JP3262936B2 - Operating method for high clean steel casting. - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a slag that has flowed into a tundish from a ladle, silica sand particles that have stopped molten steel, or slag that already exists in a tundish at a joint between charges in a continuous cast slab. The present invention relates to a technology for casting without suspending steel in molten steel, and to a continuous casting technology in the steel making industry or the non-ferrous manufacturing industry.

[0002]

2. Description of the Related Art In the steel manufacturing industry, there is a strong demand for cleaning of molten steel. Not only reduction of impurity elements such as C, P and S, but also deoxidation products in a converter, a secondary refining process, a continuous casting process, and the like. There is a demand for the production of high-purity steel slabs from which non-metallic inclusions caused by refining materials, refractories, heat insulating materials, and powder are removed as much as possible. Non-metallic inclusions that cause surface defects and internal defects in products are particularly oxidized by air oxidation, outflow of ladle slag,
It is known that suspension of tundish slag significantly increases. In the conventional continuous casting of steel, molten steel is injected into a ladle to a tundish by adjusting the opening of a sliding nozzle 2 attached to the bottom of a ladle 1 as shown in FIG. It is performed in a state where the tip of the long nozzle 3 located is immersed in the molten steel 4 in the tundish.

However, when the ladle is replaced, as shown in FIGS. 3 and 4, when the long nozzle 3 is immersed in the molten steel 4 in the tundish left by the front ladle and molten steel is injected from the rear ladle, The tip of the nozzle 3 is closed by the adhesion of the ingot 7 and the slag 5 to the surface of the molten steel in the tundish of the nozzle 3 or the falling and attachment of the silica sand particles 8 that have stopped the molten steel in the rear pan. The molten steel injection flow 9 of the
Due to the resistance of 8, it does not enter the tundish 6, but quickly fills the inside of the long nozzle 3 and blows out from the junction between the sliding nozzle 2 and the long nozzle 3. Therefore, as a safety measure, a method of lowering the molten steel surface and exposing the tip of the long nozzle 3 to the atmosphere only at the start of pouring of the rear pot is taken.

According to this method, it is possible to prevent the base metal 7, the slag 5 and the like from adhering to the long nozzle 3, and the silica sand particles 8 are washed away by the injection flow 9, so that the sliding nozzle 2 and the long nozzle 3 due to the blockage of the long nozzle 3 are formed. Of the molten steel from the joining portion of the long nozzle 3, while the slag layer 5 taken out of the ladle and floating on the surface of the molten steel 4 in the tundish at the end of the injection of the front pan is almost completely removed. The slag knocked into the molten steel 4 in the tundish has a large particle size of approximately 100 μm or more, depending on the tundish capacity, casting speed, etc. Those having the material re-emerge, but those having a diameter of 100 μm or less are injected into the mold together with the molten steel flow, and become non-metallic inclusions in the slab to significantly reduce the slab. It causes new quality deterioration.

[0005] In order to solve the above-mentioned problems, conventionally, as shown in Japanese Patent Publication No. 62-47620, at a joint portion between charges, a front ladle ladle as shown in FIG. Then, in order to supply molten steel in the pot to the tundish, the long nozzle 3 is moved upward (arrow A).
By lifting the lower end of the long nozzle above the surface of the tundish molten steel mechanically or manually, the slag in the long nozzle flows out from the gap 10 (broken arrow) and is dispersed on the upper surface of the tundish molten steel. In the state where the long nozzle is lowered to the original position (arrow B) and immersed in the steel again (FIG. 5 (B)), the method of starting the injection of molten steel in the rear pot is adopted, and the interposition of the joint slab is performed. A plan to reduce the quantity was devised.

[0006]

However, as a result of further experiments and studies conducted by the present inventors, the use of the technology disclosed in, for example, Japanese Patent Publication No. 62-47620 prevents air oxidation. It was possible to prevent the slag in the long nozzle and on the tundish molten steel surface from being knocked. If it takes too long to complete the ascent and descent, the molten steel surface of the tundish will be too low to be lower than the lower end of the long nozzle due to continuous casting, causing air oxidation or It has been found that it may be necessary to reduce the casting speed in order to prevent surface reduction.

In addition, since a preparation time of 1 to 2 minutes is required from the replacement of the pot to the start of the injection of the molten steel in the rear pot, if the casting is normally continued, the amount of the molten steel 4 in the tundish is inevitably reduced. Therefore, in order to recover the amount of molten steel 4 in the tundish, usually, the sliding nozzle in FIG. 3 is fully opened, and an operation of rapidly increasing the amount of molten steel is performed. Therefore, in the tundish, the molten molten steel in which the outflow slag 5 'of the front pan, the tundish slag, and the silica sand particles that have stopped the molten steel in the rear pan are entrained or suspended, is directly sent without any time for floating nonmetallic inclusions. It flows into the mold as a flow. For this reason, the quality of the slab on the front pan side particularly deteriorates when replacing the pan.

However, the present inventors conducted further experiments,
As a result of continued research, if the molten steel injection speed in the rear pan is appropriately controlled, it is possible to suppress the occurrence of direct flow, prevent the quality deterioration of the front pan-side slab, and use the long nozzle 11 having a trumpet shape. By using this, even if the injection of molten steel in the back pot is started while the long nozzle is kept immersed, the molten steel injection flow 9 from the back pot is subjected to the resistance of the deposits 5, 7, and 8 and the tundish 6 , The inside of the long nozzle 3 is quickly filled and blows out from the joint between the sliding nozzle 2 and the long nozzle 3.

A change in casting speed does not affect the quality of a steel type in which segregation is not a problem. However, in a steel type in which segregation is not required, it causes deterioration of segregation and lowers product quality. The present invention has been made in view of the above circumstances, and the generation and ejection of a direct flow in a tundish, which is one of the root causes of the conventional problems, by appropriately controlling the molten steel injection speed in the rear pot. The purpose of the present invention is to prevent the deterioration of the slab on the front pan side and the quality of the slab.

[0010]

SUMMARY OF THE INVENTION Accordingly, the present invention provides a method for obtaining clean steel which satisfies the strict requirements for the production of high-cleanliness steel, the gist of which is as follows. It is on the street.

As a method of injecting molten steel from a ladle into a tundish, a so-called trumpet-shaped long nozzle having an enlarged inner diameter at the nozzle tip is used, and the long nozzle is immersed in the molten steel regardless of the molten steel level in the tundish. In the continuous casting method in which casting is performed, when the molten steel in the rear pan is supplied to the tundish following the front pan, the lower end of the long nozzle is always immersed in the molten steel at least 30 mm from the end of the front pan casting to the start of the rear pan casting when replacing the pan. A method for casting highly clean steel, characterized in that the amount of molten steel supplied to the tundish: M is controlled according to the following equation (1). M = Mc + Mα (1) where 0 ≦ Mα ≦ (Vmax−Vmin) / 2 M: supply amount of molten steel to the tundish (ton / min) Mc: supply amount of molten steel required for casting (ton / min) Mα : Supply amount of molten steel required to increase the amount of molten steel in the tundish (ton / min) Vmin: Amount of molten steel in the tundish (ton) required for the lower end of the long nozzle to be immersed in the surface of the molten steel in the tundish (ton) Vmax: Tan Maximum amount of molten steel that can be held in the dish (ton)

[0012]

The details of the present invention will be described below based on an example of an apparatus used for carrying out the present invention. FIG. 1 shows an example of the present invention. In the present invention, in order to use the long nozzle immersed when replacing the pot, by starting the molten steel injection of the rear pot,
In order to prevent the molten steel from blowing out from the joint between the sliding nozzle 2 and the long nozzle 3 due to the blockage of the long nozzle 3, the inner diameter D of the tip of the long nozzle is 1.5 to 3 times the inner diameter of the passage of the sliding nozzle 2. It is necessary to use the mold long nozzle 11.

In addition, since the tundish slag 5 existing on the tundish molten steel 4 is engulfed by the injection flow 9 of the long nozzle 3 and causes the cast slab quality to deteriorate, the long nozzle 11 must always be sufficiently attached to the molten steel 4 in the tundish. It must be kept in the immersed state, and the amount of molten steel supplied to the tundish must satisfy the condition of equation (1). V
Using a tundish of max = 60 ton and Vmin = 45 ton, with a dipping depth of 30 mm in the molten steel in the tundish at the lower end of the long nozzle at the time of changing the pot, molten steel supply amount for increasing the amount of molten steel in the tundish FIG. 2 shows the relationship between the ratio of occurrence of demoted material due to internal defects in the joint portion slab laying wire when Mα is changed.

Under the above conditions, the upper limit of Mα is (60-4
5) /2=7.5 (ton / min).
The case of α = 6 ton / min) shows that the quality of the slab in the ladle changing part is improved over a wide range, and that superior product quality can be obtained as compared with the conventional method. FIG. 6 shows the immersion depth of the tip of the long nozzle in the molten steel in the tundish at the time of replacing the pot and the generation ratio of the degraded material due to the internal defect of the joint slab blast wire. It is shown that by securing the immersion depth at the tip of the long nozzle 11 at least 30 mm during the pot replacement period, which is a feature of the method of the present invention, superior product quality can be obtained as compared with the conventional method.

[0015]

According to the present invention configured as described above, a clean slab can be obtained without involving slag in the joint slab, and it is possible to improve the slab yield immediately after replacing the ladle. , The product quality is significantly improved.

[Brief description of the drawings]

FIG. 1 is an embodiment diagram of the present invention.

FIG. 2 is a diagram showing a relationship between a molten steel supply amount Mα for increasing a molten steel amount in a tundish and an occurrence ratio of a demoted material due to an internal defect of a seam portion slab scatter wire;

FIG. 3 is a diagram showing a comparative example of the present invention.

FIG. 4 shows a comparative example of the present invention.

FIG. 5 is a diagram showing a comparative example of the present invention.

FIG. 6 is a diagram showing the immersion depth of the tip of a long nozzle in molten steel in a tundish and the degrading rate due to internal defects in a joint slab blasting wire during a pot replacement period.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ladle 2 Sliding nozzle 3 Long nozzle (straight type) 4 Molten steel in tundish 5 Slag layer 6 Tundish 7 Ingot 8 Silica sand 9 Injection flow (from long nozzle) 10 Void (between long nozzle lower end and slag layer) Distance) 11 Long nozzle of trumpet type D Inside diameter of long nozzle of trumpet type long nozzle

──────────────────────────────────────────────────の Continued on front page (72) Inventor Kenichi Miyazawa 1 Kimitsu, Kimitsu City, Chiba Prefecture Inside Nippon Steel Corporation Kimitsu Works (72) Inventor Satoshi Sugimaru 1 Kimitsu, Kimitsu City, Chiba Prefecture New Japan (56) References JP-A-57-115950 (JP, A) JP-A-63-72460 (JP, A) JP-A-61-283445 (JP, A) JP-A Sho 61 -30268 (JP, A) JP-A-2-187239 (JP, A) JP-A-2-192859 (JP, A) JP-A-60-261165 (JP, A) JP-A-2-235555 (JP, A) (Japanese) Sho-57-127360 (JP, U) JP-B-62-47620 (JP, B2) (58) Investigated field (Int. Cl. ⁷ , DB name) B22D 11/103 B22D 11/10 B22D 11 / 10 320 B22D 41/50 540

Claims (1)

(57) [Claims] As a method for injecting molten steel from a ladle into a tundish, a so-called trumpet-shaped long nozzle having an enlarged inner diameter at the nozzle tip was used, and the long nozzle was immersed in the molten steel regardless of the level of molten steel in the tundish. In the continuous casting method in which casting is performed in the state, in order to continuously supply molten steel in the rear pan to the tundish following the front pan, always immerse the lower end of the long nozzle in the molten steel at least 30 mm from the end of the front pan casting to the start of the rear pan casting when replacing the pan held by the state, and
Molten steel supply to tundish: M is given by the following formula (1)
Therefore, a method for casting high-purity steel, characterized in that it is controlled. M = Mc + Mα (1) where 0 ≦ Mα ≦ (Vmax−Vmin) / 2 M: supply amount of molten steel to tundish (t
on / min) Mc: molten steel supply required for casting (t
on / min) Mα: Necessary to increase the amount of molten steel in the tundish
Supply of molten steel (ton / min) Vmin: The lower end of the long nozzle is the molten steel in the tundish
Amount of molten steel in tundish required for immersion in surface
(Ton) Vmax: Maximum amount of molten steel that can be held in the tundish
(Ton)