JPH0976049A - Flux for continuous casting of molten steel containing aluminum and continuous casting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the melting point and viscosity of the flux from being largely fluctuated by preventing generation of depression (sink defect) on the slab surface, the slag inclusion, or break-out by the restriction of the slab in continuously casting the molten steel containing Al to provide the slab of excellent surface property. SOLUTION: The flux for continuous casting to continuously cast the molten steel containing at least 0.10wt.% Al, has the composition consisting of, by weight, 1.0-5.0% T.C., 10-30% SiO2 , 15-35% Al2 O3 , 25-40% CaO, 5-15% Na2 O, 5-15% F, 0-5% Li2 O, and <=5% in total Fe2 O3 , MgO, etc., as inevitable impurities. The ratio of CaO/(SiO2 +Al2 O3 ) is 0.7-0.9, and the viscosity at 1300 deg.C of the flux is <=2.0 poise. This flux is used in the continuous casting method of the molten steel containing Al.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a flux and a continuous casting method for use in continuous casting of molten steel containing Al.
In particular, the present invention relates to a continuous casting flux and a continuous casting method capable of preventing defects such as depletion from occurring on the surface of a slab when continuously casting Al-containing molten steel.

[0002]

2. Description of the Related Art In continuous casting of steel, in order to improve the lubricity with the cast pieces of the mold and the surface properties of the cast pieces, operation is carried out while injecting a molten flux. The flux flowing into the mold melts and stays on the surface of the molten steel in the mold to form a layer, which prevents oxidation of the molten steel, and part of it enters between the molten steel and the side surface of the mold and drops by cooling. Lubricates between the slab and the mold that are being formed from. Therefore, a flux that improves the lubricity between the mold and the slab and the surface properties of the slab is used, and as a flux for continuous casting of this type, conventionally, CaO and SiO ₂ are mainly contained. As the composition, a composition having a basicity (CaO / SiO ₂ ) of 0.8, a melting point of 1000 ° C. or more and a viscosity at 1300 ° C. of 1.5 poises or more is used. It is said that it is common to have.

When continuous casting of molten steel is carried out by using the usual continuous casting flux containing CaO and SiO ₂ as the main components as described above, the composition of the flux changes during casting and the physical properties of the flux are If there is a change in the continuous casting operation, the continuous casting operation becomes unstable and various obstacles occur. For example, a depletion (a dent defect) on the surface of the slab, a dent, etc., or a breakout may occur due to the slab being restrained. Further, in continuous casting of steel, depending on the type of steel, continuous casting is easy or difficult. As the difficult-to-cast steel type, there is a steel containing Al, which is typical. When this molten aluminum-containing steel is continuously cast using the above flux, the following problems occur. That is, the slabrim is enlarged in the mold, which causes a powder inflow defect, which increases the risk of occurrence of operational problems such as breakout, and deteriorates the surface of the slab. JP 63
In No. -10052, the cause of this is that Al in molten steel and flux react with each other to generate grenite (2CaO Al ₂ O).
It is analyzed that this is due to the precipitation of ₃ SiO ₂ ).

As a solution to the problem, Japanese Unexamined Patent Publication No. Sho 63-10052 discloses CaO and S.
When continuous casting of molten steel containing at least 0.10% by weight of Al using an artificial slag forming powder containing iO ₂ as a main component, a reaction between Al in the molten steel and the artificial slag is used to produce Gehlenite. )
To prevent (2CaO Al ₂ O ₃ SiO ₂ ) from precipitating during casting, (a) basicity (CaO / SiO ₂ ) =
0.5-0.8, (b) melting point = 800-1000 ° C.,
(C) It has been proposed to use a powder adjusted so as to satisfy the condition that the viscosity at 1300 ° C. = 1.5 poise or less. In this method, by setting the above-mentioned conditions, CaO / SiO ₂ does not become so high even when Al is melted in the flux during casting, and the CaO / SiO ₂ does not enter the region of the grenite. Further, regarding continuous casting of Zr-containing steel, which is another difficult cast steel type, Japanese Patent Application Laid-Open No. Hei 3
JP-A-146245 proposes a continuous casting method using a flux containing ZrO ₂ .

[0005]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention The continuous casting method disclosed in Japanese Patent Laid-Open No. 63-10052 has the technical means that Al ₂ O ₃ enters the flux by the reaction with molten aluminum-containing steel. The basicity (CaO / SiO
₂ ) is low, in other words, even if Al ₂ O ₃ comes in using a flux having a composition with a high proportion of SiO ₂ ,
The composition is changed so that it does not enter the region of the high melting point of gehlenite. However, this is Al ₂
Since it is assumed that O ₃ will come in and the composition will change considerably, some variation in physical properties is inevitable. For this reason, it is necessary to develop a flux in which the fluctuations in the physical properties of the slag formed using the flux during continuous casting are reduced.
The present invention is directed to the inclusion of A containing at least 0.10% Al.
SUMMARY OF THE INVENTION It is an object of the present invention to provide a continuous casting flux and a continuous casting method for solving the above problems in continuous casting of molten steel, particularly Al-containing stainless molten steel.

[0006]

The present invention has solved the problem by the following means. (1) In a continuous casting flux for continuously casting molten steel containing at least 0.10% by weight of Al,
T. C. : 1.0~5.0%, SiO _2: 10~30
%, Al ₂ O ₃ : 15 to 35%, CaO: 25 to 40
%, Na ₂ O: 5 to 15%, F: 5 to 15%, Li
₂ O: 0 to 5%, Fe ₂ O as other unavoidable impurities
_A flux for continuous casting of Al-containing molten steel, characterized by containing 3 or less of MgO in total. (2) The flux for continuous casting of Al-containing molten steel according to claim 1, wherein the flux is adjusted to a composition satisfying the following conditions. CaO / a _{(SiO 2 + Al 2 O 3} ) = 0.7~0.9 mp = 1000 to 1200 ° C. 1300 ° C. Viscosity = 2.0 poises in (3) Al of at least 0.10 weight percent with a flux A continuous casting method for molten aluminum-containing steel, which comprises using the flux for continuous casting molten aluminum-containing steel according to the above (1) or (2) in the method for continuously casting the molten steel contained therein.

The inventors of the present invention have studied the mechanism of the reaction of Al in the molten steel with the powder, which is said to be the cause of the difficult casting of molten aluminum-containing steel, and the precipitation of gehlenite. It has been found that SiO ₂ in the flux reacts and the flux composition changes. That is, when continuously casting a molten steel containing at least 0.10 wt% of Al with a flux containing CaO and SiO ₂ as main components, Al in the molten steel and S in the flux
The composition of the flux changes as iO ₂ causes the reaction shown in the formula (1). Al is a strong oxide (A
L ₂ O ₃ ) forming element. Therefore, when molten steel containing Al contacts with the molten flux, Al in the steel
And SiO ₂ in the flux react according to the following equation. In the formula, the value in () means the component in the slag, and the value in [] means the component in the steel. 3 (SiO ₂ ) +4 [Al] = 3 [Si] +2 (Al ₂ O ₃ ) ... (1) When such a reaction occurs, Al ₂ in the molten flux
O ₃ increases, SiO ₂ decreases, and the viscosity and solidification temperature of the flux change significantly.

As a result, the physical properties of the flux change,
It was found that the surface quality of the slab deteriorates and the operation of continuous casting becomes poor. At this time, most of the flux is CaO.
At -SiO ₂ -Al ₂ O ₃ ternary phase diagram in, shoe dough last night (Pseudowollastonit
e) From the (CaO ・ SiO ₂ ) phase to the grenenite (2Ca
_{O · Al 2 O 3 · SiO} 2) in composition to the phase change (FIG. 1
reference). FIG. 1 shows an example of a composition change during casting of a conventional flux in a CaO—Al ₂ O ₃ —SiO ₂ ternary phase diagram. In the figure, A is Comparative Example 1 and B is Comparative Example 5.
2 shows the composition change of the flux (Table 1). Also C
Shows the composition change of the flux disclosed in JP-A-63-10052. Based on this recognition, in the present invention,
In order to minimize changes in the physical properties of the flux for continuous casting,
It was conceived that Al ₂ O ₃ was added to the flux in advance to the composition of the gehlenite phase. This is SiO ₂
The direction of the technology is completely different from that of the above-mentioned method in which the proportion of is increased so as not to reach the Gehrenite phase. Moreover, in this case, Al ₂
If only O ₃ is added, the melting point rises and the powder rim adhering to the mold wall is enlarged, so the appropriate addition amount range is set, and the melting point is lowered by adding other flux components. It is also necessary to adjust the amounts of those components at the same time. In consideration of these points, a flux for continuous casting that has a composition such that the physical properties of the flux do not change with the progress of continuous casting, and the melting point and other low melting points required for continuous casting are maintained. developed.

That is, the present invention is based on the conventional CaO-Si.
Al ₂ O ₃ is added to the O ₂ -based flux in an amount of about 20% in advance, and it is also used for gehlenite (2CaO · Al ₂
(O ₃ · SiO ₂ ) A flux whose components are adjusted to be contained in the composition of the phase, and by adding a few% of LiO ₂ , the melting point and viscosity can be adjusted, and stable casting can be performed. . In addition, F and the like are added to adjust the melting point and the like. The flux of the present invention has a composition of T.O. C. : 1.0 ~
_{5.0%, SiO 2: 10~30%} , Al 2 O 3: 15
~35%, CaO: 25~40%, Na 2 O: 5~15
%, F: 5~15%, Li 2 O: 0~5%, is intended to include more than 5% of Fe ₂ O _3, MgO, etc. in total as other unavoidable impurities.

The flux of the present invention preferably has a composition of T.I. C. : 2.0~4.0%, SiO _2: 18
_{~22%, Al 2 O 3:} 17~21%, CaO: 22~
36%, Na ₂ O: 6 to 10%, F: 7 to 11%, Li
₂ O: 2 to 4%, Fe ₂ O as other unavoidable impurities
₃ , containing 5% or less of MgO or the like in total, and more preferably having a composition of T. C. : 3.0 to 4.0
%, SiO ₂ : 19 to 21%, Al ₂ O ₃ : 18 to 20
%, CaO: 31-35%, Na ₂ O: 7-9%, F:
8 to 10%, Li ₂ O: 2 to 4%, and 5% or less in total of Fe ₂ O ₃ , MgO and the like as other unavoidable impurities.

The flux of the present invention has the following objects.
CaO / (SiO ₂ + Al ₂ O ₃ ) = 0.7 to 0.9,
It is preferable that the composition contains 15 to 35% of Al ₂ O ₃ and is adjusted with other flux components so that the viscosity at 1300 ° C. is 2.0 poise or less. Since the continuous casting is performed, the melting point is 1000 to 120.
It must be in the range of 0 ° C. FIG. 1 shows changes in the composition during casting when the flux of the present invention is used.
From the above, it is understood that D corresponds to the case of "Invention Example No. 6" of the example, and the change of the melting point is small.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The effects of each component and the reason for limiting the content range of the flux of the present invention will be described below. (TC) C (carbon), as an aggregate of the flux,
That is, it has a function of controlling the melting rate.
If it is less than 1.0%, the melting rate becomes too fast, and the amount of inflow between the mold and the slab becomes excessive. If it exceeds 5.0%, the melting rate becomes slow and the inflow becomes too small.

(Al ₂ O ₃ , CaO, SiO ₂ ) The usual flux is mainly composed of CaO and SiO _2, but the greatest feature of the flux of the present invention is that Al ₂ O ₃ is added in advance. That is. Al added in advance in this way
If the amount of ₂ O ₃ is appropriate, the reaction of the above (1) hardly occurs and the composition of the molten flux changes little. The amount of Al ₂ O ₃ added here is CaO-SiO ₂ -Al.
₂ O ₃ Determined by the ternary phase diagram. The composition of many ordinary fluxes changes from the pseudowollastonite phase to the gehlenite phase due to the reaction (1) as the Al content increases. At this time, the physical properties of the flux change greatly because it passes over the eutectic line. Therefore, Al ₂ O ₃ is added to the composition of the gehlenite phase in advance to prevent the phase change of the flux, that is, the change of the physical properties.

Further, the flux CaO / SiO ₂ is 1.0 as an index for preventing obstacles such as shavings.
It is a known fact that the amount is less than CaO / CaO / when a large amount of Al ₂ O ₃ is present as in the flux of the present invention.
It is not determined by the ratio of SiO ₂ , and this is not an index. Therefore, in the present invention, Ca is used as the index.
O / (SiO ₂ + Al ₂ O ₃ ) is used and blended so as to be less than 1.0. The content of SiO ₂ is 10 to 30%, Al ₂ O ₃ is 15 to 35%, and Ca
O is 25-40%, and CaO / (SiO ₂ + Al ₂
It is desirable that O ₃ ) be about 0.7 to 0.9.

(Na ₂ O, Li ₂ O, F) With only the above composition, the melting point and the viscosity become too high, and the flux inflow between the mold and the cast piece (or the shell formed by the solidification of the flux) is prevented. Inhibit. Therefore, the melting point and the viscosity are adjusted by adding these flux components. In this case, Na ₂ O is 5 to 15%, Li ₂ O is 0 to 5%, and F is 5 to 5%.
It is preferably about 15%. (Inevitable impurities) Fe ₂ O for such flux
Impurities such as ₃ and MgO are inevitably mixed in. The less these impurities are, the better, but the total amount should be suppressed to 5% or less.

[0016]

The present invention will be described in detail with reference to the following examples. However, the present invention is not limited to these. Al molten steel having the composition shown in Tables 1 and 2 is also
Using the flux having the composition shown in Table 2, continuous casting was performed using a casting mold for continuous casting. Casting temperature is 1500-155
It was 0 ° C. Examples according to the present invention are Invention Examples 1 to 7,
Comparative examples 8 to 12 were carried out for comparison (for convenience, sample number N
o. Sequential numbers corresponding to 1 to 12). Invention Example 1
In No. 7, there was no trouble during casting and stable operation could be performed, but in Comparative Examples 8 to 12, it was observed that the casting speed decreased. The casting results and the slab surface polishing amount index in each example are shown in Tables 1 and 2.

[0017]

[Table 1]

[0018]

[Table 2]

Further, during casting of Inventive Example 1 and Comparative Example 8, flux was sampled every 20 minutes and analyzed. FIG. 2 shows the composition change of the flux of Inventive Example 1, and FIG. 3 shows the composition change of the flux of Comparative Example 8.
In Inventive Example 1, the composition change was very small, which was a good result, whereas in Comparative Example 8, a remarkable composition change was observed. Further, in the case of a slab obtained by casting, in the case where the surface has a flaw, in order to eliminate the flaw, the surface is shaved to remove the flaw, but the invention example 1 and the comparative example 8 are performed. The scratch removal amount is shown in FIG. Invention Example 1
In the case of, the flaw removal amount was about 1/7 of that of the slab of Comparative Example 8, and a good result was obtained.

[0020]

EFFECTS OF THE INVENTION According to the present invention, in continuous casting of Al-containing molten steel, changes in the flux composition are reduced and stable operation is possible. Since the slab obtained by continuous casting has good surface properties, the production cost decreased as the flaw removal amount decreased.

[Brief description of drawings]

FIG. 1 is a CaO—SiO ₂ —Al ₂ O ₃ ternary phase diagram showing the composition of the flux etc. of the present invention and the composition change during casting.

FIG. 2 is a graph showing a change in composition with the casting time of Inventive Example 1 of the flux of the present invention.

FIG. 3 is a graph showing the composition change of the flux of Comparative Example 8 with casting time.

FIG. 4 is a diagram showing a difference in the amount of flaw removal on the slab surface in Inventive Example 1 of the present invention and Comparative Example 8.

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[Procedure amendment]

[Submission date] March 25, 1996

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0008

[Correction method] Change

[Correction contents]

As a result, the physical properties of the flux change,
It was found that the surface quality of the slab deteriorates and the operation of continuous casting becomes poor. At this time, most of the flux is CaO.
At -SiO ₂ -Al ₂ O ₃ ternary phase diagram in, shoe dough last night (Pseudowollastonit
e) From the (CaO · SiO ₂ ) phase to the grenite (2Ca
_{O-Al 2 O 3 · SiO} 2) in composition to the phase change (FIG. 1
reference). FIG. 1 shows an example of a composition change in a conventional flux during casting in a CaO—Al ₂ O ₃ —SiO ₂ ternary phase diagram. In the figure, A is Comparative Example 8 and B is Comparative Example 1.
2 shows the compositional change of flux 2 ( Table 2 ). Further, C indicates the composition change of the flux disclosed in JP-A-63-10052. Based on this recognition, in the present invention, in order to suppress the physical property change of the flux for continuous casting as much as possible, it was conceived that Al ₂ O ₃ was added to the flux in advance to the composition of the gehlenite phase. This is Si
The direction of the technology is completely different from that of the above method in which the proportion of O ₂ is increased so as not to reach the gehlenite phase. Moreover, in this case, Al is simply added to the conventional flux.
_{If only 2} O ₃ is added, the melting point rises and the powder rim adhering to the mold wall may become enlarged. Therefore, the appropriate addition amount range should be set and the melting point should be lowered by adding other flux components. , It is necessary to adjust the amounts of those components at the same time. In consideration of these points, a flux for continuous casting that has a composition such that the physical properties of the flux do not change with the progress of continuous casting, and the melting point and other low melting points required for continuous casting are maintained. developed.

Claims (3)

[Claims] 1. A continuous casting flux for the continuous casting of molten steel containing at least 0.10% by weight Al. C. : 1.0 to 5.0%, SiO ₂ : 10
_{~30%, Al 2 O 3:} 15~35%, CaO: 25~
40%, Na ₂ O: 5 to 15%, F: 5 to 15%, Li
₂ O: 0 to 5%, Fe ₂ O as other unavoidable impurities
_A flux for continuous casting of Al-containing molten steel, characterized by containing 3 or less of MgO in total. 2. The flux for continuous casting of Al-containing molten steel according to claim 1, wherein the flux is adjusted to a composition satisfying the following conditions. CaO / (SiO ₂ + Al ₂ O ₃ ) = 0.7 to 0.9 Melting point = 1000 to 1200 ° C. Viscosity at 1300 ° C. = 2.0 poise or less 3. At least 0.10 with flux.
A continuous casting method for molten aluminum containing steel, characterized in that a flux for continuous casting molten aluminum containing steel according to claim 1 or 2 is used in the method for continuously casting molten steel containing wt% Al.