JPH09239496A - Mold for continuously casting square billet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mold for continuously casting a square billet enabling high speed casting which prevents surface crack at the corner parts of a cast billet by uniformizing mold wall temp. to reduce the thickness difference between the initial stage solidified shells at the corner parts and the side parts of the square cast billet and at the same time, promotes the cooling of the cast billet by increasing the heat conductive quantity at the lower part side of the mold. SOLUTION: First vertical grooves 2 having the length L1 (mm) from the upper end of the lower part are arranged at the corner parts on the inner wall surface of the tube mold 1. Further, second vertical grooves 3 having the length L2 (mm) from the lower end to the upper part, are arranged on the outer wall surfaces of four side parts except the corner parts of the tube mold 1. The length ranges of both vertical grooves 2, 3 are regulated as follows L1 =k1 Vc , L2 = H-k2 Vc , 50<=K1 , K2 <=300. Wherein, H is the height of the tube mold (mm) and Vc is continuous casting velocity (m/min).

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a square billet mold used in a steel continuous casting facility.

[0002]

2. Description of the Related Art It has been well known that surface cracks occur at the corners of a slab when a square billet of steel is cast in a continuous casting facility. This is due to non-uniformity.

That is, as shown in FIG. 2, the tube mold is deheated by the cooling water 5 flowing through the gap between the tube mold 1 and the inner mantel 4 arranged outside the tube mold 1, and the molten steel 6 in the mold forms a solidified shell. At that time, however, since the vicinity of the corner of the cast piece is cooled from both sides sandwiching it, the solidified shell at the corner portion is thickened earlier than the side portion. Therefore, tensile force due to thermal stress acts on the corners, and surface cracks are likely to occur on the corners of the cast slab.

Therefore, in order to prevent the surface cracks of the cast slab, it is desirable to make the initial solidified shell thickness as uniform as possible.

In this regard, for example, JP-A-63-160
Japanese Patent Publication No. 75 or Japanese Patent Publication No. 57-11735 discloses a method in which a groove-shaped recess is formed on the inner wall surface of a mold to reduce the contact area with molten steel to reduce the amount of heat removal and to perform gentle cooling as a whole. .

[0006]

However, JP-A-63-16075 or JP-B-57-1173.
According to the method disclosed in Japanese Patent Publication No. 5, only the inner wall surface of the mold is simply made to have a recess, so that the effect of making the initial solidified shell thickness uniform by making the difference in the heat removal amount between the corner portion and the side portion is not effective. There wasn't.

According to the present invention, the difference in heat removal amount between the corner portion and the side portion is made uniform to make the mold wall temperature uniform, so that the difference in thickness of the initial solidified shell between the corner portion and the side portion of the square billet slab is reduced. By reducing the size, thereby preventing surface cracks at the corners of the slab, and at the same time increasing the amount of heat removed from the lower part of the mold, slab cooling is promoted, and a continuous casting mold for square billets capable of high-speed casting is provided. It is a thing.

[0008]

That is, according to the present invention, since the corner portion is likely to be overcooled at the stage of forming the initial solidified shell on the upper portion of the mold, only the inner wall surface of the corner portion is dented, and at the lower portion of the mold. It was made based on the finding that the above problem can be solved by increasing the surface area by providing a vertical groove on the outer wall surface of the side part, and the main point is the tube of the mold. It is the inner wall surface of the corner of the mold, including the quadrant, in the direction of both sides, the length of one side of the square billet is 0.05 to
Within the range of 0.2 times, a first vertical groove having a length L ₁ within the range of the following formula (1) is provided downward from the upper end of the tube mold, and the groove depth of the first vertical groove is set to 0. The length L ₂ is 5 to 1.0 mm, the pitch is 1.5 to 2.5 times the groove depth, and the length L ₂ is upward from the lower end of the tube mold on the outer wall surface of the four sides excluding the corners of the tube mold. A second vertical groove within the range of formula 2) is provided, and the groove depth of the second vertical groove is 1.0 to 3.0 mm,
It is a mold for continuous casting of square billets, characterized in that the pitch is 1.5 to 2.5 times the groove depth.

L ₁ = k ₁ · Vc, 50 ≦ k ₁ ≦ 300 (1) L ₂ = H−k ₂ · Vc, 50 ≦ k ₂ ≦ 300 (2) where L _{1 is} : Length of one vertical groove (mm) L ₂ : Length of second vertical groove (mm) H: Height of tube mold (mm) Vc: Continuous casting speed (m / min) k ₁ , k ₂ : Proportional coefficient (mm / (m / min))

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The material of the tube mold of the mold used in the present invention is copper or a copper alloy, and the slab size is mainly for manufacturing square billets of 60 mm square to 300 mm square. FIG. 1 shows an example of a tube mold of the mold of the present invention. The upper part of the figure corresponds to the inlet side in the casting direction, and the lower part corresponds to the outlet side.

At the corner portion of the inner wall surface of the tube mold 1, the length L ₁ is set downward from the upper end of the tube mold.
The provision of the first vertical groove 2 within the range of the formula (1) is to reduce the amount of heat removal by reducing the area in contact with the molten steel through the molten powder, thereby supercooling the corner portion when the initial solidified shell is formed. Therefore, it is necessary to increase the range of slow cooling as the casting speed Vc increases.

In addition, the area in which the first vertical groove 2 is formed includes the quadrant and is 0.02 of the length of one side of the square billet in the direction of both sides.
The reason for setting the range of 5 to 0.2 times is that it is empirically known that the range in which the slab corner is affected by supercooling is usually within this range.

The depth of the first vertical groove 2 is 0.5 to 1.0 m.
The reason for setting m and pitch to be 1.5 to 2.5 times the depth is that, if the pitch is larger than this, the molten powder will flow into the groove, and it will not be possible to obtain a state where the contact surface is reduced. This is because if the size of the vertical groove is smaller than this, the inner wall surface of the mold is covered with the molten powder, and the heat removal effect of the molten steel is the same as in the case of a flat inner wall surface. With the size of the flutes as described above, 30-40% slow cooling can be expected at the corners.

On the outer wall surface of the four sides excluding the corners of the tube mold, the length L _{2 is} upward from the lower end of the tube mold.
The reason for providing the second vertical groove 3 within the range of the formula (2) is to increase the contact surface of the cooling water and accelerate the cooling of the slab after the initial solidified shell is formed. Since the formation of the initial solidified shell is delayed as the casting speed Vc increases, it is necessary to lower the position of the upper end of the second vertical groove 3.

The size of the second vertical groove 3 has a depth of 1.0 to 3.0 m.
The m and pitch are set to 1.5 to 2.5 times the depth, because if it is larger than this, the strength of the mold may decrease.
On the other hand, if it is smaller than this, the effect of increasing the surface area of the outer wall surface of the mold to improve the cooling capacity is weakened, and it is the same as in the case of a flat outer wall surface. If the size of the vertical groove is as described above, it is expected that the cooling capacity will be improved by 20 to 40%.

The shape of the vertical groove is usually an equilateral triangle, but may be a triangle, a rectangle, a square or an arc. Also, the corner section here is
It does not mean only the curved portion represented by the quadrant of the corner, but also the case where it includes a part of the straight portion that follows.

[0017]

EFFECTS OF THE INVENTION By using the mold of the present invention, the corner portion is gradually cooled when the initial solidified shell is formed, and the initial solidified shell thickness is made uniform. Further, since the slab cooling rate thereafter becomes faster, high-speed casting becomes possible.

[Brief description of drawings]

FIG. 1 is a view showing an example of a tube mold of a mold of the present invention.

FIG. 2 is a view showing a general mold used in a continuous casting facility for square billets.

[Explanation of symbols]

 1 Tube Mold 2 First Vertical Groove on Inner Wall Corner of Tube Mold 3 Second Vertical Groove on Outer Wall of Tube Mold 4 Inner Mantel 5 Cooling Water 6 Molten Steel

Claims (1)

[Claims] 1. A tube which is an inner wall surface of a corner portion of a tube mold of a mold, and which includes a quadrant within a range of 0.05 to 0.2 times the length of one side of a square billet in the direction of both sides. A first vertical groove having a length L ₁ within the range of the following formula (1) is provided downward from the upper end of the mold, and the groove depth of the first vertical groove is 0.5.
~ 1.0 mm, pitch 1.5 ~ 2.5 times the groove depth,
Also, on the outer wall surface of the four sides excluding the corners of the tube mold, the length L ₂ is as follows from the lower end of the tube mold upwards.
A second vertical groove within the range of the formula (2) is provided, the groove depth of the second vertical groove is 1.0 to 3.0 mm, and the pitch is 1.5 to the groove depth.
A mold for continuous casting of square billets, which is characterized by being 2.5 times. L ₁ = k ₁ · Vc, 50 ≦ k ₁ ≦ 300 (1) L ₂ = H−k ₂ · Vc, 50 ≦ k ₂ ≦ 300 (2) where L _{1 is} the first vertical Groove length (mm) L ₂ : Second vertical groove length (mm) H: Tube mold height (mm) Vc: Continuous casting speed (m / min) k ₁ , k ₂ : Proportional coefficient ( mm / (m / min))