JPH07227653A - Method and device for reducing shrinkage hole in continuous casting - Google Patents

Abstract

PURPOSE:To restrain the developing length of shrinkage hole at the top part of a cast slab and to improve the yield of the cast slab in continuous casting of molten steel. CONSTITUTION:At the time of producing the continuously cast slab by pouring the molten steel in a ladle into a mold through a tundish, a heat insulating tube 3 is charged into the molten steel 7 which has been poured in the mold 1 to delay the solidification of the molten steel on the surface in the tube, and the shrinkage hole formed at the last position in the cast slab is reduced. By this method, the length of the shrinkage hole formed by the solidified shrinkage can be shortened and the cast slab having long sound part can continuously be cast in the high efficiency, and the productivity and the yield of the cast slab are improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for reducing shrinkage holes in continuous casting of molten steel.

[0002]

2. Description of the Related Art In continuous casting of steel, molten steel in a ladle is poured into an internal water-cooled copper mold through a tundish and a pouring nozzle, and then cooled and solidified by removing heat from the mold and the secondary cooling zone. , Becomes a solid slab.

At the final part of the slab (which is hereinafter referred to as the slab top part) which solidifies mainly after pouring into the mold, the difference in density between the liquid and solid of steel is usually considered. A large shrinkage hole is formed inside the slab due to the solidification shrinkage that occurs based on it.

The slab portion where the shrinkage holes are formed can be used as a product because the flux for continuous casting flows into the shrinkage holes and the iron oxide film is generated by the infiltration of air into the shrinkage holes after solidification. However, the current situation is that there is no other method than cutting down to iron scraps, and the longer the contraction holes, the worse the yield of the slab.

However, heretofore, a method of shortening the length of the contraction hole to improve the yield of the slab top has not been often taken.

[0006]

When the contraction hole is formed in the top part of the slab as described above, the slab part having the contraction hole cannot be used as a product, and there is no method to cut it into iron scrap, The slab yield deteriorates, leading to higher costs,
It wasn't good.

The present invention provides
(EN) Provided are a method and an apparatus for suppressing the generation length of shrinkage holes in a slab top portion and improving the yield of slabs.

[0008]

According to the method of the present invention, when molten steel in a ladle is poured into a mold through a tundish to produce a continuously cast slab, it is poured into the mold after the molten steel is poured. This is a method for reducing shrinkage holes in continuous casting, characterized in that a heat insulation tube is charged into molten steel that has been melted to reduce the shrinkage holes formed in the final portion of the cast slab.

The first part of the apparatus of the present invention is a lid having a heat insulating tube used in the method for reducing shrinkage holes, which is made of a heat-insulating metal or refractory, and has a small opening at the lower end and a small hole at the upper end. A shrinkage hole reducing device in continuous casting, characterized in that

The second aspect of the apparatus of the present invention is that the heat insulating tube used in the method for reducing shrinkage holes is equipped with a heat insulating refractory material on the inner surface of a metal tube, the lower end is open and the small hole is formed at the upper end. A shrinkage hole reducing device in continuous casting, characterized in that a lid having a is attached.

[0011]

FIG. 1 (a) shows a plan view of a heat-insulating pipe 3 having a lower end open and a small hole 4 at the upper end, which is placed in the molten steel in the continuous casting mold 1 after the completion of pouring the molten steel. A schematic diagram is shown. The heat retaining tube 3 can be installed from above the molten metal surface 2 after the completion of pouring the molten steel without decelerating the casting speed.

FIG. 1 (b) is a sectional view taken along the line AA in FIG. 1 (a). After the completion of pouring the molten steel, the continuous casting flux 5 is used.
When the heat insulation pipe 3 is installed from above the remaining metal surface 2, the solidified shell 8a develops on the outer metal surface of the heat insulation pipe 3 relatively quickly by heat removal through the metal surface 2 and the heat insulation pipe is Fixed.

When the casting speed is not reduced, the molten metal surface 2 and the heat insulation pipe 3 move downward as the cast slab is withdrawn, while the molten steel 7 moves during the movement in the mold portion and the secondary cooling zone below the mold. It solidifies by removing heat, and the solidified shell 8 grows.

When the molten steel solidifies, the molten steel 7 and the solidified shell 8
The molten steel moves in order to compensate for the solidification shrinkage due to the difference in density, but if this movement is difficult, shrink holes are formed. If the solidification of the molten steel inside the heat insulation pipe 3 is delayed by installing the heat insulation pipe 3 here, the molten steel inside the heat insulation pipe can easily move to compensate for solidification shrinkage, and the inside of the heat insulation pipe 3 can be compensated. The bath surface 2a descends.

At this time, if the small hole 4 is not provided at the upper end of the heat retaining tube 3, the pressure in the space 6 inside the heat retaining tube 3 is reduced and the molten metal surface 2a
Cannot be lowered, the movement of the molten steel to compensate for the solidification shrinkage becomes difficult, and the formation of shrinkage holes is promoted.

FIG. 2 shows an example of a cylindrical heat insulation tube.
(A) is a drawing in the shape of a cylinder of a heat-insulating metal or refractory material, the lower end of which is open and the small hole 4 at the upper end,
It is important to prevent the temperature drop and solidification of the molten steel in the heat insulation tube as much as possible. Therefore, as the heat-insulating metal, stainless steel having a low thermal conductivity, and as the refractory material, those obtained by molding fibers whose main component is alumina can be used.

FIG. 2B shows a metal cylinder 9 as the heat insulation tube 3.
It is a schematic diagram when the refractory material 10 is attached to the inner surface of the. When the outer surface of the heat retaining tube 3 is made of metal, as shown in FIG.
It is easy to connect the solidification shell 8a just below the surface of the hot water to the outer surface of the hot water pipe and the outer surface of the hot water pipe 3.
After installing in the molten steel, there is an advantage that the heat insulating tube 3 is quickly fixed. It is possible to use, for example, a stainless steel cylinder having a molded plate of fibers containing alumina as a main component attached to the inner surface thereof.

Although FIG. 2 shows an example of a cylindrical heat retaining tube, a polygonal tube is used as long as the lower end is open and the upper end has a small hole so that the molten steel inside the heat retaining tube can be kept warm. It may be in the form of a shape.

FIG. 3 is a schematic view of a vertical cross section of the cast piece 12 after complete solidification when the heat insulating tube 3 of the present invention is used, and FIG.
Shows a schematic view of a vertical cross section of the cast slab 12 in the case where a heat insulating tube is not used.

Without practicing the invention shown in FIG. 4,
Usually, the solidified shell 8a is formed in layers, and the contraction holes 11 in a relatively wide space and the contraction holes 11a that appear to be isolated are formed.

The solidified shell 8a at the uppermost end of the slab is formed into a layer by heat removal from the molten metal surface at the top of the slab, and there is a phenomenon that the internal pressure drop due to the solidification shrinkage causes it to deform slightly downward and burst. It is thought to have occurred once. Shrink hole 1
If the length of 1a is long, the yield of the cast slabs 12 becomes poor.

The contraction holes 11a which appear to be isolated are often connected to the contraction holes 11 in the upper part, and when they are connected, they are oxidized by the intrusion of air from the upper part.
Even if it is rolled and pressed in a later process, the oxide remains and the quality of the product deteriorates, so it must be discarded as iron scrap.

On the other hand, in FIG. 3, when the heat insulating tube 3 is installed as in the present invention, the molten steel inside the heat insulating tube 3 can compensate the solidification shrinkage to the end, so that the shrink hole 11 is not large and the upper end of the slab is To the lower end of the contraction hole 11 is short, and conversely, the length of the sound part of the slab with no contraction hole is long, and the slab yield at the slab top portion is extremely good.

In the above description, the case where one heat insulating tube is installed has been described. However, when the slab width is about 3 to 10 times the thickness like a slab slab, the slab width is By installing two or more heat insulation tubes in the direction, it is possible to easily supply the molten steel that supplements the solidification shrinkage, the effect thereof can be more easily exhibited, and the formation of shrinkage holes can be easily reduced.

[0025]

Example A continuous casting test of a bloom slab having a thickness of 300 mm and a width of 500 mm was conducted using a molten steel of a high carbon steel whose main component was 0.8 mass% C. In normal continuous casting of a vibrating copper mold, using mold flux, molten steel was poured from a ladle to a tundish and then injected into the mold using an immersion nozzle.

As casting conditions, the casting speed is 0.7 m /
The degree of superheat of molten steel in the tundish is approximately 1 with a constant min.
In the range of 0 to 30 ° C., water spray was used for secondary cooling of the cast piece after the mold part.

As a condition relating to the heat insulation pipe, when the heat insulation pipe is not used, the stainless steel pipe having the shape shown in FIG.
mm, wall thickness 5 mm, length 400 mm, small hole diameter 5 m
m), the shape shown in FIG. 2 (a), the main component of which is a molded fiber of alumina fiber (outer diameter 190 mm, wall thickness 15 mm, length 400 m).
m, the diameter of the small hole is 5 mm), and the main component is alumina inside the outer stainless steel pipe (outer diameter 200 mm, wall thickness 5 mm, length 200 mm, small hole diameter 5 mm) having the shape shown in FIG. A fibrous molded tube (outer diameter 190 mm, wall thickness 15 mm, length 400 mm, small hole diameter 5 mm) was used.

After the molten steel has been poured, the heat insulating pipe is used to reduce the casting speed to about 30 from the top of the molten metal into the molten steel.
It was set so as to be immersed about 0 mm.

After the casting experiment using these heat retaining tubes, the longitudinal section of the slab top was examined, and as a result, when the heat retaining tube under the conditions was not installed, as shown in the schematic diagram of FIG. There are large contraction holes and contraction holes that appear to be isolated. The length from the top of the slab to the end of the large contraction hole is about 100 cm, and the length from the top of the slab to the end of the contraction hole that appears to be isolated. Was about 220 cm.

On the other hand, the condition using the heat insulation tube,
, The number of shrinkage holes that seem to be isolated is extremely small, and the distance from the upper end of the slab to the tip of the large shrinkage hole is about 60 cm under the conditions, about 45 cm under the conditions, and under the conditions. Was about 40 cm, and it was found that the use of the heat insulation tube shortens the length of the contraction hole formed by the solidification contraction of the molten steel.

Compared to the case where the heat insulation tube is not used, under the conditions where the heat insulation tube is used ,,, the length of the sound slab without shrinkage holes is increased by 40, 55, and 60 cm, respectively. It was revealed that the one-sided yield was improved.

[0032]

As described above, according to the present invention, it is possible to reduce the formation of shrinkage holes in a slab by charging a heat insulating tube into molten steel without lowering the casting speed, and to reduce solidification shrinkage. The length of the contraction hole at the top of the slab to be formed can be shortened, and the slab with many sound parts can be stably and continuously cast at a high production rate, improving the productivity and the yield of the slab. Is possible.

[Brief description of drawings]

FIG. 1 (a) is a schematic plan view showing a case where a heat insulating tube is installed in a continuous casting mold, and FIG. 1 (b) is a diagram of FIG.
It is sectional drawing of A position.

FIG. 2 (a) is a heat insulation tube in which a heat-insulating metal or refractory material is formed into a cylindrical shape, and FIG. 2 (b) is a schematic view when a refractory material is attached to the inner surface of a metal cylinder as a heat insulation tube.

FIG. 3 is a vertical cross-sectional view of a cast piece when a heat insulating tube is used.

FIG. 4 is a vertical cross-sectional view of a cast piece when a heat insulating tube is not used.

[Explanation of symbols]

 1 Mold 2, 2a Hot water surface 3 Heat insulation pipe 4 Small hole 5,5a Flux 6 Space inside heat insulation pipe 7 Molten steel 8, 8a Solidified shell 9 Metal cylinder 10 Refractory 11, 11a Shrink hole 12 Cast slab

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiromi Takahashi 1 Kimitsu, Kimitsu-shi, Chiba Nippon Steel Corporation Kimitsu Steel Works

Claims (3)

[Claims] 1. When a molten steel in a ladle is poured into a mold through a tundish to produce a continuously cast slab, a heat insulation pipe is charged into the molten steel poured into the mold after the molten steel is poured. Then
A method for reducing shrinkage holes in continuous casting, characterized in that shrinkage holes formed at the final portion in a cast piece are reduced. 2. The heat insulation pipe used in the method according to claim 1, wherein the pipe is made of a heat-insulating metal or refractory material,
A contraction hole reduction device in continuous casting, characterized in that a lid having an opening at the lower end and a small hole at the upper end is attached. 3. A heat insulating tube used in the method according to claim 1, wherein a heat insulating refractory material is attached to the inner surface of a metal tube, and a lid having an open lower end and a small hole at the upper end is attached. A device that reduces shrinkage holes in continuous casting.