KR102237627B1 - Methods of continuous casting - Google Patents

Abstract

According to an embodiment of the present invention, provided is a continuous casting method, comprising: a first step of calculating a slab short-side transverse crack occurrence index only with a superheat degree deviation, which is the difference between a measured temperature and a target temperature of a tundish molten steel; and a second step of determining whether to input a continuous casting post-process of the slab from the calculated slab short-side transverse crack occurrence index.

Description

Continuous casting method {METHODS OF CONTINUOUS CASTING}

The present invention relates to a continuous casting method, and more particularly, to a continuous casting method capable of producing a high-quality slab.

Iron ore is manufactured by molten iron through a ironmaking process. The ironmaking process is carried out by putting iron ore together with coke and limestone into the blast furnace. The ironmaking process also includes a sintering process in a broad sense. The molten iron is manufactured from molten steel through a steelmaking process. The steelmaking process includes preliminary treatment for hotline, converter steelmaking, and secondary refining. Molten steel is formed into semi-finished steel products such as cast slabs, blooms, billets, etc. through a continuous casting process. Steel semi-finished products are finally formed into final products such as rolling coils through a rolling process. In a continuous casting process, molten steel is introduced into a continuous casting mold through a tundish in a ladle. The molten steel is first cooled in the casting mold. That is, the molten steel forms a solidified shell as the molten steel proceeds from the surface of the molten steel adjacent to the cast mold to the inside of the molten steel. The strand made of molten steel and solidified shell exits the playing mold and passes through the strand cooling device for secondary cooling. The strand is completely cooled while passing through the strand cooling device, and is then cut by a cutting machine to form a cast iron.

The background technology of the present invention is disclosed in Korean Patent Application Publication No. 10-2011-0109200 (2011. 10. 06., continuous casting method).

An object of the present invention is to provide a continuous casting method capable of reducing process load, production cost and logistics congestion and improving yield by disclosing a high-quality slab manufacturing method that predicts a short-sided lateral crack generating material in advance.

According to an aspect of the present invention, a first step of calculating an index of occurrence of lateral cracks on a short side of a slab only with a deviation of superheat, which is a difference between the measured temperature of molten tundish steel and a target temperature; And a second step of determining whether to input the slab after the continuous casting process from the calculated slab short side lateral crack generation index. It provides a continuous casting method comprising a.

In the continuous casting method, the slab short side lateral crack generation index (Y) and the superheat deviation (X) may ^{have a correlation of Y = 0.0058X 2} + 2.0508X + 12.534.

The correlation may be satisfied under conditions in which mold level hunting by dynamic bulging and an oscillation mark can be formed.

The above correlation can be satisfied under the condition that the carbon composition of molten steel is 0.08 to 0.14% by weight, and the molten steel casting speed is 1.2 to 1.5mpm.

The continuous casting method may further include the step of introducing the slab to the post process when the slab short side lateral crack generation index is less than or equal to a preset value in the second step.

The continuous casting method may further include performing a surface grinding treatment on the slab when the slab short side lateral crack generation index is greater than a preset value in the second step.

According to the continuous casting method according to the present invention, it is possible to produce a high-quality slab by predicting the correlation of the short side lateral crack defect according to the variation of the superheat degree of the tundish molten steel and determining whether the process is input or not.

1 is a view showing a continuous casting apparatus.
2 is a photograph of a deep oscillation mark (OSM) generated in the short side of the slab.
3 is a photograph of a horizontal crack appearing on the short side of a slab in which a deep oscillation mark has occurred.
4 is a flow chart illustrating a continuous casting method according to an embodiment of the present invention.
5 is a graph showing a correlation between short side lateral crack defects according to a variation in superheat degree of molten tundish steel in a continuous casting method according to an embodiment of the present invention.

Hereinafter, the present invention will be described in detail. In this case, when it is determined that a detailed description of known technologies or configurations related to the present invention may unnecessarily obscure the subject matter of the present invention, a detailed description thereof will be omitted.

Terms such as first and second may be used to describe various elements, but the elements should not be limited by the terms. The above terms are used only for the purpose of distinguishing one component from another component.

In addition, terms to be described later are terms defined in consideration of functions in the present invention and may vary according to the intention or custom of users or operators, so the definitions should be made based on the contents throughout the present specification describing the present invention.

1 is a view showing a continuous casting apparatus.

Referring to FIG. 1, the molten steel 10 is moved from a ladle to a playing mold 120 through a tundish 100 through a submerged entry nozzle 110. The molten steel 10 is first cooled in the playing mold 120.

That is, the molten steel 10 forms a solidified shell 11 as the molten steel surface in contact with the cast mold 120 is solidified into the molten steel. To this end, a cooling fluid, for example, cooling water may be supplied to the playing mold 120.

The strand 12 exiting the playing mold 120 is secondarily cooled in a strand cooling device. The strand 12 includes the molten steel 10 and the solidification shell 11, and refers to an intermediate product that appears in the process of forming the molten steel 10 into the cast piece 13 through a continuous casting device.

The strand cooling device may include a plurality of guide rollers 130 for guiding the strand 12 by contacting both surfaces of the strand 12 and a plurality of cooling nozzles 140 for injecting a cooling fluid to the strand 12. . The cooling fluid supplied through the cooling nozzle 140 may be different from or the same as the cooling fluid supplied to the playing mold 120, and may include, for example, cooling water.

The strand 12 may be bulging due to ferro-static pressure in the region A between the two guide rollers 130 spaced apart along the transport direction of the strand 12. .

That is, a phenomenon in which the solidification shell 11 swells due to the iron static pressure of the molten steel 10 among the strands 12 may occur. In addition, the strands 12 may be pressed by two guide rollers 130 that are disposed to respectively contact both surfaces of the strands 12 and to face each other in a region in contact with the guide rollers 130.

As a result, the strand 12 is repeatedly expanded and contracted by the iron static pressure of the molten steel 10 and the plurality of guide rollers 130 while passing through the strand cooling device.

This phenomenon is called dynamic bulging. It may be necessary to increase the solidification shell thickness and reduce the tundish temperature to reduce dynamic bulging. Dynamic bulging may cause fluctuations in the level of the molten steel bath 14 in the playing mold 120.

The amount of fluctuation of the level of the molten steel metal surface 14 due to the dynamic bulging may occur up to about 10 mm to 20 mm vertically. As a result, there is a high possibility that mold powder is mixed in the molten steel 10 or a crack occurs in the cast plate 13.

Therefore, in order to produce high-quality cast pieces 13, it is important to predict the possibility of dynamic bulging occurring in the strand 12, and to control the operating conditions so that dynamic bulging does not occur in the strand 12 according to the prediction result. Do.

On the other hand, dynamic bulging shows a tendency to intensify when the initial solidification of molten steel is non-uniformly in the casting mold 120, and the non-uniformity of the solidification shell 11 is different due to the contraction reaction due to phase transformation during initial solidification. Dynamic bulging can be particularly severe in peritectic steels, which are higher than those in peritectic steels.

After the strand 12 is completely cooled while passing through the strand cooling device, it is cut by the cutter 150 to be manufactured into a cast piece 13 such as a slab, bloom, or billet.

FIG. 2 is a photograph of a deep oscillation mark (OSM) occurring in the short side of the slab, and FIG. 3 is a photograph of a horizontal crack appearing on the short side of the slab in which a deep oscillation mark has occurred.

As described above, in the continuous casting process, molten steel flows into the mold from the tundish through the immersion nozzle. During continuous casting, mold level hunting occurs due to dynamic bulging in steel grades such as pojeong steel, and a deep oscillation mark (OSM) is formed in the dynamic bulging mold level hunting (see FIG. 2). When creating a deep oscillation mark, a horizontal crack occurs in the short side of the slab at the location of the oscillation mark (see FIG. 3).

Considering that the deep oscillation mark spacing and the mold level variation spacing are similar together, in conclusion, it can be understood that transverse cracking occurs due to dynamic bulging.

In the event of such a lateral crack, the entire surface of the continuously cast slab produced to reduce defects on the product surface is subjected to mechanical welding (scarping) treatment, and additional inspection is performed, and if defects remain, they must be manually removed individually. There may be many problems, such as an increase in process load, congestion of logistics due to inspection time, manual removal time, etc., incurring cutting costs, and decrease in yield.

The present invention discloses a high-quality slab manufacturing method for predicting in advance a short side lateral crack generating material according to the variation in superheat degree of molten tundish steel. That is, the present invention provides a high-quality slab manufacturing method by predicting the correlation of short side lateral crack defects according to the variation of the superheat degree of molten tundish and determining whether to input the process.

4 is a flow chart illustrating a continuous casting method according to an embodiment of the present invention, and FIG. 5 is a correlation of short side lateral crack defects according to a deviation of superheat degree of tundish molten steel in a continuous casting method according to an embodiment of the present invention. It is a graph showing.

Referring to Figures 4 and 5, the continuous casting method according to an embodiment of the present invention is a first step of calculating the slab short side lateral crack occurrence index only with the difference in superheat, which is the difference between the actual measured temperature of molten tundish steel and the target temperature ( S10); And a second step (S20) of determining whether to input the slab after the continuous casting process from the calculated slab short side lateral crack generation index. Includes.

In the first step (S10) of the continuous casting method according to an embodiment of the present invention, the slab short side lateral crack generation index (Y) and the superheat deviation (X) are Y = 0.0058X ² + 2.0508X + 12.534 It can have a correlation (see Fig. 5).

The correlation may be satisfied under conditions in which mold level hunting by dynamic bulging and an oscillation mark can be formed. For example, the correlation may be satisfied under the condition that the carbon composition of molten steel is 0.08 to 0.14% by weight, and the molten steel casting speed is 1.2 to 1.5mpm.

In the continuous casting method according to an embodiment of the present invention, the difference between the actual measured temperature and the target temperature of molten tundish steel without the need to measure variables such as heat transfer amount, carbon equivalent, and cast thickness in calculating the slab short side lateral crack generation index. It is useful in actual operation because it is possible to calculate the index of occurrence of lateral cracking on the short side of the slab with only the deviation of phosphorus superheat.

On the other hand, the continuous casting method according to an embodiment of the present invention, in the second step (S20), when the slab short side lateral crack generation index is less than or equal to a preset value, it is classified as pass, and the slab is put into a subsequent process. It may further include a step (S50).

On the other hand, in the second step (S20), if the slab short side lateral crack generation index is greater than a preset value, it is classified as rejected, and the step of performing a surface grinding treatment on the slab (S30) and surface inspection and additional removal It may further include a step (S40).

So far, a continuous casting method according to an embodiment of the present invention has been described. The present invention discloses a high-quality slab manufacturing method for predicting in advance a short side lateral crack generating material according to the variation in superheat degree of molten tundish steel.

Dynamic bulging mold level hunting forms a deep oscillation mark, and when a deep oscillation mark is created, a problem occurs in which a horizontal crack is generated in the short side of the slab at the location of the oscillation mark. It is possible to produce high-quality slabs by predicting the correlation of short-side lateral crack defects according to the deviation and deciding whether to input the process.

It will be appreciated that the present invention includes not only the disclosed embodiments, but also various modifications and other equivalent embodiments that can be derived from the disclosed embodiments by those of ordinary skill in the art to which the technology pertains. Therefore, the technical protection scope of the present invention should be determined by the following claims.

10: molten steel
11: coagulation shell
12: strand
13: Casting
14: Tangmyeon
100: tundish
110: immersion nozzle
120: playing mold
130: guide roller
140: cooling nozzle
150: cutter

Claims (6)

A first step of calculating an index of occurrence of lateral cracks on a short side of a slab only with a deviation of superheat, which is a difference between the measured temperature of the molten tundish steel and the target temperature; And
A second step of determining whether to input the slab after continuous casting process from the calculated slab short side lateral crack generation index; Containing,
Continuous casting method. The method of claim 1,
The slab short side lateral crack generation index (Y) and the superheat deviation (X) have ^{a correlation of Y = 0.0058X 2} + 2.0508X + 12.534,
Continuous casting method. The method of claim 2,
The correlation is satisfied under the condition that the carbon composition of molten steel is 0.08 to 0.14% by weight, and the molten steel casting speed is 1.2 to 1.5mpm,
Continuous casting method. The method of claim 2,
The correlation is satisfied under conditions in which mold level hunting and oscillation marks can be formed by dynamic bulging,
Continuous casting method. The method of claim 1,
In the second step, when the slab short side lateral crack generation index is less than or equal to a preset value, further comprising the step of introducing the slab to the post-process,
Continuous casting method. The method of claim 1,
In the second step, when the slab short side lateral crack generation index is greater than a preset value, further comprising performing a surface grinding treatment on the slab,
Continuous casting method.

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