JP2001047200A - Powder for continuously casting steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide fluorine-less powder added and used in a mold in the continuous casting of a steel. SOLUTION: This powder for continuously casting the steel contains 0.6-1.4 CaO (mass %)/SiO2 (mass %), 2-20 mass % Li2O, 2-20 mass % Na2O and entirely no fluorine and is regulated to satisfy the conditions : Li2O and Na2O, i.e., Na2O (mass %)/Li2 (mass %)<=2.8 (CaO (mass %)/SiO2 (mass %))-3.2 and Al2O3, i.e., 50A-50<=Al2O3 (mass %)<=25A-5, wherein; A=CaO (mass %)/SiO2 (mass %)-Li2O (mass %)/50.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a powder for continuous casting (hereinafter simply referred to as "powder") used in a continuous casting of steel in a mold.

[0002]

2. Description of the Related Art During continuous casting of steel, powder is added to a mold. The powder characteristics in this continuous casting are as follows. To completely cover the molten steel surface with the molten slag layer of powder and the unmelted powder powder layer on it to prevent oxidation of the molten steel in air and also maintain the heat retaining effect. The slag, in which the powder added is melted by the heat of the molten steel, dissolves and absorbs nonmetallic inclusions that float from the molten steel, and prevents surface slag, subcutaneous inclusions and internal inclusions in the slab. The above-mentioned molten slag flows between the mold and the slab to form a uniform slag film, performs a lubricating action between the mold and the slab, and uniformly removes heat from the slab to the mold through the film, In addition, by appropriately cooling, a solidified shell of the slab is uniformly developed to obtain a slab without surface defects.

[0003] In order to achieve the above-mentioned role, a general component of powder for continuous casting is SiO2: 20-4.
5 mass%, CaO: 20-45 mass%, Al2
O3: 1 to 10 mass%, Na2 O: 1 to 20 mass%
^{s%, F -: 1~15mass%} , C: 10mass%
It consists of the following, if necessary, MgO, TiO2,
ZrO2, B2 O3, SrO, MnO, BaO, LiO
2 mag is used. Incidentally, fluorides in the powder composition, analytical oxide and F ^-, the compound in the carbonate is denoted as oxides and C. Further, as a general powder for continuous casting, the viscosity at 1300 ° C. is 0.5 to 1
Those having 0.0 poise and a solidification temperature of 950 to 1250 ° C. are practically used.

In recent years, continuous casting technology has been remarkably developed in Japan, and more than 95% of crude steel is being produced by continuous casting. In addition, the demand for continuous casting powder, which greatly affects slab quality and operation stability, has been diversified due to the focus on high-speed casting and the implementation of continuous casting, and a wide variety of continuous casting powders has been developed. Has been put to practical use.

[0005]

SUMMARY OF THE INVENTION As mentioned above,
At present, most of the powders for continuous casting that have been put into practical use are CaF2, NaF, and Na3 that control various physical properties.
Although a fluoride such as AlF6 has been added, the fluoride-added powder has the following problems.

When powder containing fluorine is added to a mold, the slag component reacts with the refractory composition constituting the nozzle to significantly damage the nozzle, and when the progress is extremely rapid, In some cases, the nozzle must be replaced during casting. To prevent these problems, a technique to prevent nozzle erosion by adding ZrO2 or the like is disclosed in
63301 and others. Further, since fluorine is contained in the powder, the molten slag added into the mold and flowing between the slab and the mold, after exhibiting its function, comes into contact with the secondary cooling water immediately below the mold, and the cooling water The elution of F ^- into OH occurs. As a result, the cooling water P
In a continuous casting facility in which H significantly decreases and comes into contact with cooling water, there arises a problem of corroding metal facilities such as casting rolls, cooling water piping, and spray nozzles. Further, since the cooling water from which F ^- has been eluted cannot be disposed of outside the system, it has become a major problem how to treat the cooling water in accordance with recent strict environmental standards.

The invention aimed at solving these problems caused by fluorine is disclosed in Japanese Patent Application Laid-Open Nos. 50-86423, 51-132113, 56-29733, 51-93728, and 52-1982. −2830, JP-A-5
Many proposals have been made for fluorine-less powders, such as 8-125349 and JP-A-5-208250, but none of them has yielded satisfactory results in castability or quality of cast slabs.

For example, Japanese Patent Application Laid-Open Nos. 50-86423, 51-132113, and 56-29733,
The use of Fe2 O3 and B2 O3 as a substitute for fluorine has been proposed, and the use of MnO has been proposed in JP-A-51-93728.
nO has a problem of oxidizing steel, and B2 O3 is also an undesirable element in the working environment.

Accordingly, an object of the present invention is to provide a powder for continuous casting which does not contain fluoride, so that nozzle erosion by fluorine can be reduced, and there is no corrosion of the peripheral equipment of the continuous casting machine by fluorine, and An object of the present invention is to provide a practical fluorine-less powder free from environmental pollution.

[0010]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and employs the following means. (1) CaO (mass%) / SiO2 (mass
%) = 0.6 to 1.4, Li2 O: 2 to 20 mass
%, Na2 O: 2 to 20 mass%, containing no fluorine, changing Li2 O and Na2 O under the condition satisfying the following formula (1), and changing Al2 O3 under the condition satisfying the following formula (2). Regulated powder for continuous casting of steel. Na2O (mass%) / Li2O (mass%) ≤2.8 (CaO (mass%) / SiO2 (mass%)) ^-3.2 (1) 50A-50≤Al2O3 (mass%) ≤25A -5 (2) where: A = CaO (mass%) / SiO2 (mass
%)-Li2O (mass%) / 50.

(2) The powder for continuous casting of steel according to (1), wherein one or more of MgO, SrO and TiO2 are added in an amount of 0.5 to 7 mass% in the powder for continuous casting. (3) In the powder for continuous casting, 50 to 10
The powder for continuous casting according to (1) or (2), wherein a molten base material having a premass treatment of 0 mass% is used. (4) 1300 ° C. in the powder for continuous casting
Has a viscosity of 0.5 to 10.0 poise and a coagulation temperature of 10
The powder for continuous casting of steel according to any one of (1) to (3), wherein the temperature is in the range of 00 to 1260 ° C.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have conducted various studies to solve the above-mentioned problem of causing the above-mentioned adverse effects by using a fluorine-containing powder. As a result, the powder containing no fluorine is equivalent to a powder used conventionally. Or start developing a practically superior fluorine-less powder with more physical properties,
The present inventors have found the proper component range as a powder for continuous casting and have completed the present invention.

Hereinafter, the present invention will be described in detail. According to the studies of the present invention, it has been found that fluorinated powder has more severe crystallization than ordinary powder, and practical properties can be secured by simple addition of Na2O, K2O, etc. as in ordinary powder. Turned out to be impossible.
Therefore, as a result of further research, the present inventors have found that the addition of Li2O is an indispensable element in order to secure lubricity as a powder. Therefore, Li2 O
Is positioned as the most important element in the present invention. It is necessary to ensure that the addition amount is at least 2 mass%, and the maximum addition amount is up to about 20 mass% in consideration of practical use of low-viscosity powder.

FIG. 4 shows how the viscosity and the solidification temperature change when the amount of added Li 2 O is changed. The base composition of the powder in FIG.
O (mass%) / SiO2 (mass%) = 1.0
2, Li2 O = 3.6 mass%, Na2 O = 3.7 m
ass%, Al2O3 = 3.0 mass% (the same applies to FIGS. 5 and 6 described later).

The present inventors have conducted various studies on the method of adding Na 2 O. As a result, by examining the addition ratio with Li 2 O, the Na 2 O which can exhibit a stable viscosity characteristic can be obtained.
The addition region of O was found. The ratio is Na2
The relationship between the O (mass%) / Li2O (mass%) ratio and the basicity is in a range as shown in the following equation (1). Na2O (mass%) / Li2O (mass%) ≤2.8 (CaO (mass%) / SiO2 (mass%)) ^-3.2 (1)

FIG. 3 shows the practical Na2 specified by the equation (1).
The O (mass%) / Li2O (mass%) ratio is illustrated. Further, it was found that the amount of Na2 O added as a powder source was greatly restricted. That is, almost no Na2 O can be added on the high basicity side. When added, it was confirmed that the viscosity became unstable due to the generation of crystals.

Further, for Al2 O3, Li2 O
It was found that by adding the slag at a constant ratio in relation to the above, the lubricating property of the slag was maintained and a stable casting result was obtained. The composition range in which the lubricity of the slag is maintained is Al2O3, which is a range represented by the following formula (2) in relation to the basicity and Li2O. 50 · A-50 ≦ Al2O3 (mass%) ≦ 25 · A-5 (2) where A = CaO (mass%) / SiO2 (mass
%)-Li2O (mass%) / 50.

In the above formula (2), the basicity (CaO
(Mass%) / SiO2 (mass%))
The use of the index A corrected by (mass%) / 50 indicates that the range that can be actually used is expanded to the higher basicity side by the addition of Li2O. = 5 mass%, the basicity is 0.1
It became clear that it spreads.

From the above formula (2), it can be seen that the range in which the addition of Al2 O3 can be actually used is also extended to the higher basicity side. However, the upper limit of the addition of Al2 O3 is set as follows.
This is because Al2 O3 is an element that increases the viscosity, and adding more than the upper limit increases the viscosity, so that a practical powder cannot be provided. Furthermore, on the low basicity side, sufficient lubricity is maintained,
It is preferable to avoid adding more Al2 O3 than necessary. FIGS. 1 and 2 show that Li2 O is 5 mass%, 10 m
An example of the range of addition of Al2 O3 according to practical use when ass% is contained is shown.

In the above-mentioned conventional fluorineless powder, K
Although the addition of 2 O has been proposed, the present inventors have found that the addition of K 2 O, unlike Li 2 O, significantly promotes crystallization and increases the viscosity. Only about 5 mass% can be added,
Since it was also confirmed that the effect as a powder could hardly be expected even if added, in the present invention, the presence or absence of K2O was not intentionally regulated.

In the above-mentioned Japanese Patent Application Laid-Open No. 52-2830, Li2 O is not used at all. Japanese Patent Application Laid-Open No. 58-125349 discloses Na2 O, Li2 O, K2 O
However, according to the study of the present inventors, it has been found that simply adding these components does not provide satisfactory results in castability and quality. Further, in Japanese Patent Laid-Open No. 5-208250,
The high basicity side is realized by the addition of B2O3, which is completely different from the component range specified by the present invention.

In the present invention, Mg is used as a raw material for adjusting physical properties.
The amounts of O, SrO, and TiO2 added are all limited, but it has been confirmed that they have an effect as a physical property modifier, and more flexible measures can be taken to control the physical properties of the fluorine-free powder. Since it is an element, it was adopted as an additional element. FIGS. 5 and 6 show the effect of each element on the viscosity and the solidification temperature. These elements have a smaller effect on viscosity than Li2O and Na2O, but all have the effect of lowering the solidification temperature. The addition amount of each composition is up to 7 mass in consideration of the effect on the solidification temperature.
% Is the limit, and if it is added more than this, the viscosity and the coagulation temperature are increased, which is unsuitable.

In the present invention, from the viewpoint of having practical powder physical properties, physical properties equivalent to those of conventional powders and powder viscosity ranges of 0.5 to 1 are provided.
0.0 poise. To achieve this viscosity, L
i2 O needs to be added at a maximum of about 20 mass%.
On the low basicity side, it is necessary to consider adding Al2 O3 as little as possible.

The solidification temperature of the powder is defined as the temperature at which the viscosity changes abruptly when the temperature is lowered, and the solidification temperature is set in the range of 1,000 to 1,260 ° C. This is the range of the physical property values of ordinary powders, and can be realized in fluorine-less powders by employing the composition range in the present invention.

In putting the powder of the present invention into practical use, a large amount of an alkali metal carbonate such as Li 2 O and Na 2 O is added, resulting in a structure having a large Igloss. However, the addition of a large amount of carbonate is a manufacturing problem,
Since a problem in practical use occurs, in order to solve this problem, in the powder for continuous casting, 50 to 50%
The problem was solved by using a molten base material in which 100 mass% of the pre-melt treatment was performed, and the production and use of a practical powder were made possible.

[0026]

Next, an embodiment of the present invention will be described. As shown in Tables 1 and 2, powders having various components and physical properties were experimentally produced, casting tests were performed on actual machines, and the results were investigated and described in the same table. A to I in Table 1 are the fluorine-less powders of the present invention, and have the same viscosity and solidification temperature as those of conventional powders. J and K in Table 2 are powders for comparison with the powder of the present invention, which are fluorine-less powders but have a component composition that is out of the conditions regulated by the present invention. They were set to almost the same value. Similarly, L to N in Table 2 are conventionally used fluorine-containing powders.

[0027]

[Table 1]

[0028]

[Table 2]

As is clear from the examples in Tables 1 and 2, the results of the casting operation using the powders of the present invention showed that all of the powders had no problem in the melting characteristics and exhibited excellent nozzle erosion resistance. In addition, F in the cooling water ^- was to investigate the elution amount, F ^- that there is no problem even elution has been confirmed of.

On the other hand, in Comparative Example J, only Na 2 O was added as a physical property modifier, and F ⁻ was not eluted, but the amount of Na 2 O added was large, and the nozzle was damaged. There is a problem. In addition, the powder viscosity is high and the solidification temperature is extremely high, so that it is difficult to say that the composition is practical. In Comparative Example K, FeO, MnO, and B ³⁺ were added in addition to Na2 O and Li2 O. The addition of MnO was not only disadvantageous to nozzle erosion, but also
Reoxidizes the molten steel with O. Therefore, there is a problem in application to extremely low carbon steel and low oxygen steel that do not like inclusions.

Further, in this component system, the solidification temperature is 10
The temperature is extremely low at not more than 00 ° C., and there is a possibility that a problem may occur in the slab surface quality (vertical cracking) in actual use.
Furthermore, in the conventional example, the working environment worse, larger nozzle erosion, further F to the cooling water ^- has been adversely affected also to increase the continuous casting facilities elution. From the above, it became clear that the powder of the present invention has excellent characteristics.

[0032]

According to the present invention, it is possible to provide a fluorine-free powder in which Li2O, Na2O, and Al2O3 are designed in an appropriate range as a powder for continuous casting.
Compared with conventional products in physical property values of powder, it has properties comparable to conventional products, without observing any obstacles in casting work, and without problems in slabs cast using this powder, It can solve various problems caused by powdery fluorine, and its industrial value is extremely high.

[Brief description of the drawings]

FIG. 1 shows the basicity (CaO (mass) determined from the equation (1).
%) / SiO2 (mass%)) and Li2O = 5mas
The figure which shows the Al2O3 addition area | region at the time of s%.

FIG. 2 shows the basicity (CaO (mass) determined from the equation (1).
%) / SiO2 (mass%)) and Li2O = 10 ma
The figure which shows the Al2O3 addition area | region at the time of ss%.

FIG. 3 shows the basicity (CaO (mass%) according to the formula (2).
/ SiO2 (mass%) and Na2O (mass%) /
The figure which shows the proper use range of Li2O (mass%) ratio.

FIG. 4 is a graph showing changes in viscosity and solidification temperature when Li2O is added.

FIG. 5 is an example diagram showing a change in viscosity when TiO2, MgO, and SrO are added.

FIG. 6 is an example showing the change in solidification temperature when TiO2, MgO, and SrO are added.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Akira Matsuo 3-4-20, Kamitsu, Nishimachi, Yawata-nishi-ku, Kitakyushu-shi, Fukuoka (72) Inventor Noriyoshi Masoo 1808-3-404 Yaya, Buzen-shi, Fukuoka

Claims (4)

[Claims] 1. CaO (mass%) / SiO2 (ma
ss%) = 0.6 to 1.4, Li2 O: 2 to 20 mas
s%, Na 2 O: 2 to 20 mass%, containing no fluorine, Li 2 O and Na 2 O under the condition satisfying the following formula (1), and Al 2 O 3 under the condition satisfying the following formula (2). Powder for continuous casting of steel, characterized in that: Na2O (mass%) / Li2O (mass%) ≤2.8 (CaO (mass%) / SiO2 (mass%)) ^-3.2 (1) 50A-50≤Al2O3 (mass%) ≤25A -5 (2) where: A = CaO (mass%) / SiO2 (mass
%)-Li2O (mass%) / 50. 2. The powder for continuous casting according to claim 1, wherein
2. The powder for continuous casting of steel according to claim 1, wherein one or more of O, SrO and TiO2 are added in an amount of 0.5 to 7 mass%. 3. The continuous casting powder according to claim 1, wherein
The powder for continuous casting according to claim 1, wherein a molten base material having a premelt treatment of １００100 mass% is used. 4. The continuous casting powder according to claim 1, wherein
The powder for continuous casting of steel according to any one of claims 1 to 3, wherein the viscosity at 00C is in the range of 0.5 to 10.0 poise and the solidification temperature is in the range of 1000 to 1260C.