütungsstahls nicht überschreitet;- Heating the wound to the open-coil steel strip to a decarburization annealing temperature, which may be up to 20 0 C below the A c i temperature of the respective tempering steel and does not exceed the A c3 temperature of the respective tempering steel;
- Glühen des Stahlbands im Open-Coil unter einer entkohlenden Atmosphäre für eine Entkohlungsglühzeit von mindestens 90 Minuten, wobei das die entkohlende Atmosphäre bildende Entkohlungsgas durch die zwischen den Wickellagen des Open-Coils vorhandenen Zwischenräume strömt;Annealing the steel strip in the open coil under a decarburizing atmosphere for a decarburization annealing time of at least 90 minutes, wherein the decarburizing gas forming the decarburizing gas flows through the spaces existing between the winding layers of the open coil;
- beschleunigtes Abkühlen des Stahlbands,accelerated cooling of the steel strip,
so dass die ausgehend von der jeweiligen Oberfläche des Stahlbands gemessene Tiefe der Entkohlung auf einen Bereich beschränkt ist, der jeweils kleiner als ein Viertel der Dicke des Stahlbands ist. such that the decarburization depth measured from the respective surface of the steel strip is limited to a range each less than one quarter of the thickness of the steel strip.
2. Verfahren nach Anspruch 1, d a d u r c h g e k e n n z e i c h n e t, d a s s das Coil für die beschleunigte Abkühlung mit einer erhöhten Menge an Schutzgas beaufschlagt wird.2. The method of claim 1, wherein the coil for the accelerated cooling is applied to the coil for the accelerated cooling with an increased amount of inert gas.
3. Verfahren nach einem der voranstehenden Ansprüche, d a d u r c h g e k e n n z e i c h n e t, d a s s die Tiefe der Entkohlung 30 - 120 μm beträgt.3. Method according to one of the preceding claims, wherein the depth of the decarburization is 30-120 .mu.m.
4. Verfahren nach einem der voranstehenden Ansprüche , d a d u r c h g e k e n n z e i c h n e t, d a s s die Entkohlungsglühzeit maximal 120 Minuten beträgt.4. Method according to one of the preceding claims, characterized in that the decarburization annealing time is a maximum of 120 minutes.
5. Verfahren nach einem der voranstehenden Ansprüche, d a d u r c h g e k e n n z e i c h n e t, d a s s die entkohlende Atmosphäre 85 - 97 Vol.-% Stickstoff, 3 - 15 Vol.-% Wasserstoff enthält.5. A process according to any one of the preceding claims, wherein the decarburising atmosphere contains 85-97% by volume of nitrogen, 3-15% by volume of hydrogen.
6. Verfahren nach einem der voranstehenden Ansprüche, d a d u r c h g e k e n n z e i c h n e t, d a s s das Stahlband, bevor es für die Entkohlungsglühzeit der entkohlenden Atmosphäre ausgesetzt wird, im Open-Coil unter einer Schutzgasatmopshäre auf die Entkohlungsglühtemperatur erwärmt wird.6. The method of claim 1, wherein the steel strip is heated to the decarburization annealing temperature in the open coil under a protective gas atmosphere before being exposed to the decarburizing atmosphere for the decarburization annealing time.
7. Verfahren nach Anspruch 5 und 6, d a d u r c h g e k e n n z e i c h n e t, d a s s die während der Erwärmung aufrechterhaltene Schutzgasatmosphäre 85 - 97 Vol.-% Stickstoff und 3 - 15 Vol.-% Wasserstoff enthält und d a s s der Schutzgasatmosphäre nach Erreichen der Entkohlungsglühtemperatur Wasserdampf zugeführt wird, um die entkohlende Atmosphäre herzustellen.7. The method according to claim 5 and 6, characterized in that the maintained during the heating inert gas atmosphere 85 - 97 vol .-% nitrogen and 3 - 15 vol .-% Containing hydrogen and that the protective gas atmosphere after reaching the decarburization annealing temperature water vapor is supplied to produce the decarburizing atmosphere.
8. Verfahren nach Anspruch 7, d a d u r c h g e k e n n z e i c h n e t, d a s s über die Entkohlungsglühzeit durch Regelung ihres Wasserdampfanteils der Taupunkt der entkohlenden Atmosphäre im Bereich von 20 - 28 °C gehalten wird.8. A method according to claim 7, wherein the dew point of the decarburizing atmosphere is maintained in the range of 20-28 ° C over the decarburization annealing time by controlling its water vapor content.
9. Verfahren nach einem der voranstehenden Ansprüche, d a d u r c h g e k e n n z e i c h n e t, d a s s das Stahlband vor dem Wickeln zu dem Open-Coil gebeizt wird.9. Method according to one of the preceding claims, characterized in that the steel strip is pickled before winding to the open coil.
10. Verfahren nach Anspruch 9, d a d u r c h g e k e n n z e i c h n e t, d a s s das Stahlband nach dem Beizen und vor dem Wickeln zu dem Open-Coil dressiert wird.10. The method of claim 9, wherein the steel strip is tempered after pickling and before winding to form the open coil.
11. Verfahren nach einem der voranstehenden Ansprüche, d a d u r c h g e k e n n z e i c h n e t, d a s s die Erwärmung und Entkohlungsglühung des Open-Coils in einem Haubenglühofen durchgeführt wird.11. Method according to one of the preceding claims, characterized in that the heating and decarburization annealing of the open coil is carried out in a bell-type annealing furnace.
12. Verfahren nach einem der voranstehenden Ansprüche, d a d u r c h g e k e n n z e i c h n e t, d a s s die Entkohlungsglühtemperatur 680 - 780 0C beträgt. 12. The method according to any one of the preceding claims, characterized in that the decarburization annealing temperature is 680 - 780 0 C.
13. Verfahren nach einem der Ansprüche 1 bis 11, d a d u r c h g e k e n n z e i c h n e t, d a s s die Entkohlungstemperatur um 10 - 20 0C niedriger als die ACi-Temperatur ist .13. The method according to any one of claims 1 to 11, characterized in that the Entkohlungstemperatur to 10 - 20 0 C lower than the A i-C temperature.
14. Verfahren nach einem der voranstehenden Ansprüche, d a d u r c h g e k e n n z e i c h n e t, d a s s der Vergütungsstahl folgende Zusammensetzung aufweist (in Gew.-%) :14. Method according to one of the preceding claims, characterized in that the quenching steel has the following composition (in% by weight):
C: 0,4 - 1, 0 %C: 0.4 - 1, 0%
Si: 0, 1 - 0, 5 %Si: 0, 1 - 0, 5%
Mn: 0, 3 - 1,2 %Mn: 0, 3 - 1.2%
P: < 0, 02 %P: <0, 02%
S: < 0, 008 %S: <0, 008%
Al: 0, 01 - 0,05 %Al: 0, 01 - 0.05%
Cr: 0, 1 - 0,5 %Cr: 0, 1 - 0.5%
Ni: 0, 1 - 0,4 %Ni: 0, 1 - 0.4%
Mo: < 0.1 %Mo: <0.1%
Rest Eisen und unvermeidbare Verunreinigungen.Remaining iron and unavoidable impurities.
15. Verfahren nach einem der voranstehenden Ansprüche, d a d u r c h g e k e n n z e i c h n e t, d a s s im Zuge der Erzeugung des Stahlbands folgende Arbeitsschritte absolviert werden:15. Method according to one of the preceding claims, characterized in that during the production of the steel strip the following work steps are completed:
- Erschmelzen des Vergütungsstahls,- melting of the tempering steel,
- Vergießen des Vergütungsstahls zu einem Vormaterial, wie Bramme oder Dünnbramme,Potting the tempering steel to a starting material, such as slab or thin slab,
- Warmwalzen des Vormaterials zu dem Stahlband bei einer Warmwalzendtemperatur von 850 - 900 0C, Haspeln des Stahlbands bei einer 600 - 620 0C betragenden Haspeltemperatur. Hot rolling of the starting material to the steel strip at a hot rolling end temperature of 850 to 900 0 C, Winding the steel strip at a reel temperature of 600 - 620 0 C.
EP08786978.0A 2007-08-17 2008-08-07 Method for producing a surface-decarbonized hot-rolled strip Active EP2179066B1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
PL08786978T PL2179066T3 (en) 2007-08-17 2008-08-07 Method for producing a surface-decarbonized hot-rolled strip

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE102007039013A DE102007039013B3 (en) 2007-08-17 2007-08-17 Production process for surface-decarbonized hot-rolled strip involves making strip, heating to decarbonizing heat, retaining in carbon-free atmosphere and cooling
PCT/EP2008/060378 WO2009024472A1 (en) 2007-08-17 2008-08-07 Method for producing a surface-decarbonized hot-rolled strip

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EP2179066A1 true EP2179066A1 (en) 2010-04-28
EP2179066B1 EP2179066B1 (en) 2013-05-01

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US (1) US8449694B2 (en)
EP (1) EP2179066B1 (en)
JP (1) JP5599708B2 (en)
CN (1) CN101802232B (en)
DE (1) DE102007039013B3 (en)
ES (1) ES2422738T3 (en)
PL (1) PL2179066T3 (en)
WO (1) WO2009024472A1 (en)

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KR101402503B1 (en) * 2009-08-31 2014-06-03 신닛테츠스미킨 카부시키카이샤 High-strength hot-dip galvanized steel sheet and process for producing same
DE102009044861B3 (en) 2009-12-10 2011-06-22 ThyssenKrupp Steel Europe AG, 47166 Process for producing a readily deformable flat steel product, flat steel product and method for producing a component from such a flat steel product
DE102010034161B4 (en) * 2010-03-16 2014-01-02 Salzgitter Flachstahl Gmbh Method for producing workpieces made of lightweight steel with material properties that can be adjusted via the wall thickness
DE102010032919B4 (en) * 2010-07-30 2023-10-05 Air Liquide Deutschland Gmbh Method and device for humidifying a combustible gas
CN102226230A (en) * 2011-04-15 2011-10-26 广东盈泉钢制品有限公司 Production method of carbon extra-deep drawing steel belt
KR101344534B1 (en) 2011-06-28 2013-12-26 현대제철 주식회사 Method for improving corrosion-resistance of rolled steel using decarburized layer

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WO2009024472A1 (en) 2009-02-26
JP2010537045A (en) 2010-12-02
EP2179066B1 (en) 2013-05-01
US8449694B2 (en) 2013-05-28
PL2179066T3 (en) 2013-09-30
JP5599708B2 (en) 2014-10-01
US20100319812A1 (en) 2010-12-23
ES2422738T3 (en) 2013-09-13
DE102007039013B3 (en) 2008-08-14
CN101802232B (en) 2012-07-04
CN101802232A (en) 2010-08-11

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