JP3383630B2 - Powder for continuous casting of B-containing steel and 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 powder used for continuous casting of B-containing steel, and more particularly, to surface defects of a slab and instability of casting operation caused by a change with time during casting of molten powder. The present invention relates to a powder for continuous casting for preventing the above and a continuous casting method using the powder.

[0002]

2. Description of the Related Art In continuous casting of steel, in order to maintain the lubricity between the mold and the slab and keep the surface quality of the slab good, the powder for continuous casting is melted and melted in the mold. Generally, the operation is performed while injecting powder (molten powder) in a state between the mold and the slab. The components of such powder for continuous casting are generally CaO and SiO.
Those containing ₂ as the main component are used. However, when B-containing steel (mainly B-containing stainless steel) is continuously cast using this continuous casting powder, SiO ₂ in the molten powder reacts with B in the molten steel as shown in equation (1), and the molten powder The B ₂ O ₃ concentration in the inside increases, and the SiO ₂ concentration decreases. 4 [B] · 3 (SiO ₂ ) = 2 (B ₂ O ₃ ) +3 [Si] (1) However, [B]: B content (%) in molten steel (SiO ₂ ): in molten powder Content of SiO ₂ (%) (B ₂ O ₃ ): B ₂ O ₃ content of molten powder (%) [Si]: Si content of molten steel (%)

For this reason, the melting point and the viscosity of the molten powder are remarkably lowered during the operation of continuous casting, causing non-uniform excessive inflow of the molten powder between the mold and the slab, resulting in a dent defect on the slab surface. There was a problem that cracks and cracks were generated and the slab care yield was deteriorated. In addition, such a change in the characteristics of the molten powder causes problems such as breakout during operation and lowers productivity. By the way, some proposals have been made so far to deal with the above-mentioned problems in continuous casting of B-containing steel. For example, JP-A-2-155547 and JP 8-141712, the continuous casting powder CaO and SiO ₂ as a main component, pre-B ₂ O ₃ to be contained 5 to 30 wt% Discloses a technique of suppressing the reaction of the formula (1) to reduce changes in the melting point and viscosity of the molten powder during operation. In addition, JP-A-8
No. 309483 gazette, by defining the melting point of the powder for continuous casting, the casting temperature, the casting speed, the oscillation conditions, etc., by preventing the uneven inflow of the molten powder, the slab surface quality and casting A technique for improving the sex is shown.

[0004]

However, although the above-mentioned prior art can improve the deterioration of the surface quality of the slab of B-containing steel and the operational trouble to some extent, it is said that it is still not complete as a preventive measure against these problems. It was difficult. That is, under the conventional continuous casting powder having a relatively low value of CaO / SiO ₂ as a main component, even if B ₂ O ₃ is contained in advance, the molten powder produced by the reaction of the formula (1) during the operation. It was not possible to sufficiently suppress the changes in the viscosity and the melting point. In addition, the reaction of equation (1) occurs during the continuous casting operation in the first place, so it is difficult to grasp the progress of this reaction instantaneously during the operation, and therefore the continuous casting powder that changes momentarily during the continuous casting operation. It is difficult and not realistic to appropriately set the optimum casting temperature, casting speed, oscillation conditions, etc. for the melting point of

The present invention proposes a technique for solving the above-mentioned problems of the prior art, and prevents operational troubles such as surface defects and breakouts of continuously cast slabs, and enables casting. An object of the present invention is to provide a powder for continuous casting of B-containing steel and a continuous casting method using this powder for producing a slab having excellent surface properties throughout the entire operation without causing troubles in casting. And Another object of the present invention is to develop a powder for continuous casting in which the physical properties of the powder, particularly the viscosity and melting point, hardly change over the entire period of the continuous casting operation.

[0006]

SUMMARY OF THE INVENTION The inventors of the present invention have found that, during the entire period from the start to the end of continuous casting, the physical properties (melting point and viscosity) of the molten powder during continuous casting of B-containing steel and the continuous casting As a result of detailed observation of the relationship with the constituent components of the powder, CaO / SiO ₂ which has never been tried before
It has been found that particularly good casting can be performed in a high range and the surface quality of the slab is also good. The gist composition of the present invention completed based on such knowledge is as follows. (1) A continuous casting powder for continuously casting molten steel containing B in an amount of 0.1% or more by weight (hereinafter simply referred to as%).
And CaO and SiO ₂ are CaO + SiO ₂ : 35-70%,
And CaO / SiO _2: with including 3.0 or more ranges, Al
₂ O ₃ : 15-30% and B ₂ O ₃ : 5-30%,
Melting point: 950-1250 ° C, viscosity at 1300 ° C: 0.8-
A powder for continuous casting of B-containing steel, which has characteristics of 3.0 poise.

(2) Using continuous casting powder, add B to 0.1
 % When continuously casting molten steel containing
As a powder for casting, in% by weight, CaO and SiO_TwoTo
CaO + SiO_Two: 35-70% and CaO / SiO_Two: 3.0 or more
In addition to including in the range of Al_TwoO _Three: 15-30% and B_Two
O_Three: Melting point: 950-1250 ° C, 1300
Viscosity at ℃: Pow with characteristics of 0.8-3.0 poise
Continuous casting method for B-containing steel characterized by using a dar
Law.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The inventors investigated the causes of deterioration of the surface quality of slabs of B-containing steel and difficulty in casting. It was confirmed that it was due to change. That is, in the continuous casting of B-containing steel, the reaction in the formula (1) proceeds to the right, so that B in the molten steel reduces SiO ₂ in the molten powder, and SiO ₂ in the molten powder is reduced.
And the B ₂ O ₃ increase, the melting point and viscosity of the molten powder decrease significantly. For this reason, it becomes difficult to maintain good physical property values throughout the continuous casting operation, resulting in uneven and excessive inflow of molten powder, causing surface defects such as dents and cracks on the slab surface, and breakout. It is easy to cause operational troubles such as.

FIGS. 1 and 2 show changes in the composition of the molten powder when B-containing steel is continuously cast using a continuous casting powder that has been conventionally used. The continuous casting powder A contains CaO and SiO ₂ as main components, and the continuous casting powder B contains B ₂ O ₃ in addition to CaO and SiO ₂ . In FIGS. 1 and 2, for both powders A and B, B ₂ O ₃ in the molten powder sharply rises within 10 minutes from the start of casting,
SiO ₂ is rapidly decreasing. During this time, changes in the melting point and the viscosity of the powder are significantly reduced as represented by the powder B. Powder B is prepared by adding B ₂ O ₃ to the powder in advance in order to suppress the progress of the reaction of the formula (1). However, as shown in FIGS.
The reaction of equation (1) cannot be completely suppressed. The reason why such a phenomenon is brought about is that when B ₂ O ₃ is added, the melting point and viscosity of the powder are lowered,
In order to maintain the melting point and the viscosity appropriately, it is necessary to adjust the amounts of Na and F, CaO / SiO _2, etc., and therefore, the reaction of the reaction of the formula (1) is suppressed from proceeding to the right. It is thought that the balance of the ingredients in the powder, which is necessary for, is lost.

As described above, when the conventional continuous casting powder containing CaO and SiO ₂ as the main components is used, even if B ₂ O ₃ is contained in advance, (1)
It is not possible to completely suppress the changes in the viscosity and melting point of the molten powder due to the reaction of the equation. Therefore, the present inventors have proposed a continuous casting powder capable of stable continuous casting with almost no reaction between B and powder in molten steel.
Many experiments were conducted and examined. As a result, the content of SiO ₂ which causes the reaction of the formula (1) is sufficiently reduced so that the value of CaO / SiO ₂ (weight% ratio) is 3.0 or more, preferably 5.0 or more It was found that changes in the viscosity and melting point of the molten powder due to the reaction of equation (1) can be suppressed. At this time, it is also necessary to set the total content of CaO and SiO ₂ (CaO + SiO ₂ ) in the range of 35 to 70%. This is because if the amount is less than 35%, it becomes difficult to adjust the melting point and viscosity of the molten powder, and appropriate physical properties cannot be obtained. On the other hand, if it exceeds 70%, the powder has a too high melting point, which may cause insufficient inflow of the molten powder.

In this way, continuous casting with properly adjusted components
The powder for use is SiO 2 so that the reaction of formula (1) can be suppressed._Two
The content is low enough that it is a molten powder during operation.
The viscosity and melting point of the
This may cause deterioration of the surface properties of the slab and operational troubles.
It is possible to prevent uneven inflow of molten powder.
is there. CaO / SiO_TwoIn the above range and CaO
＋ SiO_TwoEven if you set the
SiO_TwoThere is a slight possibility that it will react with the powder,
In the present invention, B_TwoO_Three5-30 in powder beforehand
% Contained. B_TwoO _ThreeWhen is less than 5%, it is necessary to suppress equation (1).
Not effective, while containing more than 30% pow
Melting point and viscosity are extremely low
The surface quality of the cast slab is deteriorated due to the excessive inflow of aluminum.
In addition, B_TwoO_ThreeThe preferred content of is 5 to 25%.

The continuous casting powder of the present invention has the above-mentioned composition.
CaO, SiO_Two, B_TwoO_ThreeIn addition to Al_TwoO_Threeincluding
It is also necessary. This Al_TwoO_ThreeContent of less than 15%
Is difficult to adjust the melting point and viscosity of the powder.
Physical property values cannot be obtained. If the content exceeds 30%, the powder will melt
Insufficient inflow of molten powder due to too high point and viscosity
This will cause a breakout due to_TwoO_Three
The content should be in the range of 15-30%. CaO and SiO mentioned above_Two,
B_TwoO_ThreeAnd Al_TwoO_ThreeIn addition to the main component consisting of Zr
O_Two , TiO_Two, Na, F, C selected from
Is preferably contained in an amount of 5 to 50%. Well
In addition, Fe inevitably enters from the raw materials that are the source of these
O, MnO, MgO, etc. may be contained as impurities.

Further, the inventors have also examined appropriate physical property values of powder when continuously casting B-containing steel.
As a result, the melting point and viscosity of the powder for continuous casting are respectively melting point: 950 ° C to 1250 ° C, and viscosity at 1300 ° C:
It is often in the range of 0.8 poise to 3.0 poise, and it became clear that the powder of the present invention satisfies these physical property values. If the melting point of the molten powder is lower than 950 ° C or the viscosity at 1300 ° C is lower than 0.8 poise, the amount of molten powder inflow between the mold and the slab will be extremely large and uneven overflow will occur. Because it will wake up,
The surface quality of the slab deteriorates, and the slab's maintenance yield deteriorates. On the other hand, the melting point becomes a high melting point exceeding 1250 ° C, 13
If the viscosity at 00 ° C is higher than 3.0 poise, the flow rate of the molten powder between the mold and the slab will be extremely small, and the lubrication between the mold and the slab will be insufficient. Cause operational problems and significantly reduce productivity. From this, in order to properly control the inflow amount of the molten powder, the melting point of the powder for continuous casting is 950 to 1250 ° C, and the viscosity at 1300 ° C is
0.8 to 3.0 poise, and the preferable range of these physical properties is as follows: Melting point: 1000 to 1200 ° C, viscosity at 1300 ° C:
It is 1.0 to 3.0 poise.

[0014] Figures 5 and 6, powder for continuous casting according to the present invention _{(CaO + SiO 2: 43.0%} , CaO / Si
_{O 2: 7.4, Al 2 O} 3: 24.0%, B 2 O 3: 16.0%, N
a: 8.0%, F: 2.0%, melting point: 1100 ° C., viscosity at 1300 ° C .: 1.8 poise), when B-containing steel was continuously cast, the amount of B ₂ O ₃ and SiO _{2 in the} powder respectively It shows the change. As is clear from FIGS. 5 and 6, the powder of the present invention shows almost no changes in these compositions throughout the entire continuous casting operation. From this it is shown that continuous casting using the powder of the present invention can suppress changes in the viscosity and melting point of the molten powder during operation, maintain proper powder physical property values, and enable stable casting. .

[0015]

Example Using various powders for continuous casting having different compositions and physical properties, B-containing steel was continuously cast under the conditions shown in Table 1. The physical properties of the molten powder before and after the casting are measured, and the casting results and the maintenance yield for removing defects on the surface of the slab are also shown. The viscosity is a value measured at 1300 ° C. by the coaxial double rotation cylinder method, and the melting point is measured largely by the coaxial double rotation cylinder method at each temperature. The deviating point is obtained as the melting point.

[0016]

[Table 1]

[0017]

[Table 2]

From Table 2, using the powder of the present invention, B
When the contained steel is continuously cast, changes in the viscosity and melting point of the molten powder can be suppressed almost completely, and it is possible to operate with proper powder physical properties throughout the entire casting period, and the castability is good. The maintenance yield was 96% or more, and very good results were obtained. On the other hand, CaO and SiO
_In a comparative example cast using a conventional continuous casting powder containing _{2 as a} main component or B ₂ O ₃ in addition to these main components, a molten powder produced by the reaction of the formula (1) during operation. It was not possible to completely suppress the change in viscosity and melting point, and as a result, it was unavoidable that the physical properties of the powder largely deviated from the range of the present invention, and the maintenance yield of the slab decreased. In Comparative Example 7, a conventional continuous casting powder containing B ₂ O ₃ in addition to the main components of CaO and SiO ₂ was used, and changes in the viscosity and melting point of the molten powder could be substantially suppressed. Nevertheless, the viscosity at 1300 ° C was too high, causing breakout due to poor lubrication. In Comparative Example 2, the melting point and the viscosity were excessively low, so that an extremely nonuniform inflow was caused, a breakout occurred from a portion where the solidification of the steel was delayed, and the casting was stopped. As described above, in the conventional continuous casting powder, it is difficult to predict the degree of change in viscosity and melting point of the molten powder during casting, and it is difficult to properly control the inflow amount of the molten powder.

[0019]

As described above, according to the present invention,
B ₂ O ₃ in molten powder in continuous casting of B-containing steel
It is possible to almost completely prevent the change of the melting point and the viscosity of the molten powder due to the increase of the temperature and the decrease of SiO ₂ , to properly control the inflow amount of the molten powder, and to prevent the excessive inflow and the insufficient inflow of the powder. become able to. Therefore, according to the present invention, it is possible to prevent the occurrence of slab surface defects caused by changes in the physical properties of the molten powder during the casting period, and improve the maintenance yield. In addition, operational troubles such as breakout due to poor lubrication of the molten powder can be prevented.

[Brief description of drawings]

The [1] CaO and SiO ₂ as main components, or even using a conventional continuous casting powder containing B ₂ O _3, in the case of the B containing steel was continuously cast, B ₂ O in the molten powder It is the figure which showed the change of ₃ content.

The [2] CaO and SiO ₂ as a main component, or by using the conventional continuous casting powder further contains B ₂ O _3, in the case of the B containing steel was continuously cast, SiO ₂ content in the molten powder It is the figure which showed the change of quantity.

FIG. 3 shows the melting powder of B-containing steel continuously cast by using a conventional continuous casting powder containing CaO and SiO ₂ as main components or further containing B ₂ O ₃ .
It is a figure showing a change in viscosity at 1300 ° C.

FIG. 4 shows the change in melting point of molten powder when B-containing steel is continuously cast by using a conventional continuous casting powder containing CaO and SiO ₂ as main components or further containing B ₂ O _3. It is the figure shown.

FIG. 5: Using a continuous casting powder according to the invention,
B _{2 in} molten powder when B-containing steel is continuously cast
O ₃ is a view showing a change in content.

FIG. 6: Using a powder for continuous casting according to the invention,
SiO in molten powder when B-containing steel is continuously cast
It is the figure which showed the change of ₂ content.

[FIG. 7] Using continuous casting powders having different physical properties,
It is the figure which showed the relationship between the powder physical property value after casting and the maintenance yield of a slab in the case of continuously casting B containing steel.

Front page continuation (72) Inventor Atsushi Hongo 4-2 Kojima-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa Nihon Yakin Kogyo Co., Ltd. Kawasaki Plant (56) Reference JP-A-2-155547 (JP, A) JP-A 11-309548 (JP, A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) B22D 11/108 B22D 11/00 B22D 11/111 B22D 11/07 C21C 7/076

Claims (2)

(57) [Claims] 1. A continuous casting powder for continuously casting a molten steel containing B in an amount of 0.1% or more, the content of which is, by weight,
CaO and SiO ₂ are CaO + SiO ₂ : 35-70%, and CaO
/ SiO ₂ : Included in the range of 3.0 or more, and Al ₂ O ₃ :
15% to 30% and _B 2 _O 3: contains 5 to 30%, mp: 95
Viscosity at 0 to 1250 ℃, 1300 ℃: 0.8 to 3.0 poise
A powder for continuous casting of B-containing steel, characterized by having the following characteristics. 2. A continuous casting powder is used for 0.1% B.
When continuously casting the molten steel containing the above, as a powder for this continuous casting, CaO and SiO ₂ are added as CaO in a weight percentage.
+ SiO _2: 35~70%, and CaO / SiO _2: with including 3.0 or more ranges, Al ₂ O _3: 15~30% and B
₂ O ₃ : containing 5 to 30%, melting point: 950 to 1250 ° C., 13
Viscosity at 00 ° C: A continuous casting method for B-containing steel, characterized by using a powder having characteristics of 0.8 to 3.0 poise.