JP2022060911A - Method of producing lf-ladle magnesia-carbon brick - Google Patents

Abstract

To provide a method of producing LF-ladle magnesia-carbon bricks of low elasticity with a low graphite content, capable of suppressing opening of a horizontal joint from occurring while in use.SOLUTION: The method of producing LF-ladle magnesia-carbon bricks, includes kneading, molding and subsequently heat-treating a refractory raw material composition containing 3 to 9 mass% of scaly graphite, 1.5 to 4 mass% of aluminum, 1 to 6 mass% of silicon carbide, and 80 to 94 mass% of magnesia, with the content therein of expanded graphite being 2 mass% or less (including 0).SELECTED DRAWING: None

Description

The present invention relates to a method for producing a magcarbon brick for an LF pan used for a molten steel pan (LF pan) used in the LF (Ladle Furnace) method in a steelmaking process.
In the present invention, the molten steel pan used in the LF (Ladle Furnace) method is referred to as an "LF pan".

In the LF pan, the lining is lined with refractory material, and usually, non-fired brick containing castable or graphite is used for the metal line, and magcarbon brick (magnesia carbon brick) is used for the slag line.

Since this magcarbon brick generally contains 10 to 20% by mass of graphite, it has a high thermal conductivity, and when used as a lining brick, the iron skin temperature of the molten steel pan rises, causing the strength of the iron skin to decrease or deform. There's a problem. In addition, the heat dissipation due to this lowers the molten steel temperature, which may cause a problem of energy loss in the molten steel pan. In order to reduce this energy loss, it is conceivable to use magcarbon bricks with a low graphite content, but if the amount of graphite is reduced, the bricks will have high elasticity and high expansion, resulting in insufficient durability. There is.

In particular, since the molten steel is heated by the electrodes in the LF pan, the temperature difference becomes large as compared with other molten steel pans, and the magcarbon bricks lined in the LF pan generate a large thermal stress. For this reason, when magcarbon bricks with a reduced amount of graphite are used in the LF pan, peeling easily occurs from the working surface of the bricks due to thermal stress, and the bricks have a short life. Furthermore, the brick lined in the LF pot repeats expansion and contraction in the vertical direction (vertical direction), so that the joint opening that occurs in the horizontal joint (horizontal joint) becomes larger than that of other molten steel pots. There is a problem that the plumb bob inserted into the crack due to the opening of the joint promotes peeling.

For example, Patent Document 1 discloses a graphite-containing basic refractory in which spinel-dispersed pericule clinker is 40 to 90% by weight, graphite is 3 to 9% by weight, and the balance is magnesia clinker. It is described that this spinel-dispersed pericure clinker has an effect of dispersing and attenuating the propagation of cracks, and thus has excellent spolin resistance. However, since the spinel-dispersed pericure clinker contains 5 to 15% by weight of Al ₂ O ₃ , there is a problem that the corrosion resistance is insufficient when applied to the slag line of the LF pan.

Further, in the examples of Patent Document 2, a magcarbon brick having a graphite content of 2% by mass is disclosed, but this magcarbon brick has a problem that the brick has high expansion and high elasticity due to its low graphite content. be. As a result, when the mug carbon brick of this embodiment is used in the slag line of the LF pan, cracks parallel to the working surface are generated for the above reason, and peeling from the working surface is likely to occur.

Further, in Patent Document 3, thin-walled expanded graphite having a thickness of 12 μm or less is 1 to 12 w%, silicon carbide having a particle size of 150 mesh (Tyler standard sieve) or less is 0.5 to 10 wt%, and the balance is a fire-resistant aggregate composition mainly composed of magnesia. A magnesia-carbonite non-firing brick produced by adding a metal powder and a binder to 100 wt% is disclosed.
However, as in Patent Document 2, magcarbon bricks containing thin-walled expanded graphite have a problem of poor corrosion resistance because the filling property of the clay during molding is deteriorated and the structure has a high porosity. Therefore, when used in a slag line, the corrosion resistance is significantly reduced and the life of the LF pan is shortened.

Japanese Unexamined Patent Publication No. 63-195161 Japanese Patent No. 6026495 Japanese Unexamined Patent Publication No. 2000-319063

An object to be solved by the present invention is to provide a method for producing magcarbon bricks for LF pots, which has low elasticity even if the graphite content is low and can suppress the occurrence of joint opening of horizontal joints during use. It is in.

The present inventors have found that by adding a specific amount of silicon carbide to magcarbon bricks having a low graphite content, the elastic modulus decreases and the residual expansion increases. As a result, it was found that magcarbon bricks for LF pots having excellent durability can be obtained by suppressing the occurrence of peeling of bricks from the working surface or the occurrence of joint opening of horizontal joints.

That is, according to the present invention, the following methods 1 to 3 for producing mug carbon bricks for LF pots are provided.
It contains 3 to 9% by mass of scaly graphite, 1.5 to 4% by mass of aluminum, 1 to 6% by mass of silicon carbide, and 80 to 94% by mass of magnesia, and the content of expanded graphite is 2% by mass or less ( A method for producing graphite for LF pan, which is kneaded with a fire-resistant raw material compound according to (including 0), molded, and then heat-treated.
2. 2.
The method for producing magcarbon bricks for LF pots according to 1 above, wherein the bricks are pressure-molded with the upper and lower surfaces of the bricks as a pressure surface based on the position when the bricks are lined in the LF pot at the time of molding.
3. 3.
The method for producing magcarbon bricks for LF pans according to the above 2, wherein the thickness of the bricks after molding in the pressure direction at the time of molding is 80 to 120 mm.

The magcarbon brick for LF pan obtained by the production method of the present invention has a low elastic modulus and a large residual expansion even if the graphite content is low. As a result, even if it is used in an LF pan in which the temperature difference is large compared to other molten steel pans, it suppresses the occurrence of peeling of bricks from the working surface or the opening of horizontal joints, resulting in excellent durability. .. Moreover, since the graphite content is low, energy loss can be suppressed.

Explanatory drawing which shows the pressurizing direction at the time of molding and the shape after molding in one Example of this invention.

The fire-resistant raw material compound used in the present invention contains 3 to 9% by mass of scaly graphite, 1.5 to 4% by mass of aluminum, 1 to 6% by mass of silicon carbide, and 80 to 94% by mass of magnesia. The content of expanded graphite is 2% by mass or less (including 0).

Of these raw materials, magnesia is used as a main raw material in an amount of 80 to 94% by mass because it is a raw material having excellent slag resistance. If the amount of magnesia is less than 80% by mass, the slag resistance becomes insufficient, and if it exceeds 94% by mass, the spalling resistance becomes insufficient.
As the magnesia, fused magnesia or sintered magnesia can be used, and those having an MgO purity of 93% by mass or more can be used.

Silicon carbide is used in an amount of 1 to 6% by mass for the purpose of increasing the residual expansion and reducing the elastic modulus. If the amount of silicon carbide is less than 1% by mass, these effects are insufficient, and if it exceeds 6% by mass, SiO ₂ generated by oxidation (SiC + O ₂ → SiO ₂ + C) produces a low melting point substance, so that the corrosion resistance is lowered. It should be noted that silicon carbide also has an antioxidant effect, similar to aluminum described later.
As the silicon carbide, any silicon carbide that is generally used for refractories can be used without any problem, and silicon carbide having a SiC purity of 80% or more can be used. Further, as the particle size of silicon carbide, those having a particle size of 0.1 mm or less can be used. By setting the particle size to 0.1 mm or less, the effect of increasing the residual expansion and the effect of lowering the elastic modulus can be further enhanced.

In the present invention, the "particle size" is the size of the mesh, and for example, the particle size of 0.1 mm or less means that the particle size passes through the mesh of 0.1 mm.

It is presumed that silicon carbide in brick exists in two types, one that oxidizes to SiO ₂ as described above when heated and the other that exists as it is without oxidation. It is considered that what is oxidized to SiO ₂ contributes to increasing the residual expansion because the volume expands. On the other hand, since silicon carbide that does not oxidize has a very large difference in the coefficient of thermal expansion from that of magnesia, which is the main raw material, it is considered that a gap is generated around the silicon carbide particles due to the difference in expansion when the brick is heated. After that, even if the temperature of the brick drops, the brick remains expanded, so that a gap remains around the silicon carbide particles, and it is considered that the elastic modulus of the brick decreases. Moreover, since the magcarbon brick of the present invention has a low content of scaly graphite, the thermal stress absorption action (effect of lowering the elastic modulus) by the scaly graphite is insufficient, so that the effect of lowering the elastic modulus by adding silicon carbide is more remarkable. become.

Scale graphite is used in an amount of 3 to 9% by mass for the purpose of reducing the elastic modulus. If the amount of scaly graphite is less than 3% by mass, the elastic modulus becomes high, and if it exceeds 9% by mass, the thermal conductivity of brick becomes high and the energy loss becomes large. It is known that the thermal conductivity of magcarbon bricks is determined by the graphite content (for example, the figure of Patent Document 1), and the upper limit of the scaly graphite content in the present invention is still the slag of the LF pan. The upper limit was 9% by mass, which did not reach the practical level for line magcarbon bricks.
As scaly graphite, scaly graphite usually used for magcarbon bricks can be used.

Aluminum is used in an amount of 1.5 to 4% by mass for the purpose of preventing oxidation, imparting residual expansion and imparting strength. If the amount of aluminum is less than 1.5% by mass, the strength becomes insufficient, and if it exceeds 4% by mass, the elastic modulus becomes high.
Aluminum is oxidized to Al ₂ O ₃ , and this Al ₂ O ₃ reacts with MgO to impart residual expansion, but at the same time, it also has an action of densifying the structure. Therefore, if the amount of aluminum used is too large, there is a problem that the spalling resistance is lowered. Therefore, in the present invention, by using silicon carbide in combination, it is possible to reduce the amount of aluminum used for antioxidant and the like, and it is possible to increase the residual expansion while suppressing the decrease in spalling resistance. There is a merit that can be done.

In the present invention, expanded graphite may not be used, but if it is desired to further reduce the elastic modulus, it can be used in an amount of 2% by mass or less. However, if the expanded graphite exceeds 2% by mass, the corrosion resistance is lowered.
Here, the expanded graphite is a scale-like graphite that is rapidly heated in a state where sulfuric acid or the like is contained between its structures and expanded several tens of times or 100 times or more. In the present invention, this expanded graphite is used. It is crushed into thin-walled material. As this expanded graphite, commercially available one can be used as a raw material for refractories.

In the fire-resistant raw material compound of the present invention, as raw materials other than the above, raw materials generally used as raw materials for magcarbon bricks shall be used without adverse effects if the total amount is about 5% by mass or less. Can be done. Specifically, it is an aluminum alloy, silicon, boride, pitch, carbon black, fiber, glass and the like.

The method for producing magcarbon bricks of the present invention is characterized by using the above-mentioned fire-resistant raw material compound, and other than that, it is the same as a general method for producing magcarbon bricks. That is, an appropriate amount of binder is added to the fire-resistant raw material compound, kneaded, molded, and then heat-treated. The heat treatment temperature can be about 150 to 800 ° C. As the binder, a binder such as a phenol resin or a furan resin to which a solvent is added can be used.

In the method for producing magcarbon bricks of the present invention, it is preferable to perform pressure molding with the upper and lower surfaces of the brick as a pressure surface with reference to the position when the brick is lined in the LF pot at the time of molding. As a result, the scaly graphite is oriented parallel to the pressurized surface in the brick, so that the elastic modulus in the vertical direction (vertical direction) when the brick is lined in the LF pot can be reduced, and the elastic modulus when the brick is used can be reduced. Thermal stress can be reduced. As a result, the effect of suppressing the peeling of the brick from the moving surface can be obtained. As the molding machine, a hydraulic press or a friction press generally used for producing bricks can be used.

Further, in the method for producing a mug carbon brick of the present invention, the thickness of the brick after molding is preferably 80 to 120 mm as the thickness in the pressurizing direction at the time of molding. The thickness of the brick after molding is almost the same even after the heat treatment, and the vertical thickness of the brick (thickness in the stacking height direction of the brick) as a product lined in the LF pan is also about 80 to 120 mm. On the other hand, the thickness of the conventional general LF pot brick in the stacking height direction is 230 mm.
That is, by setting the thickness of the brick after molding to 80 to 120 mm, the number of horizontal joints when the brick is lined increases as compared with the conventional case. As a result, the horizontal joint serves as an expansion / absorption allowance, and the stress on the brick during thermal expansion of the brick can be relieved.

An appropriate amount of phenol resin is added as a binder to the fire-resistant raw material formulation shown in Table 1, kneaded, molded into a beech-shaped brick shape as shown in FIG. 1 by an oil press, and heat-treated at a maximum temperature of 250 ° C. for 5 hours. (Drying treatment) was applied to obtain magcarbon bricks.
The pressurizing method at the time of molding is the arrow direction (vertical direction) shown in FIG. 1, and the upper and lower surfaces of the brick are set as the pressurizing surface with reference to the position when the brick is lined in the LF pan. The thickness of the brick after molding was 100 mm in the pressure direction at the time of molding. The thickness of the mug carbon brick after the heat treatment (drying treatment) was also 100 mm.
A sample for measuring physical characteristics was cut out from this magcarbon brick, and the hot bending strength, residual expansion coefficient and elastic modulus were measured and the corrosion resistance was evaluated.

The hot bending strength was measured at 1400 ° C. under a nitrogen atmosphere in accordance with JIS R 2656. The hot bending strength of 12 MPa or more was accepted.

The residual expansion coefficient is a measurement result of the linear change rate after reduction firing at 1400 ° C. for 3 hours. A residual expansion rate of 0.5% or more was regarded as acceptable.

The elastic modulus is a measurement result of the sound velocity elastic modulus after reduction firing at 1400 ° C. for 3 hours. In the measurement of the sonic elastic modulus, a sample having a shape of 50 × 50 × 50 mm was embedded in a coke breeze, heated to 1400 ° C. in an electric furnace, held for 3 hours, and allowed to cool naturally. Then, the speed of sound in the pressurizing direction and the non-pressurizing direction orthogonal to the pressurizing direction at the time of molding the sample was measured, and the elastic modulus in the pressurizing direction and the elastic modulus in the non-pressurizing direction were obtained. The lower the elastic modulus, the more effective it is in improving the spalling resistance. Specifically, the elastic modulus in the pressurizing direction was 25 GPa or less and the elastic modulus in the non-pressurizing direction was 35 GPa or less.

Corrosion resistance was evaluated by a rotary erosion test. In the rotary erosion test, the inner surface of the drum having a horizontal axis of rotation was lined with a test brick, and slag was added and heated to erode the surface of the brick. The heating source was an oxygen-propane burner, the test temperature was 1750 ° C., the slag composition was CaO: 40% by mass, SiO ₂ : 20% by mass, Al _{2O 3} : 20% by mass, FeO + Fe _{2O 3} : 20% by mass. The slag was discharged and charged 10 times every 30 minutes. After the test was completed, the size of the maximum melted part of each brick (remaining size of the brick) was measured and displayed as a corrosion resistance index with the remaining size of the brick of Example 1 shown in Table 1 as 100. The smaller the value of this corrosion resistance index, the better the corrosion resistance, and specifically, 100 or less was regarded as acceptable.

In the comprehensive evaluation, the case where all the above evaluations passed was regarded as a pass (〇), and the other cases were regarded as a fail (×).

In Examples 1 to 3, the content of silicon carbide differs within the range of the present invention, and all of them are excellent in corrosion resistance and have a sufficient residual expansion coefficient and a low elastic modulus. On the other hand, Comparative Example 1 does not contain silicon carbide, has a small residual expansion coefficient, and has a high elastic modulus. In Comparative Example 2, the content of silicon carbide exceeds the upper limit of the present invention, and the corrosion resistance is lowered.

In Examples 4 to 6, the content of scaly graphite differs within the range of the present invention, and all of them have good results. On the other hand, in Comparative Example 3, the content of scaly graphite is lower than the lower limit of the present invention, and the elastic modulus is high.

In Examples 7 to 9, the aluminum content differs within the scope of the present invention, and all of them have good results. On the other hand, in Comparative Example 4, the aluminum content is lower than the lower limit of the present invention, and the hot bending strength is lowered. Further, in Comparative Example 5, the amount of aluminum added exceeds the upper limit of the present invention, and the elastic modulus is high.

Examples 11 and 12 contain expanded graphite in a range of 2% by mass or less, which is a good result. On the other hand, in Comparative Example 6, the content of expanded graphite exceeds the upper limit of the present invention, and the corrosion resistance is lowered.

Claims (3)

It contains 3 to 9% by mass of scaly graphite, 1.5 to 4% by mass of aluminum, 1 to 6% by mass of silicon carbide, and 80 to 94% by mass of magnesia, and the content of expanded graphite is 2% by mass or less ( A method for producing graphite for LF pan, which is kneaded with a fire-resistant raw material compound according to (including 0), molded, and then heat-treated. The method for producing magcarbon bricks for LF pots according to claim 1, wherein at the time of molding, pressure molding is performed with the upper and lower surfaces of the bricks as a pressure surface with reference to the position when the bricks are lined in the LF pot. The method for producing a magcarbon brick for an LF pan according to claim 2, wherein the thickness of the brick after molding in the pressure direction at the time of molding is 80 to 120 mm.

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