JP2593753B2 - Immersion nozzle for continuous casting - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an immersion nozzle for continuous casting.

[0002]

2. Description of the Related Art Various immersion nozzles for continuous casting have been proposed. Special attention is paid to the material of the slag line portion (the portion in contact with the molten slag) where the mold powder put into the mold comes into contact with the molten slag that has turned into slag and the local wear is severe, Hitherto, zirconia-carbon based materials have been used as those exhibiting excellent corrosion resistance. For example, Japanese Patent Publication No. 59-122
No. 9 discloses carbon 2-10 as the material of the slag line portion.
Japanese Patent Application Laid-Open Nos. 63-97344 and 60-148649, the disclosures of which are disclosed in Japanese Patent Application Laid-Open Nos. 63-97344 and 60-148649, and 70 to 93% by weight of zirconia, 5 to 30% by weight of silicon carbide and / or fused silica. JP-A-1-176271 also discloses a zirconia-carbon material having a similar composition.

[0003]

However, in the above-mentioned conventional materials, the emphasis is only on improving the corrosion resistance of the slag line portion, and the zirconia raw material is mainly a mixture of coarse powder and fine powder. Was something.

The present inventors have paid attention to the effect of the immersion nozzle on the quality of the billet, which is the most important requirement in steelmaking, and studied the process of generating vertical cracks (scratch) on the surface of the manufactured billet. As a result, the slag of the mold powder and the zirconia particles falling off from the matrix, not the zirconia chemically changed by the contact with the molten steel and / or the molten slag and melted into the molten steel and / or the molten slag, are formed by the molten slag. Affects the physical properties of
As a result, it was found that the quality of the produced billet was affected. In other words, when molten steel passes through the nozzle,
The amount of heat escaping to the outside through the body (cylinder wall) of the nozzle and the temperature of the molten steel in the vicinity of the nozzle decreases, so that the slag of the mold powder on the molten steel surface becomes uneven. In addition, due to contact with molten steel and / or molten slag, a matrix formed of graphite and fine zirconia powder is eroded,
The dropped relatively large diameter zirconia particles are mixed into the molten slag, changing the composition of the molten slag around the immersion nozzle, and thus changing its physical properties, particularly the flow between the solidified shell and the mold and the behavior during cooling. Let it. Therefore, the slag layer adhering to the surface of the billet drawn out of the mold becomes non-uniform, and its properties differ only in the portion where relatively large-diameter zirconia particles are located. As a result, defects such as vertical cracks occur on the billet surface. Had occurred.

In view of the above circumstances, the present inventors have considered that the zirconia particles hardly fall off without impairing the heat insulating structure of the body and the corrosion resistance of the zirconia-carbon material, and the fire resistance of the slag line portion. As a result of studying the organizational structure of a product, the present invention has been completed.

[0006] The present invention is particularly capable of casting for a long time, has good slagging of mold powder, and has excellent corrosion resistance to molten steel and / or molten slag.
It is an object of the present invention to provide a continuous casting immersion nozzle capable of producing a high-quality steel slab without vertical cracks.

[0007]

In order to achieve the above object, a continuous casting immersion nozzle according to the present invention has a heat insulating slit formed substantially concentrically over the entire length of a body thereof. At least a part of the part contacting the molten slag contains 70 to 90% by weight of zirconia and 10 to 30% by weight of scale graphite having a particle size of 500 μm or less, and the zirconia particles satisfy the following a and b. distributed, and between the zirconia particles each other beyond the adjacent 125μm
The portion is characterized by being composed of a refractory having a textured structure in which scale graphite exists at a probability of 80% or more.

A: The particle size distribution of the entire zirconia particles (hereinafter referred to as the total particle size distribution) is 30 to 65% by weight, and the particle size is 125 to 45 μm.
55% by weight, particles smaller than 45 μm are comprised between 15 and 45% by weight.

B: The entire zirconia particles are made according to JIS Z8.
When sieved with a standard sieve specified in 801 : 355 to 25
0 μm, 250-180 μm, 180-125 μm, 1
25-90 μm, 90 μm-63 μm, 63-45 μm
Particles contained in the respective ranges at least total formulation Hara
By 3 wt% exists for fee (hereinafter. Referred to the intermediate particle size distribution).

[0010]

According to the present invention, the amount of heat transmitted from the molten steel passing through the inside of the nozzle to the outside through the body portion is reduced, and the temperature of the molten steel near the nozzle is increased. In addition, by using zirconia particles having no deviation in particle size distribution, particles in the refractory are filled very densely, and large particles are retained by scale-like graphite present between particles slightly larger than 125 μm, and fall off. To prevent mixing in the molten slag. It is manufactured by uniformization of slag of mold powder on the surface of molten steel due to temperature rise of molten steel, and continuous distribution of these particles and retention of particles by scale-like graphite are prevented from dropping of zirconia particles. It is possible to manufacture a high-quality steel slab having no vertical cracks on the surface without locally changing the physical properties of the slag layer on the steel slab surface.

The heat insulating slit is made of ceramic fiber,
Alternatively, it is formed by setting in advance a material that will be burned out during firing (becoming a void after firing) and firing, and has a thickness of about 1 mm to 10 mm approximately in the middle of the thickness of the body. It is preferable to form it.

The erosion due to the contact between zirconia and molten steel and / or molten slag includes physical erosion and chemical erosion. The present invention relates to chemical erosion resistance to molten steel and / or molten slag. It is not intended to enhance the properties, and when eroded, only the matrix formed of graphite or small-diameter zirconia particles or other materials is eroded and prevents large-diameter zirconia particles from falling off. As a result, a high quality slab can be obtained without locally changing the physical properties of the molten slag.

The zirconia used in the present invention may not be stabilized, but preferably has a degree of stabilization of 30 to 30%.
90 partially stabilized zirconia is used. This is preferable in that the volume stability during thermal cycling becomes better and the thermal shock resistance is improved as compared with the unstabilized one, and this effect is most effective within the above range. The degree of stabilization indicates the percentage of cubic crystals in the zirconia particles as a percentage.

If the content of zirconia is less than 70% by weight, the corrosion resistance is poor, and the zirconia is easily melted. On the other hand, if it exceeds 90% by weight, the content of other raw materials is reduced, and spalling resistance and mechanical strength are reduced.

If the overall particle size distribution of the zirconia is out of the specified range, the particles cannot be densely packed, and the particles easily fall off. In particular, when the particles come off in the coarse direction, the mechanical strength is not sufficiently increased, that is, the effect of preventing the particles from falling is weakened due to a decrease in the holding power of the zirconia particles,
If it deviates in a fine direction, the thermal shock resistance decreases.

If there is a section of less than 3% by weight in the intermediate particle size distribution of zirconia, the packing property of the particles of the entire refractory decreases, and large-diameter zirconia particles are liable to fall off.

It is necessary that the scale graphite be contained in an amount of 10 to 30% by weight. The scaly graphite forms a part of the matrix and holds the zirconia particles so as to cover them, thereby preventing the zirconia particles from falling off. In the case where a matrix containing no flake graphite, for example, granular graphite or amorphous carbon, is used, the effect of wrapping and holding the zirconia particles is poor, and a sufficient effect of preventing falling off cannot be obtained. In the present invention, the use of scale-like graphite and these carbonaceous materials may be used.

If the scale graphite is less than 10% by weight, a sufficient effect of preventing falling off cannot be obtained, and if it exceeds 30% by weight, the corrosion resistance to molten steel is inferior, and the amount of oxidative consumption increases and the matrix becomes brittle. , A sufficient effect of preventing falling off cannot be obtained.

Further, since the scale-like graphite is present in the portion between adjacent zirconia particles exceeding 125 μm with a probability of 80% or more, the effect of enclosing the particles is increased, and the effect of preventing the particles from falling off is further improved. By satisfying these conditions, a refractory uniformly and densely filled with zirconia particles and scale graphite can be obtained. This eliminates a distinct matrix portion that is easily eroded at the contact surface with the molten steel and / or the molten slag, as well as the oxidative consumption rate of graphite,
The dissolution rate of the zirconia particles in the molten steel and / or the molten slag can be coordinated to prevent the zirconia particles from falling off.

The nozzle of the present invention cannot be obtained only by adjusting the raw materials. The raw material having the particle size distribution according to the present invention is difficult to disperse easily and uniformly, and it is necessary to carefully knead the prepared raw material for a long time or to gradually increase the amount in small amounts.

Within the scope of the invention, various known additives used in the manufacture of immersion nozzles can be used for the refractory and are included in the scope of the invention. For example, metallic silicon (Si) is added for the purpose of preventing oxidation of bound carbon derived from graphite or a binder, and maintaining strength during heating. The content of metallic silicon is preferably 2% by weight or less. If it exceeds 2% by weight, it reacts with carbon to densify the structure, thereby reducing the thermal shock resistance and the corrosion resistance. Silicon carbide (SiC) may be added for the purpose of improving thermal conductivity, thermal shock resistance and preventing oxidation. The content of SiC is preferably 5% by weight or less. SiC may be added as SiC powder at the time of production, or may be a product of reaction between metallic Si and carbon. If it exceeds 5% by weight, the content of other raw materials relatively decreases, and the desired properties cannot be obtained.

Further, boron carbide, metallic aluminum and the like may be added as a known property improving material.

[0023]

Embodiments of the present invention will be described below in detail.

Raw materials of various compositions adjusted to the particle size distributions shown in Tables 1, 2 and 3 are premixed with particles of each particle size and gradually put into a kneader so as to prevent aggregation for 45 minutes. The mixture was carefully stirred and mixed to obtain various compounded soils in which the respective raw materials were uniformly mixed. Then, in order to remove lumps formed in the compounding soil during the kneading (caking particles having an uneven raw material state), they are once passed through a predetermined sieve (3 mm) to remove them, Slag line compound soil was obtained. Separately prepared compound soil for sodzle body (Alumina 5
5% by weight of graphite, 30% by weight of graphite, 10% by weight of silica, 5% by weight of metallic silicon), a ceramic fiber serving as an adiabatic slit is buried concentrically over almost the entire length in the middle part of the thickness of the body. To form a nozzle main body, combined with a slag line composed of the above-mentioned various compounded soils, and rubber-pressed at a pressure of 1000 kgf / cm ^{2 by} a known method, and then 1000 ° C. in a non-oxidizing atmosphere.
To obtain various immersion nozzles. These sectional views are shown in FIG. In the figure, 1 is a nozzle body, 2 is a heat insulating slit, 3 is a slag line, and 4 is a discharge port. In addition, these physical properties are shown in Tables 1 to 3 (in the table, numbers 1 to
6, 10-12). Comparative examples (Nos. 7 to 9 in the table) were prepared by analyzing the particle size distribution of a conventional compound mainly composed of coarse particles and fine particles (and medium particles).
It was kneaded for 5 minutes, molded and fired.

The immersion nozzles for continuous casting of the present invention and the comparative examples shown in Tables 1, 2 and 3 have a carbon content of 0.09 to 0.16% in steel in which many vertical cracks are easily generated. For one month for continuous casting of medium carbon steel. The vertical cracking failure index at this time is also shown in Tables 1, 2 and 3.
(The vertical crack occurrence index was set to 100 for the number 7). Also, when the slag layer on the surface of the slab and the slag solidified mass adhering to the inner wall of the mold were analyzed when the vertical cracking failure occurred, a part where the slag layer was uneven was found, and the zirconia concentration An abnormally high portion was observed.

FIGS. 2 and 3 show micrographs showing the particle structure of the tissue in the eroded portion. FIG. 2 shows a product of the present invention, and FIG. 3 shows a conventional product. In the figure, 5 is zirconia particles constituting the slag line portion refractory 8, and 6 is scale-like graphite particles. When observing the working surface 9 in contact with the slag during casting, the conventional product looks whitish like the molten slag 7 because the uneven surface formed by dropping of zirconia particles, the black holed portion, and the matrix portion are oxidized and consumed. There is a part. On the other hand, in the product of the present invention, the zirconia particles did not fall off, and the graphite particles existed so as to surround the zirconia particles.

[0027]

[Table 1]

[0028]

[Table 2]

[0029]

[Table 3]

As is clear from Tables 1, 2 and 3,
The continuous casting immersion nozzle of the present invention exhibits extremely excellent corrosion resistance as compared with the conventional nozzle, does not adversely affect the molten slag, and therefore, the incidence of vertical cracking failure of the billet is significantly improved. it is obvious. Further, from FIG. 1, it is clearly understood that the structure of the nozzle of the present invention has no zirconia particles falling off as compared with the conventional structure.

[0031]

As described above, according to the present invention, the amount of heat transmitted from the molten steel passing through the nozzle through the body to escape to the outside decreases, and the temperature of the molten steel near the nozzle increases.
The slag of the mold powder on the molten steel surface is improved to form a uniform molten steel slag, and the slag layer on the billet surface is uniform, while it contains zirconia and graphite, so it is extremely excellent for molten metal and molten slag. Zirconia from slag line refractories because it has corrosion resistance, has high durability and can be used stably for a long period of time, and is very densely filled with particles and large particles are retained by scale graphite. Since the particles do not fall off, the molten slag is not affected, and a high quality steel slab free from defects such as vertical cracks can be cast together with the uniformity of the slag layer.

[Brief description of the drawings]

FIG. 1 is a sectional view of an immersion nozzle of the present invention.

FIG. 2 is a micrograph showing the grain structure of the structure of the slag line portion refractory.

FIG. 3 is a micrograph showing a grain structure of a structure of a refractory in a slag line portion of a conventional immersion nozzle.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Nozzle main body part 2 Insulation slit 3 Slag line part 4 Discharge port 5 Zirconia particle 6 Scale-like graphite particle 7 Melted slag 8 Slag line part refractory 9 Working surface

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroshi Otsuka 1st Minamito, Ogakie-cho, Kariya-shi, Aichi Pref. Toshiba Ceramics Co., Ltd. In the Kariya Works (72) Inventor Atsushi Sato 3, Kajima-cho, Kashima-gun, Ibaraki Prefecture Sumitomo Metal Industries Co., Ltd.Kashima Works (72) Inventor Hidemasa Nakajima 3, Kashima-cho, Kashima-gun, Ibaraki Prefecture Sumitomo Metal Industries (72) Inventor Hiroshi Shiroguchi 3, Kashima-cho, Kashima-gun, Ibaraki Prefecture Sumitomo Metal Industries, Ltd.Kashima Steel Works (72) Inventor Hiroshi Hikima 3, Kashima-cho, Kashima-gun, Ibaraki Sumitomo Metals (56) References JP-A-61-178465 (JP, A) JP-A 62-28051 (JP, A) JP flat 5-361 (JP, A)

Claims (1)

(57) [Claims] A heat insulating slit is formed concentrically over substantially the entire length of the body, and at least a portion of the body which comes into contact with the molten slag has a zirconia content of 70 to 90% by weight and a particle size of 500 μm or less. Scale graphite: 10 to 30% by weight
Containing particles of the zirconia below a, distributed so as to satisfy the b, and the tissue structure present is flake graphite with a probability of 80% or more at a portion between the zirconia particles each other beyond the adjacent 125μm An immersion nozzle for continuous casting, characterized by comprising a refractory having the same. a: 30 to 65% by weight of particles having a particle size distribution exceeding 125 μm, 20 to 55% by weight of particles having a particle size of 125 to 45 μm, and 15 to 45% of particles having a particle size of less than 45 μm.
Consists of weight percent. b: The entire zirconia particles are specified in JIS Z8801.
355-250 μm, 25 when sieved with a standard sieve
0-180 μm, 180-125 μm, 125-90 μ
m, each range of 90 to 63 μm, 63 to 45 μm
There by 3 wt% with respect to at least the total mixed material particles contained in the.