JPS632911B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention provides a refractory having extremely excellent corrosion resistance as a refractory for a hot metal pretreatment vessel in which treatments such as desulfurization, dephosphorization, and desiliconization of hot metal (hot metal pretreatment) are carried out. At present, typical kilns for desulfurization, dephosphorization, and desiliconization of hot metal use a ladle and a mixing wheel. The case where a pig iron mixer car is used will be explained below, but the pig iron mixer car has conventionally been used as a conveyor container for hot metal. However, recently due to desulfurization, dephosphorization, and desiliconization treatments,
It is used as a refining furnace by injecting treatment agents such as Na ₂ CO ₃ and CaO (CaF ₂ ) into the kiln through a lance pipe. Therefore, it has become impossible to obtain a stable furnace life with conventional refractories such as waxite, high-grade clay, and high-alumina bricks. For this purpose, carbon-containing refractories such as alumina-carbon and magnesia-carbon materials have been developed and used.
In other words, alumina (Al ₂ O ₃ ), magnesia (MgO), and spinel (MgO
−Al ₂ O ₃ ). However, in order to achieve 100% corrosion resistance of the refractory material, it is necessary to suppress the inclusion of impurities as much as possible, and it is particularly desirable not to include impurities in the matrix portion. However, refractories based on alumina, magnesia, and spinel are very susceptible to thermal spalling under conditions of hot metal pretreatment operations. That is, it has the disadvantage that cracks occur on the surface due to temperature change and thermal stress during use, and peeling phenomenon is likely to occur due to this. For example, alumina
High thermal conductivity with a hot linear expansion coefficient of 0.86% at 1000℃
It is relatively small at 5cal/mhr℃ at 1000℃. This is because the internal characteristic values of the refractory differ greatly between the working surface and the back during use, and therefore the generated thermal stress is large and thermal spalling is likely to occur. Therefore, graphite is used to improve such thermal spalling properties. In other words, graphite is added in the usual form, but graphite's hot linear expansion coefficient is about half that of alumina, its thermal conductivity is extremely high, 20 times higher, and it has excellent heat spalling resistance. In this way, unfired refractories are used that are based on refractory materials such as alumina, magnesia, and spinel and have graphite added thereto to improve heat spalling resistance. However, graphite inherently has extremely poor corrosion resistance against soda-based fluxes and the like, and the quality of refractories deteriorates due to oxidation of graphite. For example, in alumina-carbon refractories, the matrix portion is worn out in advance, resulting in a decrease in corrosion resistance. For these reasons, it has been concluded that the amount of graphite involved in reducing corrosion resistance should be minimized as much as possible. However, in order to suppress thermal spalling by adding conventional graphite, the following problems occur when the amount of graphite added decreases, and the cause was determined by detailed analysis of used refractories. In other words, the decrease in the amount of graphite added is due to the non-uniform distribution of graphite within the structure of the refractory, and during use, alumina grains without graphite are directly bonded to each other due to the influence of heat reception, resulting in a reduction in the structure of the refractory. It was found that the effect of suppressing thermal spalling is not sufficient due to the integrated structure of upper alumina. As a countermeasure to this, commercially available laminated graphite (specific surface area maximum of approximately 1100 cm ² /g; calculation of specific surface area is based on JIS R5201) is further peeled off to make the specific surface area at least 1500 cm ² /g. It was discovered that uniform dispersion could be achieved by adding this substance. In this case, the particle size of graphite can be determined by the specific surface area. Therefore, the present invention provides graphite for a hot metal pretreatment vessel, which is characterized in that a refractory aggregate containing 5 to 25% by weight of flaky graphite with a specific surface area of 1500 cm ² /g or more is kneaded and formed, and then dried or fired after drying. Regarding contained refractories. 5 when using a material with a specific surface area of 1500 cm ² /g or more.
It is possible to provide sufficient thermal spalling properties with a carbon blending ratio of ~25% by weight. The reason why the specific surface area of graphite is limited to 1500 cm ² /g or more as described above is that the ideal shape of graphite is to make the C axis thin, and it is better to make the a axis and the B axis as long as possible. Therefore, it is not appropriate to control by particle size, but it is better to control by specific surface area. Next, the reason why the blending amount is limited to 5 to 25% by weight is that if graphite exceeds 25% by weight, refractory materials such as alumina and magnesia that are involved in corrosion resistance decrease, and the corrosion resistance of the entire refractory decreases. Moreover, if it is less than 5% by weight, the effect of suppressing thermal spalling cannot be obtained. The fire-resistant material of the present invention uses conventional fire-resistant materials such as alumina, spinel, magnesia, silicon carbide, Al, Al-Fe metal substances, and silicon nitride as aggregates, and uses pitch and phenolic resin as binders. A refractory aggregate containing 5 to 25% by weight of scaly graphite having a specific surface area of 1500 cm ² /g or more is kneaded and formed, and then dried (unfired) or fired after drying. Example 1 Examples 1-1 to 1-5 and Comparative Examples 1-6 to 1-9 unfired refractories obtained by kneading and drying in the proportions shown in Table 1 are shown in Figure 1. Line the erosion test equipment shown in . In FIG. 1, A indicates the unfired refractories of Examples and Comparative Examples, B indicates slag, and C indicates oxygen-propane combustion gas. FIG. 2 is a sectional view taken along the line - in FIG. 1, where A indicates the unfired refractories of Examples and Comparative Examples, and B indicates slag.
The test conditions for thermal spalling and corrosion resistance tests using an erosion testing device were Na ₂ O/
A slag with a composition of SiO ₂ =3 was used and heated at 1500°C for 5 hours. The rotation speed of the device is 2
It is 1/2 rpm. The test results are shown in Table 1 and Figure 3. FIG. 3 shows the corrosion state of the cut surface when the sample was cut at - in FIG. 2, and it can be seen from this that the corrosion resistance was better as graphite was reduced. It can be seen that the comparative sample has a large amount of erosion and thermal spalling cracks, indicating that the amount of graphite added is preferably in the range of 5 to 25%.

[Table] Example 2 Unfired refractories for actual furnace testing were prepared using the compounding ratios shown in Table 2, and actual operations were carried out in a 250-ton mixed pig iron car slag line. The operation is a desulfurization operation using CaO-based treated materials. The obtained results are shown in Table 2 for Comparative Example 2-
Compared to 4 (conventional product), corrosion resistance is approximately 20% better.
There was no thermal spalling or peeling damage due to thermal stress.

【table】 [Brief explanation of the drawing]

Figure 1 is the erosion test device, Figure 2 is a cross-sectional view taken at - in Figure 1, and Figure 3 is a cross-sectional view of the sample after the erosion test taken at - in Figure 2. It is a figure showing an erosion state. In the figure: A... (Example or Comparative Example) Refractory, B... Slag, C...
...oxygen-propane combustion gas.

Claims (1)

[Claims] 1 5 to 5 pieces of flaky graphite with a specific surface area of 1500 cm ² /g or more
1. A graphite-containing refractory for a hot metal pretreatment vessel, characterized in that a refractory aggregate containing 25% by weight is kneaded and formed and then dried or fired after drying.