JPH04285059A - Refractory material and its preparing method - Google Patents

Abstract

PURPOSE:To offer stock for manufacturing a refractory material free from problems shown in the conventional refractory material as the lining of a vacuum treating vessel for molten steel, having corrosion resistance to molten steel and slag and thermal impact resistance caused by temp. change, and furthermore excellent in wear resistance to a molten steel flow. CONSTITUTION:This is a one obtd. by mixing a refractory material contg. magnesia and chromium iron ore with, by weight, 2 to 10% ferrochromium powder contg. 50 to 85% Cr with <=100mum grain diameter and 2 to 10% chromium oxide with <=100mum grain diameter and >=90% purity, and the above ferrochromium powder and chromium oxide are prepd. by preliminarily mixing each powder with <1mm grain diameter and mixing the above preliminarily mixed powder with magnesia or chromium iron ore or both. By combinedly adding relatively inexpensive ferrochromium and chromium oxide, a dense magnesia-chromium refractory having low porosity and high corrosion resistance can stably be manufactured without large chages in its manufacturing stage or the like.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a refractory material suitable for lining molten metal containers, particularly containers for vacuum processing of molten metal, and a method for preparing the same.

0002

[Prior Art] Conventionally, in the steel manufacturing process, it has been necessary to use materials that are particularly stable under vacuum as lining materials for vacuum vessels such as DH and RH equipment used for degassing treatment to remove impurities from molten steel. be.

[0003] In general, silica-based refractories tend to dissociate at high temperatures and are unsuitable for this purpose, but magnesia-chromium refractories are susceptible to chemical attack due to chemical reactions with slag or molten steel. It can be said that a fired type magnesia-chromium refractory is suitable because it is an excellent refractory that is resistant to thermal shock caused by temperature changes and has excellent wear resistance against molten steel flow.

[0004] Magnesia chromium bricks can be broadly classified into direct bond bricks and ribbon bond bricks based on their raw material composition. The former uses high-purity synthetic magnesia clinker as the magnesia source and natural chromite as the chromium source.A suitable binder is added to these mixtures, press-molded, and then heated at a high temperature of 1700℃ or higher. Manufactured by firing. On the other hand, the latter is obtained by molding in the same manner as the former, using low-impurity electrofused magnesia clinker and chromite which are melted in an electric furnace, cooled and then pulverized. There are also bricks that have properties intermediate between the two, ie, those that use a blend of magnesia clinker, chromite, and electrofused maguro, and are called semi-ribbonded bricks.

By the way, porosity is one of the factors that influences the corrosion resistance of refractories. In other words, foreign components such as slag and molten steel enter the bricks through the pores in the brick structure, and further react with the brick components, causing the bricks to be easily worn out.The lower the porosity, the better this phenomenon can be suppressed. , high corrosion resistance.

In the case of magnesia chromium bricks, regardless of direct bonding or ribbon bonding, as a means to ensure low porosity, the blended raw materials are adjusted to a particle size that provides close packing, and the bricks are filled and formed using a high-pressure press. It is known to sinter this at extremely high temperatures, and a method of promoting sintering by adding chromium oxide powder was also developed in Japanese Patent Publication No. 57-574.
It is known from Publication No. 28.

[0007] In addition to these methods, attempts have been made to obtain refractories with low porosity by adding metallic chromium or its alloys when blending raw materials for refractories, and oxidizing and expanding this during brick firing. There is. Metallic chromium blended into the raw material oxidizes in a high-temperature oxidizing atmosphere and reacts with surrounding magnesia. At this time, volumetric expansion occurs,
Since the surrounding pores are filled, a dense refractory with low porosity can be obtained.

This is the technique of blending ferrochrome, which is an alloy of iron and chromium, described in Japanese Patent Publication No. 44-18738. Ferrochrome works in the same way as metallic chromium, resulting in dense bricks with low porosity.

It is believed that the high corrosion resistance of magnesia-chromium bricks is largely due to secondary spinel containing a large amount of chromium component precipitated at grain boundaries during firing. However, in the case of ferrochrome compounding, the iron content in the brick increases, the composition of the secondary spinel becomes iron-rich, and the corrosion resistance of the secondary spinel itself decreases. Although this adversely affects the corrosion resistance of the brick and results in a low porosity,
Corrosion resistance is not significantly improved.

On the other hand, the addition of a mixture of metallic chromium and chromium oxide is also disclosed in JP-A-62-207757. Chromium oxide is a high melting point substance (melting point 1830℃
), the main purpose is to have it coexist with metallic chromium to co-fuse both at a lower temperature and promote sintering more effectively, but as mentioned above, metallic chromium has a tendency to change its structure. It is said that because of the densification, it is possible to obtain a magnesia-chromium refractory that is relatively dense and has a low porosity, along with the effect of promoting sintering. However, in reality, it is difficult to blend both powders in contact, it is difficult to control oxidation and expansion behavior, metallic chromium powder is expensive, and brick manufacturing costs are increasing due to improved corrosion resistance. It has not been put into practical use because it has no value as it exceeds the unit cost reduction.

[0011]

[Problems to be Solved by the Invention] The problems to be solved by the present invention are, in particular, to be used as a lining for a vacuum processing vessel for molten steel, without the problems of the conventional refractories mentioned above, to have corrosion resistance against molten steel and slag, and to be resistant to temperature changes. The object of the present invention is to provide a refractory material that is resistant to thermal shock and has excellent abrasion resistance against molten steel flow.

0012

[Means for solving the problems] The fireproof material according to the present invention is
50 to 85% by weight of Cr with a particle size of 100 μm or less in a refractory material containing magnesia or chromite or both.
Containing ferrochrome powder of 2 to 10% by weight and particle size of 1
Chromium oxide powder 2 with a diameter of 00μm or less and a purity of 90% by weight or more
~10% by weight.

[0013] Furthermore, this refractory material is prepared by mixing a premixture of ferrochrome powder, chromium oxide powder, and magnesia or chromite or both with a particle size of less than 1 mm into a refractory material containing magnesia, chromite, or both. It can be prepared by

[0014]

[Function] The chromium component in the present invention functions to lower the porosity of the refractory due to its volumetric expansion accompanying its oxidation. In order to stably reduce the porosity, it is necessary to dilute and disperse the material appropriately. Iron is preferred as the diluent. However, when ferrochrome, which is an alloy of iron and chromium, is added, the iron content of the secondary spinel increases and corrosion resistance decreases. To prevent this decrease in corrosion resistance, it is very effective to increase the chromium concentration in the secondary spinel by adding an appropriate amount of chromium oxide. Therefore, an appropriate amount of ferrochrome and an appropriate amount of chromium oxide are added and blended.

Ferrochrome has better dispersibility than metal chromium because it is diluted, and the amount of oxidation expansion is small, so it is possible to stably lower the porosity of the structure. Chromium oxide migrates during brick firing and is eventually concentrated in the secondary spinel. As a result, a highly corrosion-resistant magnesia-chromium brick with low porosity and developed secondary spinel rich in chromium components can be obtained.

The quality of ferrochrome is one of the factors that greatly controls the properties of refractories.

The first characteristic required of ferrochrome is
The particle size is 100 μm or less. This is because as the particles become finer, the specific surface increases, oxidation and expansion occur from lower temperatures, and bricks with low porosity can be stably obtained. If the particle size exceeds this value, the expansion behavior becomes unstable and it is difficult to obtain a good structure. Moreover, by making the particles fine, dispersibility is also improved. The second point is that the chromium component contained in ferrochrome needs to be about 50 to 85% by weight. The remainder is iron and some impurities. A dilution rate of this level improves dispersibility, stabilizes oxidation and expansion behavior, and provides bricks with low porosity.

[0018] Equally important to ferrochrome is chromium oxide. Chromium oxide has a particle size of 100μm or less and a purity of 90%.
It needs to be at least % by weight. If the particle size exceeds 100 μm, the dispersibility of chromium oxide deteriorates, making it difficult for the chromium component to move during firing, making it impossible to obtain a secondary spinel with a stable structure and appropriate composition. If the purity is less than 90% by weight, the chromium component in the secondary spinel will not be sufficiently increased, making it impossible to improve corrosion resistance.

By the way, the part that should be made denser by the effects of ferrochrome and chromium oxide is the part that corresponds to the matrix of the refractory. Usually, refractories consist of coarse particles of about 3 to 1 mm, medium particles of about 1 to 0.1 mm, and fine particles of about 0.1 mm or less. When observing the structure of refractories, it can be seen that coarse and medium grains are surrounded by fine grains. The surrounding area is the matrix. In order to achieve more effective densification, it is necessary to uniformly disperse ferrochrome and chromium oxide in this matrix portion. For this purpose, it is effective to premix medium and fine particles that will serve as a matrix, ferrochrome and chromium oxide, and further mix this with coarse particles. As a result, a refractory with a dense matrix and excellent corrosion resistance can be obtained.

[0020]

[Example] Example 1 In order to investigate the appropriate addition amount of ferrochrome and chromium oxide, a prototype brick was made and its corrosion resistance was investigated.

The raw material used has a chromium content of 64% by weight and a particle size of 1.
00 μm or less ferrochrome powder, chromium oxide powder with a purity of 90% by weight or more and a particle size of 100 μm or less, sintered magnesia with a purity of 95% by weight, and chromite with a sum of MgO and Cr2O3 components of 60% by weight. The amount ratio of sintered magnesia and chromite was 7:3. Ferrochrome powder, chromium oxide powder, magnesia of 1 mm or less, and chromite of 1 mm or less were pre-kneaded, molded into 75 x 114 x 230 mm using a friction press, dried and fired at a maximum temperature of 1850°C. A sample of approximately 30 x 70 x 230 mm was cut out from the prototype brick thus manufactured and lined on the inner wall of the vase. This was set in a vacuum induction furnace, and steel was induction melted therein and maintained at 1650°C. Furthermore, slag, which is an erosive material, was placed on top of the molten steel and melted, causing the bricks to melt away. The composition of the slag is Al2
O3 = 20, CaO = 60, CaF2 = 20 (each % by weight), the total pressure in the vacuum container was 5 torr or less, and the experiment time was 4 hours. After the erosion test was completed, the sample was taken out and cut, the remaining thickness of the maximum eroded portion was measured, and the amount of eroded loss was determined by subtracting this from the original thickness. Table 1 shows the measurement results of the amount of erosion, organized in terms of the relationship between the amount of ferrochrome added and the amount of chromium oxide added.

[0022] For reference, the results obtained by using chromium (purity of 90% by weight or more) in place of ferrochrome are also shown.

[0023]

[Table 1]

[0024] In Table 1, when the amount of ferrochrome added is changed with the amount of chromium oxide added being 0% by weight, the amount of corrosion loss does not change much, and even if ferrochrome is added without adding chromium oxide, the corrosion resistance is improved. I know it won't. On the contrary,
It can be seen that when ferrochrome is added together with chromium oxide in an amount of 2% by weight or more, the amount of melting loss is reduced by the addition. However, this effect does not appear unless 2% by weight of ferrochrome is added. The upper limit of the amount of ferrochrome added and the upper limit of the amount of chromium oxide added are both 10% by weight. If it exceeds this range, problems such as cracking in the brick structure and a decrease in corrosion resistance due to deterioration of the structure will occur, making it impractical. Therefore, the appropriate amount of addition for both chromium oxide and ferrochrome is 2 to 10% by weight.
It is.

[0025] Furthermore, in the case of adding chromium,
Even when the same 4% by weight is added, the amount of corrosion loss is greater than when ferrochrome is used, indicating that the addition of chromium has no effect on improving corrosion resistance.

[0026] The quality of the refractory aggregates used in the refractory material of the present invention, such as magnesia, chromite, and fused maguro, is as follows:
There is no problem in the same way as in normal cases. That is, magnesia has a purity of about 90% by weight or more, chromite has a sum of MgO components and Cr2 O3 components of about 45% by weight or more, and fused maguro has a purity of about 45% by weight or more.
The sum of the components is approximately 70% by weight or more.

Although the above explanation has focused on the case of fired magnesia-chromium refractories, the material according to the present invention can also be applied to unfired refractories or monolithic refractories. In other words, metal chromium is oxidized during use, and the structure can be made denser. Unfired refractories can be obtained by omitting the firing process of fired bricks, and monolithic refractories can be obtained by adding a suitable binder or the like to this material.

Example 2 Direct bond bricks were made from the material for producing refractories of the present invention and applied to a vacuum melting furnace.

[0029] Sintered magnesia clinker with a purity of 95% and chromite with a sum of MgO and Cr2O3 components of about 60% by weight are used in a weight ratio of 7:3, and a particle size of 44μ is used.
A kneaded body containing 4% by weight of ferrochrome with a particle size of 50 μm or less and a chromium content of 64% by weight, 5% by weight of chromium oxide with a particle size of 50 μm or less and a purity of 90% by weight or more, and a small amount of polysaccharide is molded using a friction press and dried. , and baked at 1850°C to produce direct bond bricks. In addition, ferrochrome, chromium oxide, magnesia of 0.1 mm or less, 0.1 m
Preliminary kneading was carried out for the chromite of m. This was used as a slag line lining in a vacuum melting furnace, and its erosion rate was compared with that of a conventional product. Table 2 summarizes the quality and erosion rate of bricks made from the material of the present invention and conventional bricks.

[0030]

[Table 2]

Bricks made of the material according to the present invention had a 25% lower erosion rate than conventional bricks and exhibited high corrosion resistance.

Example 3 Semi-ribonded bricks were made from the material for producing refractories of the present invention and applied to a DH degassing furnace.

[0033] Sintered magnesia clinker with a purity of 95%,
Chromite with a total of MgO and Cr2O3 components of about 60% by weight, and a total of MgO and Cr2O3 components of 9% by weight.
Approximately 0% by weight of electrofused maguro is used, and a particle size of 44
3% by weight of ferrochrome with a particle size of 50 μm or less and a chromium content of 64% by weight, 5% by weight of chromium oxide with a particle size of 50 μm or less and a purity of 90% by weight or more, and a small amount of polysaccharide, molded with a friction press, dried, 1850 Semi-ribboned bricks were produced by firing at ℃. Note that preliminary kneading was performed for ferrochrome, chromium oxide, magnesia of 0.1 mm or less, and chromite of 0.1 mm. This was partially applied to the bottom of a DH degassing furnace, and the erosion rate was compared with that of a conventional product. Table 3 summarizes the quality and erosion rate of bricks made of the material according to the present invention and conventional bricks.

[0034]

[Table 3]

Bricks made of the material according to the present invention had a 21% lower erosion rate than conventional bricks, and exhibited high corrosion resistance.

[0036]

[Effects of the Invention] The refractory material of the present invention is made by adding a combination of relatively inexpensive ferrochrome and chromium oxide.
It is possible to stably produce a magnesia-chromium refractory with low porosity, high density, and high corrosion resistance without major changes in the manufacturing process. According to the present invention, it is possible to manufacture a refractory with corrosion resistance 20% higher than that of conventional refractories, thereby making it possible to stably manufacture steel and reduce manufacturing costs.

Claims (2)

[Claims] Claim 1: A refractory material containing magnesia or chromite or both is mixed with 2 to 10 ferrochrome powders having a particle size of 100 μm or less and containing 50 to 85% by weight of Cr.
% by weight and 2 to 10% by weight of chromium oxide powder having a particle size of 100 μm or less and a purity of 90% by weight or more. 2. A method for preparing a refractory material, which comprises mixing a refractory material containing magnesia or chromite or both with a premixture of ferrochrome powder and chromium oxide powder and magnesia or chromite or both having a particle size of less than 1 mm. .