AT506823A1 - METHOD AND CONTINUOUS CASTING SYSTEM FOR MANUFACTURING THICK BRAMMS - Google Patents

Description

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Process and Stranoaießanlaae for producing thick slabs

Technical area

The invention relates to a method for producing thick steel slabs with a casting thickness exceeding 360 mm and a casting width exceeding 1000 mm in a continuous casting plant. Furthermore, the invention relates to a continuous casting plant for carrying out this method.

The casting of steel strands in continuous casting plants, in which the cast steel strand is first bent in a strand guide and then re-directed, becomes increasingly difficult with increasing strand thickness. The tensile and compressive stresses occurring during the deformation process lead to crack formation in the strand edge and surface area of the steel strand. So far, there are only a few continuous casting plants, with which steel strands with strand thicknesses over 360 mm poured and slabs can be produced in this thickness range.

At present, there is an increasing need for slabs in the thickness range of 360 to 450 mm for the subsequent production of correspondingly thick heavy plates on the part of the processing industry.

State of the art

A continuous casting plant of the type "Vertical Plant or Vertical Turning Plant", which has a long vertical strand guide part with subsequent bending and straightening zone, is from the publication of Dr.-Ing. Klaus Harste et al; "Construction of a new vertical caster at Dillinger metallurgical works"; MPT International 4/1998; Pp. 112-122 already known. This casting plant, whose layout is shown in Figure 8, allows the casting of steel strands with a casting widths of 1400 to 2200 mm and a casting thickness between 230 and 400 mm. It has a very long vertical strand guide with intensive strand cooling in this section to allow subsequent bending and straightening of the steel strand with solidified strand. This Aniagen concept leads to a large overall height of the continuous casting plant of about 45 m and thus to high investment costs, especially in the infrastructure and to difficult maintenance conditions. At casting thicknesses of 400 mm, the achievable casting speed is about 0.3 m / min, whereby the productivity per strand is relatively low. However, the low casting speed also means that the cast steel strand can not be kept hot enough for straightening and therefore must be kept below a critical temperature with intensive cooling to avoid Ductility problems that typically occur in temperature ranges of 600 to 850 ° C.

From DE 31 12 947 A1 a Bogenstranggießanlage for casting a steel strand with a strand thickness of 200 to 300 mm is known to be produced with good quality slabs. The shaping of the metal strand takes place here in a curved mold having a radius of curvature which corresponds to the radius of curvature in a first zone of the subsequent strand guide. In a subsequent very long straightening zone, the steel strand is re-directed, forcibly resulting in the formation of a trapezoidal cross-section of the steel strand. This cross-sectional distortion is greater the greater the strand thickness and leads to quality problems in the subsequent rolling in the plate mill.

Presentation of the invention

The object of the present invention is therefore to avoid the disadvantages of the known prior art and to propose a method for the production of thick slabs of steel and a Stranggießaniage for performing this method, wherein the production of high quality steel strands and slabs in a 360 mm crossing Casting thickness with good internal quality and low susceptibility to cracking is guaranteed.

Another object of the invention is to keep the investment and operating costs low with high productivity of the casting plant. • · • · · · · · · · · · · · ·: · · · · · · · · · · · · · · · · · · · · · ·

The object underlying the invention is achieved in a method for producing thick steel slabs with a casting thickness exceeding 360 mm and a casting width exceeding 1000 mm by the combination of the following features: Vertical casting of a metal strand with still liquid core in a straight mold vertically oriented mold cavity, - guiding the steel strand leaving the mold on a vertical transport path shorter than 4.5 m, without applying bending forces, - redirecting the cast steel strand from a vertical casting direction to a horizontal transport direction and supporting and guiding the steel strand in a strand guide which extends from the outlet of the steel strand from the mold to the entry into a dicing device, - bending the cast steel strand to a predetermined radius of curvature while the core is still liquid in a bending zone within the strand guide, Guiding the steel strand in a subsequent circular arc guide of the strand guide on this arc radius, - bending back the cast steel strand from a predetermined radius of curvature on a straight steel strand with still liquid core in a straightening zone within the strand guide, - continuously cooling the cast steel strand in the strand guide, - Maintaining the surface temperature of the steel strand in the straightening zone of the strand guide above the ductility depth of the respective steel grade, - Maintaining the proportion of the solid strand shell of the cast steel strand at a maximum of 95% of half the strand thickness during the phase of rebending in the straightening zone, - Cutting the steel strand onto slabs predetermined length in a dicing device.

The strand formation in a straight, vertically oriented mold is known for reasons of symmetry good conditions for the introduction of the molten steel in the mold and for a uniform strand shell formation. The straight mold increases the vertical length which is essential for uniform strand shell formation and improves the conditions for the deposition of non-metallic elements from the melt bath.

The bending of the cast steel strand to a predetermined radius of curvature in a bending zone and the bending back of the cast steel strand in a straightening zone corresponds to the concept of known continuous slab casters and has proven itself as such. Essential for the casting of thick slabs is that both processes take place at times at which the steel strand still has a liquid or partially liquid core, or it is necessary to regulate the cooling of the steel strand in the strand guide accordingly. With increasing strand thickness, the requirements for the most uniform possible cooling, which must necessarily be reflected in a uniform over the strand length and strand width temperature distribution at high temperature level in order to ensure a uniform elasticity of the strand and to avoid cracking due to temperature differences.

The steel strand leaving the mold on a transport path that is shorter than 4.5 m, without the application of bending forces exclusively guided vertically. By limiting the vertical guidance of the steel strand after leaving the mold, the vertical length is limited to a degree at which an optimal separation of non-metallic elements (eg casting powder particles) is achieved and at the same time the height of the continuous casting can be kept within conventional casting ,

The desired and the plant control predetermined temperature profile is determined by an inlet surface temperature of the steel strand in the straightening zone of the strand guide, so that the steel strand including the surface area should be kept in a temperature range that is above the ductility low, whereby the tendency to form surface cracks is also minimized.

Suitably, the proportion of the solid strand shell of the cast steel strand amounts to a maximum of 95% of half the strand thickness during the phase of re-bending in the straightening zone. • ·

According to an expedient further development, the thickness of the preferably semi-solid core zone near the through-solidification point of the strand is achieved by reducing the thickness of the steel strand using soft reduction or reduction, thus achieving an improved microstructure in the core region of the slab and avoiding line separations and porosities. Accordingly, a soft reduction, in particular a dynamic soft reduction, is applied to the cast steel strand in a still liquid or semi-liquid core region of the steel strand with a strand guide roll adjusting device.

According to an expedient development of the invention, the cast steel strand is bent in a bending zone within the strand guide to a radius of curvature between 9.0 m and 15.0 m, held in a subsequent circular arc guide the strand guide on this radius of curvature without further deformation and in a subsequent straightening zone within the strand guide, starting from an arc radius between 9.0 m and 15.0 m straightened again. Especially for casting thicknesses of between 360 and 450 mm, this radius of curvature, while providing the most accurate possible cooling in these areas of the strand guide, provides the best surface quality and minimizes cracking on the cast steel strand.

According to an advantageous embodiment of the invention, the cooling of the cast steel strand is controlled by applying coolant to the broad sides of the cast steel strand with a cooling device in the strand guide, wherein the impact position of the coolant jets on the steel strand at least in a portion of the strand guide based on a continuous determination the temperature profile along the transport path of the steel strand and in normal planes is regulated.

Appropriately, the amount of coolant applied to the steel strand in the strand guide until it enters the straightening zone is regulated as a function of a predetermined temperature profile along the transport path of the steel strand and in a normal plane. This is intended to achieve a further increase in the accuracy of the temperature distribution over the steel strand surface. The given temperature profile takes into account the ductility characteristics of the steel grade to be cast.

• IM II • Ο · ·

A further stabilization of the cooling conditions is achieved if the controlled cooling of the cast steel strand takes place in the partial hot operation or after the dry operation within the strand guide with the inclusion of peripherally cooled strand guide rollers. Here, the need to consider the cooling of the strand guide rollers as an essential element in the assessment of the intensity of the coolant application or to align the intensity of the coolant application in individual areas according to the needs of the strand guide rollers. This means that the strand surface temperature can be kept at a very high level, at least in the region up to the bending back of the steel strand. The cooling of the strand guide rollers takes place here almost exclusively by an internal cooling of the strand guide rollers, wherein the coolant is suitably guided in the roller sheath region as close as possible to the roller sheath surface through coolant channels.

To optimize the deposition rate of non-metallic elements, for example cast powder particles, in the region of the mold and just below, it is advantageous if the flow movement of the molten steel of the liquid core of the steel strand in the mold or in the region of the vertical guidance of the steel strand is influenced by an electromagnetic device , In addition to an increased rise of the non-metallic impurities to the bath level surface in the mold, there is a targeted mixing of the molten steel and to reduce segregation tendencies.

Preferably, the method described is used for producing thick steel strands when the steel strand is cast with a casting thickness of 360 mm to 450 mm.

The object stated in the introduction is achieved in a continuous casting plant for producing thick steel slabs with a casting thickness exceeding 360 mm, preferably at a casting thickness of 360 mm to 450 mm and a casting width exceeding 1000 mm, by the combination of the following features: a straight one Mold with vertically oriented mold cavity for producing a steel strand with a liquid core, - a strand guide for supporting and guiding the cast metal strand from a vertical casting direction in a horizontal transport direction extending from the mold to a dicing device, ····· · 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 immediately after the mold strand support devices for vertical guidance of the steel strand, ensure a vertical guidance of the steel strand over a transport distance of less than 4.5 m, - a Biegez one within the strand guide for bending the cast steel strand to a predetermined radius of curvature while the core is still liquid; a subsequent circular arc guide for guiding the steel strand to the predetermined radius of curvature; a straightening zone within the strand guide for bending back the cast strand from a predetermined radius of arc to a straight steel strand in still liquid or partially liquid core, - a cooling device in the strand guide for continuously cooling the steel strand, - a dicing device for dividing the steel strand on slabs of predetermined length.

Essential in a continuous casting of this type is the combination of a straight mold with a downstream strand guide, with a bending zone, a circular arc guide and a straightening zone, in conjunction with a cooling device for controlled cooling of the steel strand bending and straightening of the cast steel strand at liquid core and high Ensures quality requirements for the cast steel strand or slabs in the claimed thickness range.

An improvement in the quality of the steel strand or slabs produced is achieved when a vertical strand support means for vertical guidance of the steel strand are arranged in the strand guide immediately after the mold, which ensure a vertical guidance of the steel strand over a transport distance of less than 4.5 m.

An optimization of metallurgical requirements and investment and operating costs of the casting plant results when the minimum radius of curvature in the strand guide is 9.0 to 15.0 m. Thus, the overall height of the casting plant remains low and it is the quality standards that are standard for cast steel strands with, for example, 200 - 250 mm casting thickness, almost achieved.

According to an expedient development, the strand guide on a cooling device for controlled cooling of the steel strand, which is connected to a central processing unit and controlled by this and in which a mathematical model for continuous determination of the temperature profile along the transport path of the steel strand and in normal planes is deposited.

The cooling device in the strand guide is equipped with several independently controllable cooling zones over the casting width and / or height-adjustable spray nozzles with controllable adjusting devices. This is a targeted influencing the strand edge temperature by a width-dependent control of the amount of cooling water and / or a change in the distance of the spray nozzles from the steel strand surface and thus a change in the lateral distance of the coolant jet from the steel strand edge possible.

One or more electromagnetic devices, such as a stirring coil, for influencing the flow motion of the molten steel of the liquid core of the steel strand are disposed in the mold or in the region of the vertical guide of the steel strand.

Advantageously, peripherally cooled strand guide rollers are arranged in the strand guide for supporting and guiding the steel strand. By using these peripherally cooled strand guide rollers, there is a significant decoupling of the different Kühlbedarfjcies cast metal strand and the strand guide rollers, which are in direct line contact with the hot steel strand and its radiant heat are exposed.

Brief description of the drawings

Further advantages and features of the present invention will become apparent from the following description of non-limiting embodiments, reference being made to the following figures, which show:

1 shows a longitudinal section through a continuous casting plant according to the invention,

2 shows the arrangement of spray nozzles of a cooling device in a strand guide,

Fig. 3 shows a further embodiment of the cooling device with independently controllable cooling zones.

Embodiment of the invention

1 shows a schematic longitudinal section of the structural design of a continuous casting plant for producing slabs of liquid steel for a casting thickness of 400 mm.

The continuous casting plant has a straight mold 1 with vertically aligned mold cavity 1a. It is designed as an oscillating, internally cooled Verstellkokille with broad side walls and narrow side walls and allows the casting of steel strands with different strand width and possibly also different strand thickness. The mold 1 is equipped with an electromagnetic device 2, such as a stirring coil or an electromagnetic brake, for influencing the flow motion of the molten steel in the liquid core of the cast steel strand.

To the mold 1 includes a strand guide 3, which extends to a cutting machine designed as a cutting device 4 for cutting the steel strand in slabs. In the strand guide, the cast steel strand is supported and guided on its broad side walls in a tight corset of driven and non-driven strand guide rollers 5 and redirected from a vertical casting direction G to a horizontal transport direction T.

Groups of both sides of the steel strand arranged strand guide rollers 5 are summarized in strand guide segments 6.

The strand guide 3 comprises a series of successive sections with specific functions, the structure of which is essentially known. In a vertical strand support device 7, the steel strand emerging from the mold 1 is guided vertically and supported without the application of bending stresses. In a first area of this vertical strand support device 7, there is additionally a strand support with strand guide rails 5 also on the narrow sides of the steel strand. In a subsequent bending zone 8 there is a progressive bending of the steel strand to a predetermined radius of curvature. Subsequently, we transported the steel strand along a circular arc in a circular arc guide 9 without further bending stress while maintaining this radius of curvature. In a subsequent straightening zone 10, a bending back and straightening of the

Steel strand. Subsequently, the steel strand is conveyed in a horizontal strand guide 11 to the dividing device 4.

This structural design can be supplemented by various additional devices not shown and not described between and within the described sections of the strand guide, without thereby departing from the scope of the claims.

In the strand guide 3, the steel strand is subjected with its indicated by dashed lines, liquid core of a controlled cooling. The cooling device 12 includes, as shown in Figures 2 and 3, between the strand guide rollers 5 positionable spray nozzles 13, which are independently adjustable in a normal plane N to the transport direction T at least in some areas. In each cooling zone Z over the casting width B, height-adjustable spray nozzles 13 with associated adjusting devices 14 or, as shown in FIG. 3, spray nozzles 13 with control valves 18 for regulating the quantity of water are provided according to FIG. The adjusting devices 14 or the control valves 18 are actuated by a computing unit 15.

One or more of the strand guide segments 6, which are arranged between the straightening zone 10 and the dividing device 4, are associated with special positioning devices 17 for strand guide rollers 5. These segments form a soft reduction zone 16. The strand guide rollers in these segments can be wedge-shaped to the steel strand and thus allow a small reduction in the thickness of the metal strand and an improvement of the metallurgical properties in the core zone of the steel strand. ··································································

LIST OF REFERENCES: 1 straight mold 1a mold cavity 2 electromagnetic device 3 strand guide 4 dividing device 5 strand guide rollers 6 strand guide segment 7 vertical strand support 8 bending zone 9 circular arc guide 10 straightening zone 11 horizontal strand guide 12 cooling device 13 spray nozzles 14 adjusting device for spray nozzles 15 computing unit 16 Soft Reduction Zone 17 adjusting devices for strand guide rollers 18 control valves R Arc radius G Casting direction T Transport direction z Cooling zone B Casting width

Claims (17)

English:. German: v3.espacenet.com/textdoc? for producing thick slabs of steel with a casting thickness exceeding 360 mm and a casting width exceeding 1000 mm in a continuous casting plant, characterized by the combination of the following features: - vertical casting of a metal strand with still liquid core in a straight mold (1) with vertically oriented mold cavity (1a), - guiding the steel strand leaving the mold (1) on a vertical transport path (7) which is shorter than 4.5 m, without applying bending forces, - deflecting the cast steel strand from a vertical casting direction in a horizontal transport direction and supporting and guiding the steel strand in a strand guide (3) extending from the exit of the steel strand from the mold until it enters a dicing device (4) Bending the cast steel strand to a predetermined radius of curvature (R) with a still liquid core in a bending zone (8) within the strand guide (3), guiding the steel strand in a subsequent circular arc guide (9) of the strand guide (3) at this arc radius ( R), - bending back of the cast steel strand from a predetermined radius of curvature (R) on a straight steel strand with still liquid core in a straightening zone (10) within the strand guide (3), - continuous cooling of the cast steel strand in the strand guide (3 Maintaining the surface temperature of the steel strand in the straightening zone (10) of the strand guide (3) above the ductility depth of the respective steel grade. Maintaining the proportion of the solid strand shell of the cast steel strand at a maximum of 95% of the half strand thickness during the rebound phase Straightening zone (10), t • · · • Cutting the steel strand onto slabs of predetermined length in a dicing device (4). 2. The method according to claim 1, characterized in that the cast steel strand in the bending zone (8) within the strand guide (3) is bent to a radius of curvature (R) between 9.0 m and 15.0 m, in a subsequent circular arc guide ( 9) of the strand guide (3) is held on this radius of curvature without further deformation and in a subsequent straightening zone (10) within the strand guide (3) by a radius of curvature (R) between 9.0 m and 15.0 m straightened again. 3. The method according to any one of the preceding claims, characterized in that the cooling of the cast steel strand controlled by applying coolant to the broad sides of the cast steel strand with a cooling device (12) in the strand guide (3), wherein the impact position of the coolant jets on the Steel strand is controlled on the basis of a continuous determination of the temperature profile along the transport path of the steel strand and in normal planes to it. 4. The method according to any one of the preceding claims, characterized in that on the steel strand in the strand guide (3) until leaving the straightening zone (10) applied coolant quantity in response to a predetermined temperature profile, taking into account the ductility properties of the respective steel grade along the transport path of the Steel strand and in a normal plane is regulated. 5. The method according to any one of the preceding claims, characterized in that controlled cooling of the cast steel strand in the partial hot operation or after the dry operation with the involvement of peripherally cooled strand guide rollers (5). 6. The method according to any one of the preceding claims, characterized in that a soft reduction, in particular a dynamic soft reduction is applied to the cast steel strand in a region with still liquid or teilem Kem of the steel strand with a positioning device for strand guide rollers (17). 7. The method according to any one of the preceding claims, characterized in that the flow movement of the molten steel of the liquid core of the steel strand in the mold (1) or in the subsequent region of the vertical guidance of the steel strand is influenced by an electromagnetic device (2). 8. The method according to any one of the preceding claims, characterized in that the steel strand is cast with a casting thickness of 360 mm to 450 mm. 9. The method according to any one of the preceding claims, characterized in that the steel strand is poured at a casting speed between 0.5 and 1.0 m / min. Continuous casting plant for producing thick slabs of steel with a casting thickness exceeding 360 mm and a casting width exceeding 1000 mm, characterized by the combination of the following features: a straight mold (1) with vertically oriented mold cavity (1a) for producing a steel strand with a Liquid core, - a strand guide (3) for supporting and guiding the cast metal strand from a vertical casting direction in a horizontal transport direction, which extends from the mold (1) to a dicing device (4), - immediately after the mold strand support means (7) for the vertical guidance of the steel strand ensuring vertical guidance of the steel strand over a transport distance of less than 4.5 m; - a bending zone (8) within the strand guide for bending the cast steel strand to a predetermined radius of curvature (R) liquid nucleus, - a subsequent Kr bow guide (9) for guiding the steel strand at the predetermined radius of curvature (R), - a straightening zone (10) within the strand guide (3) for bending back the cast strand of one predetermined radius of curvature (R) on a straight steel strand with still liquid or partially liquid core, - a cooling device (12) in the strand guide (3) for continuously cooling the steel strand, - a dividing device (4) for dividing the steel strand on slabs of predetermined length. 11. Continuous casting plant according to claim 10, characterized in that the arc radius (R) in the strand guide (3) is 9.0 to 15.0 m. 12. Continuous casting plant according to claim 10 or 11, characterized in that the strand guide (3) has a cooling device (12) for the controlled cooling of the steel strand, which is connected to a central processing unit (15) and controlled by this and in a mathematical model for continuous determination of the temperature profile along the transport path of the steel strand and in normal planes is deposited. 13. Continuous casting plant according to one of claims 10 to 12, characterized in that the cooling device (12) in the strand guide with a plurality of independently controllable cooling zones (Z) over the casting width (B) is equipped. 14. Continuous casting plant according to one of claims 10 to 13, characterized in that the cooling device (12) in the strand guide (3) with height-adjustable spray nozzles (13) and controllable adjusting devices (14) are equipped. 15. Continuous casting plant according to one of claims 10 to 14, characterized in that an electromagnetic device (2) for influencing the flow movement of the molten steel of the liquid core of the steel strand in the mold (1) or in a strand support means (7) in the region of the vertical guide of the steel strand is arranged. 16. Continuous casting plant according to one of claims 10 to 15, characterized in that in the strand guide (3) for supporting and guiding the steel strand peripherally cooled strand guide rollers (5) are arranged. 17. Continuous casting plant according to one of claims 10 to 16, characterized in that at least one strand guide segment (6) with a controllable adjusting device for strand guide rollers (17) for performing a soft reduction, in particular a dynamic soft reduction, on the steel strand between the straightening zone (10). and the dicing device (4) is equipped in a region with still liquid or partially liquid core of the steel strand.