EP1484419A2 - Procedure for manufacturing carburized steel strips - Google Patents

Procedure for manufacturing carburized steel strips Download PDF

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Publication number
EP1484419A2
EP1484419A2 EP04013061A EP04013061A EP1484419A2 EP 1484419 A2 EP1484419 A2 EP 1484419A2 EP 04013061 A EP04013061 A EP 04013061A EP 04013061 A EP04013061 A EP 04013061A EP 1484419 A2 EP1484419 A2 EP 1484419A2
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EP
European Patent Office
Prior art keywords
coil
content
steel strip
temperature
annealing
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.)
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EP04013061A
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German (de)
French (fr)
Other versions
EP1484419A3 (en
Inventor
Jian Dr.-Ing. Bian
Karl-Ernst Dipl.-Ing. Friedrich
Giovanni Dipl.-Ing. Sabatino
Horst Walter Dr. Tamler
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ThyssenKrupp Steel Europe AG
Original Assignee
ThyssenKrupp Stahl AG
ThyssenKrupp Steel AG
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Publication of EP1484419A2 publication Critical patent/EP1484419A2/en
Publication of EP1484419A3 publication Critical patent/EP1484419A3/en
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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
    • C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
    • C23C8/20—Carburising
    • C23C8/22—Carburising of ferrous surfaces
    • 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
    • C21D9/663—Bell-type furnaces
    • C21D9/667—Multi-station furnaces
    • C21D9/67—Multi-station furnaces adapted for treating the charge in vacuum or special atmosphere
    • 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
    • C21D8/0278—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips involving a particular surface treatment

Definitions

  • the invention relates to a method for producing Steel strips in which the carbon content in one Surface layer of the respective steel strip in one separate operation is increased.
  • Carbon steels with a C content of at least 0.1 % By weight usually becomes a component first reshaped, then the carburizing piece by piece To be subjected to annealing treatment. This piece by piece carburizing takes place both with regard to the completing work steps as well as in terms of the resulting costs are complex.
  • the object of the invention was a method to indicate with which in a particularly economical manner Steel strips with a high hardness of theirs Surface layers and accordingly higher Have wear resistance created.
  • This object is achieved according to the invention by a method for producing steel strips, in which a coil which is coiled from a steel strip having an initial content of carbon in such a way that its layers are arranged at a distance from one another at a reaction temperature above the A c3 temperature is subjected to an annealing process in which a carburizing gas is passed through the space between the individual layers of the coil until in the edge layer of the steel strip there is at least 0.1% by weight, in particular at least 0.3% by weight, of the starting content. -% increased C content is reached.
  • the initial carbon content of the steel strips processed according to the invention is preferably at least 0.1% by weight. In particular, it is in the range of up to 0.4% by weight.
  • the annealing treatment then takes place, for example, in a carburizing atmosphere in a bell annealer which has been modified in accordance with the control options resulting from the method according to the invention.
  • the reaction temperature set in the carburizing annealing according to the invention is above the transition temperature A c3 , preferably up to 30 ° C. above the A c3 temperature, in particular at least 900 ° C.
  • the glow time over which the coil is on the reaction temperature is maintained for up to ten hours.
  • the method according to the invention can be used in this way produce steel strips that are particularly economical a hardened, wear-resistant surface at the same time good forming properties of the base material have.
  • Steel alloys such as case hardening or tempering steels typical carbon contents in the range of 0.1 - 0.25% by weight or 0.2-0.4% by weight.
  • a surface layer generate in which the carbon content versus the C content of the starting material by at least 0.1% by weight, in particular at least 0.3% by weight is increased.
  • the increase in the carbon content in the surface layer as well as the depth over which the carbon content at Application of the method according to the invention is increased can be determined via the annealing temperature, the annealing time and the Control the composition of the reaction gas.
  • the process can control the carbon content in each Surface layer can be increased to 0.4-0.9% by weight.
  • carbon content in the Achieve surface layer that 0.6 wt .-% to 0.9 wt .-% be.
  • the thickness of the carburized surface layer lies regularly between 50 - 500 ⁇ m, with the Depth over which it carburizes the surface layer of the Steel strips comes through the process parameters mentioned can be controlled. Depending on the desired The result of the work can be useful Process parameters during the carburizing process vary.
  • a gas mixture containing CO, H 2 and / or CO 2 can be used as the carburizing gas.
  • Such gas mixtures are composed, for example, of 20% CO, 40% H 2 and the remainder N 2 .
  • a hood annealing device can be used based to a conventional type of bell annealer Possibility of one regarding type, duration and quantity controlled gas supply is expanded.
  • the strip obtained after the annealing treatment can be cold rolled and processed into semi-finished products. if necessary it can be subjected to soft annealing.
  • the Production of the semi-finished products can involve a separation operation, like punching or cutting, and / or one Forming operations such as deep drawing or bending include. If necessary, the semi-finished products produced in this way undergo remuneration treatment.
  • the hood annealer 1 has an oven chamber 3 surrounded by a conventionally designed annealing hood 2, into which a steel strip S wound as an open coil C is inserted.
  • the known alloy specification for the steel strip S used is given in Table 1.
  • C Si Mn P S al Cr Cu Ni from 0.13 to 0.16 ⁇ 0.06 0.50-0, 60 ⁇ 0.02 ⁇ 0.012 0.015 to 0.04 ⁇ 0.06 ⁇ 0.1 ⁇ 0.06 All figures in% by weight, remainder Fe and unavoidable impurities
  • the hood annealer 1 is also provided with a gas connection 4 for a protective gas, here N 2 , with a gas connection 5 for reaction gas RGas, which is formed here by a mixture of CO, CO 2 and H 2 , with an exhaust gas discharge 6 and with different connections 7 equipped, among other things, the carbon level C P , the furnace chamber temperature T O and the composition of the atmosphere present in the furnace chamber can be detected.
  • measurements can be carried out on the coil C itself via the connections 7, for example in order to determine the progress of the heating or carburizing as well as the gas flow through the coil C.
  • a control device 8 Connected to the connections 7 is a control device 8 which, over the duration of the entire carburizing process, the development of the furnace chamber temperature T O, the carbon level C P of the atmosphere in the furnace chamber 3 and the composition ZGas of the gases passed into the furnace chamber 3 (reaction gas RGas / protective gas N 2 ) controls.
  • the hot or cold rolled, pickled if necessary Steel strip S the thickness of which is, for example, 0.8 to 3 mm and the width of which can be 600 to 1200 mm is considered dense Delivered wound coil, not shown here, whose Weight is up to 20 tons.
  • thermocouple In order to ensure a uniform temperature across the turns, a thermocouple has been installed in the inner and the middle turn of the coil C.
  • the temperature T K of the coil core (central turn) and the temperature T R of the coil edge (internal turn) were measured online with the thermocouples during the entire carburizing process.
  • the temperature profiles T K , T R and T O are shown in FIG. 2 over the process time t.
  • the open-coil C wound in this way was inserted cold into the furnace space 3 after the wrapping.
  • the oven temperature T O was 750 ° C. at the time the cold coil C was inserted.
  • the open-coil C was held for several hours until it was further heated to the reaction temperature of 900 ° C.
  • the coil C in the furnace space 3 was kept under protective gas (N2).
  • the heating rate measured on the inner turn was 0.026 ° C / s.
  • the carburization was only initiated after the temperatures T K and T R of the coil C had each reached the predetermined reaction temperature of 900 ° C.
  • the reaction temperature was reached, the reaction gas RGas was passed into the furnace chamber 3.
  • the introduction into the furnace room 3 was via the furnace ceiling.
  • the introduced reaction gas RGas was put into a gas flow by a fan, not shown, which flow was evenly distributed between the turns of the open coil C.
  • the coil C was carburized over a period t H of 8 hours.
  • the C level which is a decisive parameter for the carburizing process and primarily determines the marginal carbon content and the carburizing depth, was kept constant at 1.0% in the carburizing phase by controlling the amount of reaction gas RGas supplied.
  • the carbon potential is referred to as the "C level" which indicates to what concentration the carbon is enriched in austenite in equilibrium. It is to be understood as the C content, which is in the Equilibrium state with a pure iron sample at one certain temperature in the austenite.
  • the C level is therefore the most important parameter in practice to monitor the carburizing behavior of GasaufkohlungsatmosphDC.
  • the coil C in the furnace chamber 3 was again cooled under protective gas (N2) over a period of 12 hours to a final temperature of 80 ° C., which is below the oxidation limit.
  • the cooling rate measured on the inner turn of the coil C during the cooling time t K was 0.014 ° C./s.
  • the coil C After cooling to 80 ° C, the coil C has been removed from the oven 2. The shape of the coil was well preserved after carburizing. The turns did not stick together during the carburizing at 900 ° C. and the carburizing time t H of 8 hours.
  • FIG. 3 shows the layer structure of the steel strip S obtained after the carburizing treatment and the carbon content% C is plotted over the thickness d of the steel strip.
  • the carburization depth d K results in the high C content C% R , which drops in the direction of the base layer G of the steel strip S arranged centrally between the surface layers R to the initial content% C A ,

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Organic Chemistry (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)
  • Heat Treatment Of Strip Materials And Filament Materials (AREA)
  • Heat Treatment Of Sheet Steel (AREA)

Abstract

Production of steel strips comprises coiling a coil from a steel strip having a carbon starting content (% CA) in such a way that its layers are arranged at a distance from each other, annealing at a reaction temperature lying above the Ac3, and feeding a carburized gas (Rgas) through the space present between the individual layers of the coil until a carbon content (% CR) is increased by at least 0.1 weight % in the edge layer of the steel strip.

Description

Die Erfindung betrifft ein Verfahren zum Herstellen von Stahlbändern, bei dem der Kohlenstoffgehalt in einer Oberflächenschicht des jeweiligen Stahlbands in einem separaten Arbeitsgang erhöht wird.The invention relates to a method for producing Steel strips in which the carbon content in one Surface layer of the respective steel strip in one separate operation is increased.

Ein Verfahren, bei dem kaltgewalzte Stahlbänder mit Ausgangsgehalten an Kohlenstoff von deutlich weniger als 0,01 Gew.-% einer Aufkohlungsglühung unterzogen werden, ist beispielsweise aus der JP 63038556 A1 bekannt. Gemäß dem bekannten Verfahren wird das aus dem kaltgewalzten Stahlband gehaspelte Coil einer so genannten "Open Coil-Glühung" in einer aufkohlenden Atmosphäre bei im Bereich der Rekristallisationstemperatur (ca. 830 °C) liegenden Temperaturen unterzogen. Auf diese Weise sollen in einer Randschicht des Stahlbands, deren Dicke 1/4 bis 1/12 der Gesamtdicke des Stahlbands beträgt, durchschnittliche Kohlenstoffgehalte von 0,02 - 0,10 Gew.-% eingestellt werden. Der so erhaltene Stahl soll besonders gute Tiefzieheigenschaften besitzen.A process in which cold-rolled steel strips with Initial carbon levels of significantly less than Is subjected to a carburizing annealing known for example from JP 63038556 A1. According to the known method is the cold rolled Steel strip coiled coil of a so-called "open coil annealing" in a carburizing atmosphere in the area the recrystallization temperature (approx. 830 ° C) Subjected to temperatures. This way, in one Edge layer of the steel strip, the thickness of 1/4 to 1/12 of the Total thickness of the steel strip is, average Carbon contents of 0.02-0.10 wt .-% set become. The steel thus obtained is said to be particularly good Possess deep-drawing properties.

In der Praxis wird das "Open-Coil"-Glühverfahren hauptsächlich angewendet, um Kaltband zur Direkt-Emaillierung von Feinblech für Elektrogeräte (Weißware) zu entkohlen. Ein weiteres Einsatzgebiet stellt das Randentkohlen von gebeiztem Warmband aus Güten C55 und C45 dar. In practice, the "open-coil" annealing process mainly applied to cold strip for direct enamelling of sheet metal for electrical appliances (white goods) decarbonized. This is another area of application Edge decarburization from pickled hot strip from grades C55 and C45 represents.

Kohlenstoffhaltige Stähle mit C-Gehalten von mindestens 0,1 Gew.-% werden üblicherweise zunächst zu einem Bauelement umgeformt, um dann stückweise der aufkohlenden Glühbehandlung unterzogen zu werden. Diese stückweise erfolgende Aufkohlung ist sowohl hinsichtlich der zu absolvierenden Arbeitsschritte als auch hinsichtlich der dabei entstehenden Kosten aufwendig.Carbon steels with a C content of at least 0.1 % By weight usually becomes a component first reshaped, then the carburizing piece by piece To be subjected to annealing treatment. This piece by piece carburizing takes place both with regard to the completing work steps as well as in terms of the resulting costs are complex.

Die Aufgabe der Erfindung bestand darin, ein Verfahren anzugeben, mit dem sich auf besonders wirtschaftliche Weise Stahlbänder mit einer hohen Härte ihrer Oberflächenschichten und dementsprechend hoher Verschleißfestigkeit erzeugen lassen.The object of the invention was a method to indicate with which in a particularly economical manner Steel strips with a high hardness of theirs Surface layers and accordingly higher Have wear resistance created.

Diese Aufgabe wird erfindungsgemäß durch ein Verfahren zum Herstellen von Stahlbändern gelöst, bei dem ein Coil, das aus einem einen Ausgangsgehalt an Kohlenstoff aufweisenden Stahlband derart gehaspelt ist, dass seine Lagen mit Abstand zueinander angeordnet sind, bei einer oberhalb der Ac3-Temperatur liegenden Reaktionstemperatur einer Glühung unterzogen wird, bei der ein aufkohlendes Gas durch den zwischen den einzelnen Lagen des Coils vorhandenen Raum geleitet wird, bis in der Randschicht des Stahlbands ein gegenüber dem Ausgangsgehalt um mindestens 0,1 Gew.-%, insbesondere mindestens 0,3 Gew.-% erhöhter C-Gehalt erreicht ist. Der Kohlenstoff-Ausgangsgehalt der erfindungsgemäß verarbeiteten Stahlbänder beträgt dabei bevorzugt mindestens 0,1 Gew.-%. Insbesondere liegt er im Bereich von bis zu 0,4 Gew.-%..This object is achieved according to the invention by a method for producing steel strips, in which a coil which is coiled from a steel strip having an initial content of carbon in such a way that its layers are arranged at a distance from one another at a reaction temperature above the A c3 temperature is subjected to an annealing process in which a carburizing gas is passed through the space between the individual layers of the coil until in the edge layer of the steel strip there is at least 0.1% by weight, in particular at least 0.3% by weight, of the starting content. -% increased C content is reached. The initial carbon content of the steel strips processed according to the invention is preferably at least 0.1% by weight. In particular, it is in the range of up to 0.4% by weight.

Gemäß der Erfindung wird das jeweils zu verarbeitende Stahlband zunächst in an sich bekannter Weise zu einem "Open Coil" gehaspelt. Bei einem solchen Coil sind die einzelnen Lagen voneinander getrennt. Auf diese Weise kann das aufkohlende Reaktionsgas in den zwischen den einzelnen Lagen des Coils vorhandenen Zwischenräumen hindurch strömen, so dass bei optimierter Gasstromführung jede Oberfläche des Coils in gleicher Weise von dem Gas überstrichen wird.According to the invention, that is to be processed Steel strip first in a manner known per se "Open Coil" coiled. With such a coil they are individual layers separated from each other. That way the carburizing reaction gas in between the individual Layers of the coil through existing gaps flow so that with optimized gas flow guidance each Surface of the coil in the same way from the gas is swept over.

Die Glühbehandlung findet dann beispielsweise in einer aufkohlenden Atmosphäre in einem Haubenglühofen statt, der nach Maßgabe der sich aus dem erfindungsgemäßen Verfahren ergebenden Regelungsmöglichkeiten modifiziert worden ist. Die beim erfindungsgemäßen Aufkohlungsglühen eingestellte Reaktionstemperatur liegt dabei über der Umwandlungstemperatur Ac3, bevorzugt um bis zu 30 °C oberhalb der Ac3-Temperatur, insbesondere mindestens 900 °C.The annealing treatment then takes place, for example, in a carburizing atmosphere in a bell annealer which has been modified in accordance with the control options resulting from the method according to the invention. The reaction temperature set in the carburizing annealing according to the invention is above the transition temperature A c3 , preferably up to 30 ° C. above the A c3 temperature, in particular at least 900 ° C.

Typischerweise beträgt die Glühzeit, über die das Coil auf der Reaktionstemperatur gehalten wird, bis zu zehn Stunden.Typically, the glow time over which the coil is on the reaction temperature is maintained for up to ten hours.

Es hat sich gezeigt, dass es bei einer bei derart hohen Temperaturen erfolgenden Glühung zu einem besonders intensiven Aufkohlen in den Randschichten des verarbeiteten Blechs kommt. Überraschend war dabei, dass die Coilform trotz der thermischen Spannungen beim Aufheiz-, Halte- und Abkühlvorgang formbeständig erhalten bleibt.It has been shown that at such a high Temperatures taking place at a particular intensive carburizing in the outer layers of the processed Blechs is coming. It was surprising that the coil form despite the thermal stresses during heating, holding and The cooling process remains dimensionally stable.

Mit dem erfindungsgemäßen Verfahren lassen sich so auf besonders wirtschaftliche Weise Stahlbänder erzeugen, die eine gehärtete, verschleißbeständige Oberfläche bei gleichzeitig guten Umformeigenschaften des Grundwerkstoffs besitzen. The method according to the invention can be used in this way produce steel strips that are particularly economical a hardened, wear-resistant surface at the same time good forming properties of the base material have.

Als Werkstoffe eignen sich dazu beispielsweise sämtliche Stahllegierungen, wie Einsatz- oder Vergütungsstähle mit typischen Kohlenstoffgehalten, die im Bereich von 0,1 - 0,25 Gew.-% bzw. 0,2 - 0,4 Gew.-% liegen. Ausgehend von derartigen Stahllegierungen lässt sich durch Anwendung des erfindungsgemäßen Verfahrens eine Oberflächenschicht erzeugen, in der der Kohlenstoffgehalt gegenüber dem C-Gehalt des Ausgangswerkstoffs um mindestens 0,1 Gew.-%, insbesondere mindestens 0,3 Gew.-% gesteigert ist.For example, all are suitable as materials Steel alloys, such as case hardening or tempering steels typical carbon contents in the range of 0.1 - 0.25% by weight or 0.2-0.4% by weight. Starting from Such steel alloys can be applied by using the inventive method a surface layer generate in which the carbon content versus the C content of the starting material by at least 0.1% by weight, in particular at least 0.3% by weight is increased.

Die Erhöhung des Kohlenstoffgehalts in der Randschicht sowie die Tiefe, über die der Kohlenstoffgehalt bei Anwendung des erfindungsgemäßen Verfahrens erhöht wird, lassen sich über die Glühtemperatur, die Glühzeit und die Zusammensetzung des Reaktionsgases steuern. Bei geeigneter Prozessführung kann der Kohlenstoffgehalt in der jeweiligen Oberflächenschicht auf 0,4 - 0,9 Gew.-% gesteigert werden. Insbesondere lassen sich Kohlenstoffgehalte in der Oberflächenschicht erreichen, die 0,6 Gew.-% bis 0,9 Gew.-% betragen. Die Dicke der aufgekohlten Randschicht liegt dabei regelmäßig zwischen 50 - 500 µm, wobei auch die Tiefe, über die es zur Aufkohlung der Randschicht des Stahlbands kommt, über die genannten Prozessparameter gesteuert werden kann. Abhängig vom gewünschten Arbeitsergebnis kann es dabei zweckmäßig sein, die Prozessparameter während des Aufkohlungsprozesses zu variieren.The increase in the carbon content in the surface layer as well as the depth over which the carbon content at Application of the method according to the invention is increased, can be determined via the annealing temperature, the annealing time and the Control the composition of the reaction gas. With more suitable The process can control the carbon content in each Surface layer can be increased to 0.4-0.9% by weight. In particular, carbon content in the Achieve surface layer that 0.6 wt .-% to 0.9 wt .-% be. The thickness of the carburized surface layer lies regularly between 50 - 500 µm, with the Depth over which it carburizes the surface layer of the Steel strips comes through the process parameters mentioned can be controlled. Depending on the desired The result of the work can be useful Process parameters during the carburizing process vary.

Als aufkohlendes Gas kann ein Gasgemisch eingesetzt werden, das CO, H2 und/oder CO2 enthält. Derartige Gasgemische sind beispielsweise aus 20 % CO, 40 % H2 und als Rest N2 zusammengesetzt. A gas mixture containing CO, H 2 and / or CO 2 can be used as the carburizing gas. Such gas mixtures are composed, for example, of 20% CO, 40% H 2 and the remainder N 2 .

Für die Durchführung des erfindungsgemäßen Verfahrens kann eine Haubenglühvorrichtung eingesetzt werden, die basierend auf eine Haubenglühe konventioneller Bauart um die Möglichkeit einer hinsichtlich Art, Dauer und Menge gesteuerten Gasbeaufschlagung erweitert ist.For carrying out the method according to the invention a hood annealing device can be used based to a conventional type of bell annealer Possibility of one regarding type, duration and quantity controlled gas supply is expanded.

Um eine Oxidation des Stahlbandes bei seiner Erwärmung auf die Glühtemperatur zu vermeiden, ist es vorteilhaft, die Aufheizung des Coils unter Schutzgas durchzuführen. Ebenso ist es vorteilhaft, nach Beendigung der Glühbehandlung das aufgekohlte Stahlband unter Schutzgas abzukühlen, um eine ungewollte Entkohlung der Oberflächenschicht zu vermeiden.To oxidize the steel strip when it heats up to avoid the annealing temperature, it is advantageous to Carry out heating of the coil under protective gas. As well it is advantageous that after finishing the annealing treatment to cool a carburized steel strip under protective gas to a to avoid unwanted decarburization of the surface layer.

Das nach der Glühbehandlung erhaltene Band kann kaltgewalzt und zu Halbzeugen verarbeitet werden. Erforderlichenfalls kann es dazu einer Weichglühung unterzogen werden. Die Herstellung der Halbzeuge kann dabei eine Trennoperation, wie Stanzen oder Schneiden, und / oder eine Umformoperation, wie Tiefziehen oder Biegen, umfassen. Erforderlichenfalls können die derart erzeugten Halbzeuge eine Vergütungsbehandlung durchlaufen.The strip obtained after the annealing treatment can be cold rolled and processed into semi-finished products. if necessary it can be subjected to soft annealing. The Production of the semi-finished products can involve a separation operation, like punching or cutting, and / or one Forming operations such as deep drawing or bending include. If necessary, the semi-finished products produced in this way undergo remuneration treatment.

Mit Hilfe des erfindungsgemäßen Verfahrens lassen sich aufhärtbare, verschleißbeständige Oberflächen von Blechen in Verbindung mit guten Umformeigenschaften des Grundwerkstoffs schaffen. Aufgrund dieser Eigenschaftskombination lässt sich der erfindungsgemäß erzeugte Werkstoff besonders gut als Verbundwerkstoff einsetzten.With the help of the method according to the invention hardenable, wear-resistant surfaces of sheet metal in connection with good forming properties of the Create base material. Based on these The combination of properties can be according to the invention produced material particularly well as a composite material inserting.

Als typische Verwendungen, für die sich erfindungsgemäß erzeugte, hoch verschleißfeste, oberflächenharte Stahlbänder besonders eigenen, sind beispielsweise Nockenwellen, Lagerschalen und andere Bauelemente zu nennen, die im praktischen Einsatz hohen lokal wirkenden Belastungen ausgesetzt sind.As typical uses for which according to the invention generated, highly wear-resistant, surface hard Steel straps are particularly own, for example Camshafts, bearing shells and other components too name those that have a high local effect in practical use Are exposed to loads.

Nachfolgend wird die Erfindung anhand eines Ausführungsbeispiels näher erläutert. Es zeigen:

Fig. 1
eine Haubenglühe mit eingesetztem Coil in einer schematischen Darstellung;
Fig. 2
ein Zeit/Temperatur-Diagramm, in dem verschiedene für die Aufkohlungsglühung charakteristische Temperaturverläufe aufgezeichnet sind;
Fig. 3
den Schichtaufbau und Verlauf der Aufkohlung über die Dicke eines Stahlblechs nach der Aufkohlungsglühung in schematischer Darstellung.
The invention is explained in more detail below using an exemplary embodiment. Show it:
Fig. 1
a bell anneal with inserted coil in a schematic representation;
Fig. 2
a time / temperature diagram in which various temperature profiles characteristic of the carburizing annealing are recorded;
Fig. 3
the layer structure and course of the carburization over the thickness of a steel sheet after the carburizing annealing in a schematic representation.

Die Haubenglühe 1 weist einen von einer konventionell ausgebildeten Glühhaube 2 umgebenen Ofenraum 3 auf, in den ein als Open-Coil C gewickeltes Stahlband S eingesetzt ist. Die an sich bekannte Legierungsvorschrift für das eingesetzte Stahlband S ist in Tabelle 1 angegeben. C Si Mn P S Al Cr Cu Ni 0,13-0,16 <0,06 0,50-0, 60 <0,02 <0,012 0,015-0,04 <0,06 <0,1 <0,06 Alle Angaben in Gew.-%, Rest Fe und unvermeidbare Verunreinigungen The hood annealer 1 has an oven chamber 3 surrounded by a conventionally designed annealing hood 2, into which a steel strip S wound as an open coil C is inserted. The known alloy specification for the steel strip S used is given in Table 1. C Si Mn P S al Cr Cu Ni from 0.13 to 0.16 <0.06 0.50-0, 60 <0.02 <0.012 0.015 to 0.04 <0.06 <0.1 <0.06 All figures in% by weight, remainder Fe and unavoidable impurities

Die Haubenglühe 1 ist des Weiteren mit einem Gasanschluss 4 für ein Schutzgas, hier N2, mit einem Gasanschluss 5 für Reaktionsgas RGas, welches hier durch ein Gemisch aus CO, CO2 und H2 gebildet ist, mit einer Abgasabführung 6 und mit verschiedenen Anschlüssen 7 ausgestattet, über die u. a. der Kohlenstoffpegel CP, die Ofenraumtemperatur TO und die Zusammensetzung der im Ofenraum vorhandenen Atmosphäre erfasst werden können. Ebenso können über die Anschlüsse 7 Messungen am Coil C selbst durchgeführt werden, um beispielsweise den Fortschritt der Erwärmung oder der Aufkohlung sowie die Gasströmung durch das Coil C zu bestimmen.The hood annealer 1 is also provided with a gas connection 4 for a protective gas, here N 2 , with a gas connection 5 for reaction gas RGas, which is formed here by a mixture of CO, CO 2 and H 2 , with an exhaust gas discharge 6 and with different connections 7 equipped, among other things, the carbon level C P , the furnace chamber temperature T O and the composition of the atmosphere present in the furnace chamber can be detected. Likewise, measurements can be carried out on the coil C itself via the connections 7, for example in order to determine the progress of the heating or carburizing as well as the gas flow through the coil C.

Mit den Anschlüssen 7 ist eine Steuereinrichtung 8 verbunden, die über die Dauer des gesamten Aufkohlungsprozesses die Entwicklung der Ofenraum-Temperatur TO den Kohlenstoffpegel CP der Atmosphäre im Ofenraum 3 sowie die Zusammensetzung ZGas der in den Ofenraum 3 geleiteten Gase (Reaktionsgas RGas / Schutzgas N2) steuert.Connected to the connections 7 is a control device 8 which, over the duration of the entire carburizing process, the development of the furnace chamber temperature T O, the carbon level C P of the atmosphere in the furnace chamber 3 and the composition ZGas of the gases passed into the furnace chamber 3 (reaction gas RGas / protective gas N 2 ) controls.

Das warm- oder kaltgewalzte, erforderlichenfalls gebeizte Stahlband S, dessen Dicke beispielsweise 0,8 bis 3 mm und dessen Breite 600 bis 1200 mm betragen kann, wird als dicht gewickeltes, hier nicht gezeigtes Coil angeliefert, dessen Gewicht bis zu 20 Tonnen beträgt.The hot or cold rolled, pickled if necessary Steel strip S, the thickness of which is, for example, 0.8 to 3 mm and the width of which can be 600 to 1200 mm is considered dense Delivered wound coil, not shown here, whose Weight is up to 20 tons.

Um das für die Aufkohlungsglühung benötigte Open-Coil C zu erzeugen wird das angelieferte Coil zunächst umgehaspelt. Dabei wird in einem Abstand von ca. 30 mm an beiden Rändern des Stahlbands jeweils ein Draht in das Stahlband S eingewickelt. Der Draht ist spiralförmig gewickelt und hat eine Gesamtdicke von 3,0 mm. Auf diese Weise werden die einzelnen Windungen des aus dem Stahlband S gebildeten Open-Coils C mit definiertem Abstand zueinander gehalten, so dass eine gleichmäßige Gasströmung zwischen den Windungen C während des Glühens möglich ist.To open-coil C required for carburizing the delivered coil is first rewound. This is done at a distance of approx. 30 mm on both edges a wire into the steel strip S of the steel strip wrapped up. The wire is wound spirally and has a total thickness of 3.0 mm. In this way, the individual turns of the steel strip S formed Open coils C held at a defined distance from each other, so that a uniform gas flow between the Turns C is possible during the glow.

Um eine gleichmäßige Temperatur über die Windungen zu gewährleisten, ist jeweils ein Thermoelement in der Innenund der Mittenwindung des Coils C angebracht worden. Mit den Thermoelementen wurde die Temperatur TK des Coilkerns (Mittenwindung) und die Temperatur TR des Coilrands (Innenwindung) während des gesamten Aufkohlungsprozesses online gemessen. Die Temperaturverläufe TK, TR und TO sind in Fig. 2 über die Prozesszeit t dargestellt.In order to ensure a uniform temperature across the turns, a thermocouple has been installed in the inner and the middle turn of the coil C. The temperature T K of the coil core (central turn) and the temperature T R of the coil edge (internal turn) were measured online with the thermocouples during the entire carburizing process. The temperature profiles T K , T R and T O are shown in FIG. 2 over the process time t.

Beim hier erläuterten Betriebsversuch wurde das derart gewickelte Open-Coil C nach dem Umwickeln kalt in den Ofenraum 3 eingesetzt. Die Ofentemperatur TO betrug zum Zeitpunkt des Einsetzens des kalten Coils C 750°C. Bei dieser Ofentemperatur TO ist das Open-Coil C über mehrere Stunden gehalten worden, bis es auf die Reaktionstemperatur von 900°C weiter aufgeheizt wurde. Während der gesamten, 10 Stunden dauernden Aufheizdauer tA ist das Coil C im Ofenraum 3 unter Schutzgas (N2) gehalten worden. Die an der Innenwindung gemessene Aufheizgeschwindigkeit betrug 0,026 °C/s.In the operational test explained here, the open-coil C wound in this way was inserted cold into the furnace space 3 after the wrapping. The oven temperature T O was 750 ° C. at the time the cold coil C was inserted. At this furnace temperature T O , the open-coil C was held for several hours until it was further heated to the reaction temperature of 900 ° C. During the entire 10-hour heating period t A , the coil C in the furnace space 3 was kept under protective gas (N2). The heating rate measured on the inner turn was 0.026 ° C / s.

Die Aufkohlung wurde erst eingeleitet, nachdem die Temperaturen TK und TR des Coils C jeweils die vorgegebene Reaktionstemperatur von 900°C erreicht hatten. Mit Erreichen der Reaktionstemperatur wurde Reaktionsgas RGas in den Ofenraum 3 geleitet. Die Einleitung in den Ofenraum 3 erfolgte über die Ofendecke. Das eingeleitete Reaktionsgas RGas wurde durch einen nicht dargestellten Ventilator in eine Gasströmung versetzt, die gleichmäßig verteilt zwischen den Windungen des Open-Coils C strömte. The carburization was only initiated after the temperatures T K and T R of the coil C had each reached the predetermined reaction temperature of 900 ° C. When the reaction temperature was reached, the reaction gas RGas was passed into the furnace chamber 3. The introduction into the furnace room 3 was via the furnace ceiling. The introduced reaction gas RGas was put into a gas flow by a fan, not shown, which flow was evenly distributed between the turns of the open coil C.

Für die vorgesehene Aufkohlungstiefe dK von 250 µm sowie den Randkohlenstoffgehalt von 0,8 Gew.-% wurde das Coil C über eine Dauer tH von 8 Stunden aufgekohlt. Der C-Pegel, der eine entscheidende Größe für den Aufkohlungsprozess ist und in erster Linie den Randkohlenstoffgehalt sowie die Aufkohlungstiefe bestimmt, wurde in der Aufkohlungsphase durch Steuerung der zugeführten Menge an Reaktionsgas RGas bei 1,0 % konstant gehalten.For the intended carburizing depth d K of 250 µm and the marginal carbon content of 0.8% by weight, the coil C was carburized over a period t H of 8 hours. The C level, which is a decisive parameter for the carburizing process and primarily determines the marginal carbon content and the carburizing depth, was kept constant at 1.0% in the carburizing phase by controlling the amount of reaction gas RGas supplied.

Als "C-Pegel" wird das Kohlenstoffpotential bezeichnet, das angibt, bis zu welcher Konzentration der Kohlenstoff im Gleichgewichtszustand im Austenit angereichert wird. Es ist darunter der C-Gehalt zu verstehen, der sich im Gleichgewichtszustand mit einer Reineisenprobe bei einer bestimmten Temperatur im Austenit einstellt. Der C-Pegel bildet demzufolge die in der Praxis wichtigste Kenngröße zur Überwachung des Aufkohlungsverhaltens von Gasaufkohlungsatmosphären.The carbon potential is referred to as the "C level" which indicates to what concentration the carbon is enriched in austenite in equilibrium. It is to be understood as the C content, which is in the Equilibrium state with a pure iron sample at one certain temperature in the austenite. The C level is therefore the most important parameter in practice to monitor the carburizing behavior of Gasaufkohlungsatmosphären.

Nach Ablauf der Aufkohlungszeit tH wurde das Coil C im Ofenraum 3 wiederum unter Schutzgas (N2) über 12 Stunden bis auf eine Endtemperatur 80°C abgekühlt, die unterhalb der Oxidationsgrenze liegt. Die während der Ankühlzeit tK an der Innenwindung des Coils C gemessene Abkühlungsgeschwindigkeit betrug 0,014 °C/s.After the carburizing time t H had expired, the coil C in the furnace chamber 3 was again cooled under protective gas (N2) over a period of 12 hours to a final temperature of 80 ° C., which is below the oxidation limit. The cooling rate measured on the inner turn of the coil C during the cooling time t K was 0.014 ° C./s.

Nach dem Abkühlen bis auf 80°C ist das Coil C aus dem Ofen 2 genommen worden. Die Form des Coils war nach der Aufkohlung gut erhalten. Ein Zusammenkleben der Windungen während der Aufkohlung bei 900 °C und der 8 Stunden dauernden Aufkohlungszeit tH blieb aus.After cooling to 80 ° C, the coil C has been removed from the oven 2. The shape of the coil was well preserved after carburizing. The turns did not stick together during the carburizing at 900 ° C. and the carburizing time t H of 8 hours.

In Fig. 3 ist der nach der Aufkohlungsbehandlung erhaltene Schichtaufbau des Stahlbands S dargestellt sowie schematisch der Kohlenstoff-Gehalt %C über die Dicke d des Stahlband aufgetragen. Im Bereich der oberflächennahen, harten und verschleißfesten Randschichten R liegt über die Aufkohlungstiefe dK jeweils der hohe C-Gehalt C%R vor, der jeweils in Richtung der zentral zwischen den Randschichten R angeordneten Grundschicht G des Stahlbands S auf den Ausgangsgehalt %CA abfällt.FIG. 3 shows the layer structure of the steel strip S obtained after the carburizing treatment and the carbon content% C is plotted over the thickness d of the steel strip. In the area of the near-surface, hard and wear-resistant surface layers R, the carburization depth d K results in the high C content C% R , which drops in the direction of the base layer G of the steel strip S arranged centrally between the surface layers R to the initial content% C A ,

Claims (15)

Verfahren zum Herstellen von Stahlbändern, bei dem ein Coil (C), das aus einem einen Ausgangsgehalt (%CA) an Kohlenstoff aufweisenden Stahlband (S) derart gehaspelt ist, dass seine Lagen mit Abstand zueinander angeordnet sind, bei einer oberhalb der Ac3-Temperatur liegenden Reaktionstemperatur einer Glühung unterzogen wird, bei der ein aufkohlendes Gas (Rgas) durch den zwischen den einzelnen Lagen des Coils (C) vorhandenen Raum geleitet wird, bis in der Randschicht (R) des Stahlbands (S) ein gegenüber dem Ausgangsgehalt (%CA) um mindestens 0,1 Gew.-% erhöhter C-Gehalt (%CR) erreicht ist.Method for producing steel strips, in which a coil (C) which is coiled from a steel strip (S) with a starting content (% C A ) of carbon in such a way that its layers are arranged at a distance from one another, above the A c3 -Temperature reaction temperature is subjected to annealing, in which a carburizing gas (Rgas) is passed through the space between the individual layers of the coil (C) until in the outer layer (R) of the steel strip (S) a compared to the initial content ( % C A ) is increased by at least 0.1 wt .-% C content (% C R ). Verfahren nach Anspruch 1, dadurch gekennzeichnet, dass der Ausgangsgehalt (%CA) des Stahlbands (S) an C mindestens 0,1 Gew.-% beträgt.A method according to claim 1, characterized in that the initial content (% C A ) of the steel strip (S) of C is at least 0.1 wt .-%. Verfahren nach Anspruch 2, dadurch gekennzeichnet, dass der Ausgangsgehalt (%CA) an C maximal 0,4 Gew.-% beträgt.A method according to claim 2, characterized in that the initial content (% C A ) of C is a maximum of 0.4 wt .-%. Verfahren nach einem der voranstehenden Ansprüche, dadurch gekennzeichnet, dass in der Randschicht (R) des Stahlbands (S) ein gegenüber dem Ausgangsgehalt (%CA) um mindestens 0,3 Gew.-% erhöhter C-Gehalt erreicht wird. Method according to one of the preceding claims, characterized in that in the edge layer (R) of the steel strip (S) a C content which is at least 0.3% by weight higher than the initial content (% C A ) is achieved. Verfahren nach einem der voranstehenden Ansprüche, dadurch gekennzeichnet, dass der in der Randschicht (R) erhaltene C-Gehalt 0,4 - 0,9 Gew.-% beträgt.Method according to one of the preceding claims, characterized in that the C content obtained in the outer layer (R) is 0.4-0.9% by weight. Verfahren nach einem der voranstehenden Ansprüche, dadurch gekennzeichnet, dass das aufkohlende Gas (Rgas) durch ein CO, H2 und/oder CO2 enthaltendes Gasgemisch gebildet ist.Method according to one of the preceding claims, characterized in that the carburizing gas (Rgas) is formed by a gas mixture containing CO, H 2 and / or CO 2 . Verfahren nach einem der voranstehenden Ansprüche, dadurch gekennzeichnet, dass die Glühtemperatur mindestens um 30 °C oberhalb der AC3-Temperatur liegt..Method according to one of the preceding claims, characterized in that the annealing temperature is at least 30 ° C above the A C3 temperature. Verfahren nach einem der voranstehenden Ansprüche, dadurch gekennzeichnet, dass die Aufheizung des Coils (C) unter Schutzgas (N2) erfolgt.Method according to one of the preceding claims, characterized in that the coil (C) is heated under protective gas (N 2 ). Verfahren nach einem der voranstehenden Ansprüche, dadurch gekennzeichnet, dass die Abkühlung des Coils (C) unter Schutzgas (N2) erfolgt.Method according to one of the preceding claims, characterized in that the cooling of the coil (C) takes place under protective gas (N 2 ). Verfahren nach einem der voranstehenden Ansprüche, dadurch gekennzeichnet, dass das aufgekohlte Band (S) kaltgewalzt wird. Method according to one of the preceding claims, characterized in that the carburized strip (S) is cold rolled. Verfahren nach Anspruch 10, dadurch gekennzeichnet, dass aus dem kaltgewalzten Band (S) Halbzeuge hergestellt werden.A method according to claim 10, characterized in that semi-finished products are produced from the cold-rolled strip (S). Verfahren nach Anspruch 11, dadurch gekennzeichnet, dass die Herstellung der Halbzeuge ein Trennen umfasst.A method according to claim 11, characterized in that the production of the semi-finished products comprises a separation. Verfahren nach Anspruch 11 oder 12, dadurch gekennzeichnet, dass die Herstellung der Halbzeuge ein Umformen umfasst.14. Verfahren nach einem der Ansprüche 11 bis 13, dadurch gekennzeichnet, dass die Halbzeuge eine Vergütungsbehandlung durchlaufen.A method according to claim 11 or 12, characterized in that the production of the semi-finished products comprises forming.14. Method according to one of claims 11 to 13, characterized in that the semi-finished products undergo a remuneration treatment. Verfahren nach einem der Ansprüche 10 bis 13, dadurch gekennzeichnet, dass das kaltgewalzte Band einer Weichglühung unterzogen wird.Method according to one of claims 10 to 13, characterized in that the cold-rolled strip is subjected to a soft annealing. Verfahren nach einem der voranstehenden Ansprüche, dadurch gekennzeichnet, dass die Dicke der aufgekohlten Randschicht (R) 50 - 500 µm beträgt.Method according to one of the preceding claims, characterized in that the thickness of the carburized edge layer (R) is 50-500 µm.
EP04013061A 2003-06-05 2004-06-03 Procedure for manufacturing carburized steel strips Withdrawn EP1484419A3 (en)

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JPS6338556A (en) * 1986-08-04 1988-02-19 Nisshin Steel Co Ltd Cold rolled steel sheet for deep drawing having superior resistance to cracking by secondary working and its manufacture
JPH0394022A (en) * 1989-09-05 1991-04-18 Kobe Steel Ltd Production of hot rolled steel plate for deep drawing excellent in resistance to secondary working brittleness
JPH04272143A (en) * 1991-02-28 1992-09-28 Nippon Steel Corp Manufacture of cold rolled steel sheet for deep drawing excellent in dent resistance
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