JP3408725B2 - Steel continuous casting method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous casting method for steel, and more particularly, to a method for effectively reducing the drift of molten metal (molten steel) in a continuous casting mold. It relates to a continuous casting method to suppress. 2. Description of the Related Art As shown in FIG. 3 , for example, in a continuous casting facility, molten steel in a ladle 1 is supplied into a mold 5 via a tundish 2.
In general, the inside is supplied by adjusting the flow rate by opening and closing a slide valve 3 provided in the middle, and injecting the water from an immersion nozzle 4. [0003] Two-layer slide valves and three-layer slide valves are widely known. In a two-layer slide valve, the immersion nozzle is forced to move within the mold when opening and closing, and as a result, the nozzle axis deviates from the center of the mold (abbreviated as “nozzle shift”), so that the discharge flow is reduced. Is asymmetric. In addition, there is a problem of drift in the mold caused by asymmetric flow in the immersion nozzle when adjusting the flow rate. For example, in a slab caster,
In the case of using a hole-type immersion nozzle and a two-layer slide valve, as shown in FIG. 4 , the immersion nozzle 4 has nozzle discharge holes (discharge holes) 7 facing the short side copper plates 6, 6 of the mold facing each other. In general, the slide valve 3 is disposed so as to move in the long side direction of the mold (perpendicular to the short side of the mold). Note that the arrow 11 is the slide valve moving direction.
For this reason, at the time of flow rate adjustment, the flow velocity maximum streamline 9 in the immersion nozzle 4 is biased to one mold short side copper plate 6 side, and the discharge flow is biased to one side of the opposite mold short side copper plate 6, Deviation in the mold occurs. [0004] This drift in the mold promotes a local rise in the temperature of the molten steel in the mold, non-uniform formation of a solidified shell of the slab, and entrainment of inclusions.
The problem of slab quality deterioration due to change in crystal structure, and
This causes a problem of shortening the mold life due to a local high heat load. As a method for preventing such drift in the mold, Japanese Patent Application Laid-Open No. Hei 7-266010 discloses a method of changing the direction and magnitude of the current to discharge molten steel so as to balance the discharge flow rates on the left and right sides, thereby reducing discharge hole passage resistance. Control methods have been proposed. Japanese Patent Application Laid-Open No. 4-105756 discloses that the presence or absence of molten steel drift is detected from the temperature distribution in the width direction of the long side wall of the mold, and the temperature is passed through the immersion nozzle so that the temperature distribution is symmetrical in the width direction. A method has been proposed in which argon gas is injected into molten steel by adjusting the flow rate. On the other hand, since the three-layer slide valve has a structure in which only the intermediate plate is moved at the time of opening and closing, no nozzle shift occurs. It is superior to the two-layer type in that there is no problem. However, according to the study of the present inventors, even when the supply amount of molten steel is adjusted by using a three-layer slide valve, two-stage slide valve is required.
Although the form is different from the case of the layer type, it has been found that the drift in the mold occurs, and this drift adversely affects the quality of the slab and the life of the mold copper plate. That is, in the three-layer type, as shown in FIG. 5 , directing the discharge holes 7, 7 of the two-hole immersion nozzle 4 to the opposed short side copper plates 6, 6 is the same as in the two-layer type. There is
The slide valve 3 (in this case, the intermediate plate) is disposed so as to move in the direction of 90 ° in the horizontal plane (parallel to the direction of the short side of the mold (perpendicular to the long side of the mold)) of the two-layer type. It is common to use For this reason, when adjusting the flow rate, the flow velocity maximum streamline 9 in the cross section of the immersion nozzle 4 is deviated toward one of the copper plates 8 on the long side of the mold, and this flow deviation in the nozzle reduces the discharge flow from the discharge holes 7, 7 Acts so as to swing by a certain angle from the side-facing direction to the mold long-side facing direction, and as a result, the discharge flow is biased to one side of the mold long-side copper plates 8, 8 sandwiching the immersion nozzle 4, resulting in a drift in the mold. Occurs. The above-mentioned drift due to the three-layer slide valve is as follows.
Since it is caused by the change of the discharge flow, it cannot be prevented by the method of Japanese Patent Application Laid-Open No. Hei 7-266010 in which the discharge flow velocity in a specific direction is balanced between left and right. Further, the method disclosed in Japanese Patent Application Laid-Open No. 4-105756 can control the flow in the immersion nozzle to return directly to a symmetrical shape. However, it is difficult to say that this method is industrially advantageous because the injected argon gas has a drawback of causing cellular slab defects. As described above, the conventional technique for preventing drift in the mold has not reached a level at which the drift in the mold by the three-layer slide valve can be advantageously prevented. Accordingly, an object of the present invention is to provide a continuous casting method of steel that can advantageously prevent the occurrence of drift in a mold when controlling the supply amount of molten steel into the mold using a three-layer slide valve. I do. According to the present invention, there is provided a steel plate having a molten steel held in a tundish provided at the bottom of the tundish.
In a continuous casting method of steel supplied into a mold through a slide valve formed of a plate of layers and an immersion nozzle connected to the slide valve, an intermediate plate among the three layers of plates is parallel to a short side of the mold. The slide valve is disposed so as to move in a different direction, and the immersion nozzle has a discharge hole angle in the opposite direction to the deviation of the nozzle discharge flow caused by the deviation of the molten steel flow in the flow control part of the slide valve. A continuous casting method for steel, characterized by using a two-hole immersion nozzle provided with holes . FIG. 1 is a cross-sectional view of a discharge hole portion of a two-hole immersion nozzle. FIG. 1A shows a conventional example, FIG. The long side direction and the Y direction are the short side directions of the mold. The conventional two-hole type immersion nozzle 4 is shown in FIG.
As shown in (a), the discharge flow guiding directions of the discharge holes 7, 7 are parallel to the X direction (that is, the discharge hole angle is not provided), and therefore, the three-layer slide valve flow rate adjusting section (intermediate plate) (See FIG. 5 (a)), the flow velocity maximum streamline 9 of the molten steel flow (vertically downward) in the immersion nozzle 4 is deviated from the nozzle center to one side in the Y direction, and the discharge flow is dragged by this deviation. Is biased to the other side in the Y direction, resulting in a drift in the mold. On the other hand, in the present invention, as shown in FIG. 1 (b), the discharge holes 7, 7 are provided with a discharge hole angle 10 in a direction opposite to the bias of the conventional nozzle discharge flow. This allows
The discharge flow is guided in a direction in which the conventional bias is corrected, and is discharged as a flow that is not biased to either the positive or negative side in the Y direction.
7 can flow out into the mold, and the drift in the mold can be effectively eliminated. It is desirable to select an optimum value for the discharge hole angle in accordance with operating conditions such as throughput and slab width, but in a general continuous casting machine, it is 5 ° to 20 °. Is preferably within the range. According to the present invention thus configured, as illustrated in FIG. 2 , the symmetry of the molten steel flow in the continuous casting mold in the Y direction (short side direction of the mold) is significantly improved, and the drift is greatly reduced. The above-mentioned conventional problems caused by this drift are eliminated. Further, since the present invention is a method using an immersion nozzle in which a predetermined discharge hole angle is set, it does not involve an increase in equipment cost during implementation, and achieves a slab quality similar to that of the conventional argon gas injection method. There is no adverse effect, which is industrially advantageous. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A molten steel equivalent to SUS304 is cast at a casting speed of 0.8 while moving an intermediate plate of a three-layer slide valve in the Y direction (short side direction of a mold) by a slab continuous caster to adjust a molten steel supply amount. The present invention was carried out using a two-hole immersion nozzle having a discharge hole inclined at a discharge hole angle of 10 ° with respect to the X direction (the direction of the long side of the mold) during continuous casting at ~ 1.5 m / min. . As a result, the rate of occurrence of surface defects of the slab, which had been about 15% when the conventional method using an immersion nozzle having no discharge hole angle, was reduced by half. Further, in the conventional method, there was a problem that defects were concentrated on one surface of the slab due to the influence of the drift, but this problem was also solved. Furthermore, the localized high heat load on the mold water-cooled copper plate on the deviated side (the side with the higher flow velocity) is reduced, and the life of the copper plate, which was about 300 charges before, is reduced to about 450
Significantly extended to charge. As described above, according to the present invention, molten steel can be evenly supplied into a continuous casting mold by using a three-layer slide valve and an immersion nozzle connected to the slide valve. And the life of the mold water-cooled copper plate can be increased at the same time.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of a discharge hole portion of a two-hole immersion nozzle, where (a) is a conventional example and (b) is an example of the present invention. FIG. 2 (a) is the example of the present invention, and FIG. 2 (b) is the molten steel flow in the continuous casting mold.
Is a schematic view showing a conventional example. FIG. 3 is a schematic diagram showing an example of a general continuous casting facility. FIG. 4 is an explanatory diagram of a drift caused by a two-layer slide valve. FIG. 5 is an explanatory diagram of a drift caused by a three-layer slide valve. [Description of Signs] 1 Ladle 2 Tundish 3 Slide valve 4 Immersion nozzle 5 Mold 6 Mold short side copper plate 7 Nozzle discharge hole (discharge hole) 8 Mold long side copper plate 9 Flow velocity maximum streamline 10 Discharge hole angle 11 Slide valve movement direction

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor Toshitani Matsukawa               1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Kawasaki               Inside Steel Works Chiba Works (72) Inventor Tetsuhito Hirota               1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Kawasaki               Inside Steel Works Chiba Works (72) Inventor Hiroshi Nomura               1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Kawasaki               Inside Steel Works Chiba Works (72) Inventor Tetsuo Mochida               1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Kawasaki               Steel Works Co., Ltd.

Claims (1)

(57) [Claims 1] A slide valve formed of three layers of plates of molten steel held in a tundish provided at the bottom of the tundish and an immersion nozzle connected to the slide valve. In the continuous casting method of steel supplied into the mold by
The slide valve is arranged so that the intermediate plate of the three-layer plates moves in a direction parallel to the short side of the mold, and the immersion nozzle is caused by the deviation of the flow of molten steel in the flow control section of the slide valve. Discharge holes with discharge hole angles in the opposite direction to the deviation of the nozzle discharge flow
A continuous casting method for steel, comprising using a two-hole immersion nozzle.