JP2891307B2 - Steel continuous casting method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a casting method for continuous casting of steel, which is capable of producing a slab of excellent product quality after rolling while simultaneously preventing blockage of an immersion nozzle and erosion of the inner wall of the nozzle. A continuous casting method.

[0002]

2. Description of the Related Art In continuous casting, when molten steel 6 is injected from an immersion nozzle 4 via an upper nozzle 3 between a tundish 2 and a mold 5 shown in FIG. Inert gas is blown in the direction of the arrow from one or a plurality of locations of No. 4, alumina precipitated from the molten steel or adhered alumina grows on the inner wall of the immersion nozzle and other refractory interfaces in contact with the molten steel, and the molten steel flow path in the nozzle Is suppressed.

[0003]

Blowing an inert gas into a molten steel injection flow is generally performed for the purpose of preventing blockage of a submerged nozzle and removing inclusions from the molten steel.

However, if the flow rate is not appropriate, the effect of preventing clogging of the immersion nozzle cannot be sufficiently obtained, and abnormal melting of the nozzle may be caused to hinder the casting operation or supply of molten steel into the mold may be disturbed. Due to the effects of
There is a problem that the quality of the obtained steel is rather deteriorated.

[0005] The present invention provides a continuous casting method for steel that advantageously solves the above-mentioned problems.

[0006]

According to a first aspect of the present invention, there is provided a method of pouring a tundish from a tundish into a mold in continuous casting of steel, comprising a tundish stopper, an upper nozzle, a plate for a sliding nozzle, and an intermediate nozzle. The relationship between the flow rate of the inert gas blown from one or a plurality of refractories of the immersion nozzle and the flow rate of the molten steel is, for a curved continuous caster, an inert gas blowing flow rate Qg.
(Nl / min) and a flow rate of molten steel passing through the nozzle Qs (t / min), which is in a range indicated by the following formulas 1, 2, 3, and 4, which is a continuous casting method for steel.

[0007]

## EQU1 ## Qg> 12 (N 1 / min)

[0008]

## EQU2 ## Qg ≦ 20 ( N 1 / min)

[0009]

## EQU3 ## Qs + 0.04Q g ≧ 1 . 5

[0010]

## EQU4 ## Qs + 0.04Q g ≦ 6 . 0

According to a second aspect of the present invention, there is provided a method for pouring a tundish into a mold in continuous casting of steel, the method comprising: a tundish stopper, an upper nozzle, a plate for a sliding nozzle, an intermediate nozzle, and an immersion nozzle. The relationship between the flow rate of the inert gas blown from one or a plurality of refractories and the flow rate of the molten steel indicates that the inert gas injection flow rate Qg (Nl /
Min) and the flow rate Qs (t / min) of the molten steel passing through the nozzle is in a region indicated by the following Expressions 5, 6, 7, and 8, which is a continuous casting method for steel.

[0012]

## EQU5 ## Qg> 12 (N 1 / min)

[0013]

## EQU6 ## Qg ≦ 30 ( N 1 / min)

[0014]

## EQU7 ## Qs + 0.04Q g ≧ 1 . 5

[0015]

## EQU8 ## Qs + 0.04Q g ≦ 6 . 0

[0016]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of the present invention;

FIG. 1 shows an embodiment of the present invention. That is, in this embodiment, the tundish 2 and the mold 5 used in the continuous casting are used.
When the molten steel 6 is injected from the immersion nozzle 4 through the upper nozzle 3 between the stopper 1, the upper nozzle 3 and the immersion nozzle 4
Inert gas is blown in the direction of the arrow from one or more locations, and alumina precipitated from the molten steel or adhered alumina grows on the refractory interface in contact with the inner wall of the immersion nozzle and other molten steel, and the molten steel flow path in the nozzle Is suppressed.

If alumina adheres to the nozzle, the nozzle will eventually become blocked during casting, making it impossible to continue casting. If it occurs suddenly, the molten steel may leak from under the mold, or the nozzle may pass through the nozzle. The flow of the molten steel supplied into the mold is disturbed, deteriorating the quality of the cast slab.
Accordingly, the present invention can improve the productivity of continuous casting and improve the quality of a cast product by preventing or suppressing the adhesion of alumina in the nozzle.

A feature of the present invention is to provide conditions for the blowing of an inert gas and the casting speed which are most effective for suppressing or preventing the adhesion and precipitation of alumina at the refractory interface. In other words, the characteristic effects of the present invention are expected at the molten steel flow channel interface in the refractory located downstream of the flow of the molten steel from the location and the location where the inert gas is blown.

In the injection apparatus to which the present invention is applied, the flow rate of molten steel may be controlled by a stopper or by a sliding nozzle, and similar effects are expected by applying the present invention.

The refractory material of the injection system including the immersion nozzle used in the present invention may be any of alumina graphite, magnesia carbon, rholite, and zirconia and lime as main components. Similar effects can be obtained by applying the present invention.

FIG. 2 shows the relationship between the flow rate of the inert gas that satisfies both the prevention of clogging and the prevention of erosion of the immersion nozzle, and the flow rate of molten steel passing through the nozzle. In the figure, (a) shows a limit line of alumina attachment on the inner wall of the nozzle, and the region (a) side sandwiching this line is an area where alumina adheres and the nozzle is closed. The region (b) is a region in which no alumina adheres and the nozzle is hardly clogged.

In the figure, (b) shows a limit line at which the inner wall of the nozzle is melted, and the region (b) is a region where there is no erosion of the inner wall of the nozzle, and the region (c) is the nozzle inner wall. Is an area where erosion occurs. That is, the region (b) represents an operation condition suitable for performing continuous casting in which the nozzle is not blocked by the alumina and the nozzle is not melted.

[0024] in the figure (a) and (b), an inert gas blowing flow rate Qg (N l / min) and passed through the nozzle molten steel flow rate Qs (t / min) to a variable number of below 9, the number It is represented by 10.

[0025]

## EQU9 ## Line (a)... Qs (t / min) + 0.04Q
g (N l / min) = 1.5

[0026]

[Number 10] lines (b) ·· Qs (t / min) + 0.04Qg (N l / min) = 6.0

Therefore, a region (b) which is a preferable operating condition for performing the continuous casting is represented by the following equation (11).

[0028]

Equation 11] Qs (t / min) + 0.04Qg (N l / min) ≦ 6.0 and Qs (t / min) + 0.04Qg (N l / min) ≧ 1.5 where, Qs (t / min )> 0, Qg ( N 1 / min)> 0.

Although this condition has been confirmed by actual casting, it has been confirmed by the concept and experimental facts described below with reference to FIGS.

FIG. 3 shows the relationship between the shear force S acting on the interface between the inner wall of the nozzle and the molten steel and the function F. The function F is Qs + 0.
It is represented by 04Qg. In the figure, (c) shows the relationship between the shear force S acting on the interface between the inner wall of the nozzle and the molten steel and the function F. (D)
Indicates the lower limit of the shearing force required to separate the adhered alumina from the inner wall of the nozzle.

The shear force S increases as the function F increases. Because, as the flow rate of molten steel passing through the nozzle and the amount of inert gas bubbles increase, the flow velocity of molten steel near the inner wall of the nozzle increases, the relative velocity between molten steel and refractory near the interface increases, This is because the shearing force due to the viscosity increases.

Accordingly, the alumina deposited or adhered to the inner wall of the nozzle tends to be separated from the wall by the shearing force. When the shearing force exceeds a certain level, the alumina finally separates from the wall of the refractory, and the limiting shearing force is (c). Point B is F at the intersection of line (c) and line (d).
Indicates a value. (B) in the figure indicates the range of F ≧ B, which is a region where alumina does not adhere. (A) shows a range of F <B, which is a region where alumina adheres.

According to the above concept, when such a value of B was examined by an actual casting test, it was found that B = 1.5 as shown in FIG. That is, the condition that alumina does not adhere is Qs + 0.04Qg ≧ 1.5
It is.

FIG. 4 shows the relationship between the nozzle inner wall erosion rate and the function F, and the relationship between the alumina deposition rate and the function F. The function F is represented by Qs + 0.04Qg. In the figure, (e) shows the relationship between the nozzle inner wall melting speed and the function F.
(F) is the relationship between the alumina deposition rate and the function F.

The nozzle inner wall erosion rate increases as the function F increases. Because, as the flow rate of molten steel passing through the nozzle and the amount of inert gas bubbles increase, the rate of supply of heat to the refractory interface increases, the reaction between the molten steel and the refractory is promoted, and the reaction products are reduced. This is because the above-mentioned shearing force facilitates washing away.

On the other hand, the alumina deposition rate also increases as the function F increases. Because, as the flow rate of molten steel passing through the nozzle and the amount of inert gas bubbles increase, the frequency of collision of alumina in the molten steel with the interface of the refractory increases, making it easier for the molten layer formed at the interface of the refractory to be trapped in the molten layer. Alternatively, the alumina itself causes a sintering reaction with the refractory interface, so that the alumina easily adheres.

However, if the function F is increased to a certain degree or more, the contact time at the time of collision with the refractory interface does not take a sufficient time to react.

In a region where the result function F is equal to or larger than a certain value,
Since the nozzle inner wall erosion rate exceeds the alumina deposition rate and the thickness of the refractory gradually decreases over time,
Stable continuous casting cannot be performed. Such a limit value of F is represented by an intersection A between the line (e) and the line (f). (B) in the figure indicates a range of F ≦ A, and is a region where the erosion of the inner wall of the nozzle does not progress. (C) shows the range of F> A, in which the melting of the inner wall of the nozzle progresses and stable casting cannot be performed.

According to such a concept, when such a value of A was examined by an actual casting test, it was found that A = 6 as shown in FIG. That is, the condition that the nozzle does not melt is Qs + 0.04Qg ≦ 6.

From the above, the region (b) which is a suitable operating condition for performing the continuous casting is expressed by the following equation (12).

[0041]

Equation 12] Qs (t / min) + 0.04Qg (N l / min) ≦ 6.0 and Qs (t / min) + 0.04Qg (N l / min) ≧ 1.5 However, Qs (t / min )> 0, Qg (N l / min)> 0.

FIG. 5 shows the influence of the flow rate of the blown inert gas on the inconsistency rate of the surface defects of the rolled product.

As a result of investigation on the case of the vertical bending continuous caster and the case of the curved continuous caster, it was found that the quality of the rolled product tends to deteriorate when the flow rate of the inert gas exceeds a certain value. This phenomenon can be explained as follows.

That is, the injected inert gas reaches the inside of the mold through the immersion nozzle and floats in the mold. As the gas flow rate increases, the force for stirring the interface between the molten steel and the powder in the mold increases. As a result, the powder is involved in the meniscus where the molten steel starts to solidify,
It is considered that the frequency of generation of surface flaws and the trapping of Ar gas at the solidified shell interface during the ascent is increased, and a bubble-like defect including inclusions is generated immediately below the surface layer of the slab.

In the case of a vertical bending continuous caster, the quality deteriorates remarkably when the flow rate of the inert gas exceeds 30 (Nl / min). If the gas flow rate exceeds 20 (Nl / min), the deterioration of quality becomes remarkable. The reason that the vertical bending caster begins to deteriorate in quality is that the Ar flow rate is lower than that of the curved continuous caster because of the vertical portion, the Ar gas easily floats and the frequency of being captured at the solidified shell interface is low. Probably because it is relatively small.

As described above, the Ar gas flow rate is an important operating condition that affects product quality, and there is an appropriate flow rate range in terms of quality. That is, the Ar gas blowing flow rate is set to 20 (Nl / min) or less in the case of the curved continuous caster, and 30 (Nl / min) in the case of the vertical bending type continuous caster or the vertical type continuous caster.
/ Min) is effective for obtaining good product quality.

According to the present invention, the flow rate of molten steel passing through the nozzle and the inert gas in consideration of the above-described conditions for preventing clogging and erosion of the immersion nozzle, and conditions for blowing an inert gas to obtain good product quality are considered. This is to give an appropriate operation range in relation to the blowing flow rate, and this is shown in FIG.

In FIG. 6, the lines (a) and (b) are represented by the following equations 13 and 14, respectively.

[0049]

[Number 13] line (a): Qs (t / min) + 0.04Qg (N l / min) = 1.5

[0050]

[Number 14] lines (b): Qs (t / min) + 0.04Qg (N l / min) = 6.0

Further, the line (g) and the line (h) are expressed by the following equations 15 and 16, respectively.

[0052]

[Number 15] line (g): Qg = 20 ( N l / min)

[0053]

[Number 16] line (h): Qg = 30 ( N l / min)

(A) is a range surrounded by the lines (a), (b), (g) and the vertical axis, and (B) is a range surrounded by the lines (a),
This is a range surrounded by the line (b), the line (g), and the line (h). In FIG. 6, the proper operating conditions aimed at by the present invention for the curved continuous casting machine are represented by (A), and the proper operating conditions aimed at by the present invention for the continuous casting machine having a vertical portion are (A) and (A). B).

[0055]

According to the present invention, when the molten steel is injected from the tundish into the mold, the relationship between the molten steel injection flow rate and the inert gas flow rate blown into the molten steel injection flow is limited to a certain range, thereby preventing the immersion nozzle from being clogged by alumina. And a stable casting state without erosion of the immersion nozzle,
It is possible to manufacture cast pieces with less product quality defects after rolling, and it is possible to stabilize the operation of continuous casting and improve the quality of cast pieces.

[Brief description of the drawings]

FIG. 1 is a detailed sectional view showing an operation near an immersion nozzle of a continuous casting machine.

FIG. 2 is a diagram showing a relationship between an inert gas blowing flow rate and a flow rate of molten steel passing through an immersion nozzle.

FIG. 3 is a drawing showing a relationship between a shear force acting on an interface between a nozzle inner wall and molten steel and a function F (Qs, Qg).

FIG. 4 is a drawing showing a relationship between a nozzle inner wall melting speed, a function F, and an alumina deposition speed.

FIG. 5 is a drawing showing the effect of the flow rate of the inert gas blown on the unsatisfactory ratio of the surface defects of the rolled product.

FIG. 6 is a drawing showing a relationship between an inert gas blowing flow rate and a flow rate of molten steel passing through an immersion nozzle, showing a proper operation range.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Stopper 2 Tundish 3 Upper nozzle 4 Immersion nozzle 5 Mold 6 Molten steel

 ──────────────────────────────────────────────────の Continued on front page (72) Inventor Yasuo Maruki 1 Kimitsu, Kimitsu City, Chiba Prefecture Inside Nippon Steel Corporation Kimitsu Works (72) Inventor Shigeaki Ogibayashi 1 Kimitsu 1, Kimitsu City, Chiba Prefecture Nippon Steel Corporation Company Kimitsu Works (56) References JP-A-2-247052 (JP, A) JP-B-63-58668 (JP, B2)

Claims (2)

(57) [Claims] 1. A method of pouring a tundish into a mold in continuous casting of steel, wherein one or more of a tundish stopper, an upper nozzle, a plate for a sliding nozzle, an intermediate nozzle, and a dipping nozzle are provided. The relationship between the flow rate of the inert gas blown from the refractory and the flow rate of the molten steel depends on the flow rate of the inert gas Qg (Nl / min) and the flow rate of the molten steel passing through the nozzle Qs (t). / Min) in relation to
A continuous casting method for steel, wherein the method is located in a region indicated by 4. Qg> 12 (N 1 / min) Qg ≦ 20 ( N 1 / min) Qs + 0.04 Qg ≧ 1.5 Qs + 0.04 Qg ≦ 6.0 2. A method for pouring a tundish from a tundish into a mold in continuous casting of steel, wherein one or more of a tundish stopper, an upper nozzle, a plate for a sliding nozzle, an intermediate nozzle, and a dipping nozzle are provided. The relationship between the flow rate of the inert gas blown from the refractory and the flow rate of the molten steel is such that, for a continuous caster having a vertical portion, the flow rate of the inert gas Qg (Nl / min) and the flow rate of the molten steel passing through the nozzle Qs the following number 5 in relation to the (t / min),
A continuous casting method for steel, wherein the method is in an area indicated by 6 , 7 , or 8 . Qg> 12 (N 1 / min) Qg ≦ 30 ( N 1 / min) Qs + 0.04 Qg ≧ 1.5 Qs + 0.04 Qg ≦ 6.0