JP7636728B2 - Castable refractory and molten steel ladle using same - Google Patents

Description

The present invention relates to a castable refractory material used in steelworks and a molten steel ladle using the same.

In recent years, the proportion of castable refractories used among all refractories in steelworks has been increasing. In particular, castable refractories, which are applied by mixing raw materials with water in steelworks, are widely used as refractory linings for molten steel ladles used in secondary refining at the steelmaking stage.

Damage to refractory linings of molten steel ladles can be caused by spalling due to thermal shock or slag penetration, and _erosion by slag. Most castable refractories contain alumina cement, which contains CaO as a binder, but the CaO component generates low melting points together with _Al2O3 , MgO, and _SiO2 at high temperatures, which reduces hot strength and causes chemical erosion.

In response to this, Patent Documents 1 and 2 propose a binder for castable refractories containing strontium aluminate such as SrAl ₂ O ₄ and a technique relating to a castable refractory using the binder.

Patent No. 5290125 specification Patent No. 6499464 specification

However, binders containing strontium aluminate as disclosed in Patent Documents 1 and 2 have the problem that when CaO is dissolved in a solid solution and a large amount is added, low melting points are generated during use.

The object of the present invention is to solve the above problems and provide a castable refractory material that is easy to install and does not produce low-melting materials during use, and a molten steel ladle using the same.

The present inventors have confirmed that SrO-Al ₂ O ₃ -SiO ₂ minerals do not melt even at 1650°C, and that in castable refractories containing carbon, cracks after heat treatment can be suppressed by using cement containing strontium aluminate (hereinafter also referred to as strontium cement) instead of alumina cement containing calcium aluminate, and have developed the present invention.

That is, the present invention is a castable refractory containing alumina, carbon, and spinel, characterized in that it contains 11% by mass or more and 20% by mass or less of cement containing strontium aluminate, and a dispersant, and the CaO content in the raw materials excluding the dispersant is 0.3% by mass or less.

In the castable refractory according to the present invention configured as described above,
(1) The cement containing strontium aluminate is contained in an amount of 11% by mass or more and 14% by mass or less.
is considered to be a more preferable solution.

The present invention also relates to a molten steel ladle that uses the above-mentioned castable refractory as a lining refractory material.

According to the castable refractory of the present invention, by using cement containing strontium aluminate instead of alumina cement, the content of CaO derived from the cement is reduced, and the amount of low melting matter generated by CaO is reduced, resulting in high hot strength and excellent corrosion resistance. In addition, by setting the amount of CaO in the raw materials excluding the dispersant to 0.3 mass% or less, it is possible to obtain high hot strength without reducing corrosion resistance.

In addition, alumina cement has a structure represented by the following formula (1):
CaAl ₄ O ₇ +4Al ₂ O ₃ →CaAl ₁₂ O ₁₉ ...(1)
The reaction (1) causes volume expansion. Castable refractories that do not contain carbon shrink when sintered at 1,400°C or higher, but in castable refractories that contain carbon, the carbon inhibits sintering, so the linear change rate increases after cooling due to the reaction (1), and cracks may occur in the applied body. If cement containing strontium aluminate is used instead of alumina cement, the reaction (1) does not occur, so the residual expansion after heat treatment is not greater than necessary, and there is also the effect of preventing cracks from occurring in the applied body.

Furthermore, in the molten steel ladle according to the present invention, the castable refractory according to the present invention, which has excellent corrosion resistance and hot strength as described above, is used as the lining refractory, so that a molten steel ladle with high durability can be obtained.

The castable refractory of the present invention is a castable refractory containing alumina, carbon, and spinel, characterized in that it contains 7% by mass to 20% by mass of cement containing strontium aluminate, and a dispersant, and the CaO content in the raw materials excluding the dispersant is 0.3% by mass or less.

According to the present invention, the cement in the castable refractory material is replaced by a cement containing strontium aluminate instead of alumina cement, so that the amount of low melting substances containing CaO, such as _{Ca2Al2SiO7 and CaAl2SiO6 ,} which melt at 1600°C or less, is reduced, and instead, _SrAl2Si2O8 and _{Sr0.92Mg0.91Al10.09O17 ,} which _{do not} melt even at ₁₆₅₀ ° _C , are produced, improving corrosion resistance and hot strength. In addition, by making the CaO content _0.3 mass% or less, the amount of the low melting substances containing CaO is reduced, so that high hot strength can be obtained without reducing corrosion resistance. Furthermore, since the reaction of the above formula (1) does not occur, cracks do not occur after heat treatment.

The cement containing strontium aluminate is contained in the castable refractory in an amount of 11% by mass to 20% by mass, preferably 11% by mass to 14% by mass. If the cement containing strontium aluminate is less than 11% by mass, the strength required for removal from the form cannot be obtained. If the cement containing strontium aluminate exceeds 20% by mass, the workability decreases and the amount of water required for work increases, resulting in an increase in apparent porosity. The CaO content of the raw materials other than the dispersant is 0.3% by mass or less. If the CaO content of the raw materials other than the dispersant exceeds 0.3% by mass, the corrosion resistance and hot strength decrease.

As raw materials other than cement, alumina, carbon and spinel are contained as refractory raw materials. Here, carbon refers to scaly graphite, scaly graphite, clayey graphite, artificial graphite , carbon black, anthracite, coke, etc. As for cement containing strontium aluminate as a binder, for example, a commercially available product with SrO=17.2 mass%, Al ₂ O ₃ =76.5 mass%, CaO=1.5 mass%, SiO ₂ =0.1 mass% can be used. As a binder, alumina sol, silica sol, etc. can be used in combination with cement containing strontium aluminate. In addition, various metals such as metal silicon, carbides such as silicon carbide and boron carbide may be contained as antioxidants. Furthermore, silica fume, clay, etc. may be contained as a part of the refractory raw materials as long as it is about 5 mass% or less. In addition to the above raw materials, various dispersants such as polycarboxylic acid-based, polyether-based, polymer-based, and naphthalenesulfonic acid-based dispersants, as well as various other additives commonly used in castable refractories, may be used.

In the present invention, the contents of the CaO and other components in the raw materials excluding the cement and dispersant containing strontium aluminate are the same as those used in general castable refractories, and examples thereof include the following: In a castable refractory containing alumina, carbon, and spinel, the alumina is 12% by mass to 73% by mass, the calcined alumina is 2% by mass to 20% by mass, the carbon is 1% by mass to 10% by mass, the spinel is 17% by mass to 37% by mass, and the dispersant is 0.05% by mass to 2.5% by mass.

By using fine-grained calcined alumina as part of the alumina aggregate, it is expected that the strength will improve one day after construction when using cement containing strontium aluminate, especially in winter when the temperature is low.

Example 1
Table 1 below shows Examples 1 to 7 of the present invention and Comparative Examples 3 and 4 in which strontium cement was applied to an alumina-spinel-carbon castable refractory, Comparative Example 2 in which alumina cement was applied, and Comparative Example 1 in which alumina cement was applied to an alumina-spinel castable refractory.

Inventive Examples 1 to 4 all contain 3 mass% flaky graphite, with Inventive Example 1 being an alumina-spinel-carbon castable refractory material containing 7 mass% strontium cement, Inventive Example 2 being an alumina-spinel-carbon castable refractory material containing 11 mass% strontium cement, Inventive Example 3 being an alumina-spinel-carbon castable refractory material containing 14 mass% strontium cement, and Inventive Example 4 being an alumina-spinel-carbon castable refractory material containing 20 mass% strontium cement. Inventive Examples 5 and 6 all contain 7 mass% strontium cement, with Inventive Example 5 being an alumina-spinel-carbon castable refractory material containing 1 mass% flaky graphite, and Inventive Example 6 being an alumina-spinel-carbon castable refractory material containing 10 mass % flaky graphite.

Comparative Example 1 is an alumina-spinel castable refractory using 7% by mass of alumina cement. Comparative Example 2 is an alumina-spinel-carbon castable refractory using 7% by mass of alumina cement. Comparative Example 3 is an alumina-spinel-carbon castable refractory using 6% by mass of strontium cement, which is less than the range of the present invention. Comparative Example 4 is an alumina-spinel-carbon castable refractory using 21% by mass of strontium cement, which is more than the example of the present invention, and with a CaO content higher than the range of the present invention.

Each raw material was weighed and mixed in a separate bag according to Table 1, with only the scaly graphite, pitch, and carbon black in a separate bag, so that the total weight was 2.5 kg, and both the powder and liquid were stored overnight in a refrigerator at 5°C. The next day, it was removed from the refrigerator, and the raw materials other than the scaly graphite, pitch, and carbon black were placed in a universal mixer, and after stirring for one minute, the liquid was added, and after stirring for two minutes, the scaly graphite, pitch, and carbon black were added and stirred for another minute. It was then poured into a 40 x 40 x 160 mm mold, vibrated with a table vibrator for 30 seconds, and stored in a refrigerator at 5°C. After one day, it was removed from the refrigerator, demolded, and subjected to a bending test using a universal testing machine according to JIS R 2553. If the result of the bending test is 0.8 MPa or more, it is determined that the mold can be removed the next day even in winter.

Separately, according to Table 1, each raw material was weighed and mixed so that the total weight was 2.5 kg, with only the scaly graphite, pitch, and carbon black in separate bags. The raw materials other than the scaly graphite, pitch, and carbon black were then placed in a universal mixer and stirred for 1 minute, and the liquid was added and stirred for 2 minutes, after which the scaly graphite, pitch, and carbon black were added and stirred for another minute. The mixture was poured into a 30 x 30 x 120 mm mold for the hot bending test, and into a 40 x 40 x 40 mm mold for the slag erosion test. After pouring into the mold, it was vibrated for 30 seconds with a table vibrator. It was then removed from the mold after curing for 1 day at 20°C.

The 30 x 30 x 120 mm samples were dried at 110°C for 24 hours, and then the samples other than Comparative Example 1 were placed in a silicon carbide container together with coke breeze. The Comparative Example 1 sample was not placed in a container and was heat treated in an electric furnace at 1400°C for 3 hours. The samples were then placed in an electric furnace controlled at 1400°C together with coke breeze and subjected to a hot bending test with a crosshead lowering speed of 0.5 mm/min.

The 40×40×40 mm sample was dried at 110° C. for 24 hours, and then heat-treated at 1650° C. for 1 hour in an electric furnace while flowing nitrogen gas. A φ20×15 mm hole was drilled at the top of the sample, and 7 g of a reagent adjusted to Fe ₂ O ₃ = 0.9 mass%, SiO ₂ = 5.0 mass%, Al ₂ O ₃ = 13.2 mass%, CaCO ₃ = 77.2 mass%, and MgO = 3.8 mass% was filled in the hole, and heat-treated again at 1650° C. for 1 hour in an electric furnace while flowing nitrogen gas. After cooling, the dimensional change in the diameter of the hole before and after the test was measured to determine the thickness of the corrosion, and the thickness was normalized to 100 for Comparative Example 1, which was used as the corrosion index. The results are shown in Table 1 below.

The results in Table 1 reveal the following. Inventive Examples 1 to 6 , the bending strength after curing at 5°C for 1 day was 0.8 MPa or more, and Inventive Examples 2 to 4, which used 11% by mass or more of strontium cement, had higher strength than Comparative Examples 1 and 2, which used 7% by mass of alumina cement. Comparative Example 3, which used 6% by mass of strontium cement, had a bending strength of less than 0.8 MPa after curing at 5°C for 1 day.

Comparative Example 2, which contained 3% by mass of flaky graphite and 7% by mass of alumina cement, expanded after heat treatment at 1400°C for 3 hours, and cracks occurred in the applied body. However, all of Inventive Examples 1 to 6 had the same linear change rate as Comparative Example 1, which contained 7% by mass of alumina cement, and no cracks occurred.

Inventive Examples 1 to 6 all had a higher 1,400°C hot bending strength than Comparative Example 1, which used 7 mass% alumina cement. In addition, because the CaO content was low, the corrosion index was the same or lower than that of Comparative Example 1, and the corrosion resistance was the same or higher.

In Comparative Example 4, which contains more strontium cement than the present invention example and has a higher CaO content, the amount of CaO and the amount of water required for construction, which is large at 8.5 mass%, resulted in a higher corrosion index than Comparative Example 1 and inferior corrosion resistance.

As is clear from the above examples, the castable refractory of the present invention has high hot strength and excellent corrosion resistance, and is less likely to crack when applied. Therefore, a molten steel ladle using the castable refractory of the present invention as a refractory lining has high durability even when used under high heat.

The castable refractory material according to the present invention is not limited to the above examples, and various applications can be added within the scope of the present invention, and it can be applied to all castable refractories used in steelworks.

Claims (3)

A castable refractory containing alumina, carbon and spinel, comprising 11% by mass or more and 20% by mass or less of cement containing strontium aluminate consisting of SrO = 17.2 % _by mass, _Al2O3 = 76.5% by mass, CaO = 1.5% by mass and SiO2 = 0.1 _% by mass, and a dispersant, wherein the content of CaO derived from the cement in raw materials of the castable refractory excluding the dispersant is 0.3% by mass or less, and the composition other than the cement containing strontium aluminate and CaO is 5% by mass or less of silica fume, 12% by mass or more and 73% by mass or less of alumina, 2% by mass or more and 20% by mass or less of calcined alumina, 1% by mass or more and 10% by mass or less of carbon, 17% by mass or more and 37% by mass or less of spinel, and 0.05% by mass or more and 2.5% by mass or less of the dispersant. The castable refractory according to claim 1, characterized in that it contains 11% by mass or more and 14% by mass or less of the cement containing strontium aluminate. A molten steel ladle characterized in that the castable refractory material according to claim 1 or 2 is used as a lining refractory material.