JP2006205239A - Method for continuous casting - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for continuous casting with which the improvement of working efficiency and the reduction of working cost can be obtained. <P>SOLUTION: When the steel is continuously cast by using a continuous caster provided with a mold 1 vibrated along the casting direction of molten steel, a tundish 2 and a mold powder loading device, the vibrating condition of the mold 1 is set up so as to satisfy a conditional formula π×f×S+¾Vc¾≤0.09, where f(cpm) is the number of vibrations in the mold, S(m) is the width of the vibration in the mold and Vc(m/s) is the casting velocity of the molten metal. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a continuous casting method used for high-speed casting, and is particularly applicable to medium carbon steel.

  As a continuous casting method conventionally used for continuous casting of medium carbon steel, for example, there is a method described in Patent Document 1. In this method, molten steel in the tundish is discharged into a mold whose lower end is closed by a dummy bar, the molten steel is cooled in the mold, a slab is formed, and the dummy bar is continuously pulled out from below the mold. This is a continuous casting method for casting a slab. When the molten steel is cooled in the mold, a solidified shell is formed on the surface of the molten steel cooled in the mold, and the solidified shell descends in the mold and increases its thickness.

In the process of casting the slab, the mold is melted by the heat of the molten steel by adding mold powder to the surface of the molten steel in the mold for the purpose of lubrication of the mold and the solidified shell, heat insulation of the molten steel in the mold, etc. Powder (hereinafter, referred to as molten powder) is caused to flow between the mold and the solidified shell, and a film of molten powder is formed between the mold and the solidified shell.
In such a continuous casting method, the inflow of molten powder between the mold and the solidified shell is promoted by vibrating the mold along the moving direction of the molten steel.
JP-A-10-109142

  In the continuous casting method described above, when the mold vibration condition is f (cpm), the mold vibration width is S (m), and the casting speed of the molten steel is Vc (m / s). In addition, it is often set to satisfy the conditional expression of π · f · S + | Vc |> 0.09. However, if the vibration condition of the mold is set so as to satisfy the condition of π · f · S + | Vc |> 0.09, the amount of molten powder flowing between the mold and the solidified shell is not stable, and the mold The film thickness of the molten powder formed between the solidified shell and the solidified shell becomes nonuniform. For this reason, the amount of heat removed from the solidified shell in the mold becomes non-uniform, and stress concentration due to the shrinkage of the solidified shell occurs in the solidified delay zone where the solidified shell layer is thin, causing damage such as vertical cracks on the slab surface. End up.

  If the surface of the slab is damaged, it is necessary to cool the slab and repair the damage with a grinder or sander before passing the slab to the next process such as rolling. Work costs will increase. Further, if a solidification delay portion is formed in the solidified shell, the solidification delay portion may be broken and the molten steel inside may leak (hereinafter referred to as breakout). When a breakout occurs in the slab, it is necessary to stop various apparatuses related to continuous casting, so that the working efficiency of continuous casting is reduced.

  The present invention has been made paying attention to the above-mentioned problems, and by optimizing the vibration conditions of the mold, the film thickness of the molten powder formed between the mold and the solidified shell is made uniform. Another object of the present invention is to provide a continuous casting method capable of making the amount of heat removed from the solidified shell in the mold uniform.

In order to solve the above-mentioned problem, the invention described in claim 1 of the present invention is a continuous casting method in which mold powder is added onto the molten steel surface in a mold that vibrates along the casting direction of the molten steel. Because
When the vibration frequency of the mold is f (cpm), the vibration width of the mold is S (m), and the casting speed of the molten steel is Vc (m / s),
This satisfies the conditional expression of π · f · S + | Vc | ≦ 0.09.
According to the present invention, by optimizing the vibration conditions of the mold, the amount of molten powder flowing between the mold and the solidified shell is stabilized, and the film thickness of the molten powder formed between the mold and the solidified shell is increased. Therefore, the heat removal amount of the solidified shell in the mold is made uniform.

Next, the invention described in claim 2 is the invention described in claim 1, characterized in that a casting speed of the molten steel is set to 2.0 m / min or more.
According to the present invention, the amount of molten powder flowing between the mold and the solidified shell by optimizing the vibration conditions of the mold in high-speed casting of steel with a casting speed of molten steel of 2.0 m / min or more. Since the film thickness of the molten powder formed between the mold and the solidified shell becomes uniform, the amount of heat removed from the solidified shell in the mold is made uniform.

Next, the invention described in claim 3 is the invention described in claim 1 or 2, wherein the composition of the cast slab is C: 0.07 to 0.18% by mass. It is characterized by this.
According to the present invention, in the continuous casting of medium carbon steel in which the composition of the slab is in the range of C: 0.07 to 0.18% by mass, by optimizing the vibration conditions of the mold, Since the amount of molten powder flowing in between is stabilized and the film thickness of the molten powder formed between the mold and the solidified shell becomes uniform, the amount of heat removed from the solidified shell in the mold is made uniform.

  According to the present invention, by optimizing the vibration conditions of the mold, the amount of heat removed from the solidified shell in the mold can be made uniform, and the occurrence of vertical cracks can be prevented. Can be reduced.

Next, embodiments of the present invention will be described with reference to the drawings.
In the present embodiment, as an example of continuous casting of steel, a case where high-speed casting of medium carbon steel is performed by a slab continuous casting machine will be described.
First, the configuration of the present embodiment will be described with reference to FIG.
As shown in FIG. 1, the slab continuous casting machine used in this embodiment includes a mold 1, a tundish 2, and a mold powder addition mechanism (not shown).
The mold 1 includes a pair of opposed long side mold plates 4a and 4b and a pair of opposed short side mold plates (not shown) sandwiched between the long side mold plates 4a and 4b. The mold 1 also has an oscillation mechanism (not shown) that vibrates the mold 1 along the casting direction of the molten steel 6.

  The pair of short side mold plates are both formed to be movable in a space formed between the long side mold plates 4a and 4b, and a slab having an arbitrary width according to the amount of movement of the pair of short side mold plates. Can be cast. The tip of an immersion nozzle 8 installed at the bottom of the tundish 2 is inserted into a rectangular space formed by the long side mold plates 4a and 4b and the pair of short side mold plates. A sliding nozzle 9 for opening and closing the immersion nozzle 8 is attached to the upper part of the immersion nozzle 8. Further, cooling water for cooling the molten steel circulates inside the long side mold plates 4a and 4b and the pair of short side mold plates.

The oscillation mechanism can set the vibration conditions of the mold 1 by setting the vibration width and frequency of the mold 1 to arbitrary values with respect to the casting speed of the molten steel 6. In this embodiment, the vibration conditions of the mold 1 are as follows: the vibration width of the mold 1 is S (m), the frequency of the mold 1 is f (cpm), and the casting speed of the molten steel 6 is Vc (m / s). Sometimes, it is set so as to satisfy the conditional expression of π · f · S + | Vc | ≦ 0.09. The oscillation waveform is preferably a sine wave.
The mold powder addition mechanism has a mechanism for adding mold powder 12 onto the molten steel surface 10 in the mold 1 when the molten steel 6 is discharged into the mold 1.

Next, the operation and effect of this embodiment will be described with reference to FIGS.
When the continuous casting of steel is started, as shown in FIG. 1, the molten steel 6 in the tundish 2 passes through the immersion nozzle 8 and is discharged into the mold 1 from the discharge hole provided at the tip of the immersion nozzle 8. At this time, the mold powder 12 is added onto the molten steel surface 10 in the mold 1 by the mold powder addition mechanism.
The molten steel 6 discharged into the mold 1 is cooled in the mold 1 to form a solidified shell 14 from the outside. The solidified shell 14 is continuously drawn downward and increases in thickness, eventually solidifying to the center, and a slab is cast.

The mold powder 12 receives heat from the molten steel 6, the molten steel 6 side is melted to become a molten powder 16, and the unmolten powder 18 remains thereon. The molten powder 16 flows between the mold 1 and the solidified shell 14 and forms a film of the molten powder 16 between the mold 1 and the solidified shell 14.
At this time, the casting condition of the mold 1 is set so as to satisfy the conditional expression of π · f · S + | Vc | ≦ 0.09 in accordance with the casting speed Vc of the molten steel 6. Based on this, it vibrates along the casting direction of the molten steel 6. For this reason, the inflow amount of the molten powder 16 between the mold 1 and the solidified shell 14 is stabilized, the film thickness of the molten powder 16 formed between the mold 1 and the solidified shell 14 becomes uniform, and the inside of the mold 1 The amount of heat removed from the solidified shell 14 is made uniform.

Here, with reference to FIG. 2, when the slab is cast by the continuous casting machine set to the vibration conditions of the conventional and the present embodiment, the occurrence frequency of vertical cracks generated in the slab and π · f · S + | Vc | The relationship is shown. Conventional vibration conditions are as follows: vibration width S is 6 mm, frequency f is 160 cpm, casting speed Vc is 2.5 m / min, and the conditional expression of π · f · S + | Vc |> 0.09 is satisfied. It is set to be. The vibration conditions of this embodiment are as follows: the vibration width S is 5 mm, the frequency f is 190 cpm, and the casting speed Vc is 2.5 m / min, and π · f · S + | Vc | ≦ 0.09. It is set to satisfy the conditional expression.
FIG. 3 shows the relationship between the copper plate temperature change and π · f · S + | Vc | when the slab is cast by the continuous casting machine set to the vibration conditions of the conventional and this embodiment.

As shown in FIGS. 2 and 3, in the continuous casting machine set to the conventional vibration condition, the amount of change in the copper plate temperature is large, and the amount of heat removal on the slab surface is not uniform. On the other hand, in the continuous casting machine set to the vibration conditions of the present embodiment, the amount of change in the copper plate temperature is small, and the amount of heat removal on the slab surface is uniform, so the frequency of occurrence of vertical cracks occurring in the slab is reduced. .
Moreover, with reference to FIG. 4, using the slab continuous casting machine which has the structure similar to what is shown in FIG. 1, three types of test | inspection slabs from which a composition differs are cast, A vertical crack is carried out with respect to these test | inspection slabs. The result of having compared the incidence is shown. In addition, the vertical crack occurrence frequency shown on the vertical axis | shaft in a figure was computed from the following formula | equation (1).

In casting the inspection slab, two types of vibration conditions were set: a vibration condition of the present embodiment indicated by ● in the figure and a conventional vibration condition indicated by Δ in the figure. The vibration condition of this embodiment is set so as to satisfy the conditional expression of π · f · S + | Vc | ≦ 0.09, and the conventional vibration condition is π · f · S + | Vc |> 0. It is set so as to satisfy the conditional expression 09.
Moreover, the composition of three types of test | inspection slabs from which a composition differs is C: 0.07-0.09 mass%, C: 0.10-0.13 mass%, C: 0.14-0.18 mass%, respectively. It has become.

As shown in FIG. 4, the inspection slab cast by the continuous casting machine set to the vibration condition of the present embodiment is longer than the inspection slab cast by the continuous casting machine set to the conventional vibration condition. The cracking incidence is decreasing.
Therefore, according to the continuous casting method of the present embodiment, the amount of heat removed from the solidified shell in the mold is made uniform, and the occurrence of vertical cracks is prevented, so that the quality can be improved and the operation cost can be reduced. It is particularly suitable for high-speed casting with a casting speed of 2.0 m / min or more, and also suitable for casting medium carbon steel whose composition is in the range of C: 0.07 to 0.18 mass%.

It is a figure which shows the structure of this embodiment. It is a figure which shows the relationship between (pi) * f * S + | Vc | and generation | occurrence | production of a vertical crack. It is a comparison figure which shows the copper plate temperature variation | change_quantity in the vibration conditions of a prior art example and this embodiment. It is a comparison figure which shows the vertical crack incidence rate of a test | inspection slab.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Mold 2 Tundish 4 Long side mold plate 6 Molten steel 8 Immersion nozzle 9 Sliding nozzle 10 Molten steel surface 12 Mold powder 14 Solidified shell 16 Molten powder 18 Unmelted powder

Claims (3)

A continuous casting method of adding mold powder on the molten steel surface in a mold that vibrates along the casting direction of the molten steel,
When the vibration frequency of the mold is f (cpm), the vibration width of the mold is S (m), and the casting speed of the molten steel is Vc (m / s),
A continuous casting method characterized by satisfying a conditional expression of π · f · S + | Vc | ≦ 0.09.   The continuous casting method according to claim 1, wherein a casting speed of the molten steel is set to 2.0 m / min or more.   The continuous casting method according to claim 1 or 2, wherein the composition of the cast slab is C: 0.07 to 0.18% by mass.

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