JPH0985404A - Flux for continuously casting a1-containing molten steel and continuous casting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a slab having good surface characteristic and to prevent the variation of m.p. and viscosity of flux by preventing the development of depression (recessed defect) on the surface of a cast slab, entrapment of slag and breakage caused by the restriction of the cast slab at the time of continuously casting A1-containing molten steel. SOLUTION: In the flux for continuously casting the molten steel containing at least 0.10wt.% A1, 1.0-5.0% T.C, <=3.0% SiO2 , 10-40 Al2 O3 , 30-50% CaO, 10-15% F, 5-15% Li2 O and the other, <=5% the total of Fe2 O3 , MgO, Na2 O, etc., as the inevitable impurities, it are to be contained. It is preferable to make CaO/Al2 O3 , 1.0-1.5 the viscosity at 1300 deg.C 0.7-1.1 Poise. The A1-containing molten steel is continuously cast by using this flux.

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. Performs a lubricating action between the slab and the mold that are formed later. 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, the reaction between Al in molten steel and the artificial slag produces a grenenite (2CaO Al ₂ O ₃ S
(a) basicity (CaO / SiO ₂ ) = 0.5 to 0.8, (b) melting point = in order to prevent precipitation of iO ₂ ) during casting.
Viscosity at 800-1000 ° C, (c) 1300 ° C =
It has been proposed to use a powder adjusted to satisfy the condition of 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, in Kokoku 6-59534 discloses, the BaO in the flux is contained 4% to 8%, melting point, and suppressing the viscosity, a method of continuous casting of Al-containing molten steel is proposed, containing SiO ₂ Therefore, the reaction with the molten steel containing Al cannot be suppressed.

[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 comes in, there is a considerable change in the composition, that is, a change in the composition centering on Al ₂ O ₃ , so some fluctuations in the physical properties are unavoidable.

By the way, when the changes in the composition of the flux when the Al-containing molten steel is continuously cast using the CaO / SiO ₂ system flux including such flux, the flux changes in the flux over time. The flux composition is changed so that the Al ₂ O ₃ content increases and the SiO ₂ content decreases. Due to this composition change, the melting point and the viscosity of the flux are increased, the surface properties of the slab are deteriorated, and in the worst case, a breakout is caused and the operation is stopped. 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 provides a continuous casting flux and a continuous casting method for solving the above-mentioned problems during continuous casting of Al-containing molten steel containing at least 0.10% Al, particularly Al-containing stainless molten steel. It is intended.

[0007]

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: 3.0} % or _{less, Al 2 O 3: 10~40%} , CaO: 30~50
%, F: 10 to 15%, Li ₂ O: 5 to 15%, and a total of 5% or less of Fe ₂ O ₃ , MgO, Na ₂ O, etc. as other unavoidable impurities. Flux for continuous casting. (2) The flux for continuous casting of Al-containing molten steel according to the item (1), which has a composition adjusted to satisfy the following conditions. Melting point = 1000 to 1200 ° C. Viscosity at 1300 ° C. = 0.7 to 1.1 Poise CaO / Al ₂ O ₃ = 1.0 to 1.5 (3) For continuous casting containing CaO and Al ₂ O ₃ as main components A method for continuously casting molten steel containing at least 0.10% by weight of Al using a flux, wherein the flux for continuous casting of Al-containing molten steel according to claim 1 or 2 is used. .

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 the molten steel containing Al, and the precipitation of gehlenite. It has been found that SiO ₂ in the flux reacts and the flux composition changes. That is, following the flux mainly containing CaO and SiO _2, upon continuous casting a molten steel containing at least 0.10 wt% of Al, the SiO ₂ in the flux is reduced by the Al in the molten steel (1) The flux composition changes (SiO ₂ reduction, Al ₂ O ₃
Increase) has occurred. 3 (SiO ₂ ) +4 [Al] = 3 [Si] +2 (Al ₂ O ₃ ) ... (1) In the formula, the contents in () indicate the components in the slag, and the contents in [] indicate the components in the steel. means. When such a reaction occurs, Al ₂ O ₃ in the molten flux increases, SiO ₂ decreases, and the viscosity and solidification temperature of the flux change significantly. As a result, it has been found that the physical properties of the flux change, the surface quality of the slab deteriorates, and the continuous casting fails. At this time, many conventional fluxes are CaO-Si.
Pseudowollastonite in the O ₂ -Al ₂ O ₃ ternary system phase diagram
From the (CaO ・ SiO ₂ ) phase to the grenite (2CaO ・
The composition changes to the Al ₂ O ₃ .SiO ₂ ) phase (see FIG. 1). 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 the first of the embodiments described later.
2 shows the compositional changes of the flux of Comparative Example 8 and B of Comparative Example 12. Further, C is Japanese Patent Laid-Open No. 63-100
52 shows the composition change of the flux in Japanese Patent Laid-Open No. 52-52.

In order to suppress the progress of this reaction, SiO ₂ which is a substance to be reduced is not used in the flux,
There are three possible ways of increasing the activity of Al ₂ O ₃ in the flux and decreasing the activity of Al in the molten steel.
However, regarding Al, since Al is an alloy component and its activity cannot be changed, it is necessary to take such a measure. Therefore, in the present invention, the means of
The content of ₂ was reduced as much as possible, and an appropriate amount of Al ₂ O ₃ was added to complete the process. That is, the flux for molten Al-containing steel casting of the present invention is T.I. C. : 1.0 ~
5.0%, SiO _2: 3.0% or less, Al ₂ O _3: 10
-40%, CaO: 30-50%, F: 10-15%,
Li ₂ O: 5 to 15%, F as other unavoidable impurities
e ₂ O ₃ , MgO, Na ₂ O, etc. are contained in a total amount of 5% or less. In particular, in the above composition, SiO ₂ is 1.
0% or less is preferable.

In particular, the present invention is highly effective in the case of continuous casting of molten stainless steel containing 0.10% or more of Al, especially austenitic stainless molten steel, and by using the flux of the present invention, the surface texture can be improved. A good slab can be obtained. Furthermore, the flux of the present invention is
The components are preferably adjusted so as to satisfy the following conditions. Melting point = 1000 to 1200 ° C. Viscosity at 1300 ° C. = 0.7 to 1.1 Poise CaO / Al ₂ O ₃ = 1.0 to 1.5

On the basis of this recognition, in the present invention, in order to suppress the physical property change of the flux for continuous casting as much as possible,
The content of SiO _{2 in} the flux is made as small as possible so that the composition of the grenite phase does not occur even when ₂ O ₃ enters. This is completely different from the above-mentioned method in which the proportion of SiO ₂ is increased so as not to reach the gehlenite phase. And in this case,
To reduce the content of SiO _{2 in} the flux is
The content of l ₂ O ₃ becomes large, but if it does so, the melting point rises and the powder rim attached to the mold wall becomes enlarged. Therefore, by setting the range of the appropriate addition amount and adding other flux components, It is necessary to lower the melting points and adjust the amounts of these 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. Looking at the change in the composition during casting when the flux of the present invention was used in FIG. 1, D corresponds to the case of “Invention Example 1” (Tables 1 and 2) of the example, It can be seen that the change in 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: 1.0 to 5.0%) C (carbon) has a function of controlling the melting rate, that is, as an aggregate of the flux. 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.

(SiO ₂ : 3.0% or less) Since SiO ₂ reacts with Al in molten steel to change the flux composition, it is preferable that the content is as small as possible. If it exceeds 3.0%, the reaction of the formula (1) proceeds to the right, causing a change in the flux composition and deteriorating the surface properties of the slab, so the content is limited to 3% or less. More preferably, it is desirable not to include it at all. The unavoidable impurities may be contained in an amount of about 1.0% or less.

(Al ₂ O ₃ : 10-40%, CaO, 3
0-50%) This flux is basically CaO-Al
It is an important component because it is composed of ₂ O ₃ . Al ₂
O ₃ must be added to the flux in advance so that the reaction of the formula (1) does not proceed to the right. If it is less than 10%, the reaction of the formula (1) will proceed to the right, and if it exceeds 40%, the melting point of the flux will be high, which will hinder the lubrication of the mold and the slab, so it is limited to 10-40%. did. CaO has the effect of basically adjusting the melting point and the effect of lowering the activity of oxidizing oxides such as SiO ₂ and preventing the reaction of formula (1) from proceeding to the right. If it is less than 30%, it has a high melting point and makes SiO ₂ easily reactive, and if it exceeds 50%, the melting point rises again. Therefore, it is limited to 30 to 50%. The above two components preferably satisfy CaO / Al ₂ O ₃ = 1.0 to 1.5. If CaO / Al ₂ O ₃ is within this range,
CaO-Al ₂ O ₃ based high-melting compounds, such CaO · A
It is possible to obtain a stable slab surface property without precipitating l ₂ O ₃ , 3CaO · 5Al ₂ O ₃ .

(F: 10 to 15%) F has the effect of lowering the melting point and viscosity. When F is less than 10%, the melting point and the viscosity, especially the viscosity becomes high, which hinders the flux from flowing between the mold and the slab, and when it is more than 15%, the viscosity becomes too low and the inflow becomes excessive. Deteriorate slab surface properties. Therefore, it is limited to 10 to 15%. (Li ₂ O: 5 to 15%) Li ₂ O basically has the same function as F. If the Li ₂ O content is less than 5%, the melting point and viscosity will be high, and the flux inflow between the mold and the slab will be impeded. If it exceeds 15%, the viscosity will be too low and the inflow will be excessive, resulting in slab Deteriorates surface quality. Therefore, 10
Limited to ~ 15%. (Inevitable impurities) Other unavoidable impurities such as F
The smaller the amount of e ₂ O ₃ , MgO, Na ₂ O, etc., the better, but the total amount may be 5% or less.

The flux of the present invention is suitable for casting Al-containing molten steel. In particular, the effect is greatest when casting molten stainless steel containing 0.10% or more of Al, particularly austenitic stainless molten steel. When it is used for casting austenitic stainless steel with Al of preferably 0.20% or more, and more preferably of 0.30% or more, the effect is further enhanced. It is preferable that the components of this flux are adjusted so as to satisfy the following conditions. Melting point = 1000 to 1200 ° C. Viscosity at 1300 ° C. = 0.7 to 1.1 Poise CaO / Al ₂ O ₃ = 1.0 to 1.5

Each of these conditions is limited for the following reasons. When the melting point is 1000 ° C. or less, the amount of powder flowing between the cast piece and the mold becomes excessive and the slab surface quality deteriorates. If it is 1200 ° C. or higher, the inflow becomes too small, causing problems such as sticking. If the viscosity is less than 0.7, the inflow becomes too small and sticking occurs. If it exceeds 1.1, the inflow becomes excessive and the surface quality of the slab deteriorates. Is as described in the reason for limiting the composition.

[0018]

The present invention will be described in detail with reference to the following examples. However, the present invention is not limited to these. Al-containing molten steel having the composition shown in Table 1 was continuously cast using a flux for the composition shown in Table 2 using a casting mold for continuous casting. The casting temperature was 1500-1550 ° C. Examples according to the present invention are invention examples 1 to 7, and comparative examples 8 to 12 were performed as a comparison (for convenience, sample numbers No. 1 to 1).
2 and the corresponding serial number). In each of Inventive Examples 1 to 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. Casting result and slab surface polishing amount i in each example
The index is shown in Table 2.

[0019]

[Table 1]

[0020]

[Table 2]

Further, during casting of Inventive Example 1 and Comparative Example 8, the 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, no composition change occurred, 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. In the case of Inventive Example 1, the flaw removal amount was about 1/7 that of the slab of Comparative Example 8, and a good result was obtained.

[0022]

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 quality, the flaw removal amount was reduced and the production cost was reduced accordingly.

[Brief description of drawings]

FIG. 1 shows CaO—S showing the composition of the flux of the present invention.
iO ₂ -Al shows a ₂ O ₃ ternary system phase diagram.

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.

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 : 3.
0% or less, Al ₂ O ₃ : 10 to 40%, CaO: 30 to
50%, F: 10 to 15%, Li ₂ O: 5 to 15%, and Fe ₂ O ₃ , MgO, Na ₂ as other unavoidable impurities.
A flux for continuous casting of Al-containing molten steel, which contains O or the like in a total amount of 5% or less. 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. Melting point = 1000 to 1200 ° C. Viscosity at 1300 ° C. = 0.7 to 1.1 Poise CaO / Al ₂ O ₃ = 1.0 to 1.5 3. A continuous casting flux containing CaO and Al ₂ O ₃ as main components is used for at least 0.10% by weight.
3. The continuous casting method for molten aluminum-containing steel according to claim 1 or 2, wherein the continuous casting method for molten steel containing aluminum is used.