JPH07314095A - Mold for horizontal continuous casting - Google Patents

Abstract

PURPOSE:To obtain a mold for horizontal continuous casting which prevents rhombic deformation and internal crack of a cast billet, by arranging parallel grooves in the drawing-out direction at the lower surface of a square mold. CONSTITUTION:The plural parallel grooves are arranged in the drawing-out direction at the lower surface in the inner surface of the mold 1 for horizontal continuous casting of the square billet. Further, the arranged position of the grooves can be arranged in the whole range or a part of 1/ 2 from the lower part in the vertical surface containing the lower surface and the corner part of the lower surface not only the lower surface in the inner surface thereof. The starting point of the grooves is situated in the interval (b) between a position exceeding the drawing-out length (a) from a triple point (T) mutually contacting with the mold 1, brake ring 2 and molten steel 4 and a position (a+b) of 3/5 of the length (a+b+c) from the triple point (T) to the outlet of the mold, and the end point thereof is situated at the outlet of the mold. By this method, the rhombic deformation of the cross sectional shape is reduced, and the corner longitudinal crack and the internal crack at off-corner part can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a horizontal continuous casting mold for a square billet which is cast with two surfaces horizontal.

[0002]

2. Description of the Related Art In recent years, a horizontal continuous casting method (hereinafter referred to as a horizontal continuous casting method) has a lower height in terms of equipment than a conventional vertical continuous casting method, and it is necessary to remodel an existing building. There is no equipment cost, (2) The secondary oxidation of molten steel is small because the tundish and mold are directly connected by the connecting refractory material, and (3) Bulging is less likely to occur because the static pressure of molten steel is low and constant. And (4) maintenance and inspection are easy, and it is rapidly developing. In the horizontal continuous casting method, the molten steel flowing from the tundish into the mold is
It is cooled on the inner surface of the mold to form a solidified shell, which is withdrawn intermittently.

When the mold of the present invention has a rectangular cross-section and casting is performed with the two surfaces being horizontal, the molten steel static pressure acting on the thin solidified shell in the mold becomes maximum at the lower surface, and conversely. Since it is the smallest on the upper surface, the contact between the slab surface on the lower surface and the mold surface is better than the contact between the other surface and the mold surface, and as a result, the heat removal amount of this lower surface is larger than the heat removal amount of the other surface. The solidified shell grows faster than the other surface. Further, the surface contact between the cast piece and the mold becomes good due to the weight of the cast piece, and the amount of heat removed from the lower surface tends to increase. On the other hand, the temperature of the molten steel flowing into the mold varies depending on the position, and due to the effect of natural convection, the temperature of the molten steel flowing into the lower surface of the mold is generally low. For the above reasons, the solidified shell in the mold has a phenomenon that the lower surface grows faster and the upper surface grows later. The nonuniform growth of the solidified shell induces nonuniform thermal stress, which promotes the diamond-shaped deformation of the billet, the occurrence of internal cracks and surface defects, and, in a remarkable case, breakout.

In order to suppress the above-mentioned non-uniform solidification, a mold cooling method (JP-A-56-1140 and JP-A-57-140).
No. 25259), slab position control method (JP-A-60-250).
No. 858, JP-A-63-256241, and a method for adjusting the thickness of the mold (JP-A-56-11114, JP-A-56-56).
11142) and a method of grooving the inner surface of the mold (JP-A-4-200957).

[0005]

SUMMARY OF THE INVENTION
In the method of 6-11141, since the thickness of the lower surface portion and the corner portion of the mold is thicker than the upper portion, there is a drawback that surface defects and breakouts easily occur due to delay in solidification of the lower surface portion, Further, on the lower side, solidification of the corner portion progresses preferentially over the surface portion, so that there is a drawback that rhombic deformation is likely to occur. In the method disclosed in Japanese Patent Laid-Open No. 56-11142, only the upper constituent wall of the mold is tilted to suppress the formation of the air gap in the upper part, but this tilt causes a large resistance to the extraction of the slab and the solidified shell. It is liable to cause breakage and surface defects of the mold and requires a great deal of labor and cost to process and maintain the mold. In addition, Japanese Patent Laid-Open No. 4-2
In No. 00957, the groove is provided from the triple point to the mold outlet from within the drawing stroke, and since the molten metal flows into the groove, the cast piece surface has a shape in which the groove projects.
Since the slab comes out along the groove of the mold, heat removal inside the mold becomes large on the lower surface, and there is little effect of preventing rhombus deformation and internal cracking.

As described above, in the above-mentioned horizontal continuous casting mold, there is a problem that rhombic deformation, internal crack surface defects and breakout are caused because of delay in generation of solidified shell and increase in drawing resistance. An object of the present invention is to control rhombus deformation of a slab by controlling solidified shell growth of a vertical surface including a lower surface in a mold and corners of the lower surface in a square billet horizontal continuous casting in which casting is performed with two surfaces horizontal. A mold for horizontal continuous casting capable of preventing internal cracking.

[0007]

A first aspect of the present invention is a horizontal continuous casting mold for a square billet which is cast with two surfaces horizontal, wherein a mold is formed on the lower surface of the inner surface of the mold. From the triple point where the break ring and molten steel are in contact with each other, the starting point is between the position exceeding the length of the drawing stroke and the position of ⅓ of the length from the triple point to the mold outlet, and the mold outlet is the end point. Is a mold for horizontal continuous casting characterized by having a plurality of grooves parallel to the drawing direction, and the second invention is a mold for horizontal continuous casting of a square billet which performs casting with two surfaces being horizontal. Then, the mold, the break ring and the molten steel are in contact with each other in the whole range or a part of the lower half of the lower surface of the inner surface of the mold and the vertical surface including the lower corner portion. From the point of importance, a groove having a starting point between a position exceeding the length of the drawing stroke and a position of ⅕ of the length from the triple point to the mold outlet and parallel to the drawing direction with the mold outlet as the end point. It is a mold for horizontal continuous casting characterized by having a plurality of.

[0008]

1 is a vertical sectional view of the periphery of a mold of a horizontal continuous casting apparatus according to the present invention. The starting point of the groove, which is a feature of the present invention, is from the triple point (T) where the mold 1, the break ring 2 and the molten steel 4 of FIG. 1 are in contact with each other, from the position beyond the length a of the drawing stroke and the triple point (T). Position (a) at a third of the length (a + b + c) to the mold outlet
+ B) and b. 2 and 3 are similar to FIG.
FIG. 9A is a sectional view taken along line AA of FIG. According to the present invention, by providing a groove on the lower surface of the inner surface of the mold, the heat removal ability of the above-mentioned region is lowered, and as a result, the solidification rate is delayed despite the good adhesion between the mold and the solidified shell. Therefore, the thermal stress due to preferential solidification is relieved, and the rhombic deformation is reduced. Desirably, it is possible to control the solidification rate near the lower corners,
For the purpose of preventing rhombus deformation, it is preferable to provide a groove on the lower surface of the inner surface of the mold, and further provide a groove on the whole or a part of one half of the vertical surface including the lower corner portion from the lower side.

In the range of ½ or more of the vertical surface of the inner surface of the mold, the solidification of the lower surface and the lower side surface is delayed, and not only the frequency of breakout increases, but also the deformation of the slab becomes large. It is preferable that the range in which is provided is half or half of the entire vertical plane.
This reduction of rhombus deformation is due to the off-corner of the obtuse corner of the slab.
It has an effect of preventing internal cracks of the slab called internal cracks, especially due to deformation stress or thermal stress concentrated near the corners, and vertical corner cracks. Here, the groove is shown in FIG.
From the triple point (T) where the mold, the break ring and the molten steel contact each other as shown in FIG. 3, the starting point is between the position exceeding the length of the drawing stroke and the position of ⅕ of the length from the triple point to the mold outlet. And a groove parallel to the drawing direction with the mold outlet as the end point.

If the starting point of the groove is within the length of the drawing stroke from the triple point, the phenomenon of perspiration from the surface of the solidified shell is likely to occur, causing surface defects. Further, the molten metal will flow into the groove more frequently, and in this case, the above effect cannot be expected. Further, when the starting point of the groove exceeds the position of 3/5 of the length from the triple point to the outlet of the mold, the rhombic deformation has already progressed, and this deformation causes an increase in the frequency of internal cracking, resulting in no effect. . Therefore, the starting point of the groove is between the triple point and the position exceeding the drawing stroke length and the position of ⅓ of the length from the triple point to the mold outlet. The preferred origin of the groove is between the triple point and the position of 2.5 times the length of the drawing stroke and the position of 3/5 of the length to the mold exit. The groove may be substantially parallel to the drawing direction, and the effect can be obtained as long as the depth of the groove does not directly contact the surface of the cast slab. Further, the plurality of grooves may be arranged at equal intervals or, if necessary, may be arranged at coarse and fine intervals. Further, the shape of the groove is not particularly limited as long as it is a trapezoidal shape, a square shape, a semicircular shape, or the like, which can be easily processed and can easily remove clogging of metal powder. The optimum conditions for groove installation are hot strength, thermal expansion coefficient,
Since there are differences in the physical property values such as thermal conductivity and the extraction conditions, it is preferable to appropriately select within the above range.

[0011]

EXAMPLES Next, examples will be described. (Example 1) The cross-sectional dimension of the inner surface of the mold is 120 mm square, the length of the mold from the triple point to the mold outlet is 300 mm,
Table 1 shows the groove installation conditions of the mold, with the mold having a corner radius of curvature of 8 mm as the basic shape.

[0012]

[Table 1]

The shape of the grooves is trapezoidal as shown in FIG. 4, all the depths are 0.5 mm, and the grooves are provided at equal intervals within the groove installation range. In Table 1, the groove installation conditions for the mold are as follows: the groove pitch on the lower surface of the mold is P _H , the pitch on the vertical surface is P _V , the distance from the corner to the center of the adjacent groove is d on the lower surface of the mold, and vertical. It is designated as e in terms of plane. Furthermore, the number of grooves and the starting points of the grooves are also shown with respect to the distance from the triple point where the mold break ring and molten steel contact each other. The steel types used for melting are JIS standards SKS3 and SKD6.
It was carried out under the same conditions with the two steel types of No. 1 and the drawing speed of 1.5 m / min and the drawing stroke of 15 mm. The shape of the slab obtained by horizontal continuous casting performed under the above conditions was evaluated by the rhomboid degree defined by the following equation.

[0014]

[Equation 1]

Casting was carried out 20 times for each mold,
The rhomboidity of the slab obtained by one slab was measured at 5 locations on an arbitrary cross section, and the rhomboidity was divided according to the size of the rhomboidity, and the frequencies are summarized in Table 2 and shown in Table 2. As is clear from Table 2, the conventional mold has a wide distribution of the rhomboidity, and the measured values of the rhomboidity of 4% or more occur at a considerable ratio of 24% in SKS3 and 22% in SKD61. On the other hand, in the mold of the present invention, it can be seen that the distribution of the rhomboidity is narrow and the value is remarkably small. Table 3 shows the occurrence ratio of off-corner internal cracks and the occurrence ratio of vertical corner cracks. As is clear from the table, by using the mold of the present invention, both cracks became almost non-existent.
This is because the main cause of these cracks is related to the rhombic deformation, so that the use of the mold of the present invention significantly suppressed the rhombic deformation.

[0016]

[Table 2]

[0017]

[Table 3]

(Example 2) The starting point of the groove was 12 mm from the triple point and 200 mm from the triple point, and SKD61 molten steel was used in Example 1 using the molds of the groove installation conditions of A and D in Table 1.
It was cast under the same conditions as. As a result, on the lower surface of the slab with the starting point of the groove 12 mm from the triple point, the scratches of the transferred groove were generated in the length direction, and the rhombic deformation was not suppressed. In addition, the slab with the starting point of the groove from the triple point to 200 mm has a wide distribution of rhomboidity, a large occurrence ratio of vertical corner cracks and off-corner internal cracks, and it is a conventional mold without grooves. No difference was observed from the results of cast Tables 2 and 3.

[0019]

According to the present invention, the rhombic deformation of the cross-sectional shape of the horizontally continuously cast slab, which was conventionally insufficient, can be significantly reduced,
Since vertical cracks in the corners and internal cracks in the off-corners can be prevented, the amount of maintenance before the rolling of the slab can be reduced, the quality of the steel material after rolling can be improved, and the yield can be improved.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view around a mold of a horizontal continuous casting apparatus, showing a starting point of a groove according to the present invention.

2 is a cross-sectional view taken along the line AA in FIG. 1, showing the positions (dotted line portions) of grooves provided on the inner surface of the mold according to the present invention.

FIG. 3 is a sectional view taken along the line AA in FIG. 1, showing the positions (dotted line portions) of the grooves provided on the inner surface of the mold according to the present invention.

FIG. 4 is an enlarged view of the lower corner side of the mold showing the embodiment of the present invention.

[Explanation of symbols]

1 mold, 2 break ring, 3 the feed tube, 4 molten steel, 5 refractories, (T) triple point, P _H underside of groove pitch, groove pitch of P _V vertical plane, the length of a drawing stroke, the b triple point Length excluding a from 3/5 of the length to the mold outlet, c Length excluding (a + b) from the triple point to the mold outlet, d Center of the first groove on the lower surface from the lower corner Distance to the center of the first groove in the vertical plane from the lower corner

Claims (2)

[Claims] 1. A horizontal continuous casting mold for a square billet, in which two surfaces are horizontally cast, wherein a lower surface of the inner surface of the mold is connected to a triple point at which the mold, the break ring and the molten steel are in contact with each other. Having a plurality of grooves having a starting point between a position exceeding the length and a position of ⅕ of the length from the triple point to the mold outlet and parallel to the drawing direction with the mold outlet as an end point. Characteristic horizontal continuous casting mold. 2. A horizontal continuous casting mold for a square billet, in which casting is carried out with two surfaces being horizontal, wherein one half of the lower surface of the inner surface of the mold and the vertical surface including the lower corner portion is located from below. Between the triple point where the mold, the break ring and the molten steel contact each other over the entire range or a part, and the position exceeding the length of the drawing stroke and the position of three-fifths of the length from the triple point to the mold exit. A mold for horizontal continuous casting, which has a plurality of grooves having a starting point at, and having a mold outlet as an end point and parallel to a drawing direction.