JP6077877B2 - Castable refractories for blast furnace firewood - Google Patents

Description

  The present invention relates to a castable refractory used as a lining of a blast furnace pit.

  The blast furnace has the role of a passage from the hot metal discharged from the blast furnace to the ladle, chaos car, etc. The lining material is castable refractory from the viewpoint of workability, and the material is mainly alumina-silicon carbide-carbonaceous.

In such a blast furnace castable refractory, a technique of adding boron carbide (B ₄ C) as an antioxidant is known (see, for example, Patent Document 1). Boron carbide oxidizes to form a film on the surface of the refractory material, and this film has a function of preventing oxidation of the carbon material.

In Patent Document 2, when B ₄ C, alumina fine powder and silica ultra fine powder are used in combination, B ₂ O ₃ generated from B ₄ C reacts with Al ₂ O ₃ and SiO ₂ to produce mullite (3Al _{2 O 3 · 2SiO 2) 9Al 2} O 3 · 2B 2 O 3 solid solution (hereinafter referred to as "9A2B". columnar crystals) has been disclosed to be precipitated as entangled in the matrix portion and the gap. Precipitation of 9A2B in the matrix and voids significantly reduces the porosity of the material, improves the hot strength at high temperatures, and improves the corrosion resistance and wear resistance against slag and pig iron. ing.

JP 2000-203953 A Japanese Patent Laid-Open No. 3-164479

As described in Patent Document 1, B ₄ C generates a coating (B ₂ O ₃ ) by oxidation and functions as a surface oxidation protective film. On the other hand, B ₂ O ₃ forms a solid solution (9A2B) of Al ₂ O ₃ and B ₂ O ₃ by reacting with Al ₂ O ₃ in the castable refractory. However, when this solid solution (9A2B) is formed, B ₂ O ₃ as a surface oxidation protection film is consumed, and the function of surface oxidation protection is lowered. When the function of surface oxidation protection is reduced, the internal components of the castable refractory are exposed to the oxidizing atmosphere, so that the oxidation of the carbon material and the reaction of B ₂ O ₃ and Al ₂ O ₃ occur simultaneously, and the oxidation The layer proceeds further into the interior.

  Further, in Patent Document 2, it is said that the corrosion resistance and the wear resistance are improved by precipitation of 9A2B. However, since 9A2B is a dense sintered body, the strength of the construction body increases when 9A2B is generated, and it is unoxidized. Differences in strength occur between healthy tissues. If it does so, it will become a construction body which is easy to cause the structure deterioration of crack peeling by this strength difference. In particular, in the slag line portion of the blast furnace slag, since heating and cooling are repeated by blast furnace operation, crack peeling is likely to occur due to a change in structure due to repeated thermal history and thermal shock at that time.

In view of the above, the problem to be solved by the present invention is to provide a castable refractory for a blast furnace slag that does not deteriorate the anti-oxidation function due to B ₄ C and can prevent crack peeling of the construction body.

According to one aspect of the present invention, the SiC component is contained in an amount of 40% by mass or more and 80% by mass or less , and the B ₄ C component is contained in an amount of 0.3% by mass or more and 3.0% by mass or less . A castable refractory for a blast furnace with an Al ₂ O ₃ component content of 10% by mass or more and 40% by mass or less and an Al ₂ O ₃ component content of less than 45 μm in all raw materials is 6.9% by mass or less. Provided.

In the present invention, the content of Al ₂ O ₃ having a particle size of less than 45 μm in the total amount of chemical components of the blast furnace slag castable refractory 100% by mass ( total raw material) is limited to 6.9% by mass or less. , B ₂ O ₃ derived from the B ₄ C component is inhibited from reacting with Al ₂ O ₃ to produce 9A2B. That is, since B ₂ O ₃ reacts with Al ₂ O ₃ and is not easily consumed, the anti-oxidation function by B ₄ C is not lowered, and the generation of 9A2B is suppressed, so that the occurrence of crack peeling of the construction body is also prevented. it can.

The blast furnace refractory refractory of the present invention is typically an alumina-silicon carbide-carbonaceous material in which an alumina raw material, a silicon carbide raw material, and a carbon raw material are used as a main raw material and a boron carbide (B ₄ C) raw material is blended. A dispersant and a binder are added to this. Then, as its chemical composition, 80 wt% to 40 wt% of SiC components below, B ₄ and C component contained 0.3 wt% to 3.0 wt%, the above particle size 45μm in total feed Al ₂ The content of O ₃ component is 10% by mass or more and 40% by mass or less , and the content of Al ₂ O ₃ component having a particle size of less than 45 μm in all raw materials is 6.9% by mass or less. The content of Al ₂ O ₃ component having a particle size of less than 45 μm in all raw materials is preferably 3.9% by mass or less, and the content of B ₄ C component is 0.3% by mass or more and 1.5% by mass or less. Preferably there is. In addition, although alumina-silicon carbide-carbonaceous material also contains free C component, the content is about 1-10 mass%.

The feature of the castable refractory for a blast furnace fire of the present invention is that the content of Al ₂ O ₃ component having a particle size of less than 45 μm in all raw materials is limited to 6.9% by mass or less. The _Al 2 _{O 3} component content of less than the particle size 45μm of this total in the raw materials, in addition to _Al 2 _{O 3} component derived from the alumina raw material, _Al 2 _{O 3} components derived from the alumina cement is widely used as a binder Is also included. That is, the Al ₂ O ₃ component content of less than the particle size 45μm in the total feed, in the entire blast furnace trough castable refractory (total amount 100 mass% of the chemical components of the blast furnace trough for castable refractories), particle size Al ₂ O ₃ component content of less than 45 μm . In addition, Example 5 shown by Table 2 of the said patent document 1 contains 5 mass% of calcination alumina, and contains 3 mass% of alumina cement as an outer shell. This alumina cement contains at least 70% by mass of an Al ₂ O ₃ component having a particle size of less than 45 μm. Further, the fused alumina having a particle size of 1 mm or less contains about 2% by mass of an Al ₂ O ₃ component having a particle size of less than 45 μm. Therefore, _Al 2 _{O 3} component content of less than the particle size 45μm across castable refractory is 7 mass% or more.

  Examples of the alumina raw material used in the castable refractory for a blast furnace pit of the present invention include sintered alumina, electrofused alumina, clay shale, bauxite and the like. Of these, synthetic products such as sintered alumina and fused alumina having stable quality are preferable. You may use calcined alumina for a fine powder part.

  As a silicon carbide raw material, that whose SiC purity is 85 mass% or more is preferable, and that whose mass is 95 mass% or more is more preferable. If the content of the SiC component is less than 40% by mass, the effect of slag resistance is inferior, and if it exceeds 80% by mass, the proportion of carbon, alumina, etc. must be reduced accordingly, and the hot metal erosion resistance is inferior.

  Examples of the carbon raw material include one or more of various pitches, carbon black, artificial graphite, phosphorus-like graphite, earth-like graphite, coke, anthracite, and the like. The content of the carbon raw material (free C component) is about 1 to 10% by mass as described above.

Boron carbide (B ₄ C) is used as an antioxidant. When the content of the B ₄ C component is less than 0.3% by mass, the antioxidant effect cannot be obtained. On the other hand, when the content of the B ₄ C component exceeds 3.0% by mass, the amount of liquid phase generated increases, and crack peeling tends to occur due to oversintering action.

  Dispersants include inorganic salts such as sodium tripolyphosphate, sodium hexametaphosphate, sodium ultrapolyphosphate, sodium acid hexametaphosphate, sodium borate, sodium carbonate, polymetaphosphate, sodium citrate, sodium tartrate, polyacrylic acid, polyacrylic acid Examples include sodium acrylate, sodium sulfonate, polycarboxylate, β-naphthalenesulfonate, naphthalene sulfonic acid, and the like.

  Examples of the binder include alumina cement, magnesia cement, colloidal silica, colloidal alumina, and the like. Of these, alumina cement is preferable because the structure strength of the construction body can be easily obtained. The alumina cement is preferably JIS standard refractory alumina cement 1 type or 2 type equivalent.

  In addition to the above raw materials, silicic acid powder, drying accelerator, Al powder, Si powder, metal fiber, organic fiber, ceramic fiber, basic aluminum lactate, boron within the range satisfying the specified values of the above chemical components A compound, an antioxidant, a thickener, a curing agent, a curing retarder, a refractory coarse particle, and the like can be used.

  The castable refractory for a blast furnace slag of the present invention is constructed by adding construction water in the same manner as the conventional castable refractory for a blast furnace slag.

  Table 1 shows examples and comparative examples of the present invention.

Mixing alumina raw material, silicon carbide raw material, carbon raw material, boron carbide (B ₄ C) raw material, dispersant and binder so as to be the chemical components in Table 1, kneading after adding an appropriate amount of construction water, Cast into a mold. Subsequently, it was cured and dried to obtain a test construction body. In Examples and Comparative Examples in Table 1, electrofused alumina as an alumina raw material, silicon carbide having a purity of 95% by mass or more as a silicon carbide raw material, carbon black and pitch as a carbon raw material, boron carbide (B ₄ C as an antioxidant) ), Polyacrylic acid as a dispersant, and two types of alumina cement equivalent as a binder were used, and the chemical component values are shown. In Table 1, the “others” component includes components not shown in Table 1, a dispersant, and components of each raw material impurity.

  About the obtained test construction object, the following test was performed, the oxidation test was performed, the bending test was performed, the bending strength was measured, and comprehensive evaluation was performed.

(Oxidation test)
A test piece having a diameter of 50 mm and a height of 50 mm was prepared, dried, and fired at 1000 ° C. in the atmosphere. About the test piece after baking, the oxidation state of the surface which cut | disconnected the external appearance and the 25-mm height position in the horizontal direction was observed. In the observation of the oxidation state, the whitened portion was regarded as the oxidized portion. The case where the oxidation was not progressed was evaluated as ◯, the case where the oxidation was not advanced but the appearance of the test piece was foamed and the properties were inferior was evaluated as Δ, and the case where the oxidation was advanced was evaluated as x.

(Bending test)
A test piece of 40 mm × 40 mm × 160 mm was prepared, dried, and fired at 1000 ° C. in the atmosphere. About the test piece after baking, the bending test was done according to JISR2553 and the bending strength was measured. When Example 2 was applied to an actual machine, a result in which crack peeling was suppressed was obtained, and crack peeling occurred when the bending strength was 15 MPa or more. Therefore, a bending strength of less than 15 MPa was set as a preferred range. In addition, when the comparative example 2 was used for the actual machine, it was a result with many crack peeling.

(Comprehensive evaluation)
The oxidation test and the bending strength are items for evaluating the degree of formation of a dense sintered body (9A2B). If the oxidation test ○ and the bending strength of less than 15 MPa are satisfied in these items, the dense sintered body ( The crack peeling by 9A2B) does not occur, and the antioxidant function by B ₂ O ₃ derived from the B ₄ C component does not deteriorate. Therefore, in the comprehensive evaluation, the case where the oxidation test was ◯ and the bending strength was less than 15 MPa was evaluated as ◯, the oxidation test was Δ or ×, or the case where the bending strength was 15 MPa or more was evaluated as ×.

  As shown in Table 1, the overall evaluation of each of Examples 1 to 6 in the range of chemical components defined in the present invention was good.

In contrast, Comparative Example 1 _{B 4} is C-containing components 0.8 wt%, with _Al 2 _{O 3} Example component content of 7.2 wt% and not multi-grain size of less than 45μm in total feed Yes, compared with the examples, the oxidation resistance was inferior and the bending strength was high.

Comparative Example 2 is a further not multi Example Al ₂ O ₃ component content of less than the particle size 45μm is 11 mass% in the total feed, further oxidation resistance is deteriorated, there results also increases flexural strength It was.

Comparative Example 3 is an example in which the B ₄ C component is as low as 0.2% by mass, and since the amount of B ₂ O ₃ produced is reduced due to the small amount of B ₄ C, the solid solution with Al ₂ O ₃ (9A2B) The bending strength was not high due to the effect of suppressing the formation, but the result was inferior in oxidation resistance.

Comparative Example 4 is B _{4 C} and the large 3.1 wt% example, is improved oxidation resistance is suppressed oxidation of the specimen, the surface under the influence of B 4 _C excess is multi foaming, of the test piece The appearance properties were poor. Also, the bending strength increased because the liquid phase generation amount increased.

Claims (3)

The SiC component is contained in an amount of 40% by mass or more and 80% by mass or less , the B ₄ C component is contained in an amount of 0.3% by mass or more and 3.0% by mass or less, and the content of Al ₂ O ₃ component having a particle size of 45 μm or more in all raw materials is 10. A castable refractory for a blast furnace with an Al ₂ O ₃ component content of 6.9% by mass or less and having a particle size of less than 45 μm in all raw materials of 40% by mass or less . _{2. The} castable refractory for a blast furnace according to claim 1, wherein the content of Al ₂ O ₃ component having a particle size of less than 45 μm in all raw materials is 3.9% by mass or less. The castable refractory for a blast furnace firewood according to claim 1 or 2, wherein the content of the B ₄ C component is 0.3 mass% or more and 1.5 mass% or less.