KR100540922B1 - Method and Apparatus for Producing Thin Slabs in a Continuous Casting Plant - Google Patents

Abstract

In the processing method and apparatus of sheet slab equipment with solidification thickness between 60 and 120 mm, maximum casting speed of 10 m / min and maximum casting capacity of about 3 mio / t / a, casting is performed to secure the best surface quality and internal quality of strand. Strand thickness reduction, called continuous casting rolling, is performed with the first segment (0) of the strand guide extending vertically directly below the die,

A segment (1) arranged directly below the first segment (0) performs bending of the strand in an inner arc through a plurality of bending points

The strand is reverse bent horizontally through a number of reverse bending points prior to final solidification.

The method and device features can be described, for example, with the following features of a single core continuous casting plant:

A 1.2 m long hydraulically driven vertical casting die, opening exactly 80 mm in the meniscus in the horizontal direction, has an outlet thickness of 100 mm in its narrow area,

Segment 0, 3 m long, is formed as a narrow segment for strand thickness reduction from 100 to 80 mm with a strain rate of up to 1.11 mm / s strand,

Segment 1 has five bending points,

Segment 4 has five reverse bending points,

Segments 5 to 13 are formed in the horizontal region of the strand guide.

Description

METHODS AND APPARATUS FOR PRODUCING THIN SLABS IN A CONTINUOUS CASTING PLANT

The present invention provides for casting steel at a solidification thickness of 60 to 120 mm, for example 80 mm, a casting speed of 10 m / min and a maximum casting output of approximately 3 mio / t / a (million tons per year). The present invention relates to a method and an apparatus for the production of slabs in a continuous casting facility having a vertical-casting die mainly for thin slabs.

Laminated slab installations, which result in a reduction in slab thickness realized by continuous casting machines, are provided with one or two pairs of foot rollers, mainly in the so-called "segment 0", where the strand thickness is directly below the continuous casting die. Decrease. Over the total length of the metallurgical length of about 2 m in the segment, i.e. the segment (to stand) 0, which is not arranged vertically, the thickness of the strand is reduced to a casting speed of up to 6 m / min from 65 mm to 40 mm. This design information results in a strand thickness reduction of up to 38% and a strain rate of strand thickness of 1.25 mm / s.

During the residence of the strand using the liquid core, the strand shell of about 8-12 mm thick is strongly deformed by swelling between the continuous casting equipment rollers when entering segment 0. This internal strain increases with increasing casting speed and plant height or ferrostatic pressure and decreases with shrinking roller spacing. It is noted here that the roller diameter cannot be smaller than, for example, 120 to 140 mm because of mechanical structural criteria (structural limitations in mechanical loads, in particular in intermediate rollers). One possible mechanistic solution could be a sliding plate called a "grid", which is not suitable for carrying out a reduction in strand thickness.

This internal deformation is mainly due to normal continuous casting.

Swelling of the strands between the rollers

Bending of the strands from the vertical to the inner arc

Straightening of the strand towards the horizontal section

-Roller jumps,

-Impact of the roller and

       -According to tensile strength

The deviation from the ideal strand guideline of the roller, etc.

In addition to these internal deformations, surface-deformation should also be considered as deformations occurring through strand thickness reduction and so-called continuous casting rolling in segment zero. This particular internal deformation is in addition to the deformation that occurs in segment 0 mainly by swelling of the strands and bending from the vertical to the internal arc. Accumulation of these individual specific strains can lead to the case where the threshold of total strain is reached, and can lead to rupture of the inner strand shell and the outer strand shell.

For example, additional loads acting on the strand shell due to continuous casting or reduction in thickness during solidification in segment 0, 2 m long just below the casting die are described in DE 44 03 048 and DE 44 03 049. 1 shows an example of the diagram in detail.

According to FIG. 1 a 2 m long segment 0 is connected to a 1 m long vertical casting die with one or two pairs of foot rollers, in which the strand is bent into an internal arc over several steps and its thickness is reduced. Two simultaneous processes or deformations result in cumulative total deformation consisting of bending deformation (D-B) and casting and rolling deformation (D-Gw). The total strain D-Ge acting on the strand shell may be greater than the threshold value D-Kr of the strain and may cause the internal and external strand shells to burst. This risk rises with increasing casting speed due to roller spacing or roller diameter in segment 0, which cannot be smaller than a predetermined limit due to mechanical structural limits.

Also noteworthy in the description of this problem is that the limit strain value (D-Kr) is specific to the individual characteristics of the steel product. Deep drawing properties are less important than, for example, micro alloy steel API X 80 grades in connection with the absorption of strains which do not form a rupture.

Furthermore, the formation and expansion of the pure molten phase in the superheated melt or strand indicated by the straight line G1 dependent on the casting speed has a significant effect on the strand internal quality. In the example shown in FIG. 1, the deepest liquid-temperature or pure molten phase at the center of the strand is up to about 1.5 m below the bottom or casting level of the meniscus at a casting speed (VG) of 5 m / min, and VG 10 m / min. When it reaches up to 3.0m. Below this point, there is a two-phase region, a region composed of melt and crystals, over the entire strand thickness, which melts relative to the crystal as the distance increases in the direction of the sump edge or final solidification. Minutes are reduced.

If the crystal content is 50%, i.e., at the intermediate distance between the lowest liquid point of 1.5 m at VG 5 m / min and the final solidification occurring at about 15 m, i.e. 8.25 m (1.5 m + (15 m-1.5 m) x 0.5 = 8.25 m) (G _W -50%) the molten / crystalline phase has a viscosity of 10,000 cP. Where the crystal content is 80%, the two phase region has a viscosity of 40,000 cP, while the pure molten phase has a viscosity of only about 1 to 5 cP up to the lowest liquid point, depending on the quality of the steel, between crystals (crystal network or dendrites) The partial viscosity of does not actually rise, ie remains constant until final solidification.

If we want to relate the above viscosity to a well-known everyday material in the biphasic region, we can consider the following materials:

1 cP = 10 exp3 Ns / m exp2 at 20 ° C

-80 cP at 20 ° C olive oil

10,000cP at 20 ℃

40,000 cP at 20 ° C

-100,000cP at margarine 20 ℃

1000,000 cP at 20 ℃

These viscosities indicate that the crystal / melt-structure must be present in the core of the strand for good forced convection and hence good crushing of the crystals by reducing the strand thickness, ie the strand is already in the region of segment 0 at the maximum casting speed. It is clear that there is no longer a permeation zone which has a two-phase region in the core or increases the pure molten phase or superheated region to oxide. These conditions led to the discovery that, on the one hand, segment 0 should be vertical, on the one hand, segment 0 should serve only for strand thickness reduction and not for further bending of the strand. .

In FIG. 1 showing the above bad conditions, the superheat zone or the lowest liquid point extends to the end of segment 0, thus indicated by point 1.1 on straight line G1 at the maximum casting speed of 10 m / min. Likewise, it extends into the inner arc of the continuous casting plant. These casting conditions are also extremely disadvantageous for strand shell deformation or oxide purity.

The two-phase region between two straight lines, i.e. between straight line G1 for the arrangement of the lowest liquid point according to the casting speed and the lowest solidus point for the casting speed or the straight line G2 for final solidification, the maximum casting speed At 10 m / min, it starts at the end of segment 0 which performs strand thickness reduction.

Part 3a of FIG. 3 (see the left half of FIG. 3) shows a different phase pattern of strands, the strands being 100 mm thick at the meniscus in the casting die and the subsequent 2m long segments. The strand thickness is reduced to a solidification thickness of 0 to 100 mm to 80 mm, leading to final solidification at final segment 14 for a maximum casting speed of 10 m / min. FIG. 3A shows that the segment 0 gives the strand the maximum possible strain caused by the shrinking of the strand and the bending process from the vertical to the inner arc through the five bending points, as well as the increase of oxide into the meniscus and It clarifies the fact that it imposes a bad condition that causes casting slag.

In addition, the portion 3a shows a reduction speed of 0.833 mm / s for a strand shell that is reduced from 100 mm to 80 mm, that is, 20% at a casting speed of 5 m / min, and 1.66 mm / s at a casting speed of 10 m / min. To reach This strand thickness reduction rate is a direct measure of the deformation of the strand shell, which has a thickness of about 10.3 mm at a casting speed of 5 m / min at the inlet of segment 0 and about 7.3 mm at a casting speed of 10 m / min. Has a thickness. This strand deformation caused by casting and rolling is large and doubles from 0.83 to 1.66 mm / s, as shown by the simplified figure 1.66 mm by increasing the casting speed from 5 m / min to 10 m / min. Let the deformation follow the quadratic function.

This high deformation is additionally exerted by the bending process in segment 0, which poses a risk of cracking of the inner and outer strand shells, especially for steel products that are sensitive to cracks.

Based on the above recognition and related matters, the present invention proposes a method and equipment for continuous casting equipment for high speed slab equipment based on a device for reducing strand thickness directly below the casting die, It is based on the task of securing surface quality and internal quality.

This problem is solved with the features presented in method claim 1 and apparatus claim 7. The independent claims contain reasonable and advantageous forms of the invention. This provides an unforeseen solution to the various complex problems described above, which will be described in detail below. In particular, the invention assures in detail the following features:

The minimum plant height between the meniscus of the vibrating vertical casting die and the final solidification stage in the horizontally extending area of the strand guide, at a minimum ferrostatic pressure or preferably hydraulically driven,

A minimum strain density distribution of the total strain consisting of casting and rolling deformation and bending deformation in a vertical-bending unit having a broad surface of a concavely constructed casting die, and a predetermined roll diameter in the strand guide means and Preferably a maximum casting speed of 10 m / min,

-Superheated or increasing oxide in the vertical part of the continuous casting plant, i.e. segment 0, which performs strand thickness reduction at a maximum casting speed of 10 m / min, in order to ensure symmetry of the strands in the region of the superheated or pure molten phase. Complete removal of the transmission zone for

Prior to the end of segment 0, which performs strand thickness reduction or casting and rolling, the casting and rolling process at the maximum casting speed of 10 m / min, for example, where the melt / crystals of the two-phase zone are in the center of the strand,

Strain rate of strand shell up to 1.2 mm / s in segment 0,

The minimum bending strain density from the vertical portion in segment 1 to the inner arc, over a number of bending points, independent of the casting and rolling strain in segment 0 placed immediately before segment 1,

Preferably at an average-cast speed of 80% of the maximum casting speed, from the inner plant radius through several straightening or reverse bending points to a horizontal portion at least 12 s or at least 2 m before final solidification. Minimum calibration up to.

In FIG. 2 and in part 3b (see right half of FIG. 3), the method and apparatus of the present invention are illustrated.

2 shows the installation configuration for casting speeds 5 and 10 m / min; The distribution of the internal strain of the strands according to the invention over the length of the strand guides, along with the elongation of the pure molten phase, the final solidification and strain limits depending on the casting rate.

In the continuous casting method according to the present invention, the strand strain density is minimized over the length of the strand guide, and each type of deformation is configured to occur continuously regardless of other types of deformation. The deformation curves (D-5) and (D-10) proceed below the threshold value, that is, the limit deformation (D-Kr). The deformation curve further shows that the accumulation of deformations caused by casting and rolling and bending is avoided, because in the illustrated embodiment the strand thickness reduction (D-Gw) is performed on vertical segment 0 having a length of 3 m. This is because the bending of the strand DB is performed in subsequent segment 1 passing through five bending points.

Furthermore, FIG. 2 shows the meniscus when the lowest liquid phase (1.1) or superheated or permeable region occupies about 10% of the solidification time at 25 ° C overheating of the steel in the distributor. It extends to 3m below or extends to 2m deep into segment 0. This allows the oxides to rise freely and symmetrically in a pure molten phase in which the oxides are arranged vertically, at the same time from which crystals by casting and rolling in the region below the lowest liquid point where the two-phase region inside the strand fills the strand metal It is clear that the crushing and large segregation and the suppression of the medium scale are carried out over the length of the 1 m residual length in segment 0.

The two-phase region is located between the straight line G1 indicating the lowest position of the liquid point and the straight line G2 indicating the position of the sump edge according to the casting speed. The crystal / melt two-phase region starts at 1.5m below the meniscus (liquid point 1.2) or 0.5m after the strand enters segment 0 at a speed of VG 5m / min (approx. 2)) ends in At a casting speed of 10 m / min, the two-phase zone starts at about 3 m (1.1) and ends with a sump edge at about 30.2 m (2.1) (see Figure 2).

Strand reduction or casting and rolling with the complete two-phase zone between the strand shells proceeds over the remaining length 2.5m of segment 0 at casting speed VG 5m / min and over 1m at VG 10m / min do. In both cases, forced convection of the two-phase zone occurs, thereby improving the strand internal quality.

According to Fig. 3, for example, reverse bending a strand from a strand having an internal radius of 4 m to a horizontal portion through, for example, five calibration points, ensures a gentle reverse strain (DR) and at the same time In order to prevent the adverse effects of strand deformation on the final solidification and thus on the strand internal quality, for example, it is performed in segment 4 of 2 m length.

Furthermore, part 3b of FIG. 3 should be discussed. In particular, here, when compared with the partial view 3a, casting and rolling deformation (D-Gw) from 100 mm to 80 mm proceeds over a segment 0 of 3 m length, thus at a deformation rate of 1.11 mm / s at a casting speed of 10 m / min. And at VG 5m / min, the deformation rate is 0.55mm / s. This strain rate is significantly reduced compared to 1.66 mm / s at a 10 m / min casting speed in segment 0 of 2 m length. This results in a strain rate below the known critical value of 1.25 mm / s.

The advantage obtained by the present invention is due to the assured continuous casting method for thin slabs of solidification thickness of 60 mm to 120 mm, mainly by casting and rolling steps in segment 0 arranged vertically directly below the vertical-casting die. . As shown in FIG. 4, the steel is led into the vertical casting mold by the injection pipe Ta from the submerged distributor V. The following facts, namely

-Accurate vibration and exact deviation of the frequency of vibration and the height of vibration during the casting process

Uniform slag lubrication over the entire strand width

-Quiet Bass Level Workout

Uniform heat transfer to the casting die

-Strand progress to the center of casting die and strand guide

-High casting safety while avoiding cracks

In order to be sure it is preferably provided with a concave wide surface plate and driven hydraulically.

In order to straighten and reliably guide strands even at high casting speeds, the strand guide means can also be configured in a concave shape up to 2 x 12 mm away from linearity. This can be realized for example with a strand guide roller having a concave formed shape. In addition, the degree of concave deformation from the casting die exit or the initial strand guide roller to the final roller of the strand guide need not be constant, and functions to the minimum residual concavity or residual curvature towards the end of the strand guide. It may also decrease gradually.

Segment 0 should be arranged vertically and used exclusively for strand thickness reduction. It must have a minimum length that will result in a reduction in casting thickness of less than 1.25 mm / s at the strand at the maximum casting rate, while at the same time the complete removal of superheat at the maximum casting rate and crystallization in the crystal / melt two phase region. It must have a minimum length to ensure grinding and suppression of large and medium wells. In this example, segment 0 has a length of 3m.

According to the present invention, in segment 1, immediately following the continuous casting process of segment 0, there is a two-phase mixture between the strand shells in order to keep the strand shell deformation density small and not to accumulate with the casting and rolling deformations made earlier. In the state, the bending of the strand is carried out, for example, via five bending points with an internal arc of 4 m, for example.

For example, depending on the plant height of about 8 m and its geometrical relationship, in segment 4 it is much earlier than the final solidification that occurs at a distance of about 15 m or 30 m from the meniscus at casting speed VG 5 or 10 m / min. At a distance of about 12 meters from the meniscus, reverse bending into the horizontal part, for example, passes through five calibration points. As a result, the time between reverse bending and consequently the ultimate solidification of the inner strand shell, which is extremely sensitive to deformation and deformation, is 36s or 108s, and the slab due to adverse effects and reverse bending on the final solidification in the region of the sump edge The defect in the core of is eliminated.

The embodiment of the invention shown in FIG. 4 is characterized in that, at the exit of a vertical-casting die with a hydraulic drive, an average of 100 mm thick strand, a solidification thickness of 80 mm, a maximum casting speed of 10 m / min and a maximum of 3.0 mio / t / As a single line continuous casting plant for the production of pa, this continuous casting plant includes:

A 1.2 m long vertical-casting die with a width of up to 180 mm in the center of the meniscus and a minimum of 100 mm in the center and a width of 100 mm in the region of the narrow side of the casting die;

-Vertical segment 0 installed as a narrowing segment 3m long to reduce the strand thickness to 80mm

Segment 1 with five bending points and an inner radius of 4m

-Segments 2 and 3 in the inner circular arc

Segment 4 with five calibration points and

Segments 5 to 13. in the horizontal part of the strand guide;

The entire continuous casting plant has a metallurgical length of about 30m, of which about 4m is arranged vertically (K and 0), about 8m with arcuate (segments 1, 2, 3, 4), About 18m is arranged horizontally (segments 5 to 13). At a casting speed of up to 10 m / min, the lowest liquid point ((1.1)) extends approximately 2 m into a 3 m long segment 0, so that the oxides rise into the casting slag in an optimal manner and the oxides remaining in the steel are symmetric. While distributing the particles in the two phase region, it is possible to ensure the crushing of the crystal in the two phase region and the suppression of the core fraction in the strand. At a distance of about 16.5 m from the meniscus, the biphasic mixture with a crystal ratio of 50% (weight ratio of 50%) has a viscosity of 10,000 cP (equivalent to honey at 20 ° C.). In the final segment 13 the final solidification (2.1) is carried out away from the reverse bending of segment 4.

Between the reverse bending and the final solidification at the sump edge, there is an unobstructed solidification time of about 108 s which ensures good core solidification.

1 is a graph showing the relationship between the internal strain and the casting speed for the length of the strand guide portion in the continuous casting method according to the prior art.

Figure 2 shows the characteristics of the equipment configuration for the casting speed 5 and 10 m / min, the expansion of the pure melt phase, the solidification end according to the casting speed, the internal deformation of the strand guide portion,

FIG. 3 shows the menis in a casting die with a strand reduction of continuous thickness reduction from 100 mm to 80 mm from segment 0 to 2 m long to final solidification at final segment 14 for a maximum casting speed of 10 m / min. Figure showing the formation of different phases of 100 mm thickness by a curse, and

4 is an embodiment of the present invention.

(Explanation of symbols for the main parts of the drawing)

-(D-5) Strand internal deformation during solidification at 5m / min continuous casting speed

-(D-10) Internal deformation of strand during solidification at 10m / min continuous casting speed

-(D-B) bending deformation of the strand inner shell when bending the strand with the inner arc at the vertical part

-(D-R) reverse bending deformation of the inner shell of the strand when reverse bending horizontally through multiple reverse bending points out of the internal arc

-(D-Gw) Continuous casting rolling deformation of inner shell of strand

-(D-Ge) Total deformation of the strand inner shell (D-Ge) = (D-B) + (D-Gw)

-(D-Kr) critical or limit deformation of the inner shell of the strand

-(1) the lowest liquidus point or the lowest point of overheat spaced from the meniscus in relation to the continuous casting speed

-(1.1) the distance of the lowest liquid point from the meniscus at a continuous casting speed of 10 m / min

-(1.2) Distance of the lowest liquid point from the meniscus at 5 m / min continuous casting speed

-(Gw-50%) Two-phase mixture of about 10 000 cP (similar to honey at 20 ° C) and 50% crystal ratio at 8.25 m and 16.6 m from the meniscus at continuous casting speeds of 5 and 10 m / min

(2) the lowest freezing point or sump edge spaced m from the meniscus in relation to the continuous casting speed;

-(2.1) the distance of the sump edge from the meniscus at a continuous casting speed of 10 m / min.

-(2.2) the distance of the sump edge from the meniscus at 5 m / min continuous casting speed

-V distributor

-Ta Tang inlet

-Vertical casting dies for K hydraulic vibration drives

-Segment 0 as the 0 sandwich segment

Segment 1 as 1 bending segment

-Segment 2 as 2 arc segments

Segment 3 as 3 arc segments

Segment 4 as 4 reverse bending segments

-Segment 5 as 5 horizontal segments

-Segment 6 as 6 horizontal segments

--------

14 segments as 14 horizontal segments

Claims (14)

In the method for manufacturing sheet slab in a continuous casting facility having a vertical continuous mold, Performing exclusively thickness reduction of the strands in the first segment of the strand guide extending in the vertical direction just below the mold, wherein the length of the vertically extending first segment is the maximum casting. The pure molten phase or lowest liquid phase in velocity is dimensioned between the lower end of the first 1/3 position of the first segment and the end of the first segment, but not out of the first segment, Passing the strand through a plurality of bending points in another segment disposed directly below the first segment to perform bending to an internal arc, and -Reverse bending the strand through a plurality of reverse bending points prior to final solidification into the horizontal section. The method of claim 1 wherein the vertical mold has a light side wall having a concave profile extending symmetrically in the horizontal plane. 3. A method according to claim 2, wherein the concave contour is formed to disappear completely from the beginning of the mold, ie from the meniscus area to the end of the mold. 3. The concave contour of claim 2 wherein the concave contour is reduced during the beginning of the mold, i. Formed. 5. The method of claim 4, wherein the residual concavity is removed from the strand guides such that the strand has a minimum concavity or curvature. 2. The method of claim 1, wherein the strain rate of the strand is maintained at 1.25 mm / s or less during the strand thickness reduction operation.  A vertical continuous mold; A first segment extending vertically to perform a thickness reduction between 40 mm and 10 mm and disposed directly below the mold; In the continuous casting equipment for manufacturing a thin slab comprising: a subsequent segment disposed directly below the first segment, comprising three or more bending points, and having a circular arc between 6 m and 3 m in radius; It further comprises three or more straightening points for reverse bending the strands from the inner arc to the horizontal, the final reverse bending point at 80% of the maximum casting speed being at least 2 m away from the sump edge and within the mold. And a height between the level of the meniscus and the lower edge of the strand in the strand guide extending horizontally is 10 m or less, and the continuous casting plant has a height of 10 m or more. 8. The continuous casting machine according to claim 7, wherein the first segment extending in the vertical direction has a length of 2 m or more. 8. The continuous casting machine according to claim 7, wherein the mold has a narrow side area, and the buccal part has a width between 160 mm and 170 mm. 8. The mold of claim 7, wherein the vertically extending mold has wide side walls, the light side walls being concave and symmetrically extending in the horizontal direction, with openings in the light side wall in the meniscus region. And having an outline, wherein the opening is 40 mm or less on each light side wall. The continuous casting machine according to claim 10, wherein the concave contour of 40 mm or less on each light side wall in the meniscus region of the mold is formed so as to disappear completely at least at the end of the mold. The concave contour of 40 mm or less on each light side wall in the meniscus region of the mold is 12 mm or less on each light side wall along the water pattern from the meniscus of the mold toward the end of the mold. Continuous casting equipment, characterized in that formed to reduce the residual concave. 13. The continuous casting machine according to claim 12, wherein the mold outlet further includes a strand guide portion for reducing residual concavity to a minimum concavity or curvature of the strand along the water pattern. 8. The continuous casting machine according to claim 7, wherein the continuous casting machine is formed at a continuous casting speed of 10 m / min or less.

Images