DE102010026757A1 - Method and production line for producing a cold-rolled steel flat product from a stainless steel - Google Patents

Abstract

The invention relates to a method and a correspondingly designed production line (1) for producing a cold-rolled flat steel product (E) from a hot strip (W) that is subject to scale and consists of a stainless steel. In the course of the process according to the invention, the hot strip (W) contaminated with scale is cold-rolled to form the flat steel product (E), the cold-rolled flat steel product (E) is annealed and the annealed flat steel product (E) is descaled. According to the invention, the cold-rolled flat steel product (E) obtained after cold rolling the hot strip (W) is subjected to a descaling treatment in the as-rolled state before annealing, in which the scale present on the cold-rolled flat steel product (E) is mechanically removed. In this way, processes and production lines can be implemented with which it is possible in a cost-effective manner to produce cold-rolled flat steel products from stainless steel with an improved surface quality.

Description

The invention relates to a method for producing a cold-rolled steel flat product from a scale-bearing stainless steel strip in which the hot-rolled strip is cold-rolled to the flat steel product in which the cold-rolled flat steel product is annealed and the cold-rolled flat steel product is descaled.

Moreover, the invention relates to a production line for producing a cold-rolled flat steel product made of a stainless steel, wherein the production line comprises at least one cold rolling stand, at least one annealing furnace and at least one device for removing scale adhering to the cold-rolled steel flat product.

Here, the term "flat steel products" here from a stainless steel or a so-called "stainless steel" produced steel strips or sheets understood.

In the course of the production of cold-rolled stainless steel flat products, a suitably composite molten steel is poured into a precursor, such as slabs, thin slabs or cast strip, from which a hot strip is then hot rolled and wound into a coil. The hot strip obtained and, if necessary, subjected to a supplementary heat treatment is then cold-rolled one or more stages into a cold strip with the scale adhering to it.

In the course of cold rolling, hardening of the rolled steel strip occurs, as a result of which the cold strip obtained after cold rolling can at best be reduced to a very reduced extent. In order to eliminate this so-called "strain hardening", the cold strip is usually subjected to a heat treatment in which it is annealed at sufficiently high annealing temperatures. The then remaining fine and firmly adhering to the surface scale particles can be removed in a pickling device through which the cold strip is passed after mechanical Zunderbeseitigung.

A typical example of a production line of the kind explained above is shown in FIG DE 691 26 699 T2 ( EP 0 509 177 B1 ) known. In order to increase the efficiency with which the scale adhering to the annealed strip is removed, according to this prior art, the stain device can be combined with a mechanically acting descaling device.

In practice, a scale breaker is used in which coarser pieces of the adhesive on the annealed strip scale are removed. In addition, a ball-blasting or a brushing device is usually provided, which mechanically releases any larger scale particles that still exist from the cold-rolled strip on emerging from the scale breaker. At the end of production, the cold-rolled strip is, if necessary, still temper rolling after leaving the pickling device in order to improve its yield strength and dimensional stability.

Practical experience shows that, with a production line of the above-mentioned kind, large quantities of cold-rolled steel flat products made of stainless steel can be produced at favorable costs. However, the surface quality of steel flat products produced with such production lines often does not meet today's requirements.

Against this background, the object of the invention was to provide a method and a production line which is particularly suitable for carrying out such a method, with which it is possible in a cost-effective manner to produce cold-rolled stainless steel flat products with improved surface quality.

With regard to the method, this object has been achieved according to the invention in that the production steps specified in claim 1 are carried out in the production of cold-rolled flat steel products made of stainless steel.

With regard to the production line, the solution according to the invention of the above-mentioned object is that such a line has the features specified in claim 12.

Advantageous embodiments of the invention are specified in the dependent claims and are explained below as the general inventive concept in detail.

Like the prior art described in the introduction, the method according to the invention for producing a cold-rolled steel flat product assumes that scale-bearing stainless steel strip, known as "black plate", is cold-rolled without prior descaling. Furthermore, the method according to the invention comprises an annealing treatment in order to soften the cold-rolled material. Likewise, according to the invention, a descaling takes place in order to free the cold-rolled flat steel product from the scale which adheres to it.

According to the present invention, the cold rolled cold roll obtained after hot rolling is now obtained Steel flat product in the hard rolling state before annealing subjected to a descaling, in which on the cold-rolled steel flat product existing scale is mechanically removed. In the method according to the invention, therefore, a mechanical descaling is carried out on the still hard-cold cold strip before the cold strip is subjected to annealing. Here, on the one hand, the invention makes use of the fact that a part of the scale is already broken during cold rolling and, accordingly, can be easily detached from the cold-rolled steel flat product.

This procedure has the advantage that the cold-rolled cold strip is comparably insensitive to the forces acting on its free surfaces during mechanical descaling. Thus, the mechanical scaling of the hard material results in surface deformations which are much lower than those resulting from the conventional descaling of comparable softened steel strips after annealing.

The steel flat product largely freed from coarser scale in the manner according to the invention then passes through a conventional annealing device in which it is annealed in a manner known per se in order to eliminate the solidification which occurs in the course of cold rolling and is optionally further increased in the case of mechanical descaling.

On the other hand, unlike the annealing of corrosion-sensitive flat steel products, in the subsequent annealing of steel strips or sheets made of stainless steels, only small amounts of new scale are formed on the surface of the respective flat steel product. These can then be removed safely in a conventional pickling device. A further mechanical descaling between the exit from the annealing furnace and the entry into the pickling means therefore does not take place according to the invention.

Instead, after annealing, the stainless steel strip may optionally undergo a planarity improvement device. In the prior art, for example, stretch bending devices or the like are used for this purpose.

According to the peculiarities of the method according to the invention explained above, a production line according to the invention for producing a cold-rolled steel flat product comprising a stainless steel comprises at least one cold rolling stand, at least one annealing furnace and at least one device for mechanically removing scale adhering to the cold-rolled steel flat product, wherein the at least one device is arranged for the mechanical removal of the scale in the conveying direction of the cold rolled steel flat product seen before the entrance of the annealing furnace.

Due to the minor damage caused by the descaling carried out according to the invention after the cold rolling and before the annealing, the steel strips and sheets produced in accordance with the invention and made of a stainless steel have an optimized surface finish. This optimization succeeds solely in that the mechanical descaling is carried out in front of the annealing furnace. The necessary facilities are already available in conventional production lines, but are used according to the invention elsewhere. Consequently, the procedure according to the invention results in no additional costs if the quality of the product obtained is significantly increased.

Of course, the mechanical descaling according to the invention taking place in front of the annealing furnace can be carried out by means of a plurality of processes which may optionally be carried out in succession or combined with one another. Thus, it is conceivable to carry out the mechanical descaling by particle blasting, such as sandblasting or shot peening, or by brushing, whereby these possibilities of descaling can be particularly effective when combined with one another in a corresponding device or in separate blasting and brushing directions in succession be performed.

If the removal of the scale from the cold-rolled steel cold rolled flat product by a blast treatment, this treatment can be performed as liquid jets, such as high pressure water blasting. In order to increase the effectiveness of the scale removal, the liquid steel agent can carry particles with it, which abradingly remove the scale adhering to the cold-rolled, hard-rolled steel flat product. The particles concerned may be scale particles obtained from the scale removed from the cold-rolled steel flat product.

It is likewise conceivable to use a conventional scale breaker for mechanical descaling, in which the scale adhering to the cold-rolled, flat-rolled steel flat product is broken by deflecting the flat steel product on at least one roll.

To the dimensional accuracy, the surface roughness and the mechanical properties of steel flat products produced according to the invention to optimally, the cold-rolled steel flat product can optionally be tempered or post-rolled after annealing.

Depending on the number of cold rolling steps to be carried out and the available plant technology, the process according to the invention can be carried out batchwise or in continuous operation. In the discontinuous implementation, for example, the cold rolling can take place in several stages in a reversing stand operated independently of the operation of the annealing furnace. This has the advantage that a high overall deformation of the cold strip with a correspondingly high strain hardening and a concomitantly particularly hard, insensitive to the mechanical scaling surface can be achieved.

The implementation in a continuous pass is useful, for example, when large quantities of flat steel products are to be produced in a time-saving manner and over which one or more cold rolling stands available that pass through can be achieved with sufficient thickness reduction. Fluctuations in the conveying speed between the individual workstations of such a continuous production line according to the invention can thereby be compensated by arranging at least one strip store in the conveying path of the flat steel product.

An inventively produced, made of a stainless steel existing flat steel product has a surface roughness Ra, which is regularly in the range of 0.1-1 microns, without needing to go beyond the inventive procedure beyond measures. Particularly low surface roughness results in this case when the stainless steel strip is post-rolled after annealing at degrees of deformation of up to 10%, in particular 1-7%.

The invention will be explained in more detail with reference to a drawing illustrating an exemplary embodiment.

The sole FIGURE shows a continuous throughput in the conveying direction F production line 1 for producing a cold-rolled stainless steel strip E.

• – eine Abhaspeleinrichtung 2 zum aufeinander folgenden Abhaspeln von zu Coils C1, C2 gewickelten Warmbändern W, die aus einem nicht rostenden Stahl bestehen und an deren Oberfläche noch der bei der Warmbanderzeugung entstehende Zunder haftet,
• – eine Schweißeinrichtung 3, die dazu dient, das Ende des zu dem einen Coil C1 gewickelten Warmband W mit dem Anfang des zu dem anderen Coil C2 gewickelten Warmbands W zu verbinden, wenn das erste Warmband vollständig in die Produktionslinie 1 eingespeist ist,
• – einen ersten Bandspeicher 4 zum Ausgleichen von Schwankungen der Fördergeschwindigkeit des in die Produktionslinie 1 eingespeisten Warmbands W,
• – drei Walzgerüste 5, 6, 7, bei denen es sich um konventionelle, aus dem Stand der Technik in unterschiedlichen Ausführungen bekannte Kaltwalzgerüste handelt und in denen das Warmband W in drei aufeinander folgenden Stufen zu Edelstahlband E kaltgewalzt wird,
• – einen zweiten Bandspeicher 8 zum Ausgleichen von Schwankungen der Fördergeschwindigkeit des aus dem Kaltwalzgerüst 7 austretenden Edelstahlbands E,
• – eine erste Entzunderungseinrichtung 9, in der der auf dem Edelstahlband E haftende, in Folge der beim Durchlauf durch die Kaltwalzgerüste 5, 6, 7 eingetretene Längung des Edelstahlbands E gebrochene Zunder mittels Kugelstrahlen von dem Edelstahlband E mechanisch abgetragen wird,
• – eine zweite Entzunderungseinrichtung 10, in der der auf dem Edelstahlband E nach Verlassen der Entzunderungseinrichtung 9 noch haftende Zunder mittels Bürsten von dem Edelstahlband E mechanisch abgetragen wird,
• – einen Durchlaufglühofen 11, in dem das mechanisch entzunderte Edelstahlband E nach Verlassen der Entzunderungseinrichtung 10 im kontinuierlichen Durchlauf über eine so lange Glühzeit auf eine ausreichend hohe Glühtemperatur erwärmt wird, dass die im Zuge des Kaltwalzens und der mechanischen Entzunderung entstandenen Verfestigungen des Edelstahlbands E beseitigt werden und ein für weitere Umformvorgänge ausreichend weiches Edelstahlband E erhalten wird,
• – eine im Anschluss an den Durchlaufglühofen 11 ohne eine zwischengeschaltete mechanische Bearbeitung der Oberfläche des Edelstahlbands E durchlaufene Streckbiegeeinrichtung 17 zur Verbesserung der Planheit des Edelstahlbands E,
• – eine im Anschluss an die Einrichtung 17 ohne eine zwischengeschaltete mechanische Bearbeitung der Oberfläche des Edelstahlbands E durchlaufene Beizeinrichtung 12 zum Entfernen des auf dem Edelstandband E noch vorhandenen Zunders auf chemischem Wege,
• – einen weiteren Bandspeicher 13 zum Ausgleichen von Schwankungen der Fördergeschwindigkeit des aus dem Durchlaufglühofen 11 austretenden geglühten Edelstahlbands E,
• – ein im Auslauf des Bandspeichers 13 angeordnetes Dressierwalzgerüst 14 zum Nachwalzen des Edelstahlbands E mit einem Gesamtverformungsgrad von bis zu 10%,
• – einen letzten Bandspeicher 15 zum Ausgleichen von Schwankungen der Fördergeschwindigkeit des aus dem Dressierwalzgerüst 14 austretenden geglühten Edelstahlbands E und
• – eine mit zwei abwechselnd zum Einsatz kommenden Haspeln ausgestattete Haspeleinrichtung 16 zum Haspeln des aus dem Bandspeicher 15 austretenden Edelstahlbands E.

The production line 1 comprises in the conveying direction F in line one behind the other

• - A rewinder 2 for sequentially unwinding hot strips W wound into coils C1, C2, which are made of a stainless steel and on the surface of which still adheres the scale formed during hot strip production,
• - a welding device 3 which serves to connect the end of the hot strip W wound to the one coil C1 to the beginning of the hot strip W wound to the other coil C2, when the first hot strip is completely in the production line 1 is fed,
• - a first tape storage 4 to compensate for fluctuations in the conveying speed of the production line 1 fed hot strip W,
• - three rolling stands 5 . 6 . 7 which are conventional cold rolling stands known from the state of the art in different designs and in which the hot strip W is cold-rolled in three successive stages to stainless steel strip E,
• - a second tape storage 8th to compensate for fluctuations in the conveying speed of the cold rolling mill 7 emerging stainless steel bands E,
• A first descaling device 9 in which the adhering to the stainless steel band E, as a result of when passing through the cold rolling stands 5 . 6 . 7 occurred elongation of the stainless steel strip E broken scale is mechanically removed by shot peening of the stainless steel strip E,
• A second descaling device 10 in which the on the stainless steel band E after leaving the descaling device 9 still adhering scale is mechanically removed by means of brushes from the stainless steel strip E,
• - a continuous annealing furnace 11 in which the mechanically descaled stainless steel strip E after leaving the descaling device 10 is heated to a sufficiently high annealing temperature in a continuous pass over such a long annealing time that the hardening of the stainless steel strip E resulting from cold rolling and mechanical descaling is eliminated and a stainless steel strip E which is sufficiently soft for further forming operations is obtained;
• - one after the continuous annealing furnace 11 without an intermediate mechanical machining of the surface of the stainless steel strip E traversed stretch bending device 17 to improve the flatness of the stainless steel strip E,
• - one following the establishment 17 without an intermediate mechanical machining of the surface of the stainless steel strip E swept pickling 12 for removing the scale still present on the stainless steel band E chemically,
• - another tape storage 13 to compensate for fluctuations in the conveying speed of the continuous annealing furnace 11 emerging annealed stainless steel bands E,
• - one in the outlet of the tape storage 13 arranged temper rolling mill 14 for re-rolling stainless steel strip E with a total deformation degree of up to 10%,
• - a last tape storage 15 to compensate for fluctuations in the conveying speed of the from the temper rolling mill 14 emanating annealed stainless steel bands E and
• - A reel equipped with two alternately used reels 16 for unwinding from the tape storage 15 leaking stainless steel bands E.

The unwound from each in use coils C1 or C2, tainted, optionally in the welding device 3 Hot strip W connected to the end of the previously processed hot strip W and conventionally produced from a stainless steel is passed over the strip accumulator 4 into the first cold rolling stand 5 fed and then in the subsequently passed through cold rolling stands 6 . 7 cold rolled in a total of three stages to the cold rolled stainless steel E. As a result of the over the cold rolling stands 5 . 6 . 7 entering the thickness reduction, the stainless steel strip E is elongated, so that the scale adhering to it due to the occurring surface tensions of the hot strip W in coarse pieces flakes off or is dissolved.

The one after leaving the last cold rolling stand 7 Tinder still adhering to the now cold-rolled to desired thickness, hardened as a result of cold rolling stainless steel strip E is in the first descaling 9 mechanically descaled by directing a particle beam with high kinetic energy against the solidified surfaces of the stainless steel strip E. The particle beam may, for example, be a shot blast, as already used in the prior art for descaling, but elsewhere in the process.

In the second descaling device 10 is brushed off by the thus mechanically descaled stainless steel strip E of the remaining there scale by means of brushes. When leaving the descaling device 10 and running into the continuous annealing furnace 11 Accordingly, only small, fine scale residues adhere to the surface of the stainless steel strip E.

Alternatively or in addition to the facilities 9 . 10 a descaling device, not shown here, can be provided, in which the scale adhering to the stainless steel strip E is removed by means of a high-pressure liquid jet. The liquid jet, which has been applied under high pressure and impinges on the strip surface to be descaled with high kinetic energy, can carry particles with it in order to increase the effectiveness of the scale removal. These particles may be trapped scale particles of a certain grain size, which are added to the jet liquid, for example water.

When passing through the continuous annealing furnace 11 the stainless steel strip E is heated to a temperature at which the solidified structure of the stainless steel strip E softens again. The length of the continuous annealing furnace 11 , The flow rate and the annealing temperature are coordinated so that the desired Entablenteentfestigung at the end of the continuous annealing furnace 11 is completed. Of course, the continuous annealing furnace 11 for this purpose, be divided into several zones in which different temperatures prevail in order to achieve an optimal glowing result. Due to its alloy and the resulting minimized sensitivity to corrosion, only a small amount of new scale is formed on the stainless steel strip E despite the comparatively high annealing temperature.

The quantity of scale adhering to the stainless steel strip E as it exits the annealing furnace is so small that it is in the pickling device 12 as far as possible completely removed from the surface of the stainless steel strip E by the action of the pickling agent acting on the stainless steel strip E. Before entering the pickling facility 12 However, the stainless steel band E passes through the still in the conveying direction F behind the annealing furnace 11 arranged stretch bending device 17 , In this, the stainless steel strip E is deformed in a conventional manner by multiple changes of direction so that it is the immediately following entry into the subsequently swept pickling 12 has an overall improved flatness. The after leaving the pickling 12 Performing temper rolling used in particular to improve the surface roughness of the stainless steel strip E, in addition, the dimensional stability and the mechanical properties are optimized before it to a coil 3 or 4 in the coiler 16 is wound. As a result of the secondary rolling carried out at deformation rates of typically 5-7%, the surface roughness values can be approximately halved, so that after the finish rolling an optimally smooth product is available.

LIST OF REFERENCE NUMBERS

1

production line

2

Abhaspeleinrichtung

3

welding equipment

4

tape storage

5, 6, 7

Cold Rolling Mills

8th

tape storage

9

first descaling device

10

second descaling device

11

continuous annealing furnace

12

pickling

13

tape storage

14

Dressierwalzgerüst

15

tape storage

16

coiler

17

Device for improving the flatness

C1, C2

Coils from hot strip W

e

stainless steel band

F

conveying direction

W

hot strip

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

• DE 69126699 T2 [0006]
• EP 0509177 B1 [0006]

Claims (15)

A method of producing a cold-rolled steel product (E) from a scale-bearing stainless steel strip (W) in which the tindered hot strip (W) is cold rolled to the flat steel product (E), wherein the cold rolled flat steel product (E ) and in which the cold-rolled steel flat product (E) is descaled, characterized in that the cold-rolled flat steel product (E) obtained after the cold rolling of the hot strip (W) is subjected to a descaling treatment in the hard-rolled state before annealing, on the cold-rolled steel flat product (E) existing scale is mechanically removed. A method according to claim 1, characterized in that the descaling of the cold-rolled, hard-rolled flat steel product (E) carried out before the annealing is carried out by blasting with solid particles. Method according to one of the preceding claims, characterized in that the descaling of the cold-rolled, hard-rolled steel flat product (E) carried out before annealing is carried out by brushing. Method according to one of the preceding claims, characterized in that the descaling of the cold-rolled, hard-rolled steel flat product (E) carried out before annealing is carried out by liquid jets. A method according to claim 4, characterized in that the liquid jets carry particles with it, which remove abrasive on the cold-rolled, hard-rolled steel flat product (E) adhering scale. Method according to one of the preceding claims, characterized in that the descaling of the cold-rolled, hard-hard steel flat product (E) carried out before the annealing takes place by deflecting the flat steel product on at least one roll of a scale breaker. Method according to one of the preceding claims, characterized in that the cold-rolled flat product (E) after annealing optionally undergoes a device for improving its flatness and is pickled. Method according to one of the preceding claims, characterized in that the cold-rolled flat product (E) is tempered or re-rolled. Method according to one of the preceding claims, characterized in that its work steps are completed discontinuously. Method according to one of claims 1 to 8, characterized in that its operations are completed in a continuous pass. Method according to one of the preceding claims, characterized in that the resulting cold-rolled, consisting of a stainless steel flat steel product (E) has a 0.1-1 .mu.m, in particular 0.3-0.7 microns, amounting surface roughness Ra. Production line for producing a cold-rolled steel flat product (E) consisting of a stainless steel, comprising at least one cold rolling stand ( 5 . 6 . 7 ), at least one annealing furnace ( 11 ) and at least one institution ( 9 . 10 . 12 ) for the mechanical removal of scale adhering to the cold-rolled steel flat product (E), characterized in that the at least one device ( 9 . 10 ) for mechanically removing the scale in the conveying direction (F) of the cold-rolled steel flat product (E) before the entry of the annealing furnace ( 11 ) is arranged. Production line according to claim 12, characterized in that the cold rolling stand ( 5 . 6 . 7 ) irrespective of the operation of the annealing furnace ( 11 ) operated Reversiergerüst is. Production line according to claim 12, characterized in that the cold rolling stand ( 5 . 6 . 7 ), the facility ( 9 . 10 ) for removing the scale and the annealing furnace ( 11 ) are arranged on a conveyor line in the conveying direction (F) of the flat steel product (E) arranged one behind the other in such a way that they are passed through one after the other in a continuous sequence. Production line according to claim 14, characterized in that in the conveying path of the flat steel product (E) at least one strip accumulator ( 4 . 8th . 13 . 15 ) is arranged.

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