JP2917223B2 - Metal solidification structure refinement casting method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a casting method in which the solidification structure and segregation of a metal are controlled by an electromagnetic force, and more particularly, to a method of forming a metal product obtained by continuous casting or the like. The present invention relates to a method for reducing macro-solidification segregation of a solute which causes a material defect and achieving finer solidification structure.

2. Description of the Related Art Conventionally, in continuous casting, the quality of a product is deteriorated due to segregation of solutes during solidification.

These improvement methods include (a) a method in which solutes causing harmful segregation are reduced by refining in advance, and (b) a slab where macrosegregation (center segregation) occurs in the final solidification part of continuous casting. Or (c) a method of miniaturizing (equiaxed) the solidified structure by electromagnetic stirring (JP-A-50-23338) to reduce center segregation.

In particular, the electromagnetic stirring (c) is widely used because it is simple in terms of equipment and operability, but the effect obtained here is that stirring accompanied by the flow of molten metal occurs. Because it is obtained by making it necessary to have a certain size of field to generate the flow of molten metal, or when the large flow infiltrates the slab of nonmetallic inclusions, or when used in a mold, There was a problem of involving powder. In addition, since the solute elements accumulated between the dendrites are swept away by the strong flow of the solidification front, negative segregation of the solute elements (called white band in the case of continuous casting of steel) at the site is generated. There was a problem.

On the other hand, as a method for obtaining an equiaxed crystal having a solidification structure that is unlikely to cause the occurrence of center segregation or macrosegregation, a method of adding a substance that promotes solidification nucleation such as iron casting or Zr has been proposed. In the former case, transport problems such as nozzle blockage tend to occur, and in the latter case, a large amount of addition must be performed to obtain the effect. It was not a target.

Problem to be Solved by the Invention The present invention is a metal casting method for improving the above problems,
The dendrite is broken by the vibration of the solidification front caused by the electromagnetic force, and the dendrite is used as a nucleus to refine the solidification structure and to reduce local non-uniformity to reduce segregation.

Means for Solving the Problems The present invention provides (1) a continuous casting of a molten metal, in which an electromagnetic coil provided in a mold applies a low-frequency AC static magnetic field that does not move over time, and a low-frequency electromagnetic A method for refining the solidification structure of a metal, wherein the columnar dendrite on the solidification front surface is broken and released into the molten metal by exciting vibration. (2) In the continuous casting of the molten metal, By applying a low-frequency AC static magnetic field that does not move over time by the provided electromagnetic coil, and by exciting low-frequency electromagnetic vibration at least on the solidification front, the columnar dendrite on the solidification front is broken and released into the molten metal. (3) The coil current frequency for applying low-frequency electromagnetic vibration is 1 to
The method of (1) or (2), wherein the metal has an average magnetic flux density of 30 gauss or more and 1000 gauss or more.

That is, the present invention uses a low-frequency electromagnetic force to vibrate the molten metal when the molten metal is cooled and starts to solidify, or when the molten metal is being solidified. To obtain a fine solidified structure with less segregation of solute elements.

This method is particularly effective for small-section cast magnets that cannot achieve the same effect by flow such as electromagnetic stirring.

Operation Hereinafter, the present invention will be described in detail.

The present invention provides low-frequency vibration by an AC magnetic field at the start and / or during the progress of solidification of a molten metal, and the range for applying the vibration is preferably the entire solidification surface, In the case of casting, it is possible to provide an arbitrary axis corresponding to the thickness of the slab to obtain an equiaxed crystal. For example, a coil can be provided in a mold,
It is also possible to ground at a specific location on the strand. In addition, a higher effect can be obtained by providing a plurality of coils.

The vibration causes the solidification tip to vibrate, preferably in a direction perpendicular to the solidification generation direction. This direction can be easily changed by changing the installation angle of the electromagnetic coil. By this vibration, the solute elements (C, P, S, etc.) between the trees are not swept out into the molten metal casting, but the crystals on the solidification front face are broken, and the generation of equiaxed crystals using these as nuclei is promoted. It becomes possible.

The low-frequency vibration is generated by disposing an electromagnetic coil of a solenoid type or the like from the inside of the mold to around the strand, and applying an AC static magnetic field that gives an average magnetic flux density of 1000 gauss or more to the molten metal. If the magnetic flux density is less than 1000 Gauss, the vibration force is weak, and a sufficient effect cannot be obtained.
The coil current frequency is 1 to 30 Hz, preferably 1 to 10 Hz.
Hz. If the frequency exceeds 30 Hz, strong stirring of the molten metal occurs, which is not preferable.

Although the molten metal in the present invention is not particularly limited, it will be specifically described below with reference to examples mainly of steel.

Embodiment 1 Embodiment 1 FIG. 1 shows an embodiment of the present invention corresponding to this embodiment. That is, continuous casting of steel in the following two cases shown in FIG. 1 was performed.

(A) When the electromagnetic coil 3 is installed in the mold 1, (b) When the electromagnetic coil 3 is installed in an unsolidified portion of the strand portion 2, that is, 5 m below the meniscus.

In any case, a current of 5 Hz was passed through the electromagnetic coil 3 provided around the slab, and the average
A low frequency magnetic field of 000 gauss was generated. The mold is filled with molten steel of 1550-1555 ° C, which has a component system equivalent to a medium carbon steel plate, and the slab size obtained after casting is 1200 mm in width and thickness
The casting speed was 200 mm and the casting speed was 1 m / min. In the casting by the continuous casting machine used here, the thickness of the solidified shell 6 at the position where the electromagnetic coil 3 is installed in FIG. 1B, that is, at a position 5 m below the meniscus 4 is 50 to 52 mm in any case. Was within the range.

The slabs obtained in each of the above two cases were cut and the C cross section was corroded to observe the structure. In the case of FIG. 1 (a), the results were as shown in FIG. 2 (a). The structure of the fine equiaxed crystal 8 as shown in the entire figure was observed. In the case of FIG. 1 (b), a structure as shown in FIG. 2 (b) is generated, and fine equiaxed crystals 8 are observed within about 50 mm from the surface of the slab, and columnar crystals 7 and At the boundary of the fine equiaxed crystal 8, the second
No negative solute segregation zone (white band 10) as shown in FIG.

Embodiment 2 In the case of Embodiment 1 described above, in the case of FIG. 1B, that is, when the electromagnetic coil 3 is provided so as to surround the slab at a position 5 m below the meniscus 4, the average magnetic flux density is set to 3000 Gauss as it is. , Coil current frequency 1Hz, 2Hz, 10H
Continuous casting was carried out while changing to z, 20 Hz, 30 Hz and 50 Hz. Here, as in Example 1, molten steel of 1550 to 1555 ° C. having a component system equivalent to a cast carbon steel thick plate material is poured into a mold, and the slab size obtained after casting is 1200 mm in width and 200 m in thickness.
m and the casting speed were 1 m / min. On the other hand, the thickness of the solidified shell 6 at the position where the electromagnetic coil 3 is installed is 50 in each case.
It was within the range of ± 5 mm.

As a result, below 30 Hz, a negative segregation zone (white band 10) of the solute was not generated as shown in FIG.
At 50 Hz, a white band 10 was generated, similar to the situation in FIG. 2 (c).

Embodiment 3 Similarly, in the case of Embodiment 1 described above, the case where the electromagnetic coil 3 is provided so as to surround the slab at a position 5 m below the meniscus 4 in the case of FIG. 5 Hz as it is, and the average magnetic flux density in the coil is 500
Gauss, 1000 Gauss, 2000 Gauss, 5000 Gauss, and 10
Continuous casting was performed while changing to 000 gauss. Here, as in Example 1, molten steel of 1550 to 1555 ° C. having a component system equivalent to a medium carbon steel thick plate material was poured into a mold, and the slab size obtained after casting was 1200 mm in width, 200 mm in thickness, and the casting speed was 1 m. / mi
n. Here, the thickness of the solidified shell 6 at the position where the electromagnetic coil 3 was installed was within the range of 50 ± 5 mm in each case.

As a result, at 1000 Gauss or more, fine equiaxed crystals 8 as shown in FIG.
In Gauss, the macrosegregation 11 was generated at the center, similar to the situation in FIG. 2 (d).

Comparative Example 1 Next, instead of the electromagnetic coil 3 of FIG. 1 (a), a commonly used moving magnetic field type electromagnetic stirrer was installed in the mold part. Inject molten steel at 1551 ° C with a component system equivalent to a thick plate of carbon steel, the slab size obtained after casting is 1200 mm wide, 200 mm thick, and the casting speed is 1 m /
min. Here, the thickness of the solidified shell 6 at the position where the electromagnetic coil 3 was installed was 52 mm. The electromagnetic force was adjusted so that a molten steel flow rate of about 1 m / sec was obtained in the electromagnetic stirring device.

FIG. 2 (c) shows the C sectional structure of the slab obtained at this time. Although the inside of the slab was an equiaxed crystal 9, the grain size was larger than in either case of Example 1 described above, and a negative segregation zone (white band 10) of the solute was generated at the boundary.

Comparative Example 2 Under the same casting conditions as in Comparative Example 1, except that the electromagnetic stirrer was not operated, and therefore the solidified C-section structure of the cast slab obtained when no electromagnetic force was applied was shown in FIG. (D). Macrosegregation of solute in the center, the final solidification part of the slab
Eleven were found.

From the above results, it can be seen that the method according to the present invention is very effective for refining the solidification structure and preventing macro segregation.

Effect of the Invention In the present invention, an alternating static magnetic field applies low-frequency vibration to the solidification front, so that columnar dendrites are generated without generating negative segregation of solute elements caused by a large flow of molten metal such as electromagnetic stirring. As a result of breaking and promoting the generation of equiaxed crystals using the nuclei as a nucleus, the solidification structure can be refined and macrosegregation can be prevented. The product obtained by processing the cast slab thus obtained is very excellent in material.

This method is simple in terms of both equipment and operation, and in particular, it causes local movement due to low-frequency vibration using molten metal by using electromagnetic force. It is also particularly effective for small section castings where it is difficult to expect the effect.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an embodiment of the present invention, and FIG. 2 is an explanatory view showing an observation state of a C cross-sectional structure of the obtained cast slab. (C) and (d) are slab structures of a comparative example at the time of the invention. 1 ... mold, 2 ... strand part, 3 ... electromagnetic coil,
4 ... meniscus, 5 ... molten metal, 6 ... solidified shell, 7 ... columnar crystal, 8 ... fine equiaxed crystal, 9 ... equiaxed crystal,
10: White band, 11: Central segregation.

Claims (3)

(57) [Claims] In a continuous casting of a molten metal, an electromagnetic coil provided in a mold applies a low-frequency AC static magnetic field which does not move over time to excite a low-frequency electromagnetic vibration at least on a solidification front, so that a solidification front can be obtained. A method for refining the solidification structure of a metal, characterized in that the columnar dendrite is broken and released into the molten metal. 2. A method for continuously casting a molten metal, wherein a low-frequency AC static magnetic field which does not move over time is applied by an electromagnetic coil provided on a strand portion to excite at least a low-frequency electromagnetic vibration on a solidification front surface, whereby a solidification front surface is formed. A method for refining the solidification structure of a metal, characterized in that the columnar dendrite is broken and released into the molten metal. 3. The method of claim 1, wherein the coil current frequency for applying low-frequency electromagnetic vibration is 1 to 30 Hz, and the average magnetic flux density in the coil is 1000 gauss or more.