JPS6092054A - Method and device for preventing slag inclusion in tundish for continuous casting - Google Patents

Abstract

PURPOSE:To separate non-metallic inclusions and to prevent intrusion thereof into a casting billet by disposing successively a lower gate and upper gate in a tundish from the side nearer the long nozzle of a ladle to segment the tundish inside to a receiving bath region and a tapping bath region and floating a floating plate in the tapping bath region. CONSTITUTION:The axial line of a long nozzle 5 mounted in a receiving bath region 15 is designated as a reference line M, M and the distance from the line M, M up to the axial line N, N of an immersion nozzle 8 fixed to a tapping bath region 16 is designated as X. When the height from the inside bottom of the tundish up to the steel bath surface is designed as H and the transverse width at the lower limit level H2 of the steel bath is designated as W, a lower gate 1 having 0.67-0.75H height is disposed in the position 0.1833X from the line M, M and an upper gate 2 is disposed in the position 0.2749X from the line M, M at 0.1333-0.25H the gap G from the inside bottom of the tundish. A floating plate 3 having 0.181-0.554W.X area is floated on the steel bath on the axial line of the immersion nozzle. The unit of the above-described length is metric.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention aims to float and separate various non-metallic inclusions contained in F6 steel as quickly as possible in a continuous casting tundish in continuous casting of steel. It relates to a technology that prevents contamination in slabs as much as possible.

Inclusions contained in the molten steel before continuous casting can be improved as a means of improving the quality of slabs manufactured by the continuous casting method, Taoka strips and steel sheet products that are manufactured after going through numerous processes using the slabs as a starting point. We must reduce this as much as possible, but it is extremely difficult. Therefore, by preventing inclusions in the tundish from reaching the immersion nozzle part during continuous casting, that is, by preventing inclusions from being rolled into the mold, it is possible to prevent inclusions from entering the slab. A number of countermeasures are being taken.

For example, Japanese Patent Publication No. 48-25866, Utility Model Publication No. 52-1
According to Japanese Patent Publication No. 65105 and Japanese Patent Publication No. 55-148, in a tundish for continuous casting, a partition wall or weir is provided in the tundish for storing molten steel flowing from a ladle, and a partition wall or weir is provided in the tundish to float and separate the inclusions. Disclosed are methods and devices for preventing inclusions from being drawn into the container.

Similarly, there are two types of tundishes that have the function of flotating and separating inclusions, such as a type in which inert gas is introduced into the tundish and the gas bubbles are brought into contact with the molten steel, and the weir floats and separates the inclusions. Various types are already known, such as a type with holes, a type with a plurality of weir plates installed vertically or horizontally in the tundish, or at an angle to the bottom of the tundish, and a type that combines these types.

The function of each of these types is to divide the tundish into a receiving bath area from the ladle and a tapping bath area to the mold, and to prevent the flow of molten steel from being disturbed by the injection flow from the ladle. The tapping bath area downstream of the weir is kept as calm as possible, and the inclusion particles with small specific gravity suspended in the molten steel are floated to the surface of the steel bath in this area, thereby separating the molten steel and the inclusions. However, these methods and devices have the following problems.

(1) The disturbance of the flow of the steel bath in the tundish due to the injection flow from the ladle cannot be suppressed in the receiving bath area, and as the height of the steel bath (molten steel head) is lowered, the turbulence in the steel bath area A vortex is generated near the top of the immersion nozzle.

The conventional flotation and separation effect of each type of inclusions that exhibits this phenomenon is weak and insufficient, and therefore has the most negative effect on the quality of the cast slab and the products manufactured from the slab. It is not possible to completely remove large-scale inclusions that may affect the surface area.

(2) Recently, continuous continuous casting (hereinafter referred to as continuous casting) has been strongly promoted from the viewpoint of improving productivity and reducing manufacturing costs. The number of ladles in continuous casting, in which casting is continued while changing the ladle one after another, is on the rise. It gradually increases towards the end of the stage. For this reason, in slabs produced by continuous casting, the first problem is that more inclusions are mixed into the slab joints formed when the ladle is replaced than in the steady slab parts.

Furthermore, it becomes a problem that more inclusions are mixed into the slab joint as it approaches the final stage of casting. In order to cope with this tendency and solve the problem, the inclusion flotation separation effect possessed by the conventional types described above is completely insufficient.

(3) As shown in the above (2), the floating fraction of inclusions is 1il.
The I effect must be improved so that it is strongly effective even in continuous casting, but further improvement is desired if high-speed casting is promoted. In this sense,
The effects of each conventional type are generally weak and insufficient.

As a means to solve these problems, methods such as increasing the size of the tanditsh and the 2N4 method have been introduced, but these methods are very difficult to achieve in the current situation and are desirable in continuous casting and high-speed casting. On the other hand, there are times when it is not possible due to various restrictions, such as requiring a large amount of investment in new equipment or remodeling.

The present invention was made as a result of confirmation using actual equipment based on a number of findings obtained through water model experiments based on each of the conventional types described above.

The present invention provides a weir configuration and its optimum conditions in which the flow of molten steel is not disturbed by the injection flow from the ladle in the steel receiving bath area in the tundish, and suppresses as much as possible the vortex generated in the tapping bath area downstream from the weir. It is an object of the present invention to provide a method and an apparatus for achieving a stronger flotation and separation effect of inclusions in a tundish than before, thereby reducing the inclusion of inclusions in slabs.

The method for preventing slag entrainment in a tundish for continuous casting according to the present invention is to prevent steel from being drawn into the steel receiving bath area from the ladle and into the mold by using an upper weir and an upper weir that are sequentially arranged from the side closer to the long nozzle in the tundish. The steel bath is separated into a steel bath area and a floating plate is suspended on the surface of the steel bath in the tapping bath area to prevent slag entrainment.

Furthermore, the slag entrainment prevention device in the continuous casting tundish according to the present invention includes an upper weir and an upper weir that are sequentially arranged from the steel receiving head area side to the tapping head area side in the tundish, and protects the steel receiving bath area. It consists of a reverse order of forming and a floating plate suspended in the tapping bath area.

Therefore, the present invention will be explained in detail below with reference to the drawings.

FIG. 1 is a front sectional view of a tundish according to the present invention, and shows i! $114 is injected into the C tundish 6 through the long nozzle 5 of the ladle 4, then passes through the submerged nozzle 8 while the flow rate is controlled by the stopper device 7, and is continuously cast into a mold (not shown). Note that 13 is a slag.

When all of the molten steel 14 accumulated in the ladle 4 is poured into the tundish 6, the injection of molten steel from the ladle 4 to the tundish 6 is temporarily interrupted, and the steel inevitably flows from the inner bottom of the tundish 6. The height H (similar) to the bath surface (molten steel head, steel bath height) decreases, and conversely, when a new molten steel starts to be poured from the ladle 4, it gradually rises, and this process is repeated. It is cast one after another. In this case, the vertical center axis of the long nozzle 5 of the ladle 4 is controlled so that the height H of the steel bath in the tundish 6 is within the range between the upper limit level H and the lower limit level Hz. Then, the horizontal distance from this reference line M-M to the vertical central axis N-N of the immersion nozzle 8 fixed on the side of the tapping head 16 is X (C=)
, the height of the molten steel head from the inner bottom of the tanditshu 6 to the surface of the steel bath.

When the steel bath height) is H (11), the above reference line M is drawn from the steel receiving side to the tapping side in the tundish 6.
-M to P ~0.1833
An upper weir 1 of 0°75H (the basis of 0.67 to 0.75 will be described later) is installed at the inner bottom of the tandish 6,
Next, from the same reference line M-M, Q = 0.2749X (0,2
749 will be explained later) from the inner court of Tandish 6 to G ~0.1333H~0.25H (
The upper weir 2 is installed so as to provide a gap of 0.1333 to 0°25 (the basis of which will be described later) and to reach the upper lid 12 of the tundish 6 and cover the upper part of the tundish, and to separate the steel receiving bath area 15 and the tapping bath area. 16.

2 and 3 are side sectional views taken along line A-A and line B-B in FIG. 1, respectively, and show the upper weir 1 and the lower ts2.
The installation status is shown.

Next, a floating plate 3 having a through hole 9 so that a stopper device 7 provided on the axis N-N of the immersion nozzle 8 can move up and down.
is placed in the tapping bath area 16, and the floating plate 3 is floated on the surface of the steel bath in the tapping bath area 16.

FIG. 4 is a side sectional view taken along line CC in FIG. 1;
This shows the state in which the floating plate 3 is floating on the surface of the steel bath.

These upper weirs 1. The material of the upper@2 and the floating board 3 may be any refractory material that is easy to handle and process, but it may be made of the same material as the basic board 10 for protecting the surface of the refractory material 11 lined in the tundish 6. Anything is fine. This basic board 10 has a bulk specific gravity of about 1.8 and MgO85-90 (
It is a fireproof plate made by compression molding SiO4-7 (wt%) and others, and has a lower specific gravity than molten steel, so it can float on molten steel. Therefore, it can also be used for the floating plate 3.

The structure and operation of the present invention described above will be explained in more detail below through findings from a water model experiment and confirmation experiment results using an actual machine. In order to make the flow of inclusions and the motion of particles similar, the size is 1/1, but the first to
Several types of tundish experimental equipment with the shape shown in Figure 4 are prepared, and it is possible to visually confirm the limit of eddy current generation in the tapping bath area, as well as to measure the amount of inclusions mixed into the slab under various conditions (into the immersion nozzle area). In other words, polypropylene particles with an average particle diameter of 0.177 ("vl!;) and a specific gravity of 0.9 <K/cJ) were prepared to be used as a tracer. .

As for the specifications of the above-mentioned tundish experimental equipment, as already explained, the tundish volume is in the range of 5 to 35 (tons) based on the weight of molten steel, and the above-mentioned X is 3.8 to 5. 0 (? piece.

[■ is 0.3 to 1.3, <e;), and as shown in FIG. 5, the cross-sectional area S (rd) of the tandish is 0.23 to 1.
33 (rr?).

As shown in the figure, the inner cross-sectional shape of the tundish has an upper side length a.
(to e) and the lower side (base) length b (1! Comparison of pieces a /
b is Q, 5910.26i0.8510.5 io,
9510.5; 1.4310.57.・・・・・・・・・
··belongs to.

Furthermore, the average residence time and average moving flow rate of water in the Tanditush experimental apparatus are the same as the average residence time of general molten steel [7 minutes to 23 minutes] and the average moving flow rate of molten steel [0.21 bags/min to 0.56 e;/ minutes], select the actual operating value range, and
Experiments were carried out within this range.

First, the content of the first experiment was to investigate general conditions that are advantageous for flotation and separation of inclusions in various locations and in various tundishes according to the present invention described above and without using any floating plates. The following findings were obtained from the results of this experiment.

(i) Distance
, the molten steel head in the tundish (the height of the water in this experiment), and the open area S of the old tundish, respectively. The weight WO/injected tracer weight wixiooo%) decreases and becomes better.

Sufficient time is provided for the tracer to float and separate, and the flow velocity is relaxed, making it easier for the tracer to float and separate. Furthermore, since the floating area is expanded, the entrainment rate is reduced.

(ii) Effect on flotation separation ability of inclusions In other words, in this experiment, the distance Height) H1 Finally, the opening area S of the tandish is in order.

(iii) The above X, S [S# (a+b)XH/
2], etc., the larger the volume of the tundish, the better the entrainment ratio E decreases. Among the several types of tundishes prepared, those with a capacity of 15 (tons) or more based on the weight of molten steel have a molten steel head (
Even if the water height (H) fluctuates somewhat, the effect on the entrainment rate E will be small.

The results described in (i) to (iii) above are (X
, S, H) and the tracer entrainment rate E into the immersion nozzle part
The relationship with [Wo/WixlOO(%)] is shown in FIG. 6. Wi at the entrainment rate E in Fig. 6 is the known weight (?) of the tracer (polypropylene particles) input into the tundish together with water, while WO is not floated and separated in the tundish but flows from the submerged nozzle to the outside of the tundish. The figure shows the weight of the tracer that was drawn into the immersion nozzle section, captured by a microscopic filter in the middle, dried, and weighed.

Therefore, this entrainment rate E is the percentage of the weight of the unloaded tracer WO to the weight Wi of the tracer input (injected) into the tundish, and the smaller this value is, the more the tracer is sufficiently contained in the tundish. This indicates that it has floated and separated. From Fig. 6, as the molten steel head H becomes higher, the tracer entrainment rate decreases, as the open area S of the tundish increases, the tracer entrainment rate decreases, and as the distance 111X between the long nozzle axis and the immersion nozzle axis increases, It can be seen that the tracer entrainment rate decreases.

Based on the above knowledge, the next experiment involved investigating the optimal conditions for arranging a weir. Optimal conditions were determined to reduce the rate of tracer entrainment E into the immersion nozzle by the combination of weirs installed in the tundish, the installation positions and heights of the weirs, etc. The experimental results obtained from this test will be explained using FIGS. 7 to 9.

Figure 7 shows the °I and racer entrainment rate E to the submerged nozzle section at each upper weir installation position while changing the distance P from the reference line M-M to the upper weir 1 in prepared tundishes of several capacities. FIG.

In this figure, first, the height F of the upper weir 1 is 0.25f (and the gap G from the inner bottom of the kundish to the lower end of the upper weir 2 is 0.1333f).
Fix it at H, then from the reference line M-M. -0,1833X
, Q = 0.2749 It is a general explanatory diagram showing the tracer entrainment rate E into the immersion nozzle part at each installation position of the upper weir 1 when it is moved.

According to FIG. 7, from the reference line M-M. =0.2749
If the upper weir 2 is fixed at a distance of ．． l833X
When the upper weir I is placed at the distance #t (position), the lowest entrainment rate E=0.76% can be obtained. Note that the dotted line area in FIG. 7 is a range where no practical effect can be expected because the upper weir 1 and the upper weir 2 are close to each other.

According to the information investigated by the inventors, as shown in FIG. In most cases, the upper weir 1 was installed first, and then the upper weir 1 was installed, and the reasons and effects of this configuration were completely unclear.

The installation form of weirs 1 and 2 as shown in Figure 8 (A) is
If it is called a "normal weir", as mentioned above, from the reference line M-M to the upper weir 1. The form in which the weirs are arranged in the order of the upper weir 2 is the reverse of the normal weir, that is, it is also called the "reverse order" shown in FIG. 8 (B).

That is, the experimental results shown in FIG.
= 0.1833 Install upper weir 1 at a distance of X,
Next, from the reference line M-M, Q = 0.2749X (
7) Install upper weir 2 at a distance, and connect upper weir 1 and upper weir 2.
A new finding has been obtained that in the case of the reverse order in which the distance from -Q-P is 0.0916X, the entrainment rate E can be reduced as usual.

For example, in Fig. 7, controlled molten steel head (water height) MH=0.1 (e;h), distance MM-h<X
Taking as an example the case of a 15 (ton) class tandish with = 5 (package), the height of the upper weir 1 P = 0.2511 is 0.
175 (ζ piece (0,25X0.7 =0.175)
And the gap Q = 0.1333H from the inner bottom of the tandish to the lower end of the upper weir is 0.093 <eQ) (0,
1333X0.71.09331) and
From reference line M-M E=0.92 (m) (0,183
3X = 0.1833
49x5.0 = 1.3745)), it is possible to reach a low entrainment rate E.

Based on the above experimental results, the optimal conditions regarding the combination of upper weirs 1 and 2 and their positions (P and Q) were determined.
Figure 9 shows the results of the investigation regarding the height of .

Figure 9 shows that P = P = from the reference line M-M (based on the following experimental results) in the prepared tundishes of several capacities.
0.1833 Upper weir 1 at position X, then Q=0.
Fix the upper weir 2 at the position of 2749X, that is, each weir 1°2 at the optimal position, and then set the gap from the inner bottom of the kundish to the lower end of the upper weir as G = 0.333H, 0,25H, 0,13
For each case specified in 3H, 0,083H,
Change the height of upper weir 1 from F=0.25H to F=0°833H
FIG. 4 is a general explanatory diagram showing the tracer entrainment rate E into the submerged nozzle portion at the height F of each upper weir 1 when the height is increased gradually.

According to FIG. 9, even if the gap G from the inner bottom of the kundish to the lower end of the upper weir changes, the entrainment rate E generally tends to decrease as the height F of the upper weir increases; The gap from the inner bottom to the lower end of the upper weir is from G=0.25H to G-
The range is up to 0.133H and the height of the upper weir is F=0.6
When the range is from 7H to F=0.75H, the entrainment rate E
shows the lowest range of 0°40 to 0.30% best. For example, if we take a case where the managed molten steel head (water height) H is 0.7 (e;), then the gap G - 0,25H ~ 0.133■ (is 0.175 ~0.
093 (e;) (0,25X0.7 =0.175
io, 133
H is 0.469-0.525 (stand) (0,67X
0.7 = 0.469 io, 75X0.7 = 0゜5
25), which indicates that the lowest entrainment ratio E can be achieved by setting the gap G of the upper weir and the height F of the upper weir within this size range.

As a result of the above water model experiment results, the optimal conditions for the combination of weirs to be placed in the tundish, their installation positions, their heights, and gaps) were obtained.As a final part of the experiment, we decided to confirm the effect of the floating plates. experiment.

The floating board was a rectangular wooden board with an appropriate thickness that floated on the water. The area of this floating plate is such that it floats within the tundish as the floating plate changes the upper and lower control level (H-H) range (from the steel bath surface height to the water height) and at least up to the lower limit control level H. In order to move smoothly, the length of its short side is set to the width WI) at the lower limit level (H) of the steel bath surface in the tundish, as shown in Figure 4.
On the other hand, the length of its long side is the distance R (R=X-Q=
By appropriately dividing X-0,2749X=0.7251X), various area changes were made.

Also, as can be understood from Figure 1, which shows the state of the floating plate floating on the surface of the steel bath, there is some distance T from the position of the submerged nozzle axis N-H to the end of the tundish on the left side in the figure. Therefore, the area of the actually prepared floating board is [(fXwxX) + (Txw)] (r
J) and is calculated by assigning arbitrary real numbers to f and T.

(However, f < 0.7251 i T ≦0.10) The experimental results for confirming the floating plate effect are shown in Fig. 10 (A). Figure 1O (B) is a perspective view of the floating plate.

In Figure 10 (A), the shaded area is the entrainment rate E (0.3 to 0.4) obtained under the optimum conditions of only the upper upper weir without using the floating plate, as explained using Figure 9. %). Next, the dashed line indicates the entrainment rate E with respect to the change in area of the floating plate when only the floating plate is arranged without providing a weir in the tundish.

Although there are differences, the two show almost the same involvement rate.

The solid line in Figure 10 (A) shows the entrainment rate E when an upper weir under optimal conditions is installed inside the tundish, a floating plate is used together, and the area of this floating plate is varied. Therefore, the floating plate area is approximately (0,181 to 0.544
) XwXX (rJ), an entrainment ratio E of about 0.25%, which is much lower than both of the above, can be obtained. Furthermore, when this floating plate was used, it was well observed that the vortex flow near the immersion nozzle axis N-N was suppressed even if the molten steel surface height (water height) decreased.

The structure and operation of the present invention have been explained above through the water model experiment and the knowledge obtained therefrom, and the results of a confirmation experiment using an actual machine to which this knowledge was applied will be explained below.

a. A tundish with an internal capacity of 6.5 (g) (corresponding to the smallest volume of the tundish volumes used in the water model experiment) based on the weight of molten steel was used.

b. The material of the upper weir and floating board is the above-mentioned basic board, and the dimensions of the floating board are 0.025 (thickness) 1 (width 0.025) (on e).
470 <? The pieces used had a length of 1.50 (1!λ) and an area of 0.705 (if).

C1 and other conditions were carried out in accordance with the contents obtained in the water model experiment and the casting conditions normally carried out using an actual machine.

d, stainless steel grades 5US304 and 5US430
Casting experiments were conducted using a continuous slag caster for the following cases (1) to (5) to V (5 conditions).

Case I: A case of conventional tundish usage conditions that do not use any weir or floating board; A case of conventional tundish usage conditions using only a "normal weir"; Optimal conditions for installation conditions, height, or clearance) A case of usage conditions for the tanditsu according to the present invention using only the "reverse order" according to the conditions ■... A case of usage conditions for the tanditsu according to the present invention using only the floating board described in the above conditions ■... Installation position, height, or "Reverse order" based on the optimal conditions for gap)
The most desirable tundish usage conditions according to the present invention (Case ■10 Cases■) where a floating plate was used as well as a floating plate were used. Cut out the sample material and JI
The amount of nonmetallic inclusions in the steel was measured using a microscope according to the test method of SGO555, and the difference in cleanliness was compared and examined.

The amount of inclusions in the slab when steel type 5 US304 stainless steel is cast under the conventional tundish usage conditions that do not use any weir or floating plate, that is, the conditions of Case I, is set as an index of 1,0, and the following is obtained for each case by mesh type. Figure 11 shows the results of converting the amount of inclusions in the steel into an index.

According to the results, in the most desirable case (2) using the weir and thick plate according to the present invention, inclusions in the steel are reduced by about 1/3 compared to case (1) in which nothing is done at all. It shows that it is possible to do this and is superior to any other case.

Furthermore, even if there was a difference in physical properties between water and molten steel, the results clearly agreed with the results of the water model experiment described above.

character.

f. The conditions for using Tanditshu are the same as in Example 1 above.
The casting experiment was carried out by fixing the case in two ways, Case I and Case ■, and omitting the other cases.

Under the above casting conditions, stainless steel grade 5US30
Casting was carried out successively while replacing the ladle, which had a capacity of about 45 tons of molten steel.

A sample material was cut out from each slab of successive heat No. and was polished to a mirror finish with a 22 mm hole (
A test piece of 484-) was prepared and tested under a microscope at a magnification of 50 times to determine the size of the inclusions: 25μ or less, 26-50μ,
Amount (number) of inclusions classified into 3 classes of 51μ or more
The results of the measurements are shown in Figure 12.

According to FIG. 12, in Case 2, which uses a conventional tundish that does not do anything at all, the amount of inclusions in the slab clearly increases as casting progresses and approaches the final stage. In Case V, the inclusions were already reduced from the 1st heat compared to Case ■, and the reduction effect continued to increase as the final stage of casting approached, clearly showing that the inclusions were floated and separated in the tundish. .

In addition, the above and gold (stainless steel type only 5US4 under the same conditions)
30 was used, and as shown in FIG. 13, the same remarkable effect as in the case of steel type 5US304 was obtained.

Casting was carried out under exactly the same casting conditions (e, f) as in Example 2.

Under these casting conditions, continuous casting was carried out without replacing the ladle, which had a molten steel of about 45 (tons) made of stainless steel grade 5US304, one after another.

Test materials were cut out from successive cast slabs of different heat numbers and polished to a mirror finish of 200mm (mmC) by puff polishing.
A test piece (shown in Figure 14 (2)) of The results of counting and measuring are shown in Figure 14 (A).

In FIG. 14 (A), the vertical axis represents the amount of inclusions indicating the number of large inclusions of 100μ or more, while the horizontal axis represents continuous casting P1-No. The order is shown, and ■ indicates the amount of large inclusions in the joint portion of the slab cast when the ladle was replaced during continuous casting, and ■ indicates the amount of large inclusions in the steady slab portion.

According to FIG. 14 (A), the number of large inclusions in the slab increases as casting progresses in the conventional case (2) in which nothing is done at all, but in case V in which the present invention is implemented, the number of large inclusions increases. No large inclusions were observed up to the 8th heat, and only a few were observed in subsequent heats.

In addition, in the case of the conventional case (■), there is clearly a large difference in the amount of large inclusions in the slab joint part (■) and that in the steady slab part (■), but in the case (2) in which the present invention is implemented, the same as in the case (■) The difference in the amount of large inclusions between and (2) is only slight, and the effect of reducing the amount of large inclusions at the slab joint part (2) is particularly large.

In addition, as a result of successive castings in which stainless steel type M was changed to 5US430 in exactly the same way, the effect of reducing the amount of large inclusions was found to be greater than in the case of steel type 5US304, as shown in Fig. 15.

As described above, regarding cold-rolled stainless steel sheets manufactured by subjecting I number of slabs according to the present invention to the reverse order of the preferred conditions and using a floating plate through the known steps of hot rolling, cold rolling, annealing and pickling, The results of the investigation on the effect are shown in FIGS. 16 and 17.

FIG. 16 shows the steel type 5U in which the present invention was implemented, as described above.
This shows the results of an investigation on the occurrence rate (%) of cold-rolled steel sheet surface defects caused by non-metallic inclusions for S304 cold-rolled steel sheets. is the monthly average value of the defect occurrence rate (Ma) = 0.341%, but when the present invention is implemented, the monthly average value (Ma) = O, 175, and the defect occurrence rate is approximately halved. It is recognized that this is the case.

On the other hand, Fig. 17 shows the results of investigating the defect occurrence rate for steel type 5US430.
As in the case of , a significant reduction was observed, and a remarkable effect was observed.

As described above, by carrying out the present invention, it becomes possible to float and separate various non-metallic inclusions contained in molten steel in the continuous casting tundish as quickly as possible, and the inclusions are removed from the cast pieces. We were able to prevent it from getting mixed in as much as possible. As a result, in cold-rolled steel sheets etc. manufactured using this slab as a starting point, surface defects of the cold-rolled steel sheets caused by the inclusions can be significantly suppressed, and the formability of the steel sheets can be improved. It has been found to be highly effective in improving the quality of steel sheets, increasing the grade 1 yield, and reducing manufacturing costs. It can be easily carried out with a small investment without disturbing workability, and from the standpoint of cleanliness of the slab, it is possible to increase the number of castings over time, and it is also very effective for high-speed casting.

[Brief explanation of drawings]

FIG. 1 is a front sectional view of a tundish according to the present invention, and FIG. 3. Figure 4 shows A-A and B- in Figure 1, respectively.
It is a side sectional view taken along the line B and CC. FIG. 5 is an explanatory diagram showing the open area S of the tundish according to the present invention shown in FIG. 1 and the cross-sectional shape of the inside of the tundish. FIG. 6 is a diagram showing the relationship between the dimensions (X, H, S) of each tundish prepared for the water model experiment to explain the present invention and the rate of tracer entrainment into the immersion nozzle part. It is. FIG. 7 is a general explanatory diagram showing the rate of tracer entrainment into the submerged nozzle portion at each lower layer installation position of the tanditsh. FIG. 8 is an explanatory diagram showing the installation form of a weir in an actual machine, in which FIG. 8 (A) is a diagram showing a normal weir, and FIG. 8 (B) is a diagram showing the reverse order. FIG. 9 is a general explanatory diagram showing the rate of tracer entrainment into the submerged nozzle section depending on the height of the upper weir installed in the tundish. Figure 10 (A) shows the results of a water model experiment that confirmed the floating plate effect, and Figure 10 (B) is a perspective view of the floating plate. FIG. 11 shows the amount of inclusions in the slab by steel type under various tundish usage conditions from the conventional one to the one of the present invention. Figures 12 and 13 show steel type 5US304, respectively.
and the results of a microscopic test of the amount of inclusions in continuous slabs of SUS 430. Fig. 14 (A) shows the results of measuring the amount of large inclusions of 100 μ or more in a continuous cast slab of steel type 5US30417 by visual judgment, and Fig. 14 (B) shows the test piece. FIG. 15 is a view corresponding to FIG. 14 (A) in 5US430. Figures 16 and 17 show the incidence of cold rolled steel plate surface defects caused by non-metallic inclusions (
%). 1: Upper weir 2: Upper weir 3: Floating plate 4: Ladle 5: Long nozzle 6: Tundish 7: Stopper device 8: Immersion nozzle 9: Through hole (in floating plate) 10: Basic board 11: Refractory 12 : Upper lid 13 Varnish slug 14: Molten steel 15: Receiving bath area 16: Tapping bath area Distance [to] H: Height from the inner bottom of the tundish to the surface of the steel bath; molten steel head, wi bath height) [ζ;] H: Height of the steel bath in the tundish; Upper limit level at H) [1! ] H: Lower limit level of the steel bath height H) in the tundish [ζ;] S: Measured area of the tundish [K] a: Length of the upper side in the cross-sectional shape of the tundish [C
;] b: Length of the lower side of the cross-sectional shape in the tanditsh [1
! ] W: Lower limit control level of the steel bath surface in the tundish (Hz
) Width [Stand] E: Engagement ratio F: Height of the upper weir G: Gap between the upper surface of the bottom of the tandish and the lower end of the upper weir. Height M-M: Reference line N-'N: Axis of the immersion nozzle P: Horizontal distance between the upper weir and reference line Q: Horizontal distance between the upper weir and the reference line R: Axis of the upper weir and the immersion nozzle Horizontal distance T: Distance between the axis of the immersed nozzle and the inner wall of the tundish at the lower limit control level (Hz) of the surface of the steel bath in the tundish Patent applicant Nisshin Steel Co., Ltd. Representative Patent attorney Furu 1) Kei Tsuyoshi Figure 74 y Figure 11 Figure Case V (Article 54 Igyu), f 12 Figure 4 Nodo Heat N01III History

Claims (1)

[Scope of Claims] 1. In a tundish for continuous casting, an upper weir and an upper weir arranged sequentially from the side closer to the long nozzle in the tundish allow the steel receiving bath region from the ladle and the tapped steel layer region to reach the mold. 1. A method for preventing slag entrainment in a tundish for continuous casting, characterized in that a thick plate is suspended on the surface of the steel bath in the tapping layer region. 2. Floating plates floating in the reverse layer and tap layer area that form the steel receiving bath area, consisting of upper weirs and upper weirs arranged sequentially from the receiving area side to the tapping area side in the tandish. A device for preventing slag entrainment in a continuous casting tundish, comprising: 3. The axis of the long nozzle installed in the steel receiving bath area is the reference line, the distance from this reference line to the axis of the immersion nozzle fixed in the tapping layer area is X, and then from the inner bottom of the tundish When the height to the steel bath surface is H and the width at the II bath surface lower limit level H2 is W, 0.
The height is 0.67 to Q, 75) at the position of 1833
Claims characterized in that an upper weir is arranged so as to provide an upper weir, and a floating plate having an area of (0,181 to 0°554)·w-X is suspended on the surface of the steel bath on the axis of the immersion nozzle. 2. A device for preventing slag entrainment in a continuous casting tundish according to item 2.