JPH0952755A - Magnesia-chrome refractory - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide magnesia-Cr refractory superior in structural spalling resistance. SOLUTION: This magnesia-Cr refractory consists of 50-80wt.% electrofused magnesia-Cr clinker, 0.5-2wt.%, Fe-Cr alloy as main raw materials and one kind or more of magnesia, Cr oxide and Cr ore as the other raw materials, and fine Cr oxide powder is impregnated after firing. This refractory is a semirebonded type magnesia-Cr refractory having both thermal spalling resistance and structural spalling resistance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnesia-chromium refractory (hereinafter referred to as a magcro refractory) constituting a refining and carrying container for molten metal, and more specifically to a semi-ribbon-like magcro refractory. The present invention relates to a magcro refractory material which is impregnated with fine particles of chromium oxide and has a reduced number of open pores with a radius of 5 μm or more to prevent molten slag from penetrating and enhance resistance to structural spalls.

[0002]

2. Description of the Related Art Magkuro refractories are excellent in stability at high temperature and have high corrosion resistance to basic slag. Therefore, they are used in various steelmaking furnaces, especially AOD furnaces, VOD furnaces and RH vacuum degassing equipment. Widely used in the next refining equipment.

Generally, maguro refractories are roughly classified into three types, that is, a direct bond type, a ribbon type and a semi-ribbon type, according to raw materials used at the time of production.

The direct bond type magcro refractory is made from seawater magnesia clinker and chromite ore, and Cr ₂ O ₃ and Al ₂ in chrome ore during high temperature firing are used.
O ₃ , Fe ₂ O _{3 and the} like diffuse into the periclase in the magnesia clinker to form a solid solution having a spinel composition represented by the chemical formula of RO.R ₂ O ₃ (where R is a metal element), which form one another. It consists of joining together.

Ribbon-type magcro refractory is a raw material of electrofused magnesia-chromium (hereinafter referred to as electrofused magcro).
It uses a clinker. The electromelted magcro clinker is prepared by adjusting magnesia and chromite to target components and melting them in an electric furnace. This clinker
Since the secondary spinel develops remarkably and is relatively easy to sinter, the magcro refractory using this as a raw material is dense and has high hot strength.

[0006] Generally, ribbons are easily densified and have high resistance to slag infiltration, but on the other hand, they have low resistance to thermal spalls in which refractory is destroyed by thermal shock due to temperature change. Although the direct bond quality is excellent in heat-resistant spalling property, it has a drawback that slag easily penetrates.

For this reason, a semi-ribbon-like maguro refractory has been developed as a material having the advantages of both. This is a material in which, in addition to the electromelted magcro clinker, chromite ore and magnesia fine powder are blended as raw materials, while maintaining the ribbon-like corrosion resistance and improving the heat resistant spall resistance.

The main causes of damage to maguro refractories are (1) erosion of the operating surface due to slag, and (2) physical properties of the permeated part and the non-permeated part change due to slag infiltration, so cracks occur at this part and peel off. (Structural spall), (3) Three of the above thermal spalls are included.

Of these, the above (1) occurs on the surface of the refractory which comes into contact with the slag, so that it can be predicted to some extent over time, while the above (2) and (3) show the time of occurrence. Since it is unclear and the damage progresses greatly at the time of occurrence, it is important to suppress it.

Also in the case of the magro refractory, when the direct bond quality and the ribbon quality are compared, the latter tends to be densified and has high resistance to structural spalls, but on the other hand, it is inferior in thermal spalling property. On the contrary, the former direct bond quality has the contradictory characteristics that the slag easily penetrates because of its relatively coarse structure and is inferior to the structural spall, but has high heat spall resistance.

In consideration of these characteristics, the direct bond quality is distributed in the steelmaking furnace where intermittent operations are performed and the part where the temperature changes drastically, and the ribbon quality is distributed in the part such as the slag line where corrosion resistance is particularly required. Often. However, in a furnace such as an AOD furnace or a VOD furnace in which the molten steel is vigorously stirred, slag may be caught in the molten steel, and structural spalls due to slag infiltration may be observed in the steel bath portion. This phenomenon is difficult to deal with by conventional zone linings, and there is a demand for a magro refractory that has resistance to both thermal and structural spalls.

As a result of investigating the maguro refractory used in the tuyere of the AOD furnace, the present inventors have found that the apparent porosity is significantly reduced as compared with that before use, and that the pore size distribution has a radius of 5 It was found that the pores of about 10 μm were significantly reduced. Furthermore, it was found by chemical analysis that a large amount of SiO ₂ and CaO, which are the components of the molten slag, are present in this portion. Therefore, the apparent porosity decrease and the pore size reduction are caused by the infiltration of the molten slag. And the damage was estimated to be due to structural spalls.

However, since the tuyere is a portion which is susceptible to thermal shock, it is not a good measure as a countermeasure against heat spall to make the structure dense in order to prevent the penetration of the molten slag.

As a material that prevents the penetration of molten slag and is resistant to thermal spalls, "Refractory" 44
[1] (1992), P. 2 to 9 show magcro direct bond bricks to which Fe-Cr is added. This is because the oxides of Fe and Cr are generated during firing of the refractory, and the volume expansion at that time fills and discontinues the pores to divide the pores and improve the slag penetration resistance. is there. The wear rate of this brick is 75
It has been reported to have been reduced to%.

However, when a large refractory is manufactured by this method, since the volume expansion during firing is large, cracks may occur in the refractory, and the oxides generated during firing may cause densification of the structure. Since it occurs, there is a drawback that the heat resistant spalling property is deteriorated.

[0016]

The present invention has been made to solve the above problems. An object of the present invention is to improve the slag permeation resistance, to provide a magcro refractory having a high resistance to a structural spall caused by this, and also excellent in heat spall resistance. is there.

[0017]

The gist of the present invention resides in the following maguro refractory material.

The main raw material consists of 50-80 Wt% electro-fused magcro clinker and 0.5-2 Wt% Fe-Cr alloy, and the other raw materials consist of one or more of magnesia, chromium oxide and chrome ore. A magcro refractory material characterized by being impregnated with fine powder of chromium oxide.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION The main raw materials of the magro refractory of the present invention are 50 to 80 Wt% of electromelted magcro clinker and 0.5 to
It is a Fe-Cr alloy of 2 Wt%. Similarly, the other ingredients are
It is possible to select one or more of magnesia, chromium oxide and chromium ore.

The electromelting magcro clinker preferably has a ratio of Cr ₂ O ₃ to MgO in the clinker (hereinafter abbreviated as C / M ratio) of 0.2 to 0.3. The reason for this is
As the C / M ratio of electrofused magcro clinker increases,
This is because the heat-resistant spalling property is improved, but the corrosion resistance is reduced, and the C / M ratio is 0.2 to 0.3 so that the two are balanced. And other components such as Al ₂ O ₃ , SiO ₂ and C
The content of impurities in aO and Fe ₂ O ₃ is preferably 15 Wt% or less, and the content of CaO and SiO ₂ is particularly preferably less than 1 Wt%. This is due to the increase of these impurities in the MgO in the electrofused magcro clinker.
This is because the Cr ₂ O ₃ content is reduced and the corrosion resistance is reduced.

[0021] The amount of electrofused magcro clinker is 50 Wt%
If it is less than 1, the corrosion resistance of the refractory itself deteriorates. On the other hand, 80Wt
If it exceeds%, it becomes too dense during firing, and the resistance to thermal spalls decreases.

The purpose of blending the Fe-Cr alloy is to fill pores due to expansion when Fe and Cr oxides generated during firing are generated. For this purpose, it is desirable that the Fe-Cr alloy compounding amount be large, but if it exceeds 2 Wt%, cracking becomes remarkable due to expansion of the refractory itself due to generation of Fe and Cr oxides during firing, Manufacturing of large refractories becomes difficult. On the other hand, 0.
If it is less than 5 Wt%, the effect of filling the pores due to the composition is lost.
Therefore, the blending amount of the Fe-Cr alloy is set to 0.5 to 2 Wt%.

This Fe-Cr alloy preferably has a Cr content of 50 Wt% or more. This is because when the Fe content exceeds 50 Wt%, the corrosion resistance of the refractory itself decreases.

The mug black refractory of the present invention is a semi-ribbon material, and in addition to the above-mentioned main raw materials, one or more kinds are selected from the following three kinds of other raw materials for the purpose of maintaining the corrosion resistance. To mix.

For magnesia as another raw material, either a clinker of sintering or electrofusion may be used, but the latter is particularly preferable. MgO purity is 95Wt%
It is desirable to make the above. This is because electrofused particles have less grain boundaries and are excellent in corrosion resistance, and if the MgO purity is less than 95 Wt%, the corrosion resistance is also lowered.

Similarly, it is desirable to use chromium oxide having a chromium purity of 95 Wt% or more. This is because if the impurities exceed 5 Wt%, the corrosion resistance decreases.

Although natural ore can be used as the chromium ore, the Cr ₂ O ₃ content is 40 Wt% or more, and Al ₂ O ₃ , SiO ₂ , CaO, Fe ₂ O _{3 and the} like in the ore are contained. It is desirable to use those whose total amount is 45 Wt% or less. Particularly, SiO ₂ is preferably 5 Wt% or less. The reason is that the formation of MgO.Cr ₂ O ₃ formed during firing is hindered by these components, and particularly SiO ₂ reduces the corrosion resistance.

Next, a desirable manufacturing method and conditions until firing will be described.

In the production of the magro refractory of the present invention, a raw material having a grain size of 1 mm or more is a coarse grain and a grain size of less than 1 mm to 200
Particles with a mesh size (74 μm) or less are classified as medium particles, and particles with a size of 200 mesh or less are classified as fine particles. Electrofused Magcro Clinker
Coarse grains of about 5 to 60 Wt%, medium grains of about 5 to 60 Wt%,
Fine particles of about 5 to 60 Wt% are used in all of these particle sizes, and the Fe-Cr alloy is used only in fine particles. And, magnesia, chromium oxide, and chromium ore are used as medium particles of about 5 to 50 Wt% and fine particles of about 5 to 50 Wt% in all raw materials.

After crushing and sieving as described above,
Mix in a target ratio, knead, and mold and dry. Kneading is carried out by adding a binder such as bitter broth or magnesium sulfate together with a small amount of water. Then, the kneaded product is put into a molding die such as a metal mold and is molded into a target shape using an oil press, a friction press, a rammer or the like. The desirable molding pressure at this time is about 500 to 100 Kg / cm ² . 100 after molding
Dry at 150 ° C.

After that, firing is performed in a tunnel kiln or an electric furnace. The higher the firing temperature is, the better the formation and development of the secondary spinel, which becomes the bond structure of the refractory during firing, and therefore the firing temperature is preferably 1700 ° C or higher. 1700
If the temperature is lower than 0 ° C, the secondary spinel will be underdeveloped and the strength will be insufficient.

According to the above method and conditions, a large magcro refractory without cracks (for example, length 100 mm, width 200 mm, thickness 1
00 mm) can be easily manufactured.

The magcro refractory material of the present invention is intended to improve the resistance to a structural spall.
The cause of the structural spall is the permeation of the molten slag into the refractory and the change in the physical properties due to the permeation, as described above. To prevent the structural spall, it is effective to suppress the permeation of the slag into the pores. It is desirable to reduce open pores with a radius of 5 μm or more. Therefore, a fine powder of chromium oxide is further impregnated.

This impregnation is performed by the following method.

Refractory in a liquid medium (for example, ion-exchanged water, tar, resin, etc.) in which fine powder of chromium oxide having an average particle size of 0.5 to 1.0 μm and a purity of Cr ₂ O _{3 of} 98 Wt% or more is dispersed in an airtight container. Then, the fine powder is filled in the open pores by vacuum depressurization or pressurization at room temperature or at a temperature of 100 ° C. or lower to reduce the viscosity, and then a drying treatment is performed to agglomerate in the pores.

The desirable amount of chromium oxide fine powder added to the liquid medium is 5 to 30 Vol%, the desirable impregnation depth is the whole refractory, and the desirable apparent porosity of the impregnated portion is 8 to 10.
The range of the bulk specific gravity is about 15%, the bulk specific gravity is about 3.2 to 3.6, the range of the hot bending strength is 80 MPa or more, and the range of the ratio of the open pores having a radius of 5 μm or more to all the pores is 10% or less.

According to this method, it is possible to make open pores having a radius of 5 μm or more, which are the permeation path of the molten slag, into fine pores and make them discontinuous even if the open bubbles are present in the center of the large refractory. It becomes possible and slag penetration is suppressed. Since the impregnated chromium oxide fine powder does not chemically bond with the matrix or aggregate of the refractory, the heat resistant spalling property does not deteriorate. Further, even when the molten slag permeates into the pores, the chromium oxide filled in the pores reacts with the slag to form a highly viscous liquid phase, which prevents further permeation of the slag.

[0038]

【Example】

(Comparative Example 1) Electromelted magcroclinker and electromelted magnesia clinker having the chemical compositions shown in Table 1, and Cr60Wt
%, Fe40Wt% Fe-Cr alloy was used as a raw material to fabricate a semi-ribbon-like magcro refractory.

[0039]

[Table 1]

Raw materials having a grain size of 3 to 1 mm are coarse grains and 1 mm
Less than to less than 200 mesh (74 μm) were used as medium particles, and those less than 200 mesh were used as fine particles.

After kneading with the raw material composition and particle size blending ratio (within the conditions of the present invention) shown in Table 2, the kneaded product was filled in a mold and molded at a pressure of 1000 kg / cm ² .

[0042]

[Table 2]

After this was dried at 110 ° C. for 24 hours, it was baked at a maximum temperature of 1800 ° C. for 10 hours to obtain a semi-ribboned magro refractory. The shape is normal (230 mm × 114 mm × 65 mm), and the impregnation with chromium oxide remains untreated. No cracks were observed during firing, either by visual inspection or by a cutting inspection.

(Inventive Example) The fired refractory material obtained above was treated with ion-exchanged water (pH) containing chromium volatilized powder having an average particle size of 0.6 μm and a Cr ₂ O ₃ purity of 99 Wt% and 5 Vol% of a surfactant.
It was immersed in an aqueous solution dispersed in 7), and this was depressurized to a vacuum to impregnate the refractory pores with the chromium oxide fine powder. At this time, the amount of chromium oxide fine powder added to the above aqueous solution was 20 V.
ol%.

After the above impregnation treatment is carried out for 10 minutes so that the whole of the standard type refractory material is impregnated to the central portion, the refractory material is taken out by returning the pressure to atmospheric pressure and dried at 110 ° C. for 24 hours to obtain the target. An impregnated refractory material was obtained.

(Comparative Example 2) Using the same raw material as in Comparative Example 1,
After kneading at the particle size mixing ratio shown in Table 3 (outside the conditions of the present invention), molding, drying and firing were performed under the same conditions as in Comparative Example 1 to produce a semi-ribbon-like magcro refractory material. The chromium oxide impregnation remains untreated. Upon visual observation, cracks were found on the surface of the fired refractory material.

[0047]

[Table 3]

Comparative Example 3 Fe—Cr alloy was not used, only the raw materials shown in Table 1 were used, and the mixture was kneaded at the particle size mixing ratio shown in Table 4, followed by molding, drying and firing under the same conditions as in Comparative Example 1. Then, a semi-ribbon-shaped mug black refractory was prepared. Upon visual observation, no cracks were found on the surface of the fired refractory material.

[0049]

[Table 4]

The apparent porosity and characteristics (1) to (5) below were measured or tested for these four types of maguro refractories.

(1) Hot bending strength measurement: 3-point bending at 1400 ° C.

(2) Measurement of proportion of open pores having a radius of 5 μm or more in all pores: Measured by a mercury porosimeter.

(3) Thermal spall test: A 30 mm × 30 mm × 30 mm sample was cut out from an arbitrary part of a normal refractory material,
1400 ° C x 15 minutes heating → Air cooling (room temperature x 15 minutes) is set as one cycle and evaluated by the number of cycles until a part of the refractory is peeled off from the sample.

(4) Structural spall test: CaO / SiO ₂ =
The AOD furnace slag of 1.7 was cut out in the same manner as above 30
It was absorbed in a refractory sample of mm × 30 mm × 30 mm and evaluated in the same manner as in (3) above.

(5) Molten steel erosion test: Each refractory was placed in a high-frequency induction furnace kept in an Ar atmosphere, and the reduction amounts of the refractory cross-sectional areas due to melting damage were compared and evaluated. The erosion agent at this time is molten steel, the molten steel temperature is 1650 ° C., and the test time is 90 minutes.

The numerical value of the evaluation is represented by an index with Comparative Example 1 being 100, and the smaller the value is, the better the corrosion resistance is.

Table 5 shows the above results.

[0058]

[Table 5]

As shown in Table 5, the magcro refractory material of the present invention has improved resistance to structural spalls.

[0060]

EFFECTS OF THE INVENTION The magcro refractory of the present invention is a semi-ribbon type magcro refractory which has improved structural spall resistance of conventional magcro refractory and at the same time has heat spall resistance equivalent to that of conventional materials. .

Claims (1)

[Claims] 1. A main raw material is an electro-fused magnesia-chrome clinker of 50-80 Wt% and an Fe-Cr alloy of 0.5-2 Wt%, and other raw materials are one or more of magnesia, chromium oxide and chromium ore. A magnesia-chromium refractory which is impregnated with fine powder of chromium oxide after firing.