JP2002096146A - Mold powder for continuous casting - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mold powder for continuous casting of steel at a low cost which can assure stable continuous casting operation even without containing F or BaO an essential components. SOLUTION: The mold powder is composed of CaO, SiO2 and MgO as major components so that the main crystal at its solidification after melting becomes CaMgSi2O6. By adjusting a CaO/SiO2 wt. ratio to 0.35 to 0.55 and a (CaO+ MgO)/SiO2 wt. ratio to 0.75 to 0.95, the mold powder for continuous casting of steel containing CaO, SiO2 and MgO as major components the main crystal at its solidification after melting becomes CaMgSi2O6, and enables stabilized continuous casting operation. Furthermore, reduction of F content to less than 2 wt.% makes the mold powder for continuous casting more useful.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mold powder for continuous casting of steel which has a relatively low freezing point and viscosity and can perform a stable casting operation.

[0002]

2. Description of the Related Art Generally, in continuous casting of steel, a casting operation is performed by adding a powder flux called "mold powder" onto molten steel in a mold.
The functions required are: a) lubrication between the mold and the slab, b) heat transfer between the mold and the slab, c) absorption of inclusions, d) prevention of reoxidation of the molten steel, and e) insulation of the surface of the molten steel. ing. Therefore, as a mold powder for continuous casting of steel, CaO, SiO ₂ , Al ₂ O ₃ , Mg
It is common to use a composition containing O, Na ₂ O, NaF, CaF _{2 and the} like.

[0003] Mold powder, once added to molten steel in a mold, once melts and flows between the mold and the solidified shell, and begins to form a solidified film by heat removal at that time. In the above-mentioned general mold powder used, it is known that crystals called caspidine (Cuspidine: 3CaO.2SiO ₂ .CaF ₂ ) are precipitated in a solidified powder film. Due to the precipitation of the crystals, the effect that “the amount of heat removed from the slab to the mold is reduced and slow cooling is performed” is exerted, and the effect of preventing the surface crack of the slab is brought about. Most mold powders utilize the precipitation of cuspidin.

However, cuspidin (3CaO.2SiO ₂ .C)
In order to precipitate aF ₂ ), CaO, SiO ₂ and CaF ₂ are required as mold powder components.
If the (fluorine) component is not contained, caspidin does not precipitate, so that the heat removal through the powder film becomes too large, which causes a problem that a surface crack occurs in the slab. However, F is a component that causes corrosion of the continuous casting equipment, and is an element that may cause environmental problems if it is eluted into cooling water and leaks out of the system.

Therefore, the present inventors have previously proposed, as a mold powder for continuous casting of steel containing no or almost no F, by weight ratio of CaO: 25 to 48%, SiO ₂ : 25-48%, Al ₂ O ₃ : 1
_{~10%, B 2 O 3:} 5% or less, BaO: 3~15%, Mg
_{O: 0.5 ~5%, Na 2} O and K ₂ O and Li ₂ O:. 2 to total
30%, C: 0.1-10%, F: 2% or less, (CaO + Ba
Mold powder having a composition of O + MgO) / SiO ₂ : 0.6 to 1.7 was proposed (Japanese Patent Application 2000).
-19850). However, this mold powder
Although BaO is an essential component for lowering the freezing point and maintaining alumina absorption capacity, there is no major problem in the casting operation itself, but the problem of "selection of BaO as a component" is a problem in terms of material cost. I couldn't wipe out the concern that it might be. Because, as a BaO source, compounds other than barium sulfate cannot be used legally due to their effects on the human body. Therefore, when these are used, they must be melted with other components and vitrified. This is because

[0006]

SUMMARY OF THE INVENTION
It is an object of the present invention to provide an inexpensive "mold powder for continuous casting of steel" that can perform a stable casting operation without containing F or BaO as an essential component. It is.

[0007]

In order to achieve the above-mentioned object, the present inventors have set forth, "For that purpose, (a) the freezing point and the viscosity expected from a mold powder excluding F and BaO components. Three major problems must be solved: (b) the amount of crystal precipitation decreases, and (c) the need for alternative raw materials that leads to higher costs in place of the F and BaO components. " The study started below.

[0008] Mold powder for continuous casting of steel must be melted on molten steel in a mold. Therefore,
The freezing point of the mold powder must be lower than the freezing point of the steel to be cast. The freezing point of this mold powder is
It is determined by the freezing point of the precipitated crystal and the amount of the precipitated crystal. As described above, in normal mold powder, the precipitated crystal is cuspidin, and the melting point of this cuspidin is 1410 ° C., but it is usually necessary to add an alkali metal oxide such as Na ₂ O or a carbonate. Thus, the freezing point of the entire mold powder is lowered to some extent. But,
If the crystal itself formed by melting and solidifying the mold powder has an excessively high melting point, the melting point of the entire mold powder will be increased, so that it cannot be used as a mold powder. However, the heat removal of the slab becomes too large, which is also unsuitable.
The melting point of about 00 ° C. is very suitable for continuous casting of steel, and is a favorable result in terms of mold powder inflow between the mold and the solidified shell and the amount of crystal precipitation between the mold and the solidified shell. And it worked very well.

Accordingly, the present inventors have conducted intensive studies in search of the existence of an alternative crystal having such characteristics as cuspidin, and found that "CaMgSi ₂ containing the material component used in the conventional mold powder as a constituent component" It has been concluded that a composite oxide crystal having a chemical composition of O ₆ ″ is promising as a crystal film interposed between a mold and a solidified shell during continuous casting of steel. Because of laboratory research
CaMgSi the melting point of the ₂ O ₆ on which it is confirmed and very melting point of Kasupidin a near 1390 ° C. close, the formation of the CaMgSi ₂ O ₆ As is clear from the composition F min and Ba
This is because a special component such as O component is not required, and it is considered that the use of the component for continuous casting powder is advantageous.

Then, when molten and solidified, CaMgSi ₂
The O ₆ precipitate as a main crystal, and the continuous casting mode - Rudopauda - required freezing point as (melting point) and viscosity {freezing point: 8
As a result of further study to elucidate the flux composition that can provide about 00 to 1250 ° C. and a viscosity of about 0.1 to 10 P (foreign), it was found that “in the flux containing CaO, SiO ₂ and MgO as main components, CaO / SiO 2 ₂ 0.35 to 0.55 weight ratio
And the (CaO + MgO) / SiO ₂ weight ratio is 0.75 to 0.95
The solidification point (melting point) and viscosity meet the above-mentioned requirements for "mold powder for continuous casting of steel", and are added to the molten steel in actual operation and once melted, CaMgSi ₂ O ₆ is stably precipitated as a main crystal even when it flows between and solidifies between the solidified shells, and a very stable continuous casting operation is guaranteed ”.

The present invention has been made on the basis of the above findings and the like, and provides the following "mold powder for continuous casting of steel". Mold powder for continuous casting of steel containing CaO, SiO ₂ and MgO as main components.
Mold powder for continuous casting, characterized by being aMgSi ₂ O ₆ . Mold powder for continuous casting of steel containing CaO, SiO ₂ and MgO as main components, wherein the weight ratio of CaO / SiO _{2 is} 0.1%.
35 ~ 0.55 and (CaO + MgO) / SiO ₂ weight ratio is 0.75 ~
A mode for continuous casting characterized by being adjusted to 0.95
Ludo powder. F content is less than 2% by weight (including not containing)
The mold powder for continuous casting according to the above item or item, characterized in that:

Here, in the mold powder for continuous casting according to the present invention, CaO, MgO and SiO ₂ are essential components because they are constituent components of the target crystal. But,
Besides these, Al ₂ O ₃ , Na ₂ O, and Li ₂ O are all preferable components for lowering the freezing point (melting point) and viscosity of the mold powder, so that they are contained unless otherwise specified. Is good. As other optional components, as in the case of the conventional mold powder for continuous casting, it is possible to appropriately add an alkali metal oxide or an alkaline earth metal oxide, or to use a transition metal oxide (such as FeO) or carbonate. A salt, further, B ₂ O ₃ or the like may be added.

In the case of such a multi-component flux, it is hardly conceivable that only one kind of crystal is precipitated. However, in the case of a mold powder for continuous casting, it occupies a majority of the precipitated crystal. The crystal (main crystal) controls its physical properties. Therefore, the term "main crystal" as used in the present invention means a crystal occupying 50% or more of the crystals precipitated by melting and solidifying the mold powder.

In order to precipitate CaMgSi ₂ O ₆ as a main crystal at the time of melt solidification, the mold powder has a composition containing CaO, MgO and SiO ₂ , and the CaO / SiO ₂ weight ratio is 0.35 to 0.55. Range, and (CaO + MgO) / Si
O ₂ weight ratio must be adjusted to the range of 0.75 to 0.95. If the weight ratio of CaO / SiO ₂ or (CaO + MgO) / SiO ₂ is out of this range, the precipitated crystals will be CaMgSi ₂ O ₆
Otherwise, the solidification point of the mold powder becomes too high, and the heat removal of the slab becomes too large without the precipitation of crystals, causing problems such as cracks on the slab surface.

Regarding the F (fluorine) content, if sufficient physical properties as mold powder can be obtained due to environmental problems and equipment corrosion problems, the addition amount should be reduced as much as possible or not added at all. As described above, in the case of the mold powder for continuous casting according to the present invention, F may be reduced to a region of less than 2% by weight or not contained at all. Can also perform the same continuous casting operation as usual. Therefore, in the mold powder for continuous casting according to the present invention, the F content is preferably suppressed to less than 2% by weight (including the case where it is not contained).

Next, the present invention will be described more specifically with reference to examples.

EXAMPLES A continuous casting test of steel was carried out using 15 types of mold powders shown in Table 1. However, mold powder
When using carbon powder, a carbon powder is added as a melting rate adjuster to any powder, and the carbon powder and the original powder are added.
The components were adjusted so that the “total carbon concentration” including the carbon content of the powder shown in Table 1 as a carbonate was 2.5% by weight. Here, Na ₂ O, which is one of the powder components, is added in the form of an oxide or a carbonate, but in Table 1, the composition is represented in the form of Na ₂ O, and is therefore contained as a carbonate. Since the amount of carbon content is not shown, it is an external number in Table 1.

[0017]

[Table 1]

The continuous casting machine used in the test was of a vertical bending type, with a mold length of 900 mm and a radius of curvature of 10.5.
m, vertical part: 3.0 m. The cross-sectional dimensions of the mold used were 1200 mm in width and 270 mm in thickness. Further, in the continuous casting test, molten steel having a chemical composition shown in Table 2 was used. In Table 2, "molten steel A" is a so-called "low carbon aluminum killed steel", and "molten steel B" is a high-strength steel called "peritectic steel". It is known to be sensitive.

[0019]

[Table 2]

Table 3 shows the casting conditions and the casting results in the continuous casting test.

[0021]

[Table 3]

The casting results shown in Table 3 will be further described. In Test Nos. 1 to 6, a smooth casting operation could be performed without any trouble, and the quality of the obtained slab was very good. The main crystal deposited on the powder film between the mold and the solidified shell during casting was CaMgSi ₂ O
It was ₆ .

On the other hand, in Test No. 7 (Comparative Example), vertical cracks occurred in the slab. The main crystal deposited on the powder film at the time of casting was MgSiO ₄ , and precipitation of a small amount of the crystal was confirmed in the vitreous film. Further, in Test Nos. 8 and 9 (both comparative examples), alarms for restrictive breakout occurred frequently during casting, and the surface properties of the obtained cast pieces were also poor. The main crystal deposited on the powder film was Ca ₂ SiO ₄ (dicalcium silicate).
G) was confirmed. In test number 10 (comparative example), vertical cracks occurred in the slab. The main crystals precipitated on the powder film, although the amount of the crystals themselves is small, Mg
It was confirmed to be SiO ₄ .

In Test Nos. 11 to 17, a smooth casting operation could be performed without any trouble, and the quality of the obtained slab was very good. The main crystals precipitated on the powder film were all CaMgSi ₂ O ₆ . In Test No. 18 (Comparative Example), vertical cracks occurred in the cast slab, and the main crystal deposited on the powder film was confirmed to be MgSiO ₄ .

[0025]

As described above, according to the present invention, it is possible to carry out a stable casting operation without containing almost any F component or BaO component. ”Can be provided using inexpensive raw materials,
Industrially useful effects can be obtained, such as smooth continuous casting while minimizing equipment corrosion and environmental pollution.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masafumi Hanao 4-33, Kitahama, Chuo-ku, Osaka-shi, Osaka Sumitomo Metal Industries, Ltd. (72) Inventor Shigeru Ojiri 2-chome, Yoshiyukizaka, Fujisawa-shi, Kanagawa No. 1-116, Japan Thermochemical Co., Ltd. (72) Inventor Nobuhiko Kusubata 2-1-1, Yoshiyukizaka, Fujisawa-shi, Kanagawa Prefecture Within Japan Thermochemical Co., Ltd. (72) Inventor Atsushi Kobayashi, Fujisawa, Kanagawa Prefecture 2-1-1-16, Yoshiyuki-zaka, Japan F-term (reference) in Japan Thermochemical Co., Ltd. 4E004 MB14 NC01

Claims (3)

[Claims] A mold for continuous casting of steel containing CaO, SiO ₂ and MgO as main components, characterized in that a main crystal at the time of melt solidification is CaMgSi ₂ O ₆ . Mold powder. 2. A mold powder for continuous casting of steel containing CaO, SiO ₂ and MgO as main components, comprising CaO / SiO _2.
The weight ratio of 0.35-0.55, and (CaO + MgO) / SiO ₂ weight ratio is model for continuous casting characterized by comprising adjusted to 0.75 to 0.95 - Rudopauda -. 3. The mold powder for continuous casting according to claim 1, wherein the F content is less than 2% by weight.