JP2501155C - - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to corrosion resistance and slag infiltration resistance suitably used for lining of molten steel vacuum degassing furnaces such as DH, RH, VOD and VAD. The present invention relates to a magnesia-chrome brick having excellent hot strength and high hot strength. BACKGROUND OF THE INVENTION Lined bricks in vacuum degassing furnaces are used under severe conditions under high temperature vacuum with strong stirring of a molten steel stream containing slag. For this reason, compared to other bricks as a lining brick of a vacuum degassing furnace, it is chemically stable under vacuum, and as a bonding form of refractory particles, direct bonding in which particles are directly bonded by firing, or from inside the particles Magnesia-chromic brick, which has high hot strength and excellent corrosion resistance, is used because a secondary spinel bond formed by spinel precipitation and bonding forms a strong structure. However, in recent degassing treatments, the treatment time has been increased and the treatment temperature has been increased in order to improve the steel quality, the molten steel stirring has been enhanced by increasing the amount of argon gas blown, the oxygen refining ratio has been increased, and the flux refining ratio has been increased. And the durability of the lining refractories is reduced. [0004] Therefore, magnesia-chromic bricks having higher hot strength and better corrosion resistance than before have been required, and various attempts have been made for that purpose. For example, JP-A-59-190257 and JP-B-3-4504 disclose:
For drawing the high corrosion resistance of the magnesia-chrome brick maximally, Cr ₂ O ₃ component Pic runner chromite (MgO · Cr ₂ O ₃₎ due to an increase in growth and quality spinels, to reduce the silicate bond is a low-melting Components other than MgO · Cr ₂ O ₃ (SiO
₂ , Al ₂ O ₃ , Fe ₂ O ₃ ) have been proposed to reduce the magnesia-chromic brick as much as possible. [0006] Generally, magnesia-chromic brick uses chromite, which is a natural raw material, and an electrofused magcroclinker, which is a raw material of the chromium ore, as a raw material. SiO ₂ other than MgO · Cr ₂ O ₃ to reduce the refractoriness and corrosion resistance of the _{brick, Al 2 O 3, Fe 2} O ingredient 5 to 15% by weight of such _3, contains inevitably. For this reason, raw materials containing components that generate low-melting-point minerals are not used as much as possible. Magnesia chromium, which further uses chromium oxide and magnesia clinker in addition to an electrofused magcroclinker composed of MgO and Cr ₂ O ₃ , It can be said that high quality brick has the highest fire resistance and the highest corrosion resistance in terms of composition. [0008] However, such magnesia-chrome brick has high corrosion resistance,
On the other hand, due to the high purity, the effect of liquid phase sintering due to impurities during firing for brick production can hardly be expected, and the firing temperature is about 2200 which is theoretically the melting point of MgO.Cr ₂ O _3.
It is necessary to reach around ° C, and there is a drawback that sintering is very difficult, and it is extremely difficult to obtain a dense and high-strength product. Therefore, although it is excellent against erosion due to a chemical reaction with a foreign component, there is a problem that the foreign component easily penetrates and the bond is small, resulting in poor structural spalling and abrasion loss. The present invention has solved the problem of chromium ore, which is a natural raw material, and magnesia-chromic brick using electrofused magcroclinker, which is a raw material of the chromite ore, as a raw material. It is an object of the present invention to provide a magnesia-chrome brick excellent in spalling resistance, abrasion resistance and abrasion resistance as well as having resistance to chemical erosion. Means for Solving the Problems The present invention contains 50 to 100% by weight of electrofused magcroclinker and 0 to 50% by weight of the total amount of magnesia clinker, chromite ore, and chromium oxide. Magnesia-chromium brick fired at a temperature of at least
₂ O ₃ component 5-15% by weight, and adjusting so that the SiO ₂ component below 1.2 wt%. When the Al ₂ O ₃ component and the SiO ₂ component in the magnesia-chromic brick are held in appropriate amounts, the precipitation of the secondary spinel is promoted to obtain a high-density and high-strength material. Further, it was completed based on the finding that a dense layer mainly composed of MgO.Al ₂ O ₃ was formed in the vicinity of the operating surface during use to prevent the invasion of foreign components, and the MgO was found in the vicinity of the operating surface during use. A dense layer mainly composed of Al ₂ O ₃ is formed, which suppresses slag penetration, thereby greatly improving corrosion resistance and slag infiltration resistance. EXAMPLES Table 1 shows the results of tests on the effects of the amount of Al ₂ O _{3 on} the general physical properties and corrosion resistance of magnesia-chromic ribbon bricks. Here, 95% by weight of various electrofused magcroclinkers having different Al ₂ O ₃ contents are mixed and kneaded with 5% by weight of chromium oxide.
After molding, a sample fired at 1850 ° C. was used as a sample. The erosion test employed a high frequency induction furnace lining method. The erosion agent is CaO / SiO ₂ = 0
. The powder of No. 5 was used and kept at 1700 ° C. for 10 hours. After the test, the sample was collected, and the amount of erosion and the slag infiltration thickness were measured. Here, the erosion amount and the infiltration thickness of the sample containing 3.2% of the Al ₂ O ₃ component are shown relative to each other as an index of 100. The smaller the index, the better. As the Al ₂ O ₃ component increases, the hot strength and the amount of secondary spinel deposited increase. When the Al ₂ O ₃ component is in the range of 5 to 15%, the corrosion resistance and the slag infiltration resistance are remarkably improved. After the corrosion resistance test, microstructure observation near the working surface of the sample was performed.
_In Comparative Example 1 of the conventional product containing 3.2% of the ₂ O ₃ component, the penetration of the slag into the grain boundaries was remarkable, and most of the bonds between the grains were broken. On the other hand, in Example 2 of the present invention containing 8.1% of the Al ₂ O ₃ component, a dense layer having a thickness of about 1 mm was formed about 2 mm inside from the operating surface, and a grain boundary was formed further inside. The penetration of slag into the slag was very low and the bond was not severely broken. In order to investigate the dense layer, component analysis was performed from the vicinity of the working surface to the inside. FIG. 1 schematically shows the result, and it can be seen that the spinel component contained in the brick changes as it approaches the operating surface. That is, in the vicinity of the operating surface, FeO, Fe ₂ O ₃ , and Cr ₂ O ₃ have disappeared due to the reduction reaction, and it can be seen that the dense layer in question is formed from the remaining MgO.Al ₂ O ₃ and MgO. M
The density of gO.Al ₂ O ₃ is 3.58, MgO · Cr ₂ O ₃ (density 4.39),
It is smaller than MgO · Cr ₂ O ₃ (density 4.48) and FeO · Cr ₂ O ₃ (density 5.09). Thus (Mg, Fe) O · ( Cr, Al, Fe) composite spinel indicated by ₂ O ₃ is to cause the appropriate volume expansion changing the MgO · Al ₂ O _3, conclude that a dense layer is formed be able to. Since the formation of the dense layer suppresses slag penetration into the inside, the corrosion resistance and the slag infiltration resistance are greatly improved. The reason why the appropriate amount of the Al ₂ O ₃ component is in the range of 5 to 15% by weight is that if the amount of Al ₂ O ₃ is small, the absolute amount of the finally remaining MgO · Al ₂ O ₃ becomes insufficient, and the Al ₂ O ₃ component becomes insufficient. If the amount is too large, the volume expansion due to the conversion to MgO.Al ₂ O ₃ becomes excessive, and conversely, the structure is destroyed, and no dense layer is formed in any case. Also, Al ₂ O ₃
If the amount of SiO ₂ is large along with the amount , Al ₂ O ₃ remaining without being able to form a solid solution with MgO forms silicate and a low-melting-point mineral, which also causes a reduction in corrosion resistance. Table 2 shows the results of tests on the effects of the amount of Al ₂ O _{3 on} the general physical properties and corrosion resistance of magnesia-chromic semi-ribbon bricks. Here, 30% by weight of magnesia clinker, 15% by weight of chromium ore, and 5% by weight of chromium oxide were blended with 50% by weight of various electrofused magnesia and chromia clinkers having different Al ₂ O ₃ contents, and the same method as in Table 1 was used. Samples were prepared, and general physical properties and corrosion resistance were evaluated. The corrosion resistance test method is the same as in Table 1. As shown in Table 1, the increase in Al ₂ O ₃ component increases the hot strength and the amount of secondary spinel deposited, and the Al ₂ O ₃ component is in the range of 5 to 15%. Improves corrosion resistance and slag infiltration resistance. This is for the same reason as described above. Al ₂ O ₃ is insufficient absolute amounts of the component amount is small MgO · Al ₂ O _3, also often to the volume expansion due to MgO · Al ₂ O ₃ of destroy tissue in the opposite becomes excessive. When the amount of Al ₂ O ₃ is large, M
The remaining Al ₂ O ₃ that could not form a solid solution with gO formed silicate and low melting point minerals.
Decreases corrosion resistance. From the above, an appropriate amount of the Al ₂ O ₃ component is 5 to 15% by weight. The magnesia-chromic ribbon brick of Example 2 containing 8.1% by weight of the Al ₂ O ₃ component within the scope of the present invention is the same as the conventional example 1 containing 3.2% of the conventional Al ₂ O ₃ component. Was used at the bottom of the DH furnace instead of the magnesia-chromic ribbon brick shown in Table 1 below.
As a result, the number of times of treatment in the DH furnace was 1.9 times that of the conventional case, and the life was greatly extended. The magnesia-chromic semi-ribbon brick of Example 4, which also contains 6.3% by weight of the Al ₂ O ₃ component, which is also within the scope of the present invention, contains the conventional Al ₂ O ₃ component of 3.6% by weight. DH instead of the magnesia-chromic semi-ribbon brick of Comparative Example 4
Used for furnace ramps. As a result, the service life of the inclined portion is 1.5 times that of the conventional one, and the service life is greatly extended. Further, Table 3 shows a sample obtained by kneading with various electrofused magcroclinkers having different Al ₂ O ₃ contents, sintering the mixture at 1850 ° C. after molding. [0024] [Table 3] in the range (no correction) Table 1 Similarly Al ₂ O ₃ component is 5 to 15% and, as a SiO ₂ component,
Table 1 shows 1.0% by weight, Table 2 shows 1.0 to 1.2% by weight, and Table 3 shows 1.1% by weight.
From this, when the SiO ₂ component is 1.2% by weight or less, the hot strength,
Precipitation amount of secondary spinel increases, corrosion resistance, slag infiltration resistance is significantly improved
You can see that . According to the present invention, the following effects can be obtained. (1) A highly durable magnesia-chromium brick excellent in structural spalling resistance and abrasion resistance and capable of sufficiently coping with severe degassing can be obtained. (2) This is used as a lining of a vacuum degassing furnace such as DH, RH, VOD, VAD, etc., and by suppressing slag permeation, a significant improvement in corrosion resistance and slag infiltration resistance can be achieved. The life of the furnace can be greatly extended.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 schematically shows a change in an oxide component from the working surface to the inside of a sample after a corrosion resistance test of magnesia-chromic ribbon brick.

Claims (1)

Claims: 1. An electrofused magcroclinker comprising 5 to 15% by weight of Al ₂ O ₃ component and 1.2% by weight or less of SiO ₂ component in all chemical components, and , 1800 °
Magnesia-chrome brick fired at a temperature of C or higher. 2. An electrofused magcroclinker containing not less than 50% by weight and a total amount of magnesia clinker, chromite ore and chromium oxide of not more than 50% by weight, and A in all chemical components
the l ₂ O ₃ component is 5 to 15% by weight , the SiO ₂ component is 1.2% by weight or less , and
Magnesia-chrome brick fired at a temperature of 1800 ° C or higher.