JPS62130752A - Continuous casting method for bloom or billet - Google Patents

Abstract

PURPOSE:To prevent an increase of inclusions and to evade a breakout accident by limiting a range of magnetic field of a static magnetic field generator provided in a pouring direction from a bottom end of a single hole type submerged nozzle, and an intensity of a magnetic flux density to brake the molten steel flow from a delivering gate. CONSTITUTION:The static magnetic field generator 5 is positioned to magnetize statically for the pouring molten steel in the range of 20-30mm for advancing position from the delivering gate 3 of the single hole type submerged nozzle 2. Then, a length of the static magnetic field generator 5 is regulated to the same or more than a min. length of a section of the casting billet, and the magnetic flux density is regulated to >=1,200 gauss at the center of a mold 1. Here, the reason why the range influenced by the magnetic field is limited, is that non-metallic inclusions are easily trapped into the casting billet, as the amount of molten steel flowed to downward is increased, in case of shorter length than above-mentioned length for the static magnetic field generator. Furthermore, if the magnetic flux density is not >=1,200 gauss, the amount of non-metallic inclusions is increased as the molten steel flowed to downward is not braked.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a technology that enables high-speed casting and multi-continuous casting of blooms and billets with good internal quality using a single-hole immersion nozzle. be.

(Prior art) In recent years, due to advances in continuous casting technology, continuous casting, which has lower production costs than the ingot-blooming rolling method, has significantly increased. In order to reduce costs, efforts are being made to improve the multi-continuous casting rate and further increase the casting speed.

In continuous steel casting, an alumina graphite immersion nozzle is used to pour the molten steel in the tundish into the mold, and generally when casting blooms, the discharge outlet is immersed with a single hole or four holes. using a nozzle.

(Problems to be Solved by the Invention) When a single-hole type immersion nozzle is used, the diameter of the discharge port is large, which is advantageous against nozzle clogging, but the discharged molten steel flow is as shown in Fig. 2b. As the non-metallic inclusions are brought in with the molten steel and penetrate deeply into the slab, they become trapped within the slab, resulting in a decrease in quality.

Moreover, this tendency to increase the casting speed is exacerbated, which limits the casting speed and becomes an obstacle to increasing the casting speed.

On the other hand, the four-hole immersion nozzle, which was devised to eliminate the drawbacks of the single-hole nozzle, has four discharge holes that are oriented horizontally, upwardly, or downwardly, so the discharged molten steel flow is as shown in Figure 3a. Since non-metallic inclusions that do not penetrate deeply and enter at the same time as the molten steel float up and separate within the mold, the quality of the slab is improved compared to a single-hole immersion nozzle. However, because the diameter of the discharge port of a four-hole immersion nozzle is small, when aluminum killed steel or steel containing Ti and rare earth metals is continuously cast, oxides of AI, Ti, and rare earth metals may adhere to the inner surface of the nozzle. This method is not suitable for multi-continuous casting because nozzle clogging occurs. Therefore, in order to prevent nozzle clogging, it is possible to use melt-solidified silica as the material for the immersion nozzle, but the silica may melt or peel off and contaminate the molten steel, and the silica may melt or peel off and contaminate the molten steel. A problem arises in that the shape is not maintained. Furthermore, this four-hole immersion nozzle has a small distance between the discharge port and the solidified shell in the mold, so during high-speed casting, the solidified shell will be remelted by the discharged molten steel flow, increasing the risk of breakout. . In addition, when the nozzle is blocked, the discharged molten steel flow becomes unbalanced, and as the downward flow increases, nonmetallic inclusions may penetrate deeply, and the molten metal level fluctuates due to the increase in the upward flow.

Despite the above-mentioned problems, efforts are being made to further increase the casting speed and implement multiple continuous casting. The present invention prevents non-metallic inclusions from entering deep inside the crater and deteriorating the quality of slabs, solves the problem of nozzle clogging that occurs with submerged nozzles, and increases casting speed. The purpose is to make multi-continuous casting possible.

(Means for solving the problems) The bloom or billet continuous casting method of the present invention includes:
As shown in FIGS. 1a and 1b, a static magnetic field generator 5 having a length equal to or longer than the minimum length of the slab cross section is installed in the casting direction from the discharge port 3 of the single-hole immersion nozzle 2, and This continuous casting method of molten steel is characterized by applying an electromagnetic braking force to the discharged molten steel flow by generating a magnetic flux density of 1200 Gauss or more.

(Function) The present invention uses a single-hole submerged nozzle that is less prone to nozzle clogging, and operates the static magnetic field generator within an area where the molten steel flow discharged from the single-hole submerged nozzle advances 20 to 30 degrees from the discharge port of the nozzle. position it within the static magnetic field. In addition, in order to control the flow of discharged molten steel, the range and strength of the magnetic field are important, and experimental results show that the range needs to be at least as long as the minimum length of the slab cross section. , and it was found that it is not effective unless the magnetic flux density is 1200 Gauss or more at the center of the mold.

In other words, the reason why the range covered by the magnetic field is at least equal to the minimum length of the cross section of the slab is to realize the flow of molten steel as shown in Figure 1b. This is because non-metallic inclusions are likely to be trapped inside the slab. Further, unless the magnetic flux density is 1200 Gauss or higher, the downward flowing flow of molten steel cannot be completely braked, which also results in a large number of nonmetallic inclusions.

When molten steel is supplied into the static magnetic field set as described above, the interaction between the flow of molten steel and the static magnetic field causes the molten steel to move in the opposite direction to the direction of the discharge flow 7 of the molten steel, as shown in Fig. 1b. It receives an electromagnetic force in a direction, that is, an electromagnetic braking force Fb in a direction that decelerates the discharge flow 7 of molten steel.

Therefore, the discharge flow 7 of molten steel from the discharge port 3 is forcibly dispersed as shown by the arrows in the figure by the electromagnetic braking force pb, so that the discharge flow of molten steel can be prevented from penetrating deeply into the crater. Non-metallic inclusions are not trapped within the slab. Furthermore, since heat is supplied to the surface of the molten steel in the mold due to the flow of the molten steel as shown in the figure, skinning on the surface of the molten steel and defects caused by inclusions caused by it are reduced.

In addition, the method of the present invention aims to speed up continuous casting of billets or blooms, and the reason is that
In the case of a slab with a wide mold cross-section, when casting using a two-hole nozzle, there is little risk of re-melting to the sides and breakout.

Therefore, the effect of the present invention using a single-hole nozzle is small.

(Example) 180 A1 killed steel containing 0.030% AI and Ti that was refined in a 1-horn converter and subjected to R1+ degassing treatment
When casting Ti-containing steel with a concentration of 0.25% into a beam with a cross-sectional dimension of 300 mm thick and 400 mm wide using a curved bloom continuous casting machine, a four-hole immersion nozzle, a single-hole immersion nozzle, and the present invention are used. Each was cast according to the method. The casting speed of the method of the present invention is 1.0 to 1.8 m/min, and the thickness is 300 m/min.
The fin was cast in a mold with a width of 400 m and a static magnetic field generator with a length of 325 mm, applying a static magnetic field so that the magnetic flux density was 2000 Gauss. Further, the casting speed was set to 1.0 m/lll1n when a four-hole type immersion nozzle was used and when a single-hole type immersion nozzle was used.

A sample with a thickness of 5I11 was cut from the surface of the experimental material cast at a casting speed of 1.0 m/lll1n, and inclusions with a diameter of 100 μ or more were investigated using the X-ray transmission method. Shown in Figure 4. From this figure, it can be seen that there is an accumulation zone of inclusions at a position of about 30 mm from the surface of the slab, but when comparing the method of the present invention with the case of using a single-hole immersion nozzle or a 4-hole immersion nozzle. , the inclusions in this accumulation zone are 115 for a single-hole immersion nozzle and 17 for a 4-hole immersion nozzle.
We were able to reduce it to 2.

Further, the relationship between the inclusions in this accumulation zone and the casting speed is shown in FIG. 5, and the amount of inclusions is small and stable at casting speeds up to 1.4 m/min. On the other hand, when a 4-hole immersion nozzle is used, the discharged molten steel flow splits into a downward flow and an upward flow after colliding with the solidified shell, and this upward flow may cause the scene level to fluctuate. Some of the inclusions are caught in the mold, and the amount of inclusions varies widely. Furthermore, fluctuations in the scene level due to nozzle blockage were facilitated, and as the number of consecutive shots increased, the number of inclusions tended to increase.

Further, FIG. 6 shows the relationship between the number of casts when Al-killed steel and Ti-containing steel are cast using a 4-type immersion nozzle and when they are cast by the method of the present invention. When Al-killed steel was cast using a four-hole type immersion nozzle, the immersion nozzle became clogged at the end of three consecutive castings, making continuous casting of three or more consecutive castings difficult. Furthermore, in the case of Ti-containing steel, the immersion nozzle was almost clogged after three consecutive castings, so two consecutive castings were the limit. On the other hand, the method of the present invention enables casting up to 6 continuous castings, which is 2 to 3 times as much as with a 4-hole immersion nozzle, and nozzle clogging is hardly a problem for both steel types. However, if six or more continuous castings were carried out, non-metallic inclusions in the molten steel in the tundish would increase and the molten steel would become gradually contaminated, so six continuous castings were stopped.

(Effects of the Invention) As explained above, according to the method of the present invention, using a single-hole immersion nozzle that does not cause the solidified shell to dissolve if the nozzle is clogged,
By braking the molten steel flow from the discharge port using a static magnetic field generator, it is possible to prevent an increase in the amount of inclusions and to avoid the risk of breakout.

Further, even if the casting speed is increased, the amount of inclusions does not increase and nozzle clogging does not occur, so multiple continuous castings are possible.

[Brief explanation of drawings]

Figures 1a and 1b are diagrams showing the relationship between the mold, the immersion nozzle, and the static magnetic field generator when the method of the present invention is applied. Figures 2a and 2b are diagrams showing the flow of discharged molten steel when a single-hole immersion nozzle is used;
The figure shows the flow of discharged molten steel when a four-hole immersion nozzle is used. FIG. 4 is a diagram showing the distribution of inclusions in the slab, and FIG. 5 is a diagram showing the relationship between the casting speed and the accumulation zone of inclusions. FIG. 6 is a diagram showing the relationship between the method of the present invention, a four-hole type immersion nozzle, and the number of rows. 1... Mold 2... Immersion nozzle 3.
4...Discharge port 5...Static magnetic field generator 6.
...Mold flux 7...Discharged molten steel flow 8...
solidified shell

Claims (1)

[Claims] 1. When continuously casting blooms or billets using a single-hole immersion nozzle, a static magnetic field generator having a length equal to or longer than the minimum length of the slab cross section from the lower end of the single-hole immersion nozzle in the casting direction. and 12 at the center of the mold.
A continuous bloom or billet casting method characterized by generating a magnetic flux density of 0.00 Gauss or more to apply an electromagnetic braking force to a discharged molten steel flow.