KR20110002081U - Method and continuous casting plant for producing thick slabs - Google Patents

Abstract

The present invention is directed to a method and apparatus for producing thick slabs from steel having a casting thickness greater than 360 mm and a casting width greater than 1000 mm in a continuous casting plant. In addition, in the present invention, method steps and plant configurations are proposed in which the production of steel strips and slabs with high quality as well as good internal quality and less cracking is ensured even when casting steel strips having a thickness range of 360 to 450 mm. .

Description

METHOD AND CONTINUOUS CASTING PLANT FOR PRODUCING THICK SLABS}

The present invention is directed to a method for producing thick slabs from steel having a casting thickness exceeding 360 mm and a casting width exceeding 1000 mm in a continuous casting plant. The invention also relates to a continuous casting plant for carrying out the method.

In the casting of steel strips in continuous casting plants where the cast steel strip is first bent in a strip guide and then recalibrated, the casting process becomes increasingly difficult by increasing the strip thickness. . Tensile and compressive stresses occurring during the deformation process result in crack formation in the edge and surface regions of the steel strip. To this end, so far there are only a few continuous casting plants, by which steel strips having a strip thickness exceeding 360 mm can be cast to form slabs in the above thickness range.

There is now a growing demand in terms of the expanding processing industry of slabs having a 360 to 450 mm thickness range for subsequent formation of correspondingly thick steel plates.

Continuous casting plants of the type "vertical plant or vertical-bending plant" comprising vertical long strip guide parts with subsequent bending zones and straightening zones are available from Dr. Klaus Harste et al. .) et al .; "Construction of a new vertical caster at Dillinger Huettenwerke"; MPT International 4/1998; pp. 112-122). Such a casting plant with the layout shown in FIG. 8 of the publication implements the casting of steel strips having a casting width of 1400 to 2200 mm and a casting thickness of 230 to 400 mm. The casting plant has a vertical, very long strip guide to enable subsequent bending and straightening of the steel strip upon strip solidification, in which the strip is intensively cooled. Such a plant concept raises the overall height of a strip casting plant of about 45 m, resulting in high investment costs, particularly high investment costs for the infrastructure, and creating demanding maintenance conditions. When the casting thickness is 400 m, the reachable casting speed is about 0.3 m / min, which results in a relatively low productivity per strip. Another problem caused by this low casting rate is that the cast steel strip may not be sufficiently maintained at the high temperature levels required for adjustment / calibration, which is why ductility typically occurs in the temperature range of 600 to 850 ° C. In order to solve the problem, it has to be kept at a temperature lower than the critical temperature by intensive cooling.

DE 31 12 947 A1 discloses an arc continuous casting plant for casting steel strips having a strip thickness of 200 to 300 m, which, according to the publication, forms slabs of good quality by the continuous casting plant. do. The molding of the metal strip in this case takes place in an arc mold having a radius of curvature corresponding to the radius of curvature of the first zone of the subsequent strip guide. In the subsequent very long calibration zone, the steel strips are rearranged, in which case the steel strip cross section is necessarily trapezoidal. Such cross-sectional deformations become more severe with larger strip thicknesses and cause quality problems in subsequent rolling in steel plate rolling mills.

US 6, 241, 004, B1 is known a method and apparatus for continuous casting of steel strips, in which casting the cast strips are ejected from the mold and then vertically guided in the first section and then vertical casting Direction in the horizontal conveying direction. In the casting of strips with a casting thickness of about 220 mm, such as those already cast for a long time, Lorentz force is provided in the strip conveying direction by an electromagnetic coil to prevent core porosity and core separation. do. However, the plant structure presented in the second embodiment is suitable for adjusting steel strips having a casting thickness exceeding 360 mm.

The object of the present invention is therefore to avoid the known drawbacks of the prior art, to provide a method for producing thick slabs from steel and a continuous casting plant for implementing such a method, in which case good internal quality and less cracking. In addition to the generation, the production of high quality strips and slabs with a casting thickness exceeding 360 mm is reliably ensured.

A further object of the present invention is to increase the productivity of the casting plant while at the same time keeping the investment and operating costs low.

The problem underlying the present invention is solved by a combination of the following features in a method for producing thick slabs from steel with a casting thickness exceeding 360 mm and a casting width exceeding 1000 mm:

In a straight mold with vertically aligned mold cavities, a metal strip still having a liquid core is vertically cast,

The steel strip exiting the mold is guided on a vertical conveyance section of less than 4.5 m without the application of bending forces,

The cast steel strip is guided and supported in the vertical conveying direction in the vertical casting direction, the steel strip is guided in a strip guide extending from the steel strip outlet of the mold to the inlet to the cutting device,

With the core still in liquid phase, the cast steel strip is bent to a predetermined arc radius in the bending zone in the strip guide,

At such an arc radius, the steel strip is guided at a subsequent arc guide portion of the strip guide,

With the core still in liquid or partial liquid state, the cast steel strip is reverse bent into a straight steel strip at a predetermined arc radius at the calibration zone in the strip guide,

The cast steel strip is continuously cooled in the strip guide,

The surface temperature of the steel strip entering the calibration zone of the strip guide is maintained higher than the temperature at which the ductility of the individual steel grading is reduced,

The solid phase shell ratio of the cast steel strip is maintained at up to 95% of the half thickness of the strip during the reverse bending step in the calibration zone,

In the cutting device the steel strip is cut into slabs of a predetermined length.

Strip formation in vertically aligned straight molds obtains excellent conditions known for inflow of the steel melt into the mold and for uniform strip shell formation for reasons of symmetry. The straight mold increases the vertical length which is important for forming a uniform strip shell and improves the conditions for separating nonmetallic elements from the melt bath.

Bending the cast steel strip in the bending zone until a predetermined radius of curvature is reached and reverse bending the cast steel strip in the straightening zone corresponds to the concept of known slab-continuous casting plants and has proven to be suitable for slab manufacture. . Important for the casting of thick slabs is that the two processes are run simultaneously, during which the steel strip has a core that is still liquid or partially liquid, or has a corresponding strip guide to adjust accordingly. Cooling of the steel strip is essential. Increasing the thickness of the strip also increases the need for as uniform cooling as possible, in order to ensure uniform elasticity of the strip and to prevent cracking due to temperature differences, such cooling requires a high temperature level for strip length and strip width. The uniform temperature distribution as far as possible should be reflected.

 The steel strip exiting the mold is only vertically guided on a vertical feed section of less than 4.5 m without the application of bending forces. By limiting the vertical guiding of the steel strip after ejection from the mold, the vertical length is achieved to achieve optimal separation of nonmetallic elements (eg casting flux particles), while at the same time the overall height of the continuous casting plant is typically It is limited to a level which can be maintained in the range of casting plants used.

The predetermined temperature profile sought for plant control is determined by the inlet surface temperature into the strip guide calibration zone, so that the steel strip, including the surface area, is maintained at a temperature range above the temperature at which ductility is degraded, resulting in surface cracking. This tendency to be formed is also minimized.

Preferably the solid phase shell ratio of the cast steel strip is at most 95% of the half strip thickness during the reverse bending step in the straightening zone.

According to one preferred refinement, due to the reduction in the thickness of the steel strip, the complete mixing of the partially solidified core zone is preferably near the freezing point of the strip with the application of soft reduction or dynamic soft reduction. In addition, in the slab core region, an improved particle structure is obtained, and row separation and the onset of porosity are prevented. Correspondingly, the download ratio, in particular the dynamic download ratio, is applied to the steel strip in which the steel strip core area is still liquid or partially liquid by means of the adjusting device of the strip guide rolls.

According to one preferred refinement of the invention, the cast steel strip is bent at an arc radius of 9.0 m to 15.0 m in the bending zone in the strip guide, and as described above without further deformation in the subsequent arc guide of the strip guide. It is maintained at an arc radius, and is straightened again from an arc radius of 9.0 m to 15.0 m in the subsequent calibration zone in the strip guide. This arc radius, in particular for casting thicknesses of 360 to 450 mm, provides the best surface quality of the cast steel strip and the minimization of cracks, in addition to allowing cooling in these areas of the strip guide to be adjusted simultaneously and as accurately as possible.

According to one preferred refinement of the invention, the cooling of the cast steel strip is carried out in a controlled manner by providing coolant to the wide sides of the cast steel strip by means of a cooling device in the strip guide, in which case at least The impact location of the coolant sprayed on the steel strip in one partial region of the strip guide allows for continuous measurement of the temperature profile along the transport path of the steel strip and / or into normal planes for the transport path. It is adjusted based on this. Thus, the impact position of the coolant sprayed on the steel strip can be adjusted according to the two temperature profiles or according to the continuous measurement of the temperature profile along the transport path of the steel strip or in a standard plane for the transport path as needed. .

Preferably, the amount of coolant provided on the steel strip in the strip guide until entering the calibration zone is adjusted according to the temperature profile previously given along the transfer path of the steel strip and / or in a standard plane for the transfer path. Thus, the accuracy of the temperature distribution applied across the steel strip face further rises. The given temperature profile takes into account the ductile properties of the cast steel grading. The amount of coolant provided on the steel strip can also be adjusted according to the two temperature profiles or according to the continuous measurement of the temperature profile along the transport path of the steel strip or to the surface for the transport path.

If the controlled cooling of the cast steel strip is carried out during partial heating operation or in accordance with the drying operating characteristics in the integration of the surrounding cooled strip guide rolls in the strip guide, continuous stability of the cooling conditions is achieved. In this case, it is possible to avoid the necessary conditions of considering the cooling of the strip guide rolls as the main member when measuring the coolant spraying strength or adjusting the strength of spraying the coolant to the individual regions as required by the strip guide rolls. In other words, the strip surface temperature can be maintained at a very high level, at least in the region until the steel strip is reversely bent. The cooling of the strip guide rolls in this case is usually only by internal cooling of the strip guide rolls, where the coolant is preferably carried by the coolant channels as close to the roll jacket surface as possible in the roll jacket area.

In order to optimize the separation rate of nonmetallic elements, such as cast flux particles, in the mold region and in the region just below the mold, the liquid core melt flow movement of the steel strip is preferably electromagnetic in the mold or in the region where the steel strip is vertically guided. Affected by the device. In addition to the enhanced rise of nonmetallic materials to the hot reflective surface in the mold, the steel melt mixes as intended and the tendency for separation is reduced.

Preferably, the described method for producing thick steel strips is used when casting steel strips having a casting thickness of 360 mm to 450 mm.

The challenge presented in the introduction is a combination of the following features in a continuous casting plant for producing thick slabs from steel having a casting thickness of greater than 360 mm, preferably from 360 mm to 450 mm, and a casting width of greater than 1000 mm. Is solved by:

Straight mold with vertically aligned mold cavity for producing steel strip with liquid core,

A strip guide extending from the mold to the cutting device for supporting and guiding the cast metal strip in the vertical conveying direction in the horizontal conveying direction,

Strip support devices for vertical guiding of the steel strip directly following the mold, ensuring vertical guiding of the steel strip over a vertical conveying section of less than 4.5 m,

The bending zone in the strip guide for bending the steel strip cast to a predetermined arc radius, with the core still in liquid phase,

A subsequent arc guide portion for guiding said steel strip at said predetermined arc radius,

A calibration zone in the strip guide for reverse bending the steel strip cast into a straight steel strip at a predetermined arc radius, while the core is still liquid or partially liquid,

A cooling device in the strip guide for continuously cooling the steel strip,

Cutting device for cutting the steel strip into slabs of a predetermined length.

In this type of continuous casting plant, the combination of a straight mold and strip guides, bending zones, arc guides and straightening zones mounted after the mold is important, the strip guide being a cooling device for the controlled cooling of the steel strip. In combination with to ensure bending and straightening of the cast steel strip at high quality requirements for the cast steel strip or slabs in the liquid core and to the required thickness range.

When a vertical strip support device for vertically guiding the steel strip in a strip guide connected immediately after the mold (the strip support device ensures vertical guiding of the steel strip over a conveying section of less than 4.5 m) , The quality of the formed steel strip or slabs is improved. If the minimum arc radius in the strip guide is 9.0 to 15.0 m, the metallurgical requirements, investment and operating costs of the casting plant are optimized. As a result, the overall height of the casting plant is kept low, and most of the quality standards which are standard for cast steel strips with a casting thickness of 200-250 mm are for example achieved.

According to one preferred refinement, the strip guide comprises a cooling device for the controlled cooling of the steel strip, the cooling device being connected to and controlled by the computing unit, which is connected to a central computing unit, which transfers the steel strip to the cooling device. A mathematical model is deposited for continuously measuring the temperature profile along the path and / or with standard planes for the transfer path.

The cooling device in the strip guide has a plurality of cooling zones that are independently adjustable over the casting width and / or has height adjustable spray nozzles with drive controllable adjustment devices. Thus, the desired control of the strip edge temperature is possible by adjusting the amount of coolant along the width and / or by changing the spacing of the spray nozzles from the steel strip surface and changing the coolant spray side distance from the steel strip edge.

One or more electromagnetic devices, for example a stirring coil, for controlling the flow of the melt of the liquid core of the steel strip are arranged in the mold or in the region where the steel strip is vertically guided.

Preferably, peripheral cooling strip guide rolls are arranged for supporting and guiding the steel strip in the strip guide. By the use of such ambient cooled strip guide rolls, the different cooling conditions of strip guide rolls in direct line contact with the cast metal strip and the heated strip guide and exposed to the radiant heat of the steel strip significantly neutralize. do.

Further advantages and features of the present invention are presented in the following description of the embodiments, which is not limited by reference to the accompanying drawings:
1 is a longitudinal sectional view of a continuous casting plant according to the present invention,
2 is an arrangement of the spray nozzles of the cooling device in the strip guide,
3 is a further embodiment of a cooling device with independently adjustable cooling zones.

1 is a schematic longitudinal sectional view showing the structural design of a continuous casting plant for producing slabs having a casting thickness of 400 mm from molten steel.

The continuous casting plant has a straight mold 1 with a vertically aligned mold cavity 1a. The continuous casting plant is formed of an internally cooled vibration control mold having wide sidewalls and narrow sidewalls, and implements the casting of steel strips having different strip widths and in some cases also different strip thicknesses. The mold 1 comprises an electromagnetic device 2, such as a stirring coil or an electromagnetic braking device, for controlling the flow movement of the steel melt of the cast steel strip whose core is liquid.

A strip guide 3 is connected to the mold 1, which extends to a cutting device 4 formed of a gas cutting machine for cutting the steel strip into slabs. Within the strip guide, the wide sidewalls of the cast steel strip are supported and guided by strip guide rolls 5 which are driven and undriven in a tight corset and in the vertical casting direction G in the horizontal conveying direction T Is converted to). The groups of strip guide rolls 5 arranged on both sides of the steel strip are integrated in the strip guide segments 6.

The strip guide 3 comprises a plurality of contiguous sections with specific functions, the configuration of which sections being known in practice. In the vertical strip support device 7 the steel strip discharged from the mold 1 is vertically guided and supported without the application of bending loads. In the first region of the vertical strip support device 7 additionally the strip is supported by strip guide rolls 5 which are also on the narrow sides of the steel strip. In the subsequent bending zone 8 the steel strip is gradually bent to a given arc radius. The steel strip is then conveyed along the arc in the arc guide portion 9 while maintaining the arc radius as described above without further bending load. In the subsequent calibration zone 10 the steel strips are reverse bent and linearly aligned. The steel strip in the horizontal strip guide portion 11 is then conveyed to the cutting device 4.

This structural design may add various additional devices (not shown and described) between and within sections of the strip guide, without departing from the protection scope of the claims.

In the strip guide 3, the liquid core, indicated by the dashed line of the steel strip, is cooled. The cooling device 12 comprises spray nozzles 13 which are positionable between the strip guide rolls 5 as shown in FIGS. 2 and 3, which spray nozzles are provided in a standard plane relative to the conveying direction T. N) can be adjusted independently in at least the partial regions. In each cooling zone Z on the casting width B, the spray nozzles 13, which can be height-adjusted corresponding to FIG. 2, have associated adjusting devices 14, or as shown in FIG. 3. The spray nozzles 13 have control valves 18 for adjusting the amount of water. The regulating devices 14 or control valves 18 are drive controlled by the calculating unit 15.

One or more strip guide segments 6 arranged between the calibration zone 10 and the cutting device 4 are assigned special adjustment devices 17 for the strip guide rolls 5. The segments form a contention rate zone 16. The strip guide rolls in the segments can be wedged in the steel strip, realize a small thickness reduction of the metal strip, and improve the metallurgical properties in the core region of the steel strip.

1: straight mold
1a: mold cavity
2: electromagnetic device
3: strip guide
4: cutting device
5: strip guide rolls
6: strip guide segment
7: vertical strip support device
8: bending zone
9: arc guide part
10: correction zone
11: horizontal strip guide
12: cooling system
13: spray nozzles
14: adjusting device of the spray nozzles
15: computation unit
16: pressure reduction zone
17: Adjustment devices of the strip guide rolls
18: control valves
R: arc radius
G: casting direction
T: feed direction
Z: cooling zone
B: casting width

Claims (8)

A continuous casting plant for producing thick slabs from steel having a casting thickness exceeding 360 mm and a casting width exceeding 1000 mm,
Straight mold 1 with vertically aligned mold cavity 1a for producing a steel strip having a liquid core,
A strip guide 3 extending from the mold 1 to the cutting device 4 for guiding and supporting the cast metal strip in a vertical conveying direction in a vertical casting direction,
Strip support devices (7) connected directly after the mold for vertical guiding of the steel strip, ensuring vertical guiding of the steel strip over a vertical conveying section of less than 4.5 m,
With the core still in liquid phase, the bending zone 8 in the strip guide for bending the steel strip cast to a predetermined arc radius R,
A subsequent arc guide portion 9 for guiding the steel strip at the predetermined arc radius R,
While the core is in liquid or partially liquid phase, a calibration zone 10 in the strip guide 3 for reverse bending the cast steel strip into a straight steel strip at a predetermined arc radius R,
A cooling device 12 in the strip guide 3 for continuously cooling the steel strip,
Characterized in that it comprises a cutting device 4 for cutting the steel strip into slabs of a predetermined length,
Continuous casting plant for manufacturing slabs,
The method of claim 1,
The arc radius R in the strip guide 3 is characterized in that 9.0 to 15.0m,
Continuous casting plant for manufacturing slabs,
3. The method according to claim 1 or 2,
The strip guide 3 comprises a cooling device 12 for the controlled cooling of the steel strip, which is connected to a central computing unit 15 and controlled by the computing unit. A mathematical model is provided for continuously measuring the temperature profile along the transport path of the steel strip and / or with standard planes for the transport path,
Continuous casting plant for manufacturing slabs, 4. The method according to any one of claims 1 to 3,
Characterized in that the cooling device 12 in the strip guide has a plurality of cooling zones Z, which are independently adjustable over the casting width B,
Continuous casting plant for producing slabs. The method according to any one of claims 1 to 4,
The cooling device 12 in the strip guide 3 is characterized in that it has injection nozzles 13 and height controllable adjusting devices 14 that are height adjustable.
Continuous casting plant for producing slabs. The method according to any one of claims 1 to 5,
An electromagnetic device 2 for controlling the flow movement of the steel melt of the liquid core of the steel strip is arranged in the mold 1 or in the strip support device 7 in the region where the steel strip is vertically guided. Made,
Continuous casting plant for producing slabs. The method according to any one of claims 1 to 6,
Peripheral cooled strip guide rolls 5 are arranged in the strip guide 3 for supporting and guiding the steel strip.
Continuous casting plant for producing slabs. The method according to any one of claims 1 to 7,
At least one strip guide segment 6 with an adjusting device 17 which can adjust the strip guide rolls to effect a low down rate, in particular a dynamic low down rate, in areas where the steel strip core is still liquid or partially liquid. Is installed on the steel strip between the calibration zone 10 and the cutting device 4,
Continuous casting plant for producing slabs.

Images