JPH02145B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for adjusting the temperature of molten steel in a tundish in continuous steel casting by introducing a coolant made of small pieces of steel into the molten steel in the tundish.

[Prior art] In order to adjust the temperature of the molten steel to a temperature close to (liquidus line + 40°C) by adding steel wires or small pieces to high-temperature molten steel as a coolant, the high-temperature molten steel can be used as a coolant. It is easy because it dissolves easily. However, when adjusting the temperature to around (liquidus line +10℃), for example, the coolant is difficult to melt because the molten steel temperature is low, and it may not melt smoothly or remain unmolten, so it is easy to adjust the temperature to the desired temperature. isn't it. On the other hand, lowering the casting temperature often improves the internal structure of the slab, but the casting temperature in this case is (liquidus +10 to 20
The goal is to achieve a low temperature of 30°F (°C), and temperature control is accompanied by the difficulties described above. JP-A-54-21816 discloses a technique for continuously supplying a molten metal wire into a tundish to lower the temperature of the molten metal in the tundish. However, when the molten steel temperature is low or when a large amount of coolant is supplied, it is difficult to smoothly adjust the temperature just by continuously supplying the metal wire without any special measures. Moreover, in Japanese Patent Publication No. 54-24372, a coolant is poured into the molten steel in the tundish, and the molten steel is stirred by the energy of the molten steel injection flow from the ladle, and the temperature of the molten steel is adjusted from (liquidus line) to (liquidus line +10°C). This is a method of controlling Normally, molten steel is injected into a continuous casting mold from a tundish nozzle, but operations are often performed with the molten steel depth in the tundish being approximately constant, and the ladle nozzle is opened/closed or throttled according to changes in the ladle molten steel head. Repeat to adjust the depth of molten steel in the tundish. If the method of Japanese Patent Publication No. 54-24372 is applied in such a case, the melting of the coolant will become unstable because the molten steel injection flow hermegi will change each time the ladle nozzle is opened/closed or throttled. When this occurs, the energy of the molten steel injection flow is lost, resulting in insufficient stirring.

[Problems to be Solved by the Invention] The purpose of the present invention is to always quickly and reliably melt the coolant introduced to cool the molten steel. For example, by adjusting the temperature of the molten steel to a low temperature close to the liquidus temperature. The purpose is to adjust the temperature of the molten steel to a desired temperature with small temperature fluctuations even when the steel is heated.

[Means for Solving the Problems] The present invention provides a molten steel stirring chamber consisting of a weir in a part of the tundish, the upper end of which is connected to a ladle nozzle, and the lower end immersed in the molten steel of the molten steel stirring chamber. The molten steel in the ladle is injected into the tundish through the long nozzle, and at the same time, inert gas is blown into the molten steel in the molten steel stirring chamber at a rate of 0.5Nm ³ /Hr or more through the long nozzle, resulting in boiling by inert gas injection. This is a method for adjusting the temperature of molten steel in a tundish in continuous steel casting, which is characterized by introducing a coolant made of small pieces of steel into the bare hot water portion at a desired ratio.

[Function] In the present invention, a molten steel stirring chamber made of a weir is provided in a part of the tundish. When the molten steel in the molten steel stirring chamber of the tundish is stirred, a strong stirring force is obtained, and therefore the coolant is easily melted. FIG. 1 shows an example of the molten steel stirring chamber of the present invention, and in this example, it is preferable to charge the coolant into the chamber surrounded by the lower dam. The size of the stirring chamber varies depending on the tundish capacity, but the width _l1 of the upper weir is 1.5 to 2.5 m, and the width _l2 of the lower weir is 0.5 to 1.2 m.
In the present invention, molten steel is injected into the ladle through a long nozzle, and inert gas is blown into the molten steel in the molten steel stirring chamber through the long nozzle. In order to efficiently stir the molten steel in the ladle in the tundish, it is best to use an inert gas blown in through the same long nozzle.The molten steel easily becomes a strong molten steel flow, so the heat exchange with the coolant is prevented. Transfers will be made smoothly. Figure 2 shows an example of introducing inert gas through porous bricks. The depth at which the long nozzle is immersed in the molten steel stirring chamber is selected to suit the operation, but in the present invention, active stirring was obtained by immersing the long nozzle to approximately 250 mm. Next, it is desirable that the amount of inert gas blown is 0.5 Nm ³ /Hr or more.
Figure 3 shows the results of measuring the temperature of molten steel in the upper part between the tundish nozzles (between the inner and outer strands) during casting. When 1Nm ³ /Hr was injected without providing a molten steel stirring chamber, C is an example in which a molten steel stirring chamber was provided and 1Nm ³ /Hr was injected using the method of the present invention.
As shown in FIG. 3A, without inert gas blowing, the stirring power of the molten steel is weak and the coolant does not melt smoothly, resulting in large temperature fluctuations. Also, Figure 3B
As shown in Figure 3A, even if an inert gas is blown in without providing a stirring chamber, the coolant does not dissolve smoothly, resulting in large temperature fluctuations, as in Figure 3A. In the case of FIG. 3C, a stable and strong molten steel stirring flow is formed, and heat transfer between the molten steel flow and the coolant becomes active, thereby stabilizing the molten steel temperature in the tundish.
The blowing of this inert gas is necessary because, as a further effect, it forms bare hot water on the surface of the steel bath. That is, a slag layer 10 is formed on the surface of the steel bath in the tundish, and normally when the coolant passes through the slag layer, the surface of the coolant is covered with slag, which acts as a heat insulating layer and delays the melting of the coolant. In the present invention, since the coolant is poured into the bare hot water 11 formed by blowing inert gas, the coolant is not covered with slag, and the coolant melts quickly. Next, the coolant used in the present invention is a small piece of steel, and this will be explained. The rapidly melting coolant is preferably one with a low melting point, that is, a high carbon type. For example, the temperature of continuously cast molten steel at a casting speed of 5 tons/min is 20
To lower the temperature, approximately 50 kg/min of coolant must be added, but for a 3 mm diameter steel wire, this would result in a supply rate of approximately 1000 m/min. Therefore, a large-scale coolant supply system is required to continuously supply high-strength, high-carbon steel wire. However, in the case of a small piece of steel, for example
Small pieces of steel made by cutting 5.5mmφ wire into approximately 100mm length can be easily added to several pieces of steel at the same time using a simple conveyor or chute, and therefore can be used with simple coolant supply equipment. It is a material. Although other pieces of steel may be used as the coolant, wire rods are easily available as raw materials for the pieces of high carbon steel.

[Example] (1) Tunnel size (capacity) 15 ton weir size (upper weir width) l ₁ 1600mm (lower weir width) l ₂ 900mm Long nozzle immersion depth 250mm Inert gas supply amount 0.5 to 1.0Nm ³ /Hr Figure 4 shows the change in temperature inside the tundish from the beginning of supply of molten steel into the tundish to the end of tundish injection. As is clear from FIG. 4, according to the present invention, the temperature can be reliably adjusted and satisfies the range of ±5° C. with respect to the target temperature.

(2) The same tundish as in Example (1) and the charge under substantially the same other conditions were selected, and the incidence of undissolved coolant was compared between the presence and absence of inert gas injection and the presence and absence of a molten steel stirring chamber. The results are shown in FIG. In the present invention, there is no occurrence of undissolved material.

[Effects of the Invention] As is clear from the above explanation, in the method of the present invention, the coolant is added in a state where it is easily melted, and the molten steel in the tundish is always in contact with the coolant with a stable and strong stirring force, so that heat is transferred and received. is smooth and
Therefore, even when adjusting the molten steel temperature to a low temperature close to the liquidus temperature, for example, the coolant melts smoothly and a stable molten steel temperature can be ensured.

[Brief explanation of drawings]

Fig. 1 is a diagram showing an example of the molten steel stirring chamber of the tundish of the present invention, Fig. 2 is a diagram showing an example of the long nozzle of the present invention, Fig. 3 is a diagram showing the adjustment accuracy of the molten steel temperature, and Fig. 4 is a diagram showing an example of the long nozzle of the present invention. Relationship diagram between elapsed time, molten steel supply rate, temperature inside the tundish, and coolant injection rate, No. 5
The figure shows the incidence of undissolved coolant in the tundish.

Claims (1)

[Claims] 1 A molten steel stirring chamber consisting of a weir is provided in a part of the tundish, and the ladle molten steel is injected into the tundish through a long nozzle whose upper end is connected to the ladle nozzle and whose lower end is immersed in the molten steel of the molten steel stirring chamber. At the same time, an inert gas of 0.5 Nm ³ /Hr or more is blown into the molten steel in the molten steel stirring chamber through the long nozzle, and a coolant made of small pieces of steel is applied to the bare hot water portion formed by boiling due to the inert gas injection. A method for adjusting the temperature of molten steel in a tundish in continuous steel casting, characterized by charging the molten steel at a ratio of .