JPH02224855A - Continuous casting method - Google Patents

Abstract

PURPOSE:To produce a cast slab having good quality by arranging electromagnetic force impressing device at outer circumference of a submerged nozzle and giving the electromagnetic force to molten metal flowing down in this nozzle to straighten the molten metal stream. CONSTITUTION:By sliding a sliding plate 10b in sliding device 10 to the arrow mark direction to open the hole, the molten steel 1 is caused to flow down. At the time of opening the hole, by impressing the electromagnetic force to the molten steel stream 1A with the electromagnetic force impressing device 11, the molten steel stream 1A is straightened as column state and allowed to flow down without being brought into contact with inner face of the submerged nozzle and developing the rotating stream, and discharged as uniformly divided into two with discharge holes 2a, 2b. By varying impressing degree of the electromagnetic force according to the casting velocity or the cast slab width, etc., the adequate molten steel straightening stream can be obtd.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention is directed to a continuous casting method, specifically, to rectify the flow of molten metal in a submerged nozzle to prevent uneven flow of the molten metal in the mold, thereby producing slabs of good quality. This invention relates to a continuous casting method for manufacturing.

(Prior Art) In the continuous casting method, molten metal (hereinafter referred to as molten steel when casting steel) is injected into a mold from a tundish through an immersion nozzle. FIG. 1 shows this state. As shown, the molten steel 1 discharged from the tundish (not shown) flows through the immersion nozzle 2 and the discharge port (
2a, 2b) into the mold 3. The discharged 11111 collides with the short side mold 3 and is divided into an upward flow 1a and a downward flow 1b. At this time, if the upward flow 1a is too large, the powder 4 on the meniscus will be drawn into the molten steel and become inclusions, degrading the quality of the slab. If the upward flow 1a is small, the amount of heat supplied to the meniscus portion is insufficient, and the powder may become unmelted, resulting in pinholes, or a solidified shell called Deitskell may be formed in the meniscus portion, causing breakout. be.

For this reason, in actual operations, in order to prevent powder entrainment and Deitzker, etc., the immersion nozzle is selected according to the operating conditions, and the immersion depth of the nozzle is changed empirically.

However, even if a submerged nozzle that has been passed through the operating conditions is used and placed in an appropriate position, if casting continues for a long time, alumina suspended in the molten steel may adhere to the discharge port, or the inside of the nozzle may The discharge port is damaged by the molten steel flowing down. When the shapes of the discharge ports on the left and right sides of the nozzle differ, the amount of molten steel discharged becomes uneven, causing a drift in the molten steel in the mold.

For example, as shown in Fig. 2, if the melting damage of the discharge port 2a becomes larger than that of the discharge port 2b, the flow rate from the discharge port 2a increases and a strong upward flow occurs, causing a large change in the scene and the powder on the meniscus. 4 may be involved. In addition, when the molten steel discharge amount differs as described above, the meniscus flow becomes uneven on the left and right sides of the immersion nozzle, the flow is generated from the stronger flow to the weaker one, and a vortex 5 is formed behind the immersion nozzle. 5
Powder 4 may also get caught up in the process.

As described above, the deformation of the discharge port of the immersion nozzle during casting causes problems such as defects in the quality of the slab and unstable quality.

Various countermeasures have been taken in the past to deal with such problems. Representative examples include the following.

(1) Method of measuring the surface of molten steel with a level meter (Japanese Patent Application Laid-Open No. 2002-120002).

62-197258).

Multiple eddy current levels are installed between the immersion nozzle and the short side of the mold, and these level meters measure the raised state of the molten steel surface to estimate the degree of uneven flow of the molten steel, and then reduce the casting speed to eliminate the uneven flow. This method prevents powder from getting caught. However, once alumina adheres to the immersion nozzle and a drift occurs, the casting speed must be lowered until the drift disappears, making it unsuitable for 1 liter casting.

(2) A method of moving a stopper for controlling the flow of molten steel based on the temperature difference of cooling water (Japanese Patent Application Laid-open No. 58-53361).

Detects the drift of molten steel from the temperature difference of cooling water on the short side of the mold,
This method moves the molten steel stopper horizontally to the mold to prevent drifting. With this method, problems have been pointed out, such as small drifts are not detected because the drift is detected by the temperature difference of the cooling water, and the response is low.

(3) Method of controlling molten steel flow by applying electromagnetic force (Unexamined Japanese Patent Publication No. 6)
2-25495, JP-A-63-16840, etc.).

A magnetic pole is placed on the outside of the mold, and a perpendicular static magnetic field is applied to the molten steel flow discharged from the immersion nozzle to generate a Lorentz force, thereby controlling the molten steel flow. This is a method to prevent powder from being entrapped. However, electromagnetic brake devices are expensive and have problems such as high maintenance costs.

(4) Method of controlling molten steel flow by providing a collision plate (Unexamined Japanese Patent Publication No. 5
7-79055).

In this method, a collision plate is inserted into the reversal area that occurs when the molten steel discharged from the immersion nozzle hits the short side of the mold, thereby controlling the flow rate of the molten steel. However, the collision plate causes the molten steel in the meniscus to stagnate, forming a solidified shell called a Deitskell, which can lead to breakouts.

(5) A method of controlling the vortex by arranging a rod-shaped body around the immersion nozzle (Japanese Patent Application Laid-Open No. 62-212045).

This is a method in which a plurality of rod-shaped bodies are placed in the vortex generation area around the immersion nozzle to prevent vortices and powder entrainment. However, there is an opinion that this method is ineffective because an unstable molten steel flow occurs in the meniscus area.

(6) A method of using an immersion nozzle that is optimal for the casting conditions.

This method uses a submerged nozzle that is most suitable for the operating conditions (casting speed, slab width, etc.). However, in the case of multiple casting, alumina adheres to the inner surface of the immersion nozzle and the discharge port, making it impossible to maintain the optimal shape and angle. Furthermore, if the convergence or drawing speed is changed during casting, the optimum conditions will be greatly deviated from.

(7) A method of blowing Ar gas into the immersion nozzle.

This is a method in which Ar gas is blown into the immersion nozzle to prevent alumina from adhering to the inner surface of the nozzle or the discharge port. However, if the amount of blowing is large, there is a problem in that when the Ar gas floats up from the molten steel and is emitted from the surface of the molten steel, it causes a change in the scene.

As mentioned above, each of the conventional methods has its advantages and disadvantages, and there is no method that can be stably implemented over a long period of time.

(The invention is intended to solve! IB) The purpose of this invention is to solve the following problems: internal defects (inclusions) in slabs caused by continuous casting and surface defects in steel sheets (slipper defects, sagging defects, bulge defects, etc. that appear due to rolling). ) It is an object of the present invention to provide a continuous casting method capable of producing slabs of good quality by preventing drifting, which is the root cause of this.

(Means for Solving the Problem) In order to elucidate the drifting flow that occurs during continuous casting and to prevent it, the present inventors used a water model device as shown in Fig. 3, and as shown in Fig. 4 below. ~A test was conducted with the results shown in Figure 8. In addition, in FIG. 3, l is water used instead of molten metal, 2 is an immersion nozzle, 2a, 2b are discharge ports, 3 is a mold,
4 is liquid paraffin used instead of powder, 5a
, 5b are the water level meters, h and H are the distances between the level meters 58 and 5b and the scene (water surface), a and point A are the flow rate measurement points at the discharge port, and b and point B are the points near the short side of the mold. The flow velocity measurement point, point C1C, is a flow velocity measurement point near the nozzle.

From the results shown in Figures 4 to 8, it can be seen that: ■ The greater the difference (absolute value) in the amount of scene variation on both sides of the immersion nozzle, the more the powder entrainment frequency increases (Figure 4), ■ a, point A, b
, the ratio of flow velocities at point B, c, and point C (V, /VA, V
, /Vl, vc/vc) are constantly changing, and these changes are almost similar (Fig. 5).■The flow velocity ratio (V, /V^) at the discharge port increases (or decreases). ), the scene fluctuation difference increases as (Fig. 6), ■Flow velocity ratio V,
It has become clear that as /V becomes larger (or smaller) than 1, the frequency of powder entrainment per minute increases (Figure 7).

Furthermore, in order to investigate the cause of the drift, a test was conducted using a water model device equipped with a sliding nozzle as shown in FIG. The sliding nozzle 10 is an upper play) 10a
, sliding plate 10b and lower plate 10c
It consists of To control the flow rate with the sliding nozzle 10, the sliding plate 10b is slid in the direction of the arrow to shift the openings of the upper and lower plates 10a and 10b, and control is performed by increasing or decreasing the area.

If the opening of the sliding nozzle is circular, the ninth
As shown in the figure, the free surface of the fluid expands, so the 8th
As shown in the figure, since the molten steel flows down while swirling along the inner surface of the immersion nozzle 2, fluctuations occur in the molten steel flow, and a drift occurs in the discharged mold.

From the various test results mentioned above, it has been concluded that by rectifying the molten steel flow in the immersion nozzle, it is possible to prevent molten steel drift, and the molten steel fluctuation caused by drift and the entrainment of powder caused by this can be prevented. This conclusion was reached and this invention was completed.

That is, the gist of the present invention is ``a continuous casting method characterized by providing an electromagnetic force applying device on the outer periphery of an immersed nozzle, and applying 1! magnetic force to the molten metal flowing down inside the immersed nozzle to rectify it'' A continuous casting method characterized in that a partition plate is provided inside and the molten metal flowing down inside the immersion nozzle is rectified by the partition.

(Function) Hereinafter, the continuous casting method of the present invention will be explained using the drawings.

FIG. 10 is a schematic cross-sectional view of an apparatus for carrying out the continuous casting method of the first invention, which is equipped with an electromagnetic force applying device on the outer periphery of a immersed nozzle. In FIG.
10 is a sliding nozzle device, and 11 is an electromagnetic force applying device.

To cast using a device consisting of this configuration,
Sliding plate 10 of sliding device 10
Slide b in the direction of the arrow to open it and let the molten steel l flow down.

At the same time as the opening, molten steel flow I is applied to 1 by the magnetic force applying device 11.
When applied to A, the molten steel flow IA is rectified into a columnar shape as shown in the figure, flows down without contacting the inner surface of the immersion nozzle, and without creating a rotating flow, and is equally divided into two at the discharge ports (2a, 2b). Because it is discharged, there is no possibility of uneven flow within the mold.

Appropriate molten steel rectification can be obtained by increasing or decreasing the degree of magnetic force application in accordance with the casting speed, slab width, etc.

By the way, the reason why a molten steel flow is rectified into a columnar shape by applying electromagnetic force is based on the following principle.

That is, as shown in FIG. 11(a), when a high frequency current I flows through the coil 12 of the tim force applying device (11 in FIG. 10), the 11th [iJ A current ■ flows in the opposite direction as shown in (b). At this time, a downward magnetic field H is generated around the coils 12a and 12b according to Fleming's right-hand rule, which generates an eddy current l in the molten steel flow. This eddy current i
An electromagnetic force F is generated by Fleming's left-hand rule from the interaction with the magnetic field H, and this force acts toward the center of the molten steel flow. Since the molten steel flow is supported by this electromagnetic force F and flows down inside the nozzle, its fluctuation is suppressed and it is formed into a columnar shape.

FIG. 12 is a schematic sectional view of a casting apparatus for carrying out the continuous casting method of the second invention, in which a partition plate 13 is provided inside the immersion nozzle 2.

When casting using this method, sliding plate 1
When the molten steel 1 flows down through the opening of 0b, as shown in the figure,
The molten steel flow IA is divided into two parts by a partition plate 13.
3, is rectified and discharged from discharge ports 2a and 2b. In this way, the presence of the partition plate 13 prevents the molten steel flow IA from fluctuating or rotating, so that no drift occurs within the mold.

The thickness of the partition plate should be thin so as not to restrict the amount of molten steel flowing down, and is preferably 5-1 or less.Also, the material may be a refractory material that can withstand high temperatures, but the thickness of the partition plate may be made of zirconia. By covering with refractory material, thermal erosion resistance can be improved.

(Example) Continuous casting of two strands (curving radius 12-), thickness 200 mm, radius 1200 by the method of the present invention and the conventional method.
A slab of - was cast, and the internal defects of the slab and the surface defects of the steel plate after rolling this slab were investigated.

When casting, in the first strand, a submerged nozzle equipped with an electromagnetic force applying device as shown in Fig. 10 is used (method of the first invention), and a submerged nozzle provided with a partition plate as shown in Fig. 12 is used. (method of the second invention), and the second strand was cast using a conventional submerged nozzle.

The molten steel used at this time was low carbon aluminum killed steel, its components and casting temperature are shown in Table 1, and Table 2 shows the specifications of the immersion nozzle.

In the method of the first invention, an electromagnetic force applying device was placed around the outer periphery of the immersion nozzle, and a magnetic flux density of 5000 Gauss was applied. Further, in the method of the second invention, an immersion nozzle was used in which a partition plate made of zirconia with a thickness of 3 mm was provided inside the nozzle.

Figure 13 shows the relationship between the difference in scene variation during casting and the occurrence rate of slab inclusions. In Figure 0, the mark is the first invention method, the Δ mark is the second invention method, and the 0 mark is the conventional method. It shows. Note that the defect occurrence rate is the value obtained by dividing the number of defective slabs by the total number of slabs cast from one charge.

As can be seen from this figure, when casting is performed using the method of the first invention, the difference in the amount of variation in the scene is the smallest (the incidence of inclusions is low8). The incidence of inclusions is reduced.In contrast, in the conventional method, the difference in the amount of scene variation varies widely, and the incidence of defects is also extremely high.

Also, the amount of molten steel that can be cast with one immersion nozzle is
In the conventional method, it was 520), whereas in the method of the first invention, it was 1,820), and in the method of the second invention, it was 1,580.
This means that more than three times the amount of molten steel can be poured compared to the conventional method.

Figure 14 shows the results of a steel plate produced by rolling the slab cast in this example and inspecting the surface defects of the steel plate by magnetic particle testing. It can be seen that the method of the present invention significantly improves the problem of blistering defects (blister defects, etc.) compared to the conventional method. Especially in the case of steel sheets manufactured by the method of the first invention, the improvement effect is remarkable.The surface defect index in Figure 14 refers to the tonnage of the steel sheet cut off due to the occurrence of surface defects from the slab of the charge. It is the value divided by the total tonnage of rolled steel plate.

In this embodiment, the case of casting a slab has been described, but the method of the present invention can be used not only for casting slabs but also for casting blooms and billets.

Further, in the explanations so far, the case where the molten metal is steel has been explained, but it goes without saying that the present invention can also be applied to casting other metals in which eddy currents occur, such as aluminum, in addition to molten steel.

(Hereinafter, margin) (Hereinafter, margin) Table 1 Table 2 (Effects of the invention) As explained above, according to the method of the present invention, the molten steel flow in the immersion nozzle can be rectified. Even in the case of high-speed casting, it is possible to prevent drifting of self-melting steel in the mold. Therefore, the scene fluctuation caused by drifting is eliminated, and the pinholes and powder entrainment caused by this are eliminated, and internal defects (inclusions) or surface defects (slipper defects, sludge defects, etc. on the surface of the steel plate) are eliminated. occurrence can be significantly reduced. It also has excellent effects such as extending the life of the nozzle and reducing slab production costs.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the case where the molten metal is normally poured into the mold through the immersion nozzle, Fig. 2 is a diagram showing the state where the discharge port is set to f9tjl and uneven flow is occurring in the mold. Figure 3 is a cross-sectional view of the mold used in the water model test, Figure 4 is a diagram showing the relationship between the difference in scene variation and the frequency of powder entrainment, and Figure 5 is a diagram showing the flow velocity ratio at each point in the mold. Figure 6 is a diagram showing the relationship between the flow velocity ratio of the discharge port and the difference in scene variation, and Figure 7 is a diagram showing the relationship between the flow velocity ratio of the discharge outlet and the frequency of occurrence of powder entrainment. Figure 8 is a diagram showing a state in which fluctuations occur in the immersion nozzle, Figure 9 is a partially enlarged view of the sliding nozzle device, and Figure 10 is a diagram showing the method of the first aspect of the present invention. The cross-sectional view of the casting apparatus (with an electromagnetic force applying device installed in the immersion nozzle), Figure 11 (Figure 11 and Figure 11 0)) shows that the molten steel flow is formed into a columnar shape by the application of the electromagnetic force applying device. Figure 12 is a cross-sectional view of a casting apparatus (a partition plate is installed inside the immersion nozzle) that implements the method of the second invention of the present invention, and Figure 13 is a diagram showing the difference in scene variation and slab inclusions. FIG. 14 is a diagram showing the state of surface defects in steel plates manufactured from slabs cast by the method of the present invention and the conventional method. 1 is molten metal (molten steel) la is an upward flow, 1b is a downward flow, IA is a molten steel flow, 2 is an immersion nozzle, 2a, 2b are discharge ports, 3 is a mold, 4 is powder, 5a, 5b are vortex level meters, 10 is a sliding nozzle device, 10a is an upper plate, 10
b is the sliding plate, 10c is the lower plate, 1
1 is an electromagnetic force applying device, 12.12a and 12b are coils,
13 is a partition plate.

Claims (2)

[Claims] (1) A continuous casting method characterized in that an electromagnetic force applying device is provided on the outer periphery of the immersion nozzle, and electromagnetic force is applied to the molten metal flowing down inside the nozzle to rectify the flow. (2) A continuous casting method characterized in that a partition plate is provided inside the immersion nozzle, and the molten metal flowing down inside the nozzle is rectified by the partition plate.