JP5414062B2 - Magnesia-chromic brick - Google Patents

Description

  The present invention relates to a magnesia-chromic brick (hereinafter referred to as “magcro brick”) used for molten metal refining in the steel industry.

  Fused magnesia-chromium clinker (hereinafter referred to as “electrofused magcro clinker”) prepared by melting magnesia and chromium ore or magnesia and chromium oxide in an arc furnace and adjusting it to the target composition is the main raw material. The production of bricks is generally carried out. In this case, the melted magcro clinker once formed with spinel bonds is used as a raw material, and is shaped into a brick shape and fired again to form spinel bonds and is called a ribbony magcro brick. Yes. On the other hand, what is formed into a brick shape using magnesia and chromium ore or chromium oxide as raw materials and then fired is called a direct-quality magcro brick.

  Comparing rebonded magcro bricks with direct magcro bricks, the fused magcro clinker used in ribbon mag crocodile has a developed structure of composite spinel and is relatively easy to sinter. Is a brick with a dense organization. For this reason, ribbon-like magcro bricks are excellent in corrosion resistance, but are liable to crack when subjected to thermal shock and are inferior in thermal shock resistance. Therefore, when using these magcro bricks, considering the use conditions, a material having necessary characteristics is selected and used for each used part (see, for example, paragraph 0006 of Patent Document 1).

  On the other hand, studies for improving the characteristics of magchrom bricks have also been made. Regarding direct mag chrome bricks, Patent Document 2 describes mixing ferrochrome powder and chromium oxide powder in a refractory material containing magnesia and / or chromite or both. Therefore, it is described that it is possible to obtain a direct-bonded magcro brick with good densification of brick structure and good corrosion resistance. However, in order to achieve the high-efficiency operation that has been aimed at in recent years, further improvement in corrosion resistance is necessary, and there is a limit in the direct bond quality. In addition, it was thought that mixing a ferrochrome powder and a chromium oxide powder with ribbon-like magchrom bricks originally led to further densification of bricks having a dense structure, and cracks and cracks were likely to occur.

  As for ribbon-like magcro bricks, Patent Document 3 describes that the thermal shock resistance can be improved by combining two or more kinds of high-purity electrofused magcro clinker having different compositions. This may be useful as a melting furnace for waste or the like, which is an application envisaged by Patent Document 3, but magcro bricks obtained by Patent Document 3 are heat resistant because spinel coupling between aggregates is insufficiently developed. In the steel industry, molten metal refining equipment is exposed to intense molten steel flow, and wear is severe and difficult to apply.

JP 2000-191364 A Japanese Patent No. 2518559 JP 2004-217497 A

  The problem to be solved by the present invention is to provide a material that has high hot strength, high corrosion resistance, and thermal shock resistance in a ribbon-like magcro brick, and can obtain high durability.

  As a result of intensive studies on the improvement of the hot strength of ribbon-like magcro bricks, the present inventors have added a ferrochrome alloy alone or a chromium oxide alone to a refractory raw material aggregate mainly composed of a fused magcro clinker. Ribbon bricks manufactured from the raw material blends added in step 1 have poor thermal shock resistance and poor hot strength, but are added to the raw material blends containing both ferrochromium alloy and chromium oxide and kneaded. By forming and firing the kneaded clay obtained in this way, it was surprisingly found that a ribbon-like magcro brick not only excellent in corrosion resistance but also excellent in thermal shock resistance and hot strength was obtained, and the present invention was completed. It was.

The electrofused magcroclinker is a complex in which a fine structure is composed of minerals such as periclase (MgO), chromia (Cr ₂ O ₃ ), and picrochromite (MgCr ₂ O ₄ ). Fe in the ferrochrome alloy is particularly excellent in diffusibility into MgO and contributes to sintering of periclase. Cr in the ferrochrome alloy contributes to densification of the brick due to volume expansion due to oxidation during firing or use in an actual furnace. In addition, oxidized Cr has an effect of reacting with periclase to precipitate secondary spinel. Chromium oxide has a function of forming secondary spinel by reaction with periclase during firing or use in an actual furnace.

  The chemical composition of the ferrochrome alloy to be added preferably contains 50 mass% or more and 85 mass% or less of Cr, and the addition amount is preferably 0.5 mass% or more and 10 mass% or less as a proportion of the entire raw material mixture. If the amount of Cr is less than 50% by mass, the amount of Fe is relatively increased, and the corrosion resistance, which is the original characteristic of ribbon-like magcro brick, is lowered. On the other hand, if it exceeds 85% by mass, the amount of Fe is relatively decreased, and the effect of promoting the sintering of periclase becomes small. If the addition amount is less than 0.5% by mass, the effect of improving the hot strength, thermal shock resistance, and corrosion resistance is small, and if it exceeds 10% by mass, the amount of Fe increases and the corrosion resistance decreases.

  A finer particle size of the ferrochrome alloy contributes to the promotion of sintering of the electrofused magcro clinker, and is preferably less than 100 μm, more preferably less than 75 μm, and even more preferably less than 50 μm.

  The purity of the chromium oxide to be added is preferably 98% by mass or more. This is because the increase in impurities lowers the purity of the secondary spinel that is deposited and lowers the corrosion resistance. On the other hand, the particle size is preferably less than 100 μm. When the thickness is 100 μm or more, the surface area of the particles becomes small, and there are cases where the precipitation of secondary spinel is adversely affected due to a decrease in the chance of contact with the periclase. The addition amount of chromium oxide is preferably 0.5% by mass or more and 10% by mass or less as a ratio of the total amount of the raw material mixture.

  Here, in the present invention, the particle size of the particle is less than d means that the particle has a particle size that passes through a sieve having an opening d defined in JIS-Z8801, and the particle size of the particle is d or more. Means that the particle size remains on the same sieve.

Furthermore, in order to improve the thermal shock resistance of Magukuro brick of the present invention, to use an impurity amount defined by the following equation (1) of different fused mug black clinker two or more. In addition, the quantity of each chemical component in (1) Formula is mol% with respect to the whole electromelting magcro clinker.
Impurity amount (mol%) = (SiO ₂ + Al ₂ O ₃ + Fe ₂ O ₃ + CaO) / (MgO + Cr ₂ O ₃ ) (1)

  Impurities in the electrofused magcro clinker affect the sinterability at the time of firing, and the greater the amount of impurities, the easier the sintering, but the corrosion resistance decreases. On the other hand, if the amount of impurities is too large, the melting point of the formed bond portion is lowered even if the sinterability is improved, and the contribution to improving the hot strength is reduced. By using two or more types of electrofused magcro clinker with different amounts of impurities, synergy between a part that is difficult to sinter but has excellent corrosion resistance and hot strength and a part that is easy to sinter and contributes to densification of the entire brick Depending on the effect, a ribbon-like mug brick with an excellent balance between hot strength and corrosion resistance can be obtained. In addition, when bonds with different bond strengths are dispersed, cracks tend to propagate through the weak bond strength part, so that the magchrom that has excellent thermal shock resistance by exerting a bypass effect of cracks. Become a brick.

As a combination method of the fused magcro clinker having different amounts of impurities, 50% by mass or more of the fused mag crocliner having an impurity amount of 3.0 mol% or more and 10.0 mol% or less as a ratio to the whole raw material mixture. and 85 wt% or less, impurity amount is to use clinker less than 3.0 mol% in combination of 45 wt% or less than 10 wt%. Fused amount is more than 3.0 mol% impurity mug black clinker is possible to densify the entire relatively sintered easily Ribondo quality Magukuro Ren, you relatively large amount of addition of more than 50 wt% . However, the addition of an electrofused magcro clinker with an impurity amount exceeding 10.0 mol% is preferably a smaller addition amount because the corrosion resistance is significantly lowered. In addition, when the amount of the fused magcro clinker having an impurity amount of 3.0 mol% or more and 10.0 mol% or less exceeds 85 mass%, the amount of the impurity is relatively less than 3.0 mol%. Since the amount of crocliner used is reduced, the effect of improving thermal shock resistance is reduced.

  The magcro brick of the present invention is formed into a clay obtained by uniformly kneading by adding a binder to a raw material composition containing a refractory raw material aggregate, a ferrochrome alloy and chromium oxide, mainly composed of an electrofused magcro clinker. Can be obtained by firing. The firing temperature is, for example, preferably 1750 ° C. to 1900 ° C., more preferably 1800 ° C. to 1850 ° C. If the temperature is lower than 1750 ° C., it is difficult to form a direct bond by sintering magnesia and chromium oxide, while a temperature exceeding 1900 ° C. is not preferable because it is difficult to manufacture an industrially calcinable furnace.

  It is also possible to combine known refractory raw materials applicable to magchrome bricks as long as the effects obtained by the present invention are not significantly impaired. For example, various clinker such as magnesia, chromium ore, sintered magcro, alumina, zirconia, spinel, titania. However, since the main raw material of the refractory raw material aggregate used in the present invention is an electrofused magcro clinker, the use of other refractory raw material aggregates should be minimized. Specifically, it is preferable that the ratio of the electrofused magcro clinker is 70% by mass or more with respect to the whole refractory raw material aggregate.

  Examples of uses of the magnesia-chromium brick obtained by the present invention include RH, DH, REDA, AOD, VOD, molten steel pan, and LF pan, which are steelmaking facilities. The use of the product of the present invention for at least a part of the bricks for lining of these facilities can contribute to a long life.

  Ribbed magcro bricks of the present invention are excellent in hot strength, corrosion resistance and thermal shock resistance, and by increasing repair intervals and reducing the frequency of sudden repairs due to troubles, etc., particularly in the industrial field such as molten metal refining. Contribute.

  Hereinafter, embodiments of the present invention will be described based on examples.

Fused magcro clinker having different amounts of five kinds of impurities A to E shown in Table 1 was prepared. At the time of production, magnesia clinker, chromium oxide and chromite were blended so as to have a predetermined amount of impurities and arc-melted. The obtained electrofused magcro clinker was examined for chemical components in accordance with JIS-R2216. The amount of impurities is MgO = 40.3, Cr ₂ O ₃ = 152.0, SiO ₂ = 60.1, Al ₂ O ₃ = 102.0, Fe ₂ O ₃ = 159.7, CaO = 56.1. The molar amount was calculated using the molecular weight, and the impurity amount was calculated according to the formula (1).

Table 2 shows the results of evaluating the blending ratio of the blends used in Examples , Reference Examples and Comparative Examples of the present invention and the characteristics of the resulting bricks. Phenol resin is added as a binder to a raw material mixture composed of various electrofused magcro clinker, chromium oxide and ferrochrome alloy, and kneaded uniformly to obtain a clay, which is formed into a parallel shape and fired at 1820 ° C. Thus, a test brick was produced.

The hot bending strength as the hot strength was evaluated at a measurement temperature of 1480 ° C. in accordance with JIS-R2656. The corrosion resistance was evaluated by a rotating slag test method in accordance with the test method described in ASTM C874-77. As the slag, a synthetic slag having a basicity (CaO / SiO ₂ mass ratio) of 1.0 was used and tested at 1750 ° C. The amount of erosion of the brick after the test was measured, and the erosion index was calculated with the erosion amount of Example 1 being 100. The melting index indicates that the smaller the number, the better the corrosion resistance. For the thermal shock resistance, a 50 mm × 50 mm × 50 mm cube cut from the test brick was used as a test sample, which was inserted into an electric furnace maintained at 1400 ° C. and heated for 15 minutes. The operation of taking out the sample and taking the air-cooling for 15 minutes at room temperature was taken as one cycle, and this was repeated until the sample was destroyed due to the occurrence of cracks. Evaluate in 4 stages: x if destroyed in less than 7 times, △ if destroyed in 7 to less than 8 times, ○ if destroyed in 8 to less than 9 times, and ◎ if destroyed in 9 or more times. did. The thermal shock resistance becomes better in the order of ◎, ○, Δ, ×.

As shown in Table 2, it can be seen that the examples of the present invention have improved hot strength as compared with the comparative examples, and the corrosion resistance and thermal shock resistance are equivalent or better. In addition, comparing Reference Example 1 with Comparative Example 1 and Comparative Example 2, it is clear that the addition of only chromium oxide or ferrochrome alloy to the electrofused magcro clinker has low hot strength and poor corrosion resistance. It can be seen that it is useful to add chromium and a ferrochrome alloy in combination. Further, when Reference Examples 1 to 3, Example 5 and Example 6, Example 7 and Example 8, Example 11 and Example 12 are compared, the hot strength can be further increased by reducing the particle size of the ferrochrome alloy. It turns out that it improves. Accordingly, it can be seen that the particle size of the ferrochrome alloy is preferably less than 100 μm, more preferably less than 75 μm.

A sample from Example 4 16 is an example of using a combination of the amount of impurities different Fused mug black clinker. As shown in Examples 5 to 12 and Example 15, 85% by mass of an electrofused magcro clinker having an impurity amount of less than 3.0 mol% and 10% by mass of an impurity amount of 3.0 mol% or more. It can be seen that the thermal shock resistance can be improved by using a combination of not more than mass%. However, as shown in Reference Example 10, 55 mass% of the fused magclocliner having an impurity amount of less than 3.0 mol%, and 40 mass% of the fused magcroclinker having an impurity amount of 3.0 mol% or more. Then, the effect of improving the hot strength and thermal shock resistance is reduced, and the corrosion resistance tends to be lowered, which is not preferable.

As shown in Reference Example 13, a combination of only an electrofused magcrocliner having an impurity amount of less than 3.0 mol% is not preferable because the degree of improvement in hot strength becomes small. As shown in Reference Example 14, a combination of only an electrofused magcrocliner having an impurity amount of 3.0 mol% or more is not preferable because the thermal shock resistance and corrosion resistance tend to decrease. Further, as shown in Reference Example 16, when an electrofused magcro clinker having an impurity amount of 10.0 mol% or more is used, the corrosion resistance tends to be lowered.

  From the above, as a method of combining electrofused magclocliners having different amounts of impurities, the amount of electrofused magcroclinker having an impurity amount of 3.0 mol% or more and 10.0 mol% or less is 50 mass% or more and 85 mass% or less. It can be seen that it is most preferable to use an electrofused magcro clinker having an impurity amount of less than 3.0 mol% in a combination of 10 mass% to 45 mass%.

Claims (4)

Electrofused magnesia-Magnesia made by molding and firing a clay obtained by kneading a kneaded mixture with a ferrochrome alloy and chromium oxide added to a refractory raw material aggregate containing chrome clinker as a main raw material. in chrome brick,
As an electrofused magnesia-chromium clinker, an impurity amount defined by the formula (1) is 3.0 mol% or more and 10.0 mol% or less of an electrofused magnesia-chromium clinker with 50 mass% to 85 mass%, Magnesia-chromic brick characterized by using a combination of 10 mass% to 45 mass% of electrofused magnesia-chromium clinker with an amount of less than 3.0 mol% Impurity amount (mol%) = (SiO ₂ + Al ₂ O ₃ + Fe ₂ O ₃ + CaO) / (MgO + Cr ₂ O ₃ ) (1)   The magnesia-chromic brick according to claim 1, wherein the particle size of the ferrochrome alloy is less than 100 µm.   The magnesia-chromic brick according to claim 1, wherein the particle size of the ferrochrome alloy is less than 75 µm. RH, DH, REDA, AOD, VOD, molten steel pan or LF pan using the magnesia-chromic brick according to any one of claims 1 to 3 for at least a part of the brick for lining.