JPH05155655A - Magnesia carbon brick - Google Patents

Abstract

PURPOSE:To improve thermal spalling resistance of a magnesia carbon brick. CONSTITUTION:A magnesia carbon brick is obtained by adding a binder to a blended material of 70-90wt.% magnesia having >=1mm particle diameter, residual magnesia component composed of magnesia having <1mm particle diameter and a carbon refractory material followed by kneeding and forming. Thus, reduction of carbon content in the brick becomes to be available while keeping the thermal spalling resistance. This method contributes to the production of a high grade low carbon steel.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a magnesia excellent in heat resistant spall suitable as a lining material for steel refining equipment.
It concerns carbon bricks.

[0002]

2. Description of the Related Art At present, magnesia carbon bricks are used in various iron and steel smelting equipment such as electric furnaces, molten steel ladles, vacuum degassing furnaces, mainly converters. Magnesia
Since carbon brick is composed of high melting point magnesia and carbon that is difficult to wet with slag, it has excellent corrosion resistance. In addition, since carbon has high thermal conductivity, magnesia-carbon brick is also excellent in heat resistance spall resistance.

Such magnesia-carbon bricks are prepared by mixing magnesia clinker with carbonaceous refractory materials such as phosphorous graphite, pitch and coke, and kneading and molding a mixture containing a metal or various oxides as required. Manufactured. At this time, the magnesia clinker used has an appropriate particle size distribution to control the filling and compactness of the brick during molding. However, as disclosed in JP-A-59-35062, the magnesia clinker having a relatively coarse particle diameter of 1 mm or more is generally used in an amount of 40 to 60% by weight based on the whole magnesia clinker. is there.

[0004]

[Problems to be Solved by the Invention]
The production of high-quality steel with excellent properties is required, and the carbon concentration in the steel tends to be reduced to meet the demand. Therefore, to ensure the quality of steel, transfer of carbon from refractory to molten steel,
So-called carbon pickup is a problem. Therefore, in order to suppress the movement of carbon as much as possible, it is aimed to limit the amount of carbon in the refractory.

However, as described above, in magnesia-carbon bricks, carbon having a high thermal conductivity contributes to the heat-resistant spalling property. Therefore, as the carbon content in the brick decreases, the heat-resistant spalling property of the brick decreases. There is a problem of doing.

The present invention is intended to solve such a problem, and the object of the present invention is to reduce the amount of carbon in a magnesia carbon brick, but to provide a heat resistant spall. It is to provide a magnesia carbon brick with improved properties.

In achieving the above-mentioned object, first,
The grain size composition of magnesia used in conventional magnesia carbon bricks was reexamined. As a result, the inventors have reached the following basic consideration and completed the present invention.

That is, if the proportion of magnesia having a large particle size is increased, the total surface area of the magnesia particles is reduced. If the total surface area of the magnesia particles is reduced, the carbon abundance around each magnesia particle is relatively high even if the amount of carbon is constant. This results in that the magnesia expands with the heating of the brick, but the higher the carbon density existing around the magnesia particles, the higher the expansion and absorption capacity and the better the heat resistant spalling.

[0009]

Based on such a basic consideration, the present invention provides a magnesia carbon brick containing 70 to 92 wt% of the main components of magnesia and carbon refractory. % Is a magnesia having a particle size of 1 mm or more, and the remainder is a carbon-based refractory material and magnesia having a particle size of less than 1 mm, and a binder is added to the magnesia-carbon brick obtained by kneading and molding.

As the raw material of magnesia used in the present invention, any of electro-melting magnesia, seawater magnesia, naturally occurring magnesia and the like can be used. In the present invention, the amount of coarse-grained magnesia having a particle diameter of 1 mm or more in magnesia is set to 70 to 92 wt% of the total mixture of total magnesia and carbon-based refractory material.

When the amount of the coarse-grained magnesia having a particle size of 1 mm or more is less than 70 wt% of the total amount of the composition, the amount of the carbon-based refractory material is small, for example, 5 to reduce the amount of carbon in the composition of the brick.
If it is less than wt%, the dispersion of the carbon-based refractory material will be insufficient, and the effect of improving the heat-resistant spall property by using coarse-grained magnesia cannot be expected. If the amount of coarse magnesia with a particle size of 1 mm or more exceeds 92 wt% of the total composition, the total amount of magnesia with a particle size of less than 1 mm and the carbon-based refractory material in the composition will be less than 8 wt%. Not enough to fill the spaces between the grains. For this reason, many closed or open pores are present in the brick, which causes reduction in strength and deterioration in corrosion resistance.

The maximum particle size of the coarse-grained magnesia depends on the size and shape of the brick and is not particularly limited, but in the case of the long magnesia carbon brick used in the converter, The grain size of grain magnesia can be about 20 mm.

In the present invention, phosphorous graphite, earth graphite, pitch, coke, tar and the like can be used as the carbon-based refractory material mixed with magnesia. Further, an organic binder such as a phenol resin is used as a binder for kneading and molding a mixture of magnesia and a carbon-based refractory material. The kneaded / molded mixture is dried at a temperature of about 230 ° C. to obtain a brick.

By the way, the carbon-based refractory material composing the brick is easily oxidized at high temperature, and when the carbon and the carbon-based refractory material in the organic binder composing the matrix in the brick structure disappear due to the oxidation, the magnesia grains are slag or slag. The friction of molten steel easily flows out and the durability of the brick deteriorates. In order to prevent oxidation of such carbon-based refractory materials and prevent deterioration of durability, Al, Si, Ca, Mg, Fe and
It is effective to add one or more metal powders selected from Cr or alloys thereof such as Al-Mg powders to the blend.

The addition of such metal powders can be expected to have two major effects: prevention of carbon oxidation by preferential oxidation of metals and improvement of strength during hot working. However, the addition of the metal powder simultaneously increases the elastic modulus of the brick itself and has a negative effect on the heat-resistant spall resistance. Therefore, addition of metal powder may be inappropriate for bricks applied to places where extremely high heat resistance spall resistance is required, such as the tuyere of the bottom of a converter. In such a case, as an effective means for improving the strength, it is effective to perform the impregnation treatment by firing the brick without adding the metal powder to the composition.

This calcination is preferably performed in a reducing atmosphere at 1500 ° C. or lower. Since the volatile component in the organic binder is scattered by firing to generate pores, by impregnating the pores with pitch or tar, the strength of the brick is significantly improved and the abrasion resistance can be increased.

[0017]

As described above, increasing the use ratio of coarse-grained magnesia having a grain size of 1 mm or more means reducing the total surface area of magnesia grains in the brick structure. In other words, the amount of coarse-grained magnesia dispersed as an aggregate increases, and conversely, the amount of fine magnesia particles forming a part of the matrix decreases.

The matrix is composed of a binder and a carbon-based refractory material together with fine magnesia particles. If the amount of carbon-based refractory material used is the same, the carbon-based refractory material in the matrix is reduced due to the reduction of the fine magnesia particles. The existing density of wood increases relatively. Due to such an increase in the carbon density around the magnesia particles, the expansion and absorption of magnesia by carbon and the stress relaxation effect inside the brick are enhanced, and as a result, the improvement of heat resistant spall resistance is achieved.

When the magnesia-carbon brick is applied to a container in a reducing atmosphere at high temperature such as an RH vacuum degassing furnace, the magnesia-carbon reaction (Mg
O + C → Mg ↑ + CO ↑) progresses, and the adverse effect on the durability of bricks cannot be avoided. On the other hand, in the magnesia-carbon brick of the present invention, since the surface area of magnesia is reduced by the coarsening of magnesia, it has an effect of effectively suppressing the magnesia-carbon reaction.

[0020]

EXAMPLE Magnesia and phosphorous graphite were mixed in the proportions shown in Table 1, and a phenol resin was added to a mixture containing metal aluminum powder or a mixture containing no metal aluminum powder, followed by kneading with a fret mixer. The mixture after kneading was molded by a friction press, then dried at a temperature of 230 ° C. for 24 hours, and further reduced and fired at 1500 ° C. to obtain test bricks.

Nos. 1 to 9 shown in Table 1 are products of the present invention, No. 10 is a conventional product, and Nos. 11 to 13 are comparative products whose blending ratio deviates from the claims of the present invention. Is.
In addition, No. 9 is a reduction fired product at 1500 ° C for 3 hours. The magnesia products of the present invention, conventional products and comparative products shown in Table 1
The evaluation test described below was performed on the carbon brick. The results of the evaluation test are also shown in Table 1.

[Table 1]

Thermal spall test: A test piece of 40 × 40 × 114 mm was cut out from a prototype brick having a parallel shape and cut at 1650 ° C.
After immersing in the molten steel of No. 3 for 5 minutes at a depth of 40 mm, forced air cooling is performed for 30 minutes. After repeating this cycle 15 times, the degree of cracking was visually evaluated relatively as follows. A: There is no crack. ◯: There are fine cracks. Δ: There is a large crack. X: Peeling occurred.

At the same time as the visual observation, the ultrasonic wave propagation speed of the test piece was measured before and after the spall test, and the ultrasonic wave propagation speed ratio was calculated by the following equation.

[Equation 1]

If a crack is generated in the test piece by repeated heating / cooling by the spall test, the ultrasonic wave propagation speed becomes low. Therefore, the larger the value of this ratio, the better the heat resistant spall resistance. Figure 1 shows that the amount of graphite is the same 10 wt%
It is a graph which showed the relationship between the amount of magnesia of 1 mm or more, and an ultrasonic wave propagation velocity ratio about the brick of No. 1-5 and 10-12.

Weight reduction after reduction firing: 50 × from brick
A test piece of 50 x 50 mm is cut out, and this test piece is reduced and baked in a coke breeze at 1400 ° C for 5 hours,
The weight change rate (%) after firing was determined. Weight change (decrease)
The larger the value, the more the magnesia-carbon reaction occurs inside the brick. From the results obtained for the No. 1 to 5 and 10 to 12 bricks, the relationship between the amount of magnesia of 1 mm or more and the weight change rate after reduction firing is shown in a graph in FIG.

Corrosion resistance: A trapezoidal columnar test piece was cut out from a brick having a parallel shape and loaded on a rotating drum, and while the drum was rotating, a flame of oxygen: propane = 4: 1 was blown into the drum to reach 1650 ° C. Heated. Then 16
While maintaining the temperature at 50 ℃, CaO / SiO ₂ = 3 slag was added and an erosion test was performed for 15 minutes. Then, the slag was discharged, the same slag was newly added, and the erosion test was conducted in the same manner. After repeating this cycle 10 times, the test piece was cut to measure the amount of erosion (mm). Conventional product No. 1 from the measured melt loss
The erosion amount of 0 was set to 100 and the erosion ratios of the other test pieces were calculated. It can be said that the smaller the corrosion loss ratio, the better the corrosion resistance.

In the conventional magnesia carbon brick,
As described above, the heat-resistant spall resistance is largely owed to the carbon contained in the carbon-based fire-resistant material. Therefore, in order to improve the heat-resistant spall resistance, a method of simply increasing the carbon content of the brick has been adopted.

The present invention is intended to improve the heat-resistant spalling property from the viewpoint different from the conventional common sense that the proportion of coarse-grained magnesia having a grain size of 1 mm or more is increased. This is clearly shown in Fig. 1. As is clear from Fig. 1, even if the carbon amount is the same, the ultrasonic propagation velocity ratio becomes high as the amount of magnesia particles with a diameter of 1 mm or more increases. It was confirmed that the heat-resistant spall property was improved. Further, another effect of the present invention due to the coarsening of magnesia is shown in FIG.
In Fig. 2, the magnesia coarsening causes the magnesia
It is clearly recognized that the carbon reaction (MgO + C → Mg ↑ + CO ↑) is suppressed. Further, the products No. 8 and No. 9 of the present invention to which metallic aluminum was not added had good thermal spalling property and corrosion resistance. Especially, the result was remarkable in No. 9 which was pitch-impregnated after firing at 1500 ° C.

Further, from Table 1 of the example, even if the amount of coarse-grained magnesia is the same, the larger the maximum grain size of magnesia,
It can also be seen that the heat resistant spalling property is improved. From this, it was confirmed that the surface area of magnesia is closely related to the heat-resistant spall resistance.

[0030]

The magnesia carbon brick of the present invention contains 70 magnesia particles having a particle size of 1 mm or more in its main component.
By setting the content to ˜92 wt%, it becomes possible to secure sufficient heat-resistant spall resistance even when the carbon content in the brick is reduced. For example, the carbon-based refractory material content is 5 wt
% Or less, good heat spall resistance can be obtained. This is particularly advantageous in the production of low carbon steel.

That is, if the amount of carbon in the brick is small, the transfer of carbon from the brick to the steel in the manufacturing process can be suppressed, and high-quality low-carbon steel can be stably manufactured. As described above, the present invention greatly contributes to the upgrading of steel.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the amount of magnesia having a particle size of 1 mm or more and the ultrasonic wave propagation velocity.

FIG. 2 is a graph showing the relationship between the amount of magnesia having a particle diameter of 1 mm or more and the weight change rate after reduction firing.

Front Page Continuation (72) Tsuneo Kitai, 1-3-1, Niihama, Arai-cho, Takasago, Hyogo Prefecture Harima Ceramic Co., Ltd. Company (72) Inventor Myoukei Maekawa 1-3-1 Niihama, Arai Town, Takasago City, Hyogo Prefecture Harima Ceramics Co., Ltd.

Claims (2)

[Claims] 1. In a magnesia-carbon brick mainly composed of magnesia and a carbon-based refractory, 70 to 92 wt% of the main composition is magnesia having a particle size of 1 mm or more, and the remainder is a carbon-based refractory material and a particle size. A magnesia carbon brick characterized by being made by kneading and molding a binder added to magnesia of less than 1 mm. 2. The molded product obtained by kneading and molding is 1500 ° C.
The magnesia carbon brick according to claim 1, which is further impregnated with pitch or tar after firing in the following reducing atmosphere.