JP2518422B2 - Method of manufacturing magnesia chrome brick - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a fired magnesia / chromic brick used as a lining for a vessel for refining molten steel and the like, and particularly to a basicity (cao / sio) which easily causes brick erosion. ₍₂ ratio) 1-3 high-temperature fired magnesia / chrome bricks that exhibit excellent corrosion resistance even when used in contact with slag or in steelmaking furnaces that operate at high temperatures by causing high secondary combustion. It relates to a manufacturing method.

(Prior Art) Fired magnesia-chromic bricks (hereinafter, "magnesia-chromic bricks" are referred to as "magcro bricks", which is a term used in the industry), have thermal shock resistance in basic refractories. It is a refractory material that has excellent softening properties under load and high-temperature strength, and exhibits excellent corrosion resistance, especially for slag with low basicity. Therefore, it has been widely used for a long time in steelmaking furnace linings, cement firing furnaces, glass furnace checkers, non-ferrous metal refining furnaces, etc. However, the phase of this type of brick is M
_{gO-Cr 2 O 3 -Al 2} O 3 -FeO x -CaO-SiO 2 forms a complex oxide consisting of, not necessarily sufficient elucidated.

Generally speaking, calcined magcro bricks are obtained by using magnesia clinker and chromite as raw materials, crushing, kneading, molding, drying, and then calcination at about 1600 ° C, mainly by the reaction of silicate contained in chromite. A ceramic bond is formed.

In recent years, as refractory usage conditions have become more severe, some of the raw materials have been replaced with electromelted magcro clinker for high purity, and at the same time, they have been fired at a high temperature of 1700 ° C to 1800 ° C and partially ceramic. Magnesia bricks have been developed that form a direct bond between crystallites of magnesia and magnesia chromia-based spinel without a bond. This is called a medium-temperature or high-temperature fired maguro brick in distinction from the above-mentioned general fired maguro brick. Alternatively, it may be called a direct bond brick in distinction from the ceramic bond. In the present specification, this is referred to as high temperature fired magcro brick.

High-temperature fired magcro bricks have high strength at high temperatures, unlike conventional ones. This is attributed to the bond form in the fired brick, and may be roughly classified into direct bond type and ribbon type depending on the bond form. The former is a high-temperature calcined material from magnesia and chromite, and the latter is mainly composed of electrofused magcro clinker. In addition, there is a case where the intermediate concept of both is divided into three forms including a semi-ribboned system composed of three kinds of raw materials. Most of the fired bricks used in the iron ore manufacturing process are high temperature fired bricks of direct bond type or semi-ribbon type, and most of them are special refining furnaces such as RH and DH furnaces and special refining furnaces such as AOD, VOD and VAD furnaces. Used in steel melting furnaces.

In recent years, even in decarburization furnaces such as converters, attempts have been made to increase the secondary combustion ratio to secure a heat source in order to promote a large amount of scrap and smelting reduction of various ores from the viewpoint of cost rationalization. For such high-temperature operation, attention has been paid to magro bricks having high fire resistance, and improvement of the corrosion resistance of the material itself has been studied. In general, a method of promoting the above direct bonding by raising the firing temperature higher than usual is used, but in this case, it is not possible to achieve complete direct bonding due to the particle size constitution of the raw materials to be blended. It is difficult and cracks are likely to occur before and after firing.

In addition, addition or dispersion of chromium components by addition of chromium sources such as chromite or chromium oxide, or electrofused magcro,
High corrosion resistance of refractory constituents by blending chromium sources such as picrochromite has also been investigated, but sufficient results have not been obtained against severe operating conditions.

Among them, in the invention described in JP-A-63-252959, which focuses on the coating of magnesia with a magnesia chromia spinel, the particle size and components of the chromium source other than the magnesia clinker are manipulated to improve the corrosion resistance. . However, the operation of only blending the particle size is uncertain about the coating effect of the magnesia clinker, and if there is an uncoated portion, it causes the corrosion resistance to be impaired, and a major improvement cannot be expected.

Further, in JP-A-61-222955, a magnesia clinker is coated with fine particles of a refractory material on the surface thereof, and the magnesia clinker surface is fired at 1900 ° C. to form a magnesia chromia spinel (Mg-Cr-O) To form
An invention is disclosed that improves the slag penetration resistance of the magnesia clinker itself. Although the refractory material obtained by this method has achieved the purpose of coating the surface, it is not economically disadvantageous in actual production because it has to go through the firing step again to form a standard brick, and it is also promoted again. There is a possibility that cracks may occur in the surface coating layer due to heat stress during the temperature lowering and cooling, and the slag penetration resistance may be impaired during use. Furthermore, both of the methods described in JP-A-63-252959 and JP-A-61-222955 have the drawback that the coating thickness of the magnesia chromia spinel formed on the surface of the magnesia clinker cannot be adjusted arbitrarily. However, it is difficult to obtain a refractory having both corrosion resistance and economy.

(Problems to be Solved by the Invention) An object of the present invention is that the magnesia clinker of the aggregate is completely covered with the layered tissue of the magnesia chromia spinel structure after the brick is fired, and the slag having strong erosion is clinker. It is an object of the present invention to provide a technique for producing a high-temperature fired magcro brick that does not penetrate into grains and exhibits high corrosion resistance.

(Means for Solving the Problem) The present inventor uses the slag with strong erosion resistance of bricks (total iron content: 30%, basicity (CaO / SiO ₂ ): 3) to obtain different bonding morphologies as described above. As a result of the erosion test of the high temperature fired magcro bricks, in most cases, the elution of MgO, the main component of the bricks, proceeded significantly. A detailed observation of the working surface of the brick that was in contact with the slag revealed that the magnesia clinker particles were magnesia chromia spinel (Mg-Cr-O).
The portion covered with the layer had a small slag penetration.

The magnesia chromia-based spinel layer develops along the outer surface of the magnesia grains on the working surface of magcro bricks, which showed relatively good corrosion resistance, and on the contact surface with slag, it reacts with the iron content in the slag to form a high melting point Spinel (Fe-Cr-O
System) was generated and slag invasion into the inner layer was suppressed.

Therefore, if the magnesia clinker in the brick against the slag with relatively strong erosion, that is, the Cr source is densely distributed on the surface of the main aggregate particles, the corrosion resistance may be significantly improved. I got the knowledge.

The present inventor, based on the above findings, further, a method for reliably producing a magcro brick such that the surface of a magnesia clinker, which is an aggregate of a brick after firing, is covered with a magnesia chromia spinel layer. The present invention has been completed by making a search for the following points.

“The surface of the coarse-grained magnesia clinker was pre-coated with a fine-grained chromium source material powder using a water-insoluble binder to form an aggregate, and this aggregate was blended with electromelted magcroclinker and / or chromium iron ore powder. And then kneading, molding, drying, and baking at a high temperature, which is characterized in that the average particle size of the chromium source raw material powder is the average particle size (weighted) of the coarse magnesia clinker. 1/60 of the average
It is desirable to be 1/600.

 Hereinafter, the method of the present invention will be specifically described.

The step of coating the surface of the magnesia clinker with the chromium source raw material powder by the method of the present invention can be said to be a kind of granulation step, and an ordinary stirring-mixing type granulator is used as an apparatus. A centrifugal fluidized granulator can also be used. The coating treatment method is performed according to the following procedure. That is, a coarse-grained magnesia clinker weighed in advance is put into the above apparatus, a water-insoluble binder is added, and mixed until the surface of the particles is sufficiently wet. Furthermore, while continuing the mixing operation, a predetermined amount of fine powder of the chromium source raw material is dispensed in 2-3 times, and the mixing is continued to coat the coarse magnesia clinker particles and the surface with the fine powder of chromium source raw material. Granulate and dry with warm air. In particular, in order to obtain uniform coated particles, it is desirable to heat with an infrared heater or a steam heater while mixing after completion of dispensing. The drying temperature is 100-300 ° C to remove organic volatiles and water.

As a fine-grain chromium source material, in addition to electrofused magcro clinker and chrome iron ore powder, chromium oxide powder or picrochromite powder can be used. However, in order to suppress the formation of silicate by the magnesia clinker and the chromium source material, the amounts of SiO ₂ and CaO contained in these are respectively
It is desirable to keep it below 2.0% and below 1.0%. As long as the amount of impurities does not exceed these ranges, Mg-Cr
Waste material of -O refractory can also be used.

The average particle diameter of the fine chromium source material coated on the surface of the coarse magnesia clinker is preferably within the range of 1/60 to 1/600 of the average diameter of the magnesia clinker. By doing so, a good coating effect can be obtained as described later.

As the water-insoluble binder, synthetic resins such as polystyrene, phenol resin, furan resin, and alkyl resin, or aliphatic hydrocarbons such as liquid paraffin and polyolefin wax may be used, and the kind thereof is not limited. Linseed oil,
Some bituminous substances such as wax and tar also have slightly low adhesive strength, but they are effective in consideration of usage conditions.

The amount of these binders added varies depending on the particle size of the raw material and the type of binder, but is usually used in the range of 1 to 7% by weight relative to the coarse-grained magnesia. Also, in the case of coating treatment,
Using a water-insoluble binder whose tackiness is adjusted by a solvent (solvent), the film thickness may be adjusted, but in the adhesive coating of the present invention, simply by changing the volume ratio of fine particles to coarse particles, It has the advantage that the film thickness can be adjusted.

To the magnesia clinker surface-coated with the chromium source raw material powder obtained as described above, an electromelting magcro clinker, chromite ore, etc. are blended in a predetermined brick component ratio, and a water-soluble binder is added in a usual manufacturing procedure. After kneading and molding, it is dried and fired to make bricks. Firing is performed at a high temperature of about 1700 to 1800 ° C.

When fired at a temperature lower than 1700 ° C, the reaction between the magnesia clinker and the chromium source powder becomes extremely slow.

Firing at a temperature higher than 1800 ° C. promotes the above reaction, but the production cost increases due to an increase in energy required for firing and an increase in wear of the furnace body of the firing furnace, which is not preferable in actual production.

As the water-soluble binder, bittern, magnesium sulfate, lignin sulfonate, PVA and the like which have been used in the production of conventional basic refractories can be used.

The method of the present invention is characterized by using a water-insoluble binder in the step of coating the coarse-grained clinker. In other words, the coated clinker maintains the coating state in the kneading and molding steps, and in the baking step, strong adhesion such that the adhesion between the coarse particles and the fine particles is not broken during the evaporation process of the added water, especially crystallization water and bound water. A water-insoluble binder is used to obtain the coating.

An ordinary water-soluble binder may be used for molding.

(Function) Table 1 shows that among the coating treatment conditions for the magnesia clinker of the examples described later, the particle diameters of the coarse-grained magnesia clinker and the chromium source raw material powder for coating were changed, and after coating and molding,
It is the result of investigating the coating state of each particle after firing and the amount of binder (novolak type phenol resin) used.

As seen in Table 1, in Experiment Nos. 1 and 5 using the chromium source raw material powder having a large particle size, the adhesion of the chromium source raw material powder to the surface of the magnesia clinker was reduced, and the coarse particles at the time of the adhesion were reduced. After the coating, the space between
After the kneading and molding, the coverage after firing gradually decreases.

In addition, in Experiment Nos. 4 and 8 using the ultra-fine chromium source raw material powder of 0.004 mm or less, peeling of the coating layer after kneading and molding,
Although there is no drop-off and the sintering action in the firing step proceeds smoothly, the amount of the non-water-soluble binder added increases and the space remains after firing to lower the coverage.

Experiment No. 2 showed that the complete coating effect was obtained until after firing.
A 3,6,7, particle diameter ratio (r _C / r _M) is 1 / 80-1 / 600 for the weighted average particle size of magnesia clinker particle size of the chromium source material powder (r _C) (r _M) Is within the range of. That is, by coating the chromium source raw material powder having a particle size within the range of 1/60 to 1/600 of the weighted average particle size of the magnesia clinker with the water-insoluble binder on the clinker surface, the brick after firing The coating effect is retained even in the case of, and an effect of suppressing deterioration of corrosion resistance due to slag intrusion can be obtained.

In the fired brick structure, a magnesia chromia-based spinel layer develops around the magnesia clinker and the coated chromium sources sinter to form the outer shell of the magnesia clinker. That is, the magnesia clinker, which is poor in erosion resistance when the brick is used, is covered with the magnesia chromia spinel layer having excellent erosion resistance and the chromium source, and the slag erosion resistance is significantly improved as a whole.

Examples of the method of the present invention will be described below in comparison with comparative examples and conventional examples.

Example 1 Using the raw materials shown in Table 2, magro bricks were manufactured by the method of the present invention. Further, in this process, the coating state of the magnesia clinker was observed after the coating granulation treatment, the molding and the firing.

The grain size of the raw material (weighted average grain size) is coarse grain area: 3 mm, medium grain area:
It was classified into 0.3 mm and fine grain area: 0.03 mm, and each area was mixed with a weight ratio of 4: 3: 3. However, magnesia clinker is a coarse grain area,
The chromium source material for coating was limited to the fine grain region, and the coating thickness was adjusted by changing the fine grain weight and the addition amount of various water-insoluble binders.

First, 10 kg of magnesia clinker and a water-insoluble binder were mixed in a mixing type granulator for 5 minutes, and the chromium source raw material in the fine particle region was added in three portions. After 10 minutes of mixing, the coating treatment was terminated by drying with warm air while mixing. After the treatment, the magnesia clinker was mixed with the rest of the raw materials shown in Table 2 (medium grain size), 10 kg was weighed, 3% of the lignin sulfonate aqueous solution was added, and the mixture was kneaded for 10 minutes, then 800 kg / cm ²
A straight cylindrical briquette with a size of 50φ x 50 l (mm) was made with the molding pressure of. Then, after curing and drying these briquettes,
In a gas furnace heated to 1750 ° C to 1850 ° C (average 1805 ° C)
Got a brick for 1.5 hours.

The thickness of the coating was measured by fixing the sample after coating or molding with epoxy resin and polishing the cut surface with SEM,
Measured under an optical microscope and a real-life microscope, each measuring 10
The average value measured twice was shown.

Regarding the condition after firing, the thickness was estimated from the SEM image and the Cr distribution condition by EPMA. Both agree within an error range of ± 10%.

Table 3 shows the results of measuring the composition of the coating treatment and the coating thickness on the base material after molding.

As can be seen in the trial numbers A, B, and C in Table 3, the fine-grain chromium source raw material for coating is electromelted magchrome, chromite, chromium oxide (Cr ₂ O ₃ ) or picromromite (MgO ・ Cr ₂ O). ₃ )
Or using a resol type phenol resin, a novolac type phenol resin or polystyrene as the water-insoluble binder, the magnesia clinker coated by the method of the present invention shows a good coating state, and the coating thickness is Both were adjusted to 0.2 mm. Further, after firing, magnesia chromia spinel was uniformly formed around the aggregate. Trial Nos. E, A, and D are obtained by increasing the compounding amount of the fine-grain chromium source material in this order, and the coating thicknesses of 0.1, 0.2, and 0.3 mm are obtained according to the compounding amount. It shows another effect of the method of the present invention that the coating thickness can be adjusted simply by changing the blending amount of the coating raw material.

(Example 2) Using the magnesia clinker coated under the conditions of the trial numbers A, B, and C of Example 1, a parallel type magcro brick was manufactured by the same method as described in Example 1. However, the fourth
As shown in the table, Cr ₂ O ₃ in the chemical composition of product brick bulk
In order to unify the amount to around 20%, the coated magnesia clinker of trial number A was mixed with chromite ore and electrofused magkuro, and the coated magnesia clinker of trial numbers B and C was mixed with electrofused magcro. Further, the particle size of the chromium source material for compounding was not restricted to the medium particle size region of Example 1, and the particle size constitution of the optimum packing density was adjusted.

From the obtained 65 × 114 × 230 (mm) bricks, test pieces of the required shape were cut out and subjected to an erosion test to compare the corrosion resistance.

The erosion test method is trapezoidal (40,60) x 70 x 200
mm test pieces were lined in a high-frequency induction furnace with a capacity of 200 kg, and the melting condition of bricks was evaluated by the slag erosion test method in which the synthetic slag was introduced into the molten steel after melting the steel materials. The test conditions are as follows.

Steels ... JIS SS41, slag composition _{... CaO / SiO 2: 3,} FeO: 25%, MnO: 10% slag / metal ratio ... 40 kg / ton Temperature ... 1750 ° C. erosion time ... 2 hours The erosion index slag line of the lining The maximum amount of melt loss (mm / hr) in each part was determined, and the result of the conventional example was set as 100 and shown as a comparative value.

 Table 4 shows the main properties and test results.

Here, the comparative example is manufactured by omitting the coating step, and the composition of the raw materials is the same as that of the example of the present invention.
Further, the conventional example is a commercial product extracted from the one having the apparent porosity equal to that of the brick of the present invention and having a good brick component purity.

Comparing the present invention example and the comparative example in Table 4, the blending amount,
Although the MgO and Cr ₂ O ₃ concentrations in the brick and the apparent porosity are almost the same, the erosion index is as low as 105 in the comparative example and 80 in the present invention. This improvement in corrosion resistance results from the fact that the coated magnesia clinker is used in the examples of the present invention, whereas the magnesia clinker is used in the comparative example without coating. Example by the method of the present invention,
Comparing with the conventional example, it can be seen that by using the coated magnesia clinker of the present invention, the corrosion resistance better than that of the conventional example can be obtained with the Cr ₂ O ₃ content lower than that of the conventional example.

(Effect of the Invention) According to the method of the present invention, a magnesia brick having excellent slag corrosion resistance in which the magnesia clinker of the aggregate is covered with the layered structure of the magnesia chromia spinel structure is obtained. This highly corrosion-resistant magcro brick can sufficiently cope with the severer erosion of bricks due to the rationalization and efficiency of the steelmaking process.

Claims (2)

(57) [Claims] 1. An aggregate comprising a coarse-grained magnesia clinker pre-coated with a fine-grained chromium source raw material powder using a water-insoluble binder, and this aggregate is used as an electromelting magcro-clinker or / and chromium. A method for producing magnesia-chromic bricks, which comprises blending iron ore powder, kneading, molding, drying and firing at high temperature. 2. The method for producing a magnesia-chromic brick according to claim 1, wherein the average particle size of the chromium source raw material powder is 1/60 to 1/600 of the average particle size of the coarse magnesia clinker.