JPH0314541B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention produces killed steel with low surface negative segregation and small center segregation, particularly as a hard steel material, by a continuous casting method using electromagnetic stirring in a mold, as a bar material for automobile parts, and as a steel for tires. The present invention relates to a method for manufacturing steel materials suitable for cords, piano wire, spring materials, etc.

In the past, various attempts have been made to produce killed steel using the continuous casting method, but since it is cast through a small-diameter nozzle, it is difficult to lower the casting temperature. However, strong center defects, that is, center segregation, tend to appear in slabs cast at high temperatures. Slabs with strong center segregation had the drawback of large center segregation, low drawing area, and poor cold workability.

In order to eliminate the above-mentioned center segregation, it is necessary to increase the degree of filling in the center of the slab, and for this reason, conventionally, electromagnetic stirring is performed in the secondary cooling zone, and the tips of the growing crystals are removed by the flow of molten steel. cut,
Generates a large amount of fine equiaxed crystal nuclei in the molten steel pool, prevents bridging that occurs during columnar crystal solidification,
The above-mentioned center segregation is improved by increasing the packing density at the center of the slab.

However, in the generation of equiaxed crystal nuclei due to the flow of molten steel, the more stirring is performed in the early stages of solidification, the thinner the columnar crystals that grow from the surface of the slab are and the easier they are to cut. The generation of equiaxed crystal nuclei is also promoted by the chill effect caused by the flow of molten steel in the slab meniscus, and stirring within the mold is effective in improving center segregation. .

While performing the above-mentioned in-mold electromagnetic stirring (M stirring),
A technique for performing electromagnetic stirring (S stirring) also in the secondary cooling zone has been disclosed in US Pat. No. 2,963,758. That is, in the embodiment shown in FIG. 10 of the above-mentioned patent, a device for electromagnetic stirring inside the mold and a device for electromagnetic stirring at two positions in the secondary cooling zone, one directly below the mold and one side thereof, are installed. A technique is disclosed that combines internal electromagnetic stirring (M stirring) and electromagnetic stirring in a secondary cooling zone (S stirring).

As in the above-mentioned US patent, when M stirring and S stirring are combined, stirring is performed on the surface layer of the ingot, the tips of the columns are cut off by the flow of molten steel, and an equiaxed crystal region is generated in the center of the ingot. , from Figure 12 to the first
As is clear from the photograph of the cross section of the ingot in Figure 7, center segregation is improved, but due to the above stirring,
A clear negative segregation zone called a white band, which is generated by the flow of molten steel, is formed near the surface layer of the ingot.

In this way, as shown in the above US patent, when M stirring and S stirring are combined and M stirring is made stronger than S stirring, wider equiaxed crystal bands are generated and center segregation is improved. However, the problem of negative segregation due to stirring cannot be resolved.

As a result of various experiments and considerations regarding the above-mentioned problems, the present inventors have found that in order to obtain steel materials with less center segregation and negative segregation by continuous casting, it is necessary to solidify the slab manufactured by continuous casting. It has been found that it is preferable to cause the molten steel to flow again by performing electromagnetic stirring near the end of the process.

That is, by stirring the residual molten steel at a place where there is almost no temperature gradient in the equiaxed crystal formation region at the final stage of solidification, the entire unsolidified molten steel, which has become highly viscous due to the temperature drop at the final stage of solidification, flows. As a result, the molten steel that is concentrating at the solidification interface is dispersed between the equiaxed crystal grains, and by preventing the movement of the concentrated molten steel before and after that, subsequent solidification proceeds almost simultaneously within the molten steel pool. At the same time, as a result of confining so-called concentrated molten steel between crystal grains, center segregation becomes difficult to occur.
In addition, as a result of the entire unsolidified molten steel flowing at the final stage of solidification, the clear white band that occurs due to the molten steel flowing at the solidification interface is not generated, but is widely dispersed, and the degree of negative segregation is low.

From the above points, it is effective to perform stirring at the final stage of solidification when center segregation begins to form. The central segregation formed within this equiaxed crystal region has a V-shape as shown in Figures 10B and 11B,
Since the upper part of the V-shape is the starting position of center segregation, it is preferable to carry out the stirring at the final stage of solidification when the thickness of the solidified shell almost reaches the open part of the V-shape. The starting position of the V-shaped center segregation at the final stage of solidification of the molten steel is as shown in Fig. 10A and B for solidified rectangular slabs whose outer surface has a minor axis larger than 200 mm.
For slabs where the minor axis of the molten steel remaining at the center of the slab is within a range of 100 mm or less, and where the outer surface of the solidified rectangular slab shown in Figures 11A and B is smaller than 200 mm, The short axis of the molten steel remaining in a rectangular shape at the center is within 1/2 of the short axis of the outer surface, and it is therefore preferable to stir at the final stage of solidification of the slab that has reached this area. .

As mentioned above, when it is necessary to cast at a higher temperature to promote the flotation and separation of inclusions in the slab, the inside of the mold is By performing the stirring in the mold (M stirring) performed at , and the stirring at the end of solidification (F stirring) performed approximately 10 m below the mold,
When performing in-mold stirring and secondary cooling zone stirring (S stirring) individually, or when performing these M stirring
Compared to agitation that combines agitation,
It has been found that central segregation and negative segregation can be reduced.

The present invention aims to propose a new method for manufacturing steel materials by continuous casting based on the above considerations. Specifically, molten steel is supplied into a casting mold with an immersion nozzle, and flux is applied to the surface of the molten metal. In the method of manufacturing steel products by continuous casting while charging, in the above casting, the range of magnetic flux density (Gauss) G on the mold surface at frequency f = 1.5 to 10Hz is 268×e ^-0・^18f ≦G≦ Due to the rotating magnetic field induced by the alternating current of 604×e ^-0・^20f ,
The molten steel is continuously drawn below the mold while being stirred by electromagnetic induction around the axis of the slab, and at the final stage when the molten steel solidifies as a slab with a rectangular cross section, the short edge of the outer surface of the solidifying rectangular slab is drawn out. For slabs with a diameter larger than 200 mm, the rectangle of molten steel remaining in the center of the slab is 100 mm or less,
In addition, for rectangular slabs to be solidified whose minor axis on the outer surface is smaller than 200 mm, the area where the minor axis of the molten steel remaining in the rectangular shape in the center is 1/2 or less of the minor axis of the above-mentioned outer surface. The magnetic flux density (Gauss) at the slab surface was induced by alternating current at a frequency f = 1.5 to 10 Hz, with the range of magnetic flux density (Gauss) G at the slab surface being 895 × e ^-0・^20f ≦G ≦2137×e ^-0・^20f . Due to the rotating magnetic field,
To provide a method for producing steel products by a continuous casting method, characterized in that the molten steel remaining in the center part is stirred by electromagnetic induction around the axis of the slab to prevent center segregation of the steel material as well as negative segregation due to stirring. It is.

Furthermore, the present invention provides a method for manufacturing steel materials by the above-described continuous casting method, further comprising: downstream of the withdrawal of the slab immediately below the mold, and at an intermediate solidification stage of the slab between the final solidification stage of the slab and the casting mold; Alternating current with frequency f = 1.5 to 10Hz and magnetic flux density (Gauss) G on the slab surface in the range 268×e ^-0・^18f ≦G≦604×e ⁻⁰・^20f , or solidification at the intermediate solidification stage mentioned above. When the thickness of the shell is Dmm, the range of magnetic flux density (Gauss) G on the slab surface at frequency f = 50 to 60Hz is 750000/(D-107) ² ≦G≦750000/(D-100
) The molten steel remaining in the solidified shell layer during the intermediate solidification period is stirred by electromagnetic induction along the axis of the slab by a rotating magnetic field or a moving magnetic field induced by one of the alternating currents described in ² . The present invention provides a manufacturing method characterized by the following.

Next, embodiments of the present invention will be described with reference to characteristic diagrams shown in the drawings.

First, using a top-blown oxygen converter, 3-charge blowing is carried out, and after adjusting the components with Al, F, eMn, etc. during tapping from the converter, certain components such as C = 0.61%, Mn =
0.90%, Si=1.65%, P=0.020%, S=0.015%,
Cu=0.13%, Ni=0.01%, Cr=0.02%, Mo=
Molten steel with a chemical composition of 0.01%, Al = 0.030%, and N = 25ppm is completely sealed with Ar between the ladle, tundish, and mold to prevent atmospheric oxidation of the molten steel, and the molten steel is transferred to an immersion nozzle. For example, SiO ₂ = 33.9%, CaO = 34.0%, Al ₂ O ₃ = 4.3 as an adiabatic flux.
%, Fe ₂ O ₃ = 2.0%, Na ₂ O = 8.4%, K ₂ O = 0.6%,
Powders of MgO = 0.9%, F = 5.1%, and C = 5.5% were introduced, and the molten steel was drawn downward from the mold by electromagnetic coils installed around the molten steel in the middle and final stages of solidification, respectively. The cast slab is solidified into a slab while being electromagnetically stirred around the shaft core by a magnetic field induced by applied alternating current.

In order to electromagnetically stir the inside of the mold and the molten steel, it is necessary to allow the lines of magnetic force to reach the molten steel through the copper wall, which has low magnetic permeability, and low-frequency stirring (1.5 to 10Hz) with small attenuation is suitable. There is. On the other hand, for the effect of stirring at the final stage of solidification, it is necessary that solidification of equiaxed crystals is proceeding at the place where stirring is performed, but it is known that low temperature casting is effective for accompanied by solidification of equiaxed crystals. If it is necessary to cast at a high temperature to promote the flotation and separation of inclusions within the piece, electromagnetic stirring or double casting in the mold may be used to generate a larger amount of equiaxed crystals than the molten metal cast in the mold at a high temperature. By using electromagnetic stirring in the secondary cooling zone, center segregation of the cast slab can be reduced.

Figure 1 shows the intensity of electromagnetic stirring applied to the molten steel in the slab on the inner surface of the mold, when the magnetic flux density is varied for each number of cycles of applied alternating current.
This shows the center segregation degree and surface negative segregation degree of each obtained slab, and the magnetic flux density is determined from the viewpoint of the slab that can be used for practical use as this type of slab and the allowable range of center segregation degree and surface negative segregation degree. It can be seen that is limited within a certain range. In other words, in order to give molten steel a constant rotational flow to stir the molten steel, the magnetic flux density needs to be within a certain range defined by the frequency, but in the diagram of Figure 1, , the values within the allowable range are two poles and the frequency f is 1.5 to 10Hz.
The magnetic flux density (Gauss) G at the mold surface must be within the range of 268×e ^-0・^18f ≦G≦604×e ⁻⁰・^20f (1). In other words, when this range is exceeded, cold workability deteriorates when the center segregation of the finished slab increases, and quenching hardness decreases when the surface negative segregation increases, resulting in a high defect rate of the finished product and making it unsuitable for practical use. Sometimes it disappears.

In other words, Figure 1 shows a bloom slab with 0.60%C.
This shows the effect of stirring using a low-frequency power source (1.5 to 10Hz) in the mold on center segregation and negative segregation of the white band when steel is manufactured using the continuous casting method. Therefore, the center segregation degree on the left vertical axis shows a rapid decrease as the magnetic flux density increases, and then hardly decreases. On the other hand, the degree of negative segregation in the white band portion on the right vertical axis increases linearly as the magnetic flux density increases. In Figure 1, the central segregation degree of C is 1.1 or less, and the negative segregation degree of C is -
The zone below 0.05 is indicated by diagonal lines as the area of proper electromagnetic stirring.
In the case of Hz, it can be seen that as the frequency increases, such as from 130 to 270 Gauss, the appropriate magnetic flux density range narrows and shifts to lower values. If this situation is shown in a diagram of the relationship between frequency and magnetic flux density, the appropriate range will be shown as the shaded range in FIG. 2, and if this relationship is expressed in an equation, it will be as shown in equation (1) above.

In addition, regarding the slabs of 0.6% C steel manufactured by electromagnetic stirring in the mold under the above-mentioned allowable conditions, and the slabs manufactured without electromagnetic stirring at all,
Looking at the change in segregation within each slab in terms of the amount of change in C% from the slab surface to the center of the slab, the results are as shown in Figure 3. It can be seen that the center segregation of the specimen is small, and at the same time, the negative segregation of C, especially in the surface layer, is small. Furthermore, when observing the actual macrostructures of these two slabs, as shown in the attached reference photo, the slabs produced by in-mold electromagnetic stirring according to the present invention were manufactured without any electromagnetic stirring as in the conventional method. It can be seen that a thin equiaxed crystal band was generated in the center of the slab, and the center segregation was improved by several orders of magnitude compared to the slab. Furthermore, it has been found that the slab produced by in-mold electromagnetic stirring according to the present invention is less likely to generate a negative segregation zone called a so-called white band. In other words, the degree of central segregation is usually determined by the ratio of the concentration of alloying elements in molten steel to the concentration in the central flexible part of the slab, and the degree of negative segregation is determined by the ratio of the concentration of alloying elements in molten steel to the concentration in the negative segregation zone. This is determined by the ratio of concentrations in the wood, but in places where there is a large temperature gradient in the early stages of solidification, the dentrite spacing is small, so even if the molten steel is made to flow by electromagnetic stirring, it is difficult for the molten steel to wash out the concentrated molten steel between the trees. , therefore, it is also difficult to generate a white band. In order to further reduce the negative segregation in the white band part and the center segregation in the center of these slabs, in addition to the electromagnetic stirring in the mold as described above, a certain electromagnetic stirring is applied to the molten steel once again during the intermediate stage of solidification of the molten steel. By providing stirring, a large amount of equiaxed crystals can be generated and center segregation can be effectively reduced. That is, in the steel material and manufacturing method by the continuous casting method described above, further downstream of the drawing of the slab, the molten steel in the intermediate solidification stage of the slab is transferred between the final solidification stage of the slab and the casting mold.
= range of magnetic field density G on the slab surface at 1.5 to 10Hz 268×e ^-0・^18f ≦G≦604×e ^-0・^20f , or frequency f=50 to 20f with the thickness of the solidified shell being Dmm
By rotating magnetic field or moving magnetic field induced by alternating current with the range of magnetic flux density (Gauss) G on the slab surface at 60Hz as 750000/(D-107) ² ≦G≦750000/(D-100) ² The effect is further doubled when electromagnetic induction stirring is applied around the shaft of the slab.

In addition, the magnetic flux density of electromagnetic stirring applied during the intermediate stage of solidification of molten steel and the thickness of the solidified shell at that time are 20 mm and 60 mm.
Similarly to Figure 1, Figure 4 shows the relationship between the center segregation degree of the finished slab and the negative segregation degree of the surface layer (white band part) for mm, and the magnetic flux density on the slab surface at this time ( Similar to FIG. 2, FIG. 5 shows the appropriate stirring range in terms of the relationship between the solidified shell thickness (Dmm) and the solidified shell thickness (Dmm).

After performing the electromagnetic stirring in the mold (M stirring) and the electromagnetic stirring (S stirring) during the intermediate solidification period of the secondary cooling zone, electromagnetic stirring (F stirring) is performed at the final stage of solidification.

The electromagnetic stirring (F stirring) at the final stage of solidification of the molten steel is limited to performing electromagnetic stirring when the residual molten steel in which equiaxed crystal solidification is proceeding inside the slab is within a certain range. That is, as mentioned above, in the solidified rectangular slab shown in Fig. 10, in which the minor axis of the outer surface is larger than 200 mm, the minor axis of the molten steel remaining in the rectangular shape at the center of the slab is 100 mm or less. Perform electromagnetic stirring in a range of areas. In addition, the short diameter of the outer surface of the rectangular slab to be solidified as shown in Fig. 11 is 200 mm.
In the case of smaller slabs, the short axis of the rectangular molten steel remaining in the central portion is limited to an area that is 1/2 or less of the short axis of the outer surface. Moreover, it is effective to start this F stirring at the time when central segregation begins to form within the equiaxed crystal region, and the central segregation is V-shaped in FIGS. Since the upper part of the V is the starting position of center segregation, it is preferable to perform the stirring at the final stage of solidification when the thickness of the solidified shell reaches the open part of this V.

When the molten steel is made to flow by performing electromagnetic stirring on the pool of residual molten steel in the above range, the residual molten steel is stirred within the equiaxed crystal zone of the molten steel, and for example, a columnar crystal zone is created in the previously solidified state. Compared to stirring at the solidification interface, stirring at a place where there is almost no temperature gradient of the residual molten steel in the equiaxed crystal formation region at the final stage of solidification increases the temperature gradient, resulting in columnar crystals where the flow of molten steel near the solidification interface becomes particularly strong. Unlike stirring in the generation region, the entire unsolidified molten steel, which has become highly viscous due to the temperature drop at the final stage of solidification, flows. As a result,
The molten steel that is becoming concentrated at the solidification interface is dispersed between equiaxed crystal grains, preventing the movement of the concentrated molten steel back and forth, and the subsequent solidification proceeds almost simultaneously within the molten steel pool, and the so-called concentration As a result of trapping molten steel between crystal grains, center segregation becomes difficult to occur. In addition, as a result of the entire unsolidified molten steel flowing at the final stage of solidification,
It is possible to prevent the formation of a sharp white band that occurs due to the flow of molten steel at the solidification interface, resulting in a widely dispersed band and a low degree of negative segregation.

In view of the allowable ranges of center segregation degree and surface layer negative segregation degree of a slab that can be put to practical use as this kind of slab, it is understood that the magnetic flux density during F stirring is limited within a certain range. In other words, in order to give a constant rotational flow to the molten steel in order to stir the molten steel, it is necessary that the magnetic flux density of electromagnetic induction stirring is within a certain range in relation to the frequency. , the value that falls within the tolerance range is two poles and the frequency f
is between 1.5 and 10 Hz, and the magnetic flux density (Gauss) G on the surface of the slab is 895×e ^-0・^20f ≦G≦2137×e ⁻⁰・^20f (2). In other words, if this range is exceeded, if there is a lot of segregation at the center of the finished slab, cold working will be poor and if there is a lot of negative segregation at the surface layer, the quenching hardness will decrease and the product will have a high defective rate, making it impossible to put it into practical use. There is also.

In other words, Figure 6 shows bloom slab with 0.60%C.
The graph shows the effect of stirring using a low-frequency power source (1.5 to 10 Hz) from around the slab on center segregation and negative white band segregation when steel is manufactured using the continuous casting method, and the horizontal axis shows the magnetic flux density on the inner surface of the mold. On the other hand, the center segregation on the left vertical axis shows a rapid decrease as the magnetic flux density increases, and then hardly decreases. On the other hand, the negative segregation in the white band portion on the right vertical axis increases linearly as the magnetic flux density increases. In Figure 6, the zone where C and center segregation degree is 1.1 or less, and the negative segregation degree of C -0.05 or less is indicated by diagonal lines as the area of proper electromagnetic stirring,
400 to 950 Gauss for 4Hz, and 400 to 950 Gauss for 6Hz
It can be seen that as the frequency increases, such as from 300 to 650 Gauss, the appropriate magnetic flux density range narrows and shifts to lower values. If this situation is shown in the relationship diagram between frequency and magnetic flux density, the appropriate range is shown as the seventh diagonal line, and this relationship can be expressed by the formula (2) above.
It becomes like the formula.

In addition, 0.6% C produced by electromagnetic stirring at the final stage of solidification of the slab under the above-mentioned allowable conditions.
For steel slabs and slabs produced without any electromagnetic stirring, the change in segregation within each slab is looked at as the amount of change in C (%) from the slab surface to the center of the slab. As shown in FIG. 8, it can be seen that the slab produced by electromagnetic stirring according to the present invention has less center segregation and at the same time less generation of negative segregation bands called white bands. Furthermore, when observing the actual macrostructures of these two slabs, as shown in the attached reference photo, the slabs produced by electromagnetic stirring according to the present invention are different from the slabs produced without any electromagnetic stirring as in the past. It can be seen that a thin equiaxed crystal band is generated in the center of the slab, and the center segregation is improved by several orders of magnitude. Normally, the central segregation degree is determined by the ratio of the concentration of alloying elements in molten steel to the concentration at the center of the slab, and the negative segregation degree is determined by the ratio of the concentration of alloying elements in molten steel to the concentration in the negative segregation zone. It is determined by the ratio. Figure 9 shows 200□ as a bloom slab.
When manufacturing 0.6% C steel of ~300 x 400 by continuous casting method, there are two cases: no electromagnetic stirring, electromagnetic stirring inside the mold (M stirring), and electromagnetic stirring inside the mold (M stirring). ), electromagnetic stirring (S stirring) is carried out during the intermediate stage of solidification of molten steel within 5 m below directly below the mold.
and when electromagnetic stirring is performed at the final stage of solidification of the slab approximately 10m below the mold (F stirring).
, when electromagnetic stirring (F stirring) at the final stage of solidification of the slab is combined with electromagnetic stirring (S stirring) at the intermediate stage of solidification of molten steel, and when electromagnetic stirring at the final stage of solidification of molten steel is used in combination with in-mold electromagnetic stirring (M stirring) When (F stirring) is used in combination,
In addition, electromagnetic stirring (F stirring) is performed in the middle stage of solidification of molten steel (S stirring) and at the final stage of solidification of the molten steel.
The graph shows the center segregation degree when the negative segregation degree of the white band part is 0.05 for each case where the electromagnetic stirring in the mold and in the intermediate stage of solidification of molten steel is combined with the electromagnetic stirring at the final stage of solidification. It can be seen that when stirring is used in combination, the center segregation degree becomes smaller. More specifically, in both M stirring and S stirring, fine equiaxed crystals are generated by electromagnetic stirring to prevent blitzing during solidification of columnar crystals, and by increasing the degree of filling in the center of the slab, center defects (center Normally, the wider the equiaxed crystal zone, the finer the equiaxed crystals in the center will be, and the higher the degree of filling in the center will be. Similarly, for S stirring, it is necessary to widen the width of the equiaxed crystals as much as possible, and therefore, it was considered preferable to perform S stirring at a portion within 5 m below the mold, which is close to the mold. On the other hand, when F stirring is performed approximately 10 m below the mold, the width of the equiaxed crystal zone narrows at the final stage of solidification of the target slab, which is contrary to the conventional concept of S stirring, and is rather centered. It was believed that this method had no effect on improving defects in parts. For this reason, M+S stirring as disclosed in the conventional US patent was considered to be better than M+F stirring, but when a large amount of equiaxed crystals have already been generated in the slab due to M stirring, It can be said that there is no effect of M+S stirring. However, M+F stirring is actually different from the effect of conventional electromagnetic stirring, and the equiaxed crystals deposited at the final stage of solidification are collected in the center by F stirring, and the shape of the molten steel pool at the final stage of solidification is changed. It has the effect of making the slab flatter and preventing equiaxed crystal grains from moving to the center of the slab, and at the same time preventing concentrated molten steel from concentrating in the center, improving center segregation. In other words, M+F stirring has the advantage that center segregation can be improved if an equiaxed crystal band about the width of the molten steel pool subjected to F stirring is generated;
By controlling negative segregation by stirring, a large improvement effect on center segregation can be obtained. Therefore, by M+F stirring,
Especially steel materials for applications with severe center segregation and negative segregation restrictions, such as wire rods (spring steel, steel cord steel, hard steel wire rods such as piano wire) and bars (low alloy steel for automobiles = SCR, SCM, SC steel) It has become possible to continuously cast killed steel, which is suitable for

As described in detail in the above embodiments, the method for manufacturing steel products by the continuous casting method of the present invention includes injecting molten steel into a casting mold together with adiabatic flux through a submerged nozzle,
The above molten steel is heated in the mold at a frequency f = 1.5 to 10 Hz, and the magnetic flux density (Gauss) G on the slab surface is 268×e ^-0・
^18f ≦G≦604×e The rotating magnetic field induced by alternating current in the range of 18f≦G≦604×e ^-0・^20f causes electromagnetic induction stirring around the mold axis, and the molten steel is continuously drawn downward from the mold, and the molten steel solidifies. At the intermediate stage, the molten steel is applied again at f = 1.5 to 10 Hz, and the range of magnetic flux density G at the slab surface is 268 × e ^-0・^18f ≦G≦604×e ^-0・^20f , or the thickness of the solidified shell layer. Frequency f= as Dmm
The range of magnetic flux density (Gauss) G is 50~60Hz.
750000/(D-107) ² ≦G≦750000/(D-100) ² Secondary electromagnetic induction stirring is caused by the rotating or moving magnetic field induced by the alternating current, and the molten steel is further In the final stage of solidification as a slab, for slabs whose outer surface minor axis is larger than 200 mm, molten steel remaining in a rectangular shape at the center of the slab is removed in an area where the minor axis is 100 mm or less. ,
In addition, for rectangular slabs to be solidified whose minor axis on the outer surface is smaller than 200 mm, the area where the minor axis of the molten steel remaining in the rectangular shape in the center is 1/2 or less of the minor axis of the above-mentioned outer surface. Then, the above residual molten steel is heated to a frequency of f=1.5.
At ~10Hz, the axis of the slab is rotated by a rotating magnetic field induced by an alternating current with a magnetic flux density (Gauss) G on the slab surface of 895×e ^-0・^20f ≦G≦2137×e ^-0・^20f . It is characterized by electromagnetic induction stirring in the surrounding area, and the steel is soft with less negative segregation in the slab and less segregation in the center.
Moreover, it can be manufactured at a relatively low cost using a continuous casting method, and satisfies the conditions for reducing strain aging embrittlement during processing.

[Brief explanation of the drawing]

Figures 1 to 9 are characteristic diagrams of slabs manufactured according to the present invention, Figure 10A is a cross-sectional view of the large slab at the final stage of solidification, and Figure 10B is a vertical cross-sectional view of the large slab at the final stage of solidification. 11A and 11B are a cross-sectional view and a longitudinal cross-sectional view of a small slab at the final stage of solidification.

Claims (1)

[Claims] 1. Supplying molten steel into a casting mold with an immersion nozzle,
In a method of manufacturing steel by continuously casting flux while pouring flux onto the surface of the molten metal, in the above mold, the range of magnetic flux density (Gauss) G on the mold surface at a frequency f = 1.5 to 10 Hz is 268 × e ^-0・^18f ≦G≦604×e ^-0・^20f Due to the rotating magnetic field induced by the alternating current,
The molten steel is continuously drawn below the mold while being stirred by electromagnetic induction around the axis of the slab, and at the final stage when the molten steel solidifies as a slab with a rectangular cross section, the short edge of the outer surface of the solidifying rectangular slab is drawn out. For slabs with a diameter larger than 200 mm, the rectangle of molten steel remaining in the center of the slab is 100 mm or less,
In addition, for rectangular slabs to be solidified whose minor axis on the outer surface is smaller than 200 mm, the area where the minor axis of the molten steel remaining in the rectangular shape in the center is 1/2 or less of the minor axis of the above-mentioned outer surface. The magnetic flux density (Gauss) at the slab surface was induced by alternating current at a frequency f = 1.5 to 10 Hz, with the range of magnetic flux density (Gauss) G at the slab surface being 895 × e ^-0・^20f ≦G ≦2137×e ^-0・^20f . Due to the rotating magnetic field,
A method for manufacturing steel products using a continuous casting method, characterized in that the molten steel remaining in the center portion is stirred by electromagnetic induction around the slab axis to prevent central segregation of the steel material as well as negative segregation due to stirring. 2. In the method for producing steel materials by the continuous casting method as set forth in claim 1 above, further downstream of the withdrawal of the slab immediately below the mold, the casting process is performed between the final stage of solidification of the slab and the casting mold. In the intermediate solidification stage, the frequency f = 1.5 to 10 Hz and the range of magnetic flux density (Gauss) G on the slab surface is 268×e ^-0・^18f ≦G≦604×e ^-0・^20f , or the above Assuming that the thickness of the solidified shell in the intermediate solidification stage is Dmm, the range of magnetic flux density (Gauss) G on the slab surface at frequency f = 50 to 60Hz is 750000/(D-107) ² ≦G≦750000/(D- 100
) The molten steel remaining in the solidified shell layer during the intermediate solidification period is stirred by electromagnetic induction along the axis of the slab by a rotating magnetic field or a moving magnetic field induced by one of the alternating currents described in ² . Something that is characterized by something that has happened.