JPH07314094A - Mold for horizontal continuous casting - Google Patents

Abstract

PURPOSE:To prevent the deviation from the roundness, surface longitudinal crack and internal crack of a cast billet by arranging parallel grooves in the drawing-out direction on the lower half round surface in the inner surface of a round mold. CONSTITUTION:The parallel grooves are arranged in the drawing-out direction on the whole range or a part of the lower half round surface in the inner surface of the mold 1 for horizontal continuous casting, which casts the steel billet having round shape in the cross section. 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 joint (T) to the outlet of the mold, and the end point thereof is situated at the outlet of the mold. By this method, the solidifying speed can be made slow in spite of high stickiness of the solidified shell to the mold and the thermal stress caused by preceding solidification of the lower surface ie released, and the deformation from the roundness is reduced.

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 casting a slab having a round cross section.

[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It is cooled on the inner surface of the mold to form a solidified shell, which is withdrawn intermittently.

In the case where horizontal continuous casting is performed in which the cross-sectional shape of the inner surface of the mold is the object of the present invention, the static pressure of molten steel acting on the thin solidified shell in the mold becomes maximum at the lowermost portion, and conversely. Since it is the smallest at the uppermost part, the contact between the lower slab surface and the mold surface is better than the contact between the upper slab surface and the mold surface, and as a result, the heat removal amount on the lower surface side is the heat removal amount on the upper surface side. It becomes larger, and therefore the solidified shell grows faster than the upper surface side. Further, the surface contact between the cast piece and the mold becomes good due to the weight of the cast piece, and the heat removal amount on the lower surface side 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 part 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. This nonuniform growth of the solidified shell induces nonuniform thermal stress, which promotes the deformation of the roundness of the round slab, the occurrence of internal cracks and surface defects, and in the remarkable case, breakout occurs.

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 at the lowermost corner, 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 prevent deformation of circularity and internal cracking of a cast piece by controlling solidified shell growth on the lower surface side in a horizontal continuous casting mold for casting a cast piece having a round cross section. It is to provide a mold for horizontal continuous casting which can be used.

[0007]

DISCLOSURE OF THE INVENTION The present invention is a horizontal continuous casting mold for casting a slab having a round cross section, wherein the mold is formed on all or part of the lower semicircular surface of the inner surface of the mold. , The break ring and the 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 ⅕ of the length from the triple point to the mold outlet, and the mold outlet is The horizontal continuous casting mold is characterized in that a plurality of grooves, which are the end points and are parallel to the drawing direction, are provided.

[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, the position exceeding the length a of the drawing stroke and the triple point (T). It is at b between the position (a + b) and ⅓ of the length (a + b + c) to the outlet of the mold. Further, FIG. 2 shows AA of FIG.
It is a sectional view, and is a sectional view showing a position of a groove provided in an inner surface of a round mold. According to the present invention, by providing a groove on the lower semi-circular surface of the inner surface of the round mold, the heat removal capacity in the above region is reduced, and as a result, solidification is achieved despite the high adhesion between the mold and the solidified shell. The speed can be delayed, the thermal stress due to preferential solidification on the lower surface side is relieved, and the deformation of roundness is reduced. The reduction of the deformation of the roundness can reduce internal cracks and vertical cracks of the cast slab. If a groove is provided in the range beyond the lower half circle of the inner surface of the round mold, not only will the lowering of the solidification be delayed and the frequency of breakout will increase, but the roundness of the slab will also become more deformed. Limit the range to the whole or part of the lower semi-circular surface.

When the starting point of the groove is within the length of the drawing stroke from the triple point, the phenomenon of sweating from the surface of the solidified shell is likely to occur, which causes a surface defect. Further, the molten metal will flow into the groove more frequently, and in this case, the above effect cannot be expected. Furthermore, 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 deformation due to the thermal stress on the lower surface has already progressed, and this deformation causes the internal crack to occur more frequently. No effect. Therefore, the starting point of the groove is between the triple point and the position exceeding the length of the drawing stroke and the position of 3/5 of the length from the triple point to the mold outlet. A desirable groove start point is between the triple point and a position of 2.5 times the length of the drawing stroke and a 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, etc., which is easy to process and can easily remove clogging of metal powder and the like. Optimum conditions for installing the groove may be appropriately selected within the above range because there are differences in physical property values such as hot strength, coefficient of thermal expansion, and thermal conductivity, and differences in drawing conditions depending on the type of steel to be cast.

[0010]

EXAMPLES Next, examples will be described. (Example 1) The diameter of the inner surface of the mold for the round slab used for casting is 150 mm, and the length of the mold from the triple point to the outlet of the mold is 300 mm. As shown in the enlarged view of FIG. 3, the groove has a trapezoidal shape and a depth of 0.5 mm.
Further, within the groove installation range, the grooves were installed at equal intervals. On the other hand, Table 1 shows the conditions in which the pitch of the grooves, the number of the grooves, and the starting points of the grooves provided on the lower half surface of the round mold were changed with respect to the distance from the triple point where the mold, the break ring and the molten steel contact each other. The steel types used for casting were JIS SKS3 and SKD61, and both steel types were cast under the same conditions of a drawing speed of 1.4 m / min and a drawing stroke of 14 mm.

[0011]

[Table 1]

The suitability of the solidified state of the obtained cast piece was evaluated by measuring the roundness of the cast piece. The roundness of the slab was defined by the following equation. Roundness = minimum diameter / longest diameter For each of the above two steel types, casting was performed 20 times, and the roundness of the billet obtained by one casting was measured at 5 points on any cross section. The frequencies are shown in Table 2 by dividing them according to size.

[0013]

[Table 2]

As is clear from Table 2, in the conventional mold, the rate of occurrence of circularity of 0.94 or less is 29% in SKS3 and 2 in SKD61.
You can see that it is as high as 3%. In the mold of the present invention, there is no generation ratio of circularity of 0.94 or less, and it can be seen that a slab with good circularity can be cast. further,
The slab obtained under the above conditions was inspected for cracks by the dye penetrant flaw detection method while repeatedly grinding the slab surface with a grinder. Table 3 shows the results, which are shown separately for the occurrence ratios of surface vertical cracks and internal cracks. As is clear from Table 3, by using the mold of the present invention, neither surface vertical cracks nor internal cracks were present. This is because the main cause of these cracks is related to the deformation from the roundness, and the deformation of the roundness of the cast piece is suppressed by the mold of the present invention.

[0015]

[Table 3]

(Example 2) The starting point of the groove was set to 11 mm from the triple point and 220 mm from the triple point, and SKD61 molten steel was used in Example 1 using the molds having the groove installation conditions of B and E in Table 1.
It was cast under the same conditions as. As a result, on the lower surface of the slab where the starting point of the groove was 11 mm from the triple point, the scratches of the transferred groove were generated in the length direction, and the roundness could not be improved. Further, the slab with the starting point of the groove from the triple point to 220 mm has a wide roundness distribution, and has a large ratio of vertical corner cracks and internal cracks, and was cast by the conventional mold without grooves. No difference was observed from the results in Tables 2 and 3.

[0017]

According to the present invention, the deformation from the roundness of the cross-sectional shape of the horizontally continuously cast slab, which was conventionally insufficient, can be significantly reduced, and vertical surface cracks and internal cracks can be prevented. The amount of slabs before rolling can be reduced, the quality of steel products 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 an enlarged view of the lower surface side of the mold showing the embodiment of the present invention.

[Explanation of symbols]

1 mold, 2 break ring, 3 feed tube, 4 molten steel, 5 refractory, 6 groove, (T) triple point a length of drawing stroke b 3/5 of length from triple point to mold outlet a
Excluding the length c From the length from the triple point to the mold outlet (a + b)
Length excluding

Claims (1)

[Claims] 1. A horizontal continuous casting mold for casting a slab having a round cross section, wherein the mold, the break ring and the molten steel are in contact with each other in the entire range or a part of the lower semicircular surface of the inner surface of the mold. It has a starting point between the triple point and the position that exceeds the length of the drawing stroke and the position of three-fifths of the length from the triple point to the mold outlet, and is parallel to the drawing direction with the mold outlet as the end point. A horizontal continuous casting mold characterized by having a plurality of different grooves.