JPS61140356A - Electromagnetic stirring method in continuous casting machine - Google Patents

Abstract

PURPOSE:To obtain a billet which is clean in the front layer part and has extremely little central segregation by casting continuously a molten steel while using the electromagnetic stirrer in such a manner that the molten steel flows upward on the inside wall surface of a casting mold and flows in the transverse direction of the billet in a secondary cooling zone. CONSTITUTION:The electromagnetic stirrer 5 in the casting mold is so operated that the molten steel 1 flows upward on the inside wall surface of the mold 3 and the in-roll type electromagnetic stirrer 7 is so operated that the molten steel 1 flows in the transverse direction of the billet in the secondary cooling zone in a continuous casting machine for slab which obtains the bloom by pouring the molten steel 1 from a tundish 2 into the mold 3, supporting and drawing out a solidified shell layer 4 formed as a result of cooling by means of rolls 6 and subjecting the shell layer to secondary cooling. The increase in the size of the inclusion and the floating of the inclusion and foam are thus accelerated and the billet having good quality is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an electromagnetic stirring method in a continuous casting machine for support rods.

(Prior Art) In electromagnetic stirring in continuous slab casting, both vertical stirring in the mold and in-roll stirring in the secondary cooling zone are useful for improving the quality of the joints.

The former type of vertical stirring in the mold is a method in which an electromagnetic stirring filter is installed on the wide side of the slab in the mold to generate an upward stirring flow, and electromagnetic stirring can be performed while minimizing fluctuations in the melt level. In casting guild steel, vertical stirring is effective in removing inclusions.

Inclusions floating on the surface layer of the tin pieces in the mold are promoted to float by the upward flow of molten steel, and inclusions larger than a certain size are adsorbed by the 7 lux in the mold and separated from the molten steel.

However, fine inclusions are less affected by the flow of molten steel and do not float up to the meniscus, but are again mixed into the downward discharge flow at a position near the center of the thickness of the slab. Therefore, vertical stirring in the tribute mold is effective for cleaning the surface layer of the slab, but there are problems with the internal quality, especially inclusions. In addition, the above.

Even in the secondary cooling zone, a considerable amount of these fine inclusions remain suspended. In addition, vertical stirring in the mold is effective in removing air bubbles when casting weakly deoxidized steel.
No further explanation will be provided.

On the other hand, the latter in-roll electromagnetic stirring is a method in which molten steel is stirred in the width direction of the slab using a plurality of electromagnetic stirring coils built into rolls installed in a secondary cooling zone. It is effective in improving internal quality and center segregation, but on the other hand, there are problems in cleaning the surface layer of the slab.

(Problems to be Solved by the Invention) An object of the present invention is to provide an effective electromagnetic stirring method for obtaining slab slabs with a clean surface layer and very little center segregation in continuous bonding. It is to be.

(Means for Solving the Problems) The electromagnetic stirring method according to the present invention, in a continuous slab casting machine, uses an inertia type electromagnetic stirring device to: I) flow molten steel upward on four inner wall surfaces of a mold; Moreover, the molten steel is made to flow in the width direction of the slab in the secondary cooling zone using an in-roll type electromagnetic stirring device.

(Function) By combining vertical stirring in the mold and in-roll stirring, both the surface layer and the inside of the slab are sufficiently stirred, reducing inclusions, etc.

(Embodiment) In the continuous slab casting machine of the embodiment of the present invention, two types of electromagnetic stirring devices are arranged as schematically shown in the drawings.

In a continuous slab casting machine (230 mm t x 1250♂), molten steel 1 is injected into a tundish 2 and a mold 3, and a solidified shell layer 4 grows from the surface. The in-mold vertical stirring device 5 is arranged on all four sides of the mold 3 so as to give upward flow to the molten steel 1. The solidified shell layer 4 is formed by the mold 3
It is pulled out while being supported by rolls 6.6t... and grows as it cools, becoming a slab. The in-roll type electromagnetic stirring device 7 is arranged on the upper surface side of the slab in a position where there is no discharge flow of the molten steel 1 generated by injection, with a set of two adjacent rolls (not shown).

This is because, as disclosed by the present inventors in Utility Application No. 134812/1980, the stirring flow caused by electromagnetic stirring is stronger when two pieces 1 and 11 are used alone. (In addition, a method of further strengthening the stirring flow is disclosed in Japanese Patent Application No. 58-159440.
No. 58-159441. ) The molten steel of the low-grade aluminum killed steel for thin plates used in the examples of the present invention is subjected to preliminary treatment. The composition of the molten steel after pretreatment is as follows. C: 0.0'3~0.07%
, Si: 0.01-0.03%, Mn: 0.2
8-0.35%, P: 0.010-0°ois%,
s: o, oos ~ 0.011%, Al2 0.043
~0.060%. The degree of superheating of the molten steel 1 injected into the mold 3 is 20 to 45°C.

Electromagnetic stirring is performed as follows. The frequency of stirring in the mold is 1.5 to 10. OHz, and the stirring force is at least 4000 N/m' at a position where the thickness of the mold solidification shell layer is 20 mm. On the other hand, the frequency of the in-roll stirring is 1.5 to 10.0 Hz, and the stirring force at the solidification interface is at least 4000 N/m3. In addition, the drawing speed of the solidified slab is 0.9~
It is 1.3m/min.

The table shows the slab quality when vertical stirring in the mold and the secondary cooling zone in-roll stirring were applied alone, and the slab quality when both were used in combination (this example). Here, the /Lokami index is 1,2511Ill when the surface was treated with 1.5ml11 solvent.
The number of grooves on the top and bottom surfaces of a slab of
12 per charge, 5 charges per charge was investigated. The center segregation rate is 10 mm along the length direction of the slab.
At 20 points on the pitch, find the ratio of the check analysis value of the sample taken with a 3m1Ilφ drill to the average value in the ladle, and
It is further averaged for each stage. The analyzed carbon values were determined to the nearest 0.001%. *The average amount of oxygen is calculated by cutting out a 5φ x 100Il sample at 15 points when the slab is divided into 16 parts in the thickness direction, and then averaging the average over 5 charges.

As is clear from the slab quality table for low-aluminum killed steel for thin plates, the Norokami index in this example is improved compared to the case of secondary cooling zone in-roll stirring, and is equivalent to the case of only vertical stirring in the mold. It was kept reasonably well. On the other hand, the center segregation rate, which is a quantity representing internal quality, and especially the average oxygen content were improved compared to when only vertical stirring in the mold* or in-roll stirring in the secondary cooling zone was used. In other words, the internal quality improved due to the synergistic effect of combining the two.

This synergistic effect can be understood as follows. As mentioned at the beginning, inclusions and bubbles in the surface layer of molten steel are brought to the surface by vertical stirring in the mold, and the surface layer is cleaned, but a considerable amount of fine inclusions are also present in the secondary cooling zone. Floating. However, when the molten steel is made to flow in the width direction of the tribute piece by in-roll electromagnetic stirring in the secondary cooling zone, the growth of fine inclusions due to collision or adsorption is promoted, resulting in large inclusions. As the size increases, levitation is facilitated. After flowing in the width direction of the slab, the molten steel flows from the narrow end of the slab into an upward flow and a downward flow. The grown large inclusions float to the surface due to this upward flow. When it floats to the vicinity of the mold, it is forcibly floated by the vertical stirring inside the mold, and the melted 7
It is adsorbed to the lux and separated. For this reason, due to the synergistic effect of the two types of stirring, the produced pickled juice is clean both on the surface and inside, and has very little center segregation.

Furthermore, as disclosed in Japanese Patent Application No. 159440/1980,
Combining multiple sets of two-piece in-roll type stirring improves the stirring effect, further promotes the upward stirring flow, and further improves the quality of the pickled juice.

(Effects of the Invention) According to the present invention, a pickled juice with excellent surface and internal quality and less center segregation can be obtained in slab production.

[Brief explanation of drawings]

The drawing is a schematic cross-sectional view of a continuous casting machine incorporating two types of electromagnetic stirring devices according to the present invention.

Claims (1)

[Claims] (1) In a continuous slab casting machine, molten steel is made to flow upward on the four inner walls of the mold using an in-mold electromagnetic stirring device,
Further, an electromagnetic stirring method for a continuous casting machine, characterized in that molten steel is made to flow in the width direction of the slab in a secondary cooling zone using an in-roll type electromagnetic stirring device.