JPH0813405B2 - Method and apparatus for pouring molten steel into mold - Google Patents

Description

TECHNICAL FIELD The present invention relates to a molten steel pouring technique used during continuous casting or ingot casting while pouring molten steel from a molten steel container to a mold.

Hereinafter, in order to facilitate understanding of the present invention, the continuous casting technique will be mainly described.

[Conventional technology]

Conventionally, in continuous casting, when the degree of superheat (molten steel temperature-liquidus temperature) of the molten steel in the molten steel container poured from the molten steel container into the mold is high (20 ° C or more), solidification of the cross section of the cast slab If the solidification structure becomes columnar crystals, and if the solidification structure becomes columnar crystals in this way, center defects such as cavities and center segregation easily occur at the center of the slab, and conversely the degree of superheat of molten steel is small (0 (° C to 20 ° C), it is known that equiaxed crystals are easily generated in the center of the slab, which is preferable for the quality of the slab.

[Problems to be Solved by the Invention] Therefore, in recent years, in continuous casting, the temperature of molten steel in a molten steel container, for example, a ladle or a tundish is kept low, the degree of superheat is reduced, and the molten metal is poured into a mold. However, an immersion nozzle is usually provided between the molten steel container and the mold, and the flow rate of molten steel from the molten steel container to the mold is controlled by the bottom of the molten steel container and the nozzle opening leading to the immersion nozzle. Is it done by moving the stopper located directly above to control the distance from the nozzle port or by controlling the opening / closing amount of the slide valve installed between the nozzle outlet of the molten steel container and the immersion nozzle? Therefore, if the molten steel temperature is low as described above, clogging due to the solidification of the molten steel occurs between the stopper and the nozzle opening or the opening / closing part of the slide valve, making it impossible to pour into the mold. Bull sometimes occurs.

From such a problem, the present inventors solve the above-mentioned nozzle clogging trouble, cast with the superheat degree of the above-mentioned molten steel lowered, and the same as the equiaxed crystal amount of the obtained slab, or As a result of diligent research to develop molten steel pouring technology capable of obtaining cast pieces with more equiaxed crystals, a large degree of superheat of molten steel in the molten steel container was taken, and superheat was reached between the molten steel flow rate control and the mold. We have completed the molten steel pouring technique of pouring molten steel from the molten steel container to the mold by controlling the degree to a small degree.

[Means for solving the problem]

That is, one of the present invention is to provide a swelling portion in the pouring nozzle or injection pipe during pouring molten steel from the molten steel container to the mold, and to provide a cooling portion in the wall portion of the swelling portion, and A rotating magnetic field coil surrounding the bulging portion is provided on the outer periphery of the bulging portion, and the molten steel passing through the inside of the bulging portion is rotated while being cooled to lower the temperature of the molten steel and generate crystal nuclei in the molten steel. Is a method of pouring molten steel into a mold.
While the molten steel is poured from the molten steel container to the mold, a swelling portion is provided in the pouring nozzle or the injection pipe, and a cooling zone is provided alongside the outer peripheral wall of this swelling portion, and at the outer periphery of the swelling portion. It is an apparatus for pouring molten steel into a mold provided with a rotating magnetic field coil surrounding a bulge portion.

[Action]

Since a swelling portion is provided in the pouring nozzle of a molten steel container such as a ladle or a tundish, or an injection pipe used in the bottom pouring ingot, the molten steel is cooled by this swelling portion and poured into the mold, It is not necessary to control the degree of superheat of the molten steel in the molten steel container to be small in the molten steel container, and it is sufficient that the superheat degree is controlled to such an extent that nozzle clogging trouble does not occur.
The superheat of molten steel in the mold can be reduced and casting can be performed.

Furthermore, a rotating magnetic field coil is provided around the bulging portion to surround the bulging portion, and the molten steel in the bulging portion is rotatively stirred along the inner peripheral wall of the bulging portion. The tip of the solidified shell generated on the inner wall surface of the bulging part is cut by this rotating and stirring molten steel to become a crystal nucleus, which is taken into the molten steel and a part of it is redissolved in the molten steel. In addition to enhancing the cooling effect of the molten steel, the rest mainly becomes equiaxed nuclei in the slab.

〔Example〕

Hereinafter, embodiments according to the present invention will be described with reference to the drawings.

Example 1 FIG. 1 is a sectional explanatory view of a molten steel pouring apparatus for casting a mold according to the present invention, and FIG. 2 is an II sectional explanatory view of FIG.

In the figure, 1 is a tundish, which is provided with a nozzle 2 at the bottom thereof, and at the outlet of the nozzle 2 at the outer bottom of the tundish 1, upper and lower fixing plates 4 and 6 having molten steel flow holes 3 and between them. The slide valve 7, which is composed of the sliding plate 5 of FIG.

8 is an immersion nozzle, and an immersion nozzle 8
The bulging portion 9 having an inner diameter three times as large as the inner diameter is provided. Further, cooling gas passages 12 are provided at predetermined intervals between the outer peripheral skin 10 of the bulging portion 9 and the refractory 11 inside thereof, and the upper and lower ends of the outer peripheral skin 10 of the bulging portion 9 are provided. A cooling gas outlet 13 and a cooling gas inlet 14 are provided in each of them. Further, the rotating magnetic field coil 15 is provided on the outer periphery of the bulging portion 9 with a space therebetween, and 16 is a bottomless mold used for continuous casting.

In the apparatus for pouring molten steel into the mold configured as described above, the molten steel A poured into the tundish 1 by a conventional method and stored in a predetermined amount slides between the upper and lower fixed plates 4 and 6 of the slide valve 7. When the plate 5 is operated and the molten steel flow hole 3 is opened, it flows down through the immersion nozzle 8 and is poured into the mold 16, and inside the mold 16, it is cooled by the mold wall and begins to solidify. After that, when the molten steel A that is continuously poured reaches the predetermined position in the mold 16, while substantially maintaining this predetermined position, the molten steel A is withdrawn from the slab that has started to solidify under the mold 16 while further cooling, Molten steel A is continuously poured into the mold 16.

Thus, while the molten steel A is continuously poured into the mold 16, the molten steel A passing through the bulging portion 9 of the dipping nozzle 8 is
In addition, the descending flow velocity becomes slower and the descending flow velocity in the vicinity of the inner peripheral wall of the bulging part 9 becomes slower, so that the inner peripheral wall surface of the bulging part 9 cooled by the cooling gas cools the Part of the solidified shell 17 is generated on the inner peripheral wall surface of the bulging portion 9 and, at the same time, the molten steel A is rotatively stirred by the action of the rotating magnetic field coil 15 provided at intervals on the outer periphery of the bulging portion 9. From the above, the tip of the solidified shell 17 to be produced is cut by the molten steel A which is rotated and stirred to produce crystal nuclei, and the crystal nuclei are taken into the molten steel. Then, some of the crystal nuclei taken in the molten steel are re-melted in the molten steel to enhance the cooling effect of the molten steel, but the rest are molten steel A in the mold.
When it solidifies in 16 and becomes a slab, it becomes an equiaxed crystal nucleus and becomes a slab with good internal quality.

Next, in the molten steel pouring device for the above mold, 60Hz, 2
Pole 3-phase rotating magnetic field coil (Specification: 450 at center of coil space)
Gauss, maximum rotation speed of 200 cm / s) was used to cool S45C molten steel with a superheat of 40 ° C in the tundish at the bulging part of the dipping nozzle, and a billet with a slab size of 150 mm square at a casting speed of 1.8 m / min. When continuous casting was performed and the magnetic flux density at the coil center was changed during the continuous casting, a slab having an equiaxed crystal ratio as shown in FIG. 3 was obtained and the central portion defect was improved. Also, during this casting, continuous casting could be performed without concern about clogging of molten steel at the slide valve.

In FIG. 3, as the magnetic flux density of the rotating magnetic field coil increases, the equiaxed crystal ratio increases. As the magnetic flux density of the rotating magnetic field coil increases, the rotational stirring of molten steel A in the bulging portion 9 becomes stronger. It will be done, this amount, solidification shell
It is inferred that the amount of crystal nuclei produced by cutting the tip of 17 increases and that the heat transfer from molten steel A to the refractory is promoted by the rotary stirring.

Incidentally, FIG. 4 is a diagram schematically showing the cross-sectional structure of the obtained cast product, in which a is the thickness of the equiaxed crystal part, and b is
Indicates the thickness of the slab, and the equiaxed crystal ratio was determined by a / b × 100%.

Example 2 Using the same molten steel pouring device for casting mold as in Example 1 above,
Cool SUP6 molten steel with a superheat of 35 ℃ in the tundish at the bulge of the dipping nozzle, and cast at a casting speed of 0.8m / min.
When a 30 mm bloom was continuously cast and the magnetic flux density at the coil center was changed during that, a slab having an equiaxed crystal ratio as shown in FIG. 5 was obtained and the central defect was improved. Further, during this casting, continuous casting could be performed without any concern about clogging of molten steel at the slide valve.

Embodiment 3 FIG. 6 is a cross-sectional explanatory view showing another embodiment of the apparatus for pouring molten steel into a mold according to the present invention, in which the molten steel inflow port 9a in the bulging portion 9 of the immersion nozzle 8 is shown. And the molten steel outlet 9b are eccentric to each other, and the immersion nozzle 8 has the same structure as that of the molten steel pouring device for casting the mold shown in the first embodiment. It has substantially the same functions and effects as those of 1.

Embodiment 4 FIG. 7 is a cross-sectional explanatory view showing still another embodiment of the molten steel pouring device for a mold according to the present invention, in which the nozzle 2 is provided on the lower side of the tundish 1. At the same time, at the outlet of the nozzle 2, a slide valve 7 having the same configuration as that of the first embodiment is horizontally fixed in a sealed state. Further, at the outlet of the slide valve 7, there is provided a dipping nozzle 8 having a bulging portion 9 in the horizontal portion, the tip of which is bent into an L shape, and the tip portion reaching the mold 16. The molten steel pouring device for casting molds having such a structure also has substantially the same functions and effects as those of the first embodiment.

In addition, in this example, the bulging portion 9 can be largely bulged downward and can be used as a molten steel pool to improve the rotary stirring efficiency by the rotary magnetic field coil 15.

Example 5 FIG. 8 is a cross-sectional explanatory view showing an embodiment in which the apparatus for pouring molten steel into a mold according to the present invention is used for under-pouring, and in this apparatus, an injection pipe 18 is used. A bulging portion 19 having substantially the same configuration as that of the immersion nozzle 8 of Example 1, a cooling zone 20 provided on the outer periphery of the bulging portion 19, and further this cooling zone
A rotating magnetic field coil 21 provided at a distance from the outer circumference of 20 is provided, and molten steel A poured from a ladle 22 is swollen.
In the above, in the same manner as in the bulging portion 9 of the immersion nozzle 8 of Example 1, the superheat of the molten steel A is reduced, and at the same time, it contains a large amount of crystal nuclei and passes through the runner 23. And is supplied to the mold 24. Then, in the ingot obtained by this lower pouring ingot, equiaxed crystals, which were rarely seen in the past, were formed and the central defect was improved.

〔The invention's effect〕

According to the present invention described above, since it is possible to take a large degree of superheat of the molten steel in the molten steel container, it is possible to perform casting without fear of nozzle clogging trouble, and to lower the degree of superheating of the molten steel into the mold and etc. Since crystal nuclei that become axial crystals can be generated and poured, the amount of equiaxed crystal in the slab increases and the defects at the center of the slab are improved.

[Brief description of drawings]

FIG. 1 is a cross sectional explanatory view of a molten steel pouring device for casting a mold according to the present invention, FIG. 2 is a cross sectional explanatory view taken along the line II of FIG. 1, and FIGS. 3 and 5 are magnetic fluxes at the center of the coil. The figure which shows the relationship between the density and the equiaxed crystal ratio in a cast, FIG. 4 is a cross-sectional schematic diagram of a cast,
6 to 8 are cross-sectional explanatory views showing another embodiment of the apparatus for pouring molten steel into a mold according to the present invention. DESCRIPTION OF SYMBOLS 1 ... Tundish, 2 ... Nozzle 3 ... Molten steel flow hole, 4,6 ... Fixed plate 5 ... Sliding plate, 7 ... Slide valve 8 ... Immersion nozzle, 9,19 ... Swelling part 9a ... Molten steel inlet, 9b ... Molten steel outlet 10 ... Peripheral iron shell, 11 ... Refractory 12 ... Cooling gas passage, 13 ... Cooling gas outlet 14 ... Cooling gas inlet 15, 21 ... Rotating magnetic field coil 16, 24 ... Mold, 17 ... Solidification Shell 18… Injection pipe, 20… Cooling zone 22… Ladle, 23… Runner A… Molten steel

Claims (2)

[Claims] 1. A swelling portion is provided in a pouring nozzle or an injection pipe while pouring molten steel from a molten steel container into a mold, and a cooling portion is provided on a wall portion of the swelling portion, and A rotating magnetic field coil surrounding the bulging portion is provided on the outer periphery, and the molten steel passing through the inside of the bulging portion is rotatively stirred while cooling to lower the temperature of the molten steel and generate crystal nuclei in the molten steel to form a mold. Method for pouring molten steel into a mold characterized by pouring 2. A swelling portion is provided in a pouring nozzle or an injection pipe during pouring molten steel from a molten steel container into a mold, and a cooling zone is provided along the outer peripheral wall of the swelling portion, and Molten steel pouring device for a mold, characterized in that a rotating magnetic field coil surrounding the bulging portion is provided on the outer periphery of the bulging portion.