JP3426383B2 - Steel 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 method of adding an alloy to molten steel in a mold at one point during continuous casting to produce a slab having a different composition from the molten steel from a part of the molten steel.

[0002]

2. Description of the Related Art When continuously casting a large-capacity molten steel such as 300 tons of ladle, an alloy is added to a part of the molten steel such as 50 tons in continuous casting to produce a slab having a different composition from the original ladle molten steel. The method of doing so has been attempted as a means for producing small lot cast pieces. Specifically, there is a method in which an alloy is added to a tundish in the middle of continuous casting, molten steel having a composition different from that of ladle molten steel is made in the tundish, and the molten steel is poured into a mold.

However, according to this method, the content of the alloy component of the molten steel in the tundish is low immediately after the alloy is added, and then the content of the alloy component increases, but until the content of the desired alloy component is reached. Takes a considerable amount of time, during which the slab made from the molten steel in the tundish becomes indeterminate and non-uniform in alloy composition. Therefore, there is a problem that the slab obtained at this time cannot be used for a desired purpose.

Further, a method of adding the alloy to the molten steel in the mold during the continuous casting has been attempted. FIG. 5 is an explanatory view of this method, in which 1 is a molten steel flow to be injected, 2 is a mold, 3 is an alloy to be added, 4 is molten steel, and 5 is a solidification shell. When the addition of the alloy 3 is started to the molten steel 4 containing no alloy, the molten steel flow 1 is agitated, and the alloy concentration in the molten steel increases. This alloy concentration becomes constant after a certain period of time, but the required time depends on the mixing state of the molten steel in the molten steel pool, that is, to how deep the molten steel flow 1 is mixed.

In FIG. 5, this depth is indicated by L '.
However, this depth L'is not stable even if the casting conditions are constant, and further, the alloy concentration in the cast slab cannot be said to be constant in the mixed region. Therefore, as the mixing region becomes longer, not only the joint portion formed between the steel species without alloy addition and the steel species with alloy addition into a predetermined composition system becomes longer, but also the joint length becomes longer. It changed with each operation, leading to a decrease in yield. Further, in such a mixed state, even in a portion where the component value increased to a predetermined value due to the addition of the alloy, there were variations in the circumferential direction and the length direction of the cast piece, which was a big problem.

[0006]

DISCLOSURE OF THE INVENTION The present invention is to add an alloy to molten steel in a mold at a time during continuous casting to produce a slab of a component different from the molten steel from a part of the molten steel, An object of the present invention is to provide a method capable of preventing the generation of a slab having an uncertain content of alloy components and uneven distribution, and preventing uneven distribution of alloy components.

[0007]

According to the method for continuous casting of steel of the present invention, (1) a unidirectional magnetic field having a uniform magnetic flux density is applied across the molten steel in the continuous casting mold or the obtained slab. Using a continuous casting machine with an electromagnetic brake at the bottom of the mold or below the mold, keep the magnetic field applied to the molten steel or the slab in the casting mold during continuous casting of molten steel. However, by adding an alloy in the molten steel above the magnetic field , the electromagnetic brake
Mixing takes place in a small pool formed in the mold,
It is characterized in that the time until the degree becomes uniform is shortened, and a slab having a different composition from the molten steel is produced from a part of the molten steel.

Alternatively, (2) an electromagnetic brake for applying a magnetic field in one direction having a uniform magnetic flux density across the molten steel in the continuous casting mold or the obtained slab is provided below the mold, or more than the mold. Using a continuous casting machine that is disposed below and that is provided with an electromagnetic stirrer that stirs the molten steel in the mold above the electromagnetic brake, in the mold during casting of the molten steel during continuous casting of molten steel While maintaining the state of being applied to the molten steel or the slab, while adding the alloy to the molten steel above the magnetic field and stirring the molten steel in the mold by the electromagnetic stirring device, the mold by the electromagnetic brake
Mixing takes place in a small pool formed within the
It is characterized by shortening the time until it becomes uniform and producing a slab having a different composition from the molten steel from a part of the molten steel.

(3) In particular, in that case, when the specific gravity of the molten steel added with the alloy is larger than the specific gravity of the molten steel not added with the alloy, the production of the slab containing the alloy is carried out at the initial stage of the continuous casting of the molten steel not added with the alloy. If the specific gravity of the molten steel added with the alloy is smaller than the specific gravity of the molten steel not added with the alloy, it is advisable to manufacture the slab containing the alloy at the final stage of continuous casting of the molten steel not added with the alloy.

(4) Specifically, as a method of supplying the wire into the molten steel, the lower end is provided with a dipping nozzle having a lower end extending below the tundish, and a wire supply hole is provided in the axial center portion, and the lower end is the above-mentioned. Using a tundish that has a stopper rod arranged at the molten steel inlet at the upper end of the immersion nozzle, immerse the lower end of the immersion nozzle into the molten steel in the mold, and the wire from the upper part of the stopper rod through the wire supply hole. There is a method of inserting the wire to the molten steel inlet at the upper end of the nozzle and supplying a wire to the molten steel in the immersion nozzle together with an inert gas.

[0011]

1 is an explanatory view of an electromagnetic brake according to the present invention, which is a vertical sectional view perpendicular to a wide surface of a mold. The electromagnetic brake 7 outputs a magnetic field in one direction having a uniform magnetic flux density in the width direction of the wide surface across the molten steel 4 in the mold for continuous casting or the slab discharged from the mold so that Can be applied to the molten steel 15 in the cast. Reference numeral 8 is a static magnetic field (magnetic field) at this time.

The molten steel flow injected from the tundish into the mold 2 through the nozzle 12 reaches point f when the static magnetic field 8 is not applied. However, when the static magnetic field 8 is formed, the Lorentz force that blocks the molten steel injection flow passing through the static magnetic field 8 acts from the static magnetic field 8, and the penetration depth of the injection flow reaches the levels c and d. .

FIG. 2 is an explanatory view of the first invention of the present application, and is a vertical sectional view parallel to the wide surface of the mold. In the figure, 8 is a static magnetic field,
It flows from the front to the back of the paper. In the present invention, during continuous casting of molten steel, alloy 3 is added to the molten steel above the magnetic field while maintaining the magnetic field applied to the molten steel in the mold or the cast piece during casting. In the present invention, the magnetic field 8 is thus formed to prevent the injection flow from penetrating below the c and d levels.

As a result, the added alloy 3 has a, b,
In the molten steel pool in the range of c ′ and d ′, the molten steel flow is uniformly mixed and extruded downward from the pool at a constant speed. That is, the electromagnetic brake creates a small pool for mixing in the mold,
Since the mixing is performed within that range, the time until the concentration becomes uniform is shortened, and the flow extruded downward from this pool is less likely to form convection due to plug flow, so the electromagnetic brake At the bottom does not cause new mixing. Therefore, the length of the seam portion where the first component changes to the second component becomes the shortest.

As described above, since the alloy components are sufficiently mixed in the pool having a constant volume above the electromagnetic brake, a predetermined time has elapsed since the addition of the alloy was started, and when the alloy reaches a steady state. The component concentration in the obtained cast piece is stable, and is constant in the cross section of the cast piece and in the casting length direction. Therefore, by carrying out the present application, the length of the component change region caused by the alloy addition in FIG. 5 is significantly reduced, and the concentration of the alloy component is made uniform at any part of the cast piece, which is a problem that has been inherent in the prior art. Can be solved.

Next, the second invention of the present application will be described. Figure 2
9 is an electromagnetic stirrer. Although a known electromagnetic stirrer is used, it is disposed above the electromagnetic brake, preferably near the meniscus of the molten steel in the mold. According to this method, both the strong stirring force F ′ generated by the molten steel injection flow and the electromagnetic stirring force act on the molten steel within the range of a, b, c ′, d ′ in FIG. Mix. Therefore, it is possible to more strongly solve the conventional problem described with reference to FIG. 5 that the component concentration of the alloy fluctuates in the slab when the alloy is added.

The third invention of the present application will now be described. The cast piece 5 obtained in FIG. 3 is pulled out in the direction of the arrow 10. Therefore, after the start of the addition of alloy 3, time elapsed and c ′ was g
The position d ′ moves to the position h. As I said,
In the present invention, since the magnetic field 8 is formed at the time when the addition of the alloy 3 is started, the stirring force by the injection flow 1 from the nozzle 12 does not reach the molten steel and the slab below c′d ′. Therefore, a, b, g, and h are alloy-containing components,
g, e, and h are components containing no alloy.

According to the findings of the present inventors, a, b, g,
When the specific gravity of the molten steel of h is smaller than the specific gravity of the molten steel of g, e, and h, the molten steel does not mix with each other even after a lapse of time. However, the specific gravity of molten steel a, b, g, h is g, e,
When the specific gravity of the molten steel of h is larger than that, the density convection exceeding the braking effect of the electromagnetic brake occurs, and the molten steels of a, b, g, and h settle in g, e, and h, and mixing occurs. Therefore, in this method, of the molten steel with the alloy added and the molten steel not added with the alloy, the molten steel with the larger specific gravity is lower than the molten steel with the smaller specific gravity, The production is preceded by the production of the ingot by the molten steel having the smaller specific gravity.

In the present invention, in addition to the first or second invention, a shield plate for preventing vertical mixing of molten steel in the mold is provided on the molten steel surface of the molten steel in the mold immediately before adding the alloy. Can be charged. At this time, even if the molten steel having the smaller specific gravity is lower than the molten steel having the larger specific gravity in FIG. 3, the shielding plate causes the molten steel having the larger specific gravity to settle in the molten steel having the smaller specific gravity. Things can be prevented.

The addition of the alloy according to the present invention is preferably carried out by a method in which a wire containing an alloy component to be added is supplied into molten steel. According to this method, the alloy components to be added can be easily adjusted to have a composition that easily dissolves in the molten steel.

FIG. 4 is an explanatory view of a fourth invention of an alloy wire adding method carried out by the present inventors. That is, here
In order to supply the wire 3 to the molten steel 4 in the mold, the lower end extends below the tundish 11, and the immersion nozzle 12 is provided.
A wire supply hole 13 is provided in the axial center part, and a lower end has a stopper rod 14 arranged at the molten steel inlet at the upper end of the immersion nozzle 12.
Using a tundish 11 having
The lower end of the wire is immersed in the molten steel 4 in the mold, and the wire 3 is fed from the upper part of the stopper rod 14 to the wire feed hole 13
Insert to the molten steel inlet at the upper end of the immersion nozzle 12 via
The method of supplying the wire 3 to the molten steel in the immersion nozzle 12 together with the inert gas is adopted.

According to this method, the molten steel and the alloy are first mixed in the immersion nozzle 12, then exit the immersion nozzle 12 and are further mixed in the molten steel pool above the magnetic field 8. As a result, the molten steel and the alloy are mixed more uniformly, and a homogeneous slab with no high-concentration portion or low-concentration portion can be obtained.

[0023]

[Example 1] 3 molten steel of low carbon (C = 0.05%) component
00 tons were melted and continuously cast by the method based on FIG. After casting 250 tons of molten steel, wire-like carbon was added into the molten steel from the meniscus in the mold at a rate of 27 g / sec in order to increase the carbon concentration in the molten steel to 0.10%. Mold shape is 245 mm (thickness) × 1500 mm
(Width) and casting speed were 1.0 m / min. A DC magnetic field band having a uniform magnetic flux density in the mold width direction was set at a position of 500 to 700 mm from the meniscus in the mold. The casting was carried out according to the above casting conditions except that the magnetic field was not applied and the case where the magnetic field of 0.35 tesla was applied.

The experimental results are shown in FIG. When a magnetic field was applied, a steady state was achieved by casting 2 m after the wire was added and C = 0.10%, whereas when a magnetic field was not applied, the carbon concentration in the molten steel was about 0 as an average value. .1
It took about 5 m of casting to reach 0%. Also, apparently,
It was found that the carbon concentration in the cast slabs fluctuated by about ± 0.02% even in the steady state. Further, the carbon concentration also varied greatly in the cross section of this slab perpendicular to the casting direction.

According to the present invention, the length of the dummy slab required for the composition of the slab to change from the value in the pot to the predetermined value can be greatly shortened, the yield can be greatly improved, and when the predetermined value is reached. It became possible to remarkably suppress the component fluctuation in the casting length direction.

[0026]

[Embodiment 2] Molten steel having a low carbon content (C = 0.05%)
00 tons were melted and continuously cast by the method shown in FIG. After casting 250 tons of molten steel, iron-coated wire-like carbon was added from the in-mold meniscus into the molten steel at a rate of 27 g / sec to increase the molten steel carbon concentration to 0.10%. Mold shape is 245 mm (thickness) × 1500 mm
(Width), the casting speed was 1 m / min, and the direct current magnetic field band having a uniform magnetic flux density in the width direction of the mold was 5 mm from the mold meniscus.
It was installed at a position of 00 to 700 mm, and a magnetic field of 0.35 Tesla was continuously applied.

In addition to the above casting conditions, the electromagnetic stirrer installed in the mold is operated to form a horizontal swirl flow of about 30 cm / min at the molten steel meniscus portion, and the casting is not performed. I did. After casting,
The C concentration in the vicinity of the surface and inside the cast piece was analyzed.

The change in the average C concentration on the surface and inside of the slab in the casting length direction becomes a steady state at 2 m from the wire-added portion, as in the case where the electromagnetic brake of Example 1 is actuated, and C = 0. It was 10%. However, the variation in C concentration in the circumferential direction of the cast slab (ΔC) was ΔC = 0.03% when the electromagnetic stirring in the mold was not applied, whereas when the electromagnetic stirring in the mold was applied, ΔC = 0.01
% Or less.

As described above, according to the present invention, not only the unsteady portion length required until the component of the cast slab changes from the value in the pot to the predetermined value can be greatly improved, but also at the portion where the steady state is reached. It became possible to minimize the variation in the concentration of added solute in the circumferential direction of the slab.

[0030]

[Example 3] 3 molten steel of low carbon (C = 0.05%) was used
00 tons were melted and continuously cast by the method shown in FIG. After casting 250 tons of molten steel, iron-coated wire-like carbon was added from the meniscus in the mold into the molten steel at a rate of 27 g / sec to increase the molten steel carbon concentration to 0.10%.

The mold shape is 245 mm (thickness) x 1500 m
m (width), casting speed was 1 m / min, a DC magnetic field band having a uniform magnetic flux density in the mold width direction was set at a position of 500 to 700 mm from the mold meniscus, and a magnetic field of 0.35 Tesla was continuously applied. .

On the other hand, under the same molten steel composition and casting conditions, C wire was added to the first 50 tons of molten steel,
After that, 250 tons of molten steel were cast without adding wires. After the casting was completed, the C concentration in the vicinity of the surface of the slab and inside was analyzed.

When the wire was added to the rear part of the casting, the change in the C concentration at the wire addition site was the same as in FIG. 6 and the transition length of the concentration was 2 m. On the other hand, when the wire was added to the casting head, the change in the C concentration at the joint with the wire non-added portion had a concentration transition length of 4 to 5 m as shown by the solid line in FIG. 7. Here, the broken line is the theoretical estimated value of the concentration change on the assumption that the mixture is suppressed by the electromagnetic brake, and the solid line in FIG. 6, which is the result of the first embodiment, is in good agreement with this theoretical estimated value. , In FIG. 7, it deviates greatly.

This is because the density of the solute (carbon) added is lower than that of the molten steel, so the density of the molten steel at the bottom of the continuously cast strand pool added earlier is smaller than that of the molten steel cast thereafter. This is because the mixing due to the density instability occurred at a position below the electromagnetic brake.

[0035]

[Embodiment 4] 3 molten steels with low carbon (C = 0.05%)
00 tons were melted and continuously cast by the method shown in FIG. After casting 250 tons of molten steel, iron-coated wire-like carbon was added to the molten steel at a rate of 27 g / sec into the molten steel through a hole provided in the axis of the tundish stopper to increase the molten steel carbon concentration to 0.10%. did. The mold shape is 245
mm (thickness) × 1500 mm (width), the casting speed is 1 m / min, the DC magnetic field band having a uniform magnetic flux density in the width direction of the mold is set at a position of 500 to 700 mm from the mold meniscus, and 0.35 Tesla A magnetic field was applied continuously.

After the completion of casting, the C concentration in the vicinity of the surface of the slab and inside was analyzed. The change in the average C concentration on the surface and inside of the slab in the casting length direction caused the electromagnetic brake of Example 1 to be activated. Similar to the case, the steady state was reached at 2 m from the wire addition site, and C = 0.10%.

On the other hand, C = 0.10 cast in Example 1
% Cast, and C = 0.10 cast in this example.
%, The slabs were rolled. As a result, in the rolled plate of Example 1, there were slight defects caused by the inclusion of the continuous casting powder. However, no defects were found in the rolled sheet of cast slab obtained in this example. The defect caused by the powder entrainment in Example 1 was caused by the fact that the powder adhering to the wire surface was brought into the pool when the wire passed through the powder layer when the wire was added from the meniscus. It was confirmed that there was no problem in the case where the addition of the wire did not pass through the powder layer as described above.

[0038]

When the present invention is carried out, when an alloy is added to molten steel during the continuous casting to produce a slab containing this alloy from a part of the molten steel, the content of alloy components is It is possible to prevent indefinite and non-uniform slabs from being generated and prevent uneven distribution of alloy components.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an electromagnetic brake of the present invention.

FIG. 2 is an explanatory view of the operation of the present invention.

FIG. 3 is an explanatory view of another operation of the present invention.

FIG. 4 is an explanatory diagram of a wire supply method according to the present invention.

FIG. 5 is an explanatory view of a method of adding an alloy into molten steel during continuous casting.

FIG. 6 is a diagram showing a change state of the C amount in Example 1 of the present invention.

FIG. 7 is a diagram showing a change state of the C amount in Example 3 of the present invention.

[Explanation of symbols]

1: injection flow, 2: mold, 3: alloy wire, 4: molten steel in mold, 5: solidification shell, 6: inert gas,
7: Electromagnetic brake, 8: Static magnetic field (magnetic field), 9: Electromagnetic stirrer, 10: Slab withdrawing direction, 12: Immersion nozzle, 13: Wire supply hole, 14: Supper rod,
15: Molten steel in the slab.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI B22D 11/115 B22D 11/115 B (72) Inventor Kosaku Shioda 1 Kimitsu, Kimitsu-shi, Chiba New Nippon Steel Co., Ltd. Kimitsu (56) Reference JP-A-5-111736 (JP, A) JP-A-6-126402 (JP, A) JP-A-6-285596 (JP, A) JP-A-6-320235 (JP, A) ) JP-A 63-119959 (JP, A) JP-A 8-90173 (JP, A) JP-A 7-32098 (JP, A) JP-A 6-304718 (JP, A) JP-A 6- 292953 (JP, A) Japanese Unexamined Patent Publication No. 6-304721 (JP, A) Actual Development No. 6-77955 (JP, U) International Publication 93/022085 (WO, A1) (58) Fields investigated (Int.Cl. ⁷⁾ , DB name) B22D 11/10 B22D 11/04 311 B22D 11/108 B22D 11/11 B22D 11/115

Claims (4)

(57) [Claims] 1. An electromagnetic brake for applying a unidirectional magnetic field having a uniform magnetic flux density so as to traverse molten steel in a continuous casting mold or the obtained slab is disposed below the mold or below the mold. While continuously casting the molten steel using the continuous casting machine, the alloy is added to the molten steel above the magnetic field while keeping the magnetic field applied to the molten steel in the casting mold or the slab. Then, by the electromagnetic brake
Mixing is done in a small pool formed in the mold,
A continuous casting method for steel, characterized in that a time until the concentration becomes uniform is shortened, and a slab having a composition different from that of the molten steel is produced from a part of the molten steel. 2. An electromagnetic brake for applying a unidirectional magnetic field having a uniform magnetic flux density across the molten steel in the continuous casting mold or the obtained slab is disposed below the mold or below the mold. And using a continuous casting machine in which an electromagnetic stirrer for stirring the molten steel in the mold is arranged above the electromagnetic brake, while the molten steel is being continuously cast, the molten steel in the mold during casting of the magnetic field or the slab While maintaining the state of being applied to the molten steel, the alloy is added to the molten steel above the magnetic field and the molten steel in the mold is stirred by the electromagnetic stirring device .
And small tiny particles formed in the mold by the electromagnetic brake
The time until the concentration is uniform when mixing is performed in the pool
The method for continuous casting of steel is characterized in that a slab having a different composition from the molten steel is produced from a part of the molten steel. 3. When the specific gravity of the molten steel added with the alloy is larger than that of the molten steel not added with the alloy, a slab containing the alloy is produced at the initial stage of continuous casting of the molten steel without addition of the alloy, and the alloy is added. When the specific gravity of the molten steel prepared is smaller than the specific gravity of the molten steel not added with the alloy, the production of the alloy-added slab is carried out at the end of continuous casting of the molten steel not containing the alloy. A method for continuously casting steel as described. 4. When supplying a wire into molten steel, a lower end is provided with an immersion nozzle whose lower end extends below a tundish, and a wire supply hole is provided in an axial center portion, and the lower end is a molten steel inlet at the upper end of the immersion nozzle. Using a tundish with a stopper rod arranged in the, the lower end of the immersion nozzle is immersed in the molten steel in the mold, and the wire goes from the upper part of the stopper rod to the molten steel inlet at the upper end of the immersion nozzle via the wire supply hole. Inserting and feeding a wire into the molten steel in an immersion nozzle with an inert gas.
Or the continuous casting method for steel according to 2 or 3.