JPH04182049A - Immersion nozzle for continuous casting - Google Patents

Abstract

PURPOSE:To attain stable utilization for a long period with high durability by specifying structure constitution at a part coming into contact with a molten slag. CONSTITUTION:The part coming into contact with the molten slag incorporates 70-90wt.% zirconia and 10-30wt.% flake graphite having 500mum grain size and the zirconia grains are distributed so as to satisfy the followings (a) and (b). Further, this is constituted of a refractory having the structure constitution where the flake graphite exists at >=80% of sieve classification of adjacent zirconia grains exceeding 125mum. a: grain size distribution of the whole zirconia grains (the whole grain size distribution) is constituted of 30-65wt.% grains of >125mum, 20-55wt.% grains of 125-45mum and 15-45wt.% grains of <45mum. b: in grain size between 45-355mum of the standard sieve regulated in the JIS-Z8801 to the whole zirconia grains, zirconia grains exist at least at 3wt.% in each of 355-250mum, 250-180mum, 180-125mum, 125-90mum, 90-63mum and 63-45mum of the adjoined sieve classification.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a immersed nozzle for continuous casting, and more particularly to a immersed nozzle for continuous casting in which the refractory of the slag line portion is improved.

[Prior Art] Various materials have been proposed as immersion nozzles for continuous casting. Particular attention has been paid to the material of the slag line, which is subject to localized wear and tear due to contact with the molten slag in which the mold powder is poured into the mold and turns into slag. has been used because it exhibits excellent corrosion resistance. For example, Japanese Patent Publication No. 59-1229 discloses a material for the slag line portion consisting of 2 to 10% by weight of carbon, 70 to 93% of zirconia, and 5 to 30% of silicon carbide and/or fused silica. JP-A-63-97344, JP-A-60-148649, JP-A-1-1
Publication No. 76271 also discloses a zirconia-carbon material having a similar composition.

[Problem to be solved by the invention] However, with the above conventional materials, emphasis is placed only on improving the corrosion resistance of the slag line, and the zirconia raw material is mainly a mixture of coarse and fine powder. It was something.

The inventors of the present invention looked at the influence of immersion nozzles on the quality of steel billets, which is the most important requirement during steel manufacturing, and researched the process by which vertical cracks (scratches) etc. occur on the surface of manufactured steel billets. , chemically changed by contact with molten steel or molten slab to form molten steel or/and molten powder (slag)
It was found that zirconia particles that fall out of the matrix, rather than zirconia that dissolves into the molten slag, affect the physical properties of the molten slag, which in turn affects the quality of the manufactured steel billet. In other words, due to contact with molten steel and molten slag, the matrix formed of graphite and fine zirconia powder is eroded, and the relatively large-diameter zirconia particles that have fallen off are mixed into the molten slag, and the molten slag around the immersion nozzle is This changes the composition of the solidified shell and, in turn, its physical properties, especially its flow into the solidified shell-mold space and its behavior during cooling. Therefore, the properties of the slag layer adhering to the surface of the steel billet pulled out from the mold differ only in the portion where relatively large-diameter zirconia particles are located, resulting in defects such as vertical cracks on the surface of the steel billet.

In consideration of the above circumstances, the present inventors developed a slag line that allows casting of good-quality steel billets without zirconia particles that are difficult to fall off (and free of vertical cracks, etc.) without impairing the corrosion resistance of the zirconia-carbon material. The present invention was completed as a result of research into the materials of refractories.

The purpose of the present invention is to provide an immersion nozzle for continuous casting that is capable of casting for a particularly long period of time, has excellent corrosion resistance against molten steel or molten slabs, and can produce high-quality steel slabs without vertical cracks. It is something to do.

[Means for Solving the Problems] In order to achieve the above object, the immersion nozzle for continuous casting according to the present invention has at least the portion that contacts the molten slag made of zirconia F of 0 to 90% and a particle size of 500 μm or less. contains 10 to 30% by weight of scaly graphite, and the zirconia particles are distributed so as to satisfy the following a and b, and 80% or more of the spaces between adjacent silconi particles exceeding 125 μm contain scaly graphite. It is characterized by being composed of a refractory material that has an existing structural structure.

a: The particle size distribution of the entire zirconia particles (hereinafter referred to as the overall particle size distribution) is 30 to 65% by weight of particles exceeding 125 μm, 20 to 55% by weight of particles of 125 to 45 μm, 4
Particles smaller than 5 um consist of 15-45% by weight.

b: For the entire zirconia particle, between 45 and 355 μm of the standard sieve shortened according to JIS 28801, the distance between adjacent sieves is 355 to 250 μm, and 250 to 180 μm.
m, ill ~ 125 um, 125 ~ 9 [1 μm
, 90-63 μm, and 63-45 μm, each of which contains at least 3% by weight of zirconia particles. (Hereinafter, referred to as intermediate particle size distribution) [Function] According to the present invention, by using zirconia particles with an even particle size distribution, the particles in the refractory are packed very densely and have a diameter slightly larger than 125 μm. The large particles are retained by the scaly graphite present between the larger particles, and can be prevented from falling off and being mixed into the molten slag. The continuous distribution of the particles and the retention of the particles by the scale-like graphite combine to prevent the zirconia particles from falling off, without locally changing the physical properties of the slag layer on the surface of the manufactured steel billet. It becomes possible to produce high-quality steel pieces without vertical cracks on the surface.

The forms of erosion caused by contact between zirconia and molten steel or molten slag include physical erosion and chemical erosion, but the present invention does not improve chemical erosion resistance against molten steel or molten slag. When melting away, only the matrix formed of graphite, small-diameter zirconia particles, or other materials is melted away, preventing large-diameter zirconia particles from falling off, and as a result, the molten slag High-quality steel slabs can be obtained without locally changing physical properties.

The zirconia used in the present invention may be unstabilized, but preferably partially stabilized zirconia with a degree of stabilization of 30 to 90 is used. This is preferable in that it has better volume stability during thermal cycles and improves thermal shock resistance than those that are not stabilized, and this effect is most effective within the above range. The degree of stabilization is the ratio of cubic crystals in the zirconia particles expressed as a percentage.

If the zirconia content is less than 70% by weight, the corrosion resistance will be poor and the material will be easily damaged by melting. Moreover, when it exceeds 90% by weight, the content of other raw materials decreases, and the spalling resistance and mechanical strength decrease.

When the overall particle size distribution of zirconia is outside the specified range, dense packing of particles becomes impossible and particles tend to fall off. In particular, if the particles are dislocated in the coarse direction, the mechanical strength will not be sufficiently increased, that is, the holding power of the zirconia particles will be reduced, and the effect of preventing particles from falling off will be weakened, and if the particles are dislocated in the fine direction, the thermal shock resistance will be reduced.

In addition, if there is a 3% by weight ungrooved section in the intermediate particle size distribution of zirconia, the filling properties of the particles of the entire refractory will decrease,
Large-diameter zirconia particles tend to fall off.

It is necessary that the graphite scale is contained in an amount of 10 to 30% by weight. The scaly graphite forms part of the matrix and holds the zirconia particles so as to wrap them, thereby preventing them from falling off. When the matrix does not contain scale graphite, for example, granular graphite or amorphous carbon, the effect of enveloping and holding the zirconia particles is poor, and a sufficient effect of preventing them from falling off cannot be obtained. In the present invention, there is no problem in using scaly graphite and these carbonaceous materials together.

If 10% by weight of scaly graphite is left undropped, a sufficient drop-off prevention effect cannot be obtained, and if it exceeds 30% by weight, the corrosion resistance against molten steel will be poor, and the amount oxidized and consumed will increase, leading to weakening of the matrix. No falling-off prevention effect can be obtained.

Furthermore, since the scaly graphite is present at a ratio of 80% or more between adjacent zirconia particles exceeding 125 μm, the effect of enclosing the particles is increased, and the effect of preventing falling off is further improved.

By satisfying these conditions, it is possible to obtain a refractory that is uniformly and densely filled with zirconia particles and scaly graphite. This creates a distinct matrix area that is selectively erodible at the contact surface with molten steel or molten slab, and also harmonizes the oxidation consumption rate of graphite and the dissolution rate of zirconia particles into molten steel or molten slag. , it is possible 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 of the present invention is difficult to easily and uniformly disperse, and it is necessary to carefully knead the prepared raw material for a long time, or to gradually increase the amount little by little.

Various known additives used in the manufacture of submerged nozzles can be used within the scope of the technical idea of the present invention and are within the scope of the present invention. For example, metallic silicon is added for the purpose of preventing oxidation of bonded carbon derived from graphite or a binder and maintaining strength under hot conditions. Metal silicon (S
The content of i) is preferably 2% by weight or less. If it exceeds 2% by weight, it will react with carbon and the structure will become denser, resulting in lower thermal shock resistance and lower corrosion resistance. In addition, silicon carbide (SiCl) may be added for the purpose of improving thermal conductivity, improving thermal shock resistance, and preventing oxidation. The content of Si (: is preferably 5% by weight or less. SiC is added as SiC powder during manufacturing. However, it may also be a product of reaction between metal Si and carbon.

If it exceeds 5% by weight, the content of other raw materials will decrease relatively,
It becomes impossible to obtain the desired characteristics.

Furthermore, boron carbide, metal aluminum, etc. may be added as known property improving materials.

[Example 1 Examples of the present invention will be described in detail below.

The raw materials of various formulations adjusted to the particle size distribution shown in Table 1 are pre-mixed with particles of each particle size and gradually introduced into a mixer for 45 minutes. Various types of mixed soils with uniformly mixed raw materials were obtained.Then, in order to remove the lumps (caking grains with non-uniform raw material conditions) that were formed in the mixed wires and present in each mixed soil, - Pass through a specified sieve (3 mm) and remove them to obtain various soil mixes for the slag line. Separately prepared mix for the nozzle body (55% by weight of alumina, 30% by weight of graphite)
, 10% by weight of silica, and 5% by weight of metallic silicon) were rubber press-molded at a pressure of 100,100 O/cm'' by a known method, and then fired at 1000°C in a non-oxidizing atmosphere to form a slag line. Various types of immersion nozzles equipped with the refractories of the present invention with different formulations were obtained.The physical properties of these are shown in Table 1 (numbers 1 to 6 and 10 to 12 in the table), and comparative examples (numbers 1 to 6 and 10 to 12). In the table, numbers 7 to 8) are entered by analyzing the particle size distribution of a conventional compound mainly consisting of coarse particles and fine particles (and medium particles), which were mixed for 45 minutes and molded and baked using the usual method. be.

The continuous casting immersion nozzles of the present invention and comparative examples shown in Table 1 were used for continuous casting of medium carbon steel materials with a carbon content of 009 to 016%, which tend to have many vertical cracks. used. The vertical crack occurrence index at this time is shown in Table 1. (The vertical crack occurrence index is 100
). Furthermore, when we analyzed the slag solidified mass adhering to the inner wall of the mold when vertical cracking defects occurred, we observed areas where the zirconia concentration was abnormally high.

Furthermore, micrographs showing the grain structure of the eroded area are shown in FIGS. 1 and 2. Figure 1 shows the product of the present invention;
Figure 2 shows the conventional product. In the figure, 1 indicates zirconia particles constituting the slag line refractory 4, and 2 indicates scaly graphite particles. When observing the working surface 5 that comes into contact with the slag during casting, the conventional product has an uneven surface created by falling zirconia particles, a black holed area, and a matrix area that has been oxidized and consumed, and looks whitish like the molten slag 3. Part exists.

In contrast, in the product of the present invention, no zirconia particles were observed to fall off, and the graphite particles were present so as to surround the zirconia particles.

As is clear from Table 1, the immersion nozzle for continuous casting of the present invention exhibits extremely superior corrosion resistance compared to conventional nozzles, does not have a negative effect on molten slag, and therefore does not cause defects in longitudinal cracking of steel billets. It is clear that the rate has improved significantly. Furthermore, it is clearly understood from FIG. 1 that the structure of the nozzle of the present invention is such that zirconia particles do not fall off compared to the conventional nozzle.

(Effects) As described above, according to the present invention, since it contains zirconia and graphite, it has extremely excellent corrosion resistance against molten metal and molten slag, and is highly durable and can be used stably for a long period of time. In addition, since the particles are packed very densely and the large particles are retained by the graphite scales, the zirconia particles do not fall off from the large objects in the slag line, so they do not affect the molten slag and are It is possible to cast high-quality steel billets without defects such as cracks.

[Brief explanation of drawings]

FIG. 1 is a microphotograph showing the grain structure of the refractory material in the slag line portion of a submerged nozzle of the present invention, and FIG. 2 is a microphotograph showing the grain structure of the refractory material in the slag line portion of a conventional submerged nozzle. . 1... Zirconia particles 2... Scaly graphite particles 3...
・Melted slag 4...Slag line part refractory 5・
...Operation side applicant Toshiba Ceramics Corporation

Claims (3)

[Claims] (1) At least the part that comes into contact with the molten slag contains 70 to 90% by weight of zirconia and 10 to 30% by weight of scaly graphite with a particle size of 500 μm or less, and the zirconia particles satisfy the following a and b. 1. A submerged nozzle for continuous casting, characterized in that the submerged nozzle for continuous casting is made of a refractory having a structure in which scaly graphite is distributed in 80% or more between adjacent zirconia particles having a diameter exceeding 125 μm. a: The particle size distribution of the entire zirconia particles is 30 to 65% by weight of particles exceeding 125 μm, 20 to 55% by weight of particles of 125 to 45 μm, and 15 to 45% of particles less than 45 μm.
Composed of % by weight. b: For the entire zirconia particle. Between 45 and 355 μm of the standard sieve specified in JIS Z8801, the distance between adjacent sieves is 355 to 250 μm and 250 to 180 μm.
, 180-125 μm, 125-90 μm, 90-63
At least 3% by weight of zirconia particles are present in each of 63 to 45 μm. (2) 2% by weight of metallic silicon with a particle size of 100 μm or less
The immersion nozzle for continuous casting according to claim 1, comprising: (3) The immersion nozzle for continuous casting according to claim 1, containing 5% by weight or less of silicon carbide having a particle size of 100 μm or less.