JPH08206786A - Mold for continuous casting - Google Patents

Abstract

PURPOSE: To reduce the generation of the diamond-shaped deformation and the corner cracking by mitigating the heat transfer in the highly heat transfer zone of inverse triangular or inverse trapezoidal shape around the maximum heat transfer zone immediately below the meniscus to unify the development of the solidified shell of a side part and a corner part at the arbitrary section. CONSTITUTION: In a mold 1 to be used for the continuous casting of the steel billet or bloom, transverse grooves 13 of 1-10mm in width, and 0.05-1.0mm in depth are arranged in the inner surface of the mold 1 so that the pitch of the grooves may be small in the vicinity of the meniscus and the coarser as the grooves are located the more downward, and the length of the grooves is large in the vicinity of the meniscus and the smaller as the grooves are located the more downward, i.e., the grooves are arranged in the inverse triangular or inverse trapezoidal shape as a whole.

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,
Especially in the case of bloom or billet continuous casting molds with a square or rectangular cross section in which molten steel is injected into the mold through a single molten steel discharge nozzle arranged in the center of the mold, rhombic deformation of the bloom or billet or vertical corner cracks The present invention relates to a mold for continuous casting, which is capable of preventing the increase of casting speed.

[0002]

2. Description of the Related Art When a bloom or billet is produced by using a continuous casting mold (hereinafter, also simply referred to as a mold), the causes of these rhomboidal deformations are that the molten steel temperature is too high and the injection flow into the mold is Various factors such as poor centering, mold deformation, poor mold taper, uneven cooling of each surface inside the mold, uneven lubrication, poor foot roll alignment, and uneven spray cooling after leaving the mold are considered. However, the most influential factor is the uneven cooling in the mold. The factors that cause non-uniform cooling in the mold include factors from the outside of the cast such as deformation of the mold, non-uniform distribution of lubricating oil on the four sides of the mold, and non-uniform distribution of cooling water, as well as side parts inside the cast. The uneven development of the solidified shell at the corners promotes rhombic deformation and is a significant factor causing cracks at the corners. That is, as shown in FIG. 3, the molten steel 1 is cooled from the wall surface of the mold and solidifies inside the mold 2, but at the same time, it contracts due to a temperature drop. On the other hand, the solidified shell 4 bulges outward due to the static pressure of the molten steel 1 from the inner surface side, causing bulging, but the corner portion has a higher resistance to bulging than the central portion of the side, so only the central portion contacts the mold 2. In the corner portion and the vicinity of the corner, a gap 5 is generated between the corner portion and the mold 2. Since the heat transfer between the mold 2 and the solidified shell 4 is high at the contact portion P and low at the void portion Q, the contact portion P, that is, the side portion is cooled more than the corner portion, and the shell thickness of the side portion is smaller than that of the corner portion shell thickness. Thickening causes uneven solidification. When the delay of solidification at the four corners is not uniform, the solidified shell 4 is gradually deformed into a rhombus and is promoted as it goes downward. Further, due to the tensile stress acting on the solidified tip at the corner portion and near the corner during bulging deformation, cracks 6 occur near the corner portion when the corner radius is relatively small as shown in FIG.
When the corner radius is relatively large as shown in (A), cracks 7 occur at the corners. As shown in FIG. 5, when rhombus deformation occurs in the solidified shell 4, the tensile stress at the obtuse corner 8 becomes larger and the crack 9 also becomes larger.
It causes a breakout. Further, in the vicinity of the meniscus above the mold 2, since the solidified shell 4 is still thin and the shell temperature is high, the shell strength is low and the solidified shell 4 and the mold 2 have a high surface pressure over a wide flat area due to bulging due to the static pressure of molten steel. Although they come into contact with each other, the shell thickness increases as it goes downward, the shell temperature decreases, the shell strength increases, and the resistance to bulging increases, so that the contact area between the solidified shell 4 and the mold 2 at high surface pressure gradually converges only in the center part of the surface. Will come. That is, the area in contact with the high surface pressure has an inverted triangular shape with each surface of the mold 2 having a base near the meniscus. This is because, when the conventional mold 2 is used for a long time, the black discoloration area (high temperature area) 10 on the outer surface of the mold has an inverted triangular shape or an inverted trapezoidal shape as shown in FIG. 6 (B). I also understand. Even inside the inverted triangle, the degree of heat transfer differs depending on the strength of the surface pressure, and an isothermal line (= isothermal transfer line) 11 is obtained as shown in FIG. 6 (A). Heretofore, various attempts have been made to prevent the occurrence of rhomboidal deformation due to uneven solidification and the occurrence of corner cracks due to bulging. As one example thereof, Japanese Patent Laid-Open No. 2-703
In Japanese Patent Laid-Open No. 57-57904, a groove in the shape of a lattice is provided in the vicinity of the meniscus to cover it with plating to form a space in the shape of a lattice and the side portion is gently cooled. There is a crown type cross section of which the shape is made closer to a square (or a rectangle) toward the lower side to prevent generation of voids and generation of tensile stress at or near corners.

[0003]

However, in the method described above, since the uniform lattice-like voids are provided only near the position of the meniscus, the degree of increase in heat removal resistance is uniform within the range where the lattice-like voids are provided. It is not possible to eliminate the inverse triangular or inverted trapezoidal heat transfer gradient. Further, in the method shown above, the solidified shell is forcibly narrowed down from the crown shape into a square or a rectangle, so that the frictional force and the pulling force increase, and the rhombus deformation and the corner vertical cracking decrease, but the corner lateral cracking due to excessive friction also occurs. There is a problem in that a large amount of equipment improvement is required because it is necessary to drastically increase the pulling force and forcibly pull out to prevent sticking. The present invention has been made to solve such a problem, and it is provided about 5c directly under the meniscus.
In an arbitrary cross section, the heat conduction in the inverted triangular or inverted trapezoidal high heat transfer area (where the solidified slab and the mold contact at high pressure due to the static pressure of molten steel) centering on the maximum heat transfer area of m By uniforming the development of the solidified shells on the sides and the corners, the occurrence of rhombus deformation and corner cracks is reduced.

[0004]

A mold for continuous casting according to claim 1, which achieves the above object, is a mold used for continuous casting of steel billet or bloom, wherein the inner surface of the mold has a width of 1 to 10 mm and a depth of 0. A horizontal groove with a pitch of 0.05 to 1.0 mm is dense near the meniscus and becomes coarser as it goes downward, and becomes longer in the lateral direction near the meniscus and shorter as it goes downward and is generally triangular or inverted trapezoidal in shape. It is installed in. The continuous casting mold according to claim 2 is the continuous casting mold according to claim 1, wherein each of the lateral grooves has the widest groove width in the center of the mold surface and becomes narrower toward the corner. . A continuous casting mold according to a third aspect is the continuous casting mold according to the first or second aspect, wherein the transverse groove has a smooth U-shaped cross-section and is plated up to the groove bottom with the same plating. Further, the continuous casting mold according to claim 4 is the continuous casting mold according to any one of claims 1 to 3, wherein the length of the inverted triangular or inverted trapezoidal groove disposition area is set to the casting speed and the mold inner surface taper. 100 ~ depending on the degree
The one changed in the range of 500 mm is used.

[0005]

The operation of the continuous casting mold according to claims 1 to 4 will be described below. As shown in FIG. 2, by disposing the inverted triangular or inverted trapezoidal lateral groove 13 on the inner surface of the mold 2a, a void is generated in the lateral groove 13 portion during casting, which causes a heat insulating effect. It should be noted that although some of the lateral grooves 13 are not voids and have a portion filled with the lubricant, the thermal conductivity of the lubricant is extremely higher than that of the constituent material of the mold 2a and the material of the plating 14 formed on the inner surface of the mold. The operation is the same as when the lateral groove 13 is completely void. The pitch of the lateral grooves 13 is dense near the meniscus, and becomes coarser toward the lower side, and the lateral groove 13 has an inverse triangular shape or an inverted trapezoidal shape in which the lateral groove 13 is longer near the meniscus and shorter toward the lower side. Therefore, the heat-insulation (slow cooling) effect according to the degree of heat transfer in the high heat transfer area of the inverted triangle shape or the inverted trapezoid shape and in that area can be obtained.
Uniform cooling and uniform solidification shell 4 for the entire mold 2a
The development of a is obtained. As a result, the occurrence of rhombus deformation is suppressed, and cracks at or near the corners are reduced. Here, the width of the lateral groove 13 is set to be 1 to 10 mm. When the width is 1 mm or less, the effect does not appear, and when the width is 10 mm or more, the solidified shell 4a causes bulging and seizure in the groove portion, causing sticking and causing the shell to groove. This is because the effect is diminished because heat transfer occurs at the part that contacts the bottom. The depth of the lateral groove 13 is 0.05 to 1
mm is 0.05 mm or less because the groove bottom is in direct contact with the shell due to bulging into the groove.
This is because if the thickness is equal to or larger than mm, the effect cannot be expected to be improved, the groove processing cost becomes high, and the problem of mold strength occurs. Particularly, in the continuous casting mold according to claim 2, the lateral groove 1
Since the width of each of the 3 is wide near the center of the surface and becomes narrower toward the corners, a further heat insulating (slow cooling) effect according to the degree of heat transfer can be obtained, and uniform cooling of the entire mold 2a and A uniform solidified shell 4a development is obtained. The continuous casting mold according to claim 3, wherein the groove has a U-shaped cross-section and has the same plating as the top up to the groove bottom.
In order to reduce the cost of forming the groove and to make it economically priced, the mold copper plate is not exposed at the groove bottom to prevent damage to the copper plate at the groove bottom due to bulging of the shell and copper gets into the steel. This is to prevent the occurrence of star cracks. When the continuous casting mold according to claim 4 is provided with a taper that continuously changes corresponding to the shrinkage amount of the solidified shell, the air gap caused by the shrinkage of the solidified shell 4a is reduced. Inevitably, the bulging also becomes smaller, so the occurrence of corner cracks can be further reduced. In this case, the section where the solidified shell and the mold come into contact with each other at a high pressure is longer than that of the simple taper mold 2, so that the lateral groove construction section is also longer. The length of the grooved area (height of inverted triangle or inverted trapezoid) is 100 ~
500 mm means that the high-pressure contact area between the solidified shell and the mold (black area on the outer surface of the mold) is 100 mm or less, and 500
It is because there is practically no one with a thickness of mm or more.

[0006]

EXAMPLES Next, examples embodying the present invention will be described. 1 (A) and 1 (B) respectively show continuous casting molds 2b and 2c according to an embodiment of the present invention.
Inverted triangular region 1 corresponding to the black discoloration region 10 shown in (B)
A plurality of lateral grooves 13 as described above are formed on the inner surfaces of the molds 5 and 16 in an inverted triangular shape. That is, the pitch of the lateral grooves 13 is dense in the vicinity of the meniscus, and becomes coarser toward the lower side, and the length of the lateral groove 13 is longer in the vicinity of the meniscus and shorter in the downward direction, and has an inverted triangular shape. As shown in. Table 1 shows the conditions of occurrence of rhombus deformation and corner cracks when cast using these molds 2b and 2c and when using the conventional mold 2 which has exactly the same specifications except that there is no lateral groove 13. It shows the difference.

[0007]

[Table 1]

In Table 1, A corresponds to A shown in FIG. 5 and shows the degree of rhombus deformation. As is clear from Table 1, when the molds 2b and 2c according to the embodiment of the present invention are used, the number of rhombic deformations, corner cracks, and breakouts is reduced.

[0009]

EFFECTS OF THE INVENTION Since the continuous casting molds according to the first to fourth aspects are configured as described above, it is possible to reduce the occurrence of rhombic deformation and corner cracking. As a result, high-quality billets and blooms can be produced more efficiently.

[Brief description of drawings]

1A and 1B are explanatory views of a continuous casting mold according to an embodiment of the present invention.

FIG. 2 is a partial cross-sectional view of a mold having lateral grooves formed therein.

FIG. 3 is a cross-sectional view of a continuous casting mold according to a conventional example.

4A and 4B are explanatory diagrams of corner cracks.

FIG. 5 is an explanatory diagram of corner cracks when a diamond is deformed.

FIG. 6 is an illustration of a conventional mold.

[Explanation of symbols]

 1 molten steel 2 continuous casting mold 2a continuous casting mold 2b continuous casting mold 2c continuous casting mold 4 solidified shell 4a solidified shell 5 void 6 crack 7 crack 8 obtuse corner 9 crack 10 black discoloration area 11 isotherm 13 lateral groove 14 plating 15 inverted triangle area 16 inverted triangle area

Claims (4)

[Claims] 1. A mold used for continuous casting of steel billets or blooms, wherein the inner surface of the mold has a width of 1 to 10 mm,
A horizontal groove having a depth of 0.05 to 1.0 mm is dense in the vicinity of the meniscus and becomes coarser in the downward direction, and becomes longer in the lateral direction in the vicinity of the meniscus, and becomes shorter in the downward direction as a whole, and has an inverted triangular shape or A continuous casting mold characterized by being arranged in an inverted trapezoidal shape. 2. The continuous casting mold according to claim 1, wherein each of the lateral grooves has the widest groove width at the center of the mold surface and becomes narrower toward the corner. 3. The cross-sectional shape of the lateral groove is a smooth U-shape, and the same plating as the top is applied up to the groove bottom.
Or the casting mold for continuous casting according to 2. 4. The length of the inverted triangular or inverted trapezoidal groove disposition area is set to 1 depending on the casting speed and the degree of taper on the inner surface of the mold.
The casting mold for continuous casting according to any one of claims 1 to 3, wherein a casting mold that is changed in a range of 00 to 500 mm is used.