Manufacturing method of unburned bricks for molten iron containers

Abstract

To provide a method for producing an unburned brick for molten iron vessels, having excellent corrosion resistance and volume stability (residual expansion properties) even when used in operations under severe molten iron pre-treatment conditions.SOLUTION: A method for producing an unburned brick for molten iron vessels includes: adding an organic binder to a refractory raw material compound; kneading and molding the obtained raw material; and then heat-treating the molded raw material at 800°C or less. The refractory raw material compound comprises: 30-87 mass% of magnesia; 5-30 mass%, in total, of one or more selected from brazing stone, silica stone, and fused silica having a grain size of 1 mm or more and less than 5 mm; 5-18 mass% of graphite; and 0.1-5 mass%, in total, of aluminum and / or an aluminum alloy, wherein a content of one or more selected from brazing stone, silica stone, and fused silica having a grain size of less than 1 mm is 5 mass% or less (including 0) in total, and a content of silicon carbide is 20 mass% or less (including 0).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing unburned bricks for molten metal vessels, such as torpedo cars and ladles, that transport or store molten metal, particularly suitable as lining materials for molten metal ladles. [Background technology]

[0002] In recent years, hot metal pretreatment operations have become standardized, with desiliconization, dephosphorization, desulfurization, etc. being performed separately in blast furnace runners, torpedo cars, hot metal ladles, or dedicated hot metal pretreatment furnaces, and the treatment conditions have become increasingly severe for refractories. For example, in recent hot metal pretreatment, large amounts of hot metal pretreatment materials such as mill scale, lime, and soda ash are sometimes used, and the basicity of the slag after treatment (CaO / SiO2) has expanded from the conventional range of around 1.1 to 1.2 to a wide range of 1.1 to 4.

[0003] Typically, volumetric stability that can withstand thermal shocks associated with heating and cooling is particularly important for lining materials for hot metal ladles. Therefore, as disclosed in, for example, Patent Document 1, unburned bricks based on alumina-silicon carbide-carbon bricks have traditionally been used, with residual expansibility materials such as silica added to impart residual expansibility to prevent joints from opening during cooling. This is because joints that open during cooling are prone to molten iron penetration during operation. However, under severe operating conditions, such as when large amounts of hot metal pretreatment materials are added or when treatment temperatures are high, the durability of conventional unburned alumina-silicon carbide-carbon bricks, primarily composed of alumina, has become a problem.

[0004] In addition, in the harsh operation of molten iron pretreatment in some molten iron ladles, magnesia carbon bricks used in molten steel ladles are partially used to ensure durability, but just like in molten steel ladles, the bricks are expanded by heating (preheating) before operation to close the joints and prevent molten iron from penetrating into the joints, which requires special equipment operations for molten iron ladles and results in significant cost increases.

[0005] On the other hand, Patent Document 2 discloses a method for producing a carbon-containing refractory material by adding a carbon-based binder to a mixture containing 30 to 90% alumina material, 3 to 30% carbon material, 5 to 50% Al2O3-MgO-based spinel material with a particle size of 1 mm or less, and 0.1 to 5% glass material in terms of outer percentage, and then kneading, molding, and drying. However, the refractory obtained by this production method still has problems, particularly in that its corrosion resistance against slag is still insufficient, and its volume stability against thermal shocks associated with heating and cooling is insufficient, resulting in joint erosion.

[0006] Furthermore, Patent Document 3 discloses a carbon-containing unburned refractory brick made primarily from alumina, magnesia, pyrotechnic stone, and carbon, with a product chemical composition of 50-85 wt% Al2O3, 20 wt% or less MgO, 3-25 wt% SiO2, 3-20 wt% C, and 10 wt% or less other components. However, the brick in Patent Document 3 still has insufficient corrosion resistance, and there is a problem in that it does not provide sufficient durability improvement effect when used in a molten iron ladle. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent Publication No. 2021-4160 [Patent Document 2] Japanese Patent Application Publication No. 9-25160 [Patent Document 3] Japanese Patent Application Publication No. 6-293560 Summary of the Invention [Problem to be solved by the invention]

[0008] An object of the present invention is to provide a method for producing unburned bricks for molten iron vessels that have excellent corrosion resistance and volume stability (residual expansion) even when used in operations under severe conditions for molten iron pretreatment. [Means for solving the problem]

[0009] The present inventors have discovered that by using a refractory raw material blend that combines 30 to 87 mass % of magnesia with a total of 5 to 30 mass % of one or more of rosewood, silica, and fused silica, each having a particle size of 1 mm or more and less than 5 mm, and that also contains graphite, it is possible to obtain an unburned brick for molten iron vessels that has significantly improved corrosion resistance and excellent residual expansion properties compared to conventional unburned bricks based on alumina, silicon carbide, and carbon.

[0010] That is, according to one aspect of the present invention, there is provided the following method for producing unburned bricks for a molten iron vessel. A method for producing unburned bricks for molten iron vessels, comprising adding an organic binder to a refractory raw material mixture, kneading the mixture, forming the mixture, and then heat-treating the mixture at 800°C or less, A method for producing unfired bricks for molten iron containers, wherein the refractory raw material blend contains 30 to 87 mass% magnesia, 5 to 30 mass% in total of one or more of rosewood, silica, and fused silica having a particle size of 1 mm or more but less than 5 mm, 5 to 18 mass% graphite, and 0.1 to 5 mass% in total of aluminum and / or an aluminum alloy, and the content of one or more of rosewood, silica, and fused silica having a particle size of less than 1 mm is 5 mass% or less (inclusive of 0) and the content of silicon carbide is 20 mass% or less (inclusive of 0). [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a method for producing unburned bricks for a molten iron vessel that have excellent corrosion resistance and volume stability (residual expansion) even when used in operations under severe conditions for molten iron pretreatment, thereby improving the durability of the molten iron vessel (molten iron pretreatment vessel). DETAILED DESCRIPTION OF THE INVENTION

[0012] In the present invention, magnesia is used in an amount of 30 to 87% by mass because it has better corrosion resistance than alumina or spinel against highly basic slag. If the magnesia content in the refractory raw material blend is less than 30% by mass, sufficient corrosion resistance cannot be obtained, and if it exceeds 87% by mass, thermal shock resistance decreases and sufficient residual expansion cannot be ensured. To achieve high levels of both corrosion resistance and thermal shock resistance, the magnesia content in the refractory raw material blend can be set to 50 to 80% by mass.

[0013] Magnesia can be any type of refractory material, including electrofused magnesia, sintered magnesia, and natural magnesia obtained by heat-treating natural magnesite. In particular, because the temperature of molten iron in a hot metal ladle is generally around 1400°C, which is lower than the 1600°C of a steel ladle, natural magnesia can offer durability superior to conventional unfired alumina, silicon carbide, and carbon bricks. Therefore, natural magnesia can be used when cost is a priority. Natural magnesia, as used here, refers to magnesia obtained by heat-treating magnesite mined from the earth. It is also sometimes called sintered magnesia or natural magnesia clinker.

[0014] In the present invention, one or more of rosestone, silica, and fused silica are used for the purpose of imparting thermal shock resistance and residual expansion. Because rosestone, silica, and fused silica have a lower thermal expansion coefficient than magnesia in the temperature range of 800°C to 1300°C, the difference in expansion during use creates voids around the coarse particles. These voids can relieve thermal stress, contributing to improved thermal shock resistance. Therefore, in the present invention, even though magnesia, which has a higher thermal expansion coefficient than alumina or spinel, is used as the main raw material, it is possible to obtain thermal shock resistance equivalent to that of conventional alumina-silicon carbide-carbon unfired bricks.

[0015] In addition, when silica (quartz) is heated, it undergoes a phase transition from alpha quartz to beta quartz, and due to its transformation into cristobalite at high temperatures and its high thermal expansion and high residual expansibility caused by broaching, it is expected to be effective in preventing brick joints from opening. Furthermore, arotheca is an aggregate of quartz and pyrophyllite, with quartz comprising half to as much as 70% by mass, and pyrophyllite also changes to mullite and cristobalite at temperatures above 1200°C, expanding in volume and contributing to residual expansibility. Furthermore, when fused silica is heated to 1200°C or higher, it transforms into cristobalite and expands, contributing to residual expansibility.

[0016] In the present invention, the refractory raw material blend contains one or more of rosewood, silica, and fused silica in a total amount of 5 to 30% by mass. If the content is less than 5% by mass, the residual expansion of the resulting brick is small, the effect of preventing joints from opening during use is small, and thermal shock resistance is also insufficient. If the content exceeds 30% by mass, corrosion resistance is reduced. If it is desired to further improve the residual expansion and corrosion resistance, the content can be set to 10% to 20% by mass.

[0017] In the present invention, the pyrotechnic stone, silica stone, and fused silica basically have a particle size of 1 mm or more. The reason for this is that, when pyrotechnic stone, silica stone, or fused silica is contained in a brick mainly composed of magnesia and graphite, the amount of SiO2 increases, which causes a problem of reduced corrosion resistance, but the larger the particle size of the pyrotechnic stone, silica stone, and fused silica, the more effectively the corrosion resistance can be prevented from being reduced.

[0018] Furthermore, the unburned brick for a molten iron vessel of the present invention contains graphite mainly in the matrix, and the expansion of fine rosestone, silica, or fused silica particles with a particle size of less than 1 mm is partly absorbed in this matrix, so that the brick as a whole does not achieve a sufficient residual expansion effect. In contrast, coarse particles with a particle size of 1 mm or more have many areas in contact with the coarse particles of magnesia and are also close to each other, so that the expansion of the rosestone, silica, or fused silica is hardly absorbed in the matrix with a large amount of graphite, allowing the brick as a whole to expand.

[0019] For these reasons, in the present invention, the refractory raw material blend contains one or more of the following: rosewood, silica, and fused silica, each having a particle size of 1 mm or more and less than 5 mm, in a total amount of 5 to 30 mass %, or 10 to 20 mass %. Note that, if the total content of the following one or more of the following two types of rosewood, silica, and fused silica, each having a particle size of less than 1 mm, is 5 mass % or less, adverse effects can be reduced; however, if the content exceeds 5 mass %, corrosion resistance decreases significantly. Therefore, in the present invention, the content of the following one or more of the following two types of rosewood, silica, and fused silica, each having a particle size of less than 1 mm, is 5 mass % or less (including 0). It is preferable that the content of the following one or more of the following two types of rosewood, silica, and fused silica, each having a particle size of less than 1 mm, is 2 mass % or less (including 0).

[0020] Alumina can be used in combination with magnesia as part of the aggregate, and since it has a smaller thermal expansion coefficient than magnesia, it has the effect of improving thermal shock resistance, and since it reacts with magnesia and silica to produce spinel or mullite, it has an expansion effect, so it can be contained in an amount of 45 mass% or less.

[0021] Graphite is used to ensure thermal shock resistance, specifically at a content of 5 to 18 mass% based on 100 mass% of the refractory raw material composition. If the content is less than 5 mass%, thermal shock resistance is insufficient, while if it exceeds 18 mass%, strength development during operation is suppressed, internal cracks occur, wear resistance is reduced, and corrosion resistance is also reduced. Graphite can be any graphite commonly used as a raw material for refractories, such as flake graphite, and graphite with a particle size of less than 0.5 mm can be used.

[0022] Aluminum and / or aluminum alloys are used at a total content of 0.1 to 5 mass% based on 100 mass% of the refractory raw material mixture to prevent oxidation and provide strength. If the content is less than 0.1 mass%, sufficient corrosion resistance cannot be obtained due to insufficient oxidation resistance and strength, while if it exceeds 5 mass%, excessive sintering effects cause a decrease in thermal shock resistance, increasing the risk of cracking and peeling.

[0023] The refractory raw material composition of the present invention has an antioxidant effect due to the use of aluminum and / or aluminum alloy. However, if it is desired to further enhance the antioxidant effect or to improve thermal shock resistance, silicon carbide can be used at a content of 20% by mass or less based on 100% by mass of the refractory raw material composition. If the content exceeds 20% by mass, corrosion resistance decreases. The silicon carbide content is preferably 10% by mass or less (including 0). Silicon carbide with a SiC content of 85% by mass or more and a particle size of less than 0.3 mm is preferably used.

[0024] In addition to the above, the refractory raw material composition of the present invention may contain one or more refractory raw materials commonly used in refractories, such as metals other than aluminum or aluminum alloys, boron carbide, glass powder, carbon black, and pitch powder, in a total content of 5% by mass or less based on 100% by mass of the refractory raw material composition.

[0025] Here, the particle size referred to in the present invention refers to the size of the sieve openings when particles are sieved and separated. For example, a wax stone with a particle size of less than 1 mm is a wax stone that passes through a sieve with 1 mm openings, and a wax stone with a particle size of 1 mm or more is a wax stone that does not pass through a 1 mm sieve.

[0026] The unburned brick for hot metal vessels of the present invention is obtained by adding an organic binder such as a phenolic resin to the above-mentioned refractory raw material composition, kneading the mixture, molding, and then heat-treating it. The organic binder is used for well-known purposes, such as to obtain strength after molding and heat treatment, and to form a carbon bond by heat exposure during use. Known organic binders used in general unburned bricks can be added during kneading in a conventional ratio appropriate for the manufacturing conditions. Specifically, the binder content can be in the range of 1 to 5 mass% per 100 mass of the refractory raw material composition. Similarly, the heat-treatment temperature can be within the range of known heat-treatment temperatures for unburned bricks using ordinary organic binders. Specifically, the binder can be 160°C or higher and 800°C or lower. [Example]

[0027] The content (mass%) of each raw material in the refractory raw material composition and the evaluation results are shown in Table 1. An appropriate amount (2 to 4 mass%) of phenolic resin was added as an organic binder to each refractory raw material composition as an outer percentage relative to 100 mass% of the refractory raw material composition, and after kneading, the mixture was formed into a brick shape of 230 x 114 x 100 mm using a friction press and heat-treated at 250°C to obtain bricks for each example and comparative example. In Table 1, the natural magnesia used was sintered magnesia (MgO content: 95% by mass) made by heat-treating natural magnesite, the fused alumina used had an Al2O3 content of 97% by mass, and the silica stone (quartz) used had an SiO2 content of 97% by mass. Furthermore, the rose stone used was a low-alkali rose stone with a quartz content of 50% by mass and an Al2O3 content of 17% by mass, the fused silica used had an SiO2 content of 99% by mass, and the silicon carbide used had an SiC content of 90% by mass. Furthermore, the flake graphite used had a fixed carbon content of 85% by mass.

[0028] The bricks obtained in each of the examples and comparative examples were measured for their coefficient of permanent expansion, and their corrosion resistance and thermal shock resistance were evaluated. The residual expansion coefficient was measured using a cylindrical sample with a diameter of 50 mm and a height of 50 mm, from the change in the height of the sample before and after heat treatment at 1400°C for 3 hours under a load of 0.2 MPa. Corrosion resistance was evaluated using trapezoidal brick samples measuring 45mm top, 105mm bottom, 60mm high, and 120mm long, using a rotary slag erosion test. Corrosion was repeated five times at 1500°C for one hour, and the amount of erosion (mm) was calculated from the difference in thickness (mm) at the center line of the sample before and after the test. The erosion agent used was pig iron and slag with a CaO / SiO2 ratio of C / S = 1.0, and pig iron and slag with a CaO / SiO2 ratio of C / S = 4.0. In Table 1, corrosion resistance is expressed as an index, with the amount of erosion (mm) for Comparative Example 1 being set at 100. The smaller the erosion index, the better the corrosion resistance. To evaluate thermal shock resistance, samples measuring 40 x 40 x 190 mm were subjected to a thermal shock test in which they were reduced and baked at 800°C for three hours, then immersed in 1500°C molten iron for 180 seconds, and then air-cooled for 10 minutes. This test was repeated five times, and the state of cracks and spalling was observed. In the table, "◎" indicates no cracks or spalling after the test, "〇" indicates minor cracks or spalling, "△" indicates medium cracks or spalling, and "×" indicates major cracks or spalling. The overall pass / fail was evaluated in three stages: ◎: very good, ○: good, ×: poor. Specifically, the evaluation was based on the criteria shown in Table 2.

[0029] [Table 1]

[0030] [Table 2]

[0031] Although Examples 1 to 6 have different magnesia contents in the refractory raw material compositions, they are within the range of the present invention and result in excellent residual expansion, corrosion resistance, and thermal shock resistance. In contrast, in Comparative Example 1, the magnesia content was 20 mass %, which was below the lower limit of the present invention, and the corrosion resistance was insufficient. In Comparative Example 2, the magnesia content is 95 mass %, which exceeds the upper limit of the present invention, and the silica stone and graphite contents are accordingly low, resulting in insufficient residual expansion and thermal shock resistance.

[0032] Examples 7 to 10 have different silica stone contents, but they are within the range of the present invention and produce good results. In contrast to this, in Comparative Example 3, the silica content was below the lower limit of the present invention, and the residual expansion was insufficient. In Comparative Example 4, the content of silica stone exceeded the upper limit of the present invention, and the corrosion resistance was insufficient. Comparative Example 5 is an example in which only silica stone having a particle size of less than 1 mm was used, and the corrosion resistance was insufficient.

[0033] Example 11 contained 5 mass % of silica stone with a particle size of less than 1 mm, which was within the range of the present invention and provided good results. In contrast, Comparative Example 6 contained 10 mass % of silica stone with a particle size of less than 1 mm, and therefore had insufficient corrosion resistance. Example 12 contains pyrophyllite, Example 13 contains silica and pyrophyllite, and Example 14 contains fused silica, all of which are within the scope of the present invention and provide good results.

[0034] Examples 15 and 16 have different aluminum contents and contain pitch and boron carbide, but are within the scope of the present invention and produce good results. Comparative Example 7 was a case where no aluminum was contained, and the corrosion resistance was reduced. In Comparative Example 8, the aluminum content exceeded the upper limit of the present invention, resulting in insufficient thermal shock resistance.

[0035] Examples 17 to 19 contain silicon carbide, but are within the scope of the present invention and provide good results. In contrast to this, in Comparative Example 9, the silicon carbide content exceeded the upper limit of the present invention, resulting in insufficient corrosion resistance. In addition, in Comparative Example 10, the graphite content exceeded the upper limit of the present invention, resulting in insufficient corrosion resistance.

[0036] The bricks of Example 3 and Comparative Example 1 were used to line the slag line of the side wall of a molten iron ladle, and it was confirmed that the side wall lined with the bricks of Example 3 had a lifespan that was approximately 1.4 times longer than that of the side wall lined with the bricks of Comparative Example 1.

Claims

1. A method for producing unburned bricks for molten iron vessels, comprising adding an organic binder to a refractory raw material mixture, kneading the mixture, forming the mixture, and then heat-treating the mixture at 800°C or less, The refractory raw material blend contains 30 to 87 mass% magnesia, 5 to 30 mass% in total of one or more of rosewood, silica, and fused silica having a particle size of 1 mm or more but less than 5 mm, 5 to 18 mass% graphite, and 0.1 to 5 mass% in total of aluminum and / or an aluminum alloy, and the content of one or more of rosewood, silica, and fused silica having a particle size of less than 1 mm is 5 mass% or less (inclusive of 0) and the content of silicon carbide is 20 mass% or less (inclusive of 0).

2. 2. The method for producing an unburned brick for a molten iron container according to claim 1, wherein the refractory raw material blend contains 45 mass % or less (not including 0) of alumina.

3. 3. The method for producing unburned bricks for a molten iron vessel according to claim 1, wherein the content of magnesia in the refractory raw material blend is 50 to 80 mass %.

4. 4. The method for producing an unburned brick for a molten iron vessel according to claim 1, wherein the refractory raw material blend contains one or more of rosestone, silica stone, and fused silica having a particle size of 1 mm or more and less than 5 mm in a total content of 10 to 20 mass%.

5. 5. The method for producing an unburned brick for a molten iron vessel according to claim 1, wherein the magnesia in the refractory raw material blend is natural magnesia.

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