EP2035587B1 - A method and a system for producing hot-rolled strip silicon steel based on thin slabs - Google Patents

Description

The invention relates to a method and a plant for the production of hot strip (pre-material) from silicon-alloyed steels for further processing into grain-oriented sheets, such as electric sheets. The further processing is not the subject of the present invention; it takes place in cold rolling mills.

• Verfahren und Anlagen zum Walzen von Bändern und Blechen aus der Gießhitze sind bekannt, zum Beispiel beschrieben in Stahl & Eisen, Vol. 2, 1993, S. 37 ff . Bei der hier beschriebenen Anlage wird mittels einer Stranggießmaschine mit speziell ausgestalteter Kokille eine Dünnbramme erzeugt, in Einzellängen unterteilt und zum Temperaturausgleich einem Rollenherdofen zugeführt. Anschließend wird die Bramme auf eine deutlich höhere Einlaufgeschwindigkeit der sich anschließenden Walzstrasse beschleunigt, entzundert und der Walzstrasse zugeführt. Im stationären Produktionsbetrieb mit einer Gießgeschwindigleit von 5,5 m/min erreicht die Dünnbramme den Rollenherdofen mit einer Durchschnittstemperatur von 1080°C. Die Auslauftemperatur aus dem Rollenherdofen liegt etwa bei 1100°C. Die für den Walzprozess notwendige Energie wird somit fast vollständig aus der Wärmemenge gedeckt, die im gegossenen Strang enthalten ist. Im Walzwerk werden die Temperaturen durch Veränderung der Walzengeschwindigkeit, durch Kühlung und aus dem Walzenkontakt gesteuert, so dass sich eine Endwalztemperatur von 880°C einstellt. Es folgt eine langsame Abkühlung in der Kühlstrecke sowie ein sich anschließendes Aufhaspeln.

Various methods and systems of the generic type are known from the prior art; by way of example, reference is made to the following two publications:

• Processes and plants for the rolling of strips and sheets from the casting heat are known, for example described in Stahl & Eisen, Vol. 2, 1993, p. 37 ff , In the plant described here, a thin slab is produced by means of a continuous casting machine with specially designed mold, divided into individual lengths and fed to a roller hearth furnace for temperature compensation. Subsequently, the slab is accelerated to a much higher inlet speed of the subsequent rolling train, descaled and fed to the rolling train. In stationary production operation with a casting speed of 5.5 m / min, the thin slab reaches the roller hearth furnace with an average temperature of 1080 ° C. The outlet temperature from the roller hearth furnace is approximately 1100 ° C. The energy required for the rolling process is thus almost completely covered by the amount of heat contained in the cast strand. In the rolling mill, the temperatures are controlled by changing the roller speed, by cooling and from the roller contact, so that sets a final rolling temperature of 880 ° C. It follows a slow cooling in the cooling section and a subsequent coiling.

From the EP-A1-1 469 954 A method and plant for producing hot strip of austenitic stainless steels is known. The cast product is subjected to a rolling process in a rolling train and in a second step of a heat treatment to prevent corrosion.

The EP 1 097 764 describes a device and method for surface treatment of a continuously cast steel product in the hot state for the removal of surface defects, surface contaminants and the like where surface treatments are to provide long service life. The parts to be machined are subjected to cooling before the surface processing step.

The EP 0 392 535 describes a method for producing a grain oriented electrical steel sheet comprising the steps of: heating, hot rolling and winding. Subsequently, the hot-rolled sheet is annealed again as needed, and subjected to a cold rolling process. The cold rolling is divided into different degrees of deformation. Depending on requirements and application, an intermediate annealing is then carried out again and the cold-rolled sheet is subjected to a decarburization annealing and a final finish annealing and a subsequent hot rolling process.

Furthermore, in the DE 31 50 946 Described an apparatus for descaling a steel strand coming from a continuous casting plant, wherein the total surface is descaled with as little water as possible before the flame cutting machine.

The publication EP 0 0771 596 A1 describes a production plant for continuous or discontinuous rolling of hot strip.

Multi-stage temperature-adjusting systems for heating a cast product before it enters a rolling mill are known from EP 1 469 954 known.

Furthermore, from the EP 0 415 987 B2 a method for the continuous production of strip steel or sheet steel from thin slabs of about 50 mm thickness known, the thin slabs are produced on Bogenstranggießanlagen with horizontal outlet direction. The method comprises the process steps: rolling the thin slab after solidification of the strand in an arcuate guide shaft at temperatures of more than 1100 ° C, cooling the slabs during radiation or descaling, inductive reheating to a temperature of about 1100 ° C and rolling the thin slab in at least one rolling mill. By means of the heating, a temperature is set in the slab, so that sets a temperature gradient at the deformation means of the rolling train in such a way that when tapping into the last roll stand, the temperature is within sufficient for a good deformation order of magnitude. Here, in a third and last roll stand of the rolling train, the rolling stock temperature dropped, for example, to 988 ° C and sufficient as a tapping temperature for the last forming step. The rolling stock leaves the last mill stand with a temperature of 953 ° C or less and is then separated at a further lowered temperature in the desired lengths, stacked or reeled. If necessary, one or more stages of inductive intermediate heating may be provided between the individual stands.

Both known methods have in common that the inlet temperature is set in the finish rolling stage so that the specified Endwalztemperatur can be maintained.

The invention has for its object to optimize the heat treatment in hot strip pre-material of silicon-alloyed steels for further processing to grain-oriented sheets to the effect that in the rolling mill a desired final temperature and thus a desired microstructure can be set in the strand.

The object is achieved by the method claimed in claim 1.

With the method according to the invention, for the first time in a simple manner, an inlet temperature is set in the finishing train, which ensures a favorable precipitation morphology in the rolling stock. Known in the art single-stage temperature-adjusting systems are not able to heat the cast product to the required for setting the desired / required recrystallization state high temperatures of preferably more than 1250 ° C inlet temperature in the rolling mill. The high temperatures are advantageously achieved in the claimed method in that a two-stage preheating of the cast product, comprising a Primärergiebeheizte and an inductively heated stage is performed. The claimed two-stage heat treatment also has the advantage that it can heat the cast product not only - if necessary - to temperatures above 1250 ° C, but also to lower inlet temperatures, should this be necessary to set other desired structural or recrystallization conditions; In this respect, the claimed method is very universally applicable.

The control of the temperature in the subsequent finishing train depends on the final structure to be achieved and is set via a combination of rolling speed and use of inter-frame cooling.

In a preferred embodiment of the present invention with regard to the method, the final rolling temperature (T _WE ) and the final rolling speed of the rolling stock are set to values at which no complete recrystallization of the steel takes place, and the rolling stock becomes after the last

Stitch in the hot rolling line of the final rolling temperature (T _WE ) to a temperature (T _A ) quenched, which ensures the setting or freezing a desired Rekristallistionszustandes over the strip thickness. In this case, the final rolling temperature (T _WE ) of the rolling stock to temperatures of at least 950 ° C, preferably above 1000 ° C, set and then, preferably in immediate connection, the rolling stock to temperatures (T _A ) of below 450 ° C within 10 s deterred.

In this case, a complete recrystallization of the hot strip is suppressed. By selecting the reel temperature, the proportion of the recrystallized structure can be adjusted via the strip thickness.

According to a further embodiment feature of the present invention, it is provided that in the preheating stage, the temperature of the cast product is set to values between 1000 and 1100 ° C and that in the subsequent intensive heating stage, the temperature is increased to values of 1250 ° C. In this case, in a preferred embodiment, the preheating stage is carried out in a gas- or oil-fired oven and the subsequent intensive stage in an induction heating stage. This has the particular advantage that the preheating can take place in a roller hearth furnace, while the heating step is shifted to temperatures above 1200 ° C in an inductive heating zone. This prevents that the roller hearth furnace is charged too much, which could possibly lead to its thermal destruction.

In order to avoid the adverse effect of a highly heated primary scale on the surface quality of the rolling stock, the slab surface is descaled. For this purpose, according to a further embodiment feature of the present invention, descaling is carried out in a descaling device between the preheating stage and the intensive heating stage. The setting of the inlet temperature in the finish rolling stage is then carried out by means of induction heating. The finish rolling stage can consist of a single or multi-stand Pre-season and a mehrgerüstigen final season consist. The distance between these two can be bridged by a roller table or bezeizten heat tunnel.

In order to further improve the surface quality, it is provided according to a further embodiment feature of the present invention that, after the intensive heating stage, further descaling is carried out in a second descaling stage.

Incidentally, it is envisaged, in addition to or in addition to said descaling already before the roller hearth furnace to perform a removal of the scale to protect the roles of the furnace against scale growth and thus the slab underside against unwanted marks and to improve the heat transfer into the slab.

The object of the invention underlying above is further solved by the claimed in claim 7 system. With regard to the resulting advantages, reference is made to avoid repetition on the above-described advantages of the method according to the invention.

In the system according to the invention it is provided that the device for cooling the rolling stock comprises components for quenching the rolling stock to temperatures below 450 ° C.

It is recommended according to a further embodiment feature of the present invention that the hot rolling train is designed as a compact finishing line. According to an alternative design feature, it is provided that the hot rolling line is formed divided into at least one pre-and at least one Endwalzstaffel.

Further advantages and details of the invention will become apparent from the dependent claims and from the following description in which the embodiments of the invention shown in the figures are explained in more detail. In addition to the above-mentioned combinations of features, features alone or in other combinations are essential to the invention.

Fig. 1

eine schematische Darstellung einer Anlage zur Durchführung des erfindungsgmäßen Verfahrens.

It shows:

Fig. 1

a schematic representation of a system for carrying out the erfindungsgmäßen process.

Fig. 1 shows a plant 1 for the production of rolling stock in the form of sheets or strips of silicon-alloyed steel for further processing into grain-oriented sheets, such as electric sheets, which are heat treated and rolled without intermediate cooling to room temperature, so that then the rolling stock with desired structural properties available stands. The plant 1 comprises a continuous casting plant 1a. The near net cast strand in the form of a cast product 2 is cut in front of the roller hearth furnace 3 using a pair of scissors 4, which then come directly from the casting heat in the roller hearth furnace 3 to be heated to temperatures of 1000 to 1100 ° C or to learn a temperature compensation. The slabs are preferably thin slabs with a thickness of up to 120 mm. The heated slabs then preferably pass through a descaling device 5 and then enter an intensive heating stage 6. Here, the slabs are heated in a short rapid heating process at inlet temperatures of 1100 to 1300 ° C, preferably above 1250 ° C. The preheating stage 3 is carried out in a gas or oil-fired furnace such as a roller hearth furnace 3 and the subsequent Intensivheitstufe 6 in an induction heating. The Intensivheizstufe 6 must be designed to ensure an inlet temperature T _a of the cast product 2 in the rolling mill of more than 1200 ° C. The preheating stage 3 and the intensive heating stage 6 form a temperature Adjusting System 7. The means for performing the heat treatment include the preheating stage 3, the intensive heating stage 6, and the interstand cooling means 10.

After passing through the intensive heating stage 6, the cast product 2 is again descaled (second descaling stage 8) and introduced into a hot rolling line 9a or 9b. The hot rolling train 9a or 9b may be a compact finishing line 9a or divided into a preliminary and a final rolling 9b. The number of scaffolds in each of the two partial scales is not fixed.

In the inventive process is now provided that for setting the finish rolling temperature T _WE an inlet temperature T _a of the cast product 2 in the hot rolling line 9a or 9b is preferably set above 1250 ° C by a multi-stage heat treatment of the mill of at least 1200 ° C, wherein the cast product from the casting heat coming directly to the heat pretreatment is performed. The multi-stage heat pretreatment takes place with the temperature setting system 7, which includes the preheating stage 3 for preheating the cast product 2 and the intensive heating stage 6 for adjusting the inlet temperature T _{a of} the cast product 2 in the hot rolling line. In the method according to the invention, the final rolling temperature T _WE and the final rolling speed of the rolling stock are set to values at which complete recrystallization of the steel no longer takes place. The rolling stock is quenched after the last pass in the hot rolling line in the context of post-heat treatment from the final rolling temperature T _WE to a temperature T _A , whereby the desired Rekristallistionszustand of the rolling stock at the end of the hot rolling over the strip thickness is ensured. In this case, the final rolling temperature T _{WE of} the rolling stock to temperatures of at least 950 ° C, preferably above 1000 ° C, adjusted, and then the rolling stock to temperatures T _A of below 450 ° C within 10 seconds, quenched. Fig. 1

The post-rolling heat post-treatment is a combination of a rapid-cooling device 12 and normal cooling bars with water cooling 13. The cooled rolling stock is subsequently wound on a reeling device 14.

LIST OF REFERENCE NUMBERS

1

Plant for the production of hot strip

1a

continuous casting plant

2

Cast product (strand)

3

Device for preheating (roller hearth furnace)

4

scissors

5

descaling

6

Intensivheizstufe

7

Temperature adjustment system

8th

second descaling step

9a

compact finishing mill as hot rolling mill

9b

Pre and final rolling of the hot rolling line

10

Intermediate stand cooling device

11

Device for cooling (cooling section)

12

Quick cooling device

13

Chilled beam with water cooling

14

coiler

Claims (9)

1. Method of producing hot-strip rolling material from a cast product, for example a thin slab, wherein the cast product (2) is subjected to a heat pretreatment in a first step and the preheated cast product is subjected to a rolling process in a hot-rolling train in a second step, wherein the rolling material is in this way transferred to a recrystallisation state, which is suitable with respect to later further processing, at a desired final rolling temperature (T_WE), and the final rolling temperature (T_WE) of the rolling material is set to temperatures of at least 950° C, preferably above 1,000° C, wherein the cast product (2) within the scope of the heat pretreatment for setting the final rolling temperature (T_WE) of the rolling material in the hot-rolling train runs through at least one preheating stage (3) and intensive heating stage (6) and in this way is preheated to an entry temperature (T_ein) of at least 1,200° C for entry into the hot-rolling train (9a or 9b) and wherein descaling is carried out in a descaling device ahead of the preheating stage (3),
   characterised in that
   for producing silicon-alloyed steels for further processing to form grain-oriented sheets such as, for example, magnetic steel sheets the control of the temperature in the rolling train (9a and 9b) is set by way of a combination of rolling speed and use of intermediate stand cooling devices (10), wherein after hot rolling the rolling material is quenched to temperatures (T_A) of below 450° C within 10 seconds.
2. Method according to claim 1, characterised in that the final rolling temperature (T_WE) and the final rolling speed of the rolling speed of the rolling material are set to a value in which complete recrystallisation of the steel no longer takes place and the rolling material after the last pass in the hot-rolling train is quenched from final rolling temperature (T_WE) to a temperature (T_A) which ensures freezing of the desired recrystallisation state, which is set at the end of the hot-rolling train, over the strip thickness.
3. Method according to one of claims 1 and 2, characterised in that in the preheating stage (3) the temperature of the cast product (2) is set to values between 1,000 and 1,100° C and that in the subsequent intensive heating stage (6) the temperature is increased to values of 1,250° C.
4. Method according to any one of claims 1 to 3, characterised in that the preheating stage (3) is carried out in a gas-heated or oil-heated furnace and the subsequent intensive heating stage (6) in an induction heating stage.
5. Method according to any one of claims 1 to 4, characterised in that descaling in a descaling device (5) is carried out between the preheating stage (3) and the intensive heating stage (6).
6. Method according to any one of claims 1 to 5, characterised in that after the intensive heating stage (6) a further descaling is carried out in a second descaling stage (8).
7. Plant (1) for producing hot-strip rolling material for later further processing to form grain-oriented sheets, through use of the method according to any one of claims 1 to 6, wherein the plant comprises:

   a continuous casting plant (1 a) for producing the cast product (2);

   a temperature setting system (7) for preheating the cast products; and

   a rolling mill (9a or 9b) downstream of the temperature setting system (7), wherein the temperature setting system (7) and the rolling mill (9) serve the purpose of transferring the cast product (2) into the rolling material with a recrystallisation state, which is suitable with respect to later further processing, at a specific final rolling temperature (T_WE), wherein the temperature setting system (7) comprises, for setting the final rolling temperature (T_WE) of the rolling material in the rolling train, a preheating stage (3) for preheating the cast product (2) and an intensive heating stage (6) for intensive heating of the cast product (2) to an entry temperature (T_ein) in the hot-rolling train above 1,200° C, preferably above 1,250° C, and a descaling device is provided in front of the preheating stage (3);

   characterised in that
   a device (11) for cooling the rolling material comprises components for quenching the rolling material to temperatures below 450° C within 10 seconds and the rolling material is constructed in the form of silicon-alloyed steels such as, for example, magnetic steel plates, and the hot-rolling mill (9a, 9b) comprises intermediate stand cooling devices (10), which serve in combination with the rolling speed for controlling the final rolling temperature (T_WE).
8. Plant according to claim 7, characterised in that the hot-rolling train is constructed as a compact finishing train (9a).
9. Plant according to claim 7, characterised in that the hot-rolling train is constructed to be divided into at least one pre-rolling echelon and at least one final rolling echelon (9b).

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