JPS59146976A - Steeping nozzle for continuous casting - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a continuous casting immersion nozzle having excellent spalling resistance.

Since immersion nozzles for continuous casting are used under severe conditions in which they come into contact with high-temperature molten steel, they are required to have excellent erosion resistance and spalling resistance.

Conventionally, refractories with carbon/alumina adhesive strength values have been used in such continuous casting immersion nozzles. However, the silica in the above material has poor erosion resistance against manganese, so when casting a high manganese steel grade, a submerged nozzle made of the above material has a problem in erosion resistance.

For this reason, recently, an immersion nozzle made of a material mainly composed of carbon and alumina has been developed in which the content of silica is reduced as much as possible. However, carbon-alumina submerged nozzles have a low content of silica, which has the characteristic of a significantly low coefficient of expansion, so in order to maintain good spalling resistance, carbon-alumina submerged nozzles must have properties of elasticity and good thermal conductivity. □It was necessary to contain at least 25% by weight of carbon having the same properties.

However, immersion nozzles containing a large amount of carbon (more than 25% by weight) cannot prevent erosion due to oxidative consumption of carbon when casting steel with a high oxygen level, and furthermore, When casting low carbon steel, it is not possible to meet the requirements for low carbon steel or carbon-free material.

In view of the above, the present invention provides an immersion nozzle for continuous casting that is made of carbon/alumina and has excellent spalling resistance and molten steel erosion resistance even with a small carbon content. The main components are at least carbon: 2 to 25% by weight and β-type alumina = 2
It is characterized by containing a weight ratio of 0 to 80.

The β-type alumina contained in the immersion nozzle of this invention has a completely different crystal structure from α-type alumina,
In terms of chemical composition, it is generally 11 A t203・R20 (R
: Na, +K). In other words, α-type alumina has a hexagonal crystal structure or almost no interfold structure, and its particles are irregularly lumpy without exception, whereas β-type alumina has a hexagonal crystal structure. Although they have the same hexagonal crystal system, the crystal lattice constant is different from α-type alumina, and has a remarkable interosseous property in the direction perpendicular to the crystal axis.
The particles are elastic thin plates.

β-type alumina has the above-mentioned properties, so by blending the appropriate particle size into the raw material and molding it, elasticity is imparted to the particles that make up the nozzle, and thermal stress is generated in the nozzle. It becomes possible to prevent extreme crack development. Therefore, even if the carbon content in the raw material is 25% by weight or less, a nozzle with good spalling resistance can be obtained.

The content of the above-mentioned β-type alumina needs to be 20 to 80% by weight. That is, if the content of β-type alumina is less than 200% by weight, the desired effect described above cannot be obtained, while if the content of β-type alumina exceeds 80% by weight, the corrosion resistance will deteriorate. to degrade.

Further, the carbon content needs to be 2 to 25% by weight. That is, if the carbon content is less than 2 parts by weight, the effect of completely preventing deterioration and erosion caused by the penetration of molten steel into the brick material cannot be obtained, whereas if the carbon content exceeds 255 parts by weight, on the contrary, Problems arise in preventing carbon elution or erosion due to oxidative consumption when casting steel types with high oxygen levels, and inability to meet the demand for low carbon steel materials when casting ultra-low carbon steel. .

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

Contains 900% by weight of C as a raw material. Scale graphite (
β-type alumina containing 922% of At203 by weight, and At2 as α-type alumina.
03k fused alumina containing 95% by weight or more,
The mixture was blended with a decarburization inhibitor in the proportions shown in Table 1, 8 to 10% by weight (external weight) of phenol reson was added as a binder, and these were sufficiently kneaded.

Next, after forming this mixed wire into a nozzle shape, it is fired using a tunnel kiln, and the length a of the shape shown in FIG. 1 is 50 mm.
0 +ran, bottom diameter Suga 100 brain, pore diameter C 40
rmh test nozzle 1 was prepared.

For comparison, as a conventional example, a test nozzle containing no β-type alumina was prepared by blending the above-mentioned scaly graphite and fused alumina.

The porosity, bulk specific gravity, bending strength, and Young's modulus of the nozzles of the above examples and conventional examples are also shown in Table 1.

The above test nozzle was subjected to a spalling resistance test and a molten steel erosion resistance test.

(1) Spalling test A test piece 2 having a length a' of 200 mm as shown in FIG. 2 was cut into two pieces from the test nozzle shown in FIG. 1. These two test pieces were heated to 1400°C in an electric furnace, held at that temperature for 15 minutes, then put into water, rapidly cooled, and then dried. The test was repeated 8 times. During this period, cracks were generated in the test piece, and the condition was examined. Table 2 shows the number of repetitions (9) until cracks appear in the test piece.

Table 2 As is clear from Table 2 above, the conventional test piece (
Cracks occurred after 1 to 3 tests, but in the examples of this invention, cracks did not occur after at least 5 tests, and in Examples 2 and 4, after 8 tests, no cracks occurred even with saliva. It was confirmed that the material had excellent adhesion spalling properties.

(2) Molten steel erosion resistance test 25 x 25 x 230 m from the test nozzle shown in Figure 1.
A test piece with a size of m was cut out. This test piece was immersed in molten steel at a temperature of 1580° C. supplied into an induction furnace, and the dimensional difference between the test piece before and after immersion, that is, the amount of erosion was investigated. FIG. 3 is a graph showing the amount of erosion caused by the above tests. The immersion depth of the test piece in the molten steel was 10,071 m, the immersion time was 150 minutes, and the measurement positions of the test piece were 30 m above the lower end of the jaw piece and 60 m above the upper end of the jaw piece.

In FIG. 3, ○ marks are examples of the present invention, and △ marks are conventional examples. As can be seen from FIG. 3, it was confirmed that the test piece of the present invention had molten steel erosion resistance comparable to that of the conventional example.

As described above, according to the continuous casting nozzle of the present invention, although the material is mainly composed of alumina and carbon and has a small amount of carbon,
It has excellent spalling resistance and molten steel corrosion resistance, so when casting molten steel, there is less cracking due to thermal shock, and excellent corrosion resistance against molten steel is obtained. It brings excellent industrial effects, such as being suitable for casting steel grades and ultra-low carbon steel grades. .

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the shape of the test nozzle, FIG. 2 is a sectional view showing the shape of the test piece, and FIG. 3 is a graph showing the amount of erosion of the Test 1 test piece. In the drawings, 1... test nozzle,
2...Test piece. Applicant Akechi Go Fire Brick Co., Ltd. Agent Natsuo Shioya (and 2 others) Figure 1 Cause 3 12.345 123

Claims (1)

[Claims] A carbon-alumina continuous casting nozzle, characterized in that it contains as a main component at least carbon: 2-25 weight ratio, alumina = 20-80 weight ratio. Immersion nozzle for continuous casting.