JP2676658B2 - Continuous casting mold additive for high cleanliness molten steel casting - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates to a continuous casting mold additive for high cleanliness casting. A
l. The present invention relates to a mold additive for casting Si deoxidized steel, which requires wire drawing workability, fatigue strength, or machinability of 0.002% or less.

[0002]

2. Description of the Related Art In continuous casting of steel, additives in molds are used for the purpose of preventing air oxidation of molten steel in molds, keeping heat, absorbing non-metallic inclusions, and lubricating between molds and solidified slabs. Template additives are usually Si as a flux base material.
It is composed of metal oxides such as O ₂ , CaO, Al ₂ O ₃ , and MgO, and the melting property adjusting agent is Na ₂ O, K ₂ O, Li.
Metal oxides such as ₂ O, B ₂ O ₃ , etc. and CaF ₂ , Al
It is composed of metal fluorides such as F ₃ , NaF and LiF which are selectively added for melting point and viscosity adjustment and carbonaceous powder for melting rate adjustment. The above-mentioned oxides of alkali metals and alkaline earth metals may be selectively added from carbonates and nitrates.

When the mold additive is added to the molten steel surface in the mold, the side in contact with the molten steel surface is melted to form a molten slag layer, and the unmelted layer is covered above the molten slag layer to reduce heat radiation. ing. The molten slag flows between the mold and the slab and is consumed as a lubricant, but the melting rate is controlled by an aggregate such as carbon powder so as to maintain a constant molten slag thickness. The main component in the molten slag layer formed by melting the mold additive is, for example, SiO ₂ : 25 to 45 wt%, C
_{aO: 25~45wt%, Al 2 O} 3: 1~20wt%,
_{Na 2 O: 5~20wt%, F} : 5~20wt%, Ca
O / SiO _2: 0.5~1.8, physical characteristics 1300 ℃
Has a viscosity of 0.3 to 15 Poise and a melting point of 900
The thing of -1200 degreeC is generally used.

Further, when pouring a melt into a mold, a dipping nozzle is used for preventing air oxidation of molten steel, preventing entrainment of molten slag, and controlling the molten pouring flow. The material of the immersion nozzle is mainly alumina-graphite, zirconia-graphite, fused silica, etc., and has a property of dissolving in the above-mentioned molten slag.

[0005]

When continuous casting is continued for a long time, the erosion of the immersion nozzle due to the molten slag becomes a problem, and recently, the slag line part is made of zirconia-graphite having relatively excellent erosion resistance. Is often used, but it is not sufficient yet, and the service life is 250 minutes to 300 minutes when using a typical template additive. Therefore, in the case of continuing casting more than this, operations such as replacing the nozzle in the middle or changing the slag line level of the nozzle are performed. As a result, the quality of the slab that became unsteady casting was inevitable.

On the other hand, a mold additive has been proposed which attempts to reduce the amount of ZrO ₂ dissolved on the nozzle side by supersaturating the ZrO ₂ component in the molten slag (for example, Japanese Patent Publication No. 63-63301). . However, Zr
From the molten slag containing a large amount of O ₂ component, ZrO ₂ particles (Lime stabilized zirconi)
Since a) crystallizes and precipitates, many hard ZrO ₂ particles are found in the slag-based inclusions caught in the slab.

In addition, ZrO ₂ component is added to Baddeleyit
When ZrO ₂ powder such as e or zircon (ZrO ₂ · SiO ₂ ) powder is added to the mold additive, these ZrO 2 powders are added.
_{The two} sources exist in the molten slag in a relatively large size while maintaining the shape of the raw material powder because the dissolution rate in the molten slag is slow.
When ZrO _{2 in} molten slag is supersaturated Zr in additive
The O ₂ raw material does not dissolve and remains as large particles in the molten slag.

When these large unmelted ZrO ₂ particles, molten slag containing zircon particles, and unmelted additives are caught in the cast slab, as with the crystallized and precipitated ZrO ₂ particles, they have a high melting point and are hard. After rolling, the sol. In ultra-fine wire applications of Si deoxidized steel with Al of 0.002% or less, it causes wire breakage, causes fatigue fracture in applications where fatigue strength is a problem, and machinability in applications where machinability is required. It causes deterioration.

[0009]

SUMMARY OF THE INVENTION The present invention advantageously solves the problems of the prior art. Al. 0.0
A mold additive used when continuously casting 02% or less of Si deoxidized molten steel in a dipping nozzle made of zirconia or a material containing zircon or a nozzle having these materials in a slag line, and adjusting flux components and melting properties. The base material and the carbon powder for adjusting the melting rate of the base material in which the ZrO ₂ component is contained in an amount of 2 to less than 5% by weight in the mold additive for steady casting in which the additive is selectively added, and the whole is preliminarily melted. A mold additive for continuous casting used by mixing. Alternatively, it is the above-mentioned mold additive, which is a mold additive for continuous casting obtained by mixing a part of the melt property adjusting agent with a melt-treated base material.

The present invention will be described below with reference to the drawings.

[0011]

[Table 1A]

[0012]

[Table 1B]

Table 1 shows the steel grades applied to the present invention, and is characterized by low Al in particular. Al is a strong deoxidizing element and is useful for deoxidizing and controlling oxygen. Al is 0.0
If the content is 02% or more, non-ductile hard Al ₂ O ₃ -based inclusions are generated, which impairs fatigue properties, wire drawing properties, machinability, and the like. C is necessary for controlling the material strength, and its component range is inevitably determined depending on the application. Si is necessary for deoxidation and oxygen control together with C, and has an effect of increasing strength without significantly lowering toughness, and 0.03 to 2.50% has been put to practical use. Mn has the effect of increasing the strength and also the effect of softening the inclusions, and about 0.15 to 2.00% has been put to practical use. P and S deteriorate segregation and deteriorate the material properties, so 0.03% or less is desirable. O is an important component for controlling the composition of inclusions and has an appropriate range for the C and Si contents, but stable casting is 8
It is 0 ppm or less. If it is more than this, blow holes are generated in the slab and the casting becomes unstable. Other Cr, N
Elements such as b and V that are effective in terms of material properties and do not significantly affect deoxidation and composition of inclusions may be contained.

<Necessity of pre-melting treatment by controlling the ZrO ₂ content of the additive in the mold> Figure 1 shows zirconia
The graphite-based refractory material is dipped in the molten slag in the test furnace and heated to 50 r.p.m. p. m. It is the result of investigating the relationship between the dissolution rate and the ZrO ₂ content in the slag when rotated at. The slag composition is Zr based on the basic slag components shown in Table 2.
It was adjusted by adding O ₂ component. It can be seen that the larger the ZrO ₂ content in the slag, the smaller the erosion rate and the greater the effect of preventing nozzle erosion.

[0015]

[Table 2]

FIG. 2 shows the results of the molten slag used in the test of FIG. 1 being pumped and the cooled slag investigated by powder X-ray diffraction. Below 5%, no ZrO ₂ diffraction line was observed,
No microscopic observation of the slag cross section shows any precipitate. 7%
In addition, ZrO ₂ (Limabilized z
(irconia) diffraction line was observed, and precipitation of ZrO ₂ particles was also observed by microscopic observation. It is considered that this is mainly caused by crystallization and precipitation during cooling and solidification, and the size is about 20 μm or less. With the addition of 9%, larger ZrO ₂ particles were observed in addition to the precipitated ZrO ₂ particles. 9%
It is shown that the addition causes supersaturation even in a molten state, and a part of the ZrO ₂ source as a raw material remains without being dissolved. From the above, in order to obtain a soft vitrified base material free of hard ZrO ₂ crystals and precipitation, it is necessary to pre-melt with a ZrO ₂ content of 6 wt% or less. Further, since the melting property adjusting material has a low melting point and is soft, there is no problem in adjusting the properties such as viscosity by adding a small amount to the pre-melted base material.

[0017]

EXAMPLES The present invention will be described below based on examples. High-carbon Si deoxidized steels for wire rods were cast using the mold additives having the compositions and physical properties shown in Table 3 to evaluate the rate of nozzle melt loss and the rate of wire breakage due to hard inclusions during wire drawing. Casting was performed at a casting speed of 0.9 m / min using a dipping nozzle having a zirconia-graphite slag line in a 300 × 500 mm mold. Table 3 shows the composition and characteristics of the mold additive used in the casting test. Conventional product is Zr
Those that do not contain O ₂ . The mixture contains ZrO ₂ component as Ba
It is a mixture of ddeleyite and zircon powder added and mixed, and is a 9% ZrO ₂ supersaturated product. The mixed product was made to have a ZrO ₂ content of 3.5% with zircon, and mixed and added.
The product of the present invention is a pre-melted product having a ZrO ₂ content of 3.5%.

[0018]

[Table 3A]

[0019]

[Table 3B]

FIG. 3 shows a comparison of the nozzle erosion rate calculated from the amount of erosion after collecting the nozzle after casting. In comparison with the conventional product, the one to which ZrO ₂ is added has the effect of suppressing the nozzle melt loss. The 9% added (ZrO ₂ supersaturated) product is the most effective, but it has been shown that even the 3.5% added product has a melting loss rate of 1/2 or less.

FIG. 4 compares the number of breaks due to inclusions when a cast slab is rolled into a wire and further drawn to a diameter of 0.175 mm. The template additive mixture A is the worst. It is considered that this is due to hard ZrO ₂ -based inclusions in the mold additive that was caught during casting. The mixed product B is also inferior to the conventional product. In this case as well, it is considered that the hard ZrO ₂ component raw material in the mixed raw material is the cause. In comparison with these, the product of the present invention has a number of wire breaks comparable to that of the conventional product and is good. There are no casting problems or other operational problems, and no problems in use are observed.

[0022]

According to the present invention, the service life of the immersion nozzle is approximately doubled, and the productivity can be improved without degrading the quality.
As a result of reducing hard inclusions in the slab as compared with the ZrO ₂ mixed type, disconnection trouble during wire drawing was reduced, fatigue limit was improved, and machinability was also improved.

[Brief description of the drawings]

FIG. 1 shows the relationship between the amount of ZrO ₂ added in slag and the rate of nozzle melt damage.

FIG. 2 shows the relationship between the added amount of ZrO _{2 in} slag and the X-ray diffraction intensity.

FIG. 3 Conventional product, mixed product A, mixed product B, product of the present invention
Nozzle A meltdown rate comparison table

FIG. 4 Conventional product, mixed product A, mixed product B, product of the present invention
A comparison table of the number of disconnection of A.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Koichi Kudo, Koichi Kudo 1 Kimitsu, Kimitsu-shi, Chiba Nippon Steel Co., Ltd. Kimitsu Works (72) Inventor, Akira Matsuo 1808-3, Hachiya, Buzen, Fukuoka Prefecture ( 72) Inventor Toshio Matsuyama 1808-3, Hachiya, Buzen, Fukuoka Prefecture (56) References Japanese Patent Publication No. 63-63301 (JP, B2) Japanese Patent Publication No. 63-44463 (JP, B2)

Claims (2)

(57) [Claims] 1. A sol. Al. 0.002% or less Si
Deoxidized molten steel is a mold additive used when performing continuous casting with a dipping nozzle made of zirconia or a material containing zircon or a nozzle having these materials in a slag line, and a flux component and a melt property modifier are selectively selected. Add ₂ to 2 ZrO ₂ component to the added mold additive for steady casting.
A casting additive for continuous casting, which is used by mixing a base material containing less than 5% by weight and entirely melt-processed in advance with an aggregate such as carbon powder for adjusting a melting rate. 2. The mold additive for continuous casting according to claim 1, which is the mold additive according to claim 1, wherein a part of the melt property adjusting agent is mixed with a melt-treated base material.