JPH06297101A - Mold and method for continuous casting of steel - Google Patents

Abstract

PURPOSE:To provide a mold and a method for continuously casting steel, by which the development of solidified shell is quichened and the thickness of the solidified shell is uniformalized so as not to develop the longitudinal cracking, rhombic deformation, etc., to cause lowering of the quality. CONSTITUTION:Cross sectional shape in a mold body part 1 of the mold for continuous casting is a quadrangle connecting four linear sides with four quarter circular arcs and the inner peripheral length S is made to be large at the upper end side of the mold body art 1 and to be small at the lower end side and the reducing ratio of the inner peripheral length is made to be small from the upper end toward the lower end of the mold of the mold body part 1. By using the mold MD for continuous casting, the molten steel surface is vertically displaced, and by using the mold part having the inner peripheral length approximately equal to the shrunk outer shape at the initial solidifying stage of a cast billet, the contacting condition between the mold copper plate and the solidified shell is made to be held to the optimum condition.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous casting mold for steel and a continuous casting method.

[0002]

2. Description of the Related Art Conventionally, continuous casting molds for slabs having a rectangular cross section are roughly classified into those having a cross section similar to that of the product slab and those having at least a part having an irregular cross section, that is, the mold cross section. Some are not similar to product slabs. As the mold whose cross section is similar to that of the product cast, a single taper mold or a multi-stage taper mold in which the taper amount is changed in each step in a plurality of steps in the casting direction are known. The basic method of casting using this rectangular mold is to keep the molten steel level in the mold constant (generally, about 100 mm below the upper end of the mold). That is, it is possible to artificially move about 20 mm for the purpose of extending the life of the immersion nozzle and the mold copper plate, but the basic idea is to maintain as much as possible at a specific target level regardless of the increase or decrease of the casting speed. Is.

The above-mentioned mold having an irregular cross section is intended to increase the casting speed and prevent slab breakage and breakout, and the molds described in JP-A-4-319044 and US Pat. No. 4207941. There is. The mold described in JP-A-4-319044 is a mold 103 as shown in FIGS.
In the upper half of the upper part, the four sides are curved to project and the projecting part 109
The amount of overhang 110 is reduced downward, and the cavity 106 is formed in a substantially rectangular shape in the lower half 113 of the mold. The mold described in U.S. Pat.No. 4,207,941 has an upper end 202 of the mold as shown in FIGS.
Is a square with valleys at the corners, the middle portion 204 is tapered, the corners are formed at the lower end 206 in a V shape, and the cross section is formed in an irregular dodecagon.

[0004]

However, in the conventional casting method using a mold whose cross section is similar to that of the product slab, the molten steel level in the mold is set according to the operating conditions such as steel type, casting temperature and casting speed. Even if it changes, it is basically not changed, so the cavity size inside the mold is constrained within the mold even under the most critical operating conditions (that is, when casting a steel type with a small shrinkage due to initial solidification at high speed). A small taper was adopted that would not occur. Therefore, under normal operating conditions, the contact area between the mold copper plate and the slab is limited to the entire circumference up to 200-300 mm below the molten steel level in the mold, and below that, the contact area is limited to the center of each side. I had no choice but to operate under conditions.

In this case, in the vicinity of the corner of the cross section of the slab, cooling is faster than in each side, and in the conventional mold, the mold is separated from the copper plate immediately after initial solidification, which causes a delay in shell formation near the corner. . This forms a defective shell generation portion near the corner, prevents the casting speed from increasing, and causes quality deterioration such as vertical cracks and rhombus deformation near the corner. On the other hand, if the cross-sectional shape is changed in the casting direction as in the case of a conventional mold having an irregular cross section, it is difficult to manufacture and maintain the mold, and the wear life is also disadvantageous. Further, there is a problem that the cross section of the slab becomes a dodecagonal shape instead of a square shape.

In view of the above circumstances, the present invention is directed to the production of a mold,
Instead of using a modified cross-section mold that is difficult to maintain and maintain, a square-based mold is used to promote the formation of a solidified shell and make the thickness of the solidified shell uniform, eliminating vertical cracks, rhombus deformation, etc. that cause quality deterioration. An object of the present invention is to provide a casting mold for continuous casting of steel and a continuous casting method which are prevented from occurring.

[0007]

The continuous casting mold of the present invention is a continuous mold comprising a mold main body part in which molten steel poured is in contact with the mold copper plate and an upper margin part in which the molten steel above does not contact the mold copper plate. A casting mold, wherein the cross-sectional shape of the mold body part is a quadrangle in which four straight sides are connected by four quarter arcs, and the inner peripheral length is largely lower at the upper end side of the mold body part. It is characterized in that it is smaller on the side, and the reduction rate of the inner peripheral length is smaller from the upper end to the lower end of the mold body portion. The inner peripheral length of the mold body portion in the present invention may be changed only by the taper amount of the mold body portion, or may be changed by the taper amount of the mold body portion and the radius of a quarter arc. Good.

The continuous casting method of the present invention uses the above continuous casting mold to displace the molten steel surface up and down,
It is characterized in that a mold portion having an inner peripheral length that is approximately equal to the contracted contour of the initial solidification of the slab is always used so that the contact state between the mold copper plate and the solidified shell is kept optimal. in this case,
As a physical quantity indicating the contact state between the mold copper plate and the solidified shell,
It is preferable to use one or more combinations of the drawing resistance value in the mold, the copper plate temperature, and the temperature difference between the mold cooling water supply side and the drain side, and the molten steel level is preferably displaced vertically based on this physical quantity.

[0009]

[Function] During continuous casting, the contracted slab outer shape and the cavity shape in the mold have a good correspondence, and the smaller the air gap between the mold copper plate and the solidification shell, the wider the contact between the solidification shell and the copper plate is ensured. The formation of a solidified shell can be promoted. By the way, molten steel solidifies in the mold,
When observing the process of forming a solidified shell, it was found that the shrinkage was large within the range of 200 to 300 mm below the molten steel surface, and the shrinkage thereafter was not so large. Further, it is known that the degree of shrinkage during initial solidification largely depends on operating conditions such as steel type, casting temperature and casting speed.

Therefore, in the present invention, by intentionally changing the set level of the molten steel surface in response to changes in operating conditions, a mold portion having an inner peripheral length that closely matches the contraction of initial solidification is selectively selected. use. That is, by using the mold main body portion of the inner peripheral length approximately equal to the contracted outer shape of the slab, the slab corner portion through the action of pushing the respective slab sides facing each other to the center side, the copper plate It prevents you from trying to leave. Further, even when the operating conditions change and the contact between the initial solidified shell and the copper plate becomes excessive or insufficient, the optimum contact state can always be maintained by lowering or raising the set level of the molten steel in the mold. .

[0011]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a schematic vertical cross-sectional view of a mold MD according to the present invention, in which 1 is a mold main body portion in which the molten steel m poured is in contact with a copper plate of the mold, and 2 is an upper margin portion above it. The upper margin 2 is a portion for preventing molten steel from flowing out during pouring, and normally does not come into contact with the molten steel m during operation. The molten steel m is in contact with the mold body portion 1, and the upper end thereof is at a level where the molten steel m rises most during operation. The present invention is characterized by setting the inner peripheral length of the mold body portion 1.

The cross-sectional shape of the mold MD according to the present invention is a quadrangle, and four straight sides are connected by four quarter arcs. The quadrangle referred to in the present specification includes a long quadrangle, and the ratio of the long side A to the short side B is A / B.
Those with ≦ 2.0 are included in the present invention. The inner peripheral length S of the cross-sectional shape in the present invention is large on the upper end side of the mold body portion 1 and smaller on the lower end side, and this inner peripheral length S may be changed only by the taper of the mold body portion 1, It may be changed by both the taper and the radius of the quarter arc. When changing the taper amount, it may be changed stepwise as shown on the left side of FIG. 1 or may be changed continuously as shown on the right side of FIG. When the taper amount is changed stepwise, it may be divided into two steps of the upper portion 3 and the lower portion 4 as shown on the left side of FIG. 1, or may be divided into three or more steps. In addition, the taper of the upper end margin portion 2 may be arbitrarily attached regardless of the mold body portion 1, or may not be attached.

The decrease rate of the inner peripheral length S defined by the taper amount or the taper amount and the radius of the quarter arc of the corner in the above-mentioned mold body portion must decrease from the upper end to the lower end. That is, the degree of change in the inner peripheral length is large at the upper end, and the degree of change is small at the lower end.

Next, the manner of changing the inner peripheral length S will be described in more detail with reference to FIGS. FIG. 2 is a schematic vertical sectional view of the mold body portion, and 5 is a body plate. Generally, the body plate 5 is formed in a curved shape, but in this drawing, it is simply drawn in a straight line. 3A to 5A are cross-sectional views of the upper end, the central portion, and the lower end in FIG. 2, respectively, and FIG. 3B is an enlarged view of the corner arc portion.

As shown in FIG. 2, the origin 0 is set on the inner surface excluding the corners at the lower end of the mold, the Y axis is set in the upward direction and the X axis is set in the direction orthogonal thereto in parallel with the casting direction of the mold. y =
Let L (mm) be the distance from 0 to the upper end of the mold body, and let B be the opposite side dimension in any cross section A-A (Y = y).
(Y) and the radius of the arc of the quarter of the corner is R (y), the inner circumferential length S (y) is expressed by the following equation. S (y) = 4 {B (y) −2 · R (y)} + 2π · R (y) However, since B (y) = Bo + 2x x is expressed as a function of y as described above, x = f
(Y) and the relationship between x and taper is mold taper = 2 / Bo.dx / dy × 100, so dS (y)
/Dy=8.dx/dy-(8-2.pi.).dR(y)/d
becomes y.

Assuming that the mold taper is Tm, dS (y) / dy = Bo / 25Tm- (8-2π) dR
(y) / dy, and as is clear from the above equation, the circumference S
The change rate in the y direction is the taper Tm and the radius R of the corner arc
Is a function of the rate of change dR (y) / dy. Further, if the radius R of the arc of the corner is constant, dS (y) / dy = Bo
/ 25 · Tm, which is a function dependent only on the taper. Therefore, by changing the taper and the radius of the arc of the corner portion, or changing the taper while keeping the arc of the corner portion constant, the rate of change S (y) of the inner circumferential length of the cross section of the mold body portion 1 can be arbitrarily set.

However, if the inner peripheral length change rate S (y) is too small, it becomes impossible to use a mold portion having an inner peripheral length approximately equal to the contracted outer shape of the cast piece, which is the object of the present invention. On the other hand, if it is too large, the slab will be restrained, causing breakout. Therefore, the inner peripheral length change rate S (y) is 0 ≦
In the range of dS (y) /dy≦0.08, it is preferable that the mold body portion 1 has a large size on the upper end side and a small size on the lower end side. The cross-sectional shapes shown in FIGS. 3 to 5 are examples in which the radius R of the arc of the corner portion changes from the upper end to the lower end of the mold body portion 1 from large to small.

Next, a preferred example of the cavity size in the mold is shown below with reference to FIG. In addition,
Of course, the mold of the present invention is not limited to this. (1) Upper region of the mold (L-400 ≦ y ≦ L shown in FIG. 6 (A))
Area) 1.5 ≤ Tm ≤ 15 (% / m) 0 ≤ dR (y) / dy ≤ 0.15 0.005 ≤ dS (y) / dy ≤ 0.08 (2) Mold lower area (0 ≤ shown in Fig. 6 (B), y ≤ L-150
0 ≦ Tm ≦ 5.0 0 ≦ dR (y) /dy≦0.03 0 ≦ dS (y) /dy≦0.025 (3) Each of the above values is constant or increases as y increases. The upper margin 2 is 50 mm.

Next, the continuous casting method of the present invention using the above mold will be described. In the present invention, by intentionally changing the set level of the molten steel surface in response to changes in operating conditions, the mold portion having the inner peripheral length S that closely matches the shrinkage of the initial solidification is selectively used. But the mold body part 1
The inner peripheral length S of the mold can be changed only by the taper Tm
When MD is used, the mold body portion 1 having a peripheral length reduction rate approximately equal to the contracted outer shape of the slab is used to push the respective sides of the slab facing the copper plate toward the center side. The slab corner portion is prevented from separating from the copper plate 5.

When using a mold MD in which the inner peripheral length S of the mold main body portion 1 can be changed by the taper Tm and the radius R of the corner arc, not only the reduction ratio of the peripheral length S but also the mold cavity cross section is used. After the solidified shell having a large radius of curvature is initially formed at the corner arc portion, the radius of curvature is reduced toward the lower end of the mold to ensure contact between the solidified shell and the copper plate at the corner portion.

Further, even when the contact between the initial solidified shell and the copper plate becomes excessive or insufficient due to changes in operating conditions such as steel type, casting temperature, casting speed, etc., the set level of molten steel in the mold is lowered. By raising it, the optimum contact state can be maintained. The ascending and descending range is preferably 10 to 200 mm below the upper end margin portion 2 in FIG.

As described above, when the operating conditions such as the casting temperature and the steel grade change, the physical quantity representing the contact state of the solidified shell and the copper plate of the mold changes. Therefore, by measuring or calculating these physical quantities, It is advisable to intentionally move the level of molten steel in the mold so that the value falls within an appropriate range. Examples of the physical quantity include (1) in-mold drawing resistance, (2) copper plate temperature, (3) temperature difference between the mold cooling water supply side and drain side, etc. It can be used as an indicator.

For example, if excessive contact occurs during operation, physical quantities such as the inlet / outlet temperature difference of the mold cooling water, the copper plate temperature, and the drawing resistance value in the mold increase. If this tendency progresses further, the tensile stress of the solidified shell below the slab restrained by the mold will exceed the allowable limit and break, leading to a breakout. Therefore, when the values of these physical quantities exceed a predetermined range, it is preferable to lower the molten steel level in the mold and use a mold part having a small taper and a small change rate of the inner peripheral length. On the contrary, when the contact between the copper plate and the solidified shell is small, the physical quantity decreases. In this case, if the molten steel level in the mold is increased, the mold taper and the portion with a large change rate of the peripheral length are used, and the physical quantity is increased. Therefore, by operating while monitoring the above physical quantity,
The optimum contact state can be maintained.

Regarding the above-mentioned physical quantity representing the contact state between the mold copper plate and the cast slab, it is possible to calculate an appropriate molten steel level in the mold for the operating conditions based on the data accumulated in advance, without having to measure it at each casting. It is also possible to establish a method.

Next, specific means for detecting the physical quantity will be exemplified. FIG. 7 shows an oscillation device in which the mold MD is placed on the mold table 11. As an example of detecting the pull-out resistance in the mold, a load meter 14 is installed between the push rod 12 and the eccentric rotating body 13. It is a thing. This makes it possible to detect the drawing resistance in the mold. FIG. 8 shows thermocouples TC1 to TC6 on the back surface of the mold copper plate 5 (mold cooling water side).
Is embedded. It should be noted that this can also be used as a device using a thermocouple as a molten steel level detecting device in the mold. The thermocouple embedded in the copper plate 5 can represent the contact state between the mold copper plate 5 and the solidified shell more directly than the above physical quantity. FIG. 9 shows a cooling device for the mold MD. If the temperatures at the cooling water supply port 16 and the drainage port 17 are measured, the temperature difference between the supply water temperature and the drainage temperature can be used as a physical quantity.

[0026]

According to the present invention, by moving the molten steel level in the mold up and down, the contact between the mold copper plate and the slab can be optimized, so that the slab that is drawn from the mold is solidified. The shell has a thicker shell than the conventional one, and a uniform shell can be obtained. High-speed casting is possible without worrying about breakout, and rhombic deformation is less likely to occur.

[Brief description of drawings]

FIG. 1 is a schematic vertical sectional view of a continuous casting mold according to the present invention.

FIG. 2 is a view for explaining an inner peripheral length in a mold body portion of a mold according to the present invention.

3A is a cross-sectional view of the upper end of the mold body portion in FIG. 2, and FIG. 3B is an enlarged view of a corner arc portion.

4 (A) is a cross-sectional view of the central portion of the mold body portion in FIG. 2, and FIG. 4 (B) is an enlarged view of a corner arc portion.

5A is a cross-sectional view of the lower end of the mold body portion in FIG. 2, and FIG. 5B is an enlarged view of a corner arc portion.

FIG. 6 is an explanatory view of an upper region and a lower region of a mold body portion in a continuous casting mold according to an embodiment of the present invention.

FIG. 7 is an explanatory diagram of an oscillation device equipped with an in-mold drawing resistance detector.

FIG. 8 is an explanatory diagram of a temperature detection device for a mold copper plate.

FIG. 9 is an explanatory diagram of a cooling water temperature detection device for a mold.

FIG. 10 is a vertical cross-sectional view of a mold according to a conventional example.

11 is a plan view of the mold of FIG. 10.

FIG. 12 is a vertical cross-sectional view of a mold according to another conventional example.

13 is a plan view of the mold of FIG. 12.

[Explanation of symbols]

MD mold m Molten steel 1 Mold body 2 Top margin S S Inner circumference R Radius of corner arc

Claims (5)

[Claims] 1. A continuous casting mold comprising a mold main body portion in which molten steel poured is in contact with a mold copper plate and an upper margin portion in which the molten steel above does not contact the mold copper plate, which crosses the mold main body portion. The surface shape is a quadrangle in which four straight sides are connected by four quarter arcs, and the inner peripheral length is large on the upper end side of the mold body part and small on the lower end side, and the inner peripheral length reduction rate is A mold for continuous casting of steel, characterized in that the mold body portion is reduced from the upper end to the lower end. 2. The continuous casting mold according to claim 1, wherein the inner peripheral length of the mold body portion changes only by the taper amount of the mold body portion. 3. The continuous casting mold according to claim 1, wherein the inner peripheral length of the mold body portion changes depending on the taper amount of the mold body portion and the radius of the quarter arc. 4. A continuous casting mold according to claim 1, wherein the molten steel surface is vertically displaced to use a mold part having an inner peripheral length approximately equal to the contracted contour of the initial solidification of the slab. The method for continuous casting of steel is characterized by maintaining the contact state between the mold copper plate and the solidified shell to be optimum. 5. As a physical quantity indicating a contact state between a mold copper plate and a solidified shell, one or a combination of two or more of a drawing resistance value in a mold, a copper plate temperature, a temperature difference between a mold cooling water supply side and a drain side is used. The continuous casting method for steel according to claim 4, wherein the molten steel molten metal surface is vertically displaced based on this physical quantity.