JPH0259155A - Method for continuously casting steel and submerged nozzle - Google Patents

Abstract

PURPOSE:To prevent stagnating phenomenon and to prevent the development of flaw and internal defect caused by enclosing inclusion by forming gas blowing-out hole to outer part at tip part of a submerged nozzle and blowing out inert gas toward both longitudinal sides of a mold by the specific quantity. CONSTITUTION:At the time of executing the continuous casting, two gas blowing-out holes 8' toward both longitudinal sides 13b, 13b of the mold 13 for continuous casting at the tip part 5 of the submerged nozzle 3 and gas flowing passage in the nozzle wall 9 are arranged. Then, the inert gas of 1-2l/ton of discharged molten steel 12 is blown out toward both longitudinal sides 13b, 13b of the mold 13 for continuous casting from two gas blowing-out holes 8', 8' to the outer part. By this method, the molten steel temp. in the mold 13 is uniformized and it is promoted that the inclusion in the molten steel 12 is caught in the molten powder 17 on the molten steel surface by floating up and separating.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention aims at preventing the occurrence of flaws or internal defects due to the inclusion of inclusions in cast slabs, and processing these slabs into products. The present invention relates to a method for continuous casting of steel that can be continuously cast to produce high-quality products with high cleanliness without causing surface flaws due to the inclusion of inclusions, and an immersion nozzle used therein.

[Conventional technology]

In the continuous casting method of steel, molten steel in a ladle is poured into a tundish, and the molten steel in the tundish is poured downward into a continuous casting mold using a submerged nozzle, with the molten metal surface covered with molten powder. A method of drawing and continuous casting is generally adopted.

Hereinafter, a conventional continuous casting method for steel will be explained with reference to the drawings.

Figure 8 is an explanatory diagram schematically showing the main parts of the continuous casting process;
Fig. 9 is a longitudinal cross-sectional view of an example of a conventional immersion nozzle used in continuous casting, Fig. 10 is a sectional view taken along the line C-C in Fig. 9, and Fig. 11 is a longitudinal cross-sectional view of an example of a conventional immersion nozzle used in continuous casting. FIG. 2 is an explanatory plan view showing a flow of molten steel in a continuous casting mold during continuous casting.

First, we will provide a general overview of the continuous steel casting process.

As shown in FIG. 8, the molten steel transferred from the ladle 1 into the tundish 2 passes through the immersion nozzle 3 attached to the lower part of the tundish 2, and is discharged from its tip into the continuous casting mold 13. The surface of the molten steel 12 is cooled by a continuous casting mold 13 to form a solidified shell 12' while being moved downward, and then passed through a spray zone 14° where water is sprayed, further passed through a cooling zone 15, and then transferred to a drawing roll 16. The cast slab 12' of a predetermined size is pulled out downward by the
is cut off.

At this time, since the height of the equipment increases if the material is pulled out in the vertical direction until it is cut, many curved continuous casting equipments are used that cut the material while moving it in the horizontal direction with the drawing direction curved. During this time, the molten steel 12 increases the thickness of the solidified shell 12', and by the time it is cut, it has completely solidified to the center of the slab 12'.
'. The amount of molten steel 12 discharged from the immersion nozzle 3 is adjusted to match the amount of downward extraction. The surface of the molten steel 12 in the continuous casting mold 13 is covered with molten powder 17 supplied from above, and the nozzle tip 5 of the immersion nozzle 3 penetrates the molten powder 17 and is located below the molten metal surface. I'm being forced to do it. This molten powder 17 retains heat and suppresses oxidation of the molten steel in the process, and captures inclusions (non-metallic substances such as oxides, disulfides, nitrides, and carbides that are generated and mixed into the steelmaking process from main and auxiliary raw materials). The surface of the slab 12' is prevented from entering the steel, flows into the gap between the continuous casting mold 13 and the solidified shell 12', and prevents rapid cooling during casting, and improves the lubrication of the gap. This is to obtain an effect such as preventing cracking of the material, and for example, a material composed of C, BN, Cab, 5in2, etc. is used.

The conventional immersion nozzle 3 used in such a continuous steel casting method has a substantially tubular shape as shown in FIG.
, an outer diameter of 110 to 130 mm), the hollow nozzle hole 4 is closed at the end face at the nozzle tip 5, and the 10th
As shown in the figure, two molten steel discharge ports 6 are formed by opening at both ends of the diameter.

This molten steel discharge port 6 is diagonally upward in the direction of the molten steel discharge port.

Depending on whether it is horizontal or diagonally downward, it is formed in a shape that discharges in that direction, and FIG. 9 shows one that is directed diagonally upward. The nozzle base 7 is attached to the tundish 2. In addition to the above configuration, the conventional immersion nozzle 3 also has an internal gas outlet 8 as shown in FIG.
In some cases, the nozzle hole 4 is provided on almost the entire inner surface of the nozzle hole 4 except for the nozzle base 7 and the nozzle tip 5. This internal gas outlet 8 is configured as follows. That is, the first
As shown in Figure 0, an internal blowout slit 10 (example gap size is 1.5 to 51 m) is provided in the nozzle wall 9 along the circumferential surface, and a wall further inside the internal blowout slit 10 is provided inside the nozzle wall 9. is the breathable refractory material 9a, for example AQ 20
3-5i (consisting of h-type heavy-duty material, etc.) and is located on the outer surface of the nozzle wall 9 on the side of the nozzle base 7 and above the molten powder 17 on the molten steel 12 in the continuous casting mold 13. A gas supply plug 11 is provided in the part where the
0 is connected.

Next, the state inside the continuous casting mold 13 when continuous casting of steel is performed using the conventional immersion nozzle 3 will be described. As shown in FIG. 11, the horizontal cross-sectional shape of the casting part of the continuous casting mold 13 is approximately rectangular (for example, the long side is 1050 mm).
molten steel 12 in Figure 8).
is viewed from the front with the short side 13a in FIG. 11). The immersion nozzle 3 is attached to the bottom of the tundish 2 installed above the continuous casting mold 13, and is directed toward the center of the rectangular continuous casting mold 13, and the two molten steel discharge ports 6 are connected to the short side 13a of the continuous casting mold 13. When the molten steel 12 is discharged with the nozzle tip 5 positioned below the scene, the molten steel 12 will flow to the molten steel discharge port 6. of the immersion nozzle 3, as shown in FIG. is discharged toward the short side 13a of the continuous casting mold 13,
The molten steel solidifies while producing a molten steel flow as indicated by arrow X, and is successively drawn downward. A submerged nozzle 3 with an internal gas outlet 8 is used, and a gas supply plug 11 is used.
When continuous casting is performed while blowing an inert gas such as argon into the molten steel 12 passing through the nozzle hole 4, inclusions in the molten steel 12 mainly adhere to the inner peripheral surface of the nozzle hole 4 and solidify. As the diameter of the hole is made smaller, the flow of the molten steel 12 within the hole becomes worse, and there is no risk of clogging the nozzle hole (nozzle blockage).

In such a continuous steel casting method, the flow of the molten steel 12 discharged from the immersion nozzle 3 includes (1) preventing the molten steel surface from cooling and solidifying in a state where it is mixed with the molten powder 17; (2) It is known that it has the effect of influencing the cleanliness of the slab 12#, such as promoting the flotation and separation of inclusions suspended in the molten steel 12 and their capture in the molten powder 17 on the molten metal surface. In order to make the effect of this flow of molten steel 12 work effectively, for example, as described above, the immersion nozzle 3 is used so that the discharge direction of the molten steel 12 is diagonally upward, and the discharge port 6 is used as shown in the example of FIG.
A method in which the main stream of molten steel 12 is discharged diagonally upward toward the molten metal surface.

A method of dispersing the flow of molten steel by providing a barrier against the mainstream of the discharged molten steel 12 has been adopted.

However, since the molten steel discharge port 6 of the conventional immersion nozzle 3 is provided on the side facing the short side 13a, which is the longer distance between the outer peripheral surface of the immersion nozzle 3 and the inner wall of the continuous casting mold 13, In the above technique, the flow force of the molten steel in the region 13c between the immersion nozzle 3 and the long side 13b of the continuous casting mold 13 was the weakest, and a stagnation phenomenon occurred.

In this stagnant molten steel 12, inclusions suspended in the molten steel 12 gather and grow to form large inclusions. Since the action of the molten steel flow does not work effectively, the temperature of the molten steel 12 decreases.

As a result, the inclusions cannot float up, solidify and are pulled out while being caught in the molten steel 12, so the cast slab 12
Surface flaws and internal defects caused by inclusions had occurred in the center of the width direction. Due to this phenomenon, the slab 12
Surface flaws and internal defects are particularly likely to occur in steels containing quite a large amount of moose and Ti, such as 5US321.5US405°5US430LX,
US436L, 5US444.5US631. Al
This is often the case with stainless steels such as 5I409. As a result, the maintenance of the slab 12' increases, which unavoidably lowers the production yield and increases costs.

In addition, when such a slab 121 is further processed and manufactured into a product, surface flaws due to the inclusion of inclusions occur, reducing manufacturing and grading (inspection) yields, increasing costs, and reducing the quality of the product. There were drawbacks such as a decline in quality.

[Problem to be solved by the invention]

The object of the present invention is to eliminate the drawbacks of the prior art described above, and to prevent melting in the continuous casting mold 13. The purpose is to prevent the stagnation phenomenon of W12 and to enable continuous casting of highly clean steel without causing flaws or internal defects due to inclusions in the slab 12'.

[Means to solve the problem]

As a result of various studies, the present inventors formed an external gas outlet at the tip of the immersion nozzle and blew out a specific amount of inert gas from there toward both long sides of the continuous casting mold to flow the molten steel. The present invention was accomplished by discovering that the above-mentioned problem can be solved by actively causing the above problems.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A continuous steel casting method according to the present invention and a submerged nozzle used to carry out the method will be explained below with reference to the drawings.

FIG. 1 is a vertical cross-sectional view showing the essential parts of an example of the immersion nozzle according to the present invention, and FIG. 2 is a vertical sectional view showing the main part of an example of the immersion nozzle according to the present invention, and FIG. 2 shows the immersion nozzle shown in FIG. 3 and 4 are sectional views taken along lines A-A and B-B in FIG. 1, respectively, and FIG. Fig. 6 is a graph showing the relationship between the amount of gas blown and the height fluctuation of the scene, and Fig. 7 is a graph showing the relationship between the amount of gas blown and the large non-contact surface of the slab surface. It is a figure showing the relationship with the number of metal inclusions.

In the continuous casting method for steel according to the present invention, when performing continuous casting, two external gas blow-off ports 8' are provided at the tip 5 of the immersion nozzle 3 facing both long sides 13b, 13b of the continuous casting mold 13. A gas flow path is provided in the nozzle wall 9, and the molten steel 1 is
1 to 2 liters of inert gas per ton of discharge amount is blown out from the two external gas outlets 8'8' toward both long sides 13b, 13b of the continuous casting mold 13. In this case, the nozzle base 7
The submerged nozzle 3 is provided with an internal gas outlet 8 on almost the entire inner surface of the nozzle hole 4 except for the tip 5, and is provided with an internal gas outlet 8 and a gas flow path similar to those described above.
While inert gas is blown out from the internal gas outlet 8 into the molten steel 12 passing through, the inert gas may also be blown out from the external gas outlet 8'.

In this way, the inert gas is applied to both long sides 1 of the continuous casting mold 13.
The immersion nozzle 3 according to the present invention, which is suitably used for blowing to the side 3b, will be described.

As shown in FIGS. 1 and 3, the submerged nozzle 3 according to the present invention has a nozzle tip 5 in addition to the structure of the conventional submerged nozzle.
An external gas outlet 8' is provided in the nozzle wall 9 at an intermediate portion on both sides of the two molten steel discharge ports 6. This external gas outlet 8' is provided with a quarter-cylindrical external blowing slit 10' along the circumferential surface in the nozzle wall 9, and the wall outside the external blowing slit 10' is as described above. It is made of a breathable fireproof material 9a similar to that of the original. It is preferable that the gap between the breathable refractory material 9a and the external blowing slit 10' be 1.5 to 5 rrn, and the thickness of the breathable refractory material 9a be about 8 to 15 mm.

Moving away from FIG. 1 for a moment, an external blowout slit lO' is connected to a gas supply plug 11 provided on the outer surface of the nozzle on the nozzle base 7 side by a gas supply slit provided in the nozzle wall 9. The inert gas is supplied from outside. The gas supply slit preferably has a gap size of 1.5 to 5 m and a circumferential width of 20 to 50 m. The explanation will be given by returning to FIG. 1 again. When the immersion plug 3 is equipped with an internal gas outlet 8, the internal gas outlet 8 is provided with the external outlet slit 10' as shown in FIGS. 1 and 4. The internal blowing slit 10 is connected directly or through a short slit (forming a part of the gas supply slit) to the internal blowing slit 10.
can be configured so that it also serves as at least a part of the gas supply slit. In FIG. 1, there is a dedicated gas supply slit 10', although it is short, and if the internal blowout slit 8 is not provided, this gas supply slit 10' is connected to the gas supply plug 11. It is something that can be extended so that it can be done.

In order to continuously cast steel using the immersion nozzle 3 according to the present invention described above, the external gas outlet 8' is directed toward the long side 13b of the continuous casting mold 13, as shown in FIG.
In that case, it is attached to the bottom of the tundish 2 installed above the continuous casting mold 13 so that the molten steel discharge port 6 naturally faces the short side 13a. Then, as shown in FIG. 2, when continuous casting of steel is carried out according to a conventional method while blowing out an inert gas from the external gas outlet 8', molten steel I2 is discharged in the continuous casting mold 13 as shown in FIG. In addition to the molten steel flow in the direction of the arrow X caused by the immersion nozzle 3 and the molten steel flow in the direction of the arrow Y due to the blowing of inert gas from the external gas outlet 8', the molten steel flows on both long sides of the immersion nozzle 3 and the continuous casting mold 13. This eliminates the stagnation phenomenon between 13c and 13b.

The most characteristic feature of the present invention is that from the tip 5 of the immersion nozzle 3 to the long side 13 of the continuous casting mold 13.
The purpose is to blow out inert gas into the molten steel 12 between 13c and b, but if the amount of inert gas blown out is too large, it will cause fluctuations in the molten metal level and have the opposite effect.On the other hand, if there is too little, the molten steel
If the stagnation phenomenon is not resolved, the effect of preventing inclusions from increasing in size by promoting the rapid floating and separation of inclusions and promoting their capture in the molten powder 17 is reduced. Therefore, the inventors of the present invention conducted tests with various inert gas blowout amounts, and as a result, the height fluctuation of the scene and the obtained results were obtained with respect to the external gas blowout amount (Q/T) per 1 ton of molten steel 12 discharged. Number of large non-metallic inclusions in the slab (The test method is to cut the surface of the slab 2++v+, then give it a mirror finish, and visually check the number of inclusions with a size of 50- or more in an area of 100mm x 1020mm. The data shown in FIGS. 6 and 7 were obtained regarding the relationship with the method). And the overall result is 1.0~
2. It was discovered that the amount of gas blown to the outside during On/T has little variation in the scene, and a clean slab 12' can be obtained. Such adjustment of the amount of gas blown to the outside is performed by various conventional means, but if the gas supply slit 10' also serves as the slit 10 for internal blowing, the amount of gas blown out from the inside will also be affected. In order to blow out the target amount inward and outward in a well-balanced manner, the dimensions (area, length) of the gas flow path and its bending, and the dimensions (area, wall thickness) of the gas outlet 8, 8' inward and outward. This is done by thoroughly checking the back pressure caused by the porosity of the breathable refractory material 9a that blows gas out and out, and adjusting these dimensions and porosity.

[For production]

In the conventional continuous casting of Ti-containing steel (Ti content of about 0.1 to 1.0%) and certified steel (U content of about 0.1 to 3.5%), the internal gas outlet 8 of the immersion nozzle 3 It is said that if an inert gas is blown out from the inert gas, defects will occur in the obtained slab 12' due to bubbles of the inert gas. This is based on the results of many studies conducted regarding the present invention, and it has been found that when the flow force passing through the nozzle hole 4 of the immersion nozzle 3 is strong and blows out a large amount of gas into the molten steel I2, inert gas is engulfed in the molten steel 12. It can be solidified and cast as it is, or it can be cast as molten steel.
When it is discharged, the aggregate of gas bubbles bursts, causing a fluctuation in the melt level, solidifying and casting with the molten powder 17 still involved, resulting in surface and internal defects in the slab 12' due to gas bubbles and molten powder. This is thought to be due to the high frequency of occurrence.

In contrast, the present invention blows out an amount of inert gas that causes only a slight change in the scene where the flow of the molten steel 12 is weak, so there is no entrainment of gas into the molten steel 12 or the bursting of bubbles. Therefore, it can be applied to continuous casting of steel containing Ti or M without any problems.

In the continuous casting of steel using the immersion nozzle 3 according to the present invention, the flow force of the molten steel 1 is weakened after the inert gas is discharged.
Since the molten steel 12 in this area is blown out into the middle of the molten steel 12 (where stagnation has conventionally occurred), the molten steel 12 in this area acts to generate a flow toward the area and accelerate it. The molten steel flow resulting from this action interacts with the molten steel 12 flow discharged from the discharge port 6 to cause appropriate mixing. The molten steel 12 thus discharged and the molten steel 12 generated by the inert gas blown out from the external gas outlet 8' act synergistically to equalize the temperature of the molten steel in the continuous casting mold 13. At the same time, the inclusions in the molten steel 12 that conventionally aggregated in the discharged molten steel 12 flow are floated and separated, and are promoted to be captured in the molten powder 17 on the surface of the molten metal, thereby suppressing the increase in size of the inclusions. .

〔Example〕

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples.

According to the method of the present invention, a slab 12' is manufactured by continuous casting of Ti-containing steel using a curved continuous casting equipment and using the immersion nozzle 3 having the structure explained in FIGS. 1 to 4. A total of 200 slabs 12' were hot rolled to produce hot coils.

The method for blowing out inert gas from the immersion nozzle 3 is to provide an external gas blowout port 8' between a position 30m++ below the scene inside the continuous casting mold 13 during immersion and the lower edge of the molten steel discharge port 6, and Using argon gas as the gas, the gas blowout rate was 1.73Q for the slab pullout rate of 1.5T/min.
/min, that is, 1.5 Q/T per ton of slab.

In addition, argon gas is also supplied from the internal gas outlet 8.
It blew out at 73 Q/min.

The direction in which the molten steel 12 was discharged was such that the molten steel discharge port 6 had an upward shape as shown in FIG.

As a comparative example, continuous casting of Ti-containing steel was carried out in the same manner except that a conventional one having the structure explained in FIG. 9 was used as the immersion nozzle 3.

The attached table shows the quality results of hot coils manufactured from each of the obtained slabs. The land value number of the surface of the slab in the table is
The measurement was performed in the same manner as the method for measuring the number of large nonmetallic inclusions shown in the figure. In addition, the number of unsuitable coils refers to the number of coils that cannot be further commercialized as is, and for which surface flaws have been removed by polishing or the like. From the table, it can be seen that when continuous casting is performed by the conventional method using the conventional immersion nozzle 3, the number of unsuitable coils and the number of unsuitable coils are high due to the inclusion of large non-metallic inclusions, whereas in the case of the method of the present invention It can be seen that the surface flaws and unsuitable coils have been improved to almost zero.

Table [Effects of the Invention] As explained above, according to the present invention, the following effects can be obtained.

(1) By blowing out inert gas from the tip of the immersion nozzle into the molten steel in the continuous casting mold where the flow force of the discharged molten steel is weak, it causes a stagnation phenomenon in the molten steel in the conventional continuous casting mold. There are no molten steel parts where objects have gathered and become larger, and where the molten steel temperature has decreased.

(2) As a result, there are almost no surface flaws or internal defects caused by inclusions in the U-cast slabs, and highly clean steel can be continuously cast. Therefore, (3) the surface care of the iii piece can be reduced and the manufacturing yield can be increased, making it possible to improve productivity and reduce costs.

(4) Even when such slabs are further processed and manufactured into products, polishing of surface flaws is reduced and manufacturing and grading yields can be increased, making it possible to improve productivity and reduce costs. At the same time, the quality of the product itself can be improved.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view showing the essential parts of an example of the immersion nozzle according to the present invention, and FIG. 2 is a vertical sectional view showing the main part of an example of the immersion nozzle according to the present invention, and FIG. 2 shows the immersion nozzle shown in FIG. 3 and 4 are sectional views taken along lines A-A and B-B in FIG. 1, respectively, and FIG. Fig. 6 is a graph showing the relationship between the amount of gas blown out and the height fluctuation of the molten metal surface, and Fig. 7 shows the amount of gas blown out and the large size of the slab surface. A diagram showing the relationship with the number of nonmetallic inclusions, Figure 8 is an explanatory diagram schematically showing the main parts of the continuous casting process, and Figure 9 is a longitudinal cross-section of an example of a conventional immersion nozzle used in continuous casting. Figure 10 is a sectional view taken along the line C-C in Figure 9.
FIG. 1 is an explanatory plan view showing the flow of molten steel in a continuous casting mold when steel is continuously cast using a conventional immersion nozzle. In the drawings 1... Ladle 2... Tundish 3... Immersion nozzle 4... Nozzle hole 5... Nozzle tip 6... Molten steel discharge port a... Nozzle base 8...Internal gas outlet 8'...External gas outlet 9...Nozzle wall 9a...Breathable refractory material 10...Internal outlet slit 10'... ... Slit 10' for external blowing... Slit 11 for gas supply... Gas supply plug 12... Molten steel 12'... Solidified shell 12'... Slab I3... - Continuous casting mold 13a...Short side L3b...Long side 13c...Between the immersion nozzle and the long side 14...Spray zone 15...Cooling zone 16... ...Drawer roll 17...Height variation of molten powder scene (mm)

Claims (1)

[Scope of Claims] 1. A continuous casting mold whose casting part has a rectangular horizontal cross-sectional shape, and a substantially tubular tube attached to the bottom of a tundish installed above the continuous casting mold, facing toward the center of the rectangle. With the tip of the immersion nozzle positioned below the molten metal surface covered with molten powder in the continuous casting mold, the nozzle hole in the hollow part of the immersion nozzle touches both short sides of the continuous casting mold with the tip. During continuous casting, the molten steel is discharged toward both short sides from the two molten steel discharge ports that are open toward the side, and the solidified slab on the surface is drawn downward from the lower end of the continuous casting mold. Two external gas outlets facing both long sides of the continuous casting mold are provided at the tip, and a gas supply path is provided within the nozzle wall to achieve a flow rate of 1 to 2 gas per ton of molten steel.
A continuous casting method for steel, characterized in that 1 of inert gas is blown out from the two external gas outlets toward both long sides of a continuous casting mold. 2. An internal gas outlet is provided on almost the entire inner circumferential surface of the nozzle hole excluding the base and tip of the immersed nozzle. An external gas outlet and a gas supply path are provided in the nozzle wall at the tip of the immersed nozzle, 2. The continuous steel casting method according to claim 1, wherein the inert gas is blown out from an internal gas outlet while the inert gas is blown out from an external gas outlet into the molten steel passing through the nozzle hole. 3 The nozzle hole in the hollow part of the almost tubular nozzle (4
) is closed at the end face at the nozzle tip (5) and opened at mutually opposite parts of the outer peripheral surface to form two molten steel discharge ports (6).
In the immersion nozzle where the nozzle tip (
5), both nozzle walls (9) of the two molten steel discharge ports (6)
) is provided with a slit (10') for external blowing along the circumferential surface in the nozzle wall (9) at the middle part of the nozzle wall (9) outside the slit (10') for external blowing.
) is provided with an external gas outlet (8') made of a breathable fireproof material (9a), and the external gas outlet slit (10') is provided on the outer surface of the nozzle on the nozzle base (7) side. An immersed nozzle (3) characterized in that it is connected to a gas supply plug (11) by a gas supply slit (10'') provided in the nozzle wall (9). 4. Nozzle base (7) and tip Internal blow-off slits (
10), and the nozzle wall (9) inside the internal blowing slit (10) is made of breathable fireproof material (9).
a) is provided with an internal gas outlet (8), and the internal gas outlet slit (10) is connected to the nozzle base (
7) is connected to a gas supply plug (11) provided on the outer surface of the nozzle wall (9), and the internal blow-off slit (10) constitutes at least a part of the gas supply slit (10''). The immersion nozzle according to claim 3 (
3).