JP2007298433A - Method of evaluating corrosion resistance, abrasion resistance and oxidation resistance of carbon-containing refractory material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of evaluating the corrosion resistance, abrasion resistance and oxidation resistance of a carbon-containing refractory material with respect to slag or molten iron with high precision. <P>SOLUTION: The carbon-containing refractory material allowed to line the inside of a rotary erosion furnace is raised in temperature by an indirect heating method employing a radiant tube to suppress the wear of the carbon-containing refractory material due to oxidation during heating. Further, the carbon-containing refractory material can be uniformly heated by the heating method employing the radiant tube. By this method, the corrosion resistance, abrasion resistance and oxidation resistance of the carbon-containing refractory material can be evaluated with high precision. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for evaluating the corrosion resistance, wear resistance and oxidation resistance of a carbon-containing refractory.

Carbon-containing refractories are widely used in converters, linings of kneading vehicles, slag lines for molten steel pans and hot metal pans, etc., and contribute to extending the life of kilns. This material combines the effects of carbon slag resistance and spalling resistance, and exhibits excellent durability, and higher durability is desired for the purpose of cost reduction.
Until now, typical methods for evaluating the durability of refractories in a laboratory are typical methods such as a high-frequency induction furnace lining method and a rotary erosion method. Among them, the rotary erosion method is widely used because the experimental equipment is relatively inexpensive, does not require preparation, and the experimental operation is not complicated.

  The rotary erosion method is a test method in which a refractory is lined inside an iron drum, and slag and iron are dissolved in the drum to react with the refractory. In general, an appropriate amount of a mixed gas of oxygen and propane is burned inside the drum, and the temperature of the refractory surface is adjusted to a predetermined test temperature by the heat. According to such a rotational erosion method, the sample shape is relatively small, the equipment is simple, and the building and dismantling can be performed easily.

  However, such a rotary erosion method is difficult to control the atmosphere and involves the atmosphere together with the flame, so that damage due to oxidation of the refractory tends to be greater than in an actual furnace. In particular, carbon-containing refractories have an extremely large influence on the relative evaluation of corrosion resistance and wear resistance between samples. Although the combustion gas composition can be controlled to some extent by changing the oxygen / propane ratio, it is inevitable that the atmosphere is involved with the flame.

  On the other hand, conventionally, in a rotary erosion furnace, a protective plate is interposed between the heating source and the carbon-containing refractory, and this protective plate blocks the contact between the flame and the air entrained with the flame and the carbon-containing refractory. Those are known (for example, see Patent Document 1). In the configuration described in Patent Document 1, by using the protective plate, the carbon-containing refractory is suppressed from decarburization due to oxidation when the temperature is raised to a predetermined test temperature, and the weakening of the surface structure. It is possible to evaluate the corrosion resistance, wear resistance and oxidation resistance of an object with high accuracy.

JP 2001-356085 A

Here, in the configuration described in Patent Document 1, since the surface of the carbon-containing refractory comes into contact with gas, slag, and molten iron only after the protective plate has melted and disappeared, the durability test of the carbon-containing refractory is started. In order to make it possible, melting of the protective plate is essential.
However, it has been clarified that the melt of the protective plate has some influence on the evaluation results of the durability of the carbon-containing refractory.
Furthermore, when heating up to the prescribed test temperature, it was found that the temperature variation on the carbon-containing refractory surface was large because it was heated using a burner, and this clearly affects the evaluation results. became.

  The object of the present invention is to prevent the oxidation of carbon at the time of heating and heating the carbon-containing refractory, and to eliminate the influence of initial wear caused by melting of the protective plate that prevents the contact between the heating source and the carbon-containing refractory. Furthermore, another object of the present invention is to provide a highly accurate evaluation method for corrosion resistance, wear resistance, or oxidation resistance by minimizing temperature variations on the surface of the carbon-containing refractory.

  In view of the above points, the present invention suppresses oxidative wear of carbon during temperature rise by indirectly heating a carbon-containing refractory to a predetermined temperature with a radiant tube, and a protective plate An object of the present invention is to provide a method for evaluating the corrosion resistance, wear resistance, and oxidation resistance of a carbon-containing refractory from which adverse effects due to installation have been removed.

That is, the gist of the present invention is as follows.
(1) After heating the carbon-containing refractory lined in a rotatable container to a predetermined temperature using a radiant tube, after charging one or both of slag and molten iron into the container, A method for evaluating the corrosion resistance of a carbon-containing refractory, comprising rotating the container and measuring either one or both of the remaining thickness and the worn area of the carbon-containing refractory after a predetermined time has elapsed.
(2) After heating the carbon-containing refractory lined in a rotatable container to a predetermined temperature using a radiant tube, the wear medium is charged into the container, and then the container is rotated to obtain a predetermined value. A method for evaluating the wear resistance of a carbon-containing refractory, wherein one or both of the remaining thickness and the wear area of the carbon-containing refractory after the elapse of time is measured.
(3) After heating the carbon-containing refractory lined in a rotatable container to a predetermined temperature using a radiant tube, the combustion gas is blown into the container while rotating the container, and after a predetermined time has elapsed. The evaluation of the oxidation resistance of the carbon-containing refractory characterized by measuring one or both of the thickness of the decarburized layer and the area of the decarburized portion in the carbon-containing refractory generated by blowing the combustion gas Method.

  In the present invention, the indirect heating by the radiant tube does not cause the carbon-containing refractory to come into direct contact with the flame or the air entrained with the flame, so that wear due to oxidation of the carbon-containing refractory during temperature rise can be suppressed. Moreover, since it is not necessary to use a protective plate as described in Patent Document 1, it is possible to eliminate the influence on the evaluation result due to the melt of the protective plate. Furthermore, the temperature variation on the surface of the carbon-containing refractory can be minimized. Therefore, the corrosion resistance, wear resistance and oxidation resistance of the carbon-containing refractory can be evaluated with high accuracy.

  The present inventor uses a radiant tube when evaluating the corrosion resistance, wear resistance and oxidation resistance of a carbon-containing refractory using a test furnace lined in a rotatable container. It was newly found that it can be evaluated with high accuracy by indirect heating to a predetermined temperature. This will be described in detail below.

First, a first embodiment of the present invention will be described.
In the present embodiment, examples of the carbon-containing refractory to be evaluated include C, Al ₂ O ₃ —C, Al ₂ O ₃ —SiC—C, MgO—C, Al ₂ O ₃ —MgO—C, and MgO. _{-SiC-C, MgO-CaO-} C, such as _{Al 2 O 3 -SiO 2 -SiC-} C and the like. However, the present invention is not limited to this, and any refractory containing carbon may be used in the present invention. Further, it may be a regular refractory or an irregular refractory.

The radiant tube is mainly used in an atmosphere control heat treatment furnace, and adopts an indirect heating method in which fuel is burned in the tube, the generated heat is radiated from the tube surface, and the processed material is heated by radiant heat. Therefore, it can be heated without involving air with a flame or flame like a burner that is directly heated.
As the radiant tube in the present embodiment, in order to enable the evaluation of the corrosion resistance, wear resistance and oxidation resistance of the carbon-containing refractory in a high temperature range exceeding 1000 ° C., the high temperature heat resistance and corrosion resistance are higher than those of the metal tube. In addition, it is appropriate to use a ceramic tube that is excellent in shape stability (creep resistance) and capable of uniform heating.
Specifically, for example, a single-ended ceramic radiant tube using Eclipse silicon carbide (silicon carbide: SiC) single-ended radiant tube burner manufactured by Eclipse, CERASIC atmospheric pressure sintered SiC ceramics manufactured by Toshiba Ceramics Co., Ltd., A CRB type concentric radiant tube unit manufactured by Chugai Furnace Co., Ltd. can be used.

In this embodiment, a radiant tube is inserted into a rotatable container (hereinafter sometimes referred to as a rotary erosion furnace) lined with a carbon-containing refractory, and a combustion gas is circulated inside the tube. The surface of the carbon-containing refractory lined in the rotary erosion furnace is indirectly heated to a predetermined temperature by the radiant heat generated from the radiant tube at this time. At this time, since the combustion gas circulating in the radiant tube is shut off from the outside, the surface of the carbon-containing refractory on the lining is not contaminated by the combustion gas.
In order to heat the carbon-containing refractory as uniformly as possible, the radiant tube is preferably inserted into the central portion of the rotary erosion furnace.

  Thereafter, after heating the carbon-containing refractory to a predetermined test temperature, either or both of slag and molten iron are charged into a rotary erosion furnace, and the rotary erosion furnace is rotated at a predetermined rotational speed. Conduct erosion tests. And the corrosion resistance of a carbon-containing refractory can be evaluated by measuring any one or both of the remaining thickness of a carbon-containing refractory after a predetermined time progress, a wear area.

Here, the predetermined test temperature is not particularly specified, but is set to a temperature exceeding 1000 ° C. because it simulates an actual furnace. For example, when targeting a converter, it is preferable to heat to 1300-1700 degreeC.
Further, as the slag, for example, blast furnace slag may be used in addition to steelmaking slag such as converter slag, hot metal preliminary treatment slag, decarburization slag, electric furnace slag and the like. Moreover, molten iron means the generic name of hot metal and molten steel.

The rotational speed of the rotary erosion furnace is not particularly limited, but is usually set to about 0.5 to 3 rpm. Here, when the rotational speed is slower than 0.5 rpm, the wear amount of the carbon-containing refractory is small and it is necessary to extend the test time. Further, when the rotational speed is higher than 3 rpm, the amount of wear increases regardless of the type of the carbon-containing refractory, so that it may be difficult to make a relative comparison between samples to be evaluated. Therefore, the rotational speed of the rotary erosion furnace is preferably in the above range.
In order to quantify the evaluation conditions, stable evaluation can be performed by measuring the surface temperature of the refractory with a radiation thermometer.

In this way, the erosion test is performed by rotating the rotary erosion furnace for a predetermined time, and this predetermined time is not particularly defined and may be matched with the conditions of the equipment to be evaluated. For example, when a converter is targeted, it is preferable to set one charge for about 20 to 30 minutes and repeat this several times.
Thereafter, the corrosion resistance of the refractory can be accurately evaluated by measuring one or both of the remaining thickness and the wear area of the refractory.

Next, a second embodiment of the present invention will be described.
In the second embodiment, the wear resistance of the carbon-containing refractory is evaluated by using a wear medium in place of the slag and molten iron in the first embodiment.

  As the wear medium, it is preferable to use a material whose hardness is higher than that of the main raw material constituting the carbon-containing refractory to be evaluated, but the component is not particularly limited. Moreover, it is preferable to use a material having a melting point higher than the test temperature by 400 ° C. or more and stable around the test temperature. Specifically, it is preferable to use, for example, zirconia blocks or magnesia coarse particles.

  The particle size of the wear medium is not particularly limited, but is usually set to 10 to 100 mm. Here, if the particle size is less than 10 mm, sufficient frictional force cannot be applied to the carbon-containing refractory, and it is necessary to extend the test time. If it exceeds 100 mm, the carbon-containing refractory to be evaluated Regardless of the type, since the amount of wear increases, it may be difficult to make a relative comparison between samples to be evaluated. Therefore, the particle size of the wear medium is preferably 10 to 100 mm.

In the second embodiment, similarly to the first embodiment, the surface of the carbon-containing refractory lined in the rotary erosion furnace is heated to, for example, 1300 to 1700 ° C. by radiant heat from the radiant tube according to the test conditions. Heat.
After that, the wear medium is charged into the rotary erosion furnace, and the rotary erosion furnace is rotated at a predetermined rotation speed to perform the wear test. And the abrasion resistance of a refractory can be accurately evaluated by measuring the thickness or wear area of the carbon-containing refractory after a predetermined time has elapsed.
The wear test time is not particularly specified, and may be set as appropriate according to the conditions of the equipment to be evaluated.

Furthermore, a third embodiment of the present invention will be described.
In the third embodiment, the oxidant resistance of the carbon-containing refractory lined in the rotary erosion furnace is evaluated using the radiant tube in the first embodiment.

That is, using the radiant tube, after heating the carbon-containing refractory lined in the rotary erosion furnace to a predetermined temperature, while rotating the rotary erosion furnace, for example, by blowing combustion gas with a burner, Heat for a predetermined time. Then, the oxidation resistance of the carbon-containing refractory is evaluated by measuring one or both of the thickness of the decarburized layer of the carbon-containing refractory generated by heating and the area of the decarburized portion.
Here, the thickness of the decarburized layer of the carbon-containing refractory is a value obtained by subtracting the thickness of the non-oxide layer after the test from the initial thickness. Further, the area of the decarburized part is defined as an area obtained by approximating the area of the decarburized layer by image analysis.

In the above first to third embodiments, after the test, the rotary erosion furnace is dismantled and the carbon-containing refractory is taken out. And the evaluation of corrosion resistance, wear resistance and oxidation resistance is performed by taking the remaining dimension of the extracted carbon-containing refractory sample (in the case of oxidation resistance, the thickness of the non-oxidized layer) as the original dimension (after sample cutting, that is, raising the temperature) The amount of wear is calculated by subtracting from the previous sample dimensions).
As for wear resistance, the amount of wear is large and the shape after the test is not always linear. Therefore, the sample after the test is taken as a two-dimensional image and evaluated by obtaining the area of the worn portion. Also good. Corrosion resistance and oxidation resistance may also be evaluated by determining the area of the worn portion when the amount of wear is large. Of course, it is also within the scope of the present invention to obtain the volume of the worn portion for comparison and evaluation.
The thickness in the evaluation of corrosion resistance, wear resistance and oxidation resistance may be an average value of a plurality of points or one point, but an average value of the thicknesses of a plurality of points measured every about 10 mm is often used.

  According to the first to third embodiments described above, indirect heating using a radiant tube during heating and heating of the carbon-containing refractory can prevent the carbon in the carbon-containing refractory from being oxidized. Further, since it is not necessary to provide a conventional protective plate between the radiant tube and the carbon-containing refractory, it is possible to eliminate the influence of initial wear caused by melting of the protective plate. Further, the indirect heating of the radiant tube can minimize the variation in temperature on the surface of the carbon-containing refractory. Therefore, it is possible to realize a highly accurate evaluation method for corrosion resistance, wear resistance or oxidation resistance.

The atmosphere in the rotary erosion furnace at the time of heating in the first to third embodiments includes an oxidizing atmosphere, a non-oxidizing atmosphere such as Ar, N ₂ , He, H ₂ , and vacuum, There is no limitation to this. That is, for example, the present invention can be applied under all heating conditions in which the refractory may come into contact with oxygen including air and oxygen entrainment.

Hereinafter, an embodiment of the present invention are illustrated in Examples were evaluated the Al 2 _O 3 _-C bricks. However, the present invention is not limited to the following examples.

The Al ₂ O ₃ -C brick as an evaluation object contains 90% by mass of 98% by mass of fused alumina clinker, 7% by mass of scaly graphite having a purity of 98% by mass, and uses a phenol resin as a binder. What added 3 mass% of Al was used. The Al ₂ O ₃ —C brick is widely used as a refractory lining the converter.
As shown in FIG. 1, this Al ₂ O ₃ —C brick is cut into a trapezoidal cross section (a = 67 mm, b = 41 mm, c = 48 mm, d = 114 mm) to produce an evaluation sample (refractory 1). did.
As shown in FIG. 2, the rotary erosion furnace was assembled into a cylindrical shape by combining eight refractories 1 on the inner surface of the furnace. Each refractory 1 is named A, B, C, D, E, F, G, H. The rotational speed of the rotary erosion furnace was 2.5 rpm in any of the following tests.

  In Comparative Examples 1 to 3, as shown in FIG. 3, a hollow carbon steel pipe (protective plate 2) for general gas piping having a diameter of 150 mm and a thickness of 2 mm is incorporated inside the refractory 1 in the rotary erosion furnace. The temperature was raised by the combustion gas of the burner 3. A combustion gas having a volume ratio of propane 1: oxygen 5 was used.

  In Examples 1-3, as shown in FIG. 4, the radiant tube 6 was inserted in the furnace body, and the surface of the refractory 1 was heated from the inside by radiant heat. Note that the refractory 1 was exposed without incorporating the protective plate 2 (see FIG. 3) inside the refractory 1 in the rotary erosion furnace. The radiant tube 6 was a single-ended ceramic radiant tube using CERASIC atmospheric pressure sintered SiC ceramics manufactured by Toshiba Ceramics.

Example 1 and Comparative Example 1 will be specifically described with reference to FIG.
FIG. 5 is a graph showing the wear amount of the Al ₂ O ₃ —C brick after the erosion test was performed after the temperature of the refractory 1 was stabilized at 1600 ° C. for 15 minutes and the erosion test with the slag was completed.
The composition of the slag is CaO = 50.45 mass%, SiO ₂ = 16.85 mass%, MgO = 7 mass%, Al ₂ O ₃ = 2 mass%, MnO = 3.5 mass%, FeO = 20.2. It was set as mass%.
The test temperature was 1600 ° C., 25 minutes was 1 charge, 500 g of slag was replaced, and a total of 6 charges, 2 hours and 30 minutes, were performed.
The slag was replaced by a method of tilting and discharging the horizontal drum.
The amount of wear was determined by subtracting the remaining size of each of the refractory materials 1 to A taken out by dismantling the furnace after the test from the original size (sample size c after sample cutting, ie, before temperature rise: 48 mm). In addition, the said remaining dimension is the value which measured the thickness dimension of four places every 20 mm in the longitudinal direction of each refractory 1, and averaged these.

As a result, as shown in FIG. 5, in Comparative Example 1, a large variation in the amount of wear was recognized between the refractories 1 of A to H. This is because FeO and Fe ₂ O ₃ deposited by elution of the protective plate 2 during the temperature rise eroded C and Al ₂ O ₃ of each refractory 1 of A to H, and further the flame flow of the burner 3 This is thought to be because the temperature distribution in the furnace changed with time due to the unsteadiness.
On the other hand, in Example 1 to which the radiant tube 6 was applied, it was recognized that the variation in the amount of wear between the refractories 1 of A to H was reduced as compared with Comparative Example 1. This is presumably because the protective plate 2 is not incorporated, so that there is no influence of erosion due to FeO or the like, and the furnace temperature can be more precisely controlled by heating using the radiant tube 6.
From the above, it was found that the use of the radiant tube 6 can reduce the variation in the amount of wear between the parts of the carbon-containing refractory lined in the rotary erosion furnace, and can perform a highly accurate corrosion resistance test.

Example 2 and Comparative Example 2 will be specifically described with reference to FIG.
6, refractories 1 of the temperature After 15 minutes stabilization at 1600 ° C., subjected to wear tests by introducing the particle diameter regulating zirconia blocks particle size 30~70mm into the furnace, after the completion of the test Al ₂ O 3 _-C is a graph showing the wear amount of the brick.

In Comparative Example 2, as in Comparative Example 1, as shown in FIG. 3, the protective plate 2 was incorporated inside the refractory 1 in the rotary erosion furnace, and the temperature was raised from the inside by combustion of the burner 3.
On the other hand, in Example 2, like Example 1, as shown in FIG. 4, the radiant tube 6 was inserted in the furnace body, and the surface of the refractory 1 was heated from the inside by radiant heat.
In each of Comparative Example 2 and Example 2, after heating the refractory 1 to a test temperature of 1600 ° C., 100 g of a zirconia block having a particle size adjusted to 30 to 70 mm was introduced into the furnace body. Then, the zirconia block was replaced with 25 minutes as 1 charge, and a total 6 charges, 2 hours and 30 minutes wear resistance test was performed.
The amount of wear was determined by subtracting the remaining size of each refractory 1 of A to H taken out by dismantling the furnace after the test from the original size (sample size c after sample cutting, ie, before temperature rise: 48 mm). In addition, the said remaining dimension is the value which measured the thickness dimension of eight places every 10 mm in the longitudinal direction of each refractory 1, and averaged these.

As a result, as shown in FIG. 6, in Comparative Example 2, a large variation in the amount of wear was recognized between the refractories 1 of A to H. This is because FeO and Fe ₂ O ₃ deposited by elution of the protective plate 2 during the temperature rise eroded C and Al ₂ O ₃ of each refractory 1 of A to H, and further the flame flow of the burner 3 This is thought to be because the temperature distribution in the furnace changed with time due to the unsteadiness.
On the other hand, in Example 2 to which the radiant tube 6 was applied, it was recognized that the variation in the amount of wear among the refractories 1 of A to H was greatly reduced as compared with Comparative Example 2. This is presumably because the protective plate 2 is not incorporated, so that there is no influence of erosion due to FeO or the like, and the furnace temperature can be more precisely controlled by heating using the radiant tube 6.
From the above, it was found that by using the radiant tube 6, it is possible to reduce the variation in the amount of wear between the parts of the carbon-containing refractory lined in the rotary erosion furnace, and to perform a highly accurate wear resistance test.

Example 3 and Comparative Example 3 will be specifically described with reference to FIG.
FIG. 7 is a graph showing the thickness of the decarburized layer of Al ₂ O ₃ —C brick after the end of the test after stabilizing the temperature of the refractory 1 at 1600 ° C. and conducting a combustion gas for 3 hours with a burner. It is.

In Comparative Example 3, as in Comparative Example 1, as shown in FIG. 3, the protective plate 2 was incorporated inside the refractory 1 in the rotary erosion furnace, and the temperature was raised from the inside by combustion of the burner 3.
In Example 3, as in Example 1, as shown in FIG. 4, the radiant tube 6 was inserted into the furnace body, and the surface of the refractory 1 was heated from the inside by radiant heat.
The thickness of the decarburized layer is the original size (sample size c after sample cutting, that is, before the temperature rise: 48 mm) of the remaining size (non-oxidized layer thickness) of each refractory 1 of A to H taken out by dismantling the furnace after the test. ) Was subtracted from In addition, the said remaining dimension is the value which measured the thickness dimension of eight places every 10 mm in the longitudinal direction of each refractory 1, and averaged these. The larger the decarburized layer thickness, the greater the amount of oxidation, indicating poorer oxidation resistance.

As a result, as shown in FIG. 7, in Comparative Example 3, a large variation in the thickness of the decarburized layer was recognized among the refractories 1 of A to H. This is because FeO and Fe ₂ O ₃ deposited by elution of the protective plate 2 during the temperature rise eroded C and Al ₂ O ₃ of each refractory 1 of A to H, and further the flame flow of the burner 3 This is thought to be because the temperature distribution in the furnace changed with time due to the unsteadiness.
On the other hand, in Example 3 to which the radiant tube 6 was applied, it was recognized that the variation in the thickness of the decarburized layer between the refractories 1 of A to H was greatly reduced as compared with Comparative Example 3. . This is presumably because the protective plate 2 is not incorporated, so that there is no influence of erosion due to FeO or the like, and the furnace temperature can be more precisely controlled by heating using the radiant tube 6.
From the above, it was found that the use of the radiant tube 6 can reduce the variation in the thickness of the decarburized layer between the parts of the carbon-containing refractory lined in the rotary erosion furnace, and can perform a highly accurate oxidation resistance test.

The schematic diagram which shows the shape of the evaluation sample in one Example of this invention. The perspective view which shows the external appearance of the evaluation sample lined in the rotary erosion furnace in the said Example. The sectional side view which shows typically the rotary erosion furnace used in Comparative Examples 1-3 in the said Example. The sectional side view which shows typically the rotary erosion furnace used in Examples 1-3 in the said Example. Wherein after the corrosion test according to Example 1 and Comparative Example 1 in Examples graph showing the wear amount of the Al 2 _O 3 _-C bricks. After abrasion test according to Example 2 and Comparative Example 2 in the embodiment, the graph showing the wear amount of the Al 2 _O 3 _-C bricks. Wherein after the oxidation test according to Example 3 and Comparative Example 3 in Examples graph showing the decarburization thickness of each Al 2 _O 3 _-C bricks.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Refractory 2 ... Protection board 3 ... Burner 4 ... Slag 5 ... Filler 6 ... Radiant tube

Claims (3)

After heating the carbon-containing refractory lined in a rotatable container to a predetermined temperature using a radiant tube,
After charging one or both of slag and molten iron into the container, the container is rotated,
One or both of the remaining thickness and the worn area of the carbon-containing refractory after the elapse of a predetermined time are measured. A method for evaluating the corrosion resistance of a carbon-containing refractory. After heating the carbon-containing refractory lined in a rotatable container to a predetermined temperature using a radiant tube,
After charging the wear medium into the container, the container is rotated,
One or both of the remaining thickness and the worn area of the carbon-containing refractory after the elapse of a predetermined time is measured. A method for evaluating the wear resistance of a carbon-containing refractory. After heating the carbon-containing refractory lined in a rotatable container to a predetermined temperature using a radiant tube,
While rotating the container, the combustion gas is blown into the container,
After a predetermined time has elapsed, either one or both of the thickness of the decarburized layer and the area of the decarburized portion in the carbon-containing refractory generated by blowing the combustion gas is measured. Evaluation method.

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