DE102019200338A1 - Process for continuous heat treatment of a steel strip, and plant for hot dip coating a steel strip - Google Patents

Abstract

The invention relates to a method and a system (10) for hot dip coating a high - quality steel strip (102) moving in a transport direction (T), in particular of oxidation - sensitive AHSS grades, comprising a hot dip bath (104) into which the steel strip (102) Coating is visible, wherein - seen in the transport direction (T) of the steel strip (102) - upstream of the hot dip (104) at least a first heating chamber (107) with at least one inductor (108, 109), a rapid cooling chamber (116) and a Holding chamber (117) for a partitioning of the steel strip (102) are arranged.

Description

The invention relates to a process for a continuous heat treatment of a steel strip according to the preamble of claim 1 or to the preamble of claim 7, and a plant for the hot dip coating of a steel strip of high strength, which is moved in a transport direction.

Conventional high-strength strip steels contain Mn, Si and / or Al as alloying elements. In the recrystallizing annealing prior to the hot dip coating, these alloying elements diffuse toward the surface. Since these alloying elements are very oxygen affinitive, they are almost inevitably oxidized, as far as they are at shallow depths in the band or on its surface. The basic material iron is not oxidized. This is why we speak of selective oxidation. The oxides formed on the surface or at a shallow depth affect the wettability of a steel strip with a coating metal, e.g. in molten form, with the result of imperfections (bare spots) or poor adhesion of the metallic coating.

In view of the above-mentioned problem of selective oxidation, the state of the art as a countermeasure known as the pre-oxidation, in which a coverage of these oxides by a FeO layer and a subsequent reduction to iron (Fe) takes place. This produces a pure Fe layer on or on the surface of a steel strip to be coated, whereupon a metallic coating adheres well. In this regard, with some materials, adhesion tends to fail at greater depth because the selectively formed oxides such as MnO and the like have a tendency to break down. create a passive layer on which the adhesion of the pure Fe layer is poor.

EP 1 819 840 B1 and EP 2 732 062 B1 each disclose a method and apparatus for hot dip coating a strip of higher strength steel, as well as a method for continuous heat treatment of a steel strip according to the preamble of claim 1 of the present patent application

The object of the invention is to suppress the selective oxidation to the extent that these oxides do not interfere with the subsequent application of a metallic coating to a surface of the steel strip in order to prepare a coating of steel strips.

This object is achieved by a method having the features of claim 1 and of claim 7, as well as by a system having the features specified in claim 15. Advantageous developments of the invention are defined in the dependent claims.

1. a) Erwärmen des Stahlbands in einer Atmosphäre, die ≥ 20 %, vorzugsweise ≥ 50 % Wasserstoff (H₂) und Rest Stickstoff (N₂) enthält und einen Taupunkt von < -40 °C aufweist, wobei das Stahlband spätestens ab 750 °C mit einer Heizrate von zumindest 50 K/s auf eine Haltetemperatur zwischen ≥ 800 °C und ≤ 950 °C erwärmt wird, wobei das Stahlband in dieser Atmosphäre oberhalb von 750°C mit einer Verweildauer von maximal 180 Sekunden verweilt,
2. b) Schnellkühlen des Stahlbands auf < 500 °C unter einer wasserstoffhaltigen Atmosphäre, und
3. c) Aufbringen eines metallischen Überzugs auf zumindest eine Oberfläche des Stahlbands.

With a method according to the invention, a continuous heat treatment of a high-grade steel strip, in particular of oxidation-sensitive AHSS grades, is carried out, wherein the steel strip is moved through at least one furnace device. Such a method comprises the following steps:

1. a) heating of the steel strip in an atmosphere containing ≥ 20%, preferably ≥ 50% hydrogen (H ₂ ) and the balance nitrogen (N ₂ ) and having a dew point of <-40 ° C, wherein the steel strip latest from 750 ° C. with a heating rate of at least 50 K / s is heated to a holding temperature between ≥ 800 ° C and ≤ 950 ° C, wherein the steel strip dwells in this atmosphere above 750 ° C with a residence time of a maximum of 180 seconds,
2. b) rapid cooling of the steel strip to <500 ° C under a hydrogen-containing atmosphere, and
3. c) applying a metallic coating to at least one surface of the steel strip.

1. i) Erwärmen des Stahlbands (102) auf eine Temperatur von mindestens 600 °C durch einen direkt beheizten Vorwärmer (DFF = Direct Fired Furnace) (106) in einer Abgas-Atmosphäre mit Luftmangel,
2. ii) Erwärmen des Stahlbands (102) auf eine Temperatur zwischen 700 °C - 750 °C durch einen Induktor in einer wasserstoffhaltigen Atmosphäre,
3. iii) Wärmebehandlung des Stahlbands in einer oxidierenden Atmosphäre mit einem Sauerstoffgehalt von 2-5 % O₂, um dadurch an den Oberflächen des Stahlbandes Eisenoxidschichten auszubilden, wobei diese Wärmebehandlung eine Zeitdauer von 5-20 Sekunden hat,
4. iv) Erwärmen des Stahlbands auf eine Temperatur von bis zu 950 °C in einer Atmosphäre, die Wasserstoff (H₂), Wasserdampf und Rest Stickstoff (N₂) enthält, wobei das Stahlband bei einer Temperatur von bis zu 950 °C mit einer Zeitdauer von ≥ 40 Sekunden gehalten wird,
5. v) Schnellkühlen des Stahlbands auf < 500 °C unter einer wasserstoffhaltigen Atmosphäre, und
6. vi) Aufbringen eines metallischen Überzugs auf zumindest eine Oberfläche des Stahlbands.

A method according to the invention according to a further embodiment also serves for a continuous heat treatment of a steel strip of high-strength quality, in particular of oxidation-sensitive AHSS qualities, in which the steel strip is moved through at least one furnace device. In this case, the method comprises the following steps:

1. i) heating the steel strip ( 102 ) to a temperature of at least 600 ° C by a directly heated pre-heater (DFF = Direct Fired Furnace) (106) in an exhaust atmosphere with air deficiency,
2. ii) heating the steel strip ( 102 ) to a temperature between 700 ° C - 750 ° C by an inductor in a hydrogen-containing atmosphere,
3. iii) heat treating the steel strip in an oxidizing atmosphere having an oxygen content of 2-5% O ₂ to thereby form iron oxide layers on the surfaces of the steel strip, this heat treatment having a duration of 5-20 seconds,
4. iv) heating the steel strip to a temperature of up to 950 ° C in an atmosphere containing hydrogen (H ₂ ), water vapor and balance nitrogen (N ₂ ), the steel strip at a temperature of up to 950 ° C with a period of time of ≥ 40 seconds,
5. v) rapid cooling of the steel strip to <500 ° C under a hydrogen-containing atmosphere, and
6. vi) applying a metallic coating to at least one surface of the steel strip.

In both of the abovementioned variants of a method according to the invention, a coating device can be provided for step c) or vi) which, viewed in the transport direction of the steel strip, is arranged downstream of a furnace device. Such a coating device can be designed as a hot dip bath or in the form of a PVD (Physical Vapor Deposition) section for applying a metallic coating to at least one surface of the steel strip, preferably on the surfaces of the steel strip at its top and bottom. When designing the coating device as a hot dip, it is useful if the steel strip is dip-coated in particular with zinc.

In an advantageous embodiment of the second-mentioned method according to the invention can be provided that in step iv) the steel strip is heated by a RTF furnace section (RTF = Radiant Tube Furnace), preferably, that the steel strip at the beginning of step iv) additionally by a transverse field inductor is heated to at least 820 ° C at a heating rate of at least 50 K / s. The heating of the steel strip by means of the transverse field inductor at the beginning of step iv) leads to the advantage that because of the said high heating rate, the steel strip is brought to the desired holding temperature more quickly.

The invention likewise provides a system for hot-dip coating of a steel strip of high-strength quality moving in a transport direction, in particular of oxidation-sensitive AHSS grades. Such a plant comprises a hot dip bath, in which the steel strip can be immersed for coating, wherein - seen in the transport direction of the steel strip - upstream of the hot dip at least a first heating chamber with at least one inductor, preferably in the form of a transverse field inductor, a rapid cooling chamber and a holding chamber for a partitioning of the steel strip are arranged. Conveniently, an inductor and / or in the outlet region of the holding chamber, a further inductor may be provided in the inlet region of the holding chamber or upstream thereof.

The invention is based on the essential finding that the strip heating or the heating of the steel strip to a temperature of up to 950 ° C takes place as quickly as possible, the subsequent holding or dwell time for the steel strip has to be small at a predetermined temperature. This leads to the advantage that during the heating a selective oxidation can be (largely) suppressed. For this purpose, it is generally advantageous to set the atmosphere in which the steel strip is heated to be as reducing as possible, namely with the largest possible or maximum hydrogen content and a minimum dew point, while at the same time setting a heating rate of> 50 K / s becomes. This applies in the first-mentioned method according to the invention for step a), and in the second-mentioned method according to the invention for step iv).

In an advantageous embodiment of the invention can be provided that the temperature to which the steel strip in step a) or in step iv) is heated and preferably also maintained, is below 950 ° C and e.g. assumes a value of 945 ° C, 940 ° C, 935 ° C, 930 ° C, 925 ° C or 920 ° C. In this regard, it is also possible that this temperature, to which the steel strip is heated and preferably also held in step a) or in step iv), assumes a value which lies between the example values just mentioned, and e.g. assumes a value of 942 ° C or other intermediate values.

In order to effectively suppress the oxidation at the surfaces of the steel strip above temperatures of about 700 ° C, the residence time of the steel strip> 750 ° C must be as short as possible. To realize this, according to the invention for the heating of the steel strip to a temperature of up to 950 ° C has shown that with an atmosphere having at least a proportion of 20% hydrogen, preferably nitrogen, and a dew point of less than or less than -40 ° C residence times for the steel strip are allowed up to a maximum of 180 seconds. Depending on the nature of the steel strip to be coated, these residence times may also be shorter than 180 seconds. In any case, the material of the steel strip is partially or completely converted into austenite during the holding or residence time.

In both of the aforementioned embodiments of a method according to the invention, it is provided that rapid cooling is carried out for the steel strip under a hydrogen-containing atmosphere at <500 ° C., as defined in step a) or in step v). For such rapid cooling, the cooling rate can be at least 40 K / s, for which a high hydrogen content is expedient. Advantageously, a hydrogen-rich inert gas with a proportion of e.g. 50% hydrogen used in the heating part and / or in the slow cooling to avoid oxidation.

In an advantageous embodiment of the first-mentioned method according to the invention can be provided that the steel strip is heated to a temperature of up to 750 ° C by a directly heated preheater (DFF = Direct Fired Furnace) in an exhaust atmosphere with lack of air before step a). In such a warming, the tendency to oxidation of the steel strip is usually not critical, with heating rates of 15-20 K / s are sufficient for certain grades. Furthermore, such a heating of the steel strip advantageously achieves a higher temperature level for this, in preparation for the subsequent intensive heating in step a).

In an advantageous embodiment of the first-mentioned method according to the invention can be provided that in step a) the steel strip is heated by at least one inductor, preferably in the form of a transverse field inductor, to the holding temperature of up to 950 ° C. This makes it possible to achieve a rapid heating for the steel strip with a heating rate of at least 50 K / s.

In an advantageous embodiment of the first-mentioned method according to the invention can be provided that in step a) the steel strip is inductively heated in two stages, the steel strip by a first inductor, preferably in the form of a longitudinal field inductor, initially to a temperature of up to 720 ° C is heated and then heated by a second inductor, preferably in the form of a transverse field inductor, to the holding temperature of up to 950 ° C.

As already explained above, the residence time in the first-mentioned process according to the invention in step a) can also be less than 180 seconds. In this regard, it should be noted that this residence time in the context of the present invention also ≤ 170 seconds, preferably ≤ 160 seconds, more preferably ≤ 150 seconds, more preferably ≤ 140 seconds, more preferably ≤ 130 seconds, more preferably ≤ 120 seconds, more preferably ≤ 110 seconds, more preferably ≤100 seconds, more preferably ≤90 seconds, more preferably ≤85 seconds, more preferably ≤80 seconds, more preferably ≤75 seconds, more preferably ≤70 seconds, further preferably ≤65 seconds, further preferably ≤60 seconds , more preferably ≤ 55 seconds, more preferably ≤ 50 seconds, further preferably ≤ 45 seconds, more preferably ≤ 40 seconds, further preferably ≤ 35 seconds, more preferably ≤ 30 seconds, further preferably ≤ 25 seconds, further preferably ≤ 20 seconds preferably ≤ 15 seconds, more preferably ≤ 10 Seconds, more preferably ≤ 5 seconds may be, depending on the material properties of the steel strip to be coated.

In an advantageous embodiment of the invention can be provided that the steel strip is cooled in the rapid cooling in step b) or in step v) to a temperature which is in a range between 200 ° C and 450 ° C. In this case, it is further expedient for the steel strip to be heated to a partitioning temperature of at least 300 ° C., preferably 320 ° C., in an atmosphere which is ≥ 20 before step c) or following step v) % Hydrogen (H ₂ ) and balance nitrogen (N ₂ ) is carried out with the steel strip in this atmosphere for a period of ≥ 30 seconds dwell.

In an advantageous embodiment of the invention can be provided that a slow cooling is performed for the steel strip. In the first-mentioned method according to the invention, such slow cooling takes place between steps a) and b), whereby in the case of the second-mentioned method according to the invention, such slow cooling takes place between steps iv) and v). In any case, it is advantageous if such slow cooling takes place under a hydrogenous atmosphere, e.g. contain a proportion of at least 20% hydrogen and may have a dew point of <-40 ° C. Furthermore, it is advantageous if this atmosphere in addition to the hydrogen content then contains residual nitrogen. In any case, it is important or advantageous for slow cooling that the mixed phase region ferrite + austenite is passed through with slow cooling, depending on the alloy down to 750 ° C., in order to thereby set a defined austenite content. Therefore, the time of slow cooling with respect to the oxidation of Si is part of the above-mentioned residence time.

In an advantageous embodiment of the invention, further process steps may be provided for the continuous heat treatment of the steel strip, which may be e.g. may be a reheating and / or a holding of the steel strip. These possible further process steps are driven at temperatures of> 600 ° C and are therefore irrelevant with regard to the oxidation of Si. Although a high hydrogen content is not required in this case, it is not disadvantageous, so that it is basically possible to drive for these further process steps in the same atmosphere as the preceding rapid cooling.

• 1 eine prinzipielle Seitenansicht einer erfindungsgemäßen Anlage,
• 2 eine prinzipielle Seitenansicht einer erfindungsgemäßen Anlage nach einer weiteren Ausführungsform,
• 3 eine prinzipielle Seitenansicht einer erfindungsgemäßen Anlage nach einer weiteren Ausführungsform,
• 4 den Temperaturverlauf für ein Stahlband bei einer Behandlung in der Anlage von 3,
• 5 eine tabellarische Übersicht zu Parametern einer möglichen Fahrweise eines erfindungsgemäßen Verfahrens,
• 6 den Temperaturverlauf für ein Stahlband bei der Fahrweise von 5,
• 7 eine tabellarische Übersicht zu Parametern einer möglichen Fahrweise eines erfindungsgemäßen Verfahrens gemäß einer weiteren Ausführungsform,
• 8 den Temperaturverlauf für ein Stahlband bei der Fahrweise von 7,
• 9 eine tabellarische Übersicht zu Parametern einer möglichen Fahrweise eines erfindungsgemäßen Verfahrens gemäß einer weiteren Ausführungsform,
• 10 den Temperaturverlauf für ein Stahlband bei der Fahrweise von 9,
• 11 eine tabellarische Übersicht zu Parametern einer möglichen Fahrweise eines erfindungsgemäßen Verfahrens gemäß einer weiteren Ausführungsform, und
• 12 den Temperaturverlauf für ein Stahlband bei der Fahrweise von 11.

Hereinafter, preferred embodiments of the invention with reference to a schematically simplified drawing are described in detail. Show it:

• 1 a schematic side view of a system according to the invention,
• 2 a schematic side view of a system according to the invention according to a further embodiment,
• 3 a schematic side view of a system according to the invention according to a further embodiment,
• 4 the temperature curve for a steel strip during a treatment in the plant of 3 .
• 5 a tabular overview of parameters of a possible driving style of a method according to the invention,
• 6 the temperature curve for a steel strip in the driving style of 5 .
• 7 a tabular overview of parameters of a possible driving style of a method according to the invention according to a further embodiment,
• 8th the temperature curve for a steel strip in the driving style of 7 .
• 9 a tabular overview of parameters of a possible driving style of a method according to the invention according to a further embodiment,
• 10 the temperature curve for a steel strip in the driving style of 9 .
• 11 a tabular overview of parameters of a possible driving style of a method according to the invention according to another embodiment, and
• 12 the temperature curve for a steel strip in the driving style of 11 ,

Below are with reference to the 1 to 12 preferred embodiment of a method according to the invention for a continuous heat treatment of a steel strip 102 and a plant according to the invention 10 explained. Identical features in the drawing are each provided with the same reference numerals. At this point, it should be noted separately that the drawing is merely simplified and shown in particular without scale.

1 shows the plant 10 in principle simplified in a side view thereof. At this plant 10 it is a continuous hot dip galvanizing line (CGL) with which a steel strip 102 heat treatment in various steps, followed by at least one surface of the steel strip, preferably all surfaces thereof, in a hot-dip bath 104 , in the 1 denoted by "zinc pot", a metallic coating is applied, preferably in the form of a zinc layer. The hot dip is the same 104 filled with liquid zinc.

• - Kammer 1: Vorheizkammer, direkt befeuert; in 1 mit „105“ bezeichnet;
• - Kammer 2: erste Heizkammer zur Schnellaufheizung, optional mit einer Vor-Oxidation ausgestattet; in 1 mit „107“ bezeichnet;
• - Kammer 3: zweite Heizkammer, strahlrohrbeheizt, dient zum Langsam-Aufheizen und zum Halten; in 1 mit „112“ bezeichnet;
• - Kammer 4: Langsamkühlkammer; in 1 mit „115“ bezeichnet;
• - Kammer 5: Schnellkühlkammer; in 1 mit „116“ bezeichnet;
• - Kammer 6: Kammer für ein Partitioning bzw. Überaltern; in 1 mit „117“ bezeichnet.

For heat treatment of the steel strip 102 includes the facility 10 several chambers through which the steel band 102 successively for heating or cooling, before it is applied to apply the zinc layer in the hot dip 104 is introduced. The individual chambers of the plant 10 are the following:

• - Chamber 1 : Preheat chamber, directly fired; in 1 With " 105 "designated;
• - Chamber 2 : first heating chamber for rapid heating, optionally equipped with pre-oxidation; in 1 With " 107 "designated;
• - Chamber 3 : second heating chamber, radiant tube heated, used for slow heating and holding; in 1 With " 112 "designated;
• - Chamber 4 : Slow cooling chamber; in 1 With " 115 "designated;
• - Chamber 5 : Rapid cooling chamber; in 1 With " 116 "designated;
• - Chamber 6 : Chamber for partitioning or overaging; in 1 With " 117 " designated.

The chambers 1 - 6 These numbers will be referred to hereinafter as the first to sixth chamber.

The principle simplified side view according to 1 clarifies that the steel band 102 in a transport direction T along individual tape paths 1 -24 through the said chambers 1 - 6 is guided through. This is the steel strip 102 in the first chamber 105 passed through an inlet, then passed through the second to fifth chambers, and at the end of the sixth chamber 117 discharged through an outlet for the purpose of subsequent immersion in the hot-dip bath 102 , Between the chambers, which adjoin each other, openings or passages are formed, through which the steel strip 102 in the transport direction T is (further) led.

• - Die erste Kammer bzw. Vorheizkammer 105 ist mit zumindest einem direkt beheizten Vorwärmer bzw. Ofenteil (DFF = Direct Fired Furnace) ausgestattet, mit dem das Stahlband 102 auf eine Temperatur von zumindest 600 °C erwärmt werden kann. Insoweit erfüllt die erste Kammer 105 die Funktion einer Vorheizkammer. Die erste Kammer 105 umfasst die Bandpfade 1+2. die erste Kammer 105 dient insbesondere zum kostengünstigen Aufheizen von weniger oxidationsempfindlichen Produkten bzw. Stahlbändern 102.
• - Die zweite Kammer 107 bildet eine erste Heizkammer zur Schnellaufheizung des Stahlbands 102, und ist zu diesem Zweck mit einem ersten Induktor 108 (in 1 auch mit „Induktor 1“ bezeichnet) und mit einem zweiten Induktor 109 (in 1 auch mit „Induktor 2“ bezeichnet) ausgestattet. In der Transportrichtung T des Stahlbands 102 gesehen ist der zweite Induktor 109 stromabwärts von den ersten Induktor 108 angeordnet. Der erste Induktor 108 ist als Längsfeld- Induktor ausgebildet. Der zweite Induktor 109 ist als Querfeld-Induktor ausgebildet. Die zweite Kammer 107 umfasst die Bandpfade 3, 4 und 5.
• - Optional kann die zweite Kammer 107 mit einer Voroxidationskammer 110 ausgestattet sein, die zwischen den ersten Induktor 108 und dem zweiten Induktor 109 angeordnet ist. Für diesen Fall durchläuft das Stahlband 102, nachdem es durch den ersten Induktor 108 erwärmt worden ist, zunächst die Voroxidationskammer 110, bevor es dann von dem zweiten Induktor 109 erwärmt wird.
• - Die dritte Kammer 112 bildet eine zweite Heizkammer und ist strahlrohrbeheizt, und dient zum Langsam-Aufheizen des Stahlbands 102 auf eine bestimmte Temperatur und zum anschließenden Halten auf dieser Temperatur. Die dritte Kammer 112 bildet einen RTF-Ofenteil (RTF = Radiant Tube Furnace) 113 und ist mit einer Mehrzahl von Strahrohren 114 ausgestattet, die entlang der Bandpfade 6-13 angeordnet sind. Bei Bedarf lassen sich für das Stahlband 102 innerhalb der dritten Kammer 112 auch längere Haltezeiten einstellen. Am Ende der dritten Kammer 112 kann ein weiterer Induktor, z.B. in Form eines Querfeld-Induktors, vorgesehen sein, in 1 mit „Induktor 3“ bezeichnet. Mit dem Induktor 3 kann das Stahlband 102 z.B. mit Heizraten von zumindest 50 K/s auf eine Temperatur von zumindest 820 °C erwärmt werden, bevor es die dritte Kammer 112 verlässt. Die dritte Kammer 112 umfasst die Bandpfade 6-13.

• - Die vierte Kammer 115 dient zum Langsamkühlen des Stahlbands 102, und umfasst hierzu die Bandpfade 14 + 15.
• - Die fünfte Kammer 116 dient als Schnellkühlkammer, und ist zu diesem Zweck mit Kühleinrichtungen in Form einer „Schnellkühlung 1“ und einer „Schnellkühlung 2“ ausgestattet, die entlang des Bandpfades 16 nach- bzw. hintereinander angeordnet sind.
• - Die sechste Kammer 117 dient dazu, das Stahlband 102 auf eine Partitioning-Temperatur von zumindest 300 °C, vorzugsweise von 320 °C zu erwärmen. Im Einlaufbereich der sechsten Kammer 117 kann ein Induktor 4 vorgesehen sein, wobei im Auslaufbereich bzw. am Ende der sechsten Kammer 117 ein Induktor 5 vorgesehen sein kann. Mit diesen Induktoren 4, 5, die vorzugsweise als Längsfeld-Induktoren ausgebildet sind, kann das Stahlband 102 mit einer hohen Heizrate auf eine vorbestimmte Temperatur gebracht werden. Die sechste Kammer 117 umfasst die Bandpfade 17-24.

The individual chambers according to the embodiment of 1 are explained separately below:

• - The first chamber or preheat chamber 105 is equipped with at least one directly heated preheater or furnace section (DFF = Direct Fired Furnace) with which the steel strip 102 can be heated to a temperature of at least 600 ° C. In that regard fulfilled the first chamber 105 the function of a preheat chamber. The first chamber 105 includes the band paths 1 +2. the first chamber 105 is used in particular for cost-effective heating of less oxidation-sensitive products or steel strips 102 ,
• - The second chamber 107 forms a first heating chamber for rapid heating of the steel strip 102 , and is for this purpose with a first inductor 108 (in 1 also with "inductor 1 ") And with a second inductor 109 (in 1 also with "inductor 2 "Designated) equipped. In the transport direction T the steel band 102 seen is the second inductor 109 downstream of the first inductor 108 arranged. The first inductor 108 is designed as a longitudinal field inductor. The second inductor 109 is designed as a transverse field inductor. The second chamber 107 includes the band paths 3 . 4 and 5 ,
• - Optionally, the second chamber 107 with a pre-oxidation chamber 110 be fitted between the first inductor 108 and the second inductor 109 is arranged. For this case, the steel band passes through 102 after passing through the first inductor 108 has been heated, first the pre-oxidation chamber 110 before then from the second inductor 109 is heated.
• - The third chamber 112 forms a second heating chamber and is radiant tube heated, and serves to slowly heat up the steel strip 102 to a certain temperature and then holding at this temperature. The third chamber 112 forms a RTF furnace part (RTF = Radiant Tube Furnace) 113 and is with a plurality of tubes 114 equipped along the belt paths 6 - 13 are arranged. If necessary, can be for the steel strip 102 within the third chamber 112 also set longer hold times. At the end of the third chamber 112 a further inductor, for example in the form of a transverse field inductor, may be provided in FIG 1 denoted by "inductor 3". With the inductor 3 can the steel band 102 eg at heating rates of at least 50 K / s to a temperature of at least 820 ° C, before it is the third chamber 112 leaves. The third chamber 112 includes the band paths 6 - 13 ,

• - The fourth chamber 115 Used for slow cooling of the steel strip 102 , and includes the tape paths for this purpose 14 + 15 ,
• - The fifth chamber 116 serves as a rapid cooling chamber, and for this purpose is provided with cooling means in the form of a "rapid cooling 1 "And a" rapid cooling 2 "equipped along the tape path 16 are arranged after or behind each other.
• - The sixth chamber 117 serves to the steel band 102 to a partitioning temperature of at least 300 ° C, preferably from 320 ° C to heat. In the inlet area of the sixth chamber 117 can be an inductor 4 be provided, wherein in the outlet region or at the end of the sixth chamber 117 an inductor 5 can be provided. With these inductors 4 . 5 , which are preferably designed as longitudinal field inductors, the steel strip 102 be brought to a predetermined temperature with a high heating rate. The sixth chamber 117 includes the band paths 17 - 24 ,

• - In der ersten Kammer 105 ist eine schwach reduzierende Atmosphäre vorgesehen, die Abgas mit (leichtem) Luftmangel enthält.
• - Die Atmosphäre in der zweiten Kammer 107 („Heizkammer“) besteht aus einem Anteil von zumindest 20 % Wasserstoff (H₂), vorzugsweise einem Anteil von > 50 % H₂, und weist einen Taupunkt von < -40 °C auf. Der restliche Anteil dieser Atmosphäre besteht aus Stickstoff (N₂).
• - In der vierten Kammer 115 ist für das Langsamkühlen des Stahlbands eine Atmosphäre vorgesehen, die zumindest 20 % Wasserstoff (H2), und Rest Stickstoff (N2) enthält und dabei einen Taupunkt von < -40 °C aufweist.
• - In der fünften Kammer 116, welche die Funktion einer Schnellkühlkammer erfüllt, liegt die gleiche Atmosphäre wie in der zweiten Kammer 107 vor. Zugunsten einer gesteigerten Kühlleistung bzw. Kühlperformance liegt der Wasserstoff-Anteil vorzugsweise > 50%.

In the respective chambers of the plant 10 in which a heat treatment (heating or cooling) for the steel strip 102 carried out certain atmospheres are provided to which the steel strip 102 is exposed when passing through the individual chambers. In this regard, it should be noted that the openings or passages between the individual chambers are provided with seals, so that in each of the chambers, the designated atmosphere is maintained. For the atmospheres in the individual chambers following explanations:

• - In the first chamber 105 a weakly reducing atmosphere is provided which contains exhaust gas with (slight) air deficiency.
• - The atmosphere in the second chamber 107 ("Heating chamber") consists of a proportion of at least 20% hydrogen (H ₂ ), preferably a proportion of> 50% H ₂ , and has a dew point of <-40 ° C. The remainder of this atmosphere is nitrogen (N ₂ ).
• - In the fourth chamber 115 For the slow cooling of the steel strip, an atmosphere is provided which contains at least 20% hydrogen ( H2 ), and balance nitrogen ( N2 ) and thereby has a dew point of <-40 ° C.
• - In the fifth chamber 116 , which performs the function of a rapid cooling chamber, is the same atmosphere as in the second chamber 107 in front. In favor of an increased cooling capacity or cooling performance, the hydrogen content is preferably> 50%.

The representation of 1 further illustrates a band-bypass, as a result of which the steel band 102 - if necessary - after exiting the second chamber 109 (or the heating chamber) then directly into the fifth chamber 116 can be introduced for the purpose of a rapid cooling. This means that in this case the third chamber 112 and the fourth chamber 115 from the steel band 102 will not go through.

In the individual chambers 1 - 6 the plant 10 the heat treatment of the steel strip takes place 102 each with different heating rates or Cooling rates. This will be explained in detail below with reference to various embodiments of the invention:

The embodiment of 2 represents a simplified modification of the plant of 1 and is used to treat oxidation-sensitive AHSS steels. In view of the fact that the embodiment of 2 a shortening of the plant of 1 are in the embodiment of 2 only 10 tape paths provided and accordingly named accordingly.

In the embodiment of 2 are both the first chamber 105 as well as the pre-oxidation chamber 110 each out of service. Instead, the steel band 102 directly in the second chamber 107 ("Heating chamber") inductively heated in two stages to eg 950 ° C (band path 1 ). As explained, this is the first inductor 108 with longitudinal field and the second inductor 109 formed with transverse field. The heating rate for heating the steel strip 102 by means of inductors 108 . 109 is at least 50 K / s, and in the case of the embodiment of 2 > 85 K / s. The atmosphere inside the second chamber 107 is hydrogen-containing as explained above. Due to a short residence time within the second chamber 107 , the high hydrogen content and the low water content, the selective oxidation and the diffusion of Si and Mn to the surface (s) of the steel strip 102 largely suppressed. Due to the high temperature, a very fast full Austenitisierung takes place, for the example shown here, the required hold time is about 5 seconds, for example exactly 7 seconds. Such a short holding time is helpful to keep the steel band 102 on its surfaces still not oxidized.

In the embodiment of 2 enters the steel band 102 after leaving the second chamber 107 directly into the fifth chamber 116 (or the "rapid cooling chamber"). In that regard, the above-described possible band-bypass is realized in this embodiment.

In the fifth chamber or the rapid cooling chamber 116 is the same atmosphere as in the heating chamber 107 in front. In favor of a high cooling performance, the hydrogen content in this atmosphere is preferably> 50%. Anyway takes place within the rapid cooling chamber 116 a cooling of the steel strip 102 down to about 250 ° C, with a cooling rate of eg 70 K / s.

After the steel band 102 following the rapid cooling chamber 116 in the sixth chamber 117 occurred occurs in the inlet region of the sixth chamber 117 through the inductor 3 first a heating to the partitioning temperature of eg 320 ° C. Subsequently, the steel band 102 in the individual tape paths 5 - 10 the sixth chamber 117 kept at this partitioning temperature, before it in the outlet area of the sixth chamber 117 through the inductor 4 heated to "Zinkpot temperature" and then with this temperature the hot dip 104 ("Zinc pot") is supplied.

3 shows a further embodiment of a modified system 10 also on a simplification or shortening of the plant of 1 and is used to treat oxidation-sensitive AHSS steels. In that regard, the embodiment of 3 also on the above-mentioned possibility of a band-bypass. In contrast to the embodiment of 2 this is the first chamber 105 in operation, with the function of a directly fired preheat chamber. Because the first chamber 105 has two tape paths, thus embraces the embodiment of 3 compared to that of 2 two tape paths more, namely a total of 12 tape paths, in the representation of 3 are named accordingly.

In connection with the embodiment of 3 It should be noted that in most cases the tendency of a steel strip to oxidize up to a temperature of approx. 700 ° C is negligible. This is the heating rate for the steel strip 102 up to a temperature of about 700 ° C irrelevant, being the atmosphere within the first chamber 105 Exhaust gas from a combustion with a slight lack of air is sufficient. Thus, the first inductor 108 in the second chamber 106 eliminated and by a directly heated preheater or oven part (DFF) 106 be replaced with the first chamber 105 equipped. In other words, this is the second chamber 109 only with the second inductor 109 (designed as a transverse field inductor) equipped.

Compared to the embodiment of 2 and the electrical power consumption for the first inductor 108 has the embodiment of 3 the advantage of significantly lower heating energy costs associated with the gas heating of the DFF oven section.

The course of the temperature of the steel strip 102 over time is for the embodiment of 3 in the diagram of 4 shown. In this diagram are the paths 1 - 12 , as explained in the presentation of 3 are shown at different times the band treatment entered.

The atmosphere in the second chamber or heating chamber 106 at least from the entrance to the second inductor 109 , consists of a proportion of at least 20% hydrogen (H ₂ ), preferably> 50 % H ₂ , and has a dew point of <-40 ° C. Relevant for the suppression of the selective oxidation of Si and Mn is a sufficiently short residence time of the steel strip 102 above a temperature of 700 ° C. In the embodiment according to 3 +4, this residence time should in any case be <60 seconds, the residence time in the diagram of 4 for example, 15 seconds.

In terms of a facility 10 according to the embodiment of 1 It should be noted that a hot dip galvanizing line (CGL) is only rarely used with AHSS steels. Rather, there is often a need in industry to also produce conventional grades of steel strip such as thermoforming grades at competitive production costs, which conventional grades tend to be less susceptible to oxidation. In view of this, we recommend a multipurpose CGL that comes with a facility 10 according to 1 is realized.

In the following, further modes of operation for a method according to the invention are explained, with which a system 10 to 1 can be operated. In this regard, it is pointed out that the conditions for these driving modes are shown in tables (cf. 5 . 7 . 9 . 11 ) and the information given herein for the furnace sections to the names of 1 Respectively. The resulting gradients for the temperature of the steel strip 102 over time are shown in diagrams (cf. 6 . 8th . 10 . 12 ), wherein the band paths referred to herein 1 - 24 also the in 1 correspond to shown tape paths. In detail:

The first mode of operation of a method according to the invention with its associated parameters in the table of 5 registered or called, the resulting temperature profile in 6 is shown. This procedure is used to process AHSS steels, whereby the selective oxidation is (largely) suppressed.

According to the explanations in the table of 5 can at the first driving the chamber 1 (or the first chamber 105 ), being in the chamber 2 (or the second chamber 107 ) no pre-oxidation takes place. Accordingly, in the second chamber 107 , which in the present case fulfills the function of a heating chamber, only the first inductor 108 and the second inductor 109 provided in the transport direction T the steel band 102 arranged one behind the other. In the second chamber or heating chamber 107 becomes the steel band 102 heated to a holding temperature of up to 950 ° C at a heating rate of> 50 K / s. The exact holding temperature, which may also be below 950 °, for example at 920 ° C, depends on the desired Austenitization. For example, the holding temperature between 840 ° C and 920 ° C, possibly also above 920 ° C. The first inductor 108 with longitudinal field heats the steel strip 102 at about 700 ° C, with the second inductor 109 with transverse field, the steel strip then heated to a holding temperature of 920 ° C, for example. The required holding time with which the steel band 102 remains at this holding temperature, is a maximum of 180 seconds, possibly <180 seconds, and is in the third chamber 112 and in the fourth chamber 115 hazards. The atmosphere consists of> 20% hydrogen, with a dew point of <-40 ° C. Because of the sufficiently short residence time (<180 seconds) and the strongly reducing atmosphere, the selective oxidation of the elements Si and Mn is suppressed, which is advantageous for very oxidation-sensitive steel grades.

Regarding further details for the respective temperatures and atmospheres, which at the first driving style in the individual chambers of the plant 10 from 1 are selected or set at this point to the entries in the table of 5 and in the diagram of 6 to get expelled.

A possible second mode of operation for a method according to the invention is described below with reference to the table of FIG 7 the resulting curve of the strip temperature over time in the diagram of 8th is shown. In the same way as the above-mentioned first mode of driving, the second mode of operation also serves for the treatment or machining of AHSS steels, wherein the selective oxidation is (largely) suppressed.

In the second mode, the steel band is in the first chamber 105 ("Preheat") heated to a temperature of up to 600 ° C, under an atmosphere containing exhaust gas with air shortage. Such heating is not critical for selective oxidation. Following heating in the preheat chamber 105 becomes the steel band 102 in the second chamber 107 (or "first heating chamber") through the first inductor 108 heated to a temperature of maximum 700 ° C. Taking into account that the steel strip 102 when entering the second chamber 107 already in the preheat chamber 105 has been heated and therefore has a hear compared to the first driving temperature, can now in the second driving the first inductor 108 run at low load or with lower power, which compared to the first driving leads to the advantage of lower energy costs.

The remaining process steps of the second driving mode may correspond to the process steps of the first driving style, so that in order to avoid repetition of the above explanation of the 5 +6 may be referenced.

For the further details of the respective temperatures and atmospheres, the second driving in the individual chambers of the plant 10 from 1 are selected or set at this point to the entries in the table of 7 and in the diagram of 8th to get expelled.

At this point, it should be noted separately that the first and second driving modes are the same as the pre-oxidation chamber 110 each out of service. As a result, takes place for the steel strip 102 in the second chamber 107 ("First heating chamber") only a heating by the inductors 108 . 109 ,

A possible third mode of operation for a method according to the invention is described below with reference to the table of FIG 9 the resulting curve of the strip temperature over time in the diagram of 10 is shown. The third method of operation is for machining AHSS steels, whereby a pre-oxidation is carried out here. In detail:

In the first chamber 105 becomes the steel band 102 under open heating by means of the directly heated oven part 106 heated to a temperature of at least 600 ° C. If the steel band 102 then into the second chamber 107 enters, it is doing - in preparation for pre-oxidation - by the first inductor 108 heated to a temperature in the range of 650-700 ° C. After heating by the first inductor 108 goes through the steel band 102 the pre-oxidation chamber 110 , under a hydrogen-containing atmosphere. After that, the steel band 102 in the second chamber 107 through the second inductor 109 heated to just below austenitisation (eg about 820 ° C) with a heating rate> 50 K / s. The range of ferrite to austenite conversion is in the third chamber 112 Drive slowly through ("second heating chamber"). Depending on the driving style or activation of the second inductor 109 and the selected heating rate through the radiant tube furnace 113 in the third chamber 112 may have a different length of holding time or residence time for the steel strip 102 to adjust. This is advantageous for steel grades which, for reasons of microstructure, require slow austenitization and, in addition, a longer hold time. Anyhow takes place in the third chamber 112 and in the fourth chamber 115 the desired reduction for the steel strip 102 ,

For the third way of driving it is additionally pointed out that the second inductor 109 is operated at part load, which advantageously leads to lower energy costs. When entering the third chamber 112 (= Tape path 6 ) has the steel band 102 a temperature of 820 ° C. The heating rate in the third chamber 112 ("Second heating chamber") is well 2 K / s. This will be at the end of the path 8th for the steel band 102 reaches a holding temperature of 920 ° C (see. 10 ). For holding at 920 ° C are in the third chamber 112 the paths 9 - 13 available, the holding time is about 84 seconds.

For the further details of the respective temperatures and atmospheres, the third driving in the individual chambers of the plant 10 from 1 are selected or set at this point to the entries in the table of 9 and in the diagram of 10 to get expelled.

A possible fourth mode of operation for a method according to the invention also serves for AHSS steels with preset pre-oxidation, and is described below with reference to the table of FIG 11 the resulting curve of the strip temperature over time in the diagram of 12 is shown.

In the fourth mode, the heating of the steel strip takes place 102 in the first chamber 105 , the subsequent heating in the second chamber 107 ("First heating chamber") through the first inductor 108 and treatment in the pre-oxidation chamber 110 in the same way as in the third driving style. Note now at the fourth driving style that at the end of the second chamber 107 the second inductor 109 remains off. Thus, the steel band points 102 on entering the third chamber 112 ("Second heating chamber") only a temperature of 700 ° C. As a result, the steel band 102 in the third chamber 112 conventionally through the jet pipes 114 heated with a lower heating rate. Compared to the third mode, this is reflected in the fact that the holding temperature of 920 ° C for the steel strip 102 in the third chamber 112 only at the end of the band path 10 is reached. For holding at the holding temperature of 920 ° C are in the third chamber 112 only the paths 11 - 13 available, with the holding time or residence time is about 47 seconds.

For the implementation of the present invention, it is expedient during operation of the system 10 use fill grades to complete all transient operations to pre-set the AHSS grade conditions. This includes both the timely setting of the respective atmospheres in the individual chambers with the necessary rinsing operations as well as the ramp-up of inductive rapid heating. When changing from AHSS to filling grades, this is done in reverse order, so that the AHSS product from the beginning of the tape to the end of the tape finds the necessary conditions.

Another advantageous aspect of the operation with the inductive rapid heating is that the transmitted heat flow from electrical quantities is known with good accuracy. With heat flow and belt data can be adjusted to the temperature of the steel strip 102 getting closed. A radiation pyrometer after an inductor can be evaluated with known strip temperature on the determination of the emissivity. During pre-oxidation, the temperature of the steel strip remains 102 constant, whereby the surface and thus the emissivity can change strongly. Using a radiation pyrometer downstream of the pre-oxidation chamber 110 it is possible to detect this surface change by the pre-oxidation with. This "online" determined emissivity of the steel strip 102 can be used via the thermal furnace model for precise guidance of further heating in the radiant tube furnace.

Finally, it should be noted that, in view of the various modes of operation described above, one method of using one system 10 from 1 can be operated according to the present invention, such a system 10 is a multi-purpose CGL, with both a heat treatment of a steel strip suppressed selective oxidation and a conventional treatment with pre-oxidation is feasible, and in addition, the cost-effective production of relatively unpretentious filling grades of steel strips is possible.

LIST OF REFERENCE NUMBERS

10

Plant for hot dip coating

102

steel strip

104

hot dipping bath

105

preheating

106

directly heated preheaters (DFF = Direct Fired Furnace)

107

first heating chamber

108

(first) inductor

109

(second) inductor

110

Voroxidationskammer

112

second heating chamber

113

RTF furnace part (RTF = Radiant Tube Furnace)

114

Lance (s)

115

Slow cool chamber

116

Quick cooling chamber

117

(Partitioning) holding chamber

118

Inductor (in the outlet area of the holding chamber 117 )

1-24

Tape paths of the plant 10 in the embodiment of 1

1-10

Tape paths of the plant 10 in the embodiment of 2

1-12

Tape paths of the plant 10 in the embodiment of 3

T

Transport direction for moving the steel strip 102

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 1819840 B1 [0004]
• EP 2732062 B1 [0004]

Claims (22)

A method of continuously heat treating a high strength steel strip (102), in particular AHSS grade of oxidation sensitive, by moving the steel strip (102) through at least one furnace means, characterized by the steps of: a) heating the steel strip in an atmosphere which is ≥ Contains 20%, preferably ≥ 50% hydrogen (H ₂ ) and the balance nitrogen (N ₂ ) and a dew point of <-40 ° C, wherein the steel strip at least from 750 ° C at a heating rate of at least 50 K / s to a Holding temperature between ≥ 800 ° C and ≤ 950 ° C is heated, the steel strip (102) in this atmosphere above 750 ° C dwells for a maximum of 180 seconds, b) rapid cooling of the steel strip (102) to <500 ° C. under a hydrogen-containing atmosphere, and c) applying a metallic coating to at least one surface of the steel strip. Method according to Claim 1 , characterized in that the steel strip (102) before step a) by a directly heated preheater (DFF = Direct Fired Furnace) (106) is heated in an exhaust atmosphere with lack of air to a temperature of up to 750 ° C. Method according to Claim 1 or 2 , characterized in that in step a) the steel strip (102) by at least one inductor (109), preferably in the form of a transverse field inductor, is heated to the holding temperature of up to 950 ° C. Method according to one of Claims 1 to 3 , characterized in that in step a) the steel strip (102) is inductively heated in two stages, wherein the steel strip (102) by a first inductor (108), preferably in the form of a longitudinal field inductor, initially to a temperature of up to Is heated to 720 ° C and then by a second inductor (109), preferably in the form of a transverse field inductor, to the holding temperature of up to 950 ° C is heated. Method according to one of the preceding claims, characterized in that in step a) the residence time ≤ 170 seconds, preferably ≤ 160 seconds, more preferably ≤ 150 seconds, more preferably ≤ 140 seconds, more preferably ≤ 130 seconds, further preferably ≤ 120 seconds, more preferably ≤110 seconds, more preferably ≤100 seconds, more preferably ≤90 seconds, more preferably ≤85 seconds, more preferably ≤80 seconds, more preferably ≤75 seconds, more preferably ≤70 seconds, more preferably ≤65 seconds, further preferably ≤ 60 seconds, more preferably ≤ 55 seconds, more preferably ≤ 50 seconds, further preferably ≤ 45 seconds, more preferably ≤ 40 seconds, further preferably ≤ 35 seconds, further preferably ≤ 30 seconds, further preferably ≤ 25 seconds, further preferably ≤ 20 Seconds, more preferably ≤ 15 seconds, more preferably e ≤ 10 seconds, more preferably ≤ 5 seconds. Method according to one of the preceding claims, characterized in that between the steps a) and b) a slow cooling of the steel strip (102) to a temperature <850 ° C under a hydrogen-containing atmosphere, preferably, that this atmosphere ≥ 20% hydrogen (H ₂ ) and has a dew point of <-40 ° C, is carried out, more preferably, that the atmosphere for this slow cooling in addition to hydrogen (H ₂ ) radical nitrogen (N ₂ ) contains. A method of continuously heat treating a high strength steel strip (102), in particular AHSS grade of oxidation sensitive, in which the steel strip (102) is moved through at least one furnace means, characterized by the steps of: i) heating the steel strip (102) to a temperature of at least 600 ° C by a Direct Fired Furnace (DFF) (106) in an exhaust atmosphere with lack of air, ii) heating the steel strip (102) to 700 ° C to 750 ° C by an inductor (108) in a hydrogen-containing atmosphere, iii) heat treating the steel strip (102) in an oxidizing atmosphere (110) having an oxygen content of 2-5% O ₂ to thereby form iron oxide layers on the surfaces of the steel strip (102), said heat treatment lasting a period of Iv) heating the steel strip (102) to a temperature of up to 950 ° C in an atmosphere containing hydrogen (H ₂ ), water mf and balance nitrogen (N ₂ ), wherein the steel strip (102) is maintained at a temperature of up to 950 ° C for a period of ≥ 40 seconds, v) rapid cooling of the steel strip (102) to <500 ° C under a hydrogen-containing atmosphere, and vi) applying a metallic coating to at least one surface of the steel strip. Method according to Claim 7 , characterized in that in step iv) the steel strip (102) is heated by a RTF furnace section (RTF = Radiant Tube Furnace) (113), preferably in that the steel strip (102) is additionally crossed by a transverse field at the beginning of step iv) -Induktor (109) is heated at a heating rate of at least 50 K / s to at least 820 ° C. Method according to Claim 7 or 8th , characterized in that between steps iv) and v) slow cooling of the steel strip (102) to a temperature <850 ° C in a hydrogen-containing atmosphere, preferably that this atmosphere contains ≥ 20% hydrogen (H ₂ ) and has a dew point of <-40 ° C, more preferably, that the atmosphere for this slow cooling in addition to hydrogen (H ₂₎ balance nitrogen (N _2). Method according to one of Claims 7 to 9 , characterized in that following the step v) further process steps are provided, preferably, that in these further process steps for the steel strip, a heating, holding at a certain temperature and / or cooling is performed. Method according to one of the preceding claims, characterized in that the steel strip (102) is cooled in the rapid cooling in step b) or in step v) to a temperature which is in a range between 200 ° C and 450 ° C. Method according to Claim 11 , characterized in that prior to step c) or subsequent to step v), heating the steel strip (102) to a partitioning temperature of at least 300 ° C, preferably 320 ° C, in an atmosphere containing ≥ 20% hydrogen (H ₂ ) and balance nitrogen (N ₂ ) is carried out, wherein the steel strip (102) dwells in this atmosphere for a period of ≥ 30 seconds. Method according to Claim 12 , characterized in that the steel strip (102) at the end of the partitioning heating by an inductor (119), preferably in the form of a longitudinal field inductor, to the necessary temperature for entry into a hot dip (104), preferably to a temperature of 460 ° C, heated. Method according to one of the preceding claims, characterized in that in step c) or in step vi) the steel strip (102) is coated by means of a coating device on at least one surface thereof, preferably that the coating device is a hot dip (104), in which the steel strip is dip-coated, in particular with zinc. An apparatus (10) for hot dip coating a high strength steel strip (102) moving in a transport direction (T), in particular oxidation sensitive AHSS grades, comprising a hot dip bath (104) into which the steel strip (102) is dipable for coating, wherein the transport direction (T) of the steel strip (102) seen upstream of the Schmelztauchbad (104) at least a first heating chamber (107) with at least one inductor (108, 109), preferably in the form of a transverse field inductor, a rapid cooling chamber (116) and a holding chamber (117) for a partitioning of the steel strip (102) are arranged, preferably that in the inlet region of the holding chamber (117) an inductor (118) and / or in the outlet region of the holding chamber (117) an inductor (119) is provided. Appendix (10) to Claim 15 , characterized in that - seen in the transport direction (T) of the steel strip (102) - upstream of the first heating chamber (107) a preheat chamber (105) with a directly heated preheater (DFF = Direct Fired Furnace) (106) is arranged. Appendix (10) to Claim 15 or 16 , characterized in that a transverse field inductor (109) is provided in the first heating chamber (107), preferably that a longitudinal field inductor (108) is provided upstream of the transverse field inductor (109). Appendix (10) to Claim 17 , characterized in that between the longitudinal field inductor (108) and the transverse field inductor (109) a Voroxidationskammer (110) is provided which contains an atmosphere having an oxygen content of 2-5% O ₂ . Appendix (10) according to one of Claims 15 to 18 , characterized in that - seen in the transport direction (T) of the steel strip (102) - downstream of the first heating chamber (107) a second heating chamber (112) is arranged, the at least one RTF furnace part (RTF = Radiant Tube Furnace) (113 ) having. Appendix (10) according to one of Claims 15 to 19 , characterized in that - seen in the transport direction (T) of the steel strip (102) - upstream of the rapid cooling chamber (116) a slow cooling chamber (115) is arranged. Use of a system (10) according to one of Claims 15 to 19 to carry out a method according to one of Claims 1 to 6 , Use of a system (10) according to one of Claims 18 to 20 to carry out a method according to one of Claims 7 to 14 ,

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