JPH02274352A - Method for continuously casting steel - Google Patents

Abstract

PURPOSE:To enable adequate stirring of molten steel in a mold corresponding to discharging rate of the molten steel by arranging plural refractory bricks having different porosities and porous diameters for independent gas blowing to inner wall of a nozzle hole penetrated in an upper nozzle, sliding gate and submerged nozzle. CONSTITUTION:The refractory brick 25 having high porosity and small porous diameter and the refractory brick 26 having low porosity and large porous diameter for gas blowing, are arranged to the inner wall 24a of the nozzle hole in the upper nozzle 21. These refractory bricks 25, 26 for gas blowing arrange a gas supplying device and are made so as to be possible to independently control gas blowing flow rate with each gas flow rate control devices 31, 32. In the case of varying the discharging rate of the molten steel by adjusting the sliding gate 22, gas flow controlled with each gas flow rate control devices 31, 32 arranged to the supplying device, is blown into the molten steel flow in the nozzle hole through the refractory brick for gas blowing. The gas blown into the molten steel flow is mixed with the molten steel flow and discharged into the mold and dispersing of gas bubbles to the whole surface in the mold can be executed.

Description

[Detailed description of the invention] [Industrial application fields] The present invention relates to a continuous casting method for steel.

[Prior Art] A continuous casting method for steel is generally carried out by a continuous casting method as shown in FIG.

The molten steel 1 is injected from the tundish 2 into the mold 5 through the sliding gate 3 and the immersion nozzle 4, and the slab 6 is continuously pulled out by pinch rolls (not disclosed). In addition, mold powder 7 is sprinkled so that the slab 6 can be easily pulled out from the mold 5. As a measure to prevent the nozzle hole of the immersed nozzle 4 from being clogged due to solidification of molten steel, many proposals have been made to blow gas into the nozzle hole of the immersed nozzle. As one example, Japanese Patent Publication No. 642467 describes a method for preventing blockage of a submerged nozzle by blowing gas as shown in Fig. 5. In Fig. 0, a gas barge type stopper 8 is used as a stopper for the tundish 2, and Porous part 91 and slit 9
2, the tip 81 of the stopper is
, Supply the molten steel 1 to the mold 5 while blowing out inert gas from all of the porous part 91 and slit 92 of the immersion nozzle 9, and carry out the blowing of the inert gas at that time by selecting the indigo to satisfy the following conditions. This is a continuous casting method.

0, l≦A/(,B+C)≦5 and 0.1≦B/C≦5 where A: Amount of gas blown from the tip of the stopper B: Amount of gas blown from the porous part of the immersion nozzle C: immersion nozzle When continuous casting of steel, especially steel containing aluminum, is carried out under conditions such as the amount of gas blown out from the slit or higher, continuous casting can be performed for a long time without clogging the immersion nozzle.

In addition, if the flow of molten steel in the mold is uneven, the heat supply to the mold powder will be insufficient, and due to insufficient slag formation of the mold powder, the mold powder will intervene in the solidified shell of the meniscus area and become interposed in the slab. Various methods of electromagnetic stirring within the mold have been proposed to prevent material defects. Japanese Patent Publication No. 63-33157
As shown in FIGS. 6 and 7, the publication describes that the electromagnetic force of electromagnets 10a to 10d is applied to the molten steel 1 injected from the immersion nozzle 4 into the mold 5 in the direction shown by the arrow in the direction of the arrow in the early stage of casting. By acting in the direction shown and circulating the molten steel 1 almost horizontally in the direction shown by the thin arrow, the molten steel 1 is stirred and the amount of heat supplied to the mold powder 11 supplied to the upper part of the molten steel is increased. This promotes slag formation of the mold powder 11 and improves the surface quality of the slab. Japanese Patent Publication No. 63-331
No. 58 discloses that by applying electromagnetic force to the molten steel injected into the mold and causing an upward flow of the molten steel,
It is described that molten steel is stirred, and JP-A-63-3
Publication No. 3159 describes that the molten steel injected into the mold is stirred by applying electromagnetic force to cause the molten steel to flow in the opposite direction to the discharge flow from the immersion nozzle. Both of these methods aim to improve the surface quality of slabs by promoting the formation of mold powder into slag.

[The problem that the invention tries to solve! [fl] In recent years, in order to increase productivity in continuous steel casting methods, so-called high-speed continuous casting has been increasingly used.Furthermore, continuous casting methods using different steel types have also been adopted. There are many cases where it is necessary to adjust the amount of molten steel injected into the mold from the immersion nozzle at the end of casting. In this case, especially in the continuous slab casting method, the stirring of the molten steel in the mold tends to be uneven due to fluctuations due to the adjustment of the molten steel discharge rate, the floating effect of deoxidized products and the mold powder involved is poor, and the slab There is a problem that surface defects due to the inclusion of inclusions increase. The technology described in Japanese Patent Publication No. 64-2467 has the advantage of eliminating clogging of the immersion nozzle and allowing continuous casting for a long time, but since it is not intended to stir the molten steel in the mold, the molten steel in the nozzle hole Even if gas is blown into the flow and the self-molten steel in the mold is agitated, the gas agitation is often not adequate to accommodate fluctuations due to adjustment of the molten steel discharge rate. The technique of stirring molten steel in a mold by applying electromagnetic force can be expected to have a certain effect on stirring molten steel, but it requires the installation of an electromagnetic stirring device in a narrow space around the mold, and it is difficult to use when blowing gas. Unlike the above, the deoxidation products caused by gas bubbles and the floating effect of the entrapped mold powder cannot be expected.

The present invention aims to solve the above-mentioned problems, and aims to improve the quality of the slab by appropriately stirring the molten steel in the mold in response to fluctuations in the amount of molten steel injected into the mold. The purpose of this invention is to provide a method for continuous casting of steel.

[Means and effects for solving the problem] In order to achieve the above object, in a continuous steel casting method in which molten steel is injected into a mold through an upper nozzle connected to the bottom opening of a tundish, a sliding gate, and an immersion nozzle, A plurality of refractory bricks with different porosity and pore diameter for independent gas injection are provided on the inner wall of the nozzle hole through which the upper nozzle, the sliding gate, and the immersion nozzle pass, and the molten steel volume discharge lid of the immersion nozzle is adjusted by adjusting the sliding gate. In accordance with the change in the amount of gas blown into the refractory brick for gas blowing, the gas is blown into the molten steel flow in the nozzle hole, and the self-molten steel in the mold is agitated with the gas.

Prior to the invention, the present inventors discovered through repeated experiments that changes in the amount of molten steel discharged from the immersion nozzle and the distribution of the bubble diameter of the gas mixed into the molten steel flow in the mold caused the agitation of the self-molten steel in the mold and the resulting inclusions. We obtained knowledge that this affects the surfacing of Therefore, we installed multiple refractory bricks with different porosity and pore diameter for independent gas injection on the inner wall of the nozzle hole of the upper nozzle, and conducted various studies, and as shown in Fig. 3, changes in the molten steel discharge rate of the immersion nozzle and The invention was achieved by discovering the relationship between the amount of gas blown into a plurality of refractory bricks with different porosity and pore diameter and the corresponding distribution of bubble diameter of gas mixed into the molten steel flow in the mold. Here, gas of Ml amount is blown out from the refractory brick with high porosity and low pore diameter shown by the dotted line, and the gas mixed with the melt #1 flow forms small-diameter bubbles M2, and the low porosity shown by the solid line・N amount of gas is blown out from the refractory brick with high pore diameter, and the gas mixed with the molten steel flow forms large diameter bubbles N2. It is thought that the gas blown out from these refractory bricks collides with the molten steel flow and disperses as small and large bubbles. In the present invention, with the above configuration, the amount of each gas blown is adjusted. Since an appropriate bubble diameter can be formed as appropriate, gas bubbles can be scattered over the entire surface of the mold in response to changes in the amount of molten steel discharged from the immersion nozzle. Therefore, sufficient gas agitation of molten steel is possible. In this case, the upper part of the inner wall of the nozzle hole of the immersion nozzle is a refractory brick with high porosity and low pore size for independent gas injection, and the lower part is a refractory brick with low porosity and high pore size for independent gas injection. It is preferable to blow gas into the molten steel flow in the nozzle hole by providing a gas bubble.In this case, it is easy to form large diameter bubbles, and the gas bubbles can be scattered over the entire surface of the mold.

[Example] An example of the present invention will be described below with reference to the drawings. 1st
The figure shows that in the present invention, a plurality of refractory bricks with different porosity for blowing gas are provided on the inner walls of the nozzle holes that the upper nozzle, sliding gate, and 7+fi nozzle pass through, and gas is supplied to the molten steel flow in the nozzle holes that pass through them. FIG. 2 is an explanatory diagram of a case where the mold self-melting steel is gas-stirred by being blown into the mold. In the figure, 21 is the upper nozzle, 22 is the sliding gate, 23 is the immersion nozzle, 24 is the inner wall of the nozzle hole that penetrates these nozzles, and 25 and 26 are the independent porosity for gas blowing.
These are multiple refractory bricks with different pore sizes. A sliding gate 22 is connected to an upper nozzle 21 inserted into an opening 2b provided in the bottom 2a of the tundish 2 from the outside of the bottom 2a. The sliding gate 22 includes a support plate 27 attached to the outside of the bottom of the tundish 2;
It is composed of a fixed plate 28, a sliding plate 29, and a drive device 30 that drives the sliding plate 29. Here, the upper nozzle 21
A refractory brick 25 with high porosity and low pore diameter and a refractory brick 26 with low porosity and high pore diameter for blowing gas are provided on the inner wall 24a of the nozzle hole. These refractory bricks 25, 26 for blowing gas are provided with a gas supply device so that the gas blowing flow rate can be controlled independently by each gas flow rate adjusting device 31, 32.

When the amount of molten steel discharged from the immersion nozzle is changed by adjusting the sliding gate, the amount of change is calculated by the calculation unit 33.
The corresponding gas supply amounts are calculated and commanded from the command unit 34 to the supply device, and the gas amounts adjusted by the respective gas flow adjustment devices 31 and 32 provided in the supply device are It is blown into the molten steel stream in the nozzle hole through the blowing refractory brick. The gas blown into the molten steel flow mixes with the molten steel flow and is discharged into the mold, causing gas bubbles to scatter over the entire surface of the mold. Although their porosity and pore diameter are relative, it is appropriate that the difference in porosity is in the range of 3 to 20% and the difference in pore diameter is in the range of 10 to 30 μm. If the difference in porosity is less than 3%, it is difficult to respond to changes in the amount of molten steel discharged. When the porosity difference exceeds 20%, it is difficult to adjust the gas flow lid with low flow rate on the high porosity side. The difference in pore diameter is 1
If it is less than 0 μm, it is difficult to form bubbles that correspond to changes in the amount of molten steel discharged. When the difference in pore diameter exceeds 30 μm, it is difficult to form uniform bubbles in the mold self-melting steel.

Next, experimental examples according to the present invention will be explained in detail.

A continuous casting method of different steel types was carried out using a water-cooled mold of 250 cm in length x 1000 cm in width x 700 cm in height. Here, using a device as shown in Fig. 1, the refractory bricks 25 and 26 for blowing gas into the upper nozzle are refractory bricks with a porosity of 25% and a pore size of 20 μm, and a refractory brick with a porosity of 20% and a pore size of 40 μm, respectively. Fireproof bricks with pore size were used. A high alumina porous brick (AlI30x: 90%, 5i02: 10%) is a fire-resistant brick with a porosity of 25% and a pore diameter of 20 μm.
An alumina-silica porous brick (Af20s: 80%, 5i02: 20%) was used as the refractory brick with a 20% porosity and 40 μm. As a conventional example, a refractory brick (Aβ20s: 80%, SiO: 2Q%) with a porosity of 25% and 35 μrn was used for comparison. Continuous casting of different steel types: 1 from the following steel types ■
1 was made, and high-speed casting was performed for the subsequent steel type (2).

(Note) The other components were almost the same, and the discharge rate of the immersion nozzle was changed accordingly, but the discharge rate of the immersion nozzle for high-speed casting of the later steel types was assumed to be 100%, and the high porosity and low pore diameter were used. The ratio of the gas amount between the refractory brick and the refractory brick with low porosity and high pore size is 6.
Ar gas was blown into the molten steel flow in the nozzle hole at 0% and 40%.

In the case of the refractory brick having the porosity of the conventional example, the discharge amount of the immersion nozzle was set to 100% as above. In these cases, the state of bubbles caused by Ar gas on the mold surface was visually observed by making the mold powder thinner than usual, and the scattering locus of the Ar gas bubbles was estimated. The results are shown in Figure 2 (A).
, shown in (B).

The figure (A) shows the case of an experimental example according to the present invention, and the figure (B) shows the case of the conventional example. (A) In the figure, A mixed into the molten steel flow discharged from the discharge hole of the immersion nozzle 23 into the mold 54
It was estimated that the r gas bubbles were scattered uniformly over the entire surface of the ln #1 molten metal in the mold. 35 indicates the mold powder, and 36 indicates the trajectory of Ar gas bubbles. (B) In the diagram, A
It was observed that the r gas bubbles formed a blank area in the vicinity of the immersion nozzle 23 in the mold, and therefore it was presumed that they were not uniformly scattered on the surface of the molten steel. The results of measuring the total oxygen content of the inclusions in the slab corresponding to these are the first
Shown in the table.

As is clear from Table 1, in the case of the experimental example of the present invention, the total oxygen content of the slab was lower than in the case of the conventional example, and the number of inclusions was reduced.

[Effects of the Invention] According to the method of the present invention, the amount of gas blown into the refractory brick for gas blowing is adjusted in response to the change in the amount of melt discharged from the submerged nozzle due to the adjustment of the sliding gate. Gas is injected into the molten W4 flow to form an appropriate gas bubble distribution in the mold self-molten steel, so inclusions can be floated and removed by sufficient gas agitation of the molten steel, and as a result, the quality of the slab can be improved. I can figure it out.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of one embodiment of the present invention, Fig. 2 is a diagram showing estimation of the scattering locus of gas bubbles in the mold in an experimental example of the present invention, and Fig. 3 is a diagram showing changes in molten steel discharge rate and porosity. A diagram showing the relationship between the amount of gas blown into refractory bricks with different pore diameters and the bubble diameter distribution of the gas mixed into the molten steel flow in the mold. Figure 4 is an explanatory diagram of a continuous casting device, and Figure 5 is a diagram of a conventional immersion casting system. A diagram showing a method of blowing gas into a flow of molten steel in a nozzle, and FIGS. 6 and 7 are diagrams showing a conventional method of electromagnetically stirring molten steel in a mold. 21... Upper nozzle, 22... Sliding gate, 23... Immersed nozzle, 24... Penetrating nozzle hole inner wall, 25. 26... Independent refractory brick for gas injection,
27...Support plate, 28...Fixing plate, 29...Sliding plate, 30...Drive device, 31.32...Gas flow rate adjustment device, 33...Calculating unit, 34...・Command Department, 35・
...Mold powder 36...Trajectory of Ar gas bubbles.

Claims (2)

[Claims] (1) In a continuous steel casting method in which molten steel is injected into a mold through an upper nozzle, a sliding gate, and an immersion nozzle connected to the bottom opening of the tundish, the inner wall of the nozzle hole penetrated by the upper nozzle, sliding gate, and immersion nozzle. A plurality of independent refractory bricks with different porosity and pore diameter are provided for gas injection, and the gas of the refractory bricks for gas injection is adjusted in response to changes in the amount of molten steel discharged from the immersion nozzle by adjusting the sliding gate. A continuous steel casting method characterized by blowing gas into the molten steel flow in a nozzle hole while adjusting the blowing amount and stirring the molten steel in the mold with gas. (2) At the top of the inner wall of the nozzle hole of the upper nozzle, there is a refractory brick with high porosity and low pore diameter for independent gas injection, and at the bottom, a fireproof brick with low porosity and high pore diameter for independent gas injection. 2. The method for continuous casting of steel according to claim 1, further comprising a steel brick.