JP6457313B2 - Manufacturing method of magnesia chrome brick - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing magnesia / chrome brick obtained by kneading, molding and firing a refractory raw material composition, and more specifically, an electrofused magnesia clinker using magnesia (seawater magnesia) obtained from seawater. The present invention relates to a method for producing magnesia / chromium bricks using magnesia as a raw material.

  Magnesia / chrome brick has high stability under high temperature and vacuum, high mechanical strength in hot condition, excellent wear resistance, high hot strength, high corrosion resistance, thermal shock resistance, etc. From RH vacuum degassing furnaces, secondary refining furnaces such as AOD furnaces and VOD furnaces are widely used.

This magnesia-chromium brick is bound by the formation of composite spinel of (Mg, Fe) O. (Al, Fe, Cr) ₂ O ₃ composition by reacting raw material magnesia with chromium ore or chromium oxide. . Among them, MgO · Cr ₂ O ₃ spinel (hereinafter referred to as picrochromite) has a high melting point and, for example, high corrosion resistance against slag. Therefore, in order to improve the hot strength and corrosion resistance of magnesia / chrome brick, at least This spinel must be generated.

Further, magnesia / chrome bricks are classified into the following three types: direct bond, ribboned, and semi-ribbond, due to the difference in raw material composition.
Direct bond is a fire-resistant raw material composition composed of sintered magnesia clinker obtained by firing calcined seawater magnesia at about 1700-1800 ° C. and chromium ore to produce spinel. . Rebond is a fused magnesia clinker that has once formed spinel bonds using a fused magnesia chrome clinker (fused magcro clinker), which is obtained by electrolytic melting (electro fusion) of magnesia clinker and chromium ore in an arc furnace. Are fired and bonded again. Semilibond is a part of the electrofused magcroclinker that is fired by replacing it with magnesia clinker and chromium ore, etc. The magnesia clinker used for this is generally magnesia clinker made from magnesite ore. It is an electrofused magnesia clinker electrofused by arc heating.

  When direct bond and ribbon are compared, direct bond has more pores and is superior in thermal shock resistance, but slightly inferior in hot strength and corrosion resistance. On the other hand, since ribbond is easy to obtain a dense structure, it has excellent hot strength and corrosion resistance, but it is easily broken and inferior in thermal shock resistance, and semi-ribboned has intermediate characteristics between these direct bonds and ribbond. Therefore, these are used properly according to the characteristics.

Here, it is considered that the silicate phase in the magnesia-chrome brick plays an important role in the formation of spinel in the magnesia-chrome brick (see Non-Patent Document 1). That is, Cr ions (Cr ³⁺ ) contained in chromium ore in the firing stage diffuse into the magnesia clinker using the silicate phase as a medium, and precipitate as spinel in the cooling process after firing. The amount of spinel produced increases. However, the silicate phase has a lower melting point than magnesia and spinel and softens hot, leading to a decrease in the hot strength of the brick.

Thus, for example, Patent Document 1 discloses a direct bond magnesia-chromium brick in which the content of SiO ₂ is 2% by mass or less and the molar ratio of CaO to SiO ₂ is 0.7 to 0.9. ing. According to this Patent Document 1, as the CaO / SiO ₂ molar ratio increases, the brick becomes dense due to shrinkage after firing, but conversely, the melting point of the silicate decreases, so the hot strength decreases ( (Refer to the first paragraph in the left column of the third page of the patent gazette issued on March 14, 1983).

Further, Patent Document _2, B 2 _{O 3} content of from 0.2 to 1.0 wt%, using a magnesia clinker CaO content is less than 0.8 wt%, refractory raw material formulation magnesia-chrome brick where the SiO ₂ content of 2.5 mass% or less is disclosed as well as a CaO content of below 0.8 wt%. According to this, in addition to the behavior of CaO and SiO ₂ as described in Patent Document 1, the diffusion of Cr into the magnesia raw material particles is affected by the composition of the magnesia clinker, thereby improving the hot strength. Is required to contain 0.2% by mass or more of B ₂ O ₃ (see paragraph 0020).

Further, in Patent Document 3, since change occurs between FeO and Fe ₂ O ₃ due to temperature fluctuation or the like during the use of bricks and causes structural deterioration due to volume change, Cr ₂ O ₃ in magnesia-chrome bricks is contained. the mass ratio _{Cr 2 O 3 / Fe 2 O} 3 and iron oxide content and the terms _{of Fe} 2 _{O 3} discloses that the 3.5 to 4.5.

  As described above, conventionally, it has been considered to be important to control the flux component in order to improve the hot strength of magnesia-chrome brick. In other words, Cr ions are diffused into the brick through the silicate phase in the course of firing, and this silicate phase is the one in which impurities mainly derived from chromium ore enter the grain boundary of the magnesia clinker as a flux. Although such a silicate phase has a low melting point and reduces the hot strength of brick, it is considered necessary for the formation of spinel such as picrochromite. Therefore, in magnesia-chromium bricks, how to control the composition of impurities has been focused on so far.

  In addition, sintered magnesia clinker has been used exclusively in magnesia chrome bricks. This is because if there is a sintered magnesia clinker with relatively small crystal grains, there are many grain boundaries compared with the fused magnesia clinker with large crystal grains used in magnesia-carbonaceous refractories, etc. This is because ions are easily diffused, and spinel is precipitated on the entire clinker, which is considered to improve strength and corrosion resistance.

Japanese Patent Publication No.58-13511 JP 2010-195617 A Japanese Patent Publication No. 3-24425

Osaki et al., "Diffusion behavior of Cr203 in sintered magnesia of different purity" Refractory, 1997, (49) p31

  For example, secondary refining equipment such as RH vacuum degassing furnaces that use magnesia / chromium bricks adjust final components by reactions such as degassing, decarburization, and desulfurization in the steelmaking process. With further stricter quality and higher purity, the processing load of this secondary refining process is increasing. Therefore, it is necessary to prevent the refractory lining the smelting vessel from being damaged, and it is an urgent need to further improve the hot strength of the magnesia / chromium brick used for the lining refractory. However, in magnesia / chromium bricks, chromium ore is used as a raw material, so the inclusion of flux components (impurities) derived from gangue in the ore is inevitable, and these are further reduced to improve hot strength. It is difficult.

This invention is made | formed in view of such a prior art, and it aims at providing the manufacturing method of the magnesia-chrome brick which can raise a hot strength irrespective of a flux component.

  In order to solve the above problems, the present inventors consider that there is a limit to the improvement of the hot strength by controlling the flux component as in the past, and eagerly investigated the crystal grains and grain boundaries of magnesia clinker. Piled up. As a result, surprisingly, it is possible to improve the hot strength by using an electrofused magnesia clinker using magnesia obtained from seawater as a magnesia raw material instead of the conventional sintered magnesia clinker. The present invention was completed.

That is, the gist of the present invention is as follows.
(1) A method for producing magnesia-chromium bricks obtained by kneading, molding and firing a refractory raw material composition, using an electrofused magnesia clinker using seawater magnesia obtained from seawater as a magnesia raw material , The magnesia-chrome brick manufacturing method, wherein an average crystal diameter of a periclase crystal in a 1-mm sieve-opening particle of the electrofused magnesia clinker is 0.7 mm or more .
(2) The method for producing a magnesia-chrome brick according to (1), wherein the fusing magnesia clinker has a MgO purity of 99.0% by mass or more.
(3) the refractory raw material formulation, the fused magnesia clinker to 40-60 wt%, chromium ore 40-50 wt%, the fused magnesia chrome clinker containing 0-20 wt% (1) or (2 ) Manufacturing method of magnesia chrome brick according to .
(4) The magnesia-chrome brick according to any one of (1) to (3), wherein the ratio of the electrofused magnesia clinker composed of under-sieving particles having a sieve opening of 1 mm is 35% by mass or less. Manufacturing method.
(5) The magnesia-chromium brick according to any one of (1) to (4), wherein the ratio of the electrofused magnesia clinker composed of particles on the sieve having a sieve opening of 1 mm is 15% by mass or more. Manufacturing method.

  According to the present invention, a magnesia-chrome brick having high hot strength can be obtained without depending on the flux component.

FIG. 1 is a photograph of the state of periclase crystal grains of magnesia clinker in Examples 1 to 3 and Comparative Examples 1 to 4 observed with a digital microscope. FIG. 2 is a photograph of Example 1 and Comparative Examples 1 and 3 in which the precipitation state of picrochromite inside the magnesia clinker was observed using a digital microscope. FIG. 3 is a graph showing the relationship between the melt loss index calculated from the melt loss in the corrosion resistance test and the MgO composition ratio. FIG. 4A is a schematic explanatory view showing a state of an electrofused magnesia clinker during brick firing, and FIG. 4B is a schematic explanatory view showing a state of the electrofused magnesia clinker during cooling after firing. is there. FIG. 5A is a schematic explanatory view showing a state of a sintered magnesia clinker during brick firing, and FIG. 5B is a schematic explanatory view showing a state of the sintered magnesia clinker during cooling after firing. is there.

The present invention will be described in detail below.
In the present invention, when a refractory raw material composition is kneaded, molded and fired to obtain magnesia / chrome brick, a fused magnesia clinker using magnesia (seawater magnesia) obtained from seawater is blended as a magnesia raw material. To do.

  Currently, the magnesia clinker commonly used is a sintered magnesia clinker fired at 1700-1800 ° C using natural magnesite (magnesite ore) mined from seawater magnesia and mines, and mined from mines. There is an electrofused magnesia clinker obtained by electrolytically melting a clinker made of magnesite ore.

  Among these, the sintered magnesia clinker has small crystal grains in the structure, and a large amount of grain boundaries exist in the clinker. Therefore, when magnesia-chromium brick is produced using this sintered magnesia clinker as a raw material, as shown in FIG. 5, the flux component due to chromium ore 2 penetrates into the grain boundary 1a of the magnesia clinker 1 during firing, and the silicate phase Cr ions are diffused inside the magnesia clinker using this silicate phase as a medium [FIG. 5 (a)], and spinel 3 composed of picrochromite is deposited on the entire clinker in the cooling process after firing [ FIG. 5 (b)]. However, as described above, since the silicate phase has a low melting point, it softens at a high temperature and reduces the hot strength of magnesia-chrome brick. In addition, picrochromite 3 may also precipitate at the grain boundaries in the clinker, which may cause cracks and cracks in the brick starting from this.

  On the other hand, the electrofused magnesia clinker has relatively large crystal grains and fewer clinker grain boundaries. Therefore, if magnesia chrome brick is produced with an electrofused magnesia clinker using magnesite ore as a raw material, there is relatively little risk of softening of the silicate phase at the grain boundary or cracking starting from picrochromite. However, since magnesite ore with low MgO purity is used as a raw material, impurities in the clinker are concentrated at the grain boundaries in the baking stage of the brick and a low melting point impurity phase is precipitated.

  Therefore, in the present invention, a fusing magnesia clinker obtained by fusing seawater magnesia is used as a magnesia raw material. By using seawater magnesia as a raw material, it is possible to obtain a magnesia clinker having a higher MgO purity than when using magnesite ore as a raw material (the former is about 98.5% by mass and the latter is about 99.1% by mass). Here, the MgO content is measured by the method described in JIS R2216.), And concentration of impurities during firing can be prevented. 4 (a), (4), the fusing magnesia clinker obtained by fusing seawater magnesia can reduce the grain boundaries by forming relatively large crystal grains compared to fusing magnesia made of magnesite ore. As shown in b), it is possible to reduce the generation of pores 1b such as sintered magnesia clinker and achieve high density. Therefore, it is possible to suppress the generation of cracks and cracks starting from the grain boundaries, and Cr ions in the chromium ore are solid-phase diffused into the crystal grains of the magnesia clinker 1 during the baking of the brick, and the picrochromite 3 is formed. Rather than being formed at the grain boundary 1a of the clinker 1, it is considered that it precipitates uniformly at a relatively large size on the surface layer in the crystal grain of the clinker 1, so that the hot strength is improved. Furthermore, since it becomes difficult for the flux component in chromium ore to penetrate into the clinker, the generation of a low melting point phase can be suppressed.

  The electrofused magnesia clinker in the present invention is not particularly limited as long as it is obtained using seawater magnesia as a raw material, and a known one can be used. Preferably, it is an electrofused magnesia clinker having a MgO purity of 99.0% by mass or more. As such an electrofused magnesia clinker, for example, a commercially available electrofused magnesia clinker used in a magnesia-carbonaceous refractory can be used, and a sintered magnesia clinker made from seawater magnesia is used. An electrofused magnesia clinker obtained by further electromelting may be used. In addition, the electrofused magnesia clinker used in magnesia-carbonaceous refractories and the like is usually used as an aggregate, and after kneading with a graphite material and a binder (binder), kneaded at 250 ° C. Heated to a degree. That is, it is different from the one in which it is fired at about 1700 to 1850 ° C. like magnesia / chrome brick and spinel is generated from the reaction with chromium ore.

  Such an electrofused magnesia clinker is such that the refractory raw material composition can be kneaded more uniformly or from the viewpoint of obtaining good moldability, etc. It is preferable to have a particle size range such that ˜0.1 mm is 5 to 25 mass% and 0.1 mm or less is 5 to 20 mass%. In particular, if the electrofused magnesia clinker has a high MgO purity of 99.0% by mass or more, precipitation of impurity components at the grain boundaries is suppressed, and the periclase crystal grains are coarsened. Preferably, the average crystal diameter of the periclase crystal in the particles on the sieve having a sieve opening of 1 mm is 0.7 mm or more. Therefore, in the magnesia-chrome brick of the present invention, it is preferable to use an electrofused magnesia clinker containing 15% by mass or more of particles on the sieve having a sieve opening of 1 mm. Also, depending on the application, for example, when used for lining refractories such as refining containers, when using a fused magnesia clinker with an average crystal grain size of 0.7 mm or more, the clinker with a grain size of 0.7 mm or less In the case of particles that are almost single crystals and have a small particle size, the grain boundaries increase as a result. More preferably, the particle size is adjusted to a particle size of 35% by mass or less with 1 mm sieve opening particles. It is good to be. Note that the periclase crystal grains of the electrofused magnesia clinker are considered to be approximately the same size even after the brick is manufactured by firing, and therefore, the periclase crystal grains can be observed in a cross section obtained by cutting the brick.

  In obtaining the magnesia chrome brick of the present invention, as a refractory raw material composition, a fusing magnesia clinker made of seawater magnesia as described above and chrome ore may be blended to form a direct bond magnesia chrome brick. Furthermore, a semi-ribboned magnesia-chrome brick may be blended with an electrofused magnesia-chrome clinker. Here, as for the chromium ore, a naturally occurring chromium ore can be used. The electrofused magnesia chrome clinker is a synthetic raw material obtained by melting magnesia and chromium ore, and a material generally used as a refractory raw material can be used.

  These blending ratios can be the same as those of known magnesia / chromium bricks. For example, when a direct bond magnesia / chromium brick is obtained, the refractory raw material composition contains 40 magnesia clinker. It is preferable to contain ~ 60% by mass and chromium ore to be contained by 40 ~ 50% by mass. In the case of semi-ribboned magnesia / chromium brick, further contains electrofused magnesia chromium clinker in the range of 20% by mass or less. Can be made. In addition, sintering aids such as alumina and iron oxide can be further added as a refractory raw material composition, but the content thereof is 10% by mass or less because it may be accompanied by generation of a low melting point product. It is desirable to do.

  And like well-known magnesia chrome bricks, these refractory raw material blends are formulated so as to have a predetermined blending ratio, and if necessary, about 2 to 5% by weight binder and about 0 to 5% by weight. By adding chromium oxide or the like (the amount added is an external number) and firing at a temperature of 1700 ° C. or higher after pressure molding (generally about 1700-1850 ° C.), the magnesia-chrome brick of the present invention It is possible to obtain a magnesia / chrome brick having high hot strength and excellent corrosion resistance, thermal shock resistance and the like.

  Hereinafter, the present invention will be described in more detail with reference to examples. The present invention is not limited to these contents.

  Using Examples 1 to 3 and Comparative Examples 1 to 4 by using an electrofused magnesia clinker made from seawater magnesia, an electrofused magnesia clinker made from magnesite ore, and a sintered magnesia clinker made from seawater magnesia. Such magnesia chrome brick was produced.

These three types of magnesia clinker have the chemical components shown in Table 1. Further, in order to obtain magnesia / chrome brick, 2% by weight of the binder was added to the refractory raw material composition shown in Table 2 and kneaded and molded into a parallel shape with a friction press. Baked at ℃. At that time, the magnesia clinker was blended in advance by sieving to adjust the particle size (in Table 2, the proportion of the blended particle size is defined according to the blending amount of the magnesia clinker in the refractory raw material blend). Among them, 5 particles are taken out for each magnesia clinker from particles having a particle size of 5.0 to 1.0 mm, which are screened with a 1 mm sieve and a 5 mm sieve, embedded in an epoxy resin, polished, and then polished with an optical microscope. The maximum length of periclase crystal grains in each coarse clinker was measured, and the crystal grain size was calculated from the average of the five grains (“Crystal grain size (1 mm) in coarse clinker of 1 mm or more” in Table 2). In addition, the chrome ore used what was produced naturally. Electrofused magnesia chrome clinker (fused magcro clinker) is obtained by melting magnesia and chromium ore. Further, Table 2 shows the ratio of CaO / SiO ₂ and Cr ₂ O ₃ / Fe ₂ O _{3 in} the refractory raw material mixture as chemical component ratios (both represent mass ratios).

  The magnesia / chrome brick obtained above was measured for bulk specific gravity, apparent porosity (%), and hot bending strength (MPa). Here, the bulk specific gravity and the apparent porosity were measured according to JIS R2205. About hot bending strength, it measured at 1400 degreeC based on JISR2656. The results are summarized in Table 2. Also, FIG. 1 shows a photograph in which the state of the periclase crystal grains of magnesia clinker is observed with a digital microscope in the cross section obtained by cutting the obtained brick. FIG. It is the photograph which observed the precipitation state of the picrochromite inside a magnesia clinker about the 1 and 3 bricks, respectively using the digital microscope.

  In Table 2, Examples 1-2 and Comparative Examples 1-3 show the case where the type of magnesia clinker is changed in the direct bond magnesia / chrome brick, and the sintered magnesia clinker or magnesite ore is used as a raw material. It turns out that the hot strength improves in Examples 1-2 using the electrofused magnesia clinker using seawater magnesia as a raw material, compared with Comparative Examples 1-3 using the electrofused magnesia clinker. Further, Example 3 and Comparative Example 4 are cases where the type of magnesia clinker was changed in semi-ribboned magnesia / chrome brick, and again, Example 3 using an electrofused magnesia clinker made of seawater magnesia as a raw material was The hot strength is improved as compared with Comparative Example 4 using an electrofused magnesia clinker made of magnesite ore.

  Here, in FIG. 2 shown above, the one that appears in gray is the magnesia clinker 1, the one that appears in black is the pores 1b of the magnesia clinker, and the large white block is the chromium ore 2. A spinel 3 mainly composed of picrochromite is shown in white in the clinker. As described above, in the magnesia-chrome brick, the spinel is generated when the baking treatment is performed. When using an electrofused magnesia clinker made from seawater magnesia as in the present invention, since there are few grain boundaries, precipitation at the grain boundaries is suppressed, and spinel composed of picrochromite is generated in the crystal grains of the clinker. . Therefore, as shown in FIG. 2, compared to Comparative Example 1 using sintered magnesia clinker and Comparative Example 3 using electrofused magnesia using magnesite ore as a raw material, electromelting using seawater magnesia as a raw material. In Example 1 using the magnesia clinker, the particle size of the picrochromite 3 precipitated inside the crystal grains at the end of the clinker becomes larger. Specifically, it can be seen that picrochromite deposited between about 100 μm from the end of the clinker becomes 10 μm or more, which is considered to improve the hot strength of magnesia-chrome brick.

Moreover, the graph showing the relationship between the corrosion resistance of the magnesia-chrome brick obtained in the said Examples 1-2 and Comparative Examples 1-2 and the compounding ratio of a magnesia clinker is shown by FIG. In addition to these, FIG. 3 shows magnesia-chromium brick (corresponding to Example) obtained in the same manner as in Example 1 except that 70 mass% of electrofused magnesia clinker made of seawater magnesia is used, and sintering. Magnesia chrome brick obtained in the same manner as in Example 1 except that 70% by mass of magnesia clinker is blended (corresponding to a comparative example) is also included. Here, the corrosion resistance of the brick was evaluated by a rotary erosion test. In the rotary erosion test, a test piece brick was lined inside an iron drum having a horizontal rotation axis, slag was added, and the brick surface was eroded by heating. An oxygen-propane burner was used as the heating source, the test temperature was 1700 ° C., the slag composition was CaO / SiO ₂ = 3, and slag discharge and charging were repeated 10 times every 30 minutes. The melting loss index of the bricks tested was calculated by setting the melting loss amount of the brick generated in this test to 100 as the melting loss amount of Comparative Example 1 shown in Table 2. In addition, the MgO compounding ratio in FIG. 3 shows the compounding ratio (mass%) of the magnesia clinker described in Table 2.
As can be seen from the graph shown in FIG. 3, the corrosion resistance of the obtained magnesia-chromium brick was improved in the example compared to the comparative example, regardless of the mixing ratio of MgO.

  As described above, according to the present invention, it is possible to obtain a magnesia / chrome brick having high hot strength and excellent corrosion resistance, thermal shock resistance and the like. Therefore, for example, it can be effectively used as a refractory such as a secondary refining furnace such as an RH vacuum degassing furnace, an AOD furnace, or a VOD furnace, an electric furnace for steel making, a cement firing furnace, and the like.

1: magnesia clinker, 1a: grain boundary, 1b: pores, 2: chromium ore, 3: spinel.

Claims (5)

Kneading the refractory raw material formulation, a process for the preparation of a magnesia-chrome brick obtained by baking after molding, the fused magnesia clinker using seawater magnesia obtained from seawater magnesia raw material, the Fused A method for producing magnesia-chromium bricks , characterized in that the average crystal diameter of periclase crystals in a 1 m sieve sieve particle of magnesia clinker is 0.7 mm or more . The method for producing a magnesia-chrome brick according to claim 1, wherein the electrofused magnesia clinker has a MgO purity of 99.0 mass% or more. The refractory raw material formulation, the fused magnesia clinker to 40-60 wt%, chromium ore 40-50 wt%, to claim 1 or 2 in a proportion of 0 to 20% by weight of fused magnesia chrome clinker The manufacturing method of the magnesia chrome brick of description. The method for producing a magnesia-chrome brick according to any one of claims 1 to 3, wherein the refractory raw material composition has a proportion of electrofused magnesia clinker composed of under-sieving particles having a sieve opening of 1 mm of 35% by mass or less. The method for producing a magnesia-chrome brick according to any one of claims 1 to 4, wherein the refractory raw material composition has a ratio of electrofused magnesia clinker composed of particles on a sieve having a sieve opening of 1 mm.