JPH06246404A - Tundish for continuous casting - Google Patents

Abstract

PURPOSE:To reduce the unevenness of temp. in each strand in a tundish. CONSTITUTION:In the tundish 1 for continuous casting having plural strands, inert gas blowing nozzles 2 facing in mutual reverse direction at both side surfaces in the tundish 1 are arranged a little upward. By blowing the inert gas from the inert gas blowing nozzles 2, the stirring flows 5, 6 in the right- handed rotation and the left-handed rotation are caused while interposing a molten steel pouring hole 3. By this method, the evenness of the molten steel overheating degree DELTATmold in a mold in each strand in the tundish can drastically be reduced and the quality of the cast slab can be stabilized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous casting tundish for maintaining a constant superheating degree of molten steel in a continuous casting mold in continuous casting of steel.

[0002]

2. Description of the Related Art Continuous casting of steel is performed by injecting molten steel from a tundish into a mold having a predetermined cross-sectional shape and dimensions and continuously withdrawing it as a cast piece from below the mold. In continuous casting of such steel, powder is supplied to the surface of the molten steel in the mold, the powder forms a powder layer, a sintered layer and a molten layer by the heat of the molten steel, and the melted powder and the wall surface in the mold. It flows between the surfaces of the slab and plays a role as a lubricant, and also prevents the molten steel from being oxidized. In continuous casting of the above-mentioned steel, it is important to keep the casting temperature constant in an appropriate region in order to maintain high quality of the slab. Originally, the casting temperature should be the superheat degree ΔTmold of the molten steel on the molten metal surface in the mold (molten steel temperature in the mold-liquidus temperature), but it is impossible to measure the temperature of this part, so the conventional temperature The superheat degree ΔTmold of the molten steel in the mold is estimated by using the superheat degree ΔTt (molten steel temperature in the tundish-liquidus temperature) of the molten steel in the dish.

In the above continuous casting, in order to keep the degree of superheat ΔTmold of the molten steel in the mold constant, the degree of superheat ΔTt of the molten steel in the tundish is controlled to the secondary refining end temperature, and in order to alleviate the variation, the immersion nozzle is used. By changing the depth, measures are taken to keep the superheat degree ΔTmold of the molten steel on the molten metal surface in the mold constant. In the above continuous casting, as shown in FIG. 6, when the superheat degree ΔTmold of the molten steel in the mold is low, slag defects and mold inner skin tension are likely to occur, and the superheat degree ΔTmol of the molten steel in the mold is likely to occur.
When d is high, the frequency of breakout due to remelting of the solidified shell increases, so the degree of superheat of molten steel in the mold Δ
Tmold has the proper control region. However,
In a tundish with multiple strands,
Since the molten steel is injected from one place, as shown in FIG. 5, a difference occurs in the degree of superheat ΔTmold of the molten steel in the mold between strands, and the temperature is higher for the strands closer to the injection flow from the ladle.

As a stable operation method in the above continuous casting, the inflow condition of powder into the mold is measured, and the powder condition in the mold, the molten metal surface position measurement and the powder consumption amount are grasped. A method for controlling the inflow situation of the powder by selecting the powder and changing the charging amount, the charging time and the operating condition to prevent surface flaws and breakouts (Japanese Patent Laid-Open No. 6-58242).
7-202952 gazette), the molten steel temperature in the master ladle at the time of carrying out the molten steel treatment process of the previous process is measured, and the molten steel temperature in the master ladle at the start of the master ladle injection is measured from the measured value and the elapsed time until the start of pouring. Calculate the temperature of the molten steel in the master pot during the injection of the master pot and the temperature of the molten steel in the master pot at the start of the injection of the master pot, and calculate the elapsed time from the start of casting into the tundish and this tundish. The molten steel temperature in the tundish is calculated from the constant based on the type of the molten steel and the molten steel temperature in the master pot during the injection, and the molten steel temperature in the tundish is measured at least once per charge. Correct the molten steel temperature in the master pot and the molten steel temperature in the tundish, and adjust the molten steel temperature in the tundish or the value of the molten steel temperature in the master pot and the molten steel temperature in the tundish and the tundish from the start of use. Seeking molten steel temperature of the mold in the meniscus portion from an elapsed time, a method of secondary cooling control this casting temperature data as the initial value of the slab temperature (JP 59-15
No. 6559), molten steel superheat degree in tundish ΔTt
However, a method of pouring molten metal into a mold under the condition of 20 ° C ≤ ΔTt ≤ 100 ° C and performing a predetermined forging process on a portion of the slab drawn from the mold before solidification of molten steel is completed (special (Kaihei 2-155550), the thermal condition of the refractory in the tundish is quantified from the molten steel passing amount of the tundish, and the temperature of the molten steel from the time of tapping to the tundish is taken into consideration. Method of estimating the amount of drop and adjusting the molten steel temperature during tapping to an appropriate range (Japanese Patent Laid-Open No. 4-28)
Many proposals have been made.

[0005]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
The method disclosed in Japanese Patent No. 2952 is intended to prevent surface flaws and breakouts due to defective inflow of powder between the mold and the slab, and does not reduce the temperature variation among the strands of the tundish. In addition, JP-A-59-1
The method disclosed in Japanese Patent No. 56559 relates to the setting of the casting temperature which is the basis of the secondary cooling control using the process computer, and does not reduce the temperature variation among the strands of the tundish. Furthermore, JP-A-2
The method disclosed in Japanese Patent Publication No. 155550 is to reduce the center segregation of the slab and to reduce inclusions. The molten steel superheat degree ΔTt in the tundish is poured into a mold under the condition of 20 ° C. ≦ ΔTt ≦ 100 ° C. With hot water, the degree of superheat ΔTmold of the molten steel in the mold cannot be made constant. Furthermore, the method disclosed in Japanese Patent Application Laid-Open No. 4-28467 reduces the variation due to the charge of the molten steel temperature in the tundish, and does not reduce the temperature variation among the strands of the tundish.

An object of the present invention is to provide a tundish for continuous casting which can reduce the temperature variation among the strands of a tundish having a plurality of strands in order to keep the superheat degree ΔTmold of the molten steel in the mold in the continuous casting constant. Especially.

[0007]

[Means for Solving the Problems] The inventors of the present invention have made extensive studies to achieve the above object. As a result, in the continuous casting tundish having a plurality of strands, the degree of superheat ΔTmold of the molten steel in the mold is different depending on the strand, and a strand closer to the molten steel injection port from the ladle into the tundish has a higher degree of molten steel in the mold. Superheat ΔTmold
In order to reduce the degree of superheat ΔTmold of molten steel in the mold due to this strand, if the temperature variation of each strand is reduced by stirring the inside of the tundish with an inert gas, the overheating of molten steel in the mold of each strand It was found that the degree ΔTmold can be kept almost constant, and the present invention was reached.

That is, according to the present invention, in a tundish for continuous casting having a plurality of strands, inert gas blowing nozzles facing opposite directions are provided on both side surfaces of the tundish, and the tundish from the inert gas blowing nozzle is provided. The tundish for continuous casting is characterized by generating a clockwise and counterclockwise stirring flow in molten steel by blowing an inert gas.

[0009]

In the present invention, the opposite sides of the tundish are provided with the inert gas blowing nozzles facing in the opposite directions slightly upward, and the inert gas is blown from the inert gas blowing nozzle to the right side of the molten steel. And because it generates a counterclockwise stirring flow, the molten steel injected from the tundish inlet is stirred left and right along the clockwise and counterclockwise stirring flows due to the inert gas injection, and inside the tundish. Variations in the molten steel temperature depending on the position are reduced, variations in the molten steel temperature between the strands are eliminated, and the difference in the superheat degree ΔTmold of the molten steel in the mold between the strands can be reduced.

In the present invention, nitrogen gas and argon gas can be considered as the inert gas blown from both sides of the tundish, but it is economical to use nitrogen gas. In this invention, the blowing directions of the inert gas blown from both sides of the tundish are opposite to each other so that the molten steel injected from the molten steel injection port is divided into left and right to form a clockwise counterclockwise stirring flow. It is installed slightly upward, but it is also effective in terms of the stirring efficiency of molten steel. The rate at which the inert gas is blown into the molten steel in the tundish may be determined empirically because the stirring efficiency differs depending on the capacity of the tundish and the molten steel.

[0011]

Example No. 25t capacity with 1-4 strands
When molten steel is supplied from the tundish into the mold for continuous casting, as shown in FIG. 1 and FIG. 2, the inert gas blowing nozzles 2 are slightly upwardly directed to both side surfaces of the tundish 1 in opposite directions. 4 are provided on each side of the molten steel injection port 3, and each inert gas injection nozzle 2
Nitrogen gas at 1 Nm ³ / min to blow molten steel 4 in the mold from the strands 7 while forming clockwise and counterclockwise agitated flows 5 and 6 in the molten steel 4 in the tundish 1. It was Each strand 7 in that case
The molten steel superheat degree ΔTmold on the molten metal surface in each mold was estimated. The results are shown in FIG. 4 in comparison with the case without blowing the inert gas. As shown in FIG. The variation of the molten steel superheat degree ΔTmold at the molten metal surface in the mold at the positions of 1 to 4 strands is 10 ° C. without the inert gas blowing, whereas the variation of the molten steel stirring by the inert gas blowing of the present invention was performed. In the case of a dish, it was significantly reduced to 3.5 ° C.

The degree of superheated molten steel ΔT on the molten metal surface in the mold
Mold is estimated by the following estimation formula using the coefficient obtained by the regression formula, and the molten steel superheat degree ΔT on the molten metal surface in the mold
Estimated mold, molten steel superheat degree ΔT on the molten metal surface in the mold
When the mold was out of the appropriate value, the powder brand was changed and the nozzle immersion depth was automatically changed to perform continuous casting. As a result, the variation in the molten steel superheat degree ΔTmold on the molten metal surface in the mold was reduced by about 40% as shown in FIG. ΔTmold = 0.79 (ΔTt) +0.046 (V
c) +0.005 (EMS) +0.074 (Ph)-
0.019 (Nd) However, ΔTt: superheated degree of molten steel in tundish (° C) Vc: casting speed (mm / min) EMS: electromagnetic stirring strength (A) Ph: heat generation powder calorific value (kcal) Nd: nozzle depth (Mm)

[0013]

As described above, according to the method of the present invention, it is possible to greatly reduce the variation of the molten steel superheat degree ΔTmold in the mold for each strand of the continuous casting tundish, and to stabilize the quality of the slab. it can.

[Brief description of drawings]

FIG. 1 is a plan view conceptually showing a tundish in the present invention.

FIG. 2 is a side sectional view conceptually showing a tundish in the present invention.

FIG. 3 is a graph showing variations in molten steel superheat degree ΔTmold on a molten metal surface in a mold before and after using the present tundish in Examples.

FIG. 4 is a degree of superheated molten steel ΔTmol on the molten metal surface in the mold for each strand before and after using this tundish in Examples.
It is a graph which shows the variation of d.

5] FIG. It is a graph which shows the variation of molten steel superheat degree (DELTA) Tmold in the molten metal surface in a mold between strands at the time of using the tundish which has 1-4 strands.

FIG. 6 is a graph showing a relationship between a molten steel superheat degree ΔTmold on a molten metal surface in a mold, a slag defect rate, and a breakout frequency.

[Explanation of symbols]

 1 Tundish 2 Inert gas blowing nozzle 3 Molten steel injection port 4 Molten steel 5, 6 Stir flow 7 Strand

Claims (1)

[Claims] 1. In a tundish for continuous casting having a plurality of strands, inert gas blowing nozzles facing in mutually opposite directions are provided slightly upward on both side surfaces of the tundish, and the tundish from the inert gas blowing nozzle is provided. A tundish for continuous casting, which is characterized by generating a clockwise and counterclockwise stirring flow by sandwiching a molten steel injection port by blowing an inert gas.