JP2001321894A - Continuous casting mold and continuous casting method - Google Patents

Abstract

(57) [Problem] To provide a continuous casting mold and a continuous casting method using the same, which can prevent breakout of vertical cracking. SOLUTION: The cross-sectional shape of the inner surface of the mold is at least one pair of opposing two sides being a parallelogram, and one of the angles formed by the two parallel sides with two adjacent sides is obtuse and the other is obtuse. And a continuous casting method using the mold.

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 used for continuous casting in which a slab passes through a bent portion as in a vertical bending type continuous casting apparatus, and a continuous casting method using the mold. It is.

[0002]

2. Description of the Related Art In continuous casting of slabs, particularly in continuous casting by a vertical bending type continuous casting apparatus, stress due to bending is applied to the slab when the slab passes through a bent portion.
The slabs are thereby distorted. On the top side of the slab, the stress and strain are distributed as tensile stress and tensile strain, respectively, in the width direction of the slab, and when they reach a certain value or more, the solidified shell on the slab top side In this case, a vertical crack may occur, which may cause a so-called vertical crack breakout.

As a continuous casting method for preventing breakage of vertical cracking, for example, Japanese Patent Application Laid-Open No.
No. 82 (hereinafter referred to as "Document 1"). In this method, a plurality of circular holes are arranged in rows in the casting direction in the casting direction, and when the solidified shell grows, the solidified shell is grown non-uniformly by intentionally creating a large number of solidification delay parts. In addition, the deformation distortion of the solidified shell is dispersed in a number of places to prevent cracks in the slab. There is also a continuous casting method using a mold in which the cross-sectional shape of a continuous casting mold is different from a generally used rectangular shape. For example, Japanese Patent Application Laid-Open No. 62-220249 (hereinafter, referred to as "Document 2") discloses a continuous casting method using a modified cross-section mold, and Japanese Patent Application Laid-Open No. 8-112649 (hereinafter, referred to as "Document 3"). Apply a straight or concave curved chamfer to a pair of diagonal corners of a rectangular mold, and make the short side length after the chamfering approximately the same length as the slab thickness after unsolidification rolling. A continuous casting mold is disclosed.

[0004]

However, the above prior art has the following problems. In the method described in Document 1, a frictional force is easily generated between a hole arranged in a mold and a slab, and in the worst case, there is a possibility that the slab is restrained by the mold and breakout occurs. Further, since a large number of holes are provided in the mold, the production and maintenance costs of the mold are increased. The continuous casting method described in Literature 2 is a method proposed for continuously casting thin cast pieces, and does not consider measures to prevent breakage of longitudinal cracks, which is the subject of the present invention. Furthermore, the mold used in this method has a cross-sectional area in the mold that gradually decreases in the casting direction, so that a large frictional force is easily generated between the inner surface of the mold and the surface of the slab. There is a problem that the life of the mold is shortened due to wear of the inner surface. The continuous casting method described in Document 3 is a method proposed for facilitating deformation of a slab when continuously casting a thin slab by rolling down an unsolidified slab. In this case, the lateral cracks generated in the bulging portion of the short side are reduced by avoiding the deformation in which a large stress is applied. Therefore, there is no mention of measures to prevent breakout of vertical cracking. In addition, since a pair of diagonal corners of the mold are chamfered, the area of contact between the corner and the mold becomes relatively larger than the pair of diagonals (right angles), and the mold is cooled by the mold. May be weakly cooled and the development of the solidified shell may be insufficient. The present invention has been made to solve the above problems in the prior art, and its object is to solve the problem, particularly when used in continuous casting of steel by a vertical bending type continuous casting apparatus, and the breakout of longitudinal cracking And a continuous casting method using the same.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and the gist thereof is as follows.

(1) In the continuous casting mold of the present invention, the cross-sectional shape of the inner surface of the mold is a quadrilateral in which at least one pair of opposed two sides is parallel, and the two parallel sides are two adjacent sides. Of the angles, one is obtuse and the other is acute. It is desirable that the obtuse angle of the two angles between the long side and the adjacent short side is 100 ° or more and 110 ° or less.

(2) A continuous casting method of the present invention is characterized in that casting is performed using the above-described continuous casting mold. Further, after casting, it is desirable to apply a reduction before the slab is completely solidified. The present inventors have repeated studies by numerical analysis for the purpose of preventing the occurrence of breakout when continuously casting a flat slab by a vertical bending type continuous casting apparatus,
The present invention has been completed with the following results.

[0008] (a) The cross-sectional shape of the inner surface of the mold is at least one set of two opposing sides parallel to each other.
By making one of the angles between two sides adjacent to each other an obtuse angle and making the other an acute angle, the stress on the top side of the slab when the slab passes through the bent part of the continuous casting device is relieved. it can.

(B) Further, when such a slab having a quadrangular cross section is unsolidified and reduced, the increase in the corner angle of the slab is smaller than in the conventional method of continuously casting a slab having a rectangular cross section. This is also advantageous in improving the internal quality of the slab when the slab is unsolidified.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a continuous casting mold and a continuous casting method using the same according to the present invention will be described in detail.

FIG. 1 is a schematic diagram for explaining a perspective outline of a typical vertical bending type continuous casting apparatus to which the present invention is applied, and a width direction stress Sw and a strain Ew generated on a top surface of a slab. .

FIG. 2 is a schematic view showing the cross-sectional shape of a slab according to the present invention, and particularly shows an example in which the slab 8 has a parallelogram in cross section. In the drawing, φ indicates the angle of the obtuse corner among the angles of the corner formed by the long side and the short side. Also,
Of the angles of the two top corners of the slab 8, the acute corner is referred to as the acute corner, and the obtuse corner is referred to as the obtuse corner.

FIG. 3 is a graph showing the relationship between the maximum value of the stress in the width direction Sw and the obtuse corner angle φ in the vicinity of the obtuse corner and the acute corner of the top surface of the slab obtained by numerical analysis. is there.

FIG. 4 is a graph showing the relationship between the maximum value of the strain Ew in the width direction and the obtuse-angle corner angle φ near the obtuse-angle corner and near the acute-angle corner of the slab top surface obtained by numerical analysis. is there.

According to these analysis results, by increasing the obtuse corner angle φ, the stress Sw is maintained at about the same level as that of the slab (φ = 90 °) having a substantially rectangular cross section. Can be reduced. Further, a preferable obtuse corner angle when continuous casting is performed with the slab cross-sectional shape being a parallelogram will be described. From the results shown in FIG. 3, the effect of reducing Sw near the acute-angle side corner portion and the obtuse-angle side corner portion by making the slab cross-sectional shape a parallelogram is small when φ is less than 100 °. The effect of reducing Sw saturates at around φ = 100 ° near the obtuse corner and at around φ = 110 ° near the acute corner.

On the other hand, in the case of cooling the slab in the mold, the cooling of the corner becomes stronger as the slab corner becomes an acute angle, and becomes weaker as the slab becomes an obtuse angle. Therefore, it is not appropriate to make the corner angle of the slab too sharp or obtuse even in the slab having a parallelogram-shaped cross section proposed in the present invention.

For the above reasons, a preferable cross-sectional shape when the continuous casting is performed with the cross-sectional shape of the slab being a parallelogram is an obtuse corner angle φ of about 100 ° to 110 °.

Next, the distortion generated at the slab corner solidification interface 9 when the slab having a rectangular cross section and the slab having a parallelogram cross section are rolled down in an unsolidified state is described below.
The case of each cross section was studied.

FIG. 5 is a schematic cross-sectional view showing an increase in the corner angle when a slab having a rectangular cross-section is rolled down in an unsolidified state.

FIG. 6 is a schematic cross-sectional view showing an increase in a corner angle when a slab having a parallelogram cross-section is rolled down in an unsolidified state. Here, the symbols t and d in FIG. 5 and FIG. 6 represent the slab thickness and the unsolidified rolling reduction, respectively.

The amounts of increase θ and ψ of the respective corner angles due to the reduction in the unsolidified state were calculated by geometrical calculation, and the magnitude relation was investigated. FIG. 7 shows the angle difference (θ−ψ) obtained by the above calculation and the obtuse corner angle φ.
3 is a three-dimensional graph showing the relationship between the unsolidified rolling reduction d / t and the unsolidified rolling reduction d / t. From the results shown in the figure, (θ− （) is always obtained regardless of the obtuse corner angle φ and the reduction ratio d / t.
Is positive, and the relationship θ> ψ holds. The reason can be considered as follows. When the cross section of the slab is a target for the center plane in the slab width direction, such as a rectangular cross section indicated by a broken line in FIG. 5, the slab undergoes deformation with respect to the reduction in the thickness direction. Absorb by buckling.
On the other hand, when the cross section of the slab is a parallelogram as shown by the broken line in FIG. 6, the slab deforms due to the reduction in the thickness direction, and the cross section has a It can be absorbed by being deformed, and buckling deformation of the short side is unlikely to occur as in the case of the rectangular cross section. As a result, θ> ψ
Becomes That is, the amount of increase in the slab corner angle when the slab is unsolidified is smaller than when the slab cross-sectional shape is a parallelogram than when the slab is rectangular. The distortion generated at the solidification interface at the slab corner is smaller in the case of a slab having a parallelogram cross section than in the case of a slab having a rectangular cross section. Therefore, when casting a slab having a parallelogram cross section, compared to casting a slab having a rectangular cross section,
The risk of internal cracks occurring at the solidification interface at the corner is low.

Incidentally, the present inventors have found that the slab cross-sectional shape is
At least one pair of opposing sides is parallel, and the obtuse corner is formed even in the case of a quadrilateral in which one of the angles formed by the parallel two sides and the adjacent two sides is obtuse and the other is acute. It has been confirmed that by increasing the angle, the stress Sw can be reduced while maintaining the strain Ew at substantially the same size as that of the slab having a rectangular cross section. That is, the effect of reducing the stress Sw described above is not limited to the case where the cross-sectional shape of the mold is a parallelogram,
Of the two pairs of facing sides, one pair was confirmed even when it was not parallel.

The mold of the present invention may be a mold having a constant cross-sectional shape along the casting direction, or may have a taper corresponding to the amount by which the slab cooled in the mold thermally shrinks. The mold may be applied to the long side of the mold or the short side or both sides of the mold, and the cross-sectional shape of the mold may be gradually reduced in the casting direction by the taper. Further, the mold may have a mold cooling mechanism with a cooling groove such as a groove or a hole, or a contact area between the portion and the slab can be obtained by chamfering a part of an acute corner of a mold section. Alternatively, the mold may have a cross-sectional shape such that the sharp corners are not strongly cooled.

In a practical form of the mold of the present invention, the cross-sectional shape of the mold is a parallelogram. Further, by setting the obtuse angle to 100 ° or more and 110 ° or less, while avoiding poor cooling of the slab due to strong cooling or weak cooling at the slab corner, the stress on the top surface of the slab is further reduced. The effect can be obtained. Of course, the present mold shape does not require modification of the mold cross-sectional shape such as the above-described chamfering of the sharp corner.

Although a continuous casting method using a vertical bending type continuous casting apparatus has been described as the continuous casting method to which the present invention is applied, the present invention is not limited to the continuous casting method for bending a slab in the casting direction. Can be applied to any of the methods.

Further, the present invention has a preferable effect when applied to continuous casting with so-called unsolidified rolling, in which the slab is reduced in a state where the slab has an unsolidified layer. In this case, the preferable rolling reduction range of the unsolidified slab is up to about 1/2 of the slab thickness.

[0027]

The results of a steel casting test will be described below.

FIG. 8 is a schematic vertical cross-sectional view of a vertical bending type continuous casting apparatus used for carrying out the present invention. This continuous casting apparatus has a slab pressure reduction device 6 operated by a hydraulic device 7. The main test conditions are as follows. [Test conditions] Mold: Cross-sectional shape: Parallelogram (long side: 1600 mm, short side: 100 mm) Obtuse angle: 90 °, 95 °, 100 °, 110
°, 120 ° 130 °.

Casting speed: 5 m / min.

Unsolidified rolling reduction of slab: 0 mm, 30 mm,
50 mm.

Using the mold 2 having the above-described cross-sectional shape and obtuse corner angle, carbon steel having the chemical composition shown in Table 1 below was cast under the casting conditions shown in Table 2 below. Table 2 also shows the results.

Of the tests shown in Table 2, those which did not break out were further examined for longitudinal cracks on the top surface of the slab after casting and internal cracks at the corners of the slab. In addition, the vertical crack was investigated by visual observation of the slab surface, and the internal crack was investigated by sulfur print of the cross section of the slab.

[0033]

[Table 1]

[Table 2] Tests 1 to 6 are tests in which the unsolidified rolling of the slab was not performed. In Test 1, which was performed as a comparative method using a rectangular cross-section mold, a breakout occurred,
In Tests 2 to 6 using the mold of the present invention, no breakout occurred and continuous casting was successfully performed. In the post-casting investigation, no vertical cracks were found on the top surface of the slab. In Test 5 where the obtuse corner angle of the mold was 120 ° and Test 6 where the mold was 130 °, slight internal cracks were observed at the corners.

Tests 7 to 9 are tests in which uncoagulation reduction was performed. Although a breakout occurred in Test 7 using a rectangular cross-section mold and a non-solidification reduction amount of 30 mm performed as a comparative method, in Test 8 in which the obtuse corner angle of the mold was 100 °, Neither surface cracks nor internal cracks occurred. Furthermore, the uncoagulation reduction amount is 5
In Test 9 where the thickness was increased to 0 mm, neither surface cracks nor internal cracks occurred. As shown in the above test results, the effect of the casting method of the present invention using the mold of the present invention is clear.

[0035]

As described in detail above, according to the casting method of the present invention using the mold of the present invention, the occurrence of vertical crack breakout in the slab is prevented, and the occurrence of internal cracks in the slab is prevented. Can also be prevented. Furthermore, even in continuous casting in which the slab is subjected to unsolidification reduction, the occurrence of internal cracks can be prevented, which greatly contributes to stable operation and cost reduction.

[Brief description of the drawings]

FIG. 1 is a schematic diagram for explaining a perspective outline of a typical vertical bending type continuous casting apparatus to which the present invention is applied, and a width direction stress Sw and a strain Ew generated on a slab top surface.

FIG. 2 is a schematic view showing a slab cross-sectional shape of the present invention.

FIG. 3 is a graph showing the relationship between the maximum value of the width direction stress Sw on the slab top surface and the obtuse corner angle φ obtained by numerical analysis.

FIG. 4 is a graph showing the relationship between the maximum value of the strain Ew in the width direction of the slab top surface and the obtuse corner angle φ obtained by numerical analysis.

FIG. 5 is a schematic cross-sectional view showing an increase in a corner angle when a slab having a rectangular cross section is rolled down in an unsolidified state.

FIG. 6 is a schematic cross-sectional view showing an increase in a corner angle when a slab having a parallelogram cross section is rolled down in an unsolidified state.

FIG. 7 is a three-dimensional graph showing a relationship between a difference in corner angle (θ− コ ー ナ ー), an obtuse corner angle φ, and an unsolidified rolling reduction d / t.

FIG. 8 is a schematic longitudinal sectional view of a vertical bending type continuous casting apparatus used for carrying out the present invention.

[Explanation of symbols]

 1. Molten metal 2. Mold 3. Slab support roll 3a. Slab top support roll 3b. 9. Solidification interface

Claims (3)

[Claims] 1. A cross-sectional shape of an inner surface of a mold is a quadrilateral in which at least one pair of two opposite sides is parallel, and
A continuous casting mold for steel, characterized in that one of the angles formed by the sides with two adjacent sides is one at an obtuse angle and the other at an acute angle. 2. A continuous casting method for steel, comprising using the continuous casting mold according to claim 1. 3. The continuous casting method according to claim 2, wherein, after being drawn from the mold, the inside of the slab is reduced in an unsolidified state.