JPH10193039A - Method for continuously casting molten stainless steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain the occurrence of edge seam flaw at the time of rolling and to obtain a high quality cast slab by adding nitrogen compound-containing mold flux into a mold casting molten stainless steel and controlling N concn. on the surface layer part of the cast slab to be higher than N concn. in the deep part of the cast slab. SOLUTION: The molten ferritic stainless steel 17 is poured into the mold 12. The mold flux 15 containing the nitrogen compound of Cr2 N, etc., is changed into this mold 12. At the step of forming solidified shell, the cast slab 16 is drawn out. At this time, the mold flux 15 floated up in the molten stainless steel 17 is formed as a fused layer 15a, red layer 15b and powder layer 15c from the lowermost layer. The mold flux 15 of the fused layer 15a at the lowermost layer is entered into gap between the mold 12 and the cast slab 16 and served as a lubricant, and also N in the mold flux is infiltrated into the surface layer of the cast slab 16. The N concn. on the surface layer of the cast slab 16 becomes about 100-600ppm and the N concn. in the deep part of the cast slab 16 becomes about 10-90ppm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous casting method of molten stainless steel capable of suppressing occurrence of edge seam flaws during rolling and producing a slab having good workability and excellent slab quality at a high yield.

[0002]

2. Description of the Related Art Conventionally, there has been widely known a continuous casting method of molten stainless steel in which molten stainless steel is cast into a mold and then a slab is continuously drawn from the mold. By the way, as shown in FIG. 6, the slab 50 pulled out of the mold is supercooled in the mold and then strongly cooled in the secondary cooling zone. Therefore, even if the fine chill layer 51 is formed on the surface layer of the slab when supercooled in the mold, the columnar crystal structure 52 gradually becomes coarser when cooled in the secondary cooling zone thereafter. Will be formed. For this reason, when the plate width and the plate thickness of the slab 50 are adjusted and rolled, the metal flow at the end of the slab during rolling cannot be uniformly formed as shown in FIG. As a result, there is a problem that the resulting unevenness is further rolled, and as shown in FIG.

Therefore, Japanese Patent Publication No. Hei 7-15137 discloses alloy steel, Cu, Al, Ti, Nb, Cr, Ta,
A molten metal having a polycrystalline structure such as a metal such as Si or Mn or an alloy thereof has a higher melting temperature than the molten metal, and
A substance such as an oxide of Ni, a nitride of Ti, or another carbide that is insoluble in the molten metal is added in a fine shape having a particle diameter of 1000 mm or less and 5 wt% or less with respect to the molten metal to form a fine crystal. A metal material having formed grains has been proposed. Further, Japanese Patent Publication No. 60-23168 discloses that nitride particles are 2 to 8%, carbon particles are 0.5 to 1.5%,
There has been proposed a mold additive for continuous casting of steel, the remainder comprising a mold additive base material, a flux and less than 0 to 8% of a metal reducing agent, and a method of adding the casting agent for continuous casting of this steel has been proposed. .

[0004]

However, the technique described in the above publication still has the following problems to be solved. That is, (1) Since the metal material having the fine crystal grains has a fine crystal structure in the entire metal material, the mechanical strength of the entire metal material is increased, the workability is reduced, and the metal material is rolled. There is a problem that it cannot be used as a material. Also, Ni
Since it contains a metal oxide such as an oxide, there is a problem that the quality of the metal material is reduced. (2) The above-mentioned additive for continuous casting of steel is effective in keeping the heat of the slab, preventing oxidation, and improving lubricity with the mold, but eliminates edge seam flaws during rolling. There is a problem that can not be.

The present invention has been made in view of such circumstances, and it is possible to suppress the occurrence of edge seam flaws during rolling, and to produce a slab with good workability and excellent slab quality at a high yield. It is an object of the present invention to provide a continuous casting method of molten stainless steel that can be used.

[0006]

According to the present invention, there is provided a semiconductor device comprising:
The continuous casting method of molten stainless steel according to the method is a continuous casting method of molten stainless steel in which a molten stainless steel is cast into a hollow mold, and then a slab is continuously drawn from the mold. The N concentration in the portion is made higher than the N concentration in the deep portion of the slab. Claim 2
In the continuous casting method for molten stainless steel according to the first aspect, the N concentration in the surface layer portion of the slab is 100 to 600 ppm. The continuous casting method of molten stainless steel according to claim 3 is the continuous casting method of molten stainless steel according to claim 1 or 2, wherein the slab surface layer portion is within 20 mm from the slab surface to the slab deep portion. .

According to a fourth aspect of the present invention, there is provided a continuous casting method of molten stainless steel according to any one of the first to third aspects, wherein the molten stainless steel is cast into a mold and the molten stainless steel is cast. By adding a mold flux containing a nitrogen compound inside,
The N concentration in the surface layer portion of the slab is made higher than the N concentration in the deep portion of the slab. The continuous casting method for molten stainless steel according to claim 5 is the method for continuously casting molten stainless steel according to any one of claims 1 to 3, wherein a static magnetic field is formed in the mold, and Below the static magnetic field, cast low-N-concentration stainless steel molten steel, and further, in the mold, above the static magnetic field, by casting a high-N-concentration stainless-steel molten steel higher than the low-N-concentration stainless steel molten steel, The N concentration in the surface layer portion of the slab is made higher than the N concentration in the deep portion of the slab. The continuous casting method for molten stainless steel according to claim 6 is the method for continuously casting molten stainless steel according to any one of claims 1 to 3, wherein a static magnetic field is formed in the mold and the stainless steel is cast in the mold. Casting molten stainless steel, and further adding a nitrogen compound to the molten stainless steel above the static magnetic field, increases the N concentration in the surface layer portion of the slab as compared with the N concentration in the deep portion of the slab. .

Here, compared with the N concentration in the deep part of the slab,
It is desirable that the surface layer portion of the slab, which is a region having a high concentration, has a thickness of not more than 20 mm, preferably not more than 15 mm, more preferably not more than 5 mm from the slab surface toward the slab depth. This is because when the region where the N concentration is higher than the N concentration in the slab depth exceeds 5 mm from the slab surface toward the slab depth, it depends on the N concentration. Even if the N in the surface layer is dispersed, the N concentration in the entire slab is high, and the workability of the slab is hindered. When the N exceeds 15 mm, the tendency becomes remarkable. It is. The N concentration in the surface layer of the slab is 100 to 6%.
It is desirably 00 ppm, preferably 100 to 500 ppm. This is because the N concentration in the surface layer of the slab is 100 ppm.
If it is less than, it is not possible to form a very fine structure in the slab surface layer portion, the edge seam flaws can not be eliminated, conversely, if it exceeds 500 ppm, as described above, the slab surface layer portion in the continuous casting process Even if N is dispersed, the N concentration in the entire slab is high, and the workability of the slab is impaired.
If the content exceeds 0 ppm, the tendency becomes remarkable.

The nitrogen compound is not particularly limited. For example, Cr ₂ N, MnN ₉ , Si ₃ N ₄ , Fe ₄ N ₉ ,
One or more of Li ₃ N and the like can be used. Of course, they may be appropriately used depending on the composition of the target molten stainless steel or the like. In addition, when the nitrogen compound is used by being mixed with a mold flux, the mold flux is not particularly limited. For example, CaO—SiO ₂ —A
A material containing l ₂ O ₃ as a main component, a material obtained by adding a fluoride, an oxide of an alkali metal or an alkaline earth metal, a boride, and fine carbon particles can be used. Further, the content of the nitrogen compound to be added to the mold flux may be appropriately changed according to a desired slab surface layer N concentration. In addition, when a static magnetic field is formed in the mold and two types of stainless steel having a low N concentration and a high N concentration are cast into the mold, the N concentration of the stainless steel having a low N concentration is particularly defined. Although not a thing, for example, 10
It is desirably 90 ppm, preferably 20 to 90 ppm. This means that if the N concentration is less than 20 ppm,
This is because the production cost tends to rise, and particularly when it is less than 10 ppm, the tendency becomes remarkable, and when it exceeds 90 ppm, the workability of the slab tends to decrease similarly to the above.

[0010] In addition, the high N content stainless steel
The concentration is not particularly limited as long as it is higher than the N concentration of the stainless steel having a low N concentration.
The content is desirably 0 to 600 ppm, preferably 100 to 500 ppm. This is because, when the N concentration is less than 100 ppm, a fine structure cannot be formed in the surface layer portion of the slab and the edge seam flaws cannot be eliminated, similarly to the above, and conversely, the N concentration is 500 ppm.
If the amount exceeds 600 ppm, the workability of the cast slab tends to decrease similarly to the above, and particularly, if the amount exceeds 600 ppm, the tendency becomes remarkable. In addition, when a static magnetic field is formed in the mold, a stainless steel melt is cast in the mold, and a nitrogen compound is added, the nitrogen compound may be in any form such as a powdery form, a linear form, and a small lump. You may.

Therefore, in the continuous casting method of molten stainless steel according to the first to sixth aspects, the N concentration in the surface layer of the slab is controlled by:
Since the concentration is higher than the N concentration in the deep part of the slab, it is possible to form a microstructure by growing crystals using this N as a nucleus and to cause δ-γ transformation when cooling the slab. As a result, coarsening of the fine structure, that is, dendrite can be suppressed, and the fine structure can be maintained.
The occurrence of edge seam flaws at the time of rolling due to dendrites can be suppressed. Further, N present in the surface layer of the slab diffuses into the slab during the slab cooling process (because it has a temperature sufficient for N to diffuse in the slab even during the cooling process), It is possible to prevent the workability of the slab from decreasing. In particular, in the method for continuously casting molten stainless steel according to claim 2, the N concentration in the surface layer of the slab is 1%.
For example, since the N concentration is low and a chill layer cannot be formed, edge seam flaws occur,
It is possible to reliably prevent the workability of the slab from being lowered due to the high concentration.

In the method for continuously casting molten stainless steel according to the third aspect of the present invention, the surface layer of the slab is within 20 mm from the slab surface to the slab deep portion. It is possible to reliably prevent the workability of the piece from decreasing. And in the continuous casting method of molten stainless steel according to claim 4, the molten stainless steel is cast into a hollow mold, and the mold and the slab are formed by simply adding a mold flux containing a nitrogen compound into the mold. N in the nitrogen compound easily penetrates into the slab from the molten layer of the mold flux interposed between the slab and the N concentration in the surface layer of the slab and the N in the deep part of the slab.
It can be higher than the concentration. In the method for continuously casting molten stainless steel according to claim 5, a static magnetic field is formed in the mold, and a low N-concentrated stainless steel is formed below the static magnetic field, and a high N-concentration is formed above the static magnetic field. Stainless steel is cast, so that during continuous casting, high N concentration and low N concentration stainless molten steel which are cast above and below the mold with the static magnetic field interposed therebetween can be prevented. In the solidified shell formed by solidifying the upper high-N-concentration molten stainless steel, a low-N
By solidifying the molten stainless steel having a high concentration, the N concentration in the surface layer portion of the slab can be easily increased as compared with the N concentration in the deep portion of the slab.

Furthermore, in the method for continuously casting molten stainless steel according to claim 6, a static magnetic field is formed in the mold, and the molten stainless steel cast in the mold and above the static magnetic field is formed. Since the nitrogen compound is added, similarly to the above, during continuous casting, above and below the static magnetic field in the mold, the stainless steel molten steel having a high N concentration containing the nitrogen compound and the stainless steel molten steel having a low N concentration are formed. Section, which results in a high N above the mold.
In the solidified shell formed by the solidification of the molten stainless steel, the molten steel with a low N concentration is solidified, so that the N concentration in the slab surface layer can be easily compared with the N concentration in the deep slab. And can be higher. In addition, Claim 5,
The method according to (6) cannot satisfy the slab composition at the initial stage and the last stage of casting as compared with the method according to (4), and may reduce the yield. As a desired composition, the N concentration in the surface layer portion of the slab can be easily increased as compared with the N concentration in the deep portion of the slab.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the accompanying drawings to provide an understanding of the present invention. In addition, about the same structure about each embodiment, the same code | symbol is attached | subjected and description is abbreviate | omitted. (First Embodiment) First, with reference to FIG. 1, a description will be given of a continuous casting machine A which can be suitably used in a method for continuously casting molten stainless steel according to a first embodiment of the present invention. As shown in FIG. 1, a pair of rails (not shown) are laid on a cast floor of a building (not shown), and the pair of rails is movable to transport the tundish 11. A traveling trolley (not shown) is provided. On the floor of the above-mentioned building, a stand (not shown) is erected, and on this stand, an oscillation device (not shown) for vertically supporting the mold 12 is provided. . Further, below the mold 12, a strand 13 for supporting a slab to be drawn from the mold 12 is formed. A ladle turret that supports a ladle (not shown) is also provided on the cast floor of the building described above.

Next, a continuous casting method for molten stainless steel according to the present embodiment using the continuous casting machine A having the above-described configuration will be described with reference to FIGS. First, a ladle for storing ferritic stainless steel molten steel 17 which is an example of stainless steel molten steel is placed on a ladle turret, and tundish 11 is transported to above mold 12. In the present embodiment, 0.048 wt% of the ferritic stainless steel molten steel 17 is used.
C, 0.39 wt% Si, 0.17 wt% Mn, 0.2
7wt% Ni, 17.56wt% Cr, 60-80pp
A ferritic stainless steel molten steel of about 1500 to 1600 ° C. containing mN shall be used. A molten ferritic stainless steel 17 is poured from the ladle into the tundish 11 through a long nozzle (not shown), and ferrite stainless steel 17 is poured into the mold 12 from the tundish 11 through a dipping nozzle 14. The molten stainless steel 17 is poured.

Here, a mold flux 15 containing Cr ₂ N, which is an example of a nitrogen compound, is charged into the mold 12. In this embodiment, 2.4 wt% C,
39.8 wt% SiO ₂ , 5.9 wt% Al ₂ O ₃ , 2
9.9 wt% CaO, 11.0 wt% Na ₂ O, 3.6
wt% F, basicity [CaO / SiO _2] 0.7-1.4
To 100 parts by weight of mold flux, 5 and Cr ₂ N
15 parts by weight added shall be used. Then, when a proper amount of the molten ferritic stainless steel 17 is accumulated in the mold 12 and an appropriate solidified shell 16a is formed, a dummy bar (not shown) which has previously been waiting in the mold 12 is replaced by 0.4 to 1 mm. The slab 16 is drawn at a speed of 0.2 m / min, preferably at a speed of 0.6 to 0.8 m / min.

At this time, ferritic stainless steel molten steel 17
The mold flux 15 floating on the surface of the molten metal is, in order from the lowest layer, a molten layer 15a, an incandescent layer 15b, and a powder layer 15a.
c (see FIG. 2), and the lowermost molten layer 15
The mold flux 15 of FIG.
While entering the gap with 6, to serve as a lubricant,
N contained in the mold flux 15 is
Invading the surface layer of. Thereby, the N concentration from the surface of the slab 16 to a depth within 20 mm is 100 to 600 ppm.
And a fine structure is formed with this N as a nucleus.
When the slab 16 is cooled, a δ-γ transformation is caused to prevent the generated chill layer (not shown) from being coarsened, thereby maintaining a fine structure. When the slab 16 manufactured by the continuous casting method of the molten stainless steel described above was rolled, no edge seam flaws were observed. Further, when the slab 16 was rolled, defects such as surface cracks and corner cracks were found. Did not occur.

As described above, according to the method for continuously casting molten stainless steel according to the present embodiment, the N concentration in the slab surface layer, that is, within a depth of 20 mm from the slab surface, is determined by the N concentration in the slab deep portion. (Approximately 100 to 600 ppm) as compared to (approximately 10 to 90 ppm), so that a crystal can be grown with this N as a nucleus to form a fine structure, and when the slab 16 is cooled, By causing δ-γ transformation, coarsening of a fine structure can be suppressed, and generation of edge seam flaws due to dendrite can be suppressed.
Further, N present in the surface layer of the slab does not
Since it can be diffused in, the workability of the slab 16 can be prevented from lowering. Furthermore, since the mold flux 15 containing a nitrogen compound is added into the mold 12, the N concentration in the surface layer of the slab can be easily increased.

(Second Embodiment) Next, referring to FIG. 3, a continuous casting machine B which can be suitably used in a continuous casting method for molten stainless steel according to a second embodiment of the present invention.
Will be described. As shown, this continuous casting machine B
However, the difference from the continuous casting machine A is that on the cast floor of the building,
Two pairs of rails (not shown) are laid, and two movable carriages (not shown) for transporting the tundishes 11 and 11a are arranged on the two pairs of rails, respectively. The permanent magnets 19 are arranged substantially horizontally outside the pair of long pieces 12a of the mold 12 and substantially at the center in the height direction. The tundish 11
Stores the ferritic stainless steel molten steel 17 which is an example of a low N-concentrated molten stainless steel, and the tundish 11a stores the ferritic stainless steel molten steel 18 which is an example of a high N-concentrated molten stainless steel.
In the present embodiment, as the ferritic stainless steel molten steel 18, 0.048 wt% C, 0.39 wt%
Si, 0.17 wt% Mn, 0.27 wt% Ni, 1
A ferritic stainless steel molten steel of about 1500 to 1600 ° C. containing 7.56 wt% Cr and 100 to 600 ppm N is used.

Next, the continuous casting machine B having the above-described configuration
A continuous casting method for molten stainless steel according to the present embodiment using the method will be described. First, two ladles for storing the low-N-concentrated ferritic stainless steel molten steel 17 and the high-N-concentrated ferritic stainless steel molten steel 18, respectively, are placed on a ladle turret, and each tundish 11 , 11a are transported above the mold 12. And from one ladle,
A low N concentration ferritic stainless steel molten steel 17 is passed through one tundish 11 through a long nozzle (not shown).
The molten ferritic stainless steel 17 is poured from the tundish 11 into the mold 12 through the immersion nozzle 14. Then, the low-N-concentration ferritic stainless steel molten steel 17 is, as shown in FIG.
At the stage where the static magnetic field in the mold 12 indicated by the broken line has accumulated, the stopper nozzle (not shown) of the immersion nozzle 14 is throttled. At the same time, the high N-concentrated ferritic stainless steel molten steel 18 previously poured from the other ladle to the other tundish 11a through a long nozzle (not shown) is immersed through the immersion nozzle 14a. The molten metal is poured into the mold 12.

In this state, the mold 12
The continuous casting is started while moving the dummy bar (not shown), which has been waiting inside, at the moving speed described above. Then, the surface layer (cast piece 2) of the solidified shell 20a formed by solidifying the high-N-concentration ferritic stainless steel molten steel 18 is formed.
The N concentration in the deep portion of the solidified shell 20a formed by solidifying the low N-concentrated ferritic stainless steel molten steel 17 (within a depth of 20 mm or less from the surface of No. 0) (about 50 mm).
(About 100 to 600 ppm).
ppm). Therefore, a fine structure can be formed by using the N as a nucleus, and at the time of cooling the slab 20, δ-γ transformation occurs to prevent coarsening of the chill layer and maintain the fine structure. No edge seam flaws are observed even when rolling is performed on No. 20, and defects such as surface cracks and corner cracks do not occur during rolling. During the continuous casting operation,
High N concentration ferritic stainless steel molten steel above static magnetic field 1
The stopper nozzles of the immersion nozzles 14 and 14a are adjusted so that 8 does not exceed the static magnetic field and does not mix with the low-N-concentration ferritic stainless steel molten steel 17 below the static magnetic field.

As described above, according to the continuous casting method for molten stainless steel according to the present embodiment, the same effects as those of the first embodiment of the present invention can be obtained, and a static magnetic field is formed in the mold 12. At the same time, a molten ferritic stainless steel 17 having a low N concentration is cast below the static magnetic field and a molten ferritic stainless steel 18 having a high N concentration is cast above the static magnetic field.
As compared with the embodiment of the present invention, the equipment and operation become complicated and complicated, and furthermore, although the reduction of the slab quality at the initial and final stages of casting and the reduction of the yield based on this are inevitable, on the static magnetic field, Prevents the mixing of high N concentration and low N concentration ferritic stainless steel molten steels 18 and 17 that are cast underneath, and easily increases the N concentration in the surface layer of the slab compared to the N concentration in the deep slab. can do.

(Third Embodiment) Next, referring to FIG. 4, a continuous casting machine C which can be suitably used in the continuous casting method of molten stainless steel according to a third embodiment of the present invention.
Will be described. As shown, the continuous casting machine C
However, the difference from the continuous casting machine A is that the continuous casting machine B
Similarly to the above, the permanent magnets 19 are disposed substantially horizontally outside the pair of long pieces 12a of the mold 12 and substantially at the center in the height direction. Unlike the continuous casting machine B, a pair of rails (not shown) are laid on a cast floor of a building (not shown), and the tundish 11 is movable on the pair of rails. A suitable traveling cart (not shown) is provided.

Next, the continuous casting machine C having the above-described configuration will be described.
A continuous casting method for molten stainless steel according to the present embodiment using the method will be described. First, a ladle for storing the ferritic stainless steel molten steel 17 is placed on a ladle turret, and the tundish 11 is transported above the mold 12. Then, from the ladle to the tundish 11 via a long nozzle (not shown)
The molten ferritic stainless steel 17 is poured from the tundish 11 into the mold 12 through the immersion nozzle 14 while the molten ferritic stainless steel 17 is poured. When a suitable amount of ferritic stainless steel 17 exceeding the static magnetic field indicated by the broken line in FIG. 4 has accumulated in the mold 12, the dummy bar (not shown) that has been waiting in the mold 12 in advance is described above. The mold 12 is moved at a moving speed, and Cr ₂ N
The tip of the wire 22 is immersed.

The wire 22 is wound in a coil shape on a drum (not shown), and is fed to the molten ferritic stainless steel 17 in the mold 12 at a feeding speed according to casting conditions such as a casting speed. It has become. As a result, when the wire 22 melts into the ferritic stainless steel molten steel 17, a high N-concentrated ferritic stainless steel molten steel is stored above the static magnetic field,
In the same manner as described above, the surface layer (cast slab 2) of the solidified shell 21a formed by solidifying the high N-concentrated ferritic stainless steel melt
The N concentration in the deep portion of the solidified shell 21a formed by solidification of the ferritic stainless steel molten steel 17 (about 50 to 90 pp) is obtained.
m) (approximately 100 to 600 ppm). Therefore, similarly to the above, while forming a fine structure with the N as a nucleus, when cooling the slab 21, δ-γ
Transformation occurs, preventing coarsening of the chill layer and maintaining a fine structure. As a result, even when the slab 21 is rolled, no edge seam flaws are observed. No defects such as corner cracks occur. In this case, similarly to the above, the stopper of the immersion nozzle 14 is used to prevent the high N-concentrated ferritic stainless steel above the static magnetic field from being mixed with the low N-concentrated ferritic stainless steel below the static magnetic field. The nozzle shall be adjusted.

As described above, according to the method for continuously casting molten stainless steel according to the present embodiment, the same effects as those of the first embodiment of the present invention can be obtained, and a static magnetic field is formed in the mold 12. At the same time, it is cast into the mold 12,
Moreover, the wire 22 made of Cr ₂ N, which is an example of a nitrogen compound, is immersed and melted in the ferritic stainless steel molten steel 17 above the static magnetic field. It is possible to easily increase the N concentration in the surface layer of the slab as compared with the N concentration in the deep portion of the slab while reducing the complexity and complexity of the operation.

[0027]

EXAMPLES Next, the results of confirmation tests of the continuous casting method for molten stainless steel according to the present embodiment will be described. (Example 1, Comparative Example 1) First, in the same manner as in the first embodiment of the present invention, continuous casting of molten ferritic stainless steel 17 was performed, and the N concentration of slab 16 moving in strand 13 was determined. Cast slab 16 drawn from strand 13
(Example 1) The edge seam flaws (number of occurrences or occurrence area) occurring in the sample were investigated. The result is shown in FIG. In this experiment, as shown in Table 1, 0.048 wt% C,
0.39 wt% Si, 0.17 wt% Mn, 0.27 w
A ferritic stainless steel molten steel containing t% Ni, 17.56 wt% Cr, and 70 ppmN was used.

[0028]

[Table 1]

In this experiment, as shown in Table 2,
2.4 wt% C, 39.8 wt% SiO ₂ , 5.9 wt
% Al ₂ O ₃ , 29.9 wt% CaO, 11.0 wt%
Na ₂ O, 3.6 wt% F, basicity [CaO / Si
O ₂ ] 0.75 mold flux 100 parts by weight,
It was used after the Cr ₂ N was added 10 parts by weight.

[0030]

[Table 2]

On the other hand, as a comparative example, continuous casting of molten ferritic stainless steel 17 was performed in the same manner as described above, and the N concentration of slab 16 moving in strand 13 and the slab 16 drawn from strand 13 were generated. Edge seam flaws were investigated. The results are also shown in FIG. In this experiment, the same ferritic stainless steel molten steel 17 as described above was used. A mold flux not containing Cr ₂ N was used.

As a result, in Comparative Example 1, the N concentration of the slab was approximately 70 ppm from the slab surface to the slab depth.
However, in Example 1, the N concentration in the surface layer of the slab (from the slab surface to a depth of 10 mm) was about 27%.
It was 0 ppm, and was about 200 ppm higher than the N concentration in the deep part of the slab. Therefore, it is possible to form a fine structure by crystal growth with the N as a nucleus, and to cause δ-γ transformation when cooling the slab, thereby suppressing coarseness of the fine structure. result,
As shown in FIG. 5, the edge seam flaw occurrence index could be reduced to 0.3.

The amounts of the mold flux used in Example 1 and Comparative Example 1 were substantially the same (0.5 to 1.0 kg).
/ T-steel). In FIG. 5, the “edge seam flaw generation index” is the number of edge seam flaws (or the area where the number of edge seam flaws generated in a slab manufactured by the conventional method is 1.0). Or generation area).

(Example 2) As in the second embodiment of the present invention, a low N-concentration ferritic stainless steel molten steel 1
7 and a continuous casting of a high N-concentrated ferritic stainless steel molten steel 18 and a slab 20 moving in the strand 13
Of N and the slab 2 drawn from the strand 13
An edge seam flaw of 0 was investigated (Example 2). The results are also shown in FIG.

In this experiment, 0.048 wt% C was used as the high N-concentrated ferritic stainless steel molten steel 18.
0.39 wt% Si, 0.17 wt% Mn, 0.27 w
A ferritic stainless steel molten steel containing t% Ni, 17.56 wt% Cr, and 270 ppmN was used. The low-N-concentration ferritic stainless steel molten steel 17 is the same as described above.

As a result, as described above, the N concentration in the surface layer of the slab (from the slab surface to a depth of 10 mm) was reduced to about 270 ppm.
In addition, compared to the N concentration in the deep portion of the slab,
ppm, and the edge seam flaw generation index could be reduced to 0.3 as shown in FIG.

(Example 3) Further, in the same manner as in the third embodiment of the present invention, continuous casting of molten ferritic stainless steel 17 is performed, and cast slab 21 moving in strand 13 is formed.
Of N and the slab 2 drawn from the strand 13
The edge seam flaw No. 1 was examined (Example 3). The results are also shown in FIG. In this experiment, a wire 22 made of Cr ₂ N was used. Further, the ferritic stainless steel molten steel 17 is the same as described above.

As a result, as described above, the N concentration in the surface layer of the slab (from the slab surface to a depth of 10 mm) was reduced to about 270 ppm.
In addition, compared to the N concentration in the deep portion of the slab,
ppm, and the edge seam flaw generation index could be reduced to 0.3 as shown in FIG.

The embodiment of the present invention has been described above.
The present invention is not limited to the above-described embodiment, and all changes in conditions that do not depart from the gist are within the scope of the present invention. For example, in the first embodiment of the present invention,
A mold flux containing Cr ₂ N was used.
Mold flux containing MnN ₉ or Cr ₂ N
And a mold flux containing MnN ₉ and MnN ₉ . Further, in the second embodiment of the present invention, two tundishes 11 and 11a are used, but one tundish may be used. However, in this case, there is a weir that divides the inside into two, and furthermore, a dipping nozzle is provided for each chamber. Further, in the third embodiment of the present invention, the wire 22 made of Cr ₂ N is used, but MnN ₉
Made in the wire, or may be used Cr ₂ N-MnN ₉ made of wire. Furthermore, not only the wire but also Cr
Granules and small lumps of ₂ N and / or MnN ₉ may be used.

[0040]

As is apparent from the above description, in the continuous casting method for molten stainless steel according to any one of claims 1 to 6, the N concentration in the surface layer of the slab is higher than that in the deep portion of the slab. Therefore, it is possible to form a microstructure by growing crystals using this N as a nucleus, and to cause δ-γ transformation when cooling the slab, to suppress coarsening of the microstructure,
The occurrence of edge seam flaws due to dendrite can be suppressed. Further, N present in the surface layer of the slab can be diffused into the slab during the secondary cooling, so that a reduction in workability of the slab can be suppressed. In particular, in the method for continuously casting molten stainless steel according to the second aspect, since the N concentration in the surface layer of the slab is set to 100 to 600 ppm, it is possible to surely suppress the occurrence of edge seam flaws and a decrease in workability of the slab. Also,
In the continuous casting method for molten stainless steel according to the third aspect, the surface layer of the slab is set to a depth of 20 mm or less from the surface of the slab, so that a reduction in workability of the slab can be reliably suppressed. In the method for continuously casting molten stainless steel according to claims 4 to 6, the N concentration in the surface layer portion of the slab can be easily increased as compared with the N concentration in the deep portion of the slab.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a continuous casting machine that can be suitably used in a method for continuously casting molten stainless steel according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of a mold of the continuous casting machine.

FIGS. 3 (a) and 3 (b) are illustrations of a method for continuously casting molten stainless steel according to a second embodiment of the present invention.

FIG. 4 is an explanatory view of a continuous casting method for molten stainless steel according to a third embodiment of the present invention.

FIG. 5 is a characteristic diagram showing a comparison of an edge seam flaw occurrence index between an example and a comparative example.

FIG. 6 is an explanatory view of a cast slab manufactured by a conventional stainless steel continuous casting method.

FIG. 7 is an explanatory view of cross-rolling of the slab.

FIG. 8 is an explanatory diagram of the edge seam flaw.

[Explanation of symbols]

Reference Signs List A continuous casting machine B continuous casting machine C continuous casting machine 11 tundish 11a tundish 12 mold 12a long piece 13 strand 14 immersion nozzle 14a immersion nozzle 15 mold flux 15a molten layer 15b red heat layer 15c powder layer 16 cast slab 16a solidified shell 17 Ferritic stainless steel molten steel (stainless steel molten steel) 18 Ferrite stainless steel molten steel (stainless steel molten steel) 19 Permanent magnet 20 Cast piece 20a Solidified shell 21 Cast piece 21a Solidified shell 22 Wire

 ──────────────────────────────────────────────────続 き Continued on front page (72) Inventor Hiroshi Harada 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Corporation Technology Development Division

Claims (6)

[Claims] 1. A method for continuously casting molten stainless steel, comprising: casting a molten stainless steel into a hollow mold; and continuously drawing a slab from the mold, wherein the N concentration of a surface layer portion of the slab to be drawn from the mold is determined. ,
A continuous casting method for molten stainless steel, characterized by increasing the N concentration in a deep portion of a slab. 2. The N concentration in the surface layer of the slab is 100 to 6%.
The continuous casting method of molten stainless steel according to claim 1, wherein the content is set to 00 ppm. 3. The continuous casting method for molten stainless steel according to claim 1, wherein the surface layer portion of the slab is within 20 mm from the surface of the slab toward the deep portion of the slab. 4. Casting the molten stainless steel into a hollow mold, and adding a mold flux containing a nitrogen compound into the mold, so that the N concentration in the surface layer of the slab is reduced by the N in the deep portion of the slab. The continuous casting method for molten stainless steel according to claim 1, wherein the concentration is higher than the concentration. 5. A method for forming a static magnetic field in the mold, casting a low-N-concentration stainless steel molten steel in the mold below the static magnetic field, further comprising:
By casting a stainless steel melt having a higher N concentration than the stainless steel melt having a lower N concentration above the static magnetic field, the N concentration in the surface layer portion of the slab is increased as compared with the N concentration in the deep portion of the slab. The method for continuously casting molten stainless steel according to claim 1. 6. A method for forming a static magnetic field in the mold, casting the molten stainless steel in the mold, and further adding a nitrogen compound into the molten stainless steel above the static magnetic field to form the molten steel. The continuous casting method for molten stainless steel according to any one of claims 1 to 3, wherein the N concentration in one surface layer portion is higher than the N concentration in the deep portion of the slab.