JP2016087613A - Casting mold for continuous casting - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a casting mold for continuous casting capable of suppressing a temperature drop at corners of a cast piece.SOLUTION: A casting mold 1 for producing square billets in continuous casting comprises: a mold cavity 3 formed inside the casting mold receiving a molten metal 101 poured therein; an internal wall surface 2a facing the mold cavity 3; and an external wall surface 2b opposing the internal wall surface 2a, and meets a required R/A range between 0.15 and 0.3, where A is an interval between opposing straight side parts S in the internal wall surface 2a, and R is a curvature radius at a corner part C connecting the adjacent straight side part S in the internal wall surface 2a.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a mold used in a continuous casting facility for continuously producing a slab from a molten metal.

In the steel production line, in order to improve productivity, material uniformity and the like, continuous casting equipment for continuously casting from a molten metal is used.
As shown in FIG. 7, the mold forming the central element of the continuous casting equipment is an inlet of the molten metal 101 melted in the melting furnace into a mold (tube mold) 21 whose outer wall surface is cooled by a water cooling jacket. The slab 103 is poured from the outlet 21b and drawn out by the drawing roller as a cast piece 103 having a solidified shell 102 which is poured from the side 21a and solidified on the surface side.

With respect to this mold, techniques disclosed in Patent Document 1 and Patent Document 2 are known.
When the slab 103 is pulled out by the drawing roller, the solidified shell 102 is contracted by cooling and solidification, so that an air gap 31 is generated between the inner wall surface 21 c of the mold 21 and the surface of the slab 103. When the air gap 31 is generated, the cooling ability of the mold 21 with respect to the slab 103 is remarkably reduced, and the slab 103 is cooled unevenly, and a deformation defect is generated at the time of drawing. In view of this, Patent Document 1 proposes a mold having a predetermined taper ratio in which the inner wall surface gradually decreases toward the downstream side of the molten metal pass line.
Patent Document 2 discloses a mold for continuous casting of a square billet that can prevent surface vertical cracks at a slab corner, and the outer wall corner is a quadrant radius curve and the inner wall corner is chamfered linearly. Propose to do.

Japanese Patent No. 3233745 JP-A-9-271902

However, when continuous casting is performed using a conventional mold, the temperature of the corner portion of the slab is remarkably lowered, and there is a problem that the corner portion is easily cracked. In addition, after casting, the steel sheet is processed into a bar steel, a shaped steel, and the like through a rolling process, but once the temperature of the corner portion is lowered, it is necessary to heat up to a necessary temperature including the part before the rolling process.
This invention is made | formed based on such a subject, and it aims at providing the casting mold for continuous casting which can suppress the temperature fall of the corner part of a slab.

  The continuous casting mold of the present invention made for this purpose has a hollow cavity into which molten metal is poured, an inner wall faced to the cavity, and an outer wall surface facing the inner wall surface, A mold for obtaining a square billet by continuous casting, where A is the interval between the straight sides facing each other on the inner wall surface, and R is the radius of curvature at the inner wall surface of the corner portion connecting adjacent side straight portions. / A satisfies 0.15 to 0.3.

The continuous casting mold of the present invention is suitable for use in obtaining a square billet made of carbon steel.
Moreover, the casting mold for continuous casting of the present invention is suitable for casting of a square billet in which the distance A between the straight sides facing each other is in the range of 100 to 200 mm.
Further, in the continuous casting mold, it is preferable that the inner wall surface has a curved surface satisfying y = k ₂ x ² + c ₂ x... (1) so that the taper rate gradually decreases toward the downstream side of the molten metal pass line. .
However, x is a coordinate position in the longitudinal direction when the peripheral edge of the outlet of the mold is the origin, and y is a direction along the opening surface of the outlet when the peripheral edge of the outlet is the origin. The coordinate positions, k ₂ and c ₂ are constants.

  According to the present invention, by satisfying R / A of 0.15 to 0.3, it is possible to suppress the temperature drop of the corner portion of the slab. For this reason, it is possible to suppress the occurrence of cracks in the corner portion of the slab, and in order to provide for rolling performed after casting, the slab can be directly conveyed to the rolling mill without heating including the corner portion.

The casting mold for continuous casting in the present embodiment is shown, (a) is a partial cross-sectional side view, (b) is a transverse cross-sectional view, and (c) is a diagram for explaining parameters of equation (1). The casting_mold | template of this Embodiment with which it uses for continuous casting is shown, (a) is a partial cross section side view, (b) is a cross-sectional view, (c) has shown the result of 1st Example. It is a figure referred when explaining the reason for which the result of the 1st example is obtained. The partial cross section of the casting_mold | template used for 2nd Example is shown, (a) shows this embodiment, (b) shows the comparative example 1, (c) shows the comparative example 2. FIG. It is a figure which shows the result of 2nd Example. It is a figure showing the range to which this invention is applied to a Fe-C type | system | group equilibrium diagram. It is a figure which shows the continuous casting which uses a tube mold.

Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.
A mold (tube mold) 1 in the present embodiment is for obtaining a square billet by continuous casting. As shown in FIG. 1, the mold (tube mold) 1 is provided inside the tube mold 2 and the tube mold 2, and melted during casting. And a hollow cavity 3 into which 101 is poured. The tube mold 2 includes an inner wall surface 2a that defines the cavity 3, and an outer wall surface 2b that faces the inner wall surface 2a. A water cooling jacket (not shown) is provided on the outer wall surface 2 b of the tube mold 2. The cavity 3 has an inlet 2c into which the molten metal 101 is poured at the upper end, and an outlet 2d at which the molten metal 101 that has been poured is pulled out while being cooled.
The tube mold 2 is usually made of copper or a copper alloy in consideration of thermal conductivity.

The tube mold 2 has a taper shape in the longitudinal cross section so that the inner wall surface 2a has a smaller opening area toward the downstream side of the pass line of the molten metal 101 (lower side in FIG. 1).
The tube mold 2 includes four equal-length straight side portions S and a corner portion C that connects the adjacent straight-side portions S and S, and has a square outer cross section. Part C is rounded. In addition, as shown in FIG.1 (b), the space | interval of the inner wall surfaces 2a and 2a of the right side part S which opposes is set to A (henceforth a mold size A), and the curvature radius of the said corner part is set to R. To do.

The mold 1 mainly manufactures a square billet having a size of 100 mm square to 200 mm square, and for that purpose, the mold size A of the tube mold 2 is set to match the dimensions of each billet.
The length L in the axial direction of the tube mold 2 is appropriately set according to the mold size A, the casting speed, etc., but is selected from the range of 500 to 1000 mm, for example.
Moreover, the tube mold 2 is formed with a constant wall thickness in the transverse and longitudinal sections.

When continuously casting using the mold 1, the molten metal 101 is poured into the cavity 3 as shown in FIG. 2A in a state where the lower end portion (the outlet 2 d) of the tube mold 2 is sealed. When a predetermined amount of the molten metal 101 accumulates in the cavity 3 and the molten metal 101 in contact with the inner wall surface 2 a is cooled to form the solidified shell 102, the lower end is unsealed and the solidified shell 102 covers the periphery. The broken slab 103 is pulled out through the outlet 2d.
Usually, since the molten metal 101 is solidified and contracts, an air gap G is formed between the solidified shell 102 of the slab 103 and the inner wall surface 2 a of the tube mold 2.

  When casting using the mold 1 as described above, in the corner portion C of the tube mold 2, the molten metal 101 is cooled from the right side portions S on both sides connected to the corner portion C. The solidification progresses more rapidly than the above, and the temperature of the solidified shell 102 (slab) in that portion is significantly lowered. Therefore, cracks are likely to occur in the corner portion C of the slab. Moreover, in order to use for the rolling performed after casting, it is necessary to heat in order that the corner part C where temperature fell may be made into a temperature comparable as another part.

[First embodiment]
The mold 1 of the present embodiment proposes to suppress the temperature drop of the corner portion C by setting the radius of curvature R of the corner portion C in the inner wall surface 2a of the tube mold 2 within a predetermined range. Specifically, when the mold 1 satisfies the range of R / A of 0.15 to 0.3, the difference in the amount of heat extracted from the slab at the corner portion C and the straight side portion S is suppressed, and the corner portion C As compared with the straight side S, it is possible to prevent the temperature from being significantly lowered. It is assumed that R / A satisfies 0.15 to 0.3 over the entire length L of the tube mold 2.
FIG. 2C shows the result of evaluating the relationship between R / A and the temperature difference ΔT by simulation. The temperature difference ΔT is the difference between the surface temperature Tc at the center of the corner portion C and the surface temperature Ts at the center of the straight side portion S shown in FIG. Moreover, continuous casting was performed using the mold 1 having the same specifications as the simulation, and an actual machine evaluation for observing the corner portion C was performed.

The specifications of the mold 1 are as follows, and the R / A was changed by changing the radius of curvature R of the corner portion C while keeping the mold size constant.
Mold size (A x A): 143 x 143mm
Corner radius (R): 30mm
Mold length (L): 800 mm (distance from hot water surface 101a to outlet 2d is 700 mm)
Casting speed: 2.9 m / min Steel type: Carbon steel (JIS SD345)

  As shown in FIG. 2C, the temperature difference ΔT varies depending on R / A, and the temperature difference ΔT is reduced within the range of R / A = 0.15 to 0.3 recommended by the present embodiment. Results were obtained. On the other hand, as shown in FIG.2 (c), according to actual machine evaluation, when R / A was smaller than 0.15, the crack was observed.

As described above, the reason why the temperature difference ΔT is small in the range of R / A = 0.15 to 0.3 is not clear, but the present inventors speculate as follows. Yes.
First, when the radius of curvature R of the corner portion C is small, as shown in FIG. 3A, the surface of the slab in contact with the straight side portion S of the tube mold 2 is long, and the air gap accompanying the thermal contraction of that portion. The amount of G concentrates on the corner portion C. Therefore, the heat extraction capability at the corner portion C is reduced, and the temperature difference (ΔT) between the center of the straight side portion S and the corner portion C is increased. In addition, the arrow has shown the direction of shrinkage | contraction, and FIG.3 (b) is also the same.
Next, when the radius of curvature R of the corner portion C is large, as shown in FIG. 3B, the slab becomes close to a circle, and therefore when the slab contracts, it contracts toward the center of the slab. As the amount of air gap G increases, the temperature gap (ΔT) increases.
From the above, the preferable lower limit value of R / A is 0.175, and the more preferable lower limit value is 0.2. Moreover, the preferable upper limit of R / A is 0.275, and a more preferable upper limit is 0.25.

[Second Embodiment]
Next, the temperature distribution of the slab 102 in the direction from the molten metal surface 101a toward the outlet 2d was evaluated by simulation. The specifications of the tube mold 2 used for the evaluation are as follows. Comparative Example 1 is obtained by reducing the radius of curvature R of the corner portion C, and Comparative Example 2 is the corner portion C of Comparative Example 1. This is a chamfered side of the inner wall. Further, the distance from the molten metal surface 101a to the outlet 2d, the casting speed, and the steel type used for casting are the same as in the first embodiment. It should be noted that the temperature distribution is such that the distance from the hot water surface (meniscus) 101a at the center of the cross section to a position at a distance of 700 mm (outlet 2d) and the center of the corner C (Tc in FIGS. 4A and 4B). (Position) or the center of the chamfer (position Tc in FIG. 4 (c)) was obtained for two different parts from the molten metal surface 101a to a position at a distance of 700 mm.

[Tube mold specification]
This embodiment: R / A = 0.21 (FIG. 4A)
Mold size (A x A): 143 x 143 mm
Corner radius (R): 30mm
Comparative Example 1: R / A = 0.07 (FIG. 4B)
Mold size (A x A): 143 x 143mm
Corner radius (R): 4mm
Comparative Example 2: R / A = 0.07 (FIG. 4 (c))
Mold size (A x A): 143 x 143mm
Corner radius (R): 4mm
Chamfer: 20mm

The results are shown in FIG. 5. In this embodiment and Comparative Examples 1 and 2, the central portion is the same at a molten metal temperature of about 1000 ° C. from the molten metal surface 101 a to a distance of 700 mm. However, at the same height position, the temperature difference between the corner portion C and the central portion is as follows, and it can be seen that the temperature difference when the tube mold 2 according to the present embodiment is used is the smallest.
This embodiment: 120 ° C.
Comparative Example 1: 500 ° C
Comparative Example 2: 200 ° C

  As described above, according to the present embodiment, the temperature drop of the corner portion C can be suppressed. Therefore, it is possible to suppress the occurrence of cracks in the corner portion C of the slab. Moreover, in order to use for the rolling performed after casting, it can convey directly to a rolling mill, without performing the heating including the corner part C. FIG.

As described above, the present invention has been described based on the embodiments. However, the configuration described in the above embodiments may be selected or changed to other configurations as appropriate without departing from the gist of the present invention. is there.
For example, as long as the tube mold 2 has a condition of R / A = 0.15 to 0.3, there is basically no other restriction, but in order to obtain the effect of this embodiment more remarkably. In addition, it is preferable that the inner wall surface 2a of the tube mold 2 has a curved surface satisfying y = k ₂ x ² + c ₂ x... (1) so that the taper rate gradually decreases toward the downstream side of the molten metal 101. . Thereby, by adjusting the interface position of the molten metal 101 in the mold 1 according to the manufacturing conditions, a slab is always manufactured with an optimum taper rate, and an air gap between the inner wall surface 2a of the tube mold 2 and the slab. However, it is always minimized, the cooling efficiency for the slab is greatly improved, deformation of the slab due to non-uniform cooling is prevented, and the drawing resistance of the slab is reduced, thereby facilitating drawing.
y = k _{2 ·} x ² + c _{2 ·} x (1)
However, in equation (1), as shown in FIG. 1 (c), x is the coordinate position in the longitudinal direction when the peripheral edge of the outlet 2d is the origin, and y is the origin of the peripheral edge of the outlet 2d. In this case, the coordinate positions in the direction along the opening surface of the outlet 2d, k ₂ and c ₂ are constants.

Moreover, although 1st Example and 2nd Example demonstrated above are specific steel types (JIS SD345), this invention is applicable to other steel types.
In the steel material to which the present invention is applied, the alloy element that most affects the mechanical properties is carbon (C). Here, the average temperature of the solidified shell relevant to the present invention is 1000 ° C. The carbon content of the steel material targeted by the present invention is mainly 0.4% by mass or less, and the structure of these steel types at 1000 ° C. is consistent with the main point being austenite. Therefore, it can expand | deploy to other steel types, especially carbon steel whose carbon amount is 0.4 mass% or less. This range is represented in an Fe—C equilibrium diagram as shown in FIG.

Next, the first embodiment and the second embodiment described above are performed for a specific mold length L, but the present invention is a tube mold 2 that adopts a mold length L different from that of the embodiment. Can be applied to.
In the continuous casting machine, the thickness of the solid portion (solidified shell) at the outlet 2d is about 10 mm. This is the thickness necessary to maintain a stable shape against the static pressure of the molten steel. If the casting speed is decreased, the solidified shell becomes thicker, but such a situation is avoided because the productivity is reduced. Therefore, even if the mold length L and the casting speed are changed, the solidified shell thickness is operated to be the same, so that the generated air gap amount is the same. Therefore, the effect of the present invention can be obtained regardless of the length of the mold length L and the slow casting speed.
Further, referring to the mold size A, when the mold size A increases, the amount of heat supplied from the molten metal to the tube mold 2 increases, and therefore the casting speed tends to decrease accordingly. However, in the mold size A in the range of 100 to 200 mm, particularly 120 to 150 mm, which is the main object of the present invention, it is understood that the heat amount and the casting speed associated therewith are not greatly changed with respect to the first embodiment. The
Further, in the above description, a square type mold, in which the mold sizes A of the four straight side portions S are equal, has been described. However, the present invention also holds for a rectangular type mold. In the case of a rectangular mold, assuming that the mold size on the short side is A ₁ and the mold size on the long side is A ₂ , the equivalent side length = 2A ₁ · A ₂ / (A ₁ + A ₂ ) , R / E is in the range of 0.15 to 0.3.

DESCRIPTION OF SYMBOLS 1 Mold 2 Tube mold 2a Inner wall surface 2b Outer wall surface 2c Inlet 2d Outlet 3 Cavity 21 Mold 21a Inlet 21b Outlet 21c Inner wall 101 Molten metal 101a Molten surface 102 Cast piece 103 Solidified shell A Mold size C Corner part R Curvature radius S Straight side Tc Surface temperature Ts Surface temperature

Claims (4)

A hollow cavity into which the molten metal is poured is formed inside,
An inner wall facing the cavity and an outer wall facing the inner wall, and a mold for obtaining a square billet by continuous casting,
In the inner wall surface, the interval between the straight sides facing each other is A,
If the radius of curvature of the inner wall surface of the corner portion connecting the adjacent straight side portions is R,
R / A satisfies 0.15 to 0.3,
A casting mold for continuous casting characterized by the above. Used to obtain the square billet made of carbon steel,
The continuous casting mold according to claim 1. The A is in the range of 100 to 200 mm.
The continuous casting mold according to claim 1 or 2. In order for the inner wall surface to have a taper ratio that gradually decreases toward the downstream side of the molten metal pass line,
y = k ₂ x ² + c ₂ x... curved surface satisfying the formula (1)
The continuous casting mold according to any one of claims 1 to 3.
However, in Formula (1), x is the coordinate position in the longitudinal direction when the peripheral edge of the outlet of the mold is the origin, and y is the outlet of the outlet when the peripheral edge of the outlet is the origin. The coordinate positions k ₂ and c ₂ in the direction along the opening surface are constants.

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