EP0832990B1 - Process for producing coated metal bars, especially steel strips - Google Patents

Abstract

A method and apparatus forproducing coated slabs of metal, particularly strips of steel, in which a metal slab is guided through the bottom of a vessel filled with molten metal having the same or different composition as the metal slab, wherein the dwell time of the metal slab is selected in dependence on the melting bath level, the casting speed, the metal slab thickness and the preheating temperature of the metal slab in such a way that the molten metal deposited on the metal slab has a desired thickness of a multiple of the initial thickness of the metal slab, and wherein the metal slab with the layer crystallized onto the metal slab is subjected to a smoothing pass after emerging from the melting bath. The smoothing pass is carried out when the surface temperature of the crystallized slab is smaller than the solidus temperature of the melting bath and, thus, at least the surface of the crystallized layer is solidified.

Description

The invention relates to a method for producing coated Strands of metal, in particular of steel strips, in which a strand of metal through the bottom of a vessel filled with melt same or different composition as the metal strand, is performed, the residence time of the metal strand in Dependence on the melt pool height, the casting speed, the Metal strand thickness and the preheating temperature of the metal strand so is chosen that the deposited melt on the metal strand desired thickness of several times the initial thickness of the metal strand assumes and the metal strand with crystallized layer experiences a smooth stitch after leaving the weld pool.

Method and device deals with the generation of coated metal strands, preferably strips of a Steel grade or different steel grades, such as Mono material or composite material and here in particular also Composite material made of carbon steel, thinly coated with stainless steel.

DE 195 09 691 C1 describes an inversion casting vessel and a method known for producing thin metal strands, in particular steel, where a metal band through the bottom of a filled with melt Container passed and after crystallization of the melt is subtracted. Guide rollers guide through a channel the metal strip is melted into the container. After on If a layer of melt has crystallized, the tape becomes conveyed above the vessel by smoothing rollers in which the tape is smoothed with the crystallized layer close to final dimensions.

DE 195 09 681 C1 is a further inversion casting device and a process for the continuous production of sheet-like sheets, especially known from steel, in which a mother tape by a Melt bath of a metal is passed through to achieve a itself in the form of crystals and melt on the surface of the Mother tape depositing coating. After the mother tape that Has left the melt pool, there is expedient an immediate Smoothing the crystallized coating by means of a pair of smoothing rollers, which is located above the weld pool.

These two aforementioned inversion casting devices deal with each other but mainly with the sealing of the melt vessel opposite the incoming belt in such a way that the weld pool in the area of the mouth of the slot-shaped inlet opening for the Mother tape is cooled so intensely that a temperature drop in the meniscus and its two-phase area melt / crystal has such a high viscosity that the meniscus functions a self-renewing seal. On this There is no background in the previously known publications Indications of optimal process management and surface optimization of the tape produced during the treatment by the pair of smoothing rollers.

DE 43 19 569 C 1 describes a method for producing strip material made of metal and a device for carrying out the Method known, in which a sheet thickness tolerance of max. 2% can be met. For this, the semi-finished product is Thickness ratio of over 60 after leaving the melt pool Subjected to smoothing stitch. The steel tape shows this smoothing stitch with "pasty" surface (two phases: melt and crystal) then according to the example and the formula T = T, sol + ax (T, li - T, sol) - here the value 0.5 is chosen for a - an average temperature from T = 1497 ° C + 0.5 x (1507 ° C - 1497 ° C) = 1502 ° C in the grown up layer. This condition describes that the steel band on its surface when entering the pair of smoothing rollers is still "doughy", ie still in the two-phase area, liquid / solid is and therefore has no pure solid phase.

Disadvantage of this process condition - a crystallized Layer with a "pasty surface and pasty core" - is to that "the layer adhering to the mother tape on the one hand does is relatively solidified, but on the other hand still in its outer zone Sufficient proportions of liquid phase when entering the smoothing roller pair has ", so that the belt as it passes through the pair of smoothing rollers has severe hypothermia and thus the tendency of the Cracking occurs both lengthways and crossways to the tape direction. This Danger occurs at higher casting and rolling speeds on.

The object of the invention is now a method to find, thereby smoothing the strip with a sheet thickness tolerance of a maximum of 2% without crack formation both in the surface and is also ensured inside the belt.

The unexpected solution to the procedure is given by the Characteristic features in claims 1 to 11 reached.

The main features for the production of error-free, flat-coated Belts, for example, with a width / thickness ratio> 60 and one Total thickness of maximum 12 mm, preferably 2 to 6 mm, from one Material or from composite materials of different metal grades such as. Carbon steel as a single material or carbon steel with a stainless steel coating of at least 5% of the total strip thickness as a composite material and a thickness deviation of maximum 2% between the edge (40 mm from the edge) and the middle of the volume include marked by :

A surface temperature of the crystallized layer on entry of the belt into the pair of smoothing rollers, which is less than the solidus temperature of the weld pool, so that at least the surface the crystallized layer has solidified.

Figur 1

eine Gesamtansicht des Verfahrens und seiner Vorrichtung zur Glättung von beschichteten Strängen aus Metall vorzugsweise von Bändern aus Stahl.

Figur 2

ein Temperaturfeld des Stranges zwischen dem Bandeintritt in den Kristallisator und dem Glättrollenpaar während des Gießens,

Figur 3

ein beschichtetes Band zwischen der Schmelzbadoberfläche im Kristallisator und dem Glättrollenpaar, Detail aus Fig. 1.

1 to 3 illustrate the invention with regard to the method. Show it

Figure 1

an overall view of the method and its device for smoothing coated strands of metal, preferably of steel strips.

Figure 2

a temperature field of the strand between the strip entry into the crystallizer and the pair of smoothing rollers during casting,

Figure 3

a coated tape between the melt pool surface in the crystallizer and the pair of smoothing rollers, detail from FIG. 1.

Figures 1 and 2 give the overall view of the method and Device for smoothing coated strands, preferably tapes made of steel (1) by means of a pair of smoothing rollers (2) again. The Mother tape (1.1) is filled in the crystallizer (3) with melt (3.3), which is introduced via a melt feed (3.1), through the nozzle of a floor inlet device (3.2) with a pouring and rolling speed (7.1) from 0.05 to 10 m / s by means of a Drive roller pair (1.5) conveyed below the crystallizer.

The mother tape (1.1), with a temperature of either 20 to 800 ° C before entering the crystallizer (3), starts above of the steel meniscus (3.5) at the nozzle outlet (3.2) with the crystallization (3.6) of the melt in point (3.6.1) and withdraws the Melt (3.3) superheat and crystallization energy under simultaneous warming. This energy flow (4) from the melt takes place in the mother band when passing through the mother band the weld pool (3.3) between the meniscus (3.5) and the bath surface (3.4) over the melt pool height (3.3.1) instead. At the exit (5) of the coated tape (1) from the bath surface (3.4) of the Melting bath with a surface roughness (1.3) has one certain thickness (1.2) reached, essentially from the strip temperature when entering the crystallizer, from the melt temperature and the contact time of the strip with the melt with which the belt (1) in the roll gap (2.1) of the pair of smoothing rollers (2) comes in.

The strip (1) coated in this way is at the outlet (5) from the bath (3.4) "doughy" on the surface (two phases: melt and crystal) and has a surface roughness (1.3) of greater than 2%, the the flatness criteria of a strip with a width / thickness ratio greater than 60 does not do it justice.

When leaving the coated tape (1) from the bath (3.4) with the final thickness (5.1) the solidification runs from the outlet (5) to to the pair of smoothing rollers (2) and also in the crystallized one Layer consisting of melt and crystal from the outside inside, d. H. the energy flow (6) turns in comparison the heat flow (4) in the melt (3.3) and runs from the inside (Band center) outwards into the walls (6.1) with heat-controlled Continuity. This controlled heat flow can be through wall elements (6.2) in accordance with the temperature control of the belt (1) necessary zones in the casting and rolling direction (7) can be divided. These device features allow the heat flow (6) from Tape to the heat transfer controlled walls (6.1 and 6.2) master, d. H. to control or depending on the steel grade, the casting speed (7.1) and the position (2.4) of the To regulate the smoothing roller pair (2).

To describe and understand the unexpected solution that makes up the invention, it is also necessary the temperature fields and thus the phase states of the coated tape (1) in Interplay with the heat flows (4, 6 and 2.7) from the melt (3.3) into the mother tape (1.1), from the coated tape (1) into the Walls with a heat controlled passage (6.1) between the Bath surface (3.4) and the pair of smoothing rollers (2) and above and from the coated strip (1) in the roll gap (2.1) of the pair of smoothing rollers (2) over the roller body into the internal cooling (2.5) of the smoothing roller pair.

The crystallization (3.6) in the bath (3.3) has on its surface (4.1) a temperature (8) T-x that is greater than the solidus temperature and less than the liquidus temperature (T-li> T-x> T-sol) is and has a two-phase state consisting of Melt and crystal, on. This crystallization takes place in her Temperature from the surface perpendicular to the mother tape (1.1) steadily from. Functional to the surface profile (4.1) of the crystallization (3.6) runs the liquidus isotherm (10) in the melt pool to the bathroom surface (3.4).

When the coated tape (1) emerges from the bath (3.4) location (5) is the melted layer (9.2) of the mother tape (1.1) largest, that in the melt pool (3.3) at the point (9.1) began when the solidus temperature was reached. With the beginning of this Melting of the mother tape interposes the welding the mother tape (1.1) and the crystallized layer (3.6) a.

Above the melt begins the reversal of the energy flow (6) now the solidification of the residual melt in the crystallized Layer consisting of the phases of melt and crystal from which Surface of the belt (1) perpendicular to the belt center and in the surface itself in the direction of the pair of smoothing rollers (2) parallel to Casting and rolling direction (7) d. H. the surface temperature of the The tape sinks from the bath surface (3.4) at the point (5) in the direction of the pair of smoothing rollers (2), steadily going through the solidus temperature in point (9.3) before the inlet (2.1.1) of the coated Belt (1) in the pair of smoothing rollers (2), where they then assumes a value that lies below T - Solidus.

To control a desired temperature control of the coated Belt (1) are the position (2.4) of the pair of smoothing rollers (2), the energy flow (6) into the walls with heat-controlled passage (6.1 and 6.2) and the casting and rolling speed (7.1) in To regulate the sense of the invention so that the surface temperature of the coated tape (1) before entering the pair of smoothing rollers (2) is below the solidus temperature and thus that coated tape at least solidified in its surface is.

This condition is imperative for a crack-free surface, since the solidified phase is particularly immediately below the solidification a pronounced expansion behavior without cracking having. In contrast to this good elasticity of the material "Steel" immediately below the solidification point, T-Solidus, it is known that the deformation limit in the "pasty" Area, in the two-phase area melt / crystal and thus the avoidance of cracks is very small and depending on the steel grade is between 0.1 and 0.3%.

In the case of so-called inner-crack-sensitive steel grades, steels that in the "doughy" area with the slightest deformation d. H. Strain tend to crack, it is for the invention Process significant that the solidification profile (9) the phase boundary solid / liquid is controlled so that the Solidification (9.4) of the coated strand (1) by at the latest Exit (2.1.2 and 9.A) of the roll gap, or by at the latest Entrance (2.1.1 and 9.B) into the roller gap of the pair of smoothing rollers (2) is finished.

These conditions of the coated belt (1) in the pair of smoothing rolls can, at a given casting speed (7.1) with the help the regulation of the heat flows (6 and 2.7) by means of the wall elements (6.1 and 6.2) and / or that in position, to the distance from the mold level (2.4.1) adjustable pair of smoothing rollers (2) with internal cooling (2.5), can be set.

Ensuring at least in the surface area solidified strip (9.5) in the roll gap (2.1) with the pressed Length (2.2) can now, with decreases in thickness of up to 20% Adjustment of the pair of smoothing rollers (2) in the thickness direction (2.3), the Strip (1) with its rough surface (1.3) rolled or smoothed (1.4) without surface cracks or internal cracks in the Crystallized layer while ensuring a good weld between the mother tape (1.1) and the crystallized one Layer (3.6) occur. That so smoothed and Flat band (1.4.1) is crack-free in its surface (1.4) and in Inside its solidified, crystallized layer (3.6). The flatness or the emerging profile of the strip (1.4.1) can with one of the inventive features described above Tolerance of max. 2% of the thickness set in the transverse and longitudinal directions become.

Figure 3 shows the area of the pair of smoothing rollers (2) somewhat more in detail. The coated tape (1) with its crystallization (3.6) runs into the roll gap (2.1.1) with a surface temperature, T-2.1.1 smaller than T-Solidus on (T-2.1.1 <T-sol) and occurs with a controlled lowered temperature, T-2.1.2 smaller T-2.1.1 (T-2.1.2 <T-2.1.1 <T-sol) from the roll gap (2.1) at its outlet (2.1.2). The temperature loss in the roll gap should be checked and kept small. This can be done according to the invention by means of an appropriately controlled heat transfer Smoothing roller pair (2) with internal cooling (2.5) and heat-controlling layer (2.6) or layers can be achieved.

This requires the cooling, the materials and the thickness of the rolls (2), their layer structure (2.6) and the choice of the different ones Roll materials such as B. steel, metals, metal ceramics and / or Ceramics can be coordinated.

The entire room (11) above the bath surface (3.4) is in its temperature and atmosphere (nitrogen and / or argon) checked so that the conditions described above are ensured are avoided as well as an oxidation of the belt surface becomes.

The tape coated in this way is directly or indirectly another Rolling mill (12) and rolling process for producing finished hot strip and / or cold strip both as a mono material and as a composite material supplied with or without upstream pickling.

To control, control and / or regulate the temperature field in the coated strip (1) and on the strip surface (1.3) between the melt pool surface (3.4) and the exit of the coated and smoothed belt (1.4.1) from the pair of smoothing rollers (2) are measuring devices for temperature detection (2.8) on the inside the heat-controlled wall elements (6.2) attached.

References:

1.1 Mutterband, Ausgangs-Metallband

1.2 Dicke des beschichteten Bandes zwischen Badoberfläche und Glättrollenpaar

1.3 raube, beschichtete Bandoberfläche

1.4 plane, geglättete Bandoberfläche

1.41 beschichtetes und geglättetes Band

1.5 Antriebsrollenpaar unterhalb des Kristallisators

1.6 Detail, siehe Fig.3

1. Coated tape between the bath surface and the pair of smoothing rollers

1.1 Mother tape, initial metal tape

1.2 Thickness of the coated tape between the bath surface and the pair of smoothing rollers

1.3 rough, coated belt surface

1.4 flat, smoothed belt surface

1.41 coated and smoothed tape

1.5 pair of drive rollers below the crystallizer

1.6 Detail, see Fig. 3

2.1 Walzspalt

2.1.1 Beginn des Walzspaltes

2.1.2 Ende des Walzspaltes

2.2 gedrückte Länge im Walzspalt

2.3 Position des Glättrollenpaares in Dickenrichtung des Bandes,Walzenanstellung in Dickenrichtung

2.4 Position des Glättrollenpaares in Gieß- und Walzrichtung des Bandes

2.4.1 Abstand des Glättrollenpaares zur Badoberfläche

2.5 Innenkühlung des Glättrollenpaares

2.6 Beschichtung des Glättrollenpaares zur Kontrolle des Wärmedurchganges

2.7 Energiestrom in das innengekühlte Glättrollenpaar

2.8 Meßgeräte zur Bestimmung der Bandoberflächentemperatur

2nd pair of smoothing rollers

2.1 Roll gap

2.1.1 Start of the roll gap

2.1.2 End of the roll gap

2.2 pressed length in the roll gap

2.3 Position of the smoothing roller pair in the thickness direction of the belt, roll adjustment in the thickness direction

2.4 Position of the pair of smoothing rollers in the casting and rolling direction of the strip

2.4.1 Distance of the pair of smoothing rollers to the bath surface

2.5 Internal cooling of the pair of smoothing rollers

2.6 Coating of the pair of smoothing rollers to control the heat transfer

2.7 Energy flow into the internally cooled pair of smoothing rollers

2.8 Measuring devices for determining the strip surface temperature

3.1 Schmelzenzulauf

3.2 Düse der Bodeneinlaßvorrichtung

3.3 Schmelzbad

3.3.1 Schmelzbadhöhe

3.4 Badoberfläche

3.5 Meniskus

3.6 Ankristallisation von Schmelze

3.6.1 Beginn der Ankristallisation

3. Crystallizer

3.1 melt feed

3.2 Nozzle of the floor inlet device

3.3 weld pool

3.3.1 Melt pool height

3.4 Bath surface

3.5 meniscus

3.6 Crystallization of the melt

3.6.1 Start of crystallization

4. Energy flow in the melt pool from the melt into the mother tape
4.1 Surface and profile of crystallization in the melt pool

5. The coated tape emerges from the bath
5.1 final thickness of the crystallized layer

6.1 Wände mit wärmekontrolliertem Durchgang

6.2 wärmedurchganskontrollierte Wandelemente, unabhängig voneinander

6. Energy flow above the bath surface to the outside with heat-controlled passage

6.1 walls with heat-controlled passage

6.2 Wall elements controlled by heat transfer, independently of each other

7. Casting and rolling direction
7.1 Casting and rolling speed

8. Surface temperature, T-x of crystallization in the molten bath

9.1 Beginn der Bandoberflächenaufschmelzung und der Verschweißung von Mutterband und Ankristallisation

9.2 max. Aufschmelzzone in der Oberfläche des Mutterbandes

9.3 Beginn der Erstarrung ausgehend von der Bandoberfläche in Richtung Bandmitte, Oberflächentemperatur gleich der Solidus-Temperatur

9.4 Ende der Erstarrung, Durcherstarrung

9.5 erstarrte Bandoberfläche

9.A Erstarrungsprofil, Isotherme der Solidus-Temperatur, Durcherstarrung bis spätestens zum Ende des Walzspaltes

9.B Erstarrungsprofil, Isotherme der Solidus-Temperatur, Durcherstarrung bis spätestens zum Eintritt in den Walzspalt

9. Isotherm of the solidus temperature, solidification profile

9.1 Beginning of the band surface melting and the welding of the mother band and crystallization

9.2 max. Melting zone in the surface of the mother tape

9.3 Start of solidification starting from the strip surface towards the strip center, surface temperature equal to the solidus temperature

9.4 End of solidification, solidification

9.5 solidified belt surface

9.A solidification profile, isotherm of the solidus temperature, solidification until the end of the roll gap at the latest

9.B Solidification profile, isotherm of the solidus temperature, solidification until the entry into the roll gap at the latest

10. Isotherm of the liquidus temperature

11. Temperature and atmosphere controlled room above the Melting bath

12. Directly processing rolling mill

Claims (11)

1. Method of producing coated strips of metal, especially strips (1) of steel, in which a metal strip (1.1) is guided through the base of a vessel (3) filled with a melt (3.3) of the same composition as or different composition from the metal strip (1.1), wherein the dwell time of the metal strip (1.1) is so selected in dependence on the melt bath level (3.3.1), the casting speed, the metal strip thickness and the preheating temperature of the metal strip that the coated melt on the metal strip adopts a desired thickness of multiples of the exit thickness of the metal strip and the metal strip (1.1) with crystallised coating (3.6) is subjected to a smoothing pass (2) after exit from the melt bath (3.3), characterised in that the smoothing pass is undertaken when the surface temperature of the crystallised strip (3.6) is lower than the solidus temperature of the melt bath (3.3) and thus at least the surface (1.3) of the crystallised coating (3.6) is hardened.
2. Method according to claim 1, characterised in that the hardening of the crystallised coating (3.6) takes place after passage of the strip (1.1) through the smoothing roller pair (2).
3. Method according to claim 1, characterised in that the hardening of the crystallised coating (3.6) of the strip (1.1) takes place in the roll gap (2.1) of the smoothing roller pair (2).
4. Method according to claim 1, characterised in that the hardening of the crystallised coating (3.6) takes place before the entry of the strip (1.1) into the smoothing roller pair (2).
5. Method according to one of claims 1 to 4, characterised in that the hardening of the crystallised coating (3.6) of the strip (1.1) is determined by energy flow (6) above the melt bath into the walls of the vessel (3) with heat-controlled passage.
6. Method according to one of claims 1 to 5, characterised in that the hardening of the crystallised coating (3.6) of the strip (1.1) is determined by energy flow (2.7) by way of the roll gap (2.1) into the internally cooled smoothing roller pair (2).
7. Method according to at least of claims 1 to 6, characterised in that the crystallised and smoothed strip (1.4) is supplied to a rolling process controlled in atmosphere and/or temperature.
8. Method according to at least of claims 1 to 7, characterised in that the crystallised and smoothed strip (1.4) is cooled in oxidation-free manner and/or controlled in temperature.
9. Method according to at least one of the preceding claims, characterised in that an oxidation-free atmosphere is set above the melt bath during production of the coated strip.
10. Method according to at least one of the preceding claims, characterised in that the metal strip (1.1) (mother strip) is conveyed into the melt vessel (3) at a casting and rolling speed (7.1) of 0.05 to 10 m/sec.
11. Method according to at least one of the preceding claims, characterised in that the metal strip (1.1) is guided at a temperature of 20 to 800° C continuously and vertically through the base into the melt vessel (3).

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