JPH0289547A - Method for electromagnetic-stirring in mold in continuous casting - Google Patents

Abstract

PURPOSE:To prevent the development of accumulated zone of inclusions and to obtain a cast slab having excellent inner quality by discharging molten steel toward narrow face direction in a mold from a submerged nozzle and forming electromagnetic stirring flow in drawing direction along inside wide face. CONSTITUTION:In bending type continuous casting apparatus, discharging holes 2 in the submerged nozzle 1 are set as facing to the narrow face direction in the mold M, and by this, the molten steel is poured with the molten steel flow 3a having reverse Y shape. Further, in four faces constituting the mold M, the electromagnetic stirring device 5 generating driving force in the drawing direction is set at least near the discharging hole 2 of the submerged nozzle 1 at the inner side wide face. By this method, the molten steel flow 6 is formed in the drawing direction along molten steel solidified interface 7 formed with the inner wide face. This molten steel flow 6 is allowed to flow to the position 4 accumulating the inclusions by weakening the descending molten steel flow 3b in the above discharged molten steel flow 3a. By this method, the stagnation 8 of the inclusions is diffused and the accumulating zone of the inclusions is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for stirring a mold in a mold when continuously casting a slab of brocade in a curved continuous casting apparatus.

[Prior Art] Continuous casting is performed by injecting molten steel into a mold through a dipped nozzle in a tundish, cooling it from the periphery by the mold wall, and igniting it while forming and developing a solidified shell. In such a continuous SR manufacturing method, a immersed nozzle with a molten steel flow path formed in an inverted Y-shape is usually used in the curved continuous slab casting method, and the discharge hole of this immersed nozzle runs in the narrow direction. The pattern of the molten steel flow within the mold and directly below the mold is as shown in FIGS. 6 and 7. Therefore, in this pattern, inclusions and gas bubbles caught in the descending molten steel flow 3' solidify inside the curved slab S at the position 4" where the molten steel flow 3' weakens. It is known that these particles float to the interface side, are captured, and accumulate, causing a problem as an inclusion accumulation zone.

- On the other hand, in order to improve this problem, a curved slab continuous casting method using electronic stirring is known.

For example, in JP-A-47-33027, an electromagnetic stirring device is installed on a wide surface inside the curved part of the secondary cooling zone under the mold, and the unsolidified molten steel in the slab is moved in a direction perpendicular to the drawing direction. An electromagnetic stirring method is described in which a thrust force or a thrust force in the opposite direction to the pulling direction is applied to eliminate the inclusion accumulation zone.

In addition, JP-A No. 60-37251 discloses that an electromagnetic stirring device is installed on the wide surface of the mold divided into left and right sides, and the stirring thrust direction of the left and right electromagnetic stirring devices is adjusted according to the target steel type and casting conditions. An electric generator that improves the quality of cast slabs by switching between
f [The pressing force method is described.

Furthermore, in JP-A No. 61-269960, an electromagnetic stirring device is installed on the narrow side of the secondary cooling zone under the mold, and a thrust force is applied to the unsolidified molten steel in the slab in the opposite direction to the drawing direction. This document describes a method of stirring with an electric current f'' to reduce the inclusion accumulation zone that exists in the 1/4 thickness part of the upper surface of the slab.

[Problems to be Solved by the Invention] By the way, in the electromagnetic stirring method described in the above-mentioned JP-A-47-33027 and JP-A-61-269960, the inside of the curved part of the secondary cooling zone under the mold An electromagnetic stirrer is installed on the wide or narrow side of the steel, and support rolls are densely provided in this area to prevent bulging of the slab being drawn. For this reason, the electric Cif II stirring device can be installed on the top side of the support roll group, or it can be installed in place of the support roll, but in the former case, since there is a support roll between it and the slab, , efficient stirring cannot be expected, and even in the latter case, it is necessary to use an electromagnetic stirring device to suppress bulging. The problem is that it is difficult to provide an electromagnetic stirrer with good stirring efficiency in either method of installation.

In addition, in the electromagnetic stirring method described in JP-A No. 60-37251, the electromagnetic stirring device is divided into left and right sides within the wide surface of the mold, which increases the number of stirrers for molten steel and adapts it to the steel type and casting conditions. Although it is advantageous to be able to select an agitation flow based on these methods, it is not clear how these agitation flows are used to modify the crystal W of the slab.

As shown in the figure, the conventionally known electromagnetic stirring force 1L still has a problem, and the inclusion accumulation zone that floats to the inner solidification interface side of the curved slab as described in 11' and is captured and accumulated. This is not necessarily a sufficient method to reduce the

Therefore, in view of the above-mentioned problems, the present invention aims to provide mold-like electromagnetic stirring in continuous casting that can reliably reduce the inclusion accumulation zone that floats to the inner solidification interface side of a curved slab, is captured, and accumulates. The purpose is to provide a method.

[Means for Solving the Problems] In order to achieve the above object, the mold-like electromagnetic stirring method in continuous casting of the present invention is such that when a steel slab is cast by a curved continuous casting device, the molten steel flow path is in an inverted Y shape. An immersion nozzle formed in the shape of a mold is used, and the discharge hole of this immersion nozzle is installed facing toward the narrow surface, and the molten wA flow from the discharge hole is directed toward the narrow surface and is discharged from the four sides constituting the mold. An electromagnetic stirring device that generates a thrust in the drawing direction is installed at least near the immersion nozzle discharge hole of the inner wide surface, and a 'tatL flow in the drawing direction is formed along the molten gIiu solid surface formed by the inner wide surface. It is something.

In addition, an electromagnetic stirring device that generates a thrust in the drawing direction is installed near the immersion nozzle discharge hole on both the inner and outer surfaces of the four sides constituting the mold, and the molten steel solidification interface formed by the inner and outer surfaces is installed. Alternatively, a molten steel flow may be formed in the drawing direction.

[Function] As shown in FIGS. 1 and 2, the invention provides a discharge hole 2 of a submerged nozzle 1 in which a molten steel flow path is formed in an inverted Y shape.
Of the molten steel flow 3a discharged in the direction of the narrow surface from the molten steel flow 3a, the flow of the molten steel flow 3b weakens and inclusions accumulate (this position is determined by the drawing speed of the slab S and the flow from the discharge hole 2). Although it depends on the molten steel flow rate etc., the molten steel usually occurs between directly below the mold H and 2 m below the mold H).The electromagnetic stirring device 5 installed on the wide inner surface of the mold Since the molten steel flow 6 is caused to flow in the drawing direction along the molten steel solidification interface 7 that grows on the inner wide surface side, the molten steel flow 6 reliably reaches the position 4 where the inclusions stagnate, where the inclusion accumulation zone is formed. , it is possible to diffuse the stagnation 8 of inclusions and almost eliminate the inclusion accumulation zone.

In addition, when the electromagnetic stirring device 5 is installed on both the inner and outer wide surfaces of the mold, as shown in FIG. Similarly to the above, this flow reliably reaches the position 4 where the inclusions accumulate where the inclusion accumulation zone is formed, and can diffuse the accumulation 8 of the inclusions and almost eliminate the inclusion accumulation zone.

〔Example〕

At the center of the upper part of the mold of a curved continuous slab casting machine with a thickness of 230 mm and a width of 1250 m11, an immersion nozzle with a molten steel flow path attached to a kundishu formed in an inverted Y shape and a discharge hole facing downward at an angle of 25 degrees was installed. , installed so that its discharge hole faces in the direction of the V surface, and installed linear motors (n stirrers) on the wide inner surface of the mold at symmetrical positions in the width direction of the inner wide surface, and the steel composition shown in the table below. A1 killed steel for cold rolling was heated to 5Hz in a No. 11 electromagnetic stirrer.
Continuous casting was performed at a drawing speed of 1.2 m/min while applying 380 A and forming a molten steel flow in the drawing direction.

In order to investigate the effects of reducing inclusions and bubbles due to the above-mentioned stirring, a cross-sectional sample with a thickness of 75 mm was prepared from the slab obtained by the above-mentioned continuous casting as shown in Fig. 4 2, and as shown in Fig. 5 a. As shown in the figure, vertically cut samples with a thickness of 75 mm in the slab thickness direction and a length of 200 mm in the drawing direction were taken from the inner surface of the slab, and each was rolled to a thickness of 15 mm. The surface corresponding to the cross section of the piece and the surface corresponding to the inner surface of the longitudinally cut sample were subjected to ultrasonic testing. The results of the former are shown in No. 4nb, and the results of the subsequent test are shown in Fig. 5, 1].

In addition, for comparison, we conducted a similar investigation on slabs without electromagnetic stirring, and the results are shown in Figure 4C.
and FIG. 5C, respectively.

As is clear from the figure, the electric power KtPj! according to the present invention! When the stirring method was used, a good slab with almost no inclusions was obtained.

In addition, in the above example, an electromagnetic stirring device installed on the wide outer side of the mold in the same way as on the wide inner side was used, and the slabs in that case were also investigated in the same way as in the above example. The results showed that there were almost no inclusions, similar to the above results using only the electromagnetic stirring device provided on the inner wide surface.

[Effects of the Invention] As described above, according to the in-mold electromagnetic stirring method for continuous casting according to the present invention, the action of the molten steel flow is reliably applied to the areas where inclusions accumulate, thereby preventing the generation of inclusion accumulation zones. As a result, slough slabs with excellent internal quality can be obtained.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the molten steel flow seen from the inside wide surface side according to the present invention, FIG. 2 is an explanatory diagram of the molten steel flow seen from the narrow side of FIG. FIGS. 4 and 5 are explanatory diagrams of the melt flow seen from the narrow side according to the embodiment, and are explanatory diagrams of the effect of reducing inclusions in the slab obtained by the method of the present invention,
Figure 6 is an explanatory diagram of the molten steel flow seen from the conventional wide inner surface side.
FIG. 7 is an explanatory diagram of the molten steel flow seen from the narrow side of FIG. 6. ■ Immersion nozzle 2 Discharge holes 3a, 3b, 6.3' Molten steel flow 4.4' Position where inclusions accumulate 5 Electromagnetic stirrer 7) 8 Steel solidification interface 8 Stagnation of inclusions S Slab M Mold patent applicant Stock Company Kobe Steel

Claims (2)

[Claims] (1) When casting steel slabs using a curved continuous casting device, a immersion nozzle with a molten steel flow path formed in an inverted Y shape is used, and the discharge hole of this immersion nozzle is installed with the discharge hole facing the narrow side. , while discharging the molten steel flow from the discharge hole in the direction of the narrow surface, an electromagnetic stirring device that generates a thrust in the drawing direction is installed near the immersion nozzle discharge hole on at least the wide inner surface of the four sides constituting the mold; An in-mold electromagnetic stirring method in continuous casting characterized by forming a molten steel flow in the drawing direction along a molten steel solidification interface formed by an inner wide surface. (2) An electromagnetic stirring device that generates a thrust in the drawing direction is installed near the immersion nozzle discharge hole on both the inner and outer wide surfaces of the four surfaces constituting the mold, and the molten steel solidification interface is formed by the inner and outer wide surfaces, respectively. The in-mold electromagnetic stirring method in continuous casting according to claim 1, characterized in that a molten steel flow is formed in the drawing direction along.