JPS63108951A - Production of cast slab having high cleanness - Google Patents

Abstract

PURPOSE:To effectively execute the floating up and the separation of non-metallic inclusion by arranging linear motor type shifting magnetic field between rolls having the prescribed distance from meniscus part in a bending type continuous casting machine and giving the thrust vertically upward to non-solidified part of a cast slab. CONSTITUTION:In the continuous casting machine, molten steel 2 in a mold 1 becomes to the cast slab 3 and sends out by drawing or through the bending passage of rolls 4 for guiding. Then, three low frequency AC shifting the cycles by one-third is conducted to plural conducting bars 5 respectively arranged in parallel with roll 4 axes between the rolls 4 in the range of 0.5-8.0m from the meniscus part. Thus, the electromagnetic force is generated to vertical upward direction in the non-solidified part in the inner part of cast slab 3, to execute the electromagnetic stirring. In this way, at the narrow position of top zone, the floating up and separation of non-metallic inclusion is effectively executed.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention is based on continuous! The present invention relates to a method of manufacturing a highly clean slab by stirring the unsolidified portion inside the slab sent out from a mold of a molding machine using electromagnetic force to promote floating separation of non-metallic inclusions.

[Conventional technology]

The slab sent out from the mold of the continuous casting machine contains alumina,
When slag, powder, etc. are entrapped and remain inside the slab, they cause deterioration in the properties of the product. In addition, nonmetallic elements such as carbon, phosphorus, and sulfur tend to segregate in the unsolidified portion at the center of the slab, deteriorating the mechanical properties, chemical properties, etc. of the product.

For example, curved continuous casting machines are widely used because of their low equipment cost and ability to increase casting speed. In this type of continuous casting machine, the slab sent out from the mold is bent along the curved part while remaining partially unsolidified, causing minute inclusions such as alumina, slag, and powder to float vertically upward. Separation is suppressed and it tends to accumulate near the upper solidified shell of the curved part. FIG. 3 shows the influence of different types of continuous casting machines on the distribution of inclusions. As is clear from this figure, when a curved continuous casting machine is used, the concentration of inclusions is particularly high near the upper solidified shell of the curved portion.

When such slabs are subsequently cold-rolled, the smallest inclusion accumulation areas appear on the surface, causing flange cranks when the resulting plates are processed into cans, and bald spots when used as tin plates. This will cause this to occur.

Therefore, methods of floating and separating nonmetallic inclusions by electromagnetic stirring have been proposed in Japanese Patent Laid-Open No. 49-94522 and Japanese Patent Laid-Open No. 54-
This method has been proposed in Japanese Patent Application No. 14''1132.

Continuous casting Vt1ffi of JP-A No. 49-94522
In this method, the first
The electromagnetic stirring means electromagnetically stirs the unsolidified portion inside the slab, promoting floating separation of mixed slag, gas, etc., and reducing nonmetallic inclusions remaining in the product.

Furthermore, in the 'r4 magnetic stirring method disclosed in JP-A-54-147132, a plurality of electromagnetic stirring devices are arranged between the mold and the drawing roll, and the unsolidified portion inside the slab is solidified while being stirred. There is. By this stirring, nonmetallic inclusions are evenly dispersed in the slab, and defects caused by segregation are prevented from occurring.

, [Problem to be solved by the invention] In order to effectively float and separate these nonmetallic inclusions and obtain a clean slab, it is necessary to apply vertically upward electromagnetic thrust to the molten steel falling close to the mold. It is necessary to apply it to the unsolidified part at a position where the influence of the flow is small. However, the upper part of the bend in the secondary cooling zone, the so-called top zone, is a narrow place.
Due to space constraints, a regular electromagnetic stirring device cannot be installed.

In addition, in the electromagnetic stirring device shown in the above-mentioned Japanese Patent Application Laid-Open No. 54-147132, in order to reduce the loss of electromagnetic force, the roll adjacent to it needs to be made of stainless steel, which increases the equipment cost. was causing the price to soar. Furthermore, when looking at the electro-Na agitation by this method from a microscopic perspective, the agitation force is divided, and the electromagnetic force cannot be efficiently used to float inclusions.

Therefore, an object of the present invention is to efficiently float and separate non-metallic inclusions by performing 1111' on the slab without contact and applying a uniform vertically upward thrust to the unsolidified portion. shall be.

[Means for solving problems]

In order to achieve the objective, the method for producing high-cleanliness slabs of the present invention has the following advantages:
A plurality of conductor rods are arranged parallel to the axis of the rolls between the rolls within a range of 8.0 m, and each of the conductor rods has a
It consists of a linear motor that generates a moving magnetic field by passing three-phase low-frequency alternating current with a three-phase alternating cycle, and stirs the unsolidified portion inside the slab by applying a vertically upward thrust to it. Features.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below, together with its effects, with reference to the drawings.

FIG. 1 is a diagram showing essential parts of the present invention.

Molten steel 2 in a mold 1 of a continuous casting machine becomes a slab 3 and is sent out through a curved path by rolls 4 for drawing or guiding. At this time, in the present invention, the conductor rod 5 is arranged between the plurality of rolls 4 along the axial direction of the rolls 4. These conductor rods 5 are connected to three-phase alternating current U phase, V phase, and W phase.
When energizing the phases one after the other, a moving magnetic field is generated. This moving magnetic field generates an eddy current inside the slab 3, and this eddy current and magnetic flux generate an electromagnetic force directed upward perpendicularly to the slab 3, causing the unsolidified portion inside the slab 3 to undergo electromagnetic stirring. be done.

This electromagnetic force acts continuously and uniformly over the entire length of the slab 3 on which the conductor rod 5 is provided. Therefore, compared to conventional electromagnetic stirring devices, the stirring range is wider and a rectified unidirectional stirring flow is formed. Therefore, the unsolidified portion is uniformly and sufficiently stirred in one direction without creating a vortex near the solidifying molten steel, and the floating separation of nonmetallic inclusions is ensured without being inserted or captured. becomes. Also, a conductor rod 5 is placed between the rolls 4.
A predetermined electromagnetic force can be obtained by simply arranging the conductor rod 5, and there is no need to reduce the diameter of the roll 4 or make it non-magnetic near the conductor rod 5.

At this time, the current supplied to the conductor bar 5 is a low frequency alternating current of 25 Hz or less. The electromagnetic force during electromagnetic stirring is
Generally speaking, it is proportional to the frequency of the current being applied, but in a frequency range above a certain level, the electromagnetic force does not increase, but on the contrary shows a tendency to decrease. Therefore, in order to efficiently obtain the maximum electromagnetic force, 25H2 or less is required.

The position where this electromagnetic force is applied, that is, the location where the conductor rod 5 is installed is determined as follows.

The distribution of inclusions in the slab thickness direction depends on the casting speed and slab 3W.
! It is determined according to the curvature of the feeding path. In this regard, in the current curved continuous casting machine, as shown in Fig. 3, the slab
Most of the microscopic inclusions accumulate between 20 and 60 mm from the top surface. That is, it is trapped in the solidified shell of this part.

On the other hand, the position of the maximum accumulation probability of minute inclusions depends more on the casting speed than on the curvature of the conveyance path of the slab 3. Moreover, when the curvature of the slab 3 conveyance path is the same, the distance from the upper surface of the slab 3 to the accumulation position of minute inclusions decreases as the casting speed increases.

Here, when the cooling conditions are the same, the thickness of the solidified shell d(
IIm) is the casting speed t(m
/min) and the distance ML (m) from the meniscus.

However, k is a constant determined depending on the cooling conditions, and is hereinafter referred to as a solidification coefficient. This solidification coefficient varies depending on the cooling conditions depending on the material of the slab 3 to be cast, but is usually a value of about 25 to 31. For example, for M-killed material used as can stock, kζ
It is 28.

Therefore, when we set the casting speed t to 1 to 1.7 m/min and consider a can stock with a solidification coefficient of -28, as mentioned above, the slab 3
Since most of the microscopic inclusions are captured in the solidified shell located 20 to 60 m from the top surface of the , becomes as follows.

When this is calculated, L = 0.51 to 7.8. Therefore, when the conductor rod 5 is arranged within this distance range and the unsolidified portion is stirred using the principle of a linear motor, it is calculated that minute inclusions are less likely to be captured in the solidified shell.

However, this L-0,51~7.8 is the casting speed difference=1
This is the value when ~1.7 m/min and the coagulation coefficient = 28, so we added some inclusion to this and set the distance to 0.5.
~8.0m. Also, this distance is 0.5m
When it is smaller, the influence of the downward injection flow is large in the region where the inclusions are pushed, so the effect of promoting the floating of the inclusions by electric stirring is small. On the other hand, 8.
Even if electric NU stirring is applied to the slab 3 located at a distance of 0 m or more,
Since it is outside the flotation area of the inherent inclusions, the effect of flotation and separation of the inclusions is reduced.

〔Example〕

EXAMPLES Hereinafter, the effects of the present invention will be specifically explained with reference to Examples.

FIG. 2 shows a roll segment incorporating conductor rods according to the invention.

A conductor rod 5 is disposed between a plurality of rolls 4 that pull out or guide the slab 3 that has descended from the mold 1, and the entire body is attached to a segment frame 6. A power supply section 7 that supplies electricity to the conductor rod 5 is provided on the outer periphery of the segment frame 6.
has been established. These roll segments can be provided on both sides of the slab 3, but they may also be placed only on the upper side where nonmetallic inclusions are likely to be captured by the solidified shell. By doing so, assembly and removal work for maintenance and inspection becomes easier.

Further, when compared with the conventional roll segment, the only difference in the roll segment in this example is that a conductor bar 5 is interposed between the rolls 4. In this way, it is also a feature of the present invention that the force required for electrolyte pil agitation can be obtained with extremely small design changes. In addition, although FIG. 2 shows a state in which three conductor rods 5 are arranged, this is only to simplify the drawing, and in reality, the rolls are arranged according to the size of the continuous casting machine. Of course, an appropriate number of conductor rods 5 are provided corresponding to the number of conductor rods 4.

Then, three-phase alternating current is applied to these conductor rods 5, U-phase,
Activate around J of phase ■ and W phase. For example, temporary yJ, 25
A current of approximately 4000 A is applied to the slab 3 at a distance of 0 m.
Electricity was applied to six conductor rods 5 arranged in a range of IL=0.5 to 8.0 m. As a result, the unsolidified portion inside the slab 3 is sufficiently stirred over the entire area where the conductor rod 5 is provided, and the floating and separation of minute inclusions is effectively achieved. When a slab with a plate thickness of 25 fbm was produced while stirring, the distribution of inclusions along the width direction of the slab is shown as an average value at multiple measurement points.

The table also lists the distribution of inclusions in slabs obtained without electromagnetic stirring for comparison.

(Hereinafter, the margin of this page) As is clear from this table, the absolute amount of inclusions is small in the slab subjected to 1iN'lB stirring in this example, and the distribution thereof is also in the width direction of the slab. It is uniform along the

For this reason, it was possible to suppress the occurrence of defects due to inclusions being exposed on the surface in the plate material or strip material obtained by hot rolling or cold rolling the slab.

〔Effect of the invention〕

As explained above, the high efficiency of the present invention? f? In the method for manufacturing clean slabs, a plurality of conductor rods are provided between the rolls so that electromagnetic force continuously acts on locations where nonmetallic inclusions are likely to be captured by the solidified shell.

Therefore, the vertically upward thrust acts evenly on the unsolidified portion inside the slab, promoting floating separation of non-metallic inclusions, resulting in a slab with less segregation and high cleanliness. Also,
The electromagnetic force is applied to the slab using a linear motor system, and because it does not take up space unlike conventional electromagnetic stirring devices, it can take up ample installation space even in a narrow space directly under the mold. The slab thus obtained according to the present invention has a high price. Because of the NN variation, it can be hot-rolled or cold-rolled to produce a plate material with excellent mechanical properties, chemical properties, and workability, and without surface defects.

[Brief explanation of the drawing]

FIG. 1 shows an overview of the apparatus used in the present invention, and FIG. 2 shows an example of a roll segment. Moreover, FIG. 3 shows the influence that different types of continuous casting machines have on the distribution of inclusions.

Claims (1)

[Claims] 1. 0.5 to 8.
A plurality of conductor rods are arranged parallel to the axis of the rolls between the rolls within a range of 0 m, and a three-phase low-frequency alternating current with a period shifted by 1/3 is applied to each of the conductor rods. 1. A method for producing a high-cleanness slab, characterized in that a linear motor is configured to generate a moving magnetic field, and the unsolidified portion inside the slab is stirred by applying a vertically upward thrust to the unsolidified portion.