JPH09122848A - Cleaning method for molten steel in tundish - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve cleanness of a slab part corresponding to non-stationary casting at casting start time so as to improve product quality as well as heating efficiency by controlling a flow of molten steel to promote floating/separating of inclusion at the initial phase of pouring of molten steel to a tundish. SOLUTION: A tundish 1 having a bottom shape of varying depth of molten steel is used and a gas injection body 7 is arranged to the bottom part at the position where a depth of steel bath is deeper, inert gas is bottom-injected, further, a molten steel heating device is arranged above the molten steel surface of inert gas injecting part, a flow of molten steel is controlled while heating molten steel. The molten steel heating device is arranged within <=2.0m from the inert gas injecting part, heating with an output of <=5MW. A gas injection body occupying area is 0.1-2.0m<2> , an injecting volume is 80-800Nl/min.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for improving the cleanliness of molten steel injected into a tundish at the beginning of casting in continuous casting of steel.

[0002]

2. Description of the Related Art In continuous casting of steel, molten steel is temporarily stored in a tundish from a ladle and then cast in a mold. The main functions of this tundish are to separate the molten steel into a large number of molds, to float and separate inclusions such as slag in molten steel and alumina of deoxidation products, and to adjust molten steel temperature and molten steel components. A number of methods for promoting this function have been proposed as prior art. For example, by installing a weir in the tundish and forcibly forming an upward flow in the molten steel to float and separate inclusions, or by installing multiple weirs or various types of weirs in the tundish, A method has been proposed in which a short-circuit flow is prevented and the residence time in the tundish is made uniform to float and separate inclusions.

In the method of blowing gas into molten steel, Japanese Patent Laid-Open No. 154357/1982 discloses a method of blowing gas into the molten steel in a tundish to bottom so as to capture inclusions and promote floating separation. JP-A-3-285007 discloses a method of blowing an inert gas into molten steel from a blowing hole provided in a weir in a tundish to reduce inclusions (hereinafter referred to as "prior art 1"). JP-A-5-277676 discloses a method of removing inclusions by combining gas injection from the tundish bottom and a weir (hereinafter referred to as "prior art 3"). ing.

[0004]

However, the above-mentioned technique has some problems. When the weir in the tundish according to the conventional technique is used, it takes a long time to float the minute inclusions, so that the effect of floating and separating is small, and the installation of the weir increases the refractory cost. Further, when the tundish in a high temperature state is circulated and used, the shape of the weir is limited in order to efficiently perform the slag work from the tundish after casting.

On the other hand, in the case of capturing and floating the inclusions by blowing gas as in the prior arts 1, 2 and 3, it is important to obtain fine bubbles, but the upper limit of the gas flow rate for that purpose is limited. However, the effect of gas blowing may not be fully exerted.

Further, the above-mentioned conventional technique is
That is, the amount of molten steel injected into the tundish and the amount of molten steel cast from the tundish into the mold are almost equal, and the casting is continued in a state where the molten steel in the tundish is sufficiently secured. Expected to be effective. Therefore, in comparison with the prior art, during the unsteady casting in which the molten steel flow pattern in the tundish is different from that in the steady casting, the inclusions are removed to clean the molten steel especially at the beginning of the start of the molten steel injection into the tundish. The effect cannot be expected, and a separate technology is required.

Usually, in order to float and separate inclusions at the initial stage of continuous casting of molten steel, after pouring the molten steel into a tundish, a predetermined amount is stored without starting casting (hereinafter, referred to as
A method of waiting for the inclusions to float naturally from the molten steel due to the difference in specific gravity between the inclusions and the molten steel by allowing the molten steel to be stored still is considered. But,
Since the floating speed of inclusions due to the difference in specific gravity is slow, it is necessary to store for a sufficient time for the floating separation of inclusions.As time passes, the molten steel temperature in the tundish decreases, and Molten steel solidifies in the nozzle, and there are many problems that molten steel cannot be supplied from the tundish to the mold. In addition, if molten steel with an initial temperature that has been raised in advance is to be injected into the tundish as much as the temperature drops due to storage, a secondary problem such as melting of refractory in the refining process, which is the upper process, will occur. It also causes a problem that the molten steel temperature in the tundish exceeds the control upper limit during steady casting, so it is difficult to improve the cleanliness of the molten steel by pooling.

Therefore, in order to solve the above-mentioned problems in continuous casting of molten steel, an object of the present invention is to control the flow of molten steel in the tundish and to control the molten steel temperature at the beginning of injecting molten steel into the tundish. Proposal of a method for cleaning molten steel in tundish that improves the floatability of inclusions by ensuring the quality, manufactures high quality slabs even during unsteady casting at the start of casting, and improves product yield. It is in.

[0009]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies to develop a technique for cleaning molten steel that has been injected into a tundish from the above viewpoint. As a result, we obtained the following findings. That is, even during unsteady casting at the beginning of casting, the distribution of the steel bath depth in the tundish and the gas blowing conditions from the bottom of the tundish to the molten steel are optimized, and the molten steel is maintained at an appropriate temperature. By doing so, it is possible to early control the molten steel flow pattern so that the inclusions in the molten steel can be easily floated and separated, and suppress the nozzle clogging due to the solidified metal in the tundish nozzle. I found that

The present invention has been made on the basis of the above-mentioned findings, and the method for cleaning molten steel in a tundish according to the first aspect of the invention is characterized in that prior to casting molten steel from the tundish into a mold, This is a method of cleaning the molten steel injected into the tundish by blowing an inert gas from the bottom of the tundish into the molten steel being injected into the tundish and / or the molten steel after the injection. As the tundish used here, a tundish having a bottom shape in which the steel bath depth in the tundish is not constant is used. Moreover, a plurality of gas blowing ports are provided at the bottom of the tundish where the depth of the steel bath is deeper, or porous bricks are embedded, and an inert gas is blown into the molten steel from there.
Further, by arranging a molten steel heating device above the molten steel surface of the inert gas blowing part, by controlling the flow of the molten steel while heating the molten steel by this, the inclusions in the molten steel are floated and separated. Is to have.

According to a second aspect of the present invention, there is provided a method for cleaning molten steel in a tundish according to the first aspect of the invention, in which the molten steel heating device is placed horizontally from a gas blowing port or a central axis of an area occupied by the porous brick. It is characterized in that it is arranged within 2.0 m in the direction and the output of the molten steel heating device is set to 5 MW or less.

According to a third aspect of the present invention, there is provided a method for cleaning molten steel in a tundish according to the first or second aspect of the present invention, wherein argon gas is used as an inert gas, the total area of gas inlets, and The sum of the areas of the gas outlets of the porous bricks was adjusted within the range of 0.1 to 2.0 m ² , and the amount of argon gas blown was 8
It is characterized by being set within the range of 0 to 800 Nl / min.

First, at the initial stage of placing the molten steel pool in the tundish, vortices are generated everywhere due to natural convection accompanying injection. However, with the passage of time, the temperature drop in the shallow part of the tundish (hereinafter referred to as "shallow") is large, and the molten steel bottoms from the shallow part to the deep part of the tundish (hereinafter referred to as "deep"). Crawling flows, and macro convection is formed that flows from the depth to the shallow surface.

FIG. 1 shows a flow pattern of molten steel in the initial stage of placing the molten steel in the tundish, and FIG. 2 shows a flow pattern after a predetermined time has passed after the placing. For the floating separation of inclusions, the flow pattern shown in FIG. 2 in which vertical stirring is weak is more advantageous than the flow pattern shown in FIG. Therefore, by blowing an inert gas from the bottom of the tundish on the deeper side of the bath, the molten steel flow can be forcibly changed, and the time when the flow pattern of FIG. 1 changes to the flow pattern of FIG. 2 can be advanced. However, if the gas injection flow rate is less than 80 Nl / min, it is insufficient to forcibly change the flow of molten steel to the pattern of FIG. 1 to FIG. On the other hand, the gas flow rate is 800
If it exceeds Nl / min, the stirring energy becomes too large to disturb the surface of the molten steel, so-called splash is generated, and the cleanliness of the molten steel deteriorates due to air oxidation or the like. Therefore, the blowing flow rate of the bottom blowing gas is 80 to 800 Nl /
It is desirable to set it within the range of min. Furthermore, by heating the molten steel 4 that has been stored in the reservoir, the temperature can be secured at an appropriate value, so that solidification metal sticking to the inside of the immersion nozzle 3 does not occur and nozzle clogging can be prevented. it can.

[0015] In the present invention, a plurality of inert gas blowing inlet, or blowing argon gas into molten steel in the tundish by using a porous brick, and the argon gas blowing area 0.1 m ² or more 2.0 m ² It is desirable to set it within the following range. As described above, by supplying the inert gas in the tundish in a wide range with a low flow density, it is possible to obtain fine bubbles even when the flow rate of the inert gas is large. The runout of molten metal on the molten steel surface is suppressed. In addition, since blowing a large amount of inert gas activates the flow of molten steel, the role of the molten steel stirring effect to avoid the so-called upper heating phenomenon in which the heated molten steel stays on the molten steel surface in the tundish due to the effect of buoyancy Also bears. If the blowing area is less than 0.1 m ² , fine bubbles cannot be obtained because the inert gas is blown at a high density from a small area. On the other hand, the blowing area is 2.0m ²
If it exceeds, the blowing position is too wide, and it becomes difficult to forcibly form the flow shown in FIG.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 3 is a schematic vertical sectional view of a tundish for explaining one embodiment of the present invention. 1
Is a tundish, 2 is an air seal pipe for injecting molten steel attached to the bottom of the ladle 5, 3 is an immersion nozzle for casting molten steel from the tundish 1 into a mold, 4 is molten steel,
Further, 7 is an area occupied by the gas blower. As shown in the figure, molten steel 4 is poured into the tundish 1 from the ladle 5 through the air seal pipe 2. From the time when the molten steel is injected into the tundish 1 or when a predetermined amount of the molten steel 4 is injected into the tundish 1, the inert gas 6 is melted from the gas blower occupying area 7 attached to the bottom of the tundish 1. Blow in. As the tundish 1, the steel bath depth (h ₁ ) on the side where the molten steel 4 is injected is
The one that is shallower than the steel bath depth (h ₂ ) on the side where the molten steel 4 is cast from the tundish 1 into a mold (not shown) is used. Then, the inert gas 6 is blown from the gas blower occupying region 7 attached around the immersion nozzle 3 attached on the deeper side of the steel bath. The molten steel heating device 1 is provided above the molten steel surface above the gas blower occupied area 7 of the inert gas.
0 is placed and the molten steel 4 in the tundish 1 is heated.

When the molten steel 4 in the tundish 1 reaches a predetermined amount in this way, the tundish 1 is removed from the ladle 5.
The injection of the molten steel 4 into the molten steel is stopped, and thereafter the inert gas 6 is blown in and the molten steel is heated. In this way, after a predetermined time has passed, molten steel is cast into the mold through the immersion nozzle 3. Simultaneously with the start of casting the molten steel in the mold, the molten steel is poured from the ladle 5 into the tundish 1 to start continuous casting. In addition, in FIG. 3, although the tundish for 1 strand which has one immersion nozzle was illustrated, in the case of the tundish for multiple strands which has a plurality of immersion nozzles, the immersion nozzle and A plurality of inert gas blowing ports are provided, and the method according to the above embodiment is adopted. Further, instead of providing the gas blowing port, a porous brick may be embedded.

[0018]

EXAMPLES The present invention will be described in more detail by way of examples. (Example 1) As shown in FIG. 3, the molten steel in the tundish 1 was melted from the time when the molten steel was poured into the tundish 1 from the ladle 5 through the air seal pipe 2 and 45 tons of the molten steel 4 was finished. Bubbling of argon gas was started by bottom blowing, and molten steel was continuously stored in the tundish 1, while a cleaning test of the molten steel was conducted. The tundish used had a steel bath depth (h ₁ ) of 1.2 m on the molten steel injection side and a steel bath depth (h ₂ ) of 2.0 m on the molten steel outlet side to the mold during steady casting. The steel bath depth when 45 tons of molten steel is stored is about 1.2 m on the molten steel outlet side. FIG. 4 is a schematic plan view of the tundish used in this example, which is a molten steel outlet from the tundish 1 to a mold (not shown), that is, 500 mm width × 500 mm length including the installation position of the immersion nozzle 3. Eight porous bricks 9 were installed within the range of the depth, and argon gas was blown into the molten steel from here. The amount of argon gas blown is
4 of 80, 400, 800 and 1200 Nl / min
It was set to the level and was also tested when argon gas was not blown.
On the other hand, as a molten steel heating device, a plasma heating device 10 having a capacity of 2 MW is used, as shown in the figure, when the distance (x) (see FIG. 3) from the central axis of the installation region of the gas-blowing porous brick 9 is set. It was installed at a position of 500 mm, and the molten steel was heated with an output of 2 MW. The test was also conducted when the molten steel was not heated by plasma.

With reference to the completion of the injection of 45 tons of molten steel into the tundish 1, the reference time, that is, the storage time 0
At each time point of 5 minutes, 5 minutes and 10 minutes, a molten steel sample was taken by immersing the disc sampler in the molten steel from the molten steel outlet side of the tundish. To evaluate the cleanliness of molten steel, observe the cross-sectional polished surface of the disk sample after solidification with a microscope,
It performed by the inclusion number of 20 micrometer or more.

FIG. 6 shows the results of the above test, and shows the relationship between the pooling time of the molten steel in the tundish and the index of inclusion count (hereinafter referred to as “inclusion index”), the amount of argon gas blown, 7 is a graph in which the molten steel is stratified by the presence or absence of plasma heating. The following matters are clear from the figure. The inclusion index decreases as the storage time elapses, and the inclusions float and separate from the molten steel and decrease, but when argon gas is blown into the molten steel, the effect becomes even greater. When argon gas is blown into the molten steel and plasma heating is performed, the cleanliness of the molten steel is further improved, and particularly when the blowing amount of the argon gas is 800 Nl / min, a remarkable cleaning effect is exhibited. However, the amount of argon gas blown is 1200 N
When the amount was increased to 1 / min, the cleanliness was lower than in the case of 800 Nl / min. This is argon gas 1200
This is because when Nl / min was blown into the tundish, argon gas released to the atmosphere on the molten steel surface disturbs the molten steel surface, and so-called splash occurs.

Table 1 shows whether or not splash of molten steel is generated when various amounts of argon gas are blown. From the table, it can be seen that the amount of argon gas blown in should be 800 Nl / min or less in order to prevent the generation of splash.

[0022]

[Table 1]

(Embodiment 2) As shown in FIG.
Through the air seal pipe 2 from the tundish 1 during and after injecting 45 tons of molten steel into the tundish 1.
Argon gas was blown into the inner molten steel by bottom blowing, and at the same time, the molten steel was heated by a plasma heating device. Forty-five tons of molten steel 4 was stored in the tundish 1 and, during that time, a cleaning test for molten steel was conducted. The tundish used had a steel bath depth (h ₁ ) of 1.2 m on the molten steel injection side and a steel bath depth (h ₂ ) of 2.0 m on the molten steel outlet side to the mold during steady casting. The steel bath depth when 45 tons of molten steel is stored is about 1.2 m at the molten steel outlet side.
It is. FIG. 5 is a schematic plan view of the tundish used in this example, which includes the molten steel outlet from the tundish 1 to the mold, that is, the installation position of the immersion nozzle 3.
Within a range of mm width × 450 mm length, 30 gas blowing ports 8 were embedded, and argon gas was blown into the molten steel from there. Argon gas blowing rate is 400Nl /
The min was kept constant. On the other hand, the plasma heating device 10 capable of adjusting the output of 0 to 6.0 MW was used to heat the molten steel at the output of 5 MW. The installation position is as shown in FIG.
Distance (x) from the central axis of the occupied area of the gas inlet
Was set to various positions within a range of 0 to 2.5 m, and an evaluation test of inclusions in molten steel and measurement of molten steel temperature in each case were performed.

The time for collecting the sample for evaluating inclusions and the time for measuring the temperature are 5 minutes after the completion of the injection of 45 tons of molten steel into the tundish 1, that is, the time of storage for 5 minutes. For the sample collection, a molten steel sample was collected by immersing a disc sampler from the molten steel surface on the molten steel outlet side of the tundish. In addition, the temperature was measured at 5 locations within 1m from the plasma heating position (hereinafter referred to as "5 locations near the heating location") and 5 locations near the pouring flow drop point from the ladle to the tundish (hereinafter "tandem"). It is carried out by an immersion type thermometer in "5 places near the dish injection flow". The cleanliness of the molten steel was evaluated by microscopically observing the polished surface of the cross-section of the solidified disk sample and counting the number of inclusions of 20 μ or more.

FIG. 7 is a graph showing the relationship between the plasma heating position of the molten steel and the inclusion index, and FIG. 8 is a graph showing the relationship between the plasma heating position of the molten steel and the temperature difference of the molten steel in the tundish. . However, the temperature difference of the molten steel in the tundish is represented by the difference between the temperature measurement average value at five points near the heating position and the temperature measurement average value at five points near the tundish injection flow. As shown in FIG. 7, the plasma heating position has no significant effect on the cleanliness of the molten steel as long as it is within 2.5 m from the central axis of the area occupied by the argon gas blowing port, as can be seen from FIG. 7. On the other hand, with respect to the uniformity of the molten steel temperature in the tundish, as can be seen from FIG. 8, when the plasma heating position is more than 2.0 m away from the central axis of the area occupied by the argon gas blowing port, the effect is obtained. Get smaller. This is because the heated molten steel is not agitated by the argon gas, so that it becomes so-called heat and the heat deposition efficiency to the molten steel by plasma heating is reduced.

Next, the amount of gas blown into the molten steel is 400N.
With the constant value of 1 / min, the output of the plasma heating device was changed within the range of 0 to 6 MW, and the heat deposition efficiency on the molten steel with respect to the output of the device was tested. Here, at the plasma heating position, the distance x is 500 mm, and the test time is at the time when the molten steel is stored for 5 minutes. FIG. 9 is a graph showing the relationship between the output of the plasma heating apparatus obtained in the above test and the heat deposition efficiency on molten steel. As is clear from the figure, even if the output is 5 MW or more, thermal diffusion due to gas injection is not sufficiently performed, so that a so-called upper heat phenomenon occurs and the efficiency of heat deposition on molten steel by plasma heating decreases. Therefore, injecting gas into the molten steel is essential to improve the heating efficiency of the molten steel.

(Embodiment 3) As shown in FIG.
From the time when the molten steel is injected into the tundish 1 through the air seal pipe 2, the bottom of the molten steel is blown with argon gas, the molten steel is heated by the plasma heating device, and the molten steel storage time in the tundish passes for 5 minutes. Continued until. The tundish used had a steel bath depth (h ₁ ) of 1.2 m on the molten steel injection side during steady casting.
The steel bath depth (h ₂ ) on the molten steel exit side to the mold is 2.0 m, and the steel bath depth when 45 tons of molten steel is stored is about 1.2 m on the molten steel exit side. is there. Tundish 1
A porous brick 9 was installed at the molten steel outlet from the mold to the mold, that is, at the periphery of the installation position of the immersion nozzle 3, and argon gas was blown into the molten steel from here. The embedding area of the porous brick 9 was tested for various widths within the range of 0.01 to 2.2 m ² . The test was also performed when the porous brick 9 was not embedded. The amount of argon gas blown was 400 Nl / min, the output of the plasma heating device was 2 MW, and the installation position of the plasma heating device was 500 m at a distance (x) from the central axis of the porous brick occupied area.
The position is m.

A molten steel sample was taken by immersing the disk sampler in the molten steel from the molten steel outlet side of the tundish at the time point of 5 minutes, based on the time point when the injection of 45 tons of molten steel into the tundish 1 was completed. The cleanliness of the molten steel was evaluated by microscopically observing the cross-section polished surface of the solidified disk sample and counting the number of inclusions of 20 μ or more.

FIG. 10 is a graph showing the above-mentioned test results and showing the relationship between the argon gas blowing area and the inclusion index. The following matters are clear from the figure. The cleaning effect of 20% or more was revealed as compared with the case where the argon gas was not blown in because the area where the argon gas was blown was 0.1 to 10.
The case was within the range of 2.0 m ² . When the area where the argon gas is blown in exceeds 2.0 m ² , the horizontal cross-sectional area in which the gas floats becomes large, so the flow pattern shown in FIG. 2 cannot be formed, and the quality improvement effect of the molten steel in the tundish is reduced. I found out that

[0030]

According to the present invention, since it is configured as described above, the flow of molten steel in the tundish is promptly optimized at the time of unsteady casting in the continuous casting operation, especially at the beginning of the start of molten steel injection into the tundish. The inclusions float and separate from the molten steel injected into the tundish in a short time. As a result, the cleanliness of the slab portion corresponding to the unsteady casting work at the start of casting can be improved. Further, the heat deposition efficiency by heating the molten steel is also improved. In this way, it is possible to provide a method for cleaning molten steel in a tundish, which has industrially beneficial effects.

[Brief description of the drawings]

FIG. 1 is a diagram showing a flow pattern of molten steel in the initial stage of placing molten steel in a tundish.

FIG. 2 is a diagram showing a flow pattern of molten steel after a predetermined time has passed after the molten steel was stored in a tundish.

FIG. 3 is a schematic vertical sectional view mainly showing a tundish for explaining one embodiment of the present invention.

FIG. 4 is a schematic plan view of a tundish in which porous bricks are embedded, which is used in Example 1 of the present invention.

FIG. 5 is a schematic plan view of a tundish provided with a gas blowing port, which is used in Example 2 of the present invention.

FIG. 6 is a graph showing the relationship between the pooling time of molten steel for tundish and the inclusion index of molten steel samples in Example 1 of the present invention.

FIG. 7 is a graph showing a relationship between a plasma heating position of molten steel in a tundish and an inclusion index of a molten steel sample in Example 2 of the present invention.

FIG. 8 is a graph showing the relationship between the plasma heating position of molten steel in the tundish and the temperature difference of molten steel in the tundish in Example 2 of the present invention.

FIG. 9 is a graph showing the relationship between the output of plasma heating and the heat deposition efficiency on molten steel in Example 2 of the present invention.

FIG. 10 is a diagram showing a relationship between an argon gas blowing area and an inclusion index of a molten steel sample in Example 3 of the present invention.

[Explanation of symbols]

1 Tundish 2 Air seal pipe 3 Immersion nozzle 4 Molten steel 5 Ladle 6 Inert gas 7 Gas blower occupied area 8 Gas blow inlet 9 Porous brick 10 Plasma heating device x Central axis of the gas blower occupied area and plasma heating position The distance

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication C21C 7/072 C21C 7/072 Z (72) Inventor Masayuki Nakata 1-1-1 Marunouchi, Chiyoda-ku, Tokyo No. 2 Nihon Steel Tube Co., Ltd. (72) Inventor Hiroshi Shimizu 1-2 1-2 Marunouchi, Chiyoda-ku, Tokyo Nihon Steel Tube Co., Ltd.

Claims (3)

[Claims] 1. Prior to casting molten steel from the tundish into a mold, during pouring and / or into the tundish.
Or in the molten steel after injection, a method of cleaning the molten steel injected into the tundish by blowing an inert gas from the bottom of the tundish, as the tundish, in the tundish Using a tundish having a bottom shape such that the steel bath depth is not constant, the bottom of the tundish at which the steel bath depth is deeper is provided with a plurality of gas blowing ports, or Embedding a porous brick, and, the gas blowing port, or, blowing an inert gas into the molten steel from the porous brick, further, the molten steel heating device is disposed above the molten gas surface of the inert gas blowing portion. , Floats and separates the inclusions in the molten steel by controlling the flow of the molten steel while heating the molten steel by the molten steel heating device A method for cleaning molten steel in a tundish, which is characterized in that 2. The molten steel heating device is arranged within a distance of 2.0 m in the horizontal direction from the gas blowing port or the central axis of the occupied area of the porous brick, and the molten steel heating device is The cleaning of molten steel in a tundish according to claim 1, wherein the molten steel is heated by using the molten steel heating device having an output of 5 MW or less and having such an arrangement and a limited output. Method. 3. Argon gas is used as the inert gas, and the sum of the area of the gas blowing port and the sum of the area of the gas blowing ports of the porous brick are both 0.1 to 2.0 m. Adjusted within the range of ² , and the blowing amount of the argon gas is 80 to 800 Nl / min.
The method for cleaning molten steel in a tundish according to claim 1 or 2, wherein the temperature is within the range.