JP7824533B2 - Magnesia-chrome brick composition and manufacturing method thereof - Google Patents

Description

The present invention relates to a magnesia-chrome refractory raw material composition and a method for producing magnesia-chrome bricks.

Magnesia-chrome bricks have high hot strength and excellent corrosion resistance, making them ideal for use as lining materials in secondary steel refining furnaces (DH, RH, AOD, etc.), which are subject to strict operating conditions. However, the production of magnesia-chrome bricks requires high-temperature firing at over 1,800°C, which places a significant burden on the environment.

Patent Document 1 discloses a basic refractory material made using clinker in which there is no exsolution-precipitated spinel on the surface of the periclase and the lattice constant of the periclase is 4.206 Å or less, with the goal of lowering the firing temperature without compromising brick quality.

Furthermore, Non-Patent Document 1 discloses the hot properties of magnesia-chrome clinker containing 10.51 mass % of Fe ₂ O ₃ .

Special Publication No. 57-037552

Norio Yoshizawa et al., "Hot Properties of Electrofused Magnesium-Chromium Raw Materials, Refractories", 51 [1] (1999) P32-33

Patent Document 1 claims that high hot bending strength was achieved even at a low firing temperature of 1,300°C. However, the hot bending strength after firing at 1,300°C for two hours was less than half that of the strength after firing in a tunnel kiln at 1,800°C. This is not of sufficient quality for use in secondary steel refining furnaces, which require high loads.

Furthermore, Non-Patent Document 1 discloses the hot properties of magnesia-chrome clinker containing 10.51 mass % of Fe ₂ O ₃ , but the firing temperature is 1750° C., which places a heavy burden on the environment as described above.

The present invention was proposed in light of the above-mentioned conventional circumstances, and aims to provide a magnesia-chrome refractory raw material composition that exhibits excellent hot bending strength and corrosion resistance even when the brick firing temperature is lowered, as well as a method for producing magnesia-chrome bricks.

The present invention provides a magnesia-chrome refractory raw material composition containing 50% by mass or more and 95% by mass or less of an electrofused magnesia-chrome raw material having _{an Fe2O3} content of 14 % by mass or more and 30% by mass or less, and 5% by mass or more and 35% by mass or less of a magnesia raw material having an MgO content of 90% by mass or more.

The present invention also provides a method for producing magnesia-chrome bricks, which comprises firing the magnesia-chrome refractory raw material composition at a temperature of 1200°C or higher and 1600°C or lower.

By using this magnesia-chrome refractory raw material composition, it is possible to produce magnesia-chrome bricks with excellent corrosion resistance and hot bending strength, even at firing temperatures of 1200°C to 1600°C. Furthermore, lowering the firing temperature reduces the environmental impact of production.

The present invention relates to a raw material composed of the following electrofused magnesia-chromium raw material and magnesia raw material.

In the present invention, the electrofused magnesia-chrome raw material contains 10 to 30 mass % of Fe ₂ O _3. When a brick is produced by firing a composition of an electrofused magnesia-chrome raw material containing Fe ₂ O ₃ in the above range and a magnesia raw material, sintering is promoted even at a low firing temperature, and the bonds within the brick are developed, resulting in a denser structure, and it is believed that a brick having both excellent corrosion resistance and hot bending strength can be produced.

<Electrofused Magnesium-Chromium Raw Material>
The electrically fused magnesia-chrome raw material has an _Fe2O3 content of 10 _% by mass or more and 30% by mass or less. The electrically fused magnesia-chrome raw material can be produced by a known method. Specifically, calcined magnesia, magnesia _clinker , chromite, iron oxide, etc. are blended and melted in an electric furnace so that the _Fe2O3 content is 10% by mass or more and 30% by mass or less.

If _{the Fe2O3} content is less than 10% by mass, the hot bending strength of the brick will decrease when the firing temperature of the brick is reduced to 1200°C or less. Also, if _{the Fe2O3} content exceeds 30% by mass, the corrosion resistance of the brick will decrease.

<Magnesia-Chromium Refractory Raw Material Composition>
The magnesia-chrome refractory raw material composition preferably contains 50 to 95 mass% of an electrofused magnesia-chrome raw material having _{an Fe2O3} content of 10 to 30 mass% by mass. By adjusting the content within this range, it is possible to produce magnesia-chrome bricks that have high hot bending strength and excellent corrosion resistance even when fired at a low temperature.

As long as the electrofused magnesia-chrome raw material having an Fe ₂ O ₃ content of 10 to 30% by mass is blended in an amount of 50 to 95% by mass, electrofused magnesia-chrome raw materials of other compositions may be used in combination.

If the amount of the electrofused magnesia-chrome raw material is less than 50% by mass, the hot bending strength and corrosion resistance of the brick will decrease. On the other hand, if the amount of the electrofused magnesia-chrome raw material exceeds 95% by mass, the heat spalling resistance of the brick will decrease.

<Magnesia raw material>
Known magnesia raw materials can be used as the magnesia raw material. Examples include electrofused magnesia, seawater magnesia, natural magnesia, and sintered magnesia. The MgO content in the magnesia raw material is preferably 90% by mass or more, and more preferably 95% by mass or more. By adjusting the MgO content in the magnesia raw material to this range, corrosion resistance is improved.

It is preferable to blend 5% to 35% by mass of magnesia raw material. By using this range, it is possible to produce magnesia-chrome bricks that have high hot bending strength and excellent corrosion resistance, even when fired at a low temperature.

If the magnesia raw material is less than 5% by mass, the heat spalling resistance of the brick will decrease. On the other hand, if the magnesia raw material exceeds 35% by mass, the amount of electrofused magnesia-chrome raw material will be reduced, and the desired effect of this invention will not be achieved.

<Other ingredients>
Commercially available chromium oxide may be added. When chromium oxide is used, its content is preferably 10% by mass or less relative to 100% by mass of the magnesia-chrome refractory raw material composition. By adjusting the content within this range, it is possible to produce a magnesia-chrome brick that has high hot bending strength and excellent corrosion resistance even when the firing temperature is low.

When the chromium oxide content is 10% by mass or less, it is possible to prevent a decrease in yield due to lamination occurring after molding and cracks due to reaction with magnesia during firing. On the other hand, while it is not absolutely necessary to add chromium oxide, adding it will improve the corrosion resistance of the brick.

Other known materials such as chromium ore, red iron oxide, and recycled magnesia-chrome bricks may also be blended, provided that they do not impair the effects of the present invention. Known sugars, phenolic resins, and the like can be used as binders. A magnesia-chrome refractory raw material composition can be obtained by blending and kneading these raw materials.

<Magnesia-chrome brick manufacturing method>
The magnesia-chrome refractory raw material composition described above is press-molded in a conventional manner and fired at 1200° C. to 1600° C. to obtain a magnesia-chrome brick.

Table 1 shows the compositions of four types of electrofused magnesia-chrome raw materials with different Fe ₂ O ₃ contents.

Table 2 shows the formulations of magnesia-chrome refractory raw material compositions using the above four types of electrofused magnesia-chrome raw materials, and the evaluation of magnesia-chrome bricks produced using the same.

To create the test specimens, a hydraulic press was used to mold standard JIS R2101 bricks (length 230 mm, width 114 mm, thickness 65 mm). The firing temperature was varied from 1100°C to 1800°C, and magnesia-chrome bricks were obtained.

<Hot bending strength>
The hot bending strength was measured in accordance with JIS R 2656. The test temperature was 1400°C.

<Corrosion resistance>
The amount of corrosion was measured by a horizontal rotary corrosion test. That is, the sample was lined in a drum-shaped rotary furnace, an erosion agent was placed inside, and the sample's amount of corrosion was measured by heating. The heating method was electric arc heating, the heating temperature was 1700°C, and the holding time was 5 hours. The erosion material used was slag with a CaO/SiO2 _ratio of 1.0, which was replaced with a new one every hour. After the test, the test piece was recovered, cut, and the amount of corrosion was measured. The corrosion resistance was expressed as an index, with the amount of corrosion in Example 11 being 100. A smaller index indicates less wear.

In Experimental Examples 1 to 5, the blending ratio of electrofused magnesia-chrome raw material A was fixed within the range of the present invention, and the firing temperature was varied from 1100°C to 1800°C. Good results were obtained at firing temperatures of 1200°C or higher. Firing at 1800°C also provided good bending strength and corrosion resistance, but did not achieve the reduction in environmental impact achieved by low-temperature firing, which is the objective of the present invention.

In Experimental Examples 6 to 8, the blending ratio of the electrically fused magnesia-chrome raw material was varied within the range of the present invention, and the firing temperature was fixed at 1450°C, and good results were obtained in all cases. In Experimental Examples 9 and 10, the _Fe2O3 content of the electrically fused magnesia- _chrome raw material was varied within the range of the present invention, and the firing temperature was fixed at 1450°C, and good results were obtained in all cases.

In Experimental Example 11, the Fe ₂ O ₃ content of the electrofused magnesia-chrome raw material was outside the range of the present invention, and the firing temperature was 1450° C., resulting in poor hot bending strength and corrosion resistance.

As explained above, the present invention uses an electrofused magnesia-chrome raw material with an Fe ₂ O ₃ content of 10% by mass or more and 30% by mass or less, thereby making it possible to obtain magnesia-chrome bricks with excellent corrosion resistance and hot bending strength even at firing temperatures of 1200° C. to 1600° C. Furthermore, lowering the firing temperature reduces the environmental impact of production.

Claims (2)

A magnesia- _chrome refractory raw material composition comprising 50% by mass or more but 95% by mass or less of an electrofused magnesia-chrome raw material having an _Fe2O3 content of 14 % by mass or more but 30% by mass or less, and 5% by mass or more but 35% by mass or less of a magnesia raw material having an MgO content of 90% by mass or more. A method for producing a magnesia-chrome brick, which comprises molding the magnesia-chrome refractory raw material composition according to claim 1 and then firing the molding at a temperature of 1200°C or higher and 1600°C or lower.