JP2609399B2 - Mold powder for continuous casting - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for continuously casting steel containing a slag reducing metal element such as Al, Ti, and REM.
The present invention relates to a mold powder for continuous casting (hereinafter abbreviated as powder) which is effective for preventing deterioration of cast slab surface quality and preventing breakout due to poor lubrication (deterioration) of mold powder during continuous casting.

[0002]

2. Description of the Related Art Conventionally, Al is 0.010 wt% (hereinafter abbreviated as%).
In continuous casting of steel containing the above, Al in molten steel is mixed with (1) and (1) and ( ₂ ) which are low-grade oxides in powder used for lubrication with a mold / slab or for coating a molten metal surface. 2) A reduction reaction as shown in the equation is performed to produce Al ₂ O ₃ . Further, Al ₂ O ₃ (deoxidation product, produced by molten steel secondary oxidation) in the molten steel floats in the mold and is taken into the powder. (In molten steel) (in molten powder) (in molten powder) (in molten steel) 4 Al + 3 (SiO ₂ ) → 2 (Al ₂ O ₃ ) + 3 Si (1) 2 Al + 3 (MnO) → (Al ₂ O ₃ ) +3 Mn (2) This makes the composition of the molten powder 2CaO.Al ₂ O ₃ .SiO ₂
(Gehlenite) was changed to a component which was easily precipitated, slag bear was easily generated, and lubrication performance was deteriorated.

On the other hand, in order to prevent such a change in composition even if Al ₂ O ₃ in the powder increases, to ensure stable casting and at the same time prevent deterioration of slab surface quality, BaO
And Li ₂ O, and BaO + CaO + SiO ₂ = 60-80%,
Powder adjusted to CaO / SiO ₂ = 0.30 to 0.60
−186155), CaO / SiO ₂ = 0.6 to 0.8, melting point =
Powder having a viscosity of 800 to 1000 ° C and a viscosity (1300 ° C) of <1.5 poise (Japanese Patent Application Laid-Open No. 61-10052);
O ₂ is 10 to 20%, Al ₂ O ₃ is 15% or less, and SiO ₂ and A
A powder in which l ₂ O ₃ is adjusted to satisfy a specific relationship (Japanese Patent Laid-Open No. 3-77753) has been proposed.

[0004] However, all powders contain 10 to 40 SiO ₂ .
%, The conventional problems cannot be completely prevented, and the thermite reaction (exothermic reaction) according to the above formulas (1) and (2) occurs. Bleed (small fracture of solidified shell) along the oscillation mark due to solidification delay at the meniscus. Reduced Si melts into the molten steel, and the Si in the molten steel does not match the target component. Conversely, the Al in the molten steel becomes Al ₂ O ₃ , the Al does not match, and the composition ratio of the molten steel decreases. Since a flame is blown out by the thermite reaction, it is dangerous in operation, and it becomes difficult to continue casting.

On the other hand, there has been proposed a method (JP-A-63-56019) in which the reaction of formula (1) does not occur without adding SiO ₂ to the powder as much as possible. The powder viscosity becomes extremely unstable due to the fluctuation of the components, and the uniform inflow of the powder tends to be poor.

[0006]

DISCLOSURE OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and has been made in consideration of Al, Ti, REM
It has been made to provide powder capable of preventing deterioration of slab surface quality and preventing breakout due to poor lubrication (deterioration) of powder when continuously casting steel containing a slag reducing metal element. are those, containing no SiO ₂ little, there is provided _{CaO, Al 2 O 3, TiO} 2, Li 2 O, BaO, a powder composed mainly of MgO and Na ₂ O.

[0007]

According to the present invention, CaO: 10 to 35
%, Al ₂ O ₃ : 10 to 35%, TiO ₂ : 3 to 15%, Li ₂ O: 3 to 20
%, BaO: 5~40%, F -: 15% or less, Na ₂ O: containing 20% or less, further optionally MgO: containing 10% or less, further BN as an aggregate: 0.5 to 4.0 %, C: 0.5 ~
It is a mold powder for continuous casting, characterized in that it contains at least one of 4.0% and the remainder is constituted by unavoidable impurities.

[0008]

According to the experiments conducted by the inventors, the above-mentioned problem was caused by adding an appropriate amount of TiO ₂ and Li ₂ O having a large melting point depressing action to the basic composition of the CaO-Al ₂ O ₃ system without adding SiO ₂ as much as possible. It turns out that it can be solved by using powder.
_{That, CaO: 10~35%, Al 2} O 3: 10~35%, TiO 2:
_{3~15%, Li 2 O: 3~20} %, BaO: 5~40%, F -: 15
% Or less, Na ₂ O: contains 20% or less, and if necessary
MgO: A powder containing 10% or less and further containing C, BN, etc. as aggregate.

The role of SiO ₂ in the conventional powder is to lower the melting point and promote vitrification. However, since the powder contains a large amount of SiO ₂ , the Al ₂ O ₃ in the powder has the formula (1) When it is increased by the reaction, 2CaO.Al ₂ O ₃ .SiO ₂ (gehlenite) having a high melting point is formed. Powder according to the present invention with the addition of TiO ₂ 3 to 15%, instead of SiO ₂ against this, TiO ₂ is Si
Similarly, there is the effect of promoting vitrification and O _2, moreover in the molten steel
The reduction rate of TiO ₂ by Al is halved compared to SiO ₂ and C
For aO-Al ₂ O ₃ system, the addition of TiO ₂ 3 to 15% compared to powder without addition of TiO ₂ melting point there is an effect that also decreases 200 to 300 [° C.. However, less than 3% or 15
%, No effect of lowering the melting point is observed. Therefore, the content of TiO2 in the powder is limited to ₃ to 15%.

Further, Li ₂ O is added to the CaO—Al ₂ O ₃ —TiO ₂ system.
Be added to 20% is effective similar melting point depressant and when TiO ₂ addition. It also has the effect of increasing the activity of Al ₂ O ₃ and suppressing the oxidation of Al in the molten steel. If its content is less than 3%, the effect is small and not practical. If it exceeds 20%, although the effect of lowering the melting point can be seen, Li ₂ O is easily reduced according to the equation (3), and rather, the formation of Al ₂ O ₃ is promoted and the melting point is increased. Therefore, the content of Li ₂ O is 3 to 20.
%.

M (Li ₂ O) + n M → 2m Li + (MnOm) (3) where M is a reducing element, and m and n are coefficients. CaO and
The appropriate content of Al ₂ O ₃ is 10 to 35%, respectively. That is, it is necessary to limit the upper limit so that the melting point and the viscosity are not increased and the lubricating function as the powder is not impaired. Also, it is necessary to prevent significant changes in physical properties even when CaO and Al ₂ O ₃ are mixed as foreign inclusions. From such a viewpoint, considering the relationship with other components, the upper limit is 35% for both CaO and Al ₂ O ₃ .

On the other hand, when the content is less than 10%, the mixing ratio of other components increases, and exceeds the upper limit of each component described above. Therefore, the lower limit was set to 10%. F ^- is the melting point,
Those required for the viscosity modifier, more than 15% F ^- gasification of fluorides occur by reaction with other components in the powder, in an amount in excess of 15% F ^- is acting as a physical property modifier And the workability is impaired by the generation of white smoke. Therefore F ^- content is limited to 15% or less.

Na ₂ O has the same effect as F ^−, and its content is varied depending on the target casting speed and powder consumption, and an appropriate amount is 20% or less. If it exceeds 20%, there is a risk of erosion of the immersion nozzle. The reason for containing 5 to 40% BaO is
It is a value determined from the viewpoints of viscosity reduction and crystal precipitation prevention. Also, the reason that the reduction reaction by Al does not occur is included.

If the content of BaO is less than 5%, there is no effect in terms of preventing crystal precipitation, and if it exceeds 40%, the effect of lowering the viscosity is saturated. Therefore, the content of BaO is limited to 5 to 40%. MgO can be contained as needed, but the reason for reducing MgO to 10% or less is that, like Li ₂ O and TiO ₂ , the effect of powder melting point drop is 10%.
It is because it is recognized in the following range. In addition, BaO or MgO
In addition, metal fluorides such as LiF and NaF are used as a solvent and C and BN are used as aggregates.

The reason why BN is used in addition to C, which is usually used as an aggregate, is that, in the case of C, if the amount of C is too large, an exothermic reaction occurs during casting due to equations (1), (2) and (3). When C is used as aggregate, it burns and a flame is generated, causing a safety problem in the casting operation. However, in the case of 0.5 to 4.0% C or BN,
This is because there is no safety problem associated with the burned flame.

[0016]

Example: 200 mm of steel having three chemical compositions shown in Table 1.
Table 2 shows the results of continuous casting of slabs
Powder according to the present invention having the composition shown in
Casting was performed using a CaO-SiO ₂ powder (a component described in JP-A-61-186155). Table 3 shows the results of casting, powder biting defects on the slab surface, the number of bleeds, maintenance yields, and the like.

As is apparent from Table 3, the use of the powder according to the present invention significantly reduces slab surface defects during continuous casting of steel containing a slag reducing metal element such as Al, Ti, and REM. Slab surface maintenance yield [{(weight before maintenance-weight reduced by maintenance) / (weight before maintenance)} ×
100%] has greatly improved.

[0018]

[Table 1]

[0019]

[Table 2]

[0020]

[Table 3]

[0021]

According to the present invention, an oxide which easily reacts with a strong reducing element such as Al, Ti, REM, etc. in molten steel is contained as little as possible and a component system which does not impair the powder characteristics is used. According to the present invention, the problems of bleeding and powder biting defects on the surface of the slab, reduction in yield due to care for the defects, and generation of flame during casting are greatly improved.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Toshikazu Sakuraya 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Engineering Co., Ltd. (72) Kenichi Sorimachi 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba (72) Inventor Saburo Moriwaki 1st Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Kawasaki Steel Corporation Chiba Works (72) Inventor Sumio Yamada 1st Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Chiba Works, Ltd. (72) Inventor Mutsumi Tada 1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Kawasaki Steel Corporation Chiba Works, Ltd. (72) Inventor Masafumi Maeda 7-22-1, Roppongi, Minato-ku, Tokyo Tokyo University Production Inside the Technical Research Institute (72) Inventor Takahiro Mitsumune 3-1-26 Oikecho, Suma-ku, Kobe-shi, Hyogo Sakai Chemical Co., Ltd. Kobe Factory (72) Inventor Shinichi Kaneko 3-26 Oikecho, Suma-ku, Kobe City, Hyogo Prefecture Sakai Chemical Industry Co., Ltd. Kobe Factory (56) References JP-A-57-142762 (JP, A ) Tokiko 63-56019 (JP, B2)

Claims (2)

(57) [Claims] 1. CaO: 10 to 35 wt%, Al ₂ O ₃ : 10 to 35 wt%
_{%, TiO 2: 3~15wt%,} Li 2 O: 3~20wt%, BaO: 5~
40wt%, F ^-: 15wt% or less, Na ₂ O: contains less 20 wt%, further BN as a bone agent: 0.5~ 4.0wt%, C: 0.5~
A mold powder for continuous casting, characterized in that it contains at least one of 4.0 wt% and the balance is composed of unavoidable impurities. 2. CaO: 10 to 35 wt%, Al ₂ O ₃ : 10 to 35 wt%
_{%, TiO 2: 3~15wt%,} Li 2 O: 3~20wt%, BaO: 5~
40wt%, MgO: 10wt% or less, F ^-: 15wt% or less, Na ₂ O:
Contains 20wt% or less and BN: 0.5 ~ 4.0
wt%, C: contains one or more of 0.5 to 4.0 wt%,
A mold powder for continuous casting characterized in that the remainder is constituted by unavoidable impurities.