JP3373313B2 - Mold for continuous billet casting - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a billet having a small rhombus deformation.
The present invention relates to a mold used in a continuous casting method for a cast . 2. Description of the Related Art When a billet is continuously cast, FIG.
As shown in FIG. 7, molten steel 51 is poured from the upper tundish into a mold 50 having an approximately square inner cross section and vertically oscillating, absorbing heat from the water-cooled side of the mold 50 and solidifying on the inner surface of the mold. The shell 52 was formed and gradually pulled out, and the molten steel in the core was gradually solidified to form a billet. The inner surface of the mold and the solidified shell 52
In order to achieve lubrication, repseed oil (an example of lubricating oil) was injected little by little from the top of the mold 50, and the repseed oil was carbonized as a lubricant. However, when the billet is cast at a high speed (for example, 3 m / min), the gap between the solidified shell 52 and the mold 50 is not uniform on the four outer peripheral surfaces of the billet. This caused a difference in solidification shrinkage due to non-uniform cooling, resulting in a rhombic deformation in the cross section of the resulting product. Therefore, in the conventional method for continuous casting of billets, since the operation is performed within the range of the speed at which the diamond-shaped deformation is allowed, there is a problem that the casting speed is relatively low and the productivity is poor. On the other hand, in continuous casting of a slab having a rectangular cross section, as shown in Japanese Patent Publication No. 57-11735, a large number of concave portions having a width or a diameter of 2.5 mm or less are uniformly formed on the entire surface or a part of the inside of a mold. Provision is made for a continuous casting mold aimed at preventing defects such as vertical cracks and sticking of the slab, but when this technology is applied to continuous casting of billets, the diameter of the concave portion becomes 2.5 mm. Because of the following, it was found that there was a problem that carbon powder as a lubricant gradually clogged in the concave portions, making it difficult to perform stable casting. The present invention has been made in view of such circumstances, and a method of continuous casting of a billet capable of high-speed stable casting without causing rhombic deformation of the billet.
It is intended to provide a template for use in the method . [0004] A first aspect of the present invention is to meet the above object.
The mold used for the continuous casting method of the billet described above is vertically oscillated, the molten metal is injected from the top and a small amount of lubricating oil is injected to continuously cast the billet. Is a linear taper that gradually decreases downward, and an air gap portion formed of one or a plurality of lateral grooves is formed on four inner surfaces of the mold within 200 mm below the lowermost position of the meniscus in a steady operation state. Each of the lateral grooves has an average air gap depth of 20 μm or more, and has a vertical width (W).
Satisfies the following equation. 3 mm ≦ W ≦ (oscillation amplitude of mold) × 2 + 10 mm (1) The method according to claim 1 is used for the continuous casting method of billets.
200m from the bottom of the meniscus
Since the air gap portion comprising one or more lateral grooves is provided substantially uniformly on the inner surface of the mold within m, a gap is forcibly formed between the billet and the mold. Since the inner surface of the mold has a linear taper that gradually decreases downward, the eccentricity of the billet in the mold is prevented, and the heat flux is reduced substantially evenly. Only the mold is in close contact with the mold and is not unevenly cooled. As a result, the solidified shell shrinks substantially uniformly, and a billet with less rhombus deformation can be produced even at high speed casting. Hereinafter, the operation of the present invention will be described in detail. A position 200 mm below the lowermost position of the meniscus
In the range, the heat flux extracted from the molten metal to the mold is the largest. The magnitude of this heat flux mainly depends on the air gap between the solidified shell and the mold, and the relationship is shown in FIG. By the way, in the conventional continuous casting of billets, due to the gap between the billet and the inner surface of the mold, eccentricity of the billet occurs, whereby the air gap between the mold and the solidified shell becomes uneven between the faces of the billet, Due to the air gap deviation Δd ₁ , a deviation ΔQ ₁ occurs in the heat flux between billet surfaces. As a result, imbalance occurs in the solidification shrinkage of the billet side surface, and a diamond-shaped deformation occurs in the product. FIG. 1 shows the result of an experiment to determine the relationship between the heat flux deviation between billet surfaces and the rhombus deformation. From this graph, in order to keep the rhombus deformation within 3 °, ΔQ ≦ 1,000,000 kcal / m ² hr. It is necessary to do. Here, as means for reducing the heat flux deviation ΔQ, (1) First, an air gap portion having an appropriate depth or more is uniformly provided below the meniscus to reduce the heat flux size to, for example, 4 million kcal / m. ^Two
hr to 3 million kcal / m ² hr.
(2) Further, there is a means for reducing the gap between the billet and the mold (for example, reducing the average air gap deviation Δd ₁ from 20 μm to 10 μm) by making the mold taper a linear and appropriate value. By using the means (1) and (2) together, the heat flux deviation between the faces of the billet is reduced, so that the billet is uniformly cooled by the mold. Therefore, high speed (for example, 3.4 m /
min), a billet with few defects is produced. By the way, as means to reduce the heat flux deviation between surfaces,
If the gap between the billet and the mold surface is set to 0, it is theoretically possible to set ΔQ to 0, but for this purpose, the mold taper must be a complex curved shape along the solidification shrinkage profile of the shell. The air gap must be completely zero due to the microscopic irregularities on the slab surface.
Is impossible in practice. It is also considered that the heat flux deviation can be sufficiently reduced only by the slow cooling effect of the artificial air gap portion. However, when the mold taper is inappropriate (for example, straight) and the eccentricity of the slab is large, Cannot reduce the heat flux deviation. Next, the slow cooling effect of the air gap portion of the groove portion is as shown in FIG. 3 according to the concave area ratio and the groove depth. About 2 to 84% of the concave area ratio is effective in preventing rhombic deformation. The recess area ratio is increased 2% less than the heat flux, as in the prior art increases the temperature deviation of the mold inner surface, 84% is exceeded and the solidified shell is reduced portion contacting the mold, the result As a result, wear on the inner surface of the mold increases, and the life of the mold is shortened. Regarding the groove depth, when the recess area ratio is several tens% or more,
At a depth of 0.1 to 0.2 mm or more, the degree of slow cooling becomes substantially constant, so that even if the groove depth is further increased, there is no substantial effect. In the conventional continuous casting, the heat flux at the lower portion of the meniscus sharply decreases as it goes below the meniscus, whereas in the continuous casting according to the present invention, FIG.
The level is substantially constant as shown by the broken line a on the left side of FIG. As a result, while the shrinkage profile of the solidified shell conventionally has a complicated curved shape b according to a rapid change in heat flux, it can be approximated to a simple linear shape as shown by a broken line c in FIG. . Therefore, by forming a linear mold taper at an appropriate angle (for example, 0.3 to 1.2% / m) on the inner surface of the mold, the gap between the billet and the mold can be easily reduced, and the slab (billet) can be formed. ) Can be reduced. [0007] The air gap 1 is formed.
Alternatively, since the two or more transverse grooves are formed within a range of 200 mm from the lowermost position of the meniscus which moves up and down in a steady operation state, a solidified shell is formed in this portion, and the molten metal and the air gap are formed through the solidified shell. As a result, the molten metal is no longer inserted, and a groove sufficiently wider than a concave portion having a width or a diameter of 2.5 mm or less described in Japanese Patent Publication No. 57-11735 can be formed. This also eliminates clogging due to carbon powder as a lubricant. FIG. 5 shows actual operation data. The air gap is formed in a range of about 15 mm from the lowermost position of the meniscus (more preferably, about 20 mm from the meniscus as shown in FIG. 6) and in a range of 200 mm. It is preferable to eliminate surface defects such as double skin and breakout, and to further increase the casting speed. When the air gap exceeds 200 mm from the meniscus,
Since the thickness of the solidified shell is large, there is almost no effect of preventing rhombic deformation. [0008] In particular, continuous casting of the billet according to claim 1
In the mold used in the method, a lateral groove (slit) having an average air gap depth of 20 μm or more is formed on the inner surface of the mold. This is because, as is clear from the data shown in FIG. 7, when the average air gap depth is smaller than 20 μm, the rhombus deformation angle becomes 3 degrees or more. When the depth of the lateral groove is 0.1 mm or more, the heat flux is stable and the rhombus deformation angle is also 1 degree or less. Therefore, it is preferable to operate in this state. The width (W) of the lateral groove is as shown in the above equation (1).
m or less, carbon powder as a lubricant is clogged in the lateral groove in the normal operation as described above, and as a result, the lateral groove disappears, and the diamond-shaped deformation angle becomes 3 degrees or more as shown in FIG. Becomes Then, as shown in FIG.
0 is oscillated up and down.
Width where the horizontal groove is always formed (x)
Becomes (W-2a). On the other hand, if the lateral groove 11 formed on the inner surface of the mold 10 is wide, the solidified shell 13 is pushed into the groove by the molten metal 12 filled inside the solidified shell 13, causing defects in the product. Furthermore,
As is clear from FIG. 8, if the value obtained by subtracting the double oscillation stroke (a) exceeds 10 mm, the rhombus deformation angle becomes 3 degrees or more, so that it is determined as in the above equation (1). For example, a billet having a rhombus deformation angle of 3 degrees or less can be continuously cast. Considering the case where the air gap portion is formed by a vertical groove, the vertical groove is formed continuously on the inner surface of the mold in the direction of travel of the solidified shell.
By the continuous insertion of the solidified shell pressed by the molten metal, the longitudinal grooves are transferred to the billet surface, and as a result, the surface properties of the slab are significantly impaired, and the surface cracks of the billet slab, or cracks during rolling, etc. Prone to product defects. Further, at the time of high-speed casting, there is a problem that a breakout occurs from a solidification delay portion corresponding to the vertical groove below the mold. On the other hand, the method for continuously casting billets according to claim 1
In the mold used in (1) , since the air gap is formed by the lateral groove as described above, these shapes are not transferred to the billet surface, and the above-described defects do not occur. Next, an embodiment of the present invention will be described with reference to the accompanying drawings to provide an understanding of the present invention. Here, FIG. 10 is a cross-sectional view of a mold used for continuous casting of a billet according to one embodiment of the present invention, FIG. 11 is a partial perspective view of the same, FIG. 12 is a detailed view of the same part, FIG.
14 is a graph showing the surface temperature deviation between the mold according to the embodiment and the conventional mold, FIG. 15 is a graph showing the temperature deviation between the mold according to the embodiment and the corner according to the conventional example,
FIG. 16 is an explanatory diagram of usable areas of the mold according to the embodiment of the present invention and the mold of the conventional example. As shown in FIGS. 10 to 12, a mold 15 used for continuous casting of a billet according to one embodiment of the present invention has a mold taper of 0.6% / m and an upper inner periphery of 13%.
It is a square of 3 mm × 133 mm, and the distance h from the upper end of the mold 15 to the lowermost position M of the meniscus formed in a steady state (hereinafter, simply referred to as meniscus) is about 100 m.
m. And the distance g from the meniscus M
(= 20 mm) at a pitch p (= 25 mm), a width W (= 12 mm), a length k (= 70 mm), and a depth d
An air gap portion 17 composed of three (= 1 mm) lateral grooves 16 is formed (see FIG. 13). Using this mold 15, continuous casting of molten steel having the components and properties shown in Table 1 was performed to produce a billet of 130 mm square. [Table 1] FIG. 14 and FIG. 15 show the results of measuring the temperature deviation (maximum temperature-minimum temperature) between the central surface and the corner portion of the mold copper plate about 150 mm from the upper end of the mold 15. (A mold with no part formed), as shown in the figure,
It can be seen that the temperature deviation of the embodiment (A) is smaller than that of the mold (B) according to the conventional example. As a result, FIG.
As shown in FIG. 0, the deviation of the gap between the mold 15 and the solidified shell 18 was reduced, the uneven cooling of the four surfaces of the solidified shell 18 was alleviated, and the rhombic deformation of the billet was reduced (1 degree or less). Also, since the solidified shell 18 is sufficiently formed in the air gap portion 17, even when the solidified shell 18 is pushed by the molten steel 19, the solidified shell 18 does not bite into the lateral groove 16 and can be used for a long time. However, no clogging occurred due to carbide of repseed oil, which is an example of the lubricating oil injected from the upper part of the mold 15. Table 2 shows the frequency of rhombic deformation when the groove depth (d), the concave area ratio, the groove width (W), the width (A), and the groove pitch (p) are variously changed. Even in the case of, it shows that it is good. [Table 2] FIG. 16 shows a comparison between a case where a billet is manufactured using the mold shown in the above-mentioned embodiment and a case where a billet is manufactured using the mold according to the conventional example. It can be seen that the use of the mold according to the example has a smaller rhombus deformation angle of 1 degree or less even in the high-speed casting region. In the above embodiment, the linear taper is one step, but the present invention is applicable to a two-step taper or a multi-step taper. The method for continuously casting billets according to claim 1
In the mold used in the above method, a billet with less rhombus deformation can be manufactured even by high-speed casting, and the productivity of high-quality products is improved. In addition, due to the slow cooling by forming the air gap portion, the service life of the mold is greatly extended, and the occurrence of depression (dent deformation) can be prevented.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing a relationship between a heat flux deviation between billet surfaces and a rhombus deformation angle. FIG. 2 is a graph showing a relationship between an average air gap depth and a heat flux. FIG. 3 is a graph showing a relationship between a lateral groove and a heat flux. FIG. 4 is an explanatory diagram of a generation state of a solidified shell. FIG. 5 is a graph showing a relationship between a groove formation start position and a slab surface defect occurrence rate. FIG. 6 is an explanatory view showing an air gap (recess) adding position; FIG. 7 is a graph showing a relationship between an average air gap depth and a rhombus deformation angle. FIG. 8 is a graph showing a relationship between a groove width and a rhombus deformation angle. FIG. 9 is an explanatory view of oscillation of a mold. FIG. 10 is a sectional view of a mold used for continuous casting of a billet according to one embodiment of the present invention. FIG. 11 is a partial perspective view of the same. FIG. 12 is a detailed view of the same part. FIG. 13 is an enlarged view of the same part. FIG. 14 is a graph showing the surface temperature deviation between the mold according to the example and the mold according to the conventional example. FIG. 15 is a graph showing the temperature deviation between the corners of the mold according to the embodiment and the mold according to the conventional example. FIG. 16 is an explanatory diagram of usable areas of a mold according to an embodiment of the present invention and a mold of a conventional example. FIG. 17 is an explanatory view of a mold according to a conventional example. [Description of Signs] 15: Mold used for continuous casting of billet, 16: lateral groove, 17: air gap, 18: solidified shell, 19:
Molten steel, M: meniscus

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Toshiki Sato 46-59, Ohara Nakahara, Tobata-ku, Kitakyushu-shi, Fukuoka Nippon Steel Corporation Machinery & Plant Business Department (72) Inventor Teruo Fujinaga Yamauchi-machi, Kishima-gun, Saga Prefecture 11125, Tsubakihara, Kojiyu, Kyushu Steel Co., Ltd. (72) Inventor Nakao Temporary, Tsubakihara, Kunishima, Kyushu Steel Co., Ltd. (125) Reference: JP-A-6-297103 (JP, A) JP-A-6-304710 (JP, A) JP-A-6-297101 (JP, A) JP-A-2-70358 (JP, A) JP-A-2-20645 (JP, A) JP-A-51-50819 (JP, A) JP-A-57-124555 (JP, A) JP-A-61-92756 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B22D 11 / 04 311 B22D 11/16 105

Claims (1)

(57) [Claim 1] In a mold having an approximately square inner cross section, which is vertically oscillated, injects a molten metal from an upper portion and injects a small amount of lubricating oil to continuously cast a billet. The inner surface is a linear taper that gradually decreases downward, and further, an air gap portion formed of one or a plurality of lateral grooves on four inner surfaces of the mold within 200 mm below the lowermost position of the meniscus in a steady operation state. And an average air gap depth of the lateral groove is 20 μm or more, and a vertical width (W) thereof satisfies the following expression. 3mm ≦ W ≦ (oscillation amplitude of mold) × 2 + 10mm