JPS6174762A - Continuous casting method of different steel kind - Google Patents

Abstract

PURPOSE:To provide an improvement in yield, decrease in the rate of segregation and prevention of a leakage accident in a titled casting method using the same tundish by casting different kinds of steel while executing gas bubbling and adopting a specific joint block. CONSTITUTION:A ring 2 consisting of errosion-resistant refractories provided with suitable lines of annular slits on the inside circumferential surface is mounted to the inside circumferential part of a stationary board 1 attached to the nozzle in the bottom of the tundish 5. The gas bubbling is executed by using a molten metal discharge device 4 provided with a gas introducing hole 3 communicating with said slits of the ring 2 from the outside and the casting is so ended that the remaining steel in the tundish 5 is <=20% of the capacity of the tundish 5. While the clogging of the above-mentioned nozzle part as a result of solidification is prevented by the gas bubbling, the joint block 6 is inserted into the casting mold and thereafter the casting of the next different steel kind is started.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a continuous one-shot casting method for dissimilar steel boxes, and in particular can improve yield by reducing the amount of cut-off in the mixed portion of different steels. This relates to a continuous casting method for different steel types.

(Prior art) Conventionally, as a method for continuously casting molten steel of different steel types, at the end of the previous casting, when the slag floating on the surface of the molten steel is not injected into the mold from the tundish, the slag remains and the injection is stopped. After that, a so-called partition plate was inserted on the dead surface of the mold to separate the previous steel 1 and the next steel grade, and then casting of the next steel grade was started.

(Problems to be Solved by the Invention) However, the above-mentioned casting method has one drawback as shown below.

■ Yield decrease due to increase in cut-off slabs in the mixing area between the previous steel grade and the next steel grade.When finishing casting the previous steel d, in order to prevent slag from flowing into the mold, the molten steel was poured into a tandate 7U with a grade of 30. Since molten steel of the next steel grade is injected into this, the amount of mixed section slabs that are affected by the molten steel of the previous steel grade increases and the yield decreases.

■ Occurrence of steel leakage accidents at slab joints The boundary between molten steel of the previous steel grade and molten steel of the next steel grade is connected by a solidified shell of molten steel by inserting a simple partition plate.
Steel leakage accidents are likely to occur due to poor solidification, etc.

■Deterioration in the quality of the slab at the boundary between the 11 previous grades of molten steel and the next grade of molten steel.■As the molten steel of the previous grade remains in the tundish, component segregation occurs and abnormal slabs are generated.

■A simple partition plate is inserted at the boundary between molten steel of the previous steel grade and molten steel of the next steel grade, so the partition is unstable due to poor solidification, etc. Therefore, molten steel of the next steel type may flow into the previous slab, resulting in an abnormal slab.

When molten steel of the 6th grade steel is poured into the tundish, the head of the molten steel in the tundish is lowered, which causes slag slapping and inclusions to increase.

■When drilling holes for the next casting of the steel type, the inside of the upper nozzle will be solidified, so clean it with oxygen gas and open the hole. Therefore, oxides increase and inclusions occur.

(Means for Solving the Problems) The present invention has been made to solve the above problems, and the gist thereof is to provide a method for continuously casting molten steel of different steel types using the same tundish. A ring metal made of erosion-resistant refractory material with multiple slits provided on the inner periphery of the fixed plate attached to the nozzle is attached to the inner periphery of the fixed plate, and a gas introduction hole communicating with the slits from the outside is attached. slag and molten steel are separated by performing gas bubbling using a molten metal discharge device equipped with a molten metal discharge device, and the casting of the previous steel type is completed so that the residual steel in the tundish becomes 20- or less of the tundish capacity, Thereafter, the joint block is inserted into the mold while preventing solidification and clogging of the nozzle portion by performing gas bubbling in the same manner, and then casting of the next steel type different from the previous steel type is started.

That is, the first feature of the present invention is that, as shown in FIG. Gas bubbling is performed using a molten metal discharge 4tQt41, which is equipped with a ring +2+ made of an elution-resistant refractory, and is provided with a gas introduction hole (31) that communicates with the slit of the ring (2) from the outside. As a result, the slag and molten steel in the tundish (5) are separated, and casting can be performed until the remaining steel in the tundish is reduced to the smallest possible amount.

As a result, the amount of cut-off slabs in the mixed portion of the previous steel grade and the next steel grade is reduced, and the yield is improved. In other words, the quality deterioration of the slab at the boundary between the molten steel of the previous steel grade and the molten steel of the next steel grade is reduced.

The second feature of the present invention is that a joint block (6) having a shape as shown in FIG. 3, for example, is employed at the slab connection between the previously cast molten steel and the next cast molten steel, By using such a joint block (61), it is possible to prevent the occurrence of water leakage accidents due to poor coagulation, etc., which occurs when conventional simple partition plates are used.

Furthermore, the third feature of the present invention is that gas bubbling is performed after the previous molten steel casting is completed until the next molten steel casting is started.

As a result, the next time you cast molten steel, you can start with natural holes.
The conventional hole-opening operation using O1 gas can be eliminated, and the generation of inclusions can be prevented.

In addition, ■ in the figure is the upper nozzle, t81H slide plate, (9+
is the lower nozzle, and the head is the mold.

Next (In the present invention, the reason why the residual steel in the tundish of the previous molten steel is set to be less than 20 - of the tundish capacity is 20
This is because, if this exceeds 1, the mixing zone between the previous molten steel and the next molten steel becomes long, resulting in poor yield, as is clear from the examples shown below, and the effects of the present invention cannot be expected.

(Example) Continuous casting of different tXS was performed by the method of the present invention under the conditions shown below.

■Gas pressure 7 n/- ■Gas flow rate 100 t/- ■Gas composition Mur gas Figure 4 shows the experimental results of segregation (component difference ≦ 40 points) in the mixed steel types of slabs produced by the method of the present invention. As is clear from the figure, according to the method of the present invention (residual steel in the tundish is 20 or less), the amount of segregation in the mixed steel part is small and the length of the slab in the mixed part is short. was gotten.

(Effects of the Invention) As described above, the method of the present invention performs casting while performing gas bubbling, so that the molten steel and slag in the tundish can be separated and the remaining steel in the tundish can be cast as small as possible. The mixing area of the previous molten steel and the next molten steel is reduced, improving the yield and reducing the amount of segregation. In addition, the method of the present invention uses a joint block instead of the conventional simple partition plate at the connection between the previous molten steel and the next molten steel, so it eliminates the drawbacks of the conventional method, such as preventing steel leakage accidents due to poor solidification. It has a great effect on solving problems.

[Brief explanation of the drawing]

Figures 1 (a) to (c) are explanatory diagrams of the method of the present invention, Figure 2 is a longitudinal sectional view showing an example of a molten metal discharge device used in the method of the present invention, and Figure 3 is also used in the method of the present invention. FIG. 4 is a perspective view showing an example of a joint block, and FIG. 4 is a diagram showing the relationship between the amount of PP4 segregation and the length of the slab in the mixing section, showing an embodiment of the method of the present invention. (υ is a fixed plate, (21 is a ring, (3) is a gas introduction pipe,
(41 is the molten metal discharge device, (6) is the joint block, (
7) is the upper nozzle. Patent applicant: Sumitomo Metal Industries, Ltd. Figure 1 (R αυ (C) Figure 2 Figure 4 ↓ L combination S one length)

Claims (1)

[Claims] (1) In a method of continuously casting molten steel of different steel types using the same tundish, a plurality of slits are provided on the inner peripheral surface of a fixed plate attached to a nozzle at the bottom of the tundish to prevent melting and damage. By attaching a ring made of a steel refractory and performing gas bubbling using a molten metal discharge device equipped with a gas introduction hole that communicates with the slit from the outside, the remaining steel in the tundish is removed from the casting of the previous steel type. The process is finished so that the tundish capacity is 20% or less, and then the joint block is inserted into the mold while preventing solidification and clogging of the nozzle part by gas bubbling, and casting of the next steel type different from the previous steel type is started. A continuous casting method for different steel types.