JP2727886B2 - Horizontal continuous casting method - Google Patents

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 method for billets or blooms, and more particularly to a method for horizontally casting a bloom or billet for hot extrusion of carbon steel, low alloy steel, stainless steel, high alloy steel, superalloy or the like. The present invention relates to a horizontal continuous casting method capable of suppressing the existence range and size of cavities and porosity generated at the center of a slab during continuous casting.

[0002]

2. Description of the Related Art Generally, in a hot extrusion pipe making method such as the Ugine-Sejournet method, the center portion is drilled at the time of pipe making. Removed, no quality problem. However, if the existing diameter of the cavity is larger than the diameter of the perforation, if the pipe is made as it is, it will cause flaws on the inner surface of the pipe,
This leads to poor quality of the tube. On the other hand, if the porosity is removed by increasing the diameter of the hole at the time of drilling in order to prevent the occurrence of a flaw on the inner surface of the pipe, the yield loss is caused by the amount of the hole and the economic efficiency is deteriorated.

[0003] Horizontal continuous casting equipment is lower in height than vertical and curved continuous casting equipment, and does not require a large slab support mechanism.
There are also advantages such as easy maintenance and inspection. For this reason, practical use has been attempted for small lots, various kinds of stainless steel, etc., for which continuous casting has been delayed. In addition, since continuous continuous casting does not require bending or straightening at high temperatures, continuous casting by this method has been further promoted in recent years for high alloy steels and Ni-based superalloys that are highly sensitive to hot cracking. I am trying to do.

However, in horizontal continuous casting, as described above, since the height of the equipment is low, the static pressure of molten steel in the vicinity of the final solidification position of the slab becomes small. It is easy to occur and the cavity tends to remain in the center. The cavity at the center tends to be generated as the sectional area or thickness of the slab or the casting speed increases, and the existing diameter of the cavity tends to increase. In addition, such as stainless steel, high alloy steel, and Ni-based superalloy, which have a lower melting point and a wider solid-liquid coexisting phase temperature range than general steel, are more likely to generate cavities. In order to solve the above-mentioned problems, Japanese Patent Laid-Open No. 57-75258 discloses that at least two stages of a linear electromagnetic stirrer are installed and a center porosity is prevented by moving an equiaxed crystal piece to a crater end side. A method has been proposed.

Japanese Patent Application Laid-Open No. 59-133957 discloses that at least two rotating magnetic field type electromagnetic stirrers are provided with a fixed interval determined from a slab drawing speed and a liquid core value at the rear end of the first stage electromagnetic stirrer. A method has been proposed in which sedimentation of equiaxed crystal nuclei is prevented by agitating an unsolidified molten metal, and the microcavity in the center of a slab is improved. All of these methods attempt to disperse equiaxed crystal nuclei or equiaxed crystal pieces in the unsolidified molten metal by electromagnetic stirring. However, even in such a conventional method, the porosity and the cavity at the center of the slab were not sufficiently suppressed.

[0006]

In order to solve such problems of the prior art, the present applicant has filed Japanese Patent Application No. 3-232.
As No. 660, a method was proposed in which three-stage electromagnetic stirring was performed to suppress the formation of porosity and cavities in the center of the slab. Was found.

(1) In the case where the casting speed is increased to improve the productivity, when the electromagnetic stirring is performed in three stages as in the method described above, the effect is insufficient and the center porosity or the existing diameter of the cavity is large. Therefore, there is a problem that the diameter of the perforation must be increased. This is because the unsolidified region becomes longer as the casting speed increases, and the chance of equiaxed crystal bridging increases, so that the effect of electromagnetic stirring in the final stage of solidification becomes relatively weak.

(2) Further, when the stirring intensity at the end of solidification is increased to reduce the bridging, although the center porosity or the cavity is reduced, this time, due to the strong stirring, the center porosity or the cavity is reduced. The segregation of the components became remarkable, resulting in non-uniform components in the radial direction.

Here, an object of the present invention is to provide a horizontal continuous casting method which does not have the problem of segregation in the direction of the center of the slab and has no problems of center porosity and cavity.

[0010]

The present inventor has conducted various experimental studies to solve the above-mentioned problems, and as a result, has found that the following means can solve the problems. (1) The first-stage electromagnetic stirring is performed at a position corresponding to the solidification start position in the mold. (2) The second-stage electromagnetic stirring is performed at a position where the solid phase ratio between the mold outlet and the center of the slab becomes zero. (3) On the downstream side of the electromagnetic stirring described above, from the time when the center of the slab starts to solidify, the time when the center of the slab completely completes solidification, (4) By the above method, the center porosity or the cavity can be reduced without the problem of segregation toward the center of the slab.

Here, the gist of the present invention is as follows.
When producing a billet or bloom by horizontal continuous casting, at least two stages of a rotating magnetic field type electromagnetic stirrer are arranged in series, and the first stage of electromagnetic stirring is performed at a position corresponding to a solidification start position in a mold. The electromagnetic stirring of the stage is performed between the mold outlet and a position where the solid phase ratio at the center of the slab does not exceed 0, and at the downstream side of the installation position of these electromagnetic stirring devices and at the center of the slab. Solidified on the slab surface from the point when the solid phase ratio exceeds 0 until the solid phase ratio at the center of the slab becomes 1.0
Strong cooling that can apply compression force to compensate for shrinkage
A horizontal continuous casting method characterized in that the method is performed on a slab surface .

In the present invention, the “solid fraction” is defined as
It refers to the volume ratio of the solid phase to the total volume in a certain region of the molten metal that is the solid-liquid coexisting phase. There is a one-to-one correspondence between the solid phase ratio and the temperature. The solid phase ratio is 0 above the liquidus temperature, and 1 below the solidus temperature. The distribution of the solid fraction can be calculated by actually measuring the temperature distribution in the slab or by calculating the heat transfer.

[0013]

Next, the operation of the present invention will be described in more detail with reference to the accompanying drawings. FIG. 1 is a schematic explanatory view of a horizontal continuous casting facility used in the present invention. In the figure, a molten metal 10 once stored in a tundish 4 is cooled through a mold 5 and a secondary cooling zone 6 so that a solidified shell 9 is grown and a slab 8 is formed.
Then, it is pulled out horizontally by the pinch roll (not shown) through the terminal-stage cooling device 3 (the right-hand direction in the drawing).

According to the invention, a diameter of 265 mm × length
An example of casting stainless steel at a casting speed of 1.2 m / min using a 300 mm mold will be described below. According to the present invention, the first
The electromagnetic stirrer 1 in the mold at the second stage, the electromagnetic stirrer 2 at the second stage, and the terminal cooling device 3 are provided at predetermined positions. In other words, the cooling of the molten metal and the slab is controlled based on the positions of the electromagnetic stirring devices and the terminal cooling devices.

The specifications of these electromagnetic stirrers are almost the same as those described in Japanese Patent Application No. 3-232660, for example, as shown in Table 1 below. As the electromagnetic stirrer, a commonly-used electromagnetic stirrer may be appropriately used and is not particularly limited as long as it has a required stirring ability.

The reason why the position of the first and second stages of electromagnetic stirring is defined in the present invention is as follows. First, the first-stage electromagnetic stirrer 1 has an effective electromagnetic stirring length of 200 mm, and a mold so that the molten metal 10 in the mold 5 at a position where the initial solidified shell 9 starts to be formed can be sufficiently stirred. 5 is arranged near the outer periphery.

The reason why the electromagnetic stirring is performed at the position corresponding to the solidification start position in the mold 5 is that the stirring action of the molten metal 10 is performed on the front surface of the solidified shell 9 which solidifies at the time when the cooling rate is the fastest. This is because a large number of fine equiaxed crystal nuclei can be dispersed and released in the molten metal 10 by applying.

In this example, the intensity of the electromagnetic stirring at the first stage is, for example, 1200 gauss for the center magnetic flux density and 3 for the magnetic field rotation speed.
It is obtained by applying a rotating magnetic field of Hz, but if the rotation speed is too high with a magnetic flux density higher than this, negative segregation will occur at the solidification interface, which will hinder the uniformity of the slab, which is not desirable. Next, the electromagnetic stirring device 2 of the second stage has an effective electromagnetic stirring length of 300 mm, and at the position of the electromagnetic stirring device 2, the solid phase ratio (fs) at the center of the slab is 0; Has a liquid phase-only melt.

The reason why the electromagnetic stirring position of the second stage is set between the exit of the mold and the position where the solid phase ratio at the center of the slab does not exceed 0 is that the stirring is performed during this period to remove the unsolidified molten metal. The superheat is made uniform to prevent the growth of the equiaxed crystals dispersed and liberated in the molten metal 10 to increase the particle size, and to generate new equiaxed crystal nuclei on the front surface of the solidified shell 9 to produce fine particles. This is because the number of equiaxed crystals can be increased and sedimentation of equiaxed crystals can be prevented.

On the other hand, when the solid fraction at the center of the slab 8 exceeds 0, the superheat of the molten metal 10 cannot be used and the flow resistance rapidly increases, so that the above-mentioned effects cannot be expected. .

From the time when the center of the slab 8 starts to solidify, to the time when the center of the slab 8 completes solidification, a final stage of a cooling water spray device provided for cooling the slab surface. A cooling device 3 is provided. In the illustrated example, the last-stage cooling device 3 is installed between 8.5 and 22 m from the mold inlet. In the casting conditions here, from the meniscus
The position of 8.5 m corresponds to the position where the center of the slab starts solidification, and the position of 22 m corresponds to the position where the center of the slab ends solidification.

The reason for cooling the surface of the slab in the final stage of solidification is that the surface is shrunk by cooling the surface, and as a result, a compressive force is applied to the inside of the slab, causing a cavity or porosity. The amount of coagulation shrinkage can be compensated, and the occurrence thereof can be suppressed. In contrast to the latter stage, which is effective in preventing bridging due to the coalescence of equiaxed crystals, the method according to the present invention is intended to suppress the formation of cavities or porosity itself by applying more compressive force. It is assumed that. Therefore, the cooling capacity at this time, that is, “strong cooling” in the present invention can be said to be a cooling capacity capable of applying such a compressive force.
~ 2 ° C / sec is desirable.

The starting point of the cooling is defined as the time when the solidification of the center of the slab starts, because the solidification shrinkage starts at the center of the slab from this point, and until the center of the slab is completely solidified. Since the solidification shrinkage is continued, cooling is performed during that time, and cooling is not required once solidification is completed.

[0024]

EXAMPLE Next, according to the present invention, a casting test was conducted using the horizontal continuous casting equipment shown in FIG. The results are shown in comparison with those of the comparative example. As casting conditions, diameter 26
Using a 5 mm, 300 mm long mold, the casting speed is 0.8-1.6
Changed between m / min. The first and second stages of the electromagnetic stirrers were arranged and specified as shown in Table 1.

In the last stage cooling, the solidification start and end points at the center of the slab are obtained by measuring the slab temperature, tacking test, heat transfer calculation, etc., according to the slab diameter and casting speed. Was determined. The cooling water volume at the end of the period was also changed according to the casting speed and slab diameter, and the specific water volume was 0.25 l / kg-steel.
And

As a comparative example, the casting conditions were exactly the same as those described above, except that the terminal part was not cooled.
The last stage magnetic stirring shown in No. 2660 was performed. FIG. 2 shows the change of the center porosity or the existing diameter of the cavity at each casting speed in comparison with the present invention example and the comparative example.

Although the diameter of the center porosity cavity increases with an increase in the casting speed, the diameter of the center porosity cavity is small in the case of the method of the present invention.
Even at 23 mm and a casting speed of 1.6 m / min, the value is as low as about 23 to 30 mm. On the other hand, in the case of the comparative example, it is 28 to 33 mm at a casting speed of 0.8 m / min, and 46 to 54 mm at a casting speed of 1.6 m / min. Therefore, it can be understood from these results that the effect of the present invention is remarkable.

[0028]

[Table 1]

[0029]

According to the present invention, it is possible to suppress the formation of the center porosity or the cavity, which is a serious problem in the slab of horizontal continuous casting. In addition, even under a wide range of casting conditions, the center porosity or the existing diameter of the cavity can be reduced to a range smaller than the diameter of the hole bored during the production of Eugene.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view of a horizontal continuous casting facility for carrying out the present invention.

FIG. 2 is a graph showing a change in center porosity or an existing diameter of a cavity when a casting speed and a slab diameter are changed, in comparison with an example of the present invention and a comparative example.

[Explanation of symbols]

1: 1st stage electromagnetic stirrer 2: 2nd stage electromagnetic stirrer 3: terminal cooling unit 4: tundish 5: mold 6: secondary cooling zone 8: slab 9: solidified shell 10: molten metal

Claims (1)

(57) [Claims] When producing a billet or bloom by horizontal continuous casting, at least two stages of a rotating magnetic field type electromagnetic stirrer are arranged in series, and the first stage of electromagnetic stirring corresponds to a solidification start position in a mold. The second stage of electromagnetic stirring is performed between the mold outlet and the position where the solid phase ratio at the center of the slab does not exceed 0, and the casting is performed downstream of the installation position of these electromagnetic stirring devices. From the time when the solid fraction at the center of the slab exceeds 0 to the solid fraction at the center of the slab becomes 1.0,
Applying compressive force to compensate for solidification shrinkage on the slab surface
A horizontal continuous casting method, characterized in that as much cooling as possible is performed on the slab surface .