JP2005047757A - Graphite-containing castable refractory - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide graphite-containing castable refractory showing the strength in a wide temperature range from a low temperature to a high temperature which is required for the graphite-containing castable refractory used in iron industry and particularly having improved high temperature strength against molten metal or the like under a high temperature exceeding 1500°C. <P>SOLUTION: The graphite-containing castable refractory contains a mixture of pitch and metal powder with alumina cement and a metallic fiber in which the relation between the content [P] of the pitch and the content [M] of the metal powder satisfies 0.6≤[P]/([P]+[M])≤0.9, the content of alumina cement is controlled to ≤1.5 mass% of and the metallic fiber is contained by 2-4 mass% per mass of the mixture. excluding the metallic fiber. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a castable refractory used in the steel industry, and more particularly to a castable refractory containing graphite and exhibiting high strength in a wide temperature range from low temperature to high temperature.

In the steel industry, various containers and reactors that hold molten metal such as hot metal and molten steel are used. For the purpose of improving the corrosion resistance against such hot molten metal, refractory bricks containing graphite (below) Graphite-containing refractory bricks). As graphite-containing refractory bricks, MgO-C bricks generally used in converters and Al ₂ O ₃ -C refractory bricks used in continuous casters are widely known. Is effective.

In recent years, not only monolithic refractory, such as graphite-containing refractory bricks, expect the effect of the high corrosion resistance improvement by graphite, blast furnace main trough for Al ₂ O ₃ -SiC-C castable refractories, devote gutter for Al ₂ Indeterminate refractories such as O ₃ —MgO—C castable refractories and MgO—C castable refractories for ladle slag lines are used. In these applications, if the high corrosion resistance of graphite is utilized to prevent slag permeation and exhibit high spalling resistance, improvement in durability can be expected. However, castable refractories containing graphite (hereinafter referred to as graphite-containing castable refractories) such as SiC-C castable refractories and MgO-C castable refractories currently used do not necessarily improve durability. However, there was a problem that wear was observed.

The inventors investigated the cause, and in the graphite-containing castable refractory, the graphite particles do not combine with other graphite particles, Al ₂ O ₃ , or MgO even at high temperatures. When the molten metal exists and is used in a flowing part, when the refractory structure around the graphite particles is worn out, the graphite particles fall off, thereby further damaging the surrounding refractory structures. It was found that this phenomenon occurs. Therefore, it has been found that the strength of the refractory structure needs to be improved in order to take advantage of the corrosion resistance improvement effect of graphite.

  As a technique for improving the hot strength of the castable refractory, there is a technique disclosed in Patent Document 1. This is a technology related to mortar used in high-temperature containers, but here, by using a castable refractory containing tar pitch and metallic silicon, a Si-C bond is formed in the hot state as a hot mortar. This is a technique for improving the adhesion of the material.

  Patent Document 2 describes a technique in which bending strength after firing can be improved by uniformly dispersing and adding metal fibers to an irregular refractory.

  However, castable refractories used in the steel industry such as blast furnace chiefs and ladles are used in harsh conditions where they are molded at the site of use, dried and heated, and then used as they are. It is necessary to withstand use in a wide temperature range from the low temperature condition at the start of use to the condition for holding molten metal exceeding 1500 ° C thereafter.

  In this respect, the mortar disclosed in Patent Document 1 exhibits its strength only when the pitch and metal are in a high temperature condition and a connective structure such as SiC bond grows. When used as a mortar, there is almost no direct contact with the molten metal, so strength in the temperature rising process after the start of use is not necessary. However, under the use conditions as intended in the present invention, there is direct contact with the molten metal even at relatively low temperature conditions at the start of use of the castable refractory, but before the SiC bond grows. In addition, there is a possibility that significant wear may progress due to poor strength.

In addition, with the technique described in Patent Document 2, it can be expected that the mechanical strength after firing is increased to about 1000 ° C. due to the effect of the metal fiber, but the metal fiber itself is used under the conditions of contact with molten metal exceeding 1500 ° C. There is a problem that improvement in hot strength cannot be expected due to a decrease in strength.
Japanese Patent Publication No. 60-41027 Japanese Patent Laid-Open No. 11-157948

  The present invention can exhibit strength in a wide temperature range from low temperature to high temperature required for the graphite-containing castable refractories used in the steel industry as described above, and in particular, high temperature conditions exceeding 1500 ° C. The purpose of the present invention is to provide a graphite-containing castable refractory having a high temperature strength such as molten metal.

  In the case of a graphite-containing castable refractory used in the iron and steel industry, the usage conditions range from a low temperature to a high temperature. In reality, a castable refractory containing graphite is molded at room temperature, then dried and heated by a flame, etc., and then the temperature around 1500 ° C, which is the temperature of the molten metal, etc., while repeatedly receiving and discharging the molten metal, etc. Retained. For this reason, it is desirable to be a graphite-containing castable refractory that retains the low temperature strength during the initial temperature rise and continues to maintain the high temperature strength even after the temperature rises.

  The present inventors have conceived the configuration of the present invention in consideration of such use conditions. In other words, under relatively low temperature conditions in the process of forming, drying, and raising the temperature of castable refractories, the strength is increased by metal fibers and the formation of metal carbides related to the pitch and metal powder composition is promoted to raise the temperature. Later, invented a graphite-containing castable refractory that can maintain strength in a wide temperature range from low temperature to high temperature by utilizing the change over time due to temperature rise, in which the generated metal carbide develops strength and improves hot strength. It was.

  In addition, when confirming the strength development effect of graphite-containing castable refractories having such a structure, alumina cement, which is usually used as a binder, causes cement collapse in a high temperature region exceeding 800 ° C. The present invention has been found out that it is disadvantageous for strength development.

  That is, the present invention is a castable refractory containing graphite, comprising pitch, metal powder, a mixture of alumina cement and metal fiber, and the pitch content (mass%) and the metal powder content (mass%). Satisfies the following formula (1), restricts the content of the alumina cement to 1.5% by mass or less, and contains 2 to 4% by mass of the metal fiber based on the mass of the mixture. This is a graphite-containing castable refractory characterized by

0.6 ≦ [P] / ([P] + [M]) ≦ 0.9 (1)
[P]: Pitch content (% by mass)
[M]: Metal powder content (% by mass)

  In the present invention, it is possible to obtain a graphite-containing castable refractory having a small strength drop from room temperature to high temperature by reducing alumina cement, adding a small amount of metal fiber, and adding pitch and metal powder in a predetermined ratio.

  The graphite-containing castable refractory according to the present invention has an alumina cement content of 1.5% by mass or less. If alumina cement is added in excess of 1.5% by mass, the cement collapse becomes noticeable at around 800 ° C in the process of heating the graphite-containing castable refractory after construction, and the hot strength of the entire construction body decreases. In addition, when the temperature is further increased and used at a temperature exceeding 1500 ° C. that accepts high-temperature hot metal or molten steel, there is a possibility that a decrease in strength occurs due to generation of a liquid phase. Therefore, alumina cement must be limited to 1.5% by mass or less.

  However, when the amount of alumina cement added is small, when the graphite-containing castable refractory is applied, dried, and used, the material strength in the temperature rising process is insufficient and wear tends to increase. Therefore, in this invention, 2-4 mass% of metal fibers are contained in a graphite containing castable refractory. By adding metal fiber, the strength of the construction body of castable refractory containing graphite from room temperature to about 1100 ° C can be strengthened, and the wear of the construction body during temperature rise can be reduced.

  When the addition amount of the metal fiber is less than 2% by mass, the developed strength is small and the effect of reducing wear during temperature rise is poor. On the other hand, adding over 4% by mass is not preferable because the thermal expansion of the metal fiber itself or the permanent expansion due to oxidation causes cracking due to the stress generated in the construction body of the graphite-containing castable refractory, resulting in a decrease in strength. The material of the metal fiber is preferably a material that is difficult to carburize, but steel fiber or stainless fiber used in ordinary castable refractories is also sufficient.

  The metal fiber preferably has an average diameter of 0.3 to 0.6 mm and a length of about 20 to 40 mm. If the metal fiber is too short, the effect of improving the strength is reduced, and if it is too long, the workability as a castable refractory deteriorates. There are straight and corrugated shapes, but any of them may be used.

  Even if about 5% by mass of basic aluminum lactate, hydraulic alumina or the like is added in place of alumina cement as a strength developing agent at a relatively low temperature such as during temperature rise, the effect of the present invention is not reduced. Absent.

  In order to develop strength at a temperature exceeding 1100 ° C., pitch and metal powder such as Al and Si are added in the present invention. By adding these, the carbide | carbonized_material production | generation reaction by the volatile matter in a pitch and metal powder arises, and this carbide | carbonized_material contributes to intensity | strength expression. Therefore, in order to obtain high strength, it is desirable to generate a large amount of volatile matter from the pitch. However, if too much volatile matter is generated, the construction body has increased pores and the corrosion resistance of the entire graphite-containing castable refractory is reduced. . From this point of view, in the present invention, it is preferable to add a pitch that is solid at room temperature and has a volatile content of 20 to 40% in a range of 3% by mass to 10% by mass.

  As the shape of the pitch, spherulites or crushed materials can be used, and the particle size is preferably about 2 mm or less. More preferably, it is 1 mm or less. The pitch softens when heated and flows and diffuses through the pores of the refractory. Since the original place becomes a cavity, the use of a pitch having a large particle diameter causes a decrease in strength.

  The metal powder has a particle size of about 100 μm or less. A fine metal powder is preferred because it is more reactive.

The ratio between the pitch and the metal powder is preferably in an appropriate range for producing carbides such as Al ₄ C ₃ and SiC.
0.6 ≦ [P] / ([P] + [M]) ≦ 0.9 (1)
[P]: Pitch content (% by mass)
[M]: Metal powder content (% by mass)
And Even if pitch and metal powder are added at a ratio exceeding 0.9, pitch and metal powder that do not contribute to carbide formation increase, and the effect of strength development by carbide is diminished. On the other hand, if it is less than 0.6, carbides are not sufficiently generated, and the effect of strength development cannot be obtained.

  In this way, in the present invention, even if the alumina cement content of the graphite-containing castable refractory is 1.5% by mass or less and no alumina cement is added (that is, the alumina cement content is zero), the metal fiber, pitch, metal By containing the powder, the wear of the construction body of the graphite-containing castable refractory can be reduced.

  There is no restriction | limiting in particular in the graphite raw material used for the graphite containing castable refractory of this invention, Scaly graphite, artificial graphite, earthy graphite, etc. can be used. These graphite raw materials can be subjected to a surface treatment that improves the dispersibility in water and the filling property during construction.

  Other refractory raw materials are not particularly limited, and generally used aggregates, fine powders, ultrafine powders, antioxidants, dispersants, and other additives are used for various properties (fluidity, As long as the pot life, curing time, etc. are not impaired, they can be used at any blending ratio without problems. Further, the combined use of carbonaceous raw materials other than graphite and pitch, such as powdered phenol resin, carbon black, and carbide raw materials such as silicon carbide and boron carbide, does not impede the effects of the present invention.

As an example of a graphite-containing castable refractory, the characteristics of Al ₂ O ₃ —MgO—C castable refractory and Al ₂ O ₃ —Spinel-C castable refractory used as tilting bedding materials were investigated. In the investigation, Si powder was added as metal powder to each refractory, and SUS fiber (SUS304, average diameter 0.45 mm, length 25 mm, corrugated) was added as metal fiber. Further, a certain amount of SiO ₂ fine powder, artificial graphite and carbon black were added, and Al ₂ O ₃ , MgO, alumina cement, pitch (pulverized product with a particle size of 1 mm or less) and Si powder (75 μm sieve, average particle size 46 μm) ) Content was varied. The content was all within the scope of the present invention. This is an invention example. The composition is as shown in Table 1. The added water in Table 1 is a value calculated by the following equation (2).

Added moisture (mass%) = 100 x W / (R + F) (2)
W: Mass of added water (kg)
R: Mass of castable refractory containing graphite (kg)
F: Mass of SUS fiber (kg)
On the other hand, as a comparative example, the characteristics of an Al ₂ O ₃ —MgO—C castable refractory outside the scope of the present invention were also investigated. The composition is also shown in Table 1.

Invention Examples 1 to 6 are Al ₂ O ₃ —MgO—C castable refractories (that is, graphite-containing castable refractories) of the present invention. On the other hand, Comparative Example 1 is an example not including pitch and Si powder, and the value of [P] / ([P] + [M]) in equation (1) cannot be calculated. Further, Comparative Example 2 does not include pitch (1) [P] / ([P] + [M]) value of the formula is smaller than the range of the present invention, Comparative Example 3 does not include Si powder (1) [P] / ([P] + [M]) values in the formula exceed the range of the present invention, Comparative Example 4 does not include SUS fiber, and Comparative Example 5 includes the added amount of SUS fiber within the range of the present invention. Comparative Example 6 is an example in which alumina cement exceeds the scope of the present invention. Invention Example 7 and Comparative Example 7 are examples of Al ₂ O ₃ -spinel-C castable refractories.

  Inventive Examples 1 to 5 and Comparative Examples 1 to 5 were examined for strength after drying and hot bending strength. The results are shown in Table 2.

  Here, the strength after drying is 110 ° C. dry body strength. After adding water to the refractory and kneading so that the flow value after tapping 15 times in the flow test is 140, it is shaped into a square column of 40 x 40 x 160 mm, after curing for 24 hours after molding, The result of a three-point bending test performed on a test piece removed from the frame and dried at 110 ° C. for 24 hours with a Michaelis-type bending tester is displayed in MPa.

  The 800 ° C hot bending strength is a 30 × 30 × 140mm square shaped dry body sample made of refractory under the same conditions as a 110 ° C dry body strength sample. The results of a three-point bending test in an electric furnace maintained in a nitrogen atmosphere (800 ° C.) after heat treatment for 3 hours are displayed in units of MPa. What is 1400 ° C hot bending strength? A dry sample prepared under the same conditions as 800 ° C hot bending strength is heat treated in coke breeze at 1400 ° C for 3 hours, and then in a nitrogen atmosphere (1400 ° C). The results of a three-point bending test in a held electric furnace are displayed in units of MPa.

  As is apparent from Table 2, Invention Examples 1 to 7 all have a strength after drying at 110 ° C. of 0.8 MPa or more, a hot bending strength of 800 ° C. of 3.8 MPa or more, and a hot bending of 1400 ° C. The strength was 2.2 MPa or more, and a construction body with no strength reduction was obtained in all temperature ranges when used in an actual furnace.

  On the other hand, in Comparative Examples 1-3, sufficient hot bending strength was not obtained at 1400 degreeC. In Comparative Example 4, the strength after drying at 110 ° C. and the hot bending strength at 800 ° C. were insufficient. In Comparative Example 5, the hot bending strength at 800 ° C. is smaller than that of the inventive example. In Comparative Examples 6 and 7, the hot bending strength at 800 ° C. and 1400 ° C. was insufficient.

Claims (1)

The castable refractory containing graphite contains a mixture of pitch, metal powder, alumina cement and metal fiber, and the pitch content (mass%) and the metal powder content (mass%) are as follows: ), The content of the alumina cement is limited to 1.5% by mass or less, and the metal fiber is contained in an external number of 2 to 4% by mass with respect to the mass of the mixture. Graphite-containing castable refractory.
0.6 ≦ [P] / ([P] + [M]) ≦ 0.9 (1)
[P]: Pitch content (% by mass)
[M]: Metal powder content (% by mass)