JP4802178B2 - Microwave heat treatment method for Al or / and Al-Mg alloy-added MgO-C brick - Google Patents

Description

The present invention relates to a non-fired refractory Al or / and Al-Mg alloy-added MgO-C brick, which is mainly used in steelmaking converters, molten steel pans, and degassing facilities, by microwave. it relates to how to heat treatment.

  MgO-C brick is usually produced as follows. First, a magnesia raw material as an MgO source and a powdered carbon raw material such as scaly graphite, powder pitch, and carbon black as a carbon source, and Al and Al-Mg alloy as a metal source, and a novolac phenol resin as a binder. Add. Further, these are kneaded with a kneader or the like, and the kneaded material is subjected to uniaxial oil press, friction press, or isotropic pressure molding. This molded body is heat-treated at 150 ° C. to 300 ° C. as a drying process for curing the novolac phenol resin, and becomes a non-fired refractory product.

This unfired refractory is built and used in a degassing furnace such as a converter, a ladle, and RH. For example, in the MgO-C brick built in the converter, after the construction is completed, coke is inserted into the furnace, oxygen is blown from the upper lance, the temperature is raised to 1000 ° C. or more as the ambient temperature, and then the hot metal is received. Used as a hot metal decarburization reaction vessel.
On the other hand, a ladle, RH, etc. are usually heated to an atmospheric temperature of 1000 ° C. or more using a gas burner, and then used as a molten steel transport container in the ladle, and as a degassing furnace in RH. The

Here, as a technique for imparting oxidation resistance to a carbon-containing refractory such as MgO—C brick, adding a metal powder selected from the group of Al, Si, Cr, Ti, and Mg to Patent Document 1 The function is described in detail as follows.
That is, a mixture of a raw material refractory powder and carbon powder or a carbon material that generates carbon by thermal decomposition is formed by molding a metal powder having a higher oxygen affinity than carbon in a high temperature range, usually 1000 ° C. or higher. Normally, heating to 1000 ° C. or higher generates an oxide of the metal powder, and the volume expansion during the formation of the metal oxide closes the particle gap at the time of molding and simultaneously achieves high strength. ing. That is, Patent Document 1 discloses a carbon-containing refractory obtained by adding a metal having a large oxygen affinity and then firing it to 1000 ° C. or higher at which this metal reacts.

Further, Patent Document 2 describes a method for producing a carbon-containing unfired refractory fired at 500 ° C. or lower to which a metal powder selected from the group of Al, Si, Cr, Ti, and Mg is added. Its function is described in detail as follows.
That is, a raw material refractory powder and carbon powder or a mixture of carbon substances that generate carbon by thermal decomposition are formed by arranging a metal powder having a higher oxygen affinity than carbon at a high temperature range, usually 1000 ° C. or higher, If necessary, an unfired product dried or baked at 500 ° C. or lower is heated during use in an actual furnace to generate an oxide of the metal powder, and by volume expansion during the production of the metal oxide, molding is performed. It is said that high strength is achieved at the same time as the particle gaps are closed.

Non-Patent Document 1 thermodynamically describes an antioxidant mechanism for metallic Al added to MgO—C. First, Al reacts with carbon to produce Al ₄ C ₃ stable on the Al particle surface under CO gas. On the other hand, Al inside the particles that cannot be reacted becomes gas and reacts with CO gas to become Al ₂ O ₃ , or reacts with N ₂ entrained at the time of molding to produce AlN. Reacts with CO gas to become Al ₂ O ₃ .

Non-Patent Document 2 reports the mineral composition after heat-treating MgO-C bricks containing Al and Si in coke powder, and Al ₄ C ₃ is produced by the treatment at 1000 ° C to 1400 ° C. It has been reported that

That is, when an Al-based metal is added to MgO-C brick, when heat treatment is performed at 1000 ° C. to 1400 ° C., Al ₄ C ₃ and AlN are changed in the process of finally changing to Al ₂ O _3. Although it is known to form, Al ₄ C ₃ and AlN are easily hydrated compounds. That is, in a carbon-containing refractory to which an Al-based metal is added, Al ₄ C ₃ is generated when cooled after firing. The building is constructed in this state and reheated at the stage of use in an actual furnace, and the hydrates of Al ₄ C ₃ and AlN have the disadvantage that the decomposition of the refractory is caused by decomposition.
Among the techniques for imparting oxidation resistance obtained by the technique disclosed in Patent Document 1 by this, in particular, a technique of building a refractory containing Al or Al—Mg alloy added carbon after heat treatment at 1000 ° C. or higher. Is actually not adopted due to the above-mentioned drawbacks.

  On the other hand, in Patent Document 2, a metal powder having a higher oxygen affinity than carbon is disposed in a mixture of raw refractory powder and carbon powder or a carbon substance that generates carbon by thermal decomposition at a high temperature, usually 1000 ° C. or higher. The unburned product that is molded and then dried or baked at 500 ° C. or lower as required is used, but the volatile components are not completely removed from the mixture of carbon materials that generate carbon by thermal decomposition, For this reason, this volatile matter is released by being heated during use of the actual furnace, and when this volatile matter is released, the tissue is deteriorated.

JP 54-39422 A JP 54-163913 A Carbon-containing refractories 63-P. 68 Issued March 15, 2006 Okayama Ceramics Technology Foundation Kawasaki Steel Technical Report Vol. 5P. 45-P. 53 No. 2 1983

From the above, in MgO-C brick to which Al or / and Al-Mg alloy was added, heat treatment was required to completely remove volatile components from the novolac phenolic resin as a binder, but 1000 ° C When the heat treatment at the above high temperature is performed, there is a problem that Al ₄ C ₃ and AlN rich in hydration properties are generated from the Al component as described above.

The present invention has been made in view of the above points, and in an MgO—C brick to which Al or / and an Al—Mg alloy is added, the temperature is higher than the temperature at which Al ₄ C ₃ or AlN is generated as described above. The object is to heat-treat at a low temperature, and to completely remove volatile components from the novolac phenol resin as a binder, thereby making the strength higher than before.

  Based on various experiments, the inventors have confirmed that the structure strength of MgO-C brick is maintained in Al or / and Al-Mg alloy-added MgO-C brick, and that the added metal Al or / and Al-Mg alloy is We have found that there exists an appropriate microwave heat treatment temperature that does not react with carbon.

  In other words, by performing microwave heating instead of conventional atmospheric heating by an electric furnace or the like, the volatile matter removal process is promoted, and the structure obtained by carbonizing the phenol resin in the microwave heating process is a high-strength structure having a substantially constant structure strength. I found out that It was also found that by using this microwave, the binder curing treatment and the carbonization treatment can be performed continuously. And as demonstrated in the below-mentioned Example, when heat-processing with a microwave, it discovered that such high intensity | strength could be ensured in the process temperature of the range of 400 to 850 degreeC. According to the knowledge of the inventors, the treatment temperature of 400 ° C. is a temperature at which volatile matter derived from the phenol resin can be removed. The processing temperature of 850 ° C. is the upper limit of the temperature at which no Al—C compound is generated.

That is, the present invention relates to a microwave heat treatment method of Al or / and Al-Mg alloy-added MgO-C brick formed using a novolac-based phenol resin, and the heat treatment temperature is in a temperature range of 400 ° C to 580 ° C. It is characterized by heating by waves.

According to the present invention, since heat treatment is performed in the temperature range of 400 ° C. to 580 ° C. by microwaves, Al ₄ C ₃ and AlN rich in hydration properties are not generated from the Al component, and the examples described later are used. As described in, the volatile matter can be completely removed, and deterioration of the brick structure is not caused. Further, since a novolac phenol resin is used, the change in the hardness of the germ soil after kneading is small, and the moldability after kneading is good.

  The MgO—C brick used in the present invention has a carbon content of 1% by mass to 30% by mass, an MgO content of 98% by mass to 67% by mass, Al or / and an Al—Mg alloy content of 1 to 1. It is preferable that it is 3 mass%. When the carbon content is less than 1% by mass, slag penetration increases when the actual machine is used, and damage tends to increase. On the other hand, if the carbon content exceeds 30% by mass, the oxidation resistance of the brick tends to be impaired. When the content of Al or / and Al-Mg alloy is more than 3% by mass, the brick is easily cracked.

According to the present invention, Al ₄ C ₃ and AlN are not generated from the Al component, and the volatile matter can be completely removed from the novolac phenolic resin used as the binder. Can be provided.

  Hereinafter, preferred embodiments of the present invention will be described in detail. Prior to that, microwave heating is first performed for each component constituting the MgO-C brick, and microwave heating of the MgO-C brick is performed. A basic property survey was conducted. This experimental method is described below.

  First, electrofused magnesia coarse particles (average particle size 2 mm) as a magnesia source, 98-mass percent scaly graphite coarse particles (average particle size 250 μm) as a carbon source, Al powder (average particles 99% purity) A novolac phenol resin solution having a diameter of 100 μm and a novolac content of 55% by mass was prepared.

  This sample was placed in a PTFE (polytetrafluoroethylene) crucible, and the temperature rise behavior was measured using the experimental apparatus schematically shown in FIG. The applicator 1 as a processing container in this experimental apparatus has a container main body made of, for example, a grounded metal panel, and is subjected to microwave leakage prevention processing. A sample table 2 is provided in the applicator 1, and a crucible 3 for storing the sample is placed on the sample table 2.

  The crucible 3 in the applicator 1 is irradiated with microwaves from the microwave oscillator 11. More specifically, the microwave oscillator 11 is configured to oscillate, for example, a microwave having a frequency of 2.45 GHz. The microwave oscillated from the microwave oscillator 11 is reflected by the reflected microwave. An isolator 12 that prevents the wave from entering the wave oscillator 11, a power monitor 13 that monitors the output of the reflected and reflected microwave into the applicator 1, and a waveguide 14 that introduces the microwave into the applicator 2. The crucible 3 in the applicator 1 is irradiated through the tuner 15 that adjusts the impedance of the antenna and the waveguide 14.

  The temperature in the crucible 3 is detected by the optical fiber temperature sensor 4, measured by the optical fiber thermometer main body 5 installed outside the applicator 1, and output from the data logger 6.

  Using the experimental apparatus configured as described above, irradiation with a microwave output of 100 W was performed for 2 minutes, and the temperature rising behavior was measured. The measurement results are shown in FIG. According to this, it was found that the novolac-based phenol resin D was heated up the best, and then the temperature was increased in the order of scaly graphite C and Al powder A. On the other hand, the temperature of the electrofused magnesia coarse particle B hardly increased.

  From this, it can be seen that heating the MgO-C brick with microwaves can be done by absorbing the microwaves by the novolac phenolic resin, graphite, and Al.

  Next, what happens when microwave heating is performed with a single novolak phenol resin that generates volatile matter, the apparatus shown in FIG. 1 is used, the crucible is changed to MgO, and the temperature measurement method is also 8 mmφ sheath. A heating experiment was conducted by inserting a type K thermocouple into the phenol solution. In the experiment, 30 g of a novolac phenol resin was put in an MgO crucible, and an experiment was performed in which the output was gradually increased to a microwave output of 300 W to 900 W.

  The experimental results are shown in FIG. In the figure, a represents the microwave output, and b represents the temperature of the novolac phenol resin. According to this, it can be seen that the novolac phenolic resin shows a rapid temperature increase from 400 ° C. by microwave heating. This indicates that the microwave absorption capacity, that is, the dielectric constant and dielectric loss of the novolak phenol resin increased at 400 ° C., and it is considered that the carbon state was obtained by carbonization. In other words, the OH group bonded to the benzene ring was heated and vibrated by microwaves, and volatile components were released. As a result, the carbonization reaction of the novolak phenol resin occurred at 400 ° C. under microwave heating. it is conceivable that.

Therefore, using the experimental apparatus of FIG. 1, 30 g of the novolak phenol resin is heated by microwaves, and the microwave output is increased or decreased so as to maintain the temperature at 400 ° C., which is a temperature at which devolatilization caused by the phenol resin can be removed. After holding for 1 hour, the residual carbon ratio of this novolak phenol resin was measured. As a result, a value with a residual carbon ratio of 42% was obtained. For comparison, 30 g of novolac phenol resin was similarly weighed in a magnesia crucible with a lid, buried in a coke breeze, and heat-treated at 900 ° C. for 1 hour in an electric furnace. The value of 42%, which was the same as in the case of microwave treatment, was obtained. From this fact, it was proved that the novolak phenol resin was completely removed by holding at 400 ° C. under microwave heating. It was done.
Here, the “residual carbon ratio” is obtained by the following formula, where the total mass of the resin is the reference mass Wb and the residual mass Wt when heat-treated. That is, the remaining carbon ratio ΔW = Wt / Wb × 100 (%).

Based on such experimental results, an MgO-C brick was actually made as a prototype and subjected to microwave heat treatment according to the present invention. For comparison, MgO-C brick was heat treated by conventional heating in an electric furnace, and the physical properties of each heat treatment were examined. The composition of the MgO-C brick to be heat-treated is as follows: MgO: 78% by mass, scale-like graphite: 18% by mass, novolac phenol resin having a novolac content of 55% by mass: 3% by mass, Al: 1% by mass, or Instead of Al, a composition of Al-Mg: 1% by mass was prepared (Example 2, Reference Example 3 , Comparative Examples 5, 10). Furthermore, instead of Al, an alloy containing 0.5% by mass of Al and 0.5% by mass of an Al—Mg alloy was also verified (Example 4 and Reference Example 4 ).

The configuration of the microwave heating apparatus used for microwave heating is schematically shown in FIG. This microwave heating apparatus basically has the same configuration as the experimental apparatus shown in FIG. 1, but the internal configuration of the applicator 1 is different. More specifically, the configuration of the applicator 1 itself is the same as that of the experimental apparatus shown in FIG. 1, and the microwave oscillator 11, the isolator 12, the power monitor 13 for irradiating the applicator 1 with microwaves, The waveguide 14 and the tuner 15 are also employed in the same configuration. And in the applicator 1, the MgO-C brick 21 used as a heating object is accommodated in the heat insulation box 22. FIG. The heat insulating box 22 is filled with SiO ₂ powder 23, and the MgO—C brick 21 is embedded in the SiO ₂ powder 23. The outside of the heat insulation box 22 is entirely covered with a ceramic fiber panel 24.

  The temperature of the MgO-C brick is detected by the sheath thermocouple 25 and output from the data logger 6. The temperature detected by the sheath thermocouple 25 was raised by microwave so that the temperature was between 350 ° C. and 900 ° C., and kept at that temperature for 8 hours.

On the other hand, in the heat treatment of the MgO-C brick by the electric furnace performed for comparison, the MgO-C brick was buried in the coke breeze, the temperature was raised to the same temperature by the electric furnace, and kept for the same time. . After these heat treatments, the mass reduction rate, porosity, and bending strength of the sample MgO-C brick were measured. The mass reduction rate is obtained from the change in mass of the sample MgO-C brick before and after heat treatment, and the porosity is measured by the vacuum method of JIS R2205 for the test piece cut out for measurement. The bending strength is measured by a three-point bending method according to JIS R2213 on a test piece cut out for measurement.
Furthermore, the increase / decrease in the peak of metallic Al added together was investigated. The peak of metal Al here means the peak of metal Al obtained by XRD (powder X-ray diffraction method). In the case of metal Al, the peak of the cubic (hkl) = (111) plane is maximum. The peak is obtained by this identification.
The decrease in the peak of metal Al means that a reaction between metal Al and carbon has occurred, and it is considered that a hydration reaction occurs. The measurement results are shown in Tables 1 and 2. Table 1 shows the measurement results of the examples, and Table 2 shows the measurement results of the comparative examples.

According to the results in Table 1, first, the temperature at which the volatile components were completely removed from the novolak phenol resin was 400 ° C. or higher in the microwave heat treatment experiment results in Table 1 (Examples 1 to 4 and Reference Example). 1 to 4 and Comparative Example 2), the mass reduction rate shows a value of about 1.8% or more. On the other hand, in the firing in a normal coke breeze, this weight reduction is caused by firing at 850 ° C. or more in Comparative Example 8. Since the rate is 1.8% or more, it can be seen that if the heat treatment is performed at a temperature of 400 ° C. or higher with the same microwave as the experimental result of the phenol resin alone, the volatile matter is completely removed. Further, in the heat treatment state in the microwave of 400 ° C. or higher from which the volatile components have been removed, the porosity is approximately constant 7%.
On the other hand, in the normal electric furnace heat treatment shown in Comparative Examples 7 to 10, the porosity was 8% or more at 720 ° C. or higher, and the porosity was higher than that of microwave treatment.

  The cause is presumed as follows. The novolac phenol resin used as a binder, which is a cause of volatile matter, is coated relatively uniformly on the outer peripheral surface of MgO particles and scaly graphite particles. When microwaves are irradiated in this state, the MgO particles have poor microwave absorption ability, so the MgO particles are transmitted. It is estimated that the temperature of the brick is increased by absorbing the waves, and the entire brick is heated uniformly by heat conduction from these waves.

  In other words, by heating with microwaves and raising the temperature, the novolac phenol layer itself is heated, and the microwaves penetrate into this brick, and this heating phenomenon occurs evenly throughout the MgO-C brick. Is guessed. Immediately after this microwave irradiation, the volatile matter is continuously exhausted from the system through the vent made of the volatile matter generated from the novolac phenolic resin during curing and even during carbonization, and as a result, the conventional heated product It is thought that it is the cause of the low porosity compared with. Moreover, it is estimated that this low porosity has achieved the high intensity | strength of MgO-C brick as a result.

  On the other hand, in the heating by the conventional electric furnace, since it is heated only by heat conduction from the outside of the MgO-C brick, it is not heated to a temperature at which the volatile matter of the novolac phenol resin is generated. Of course, no volatile matter will be generated. In addition, the volatile matter is heated from the outside to the inner surface by heat conduction, and the volatile matter is not generated until the temperature rises to a predetermined temperature at which the volatile matter is generated. In other words, when the volatile matter generated from the inside moves to the outside, it is exposed to an external temperature, and a pressure due to an increase in volume accompanying this temperature rise is generated. Because of the high porosity, it is estimated that the strength of the brick decreases.

  Next, from the investigation results of Al peak reduction of Al added and / or Al-Mg alloy, in the microwave heat treatment, when heat treatment was performed at 900 ° C. (Comparative Example 2), Al peak decrease was observed. It can be seen that the carbide is formed. On the other hand, in the ordinary electric furnace heat treatment, the Al peak lowering phenomenon was not confirmed in the heat treatment up to 900 ° C. Summing up these results, when heat-treating Al or / and Al-Mg alloy-added MgO-C brick molded with a novolac phenol resin in a microwave heat treatment method, the heat treatment temperature is 400 ° C to 850 ° C. When heated by microwaves, the volatile matter from the novolac phenolic resin can be completely removed, and the added Al or / and Al-Mg alloy can also maintain the metallic state without reacting with carbon. Therefore, it was proved that there is no need to worry about the hydration reaction even if such heat treatment is performed.

Next, the durability of this microwave-treated product was investigated. As a test sample, it is the same process as used for drying in an electric furnace that has been conventionally used, Comparative Example 3 (350 ° C. treatment), and Example 1 (400 ° C. treatment) heat-treated with microwaves. Four types of bricks were prepared: Reference Example 2 (850 ° C. treatment), which was also heat-treated with microwaves, and Comparative Example 8 (850 ° C. treatment) heat-treated in the electric furnace at the same temperature as Reference Example 2. The corrosion resistance was evaluated by the rotational erosion test method.

As test conditions, a synthetic slag containing 10% by mass of FeO in a composition of basicity CaO / SiO ₂ = 3.5 (mass base) was prepared in advance, and the atmosphere in the rotary erosion furnace was burned to 1650 ° C. Then, this synthetic slag is added and eroded for 30 minutes. Thereafter, the slag was scraped out, and a new synthetic slag having the same composition was again introduced and eroded for 30 minutes, so that a total of 12 cycles were repeated. Thereafter, the sample was cut, and the corrosion resistance index was investigated at the depth of the maximum worn portion. With respect to the corrosion resistance index, the values of all the samples were displayed with the corrosion resistance index 100 as the value of the amount of wear in Comparative Example 3, which is considered to be the same as that conventionally used. The corrosion resistance evaluation results are shown in FIG.

  Compared to Comparative Example 3, an improvement of about 5% was observed in Comparative Example 8, but the Example of the present invention led to an improvement of 20% or more.

  The present invention is useful when heat-treating AlO and / or Al-Mg alloy-added MgO-C bricks molded with a novolac phenol resin.

It is explanatory drawing which showed typically the structure of the experimental apparatus used when demonstrating this invention. It is a graph which shows the temperature change by the microwave irradiation to a constituent raw material. It is a graph which shows the temperature change by the microwave irradiation to a novolak-type phenol resin. It is explanatory drawing which showed typically the structure of the microwave heating apparatus used in embodiment. It is a graph which shows the corrosion-resistance evaluation result of an Example, a reference example, and a comparative example.

Explanation of symbols

1 applicator 2 sample base 3 crucible 4 fiber optic temperature sensor 5 fiber optic thermometer body 6 data logger 11 microwave generator 12 isolator 13 power monitor 14 waveguide 15 Tuner 21 MgO-C brick 22 insulation box 23 SiO ₂ powder 24 Ceramic Fiber Panel 25 Sheath Thermocouple

Claims (2)

A method of heat-treating AlO and / or Al-Mg alloy-added MgO-C brick formed using a novolac phenol resin,
A microwave heat treatment method for AlO and / or Al-Mg alloy-added MgO-C bricks, characterized in that the MgO-C bricks are heated by microwaves in a temperature range of 400 ° C to 580 ° C. The MgO-C brick is
The carbon content is 1% by mass to 30% by mass,
MgO content is 98 mass% to 67 mass%,
2. The microwave heat treatment method for Al or / and Al—Mg alloy-added MgO—C brick according to claim 1, wherein the content of Al or / and Al—Mg alloy is 1 to 3% by mass.

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