JP2022040739A - Forming sedative - Google Patents

Abstract

[Problem] To provide a foaming calming material that contains by-products generated in the steelmaking process and is capable of sufficiently calming the foaming of slag. [Solution] The foaming calming material contains refractory material, slag, and more than 4 mass% water, has an apparent density of 1250 kg/m3 or more, is preferably a molded body in which the proportion of grains of 5 mm or more is 50 mass% or more, and further contains cement as a binder. [Selected Figure] None

Description

The present invention relates to a forming sedative that can be manufactured at low cost.

CO bubbles generated by the reaction between C in molten iron and FeO (iron oxide) in slag at the interface between molten iron and steelmaking slag (hereinafter referred to as slag) during or after refining the molten iron, or the slag itself. A phenomenon (hereinafter referred to as forming) may occur due to CO bubbles generated by the reaction between FeO in the slag and C in the grain iron contained in the slag inside. If the forming of this slag is intense, the slag at 1300 to 1650 ° C. may overflow from the smelting equipment and the transport container, and if the slag equipment and the transport container are damaged, a great deal of time and labor is required for restoration. When the FeO concentration in the slag is high, a large amount of CO bubbles are generated, so that the slag having a high FeO concentration has a strong forming property (characteristic of rapidly expanding and easily overflowing).

In order to calm the forming of the slag, it is necessary to destroy the layer in which the CO bubbles stay (hereinafter referred to as the foam layer) and shrink the slag. Therefore, a method is generally known in which a lump (soothing material) that gasifies inside the slag is put into the slag, and the foam layer is destroyed by using the volumetric expansion energy when the lump is gasified by thermal decomposition. ing.

Here, as a kind of molten iron refining process, after dephosphorization treatment is performed in a converter, a part of slag is discharged (intermediate discharge) to a slag pot outside the furnace, and then decarburization treatment is performed in the same converter. The multifunctional converter method to be performed is generally known. In this multifunctional converter method, if the forming of slag becomes intense during the dephosphorization and the slag is about to overflow from the furnace mouth of the converter, the dephosphorization and blowing must be interrupted and the dephosphorization reaction proceeds. Will be insufficient. Therefore, in order to increase the dephosphorization rate in the decarburization blowing in the next step, it is necessary to add extra CaO in the converter, which leads to an increase in refining cost and an increase in the amount of slag generated. Further, even in the decarburization smelting, if the forming of the slag progresses violently, there is a concern that the slag will flow out from the furnace mouth of the converter when the converter is tilted at the time of steelmaking. For the above reasons, it is necessary to put a sedative material into the converter at least during the dephosphorization treatment and the decarburization treatment.

As a sedative material for sedating forming, various sedative materials such as molded products of papermaking waste have been proposed. On the other hand, in order to reduce the cost in the steelmaking process, it has been proposed to use the by-products generated in the steelmaking plant as a raw material for a sedative.

Patent Document 1 includes 100 parts by mass of a refractory containing 5 to 70% by mass of a maximum particle size of 0.5 mm or more and 0.15 mm or less of a particle size, and 5 to 50 parts by mass of water, which are heat-dissipating containers. Disclosed is a converter slag forming sedative material using a refractory waste material, which is contained in the above. Further, Patent Document 2 discloses a technique in which a free CaO is 2.7% or less, a water absorption rate is 4.0% by mass or less, and a raw material for kiln is used as a sedative material. Further, Patent Document 3 discloses a technique of crushing a block of a refractory material and using it directly as a forming sedative material.

Japanese Patent No. 4669437 Japanese Patent No. 4351490 Japanese Unexamined Patent Publication No. 2004-2915

However, in the case of producing the sedative material described in Patent Document 1, it is necessary to separate the refractory powder waste material independently, adjust the particle size, and further enclose it in a container together with water, resulting in high production cost. Become. Further, the forming slag could not be sufficiently sedated by the sedative material raw material having a water absorption rate of 4.0% by mass or less described in Patent Document 2. Further, also in the case of the sedative material described in Patent Document 3, almost no gas was generated, and the forming slag could not be sufficiently sedated.

In view of the above-mentioned problems, it is an object of the present invention to provide a forming sedative material containing by-products generated in the steelmaking process and capable of sufficiently quelling the forming of slag.

From the viewpoint of reducing steelmaking costs, the present inventors have diligently studied a method of utilizing by-products generated in the steelmaking process as a forming and calming material for slag. Therefore, the present inventors first focused on the used refractory powder mixed with slag, which cannot be used as an auxiliary raw material for converters. Although some of these can be used for roadbed materials, etc., the amount of demand is small compared to the amount generated, and since there is no effective recycling means, most of the rest is disposed of in landfills at a large cost. There is. Therefore, if this refractory powder can be utilized as a forming sedative, the raw material cost and disposal cost can be kept low.

The present inventors have diligently studied a method of utilizing the refractory powder mixed with slag as a sedative material. As a result, when this refractory powder is used alone or a substance in which water and a binder are mixed with the refractory powder is used as a calming material, a calming efficiency equal to or higher than that of a conventional paper sludge-based calming material can be obtained. In the case of molding, it was confirmed that it can be efficiently and safely added to the furnace from the auxiliary raw material input hopper on the converter, and that it can be used stably on an industrial scale.

The details of the invention are described below.
In order to investigate the calming effect of forming when the refractory is used alone, the present inventors put the refractory in the form of a lump having a particle size of about 50 to 100 mm on a scoop-type loading jig alone. A test was conducted in which the slag was added to the forming slag in the converter from the furnace opening. As a result, it was found that this refractory has a lower sedative effect than the sedative material of the conventional papermaking waste molded product, and is not practical. Here, the papermaking waste material molded product is, for example, a mixture of papermaking waste material: 30 to 50% by mass, moisture: 10% by mass, steelmaking slag, etc., in a cylindrical mass having a diameter of 30 to 50 mm and a height of 30 to 50 mm. It is a molded product. Paper waste molded products contain cellulose as the main component, which is decomposed and gasified by the heat of slag, and the foam layer is destroyed by the volume expansion energy due to gasification, and the forming is calmed down.

Next, the slag sedative effect was investigated when only the slag-mixed refractory powder generated when the refractory was crushed after use, or when the powder was molded and used as a sedative material. Here, the refractory powder mixed with slag is a powdery substance having a maximum particle size of 5 mm or less and 50% by mass or more thereof having a particle size of 2 mm or less. As a result, a forming soothing effect equivalent to that of the papermaking waste molded product was obtained, and the soothing effect was greatly improved as compared with the above-mentioned lumpy refractory.

In order to investigate the cause of this, the present inventors first measured the water content of the sedative material between room temperature and 1400 ° C. using a heat content analyzer. As a result, it was found that the refractory powder contained water, and the average content was about 6% by mass. Further, the present inventors have identified that the water is absorbed in the slag rather than the refractory, and the water is adsorbed by using the refractory powder mixed with the slag instead of the refractory alone.

When refractory powder mixed with slag is added to the formed slag, the water adsorbed in the slag becomes water vapor, destroying the foam layer of the forming slag, and it is thought that it has the effect of calming the slag. Be done. However, it was also found that the amount of gas generated by the powder of this refractory is very small compared to the papermaking waste material molded product, and the gas generation volume ratio is as small as about 1/6 of the papermaking waste material molded product. rice field.

Therefore, the present inventors investigated various factors and focused on the fact that the apparent density of the powder of the refractory material mixed with slag is higher than that of the papermaking waste material molded product. That is, when the powder of this refractory material is added to the slag, it settles deeper than the molded papermaking waste material, and gas is generated in the deeper part. Therefore, it was found that the foam layer can be efficiently destroyed and the formed slag can be calmed down even if the amount of gas generated is smaller than that of the papermaking waste material molded product.

Here, the apparent density is the density of the substance including the volume of the pores contained therein, and in the present invention, there is almost no difference from the bulk density, so that the bulk density may be used. The apparent density or bulk density can be measured, for example, by the method described in JIS Z8807: 2012. Further, when the scope of the present invention is defined by the specific gravity, the specific gravity can be calculated by dividing the value of the apparent density or the bulk density by the density of a standard substance such as water. For simplicity, the apparent density or the bulk density (both units are kg / m ³ ) may be divided by 1000 to calculate.

The present invention is as follows.
(1)
A forming sedative that contains refractory, slag, and more than 4% by mass of water and has an apparent density of 1250 kg / m ³ or more.
(2)
The forming sedative material according to (1) above, which is a refractory powder mixed with slag having a particle size of 2 mm or less and a proportion of 50% by mass or more.
(3)
The forming sedative material according to (1) above, wherein the molded product has a particle size of 5 mm or more and a proportion of 50% by mass or more.
(4)
The forming sedative material according to any one of (1) to (3) above, which further contains cement as a binder.
(5)
The forming sedative material according to any one of (1) to (4) above, which has an apparent density of 1500 kg / m ³ or more.
(6)
The forming sedative material according to any one of (1) to (5) above, wherein the mass of the refractory is 0.5 times or more and 4 times or less with respect to the mass of the slag.

According to the present invention, it is possible to provide a forming sedative material containing by-products generated in the steelmaking process and capable of sufficiently quelling the forming of slag.

Hereinafter, the slag forming sedation method according to the embodiment of the present invention will be described in detail. Hereinafter, a converter operation will be described as an example of the present embodiment, but the present invention can be applied not only to the converter but also to the operation in a refining container such as a slag pot. Also, it is not limited to the temperature of the slag.

The addition of the sedative material into the smelting pot is performed, for example, via a hopper laid in the vicinity of the smelting pot. This hopper is connected to a bunker that stores sedatives, and it is possible to add any amount of sedatives set by the operator. As for the timing of adding the sedative material, it is preferable to add the sedative material of the material described later when the slag formed in the smelting furnace reaches a height of about 4/5 in the height direction of the smelting furnace. .. Examples of the method for measuring the slag height include a method of measuring using vibration information of a lance, a method of measuring using μ waves, and a method of predicting from the acoustic level in the furnace.

The sedative may be added under the condition that the height of the slag is lower than the height of 4/5 in the height direction of the smelting furnace, but the slag is not sufficiently formed and the sedative effect of the sedative is reduced. As a result, the amount of sedative required may increase. On the other hand, when the slag height reaches a height of 4/5 or more in the height direction of the smelting furnace, the slag may flow out from the furnace mouth due to subsequent forming. It is preferable to add the sedative material before the slag flows out from the furnace opening by forming, but the effect is also exhibited when the above-mentioned sedative material is added after the slag flows out from the furnace mouth of the smelting furnace by forming. ..

Next, the sedative material according to the embodiment of the present invention will be described in detail. The sedative material according to the present embodiment is characterized by containing a refractory material, slag, and more than 4% by mass of water, and having an apparent density of 1250 kg / m ³ or more.

The refractory material contained in the sedative material according to the present embodiment is not limited to its type and shape. For example, it is possible to use refractories generated in various processes such as MgO system, Al ₂ O ₃ system, Al ₂ O ₃ −SiO ₂ system, ironmaking, steelmaking process, rolling process and the like. This is because the weight of the refractory has almost no difference and has almost no effect on the apparent density. Further, the refractory can be easily obtained, for example, by recovering the refractory disassembled due to deterioration, wear, etc., and crushing / magnetically separating the refractory from the refractory.

Further, the type of slag contained in the sedative material according to the present embodiment is not particularly limited, and is, for example, slag generated in the ironmaking process or the steelmaking process. The composition of the slag is, for example, CaO = 20 to 50% by mass, SiO ₂ = 20 to 50% by mass, T.I. Fe = 10 to 30% by mass, MgO = 5 to 30% by mass, and the balance consists of MnO, P ₂ O ₅ , Al ₂ O ₃ , and other oxides generated in each process. Further, it is preferable that the sedative material contains slag having a high CaO concentration and a SiO ₂ concentration. This is because CaO absorbs water and changes to hydroxide, and CaO and SiO ₂ form hydrates, so that the water content can be increased.

In addition, the sedative material according to the present embodiment contains more than 4% by mass of water. If the content of water is 4% by mass or less, the amount of gas (water vapor) generated when the sedative material is added to the formed slag is insufficient, and the effect of destroying the foam layer of the slag and sedating the slag is insufficient. Preferably, it contains more than 15% by weight of water. The upper limit of the water content is not particularly limited, but if the water content exceeds 25% by mass, the refractory powder mixed with slag and the binder cannot sufficiently absorb the water, and the soothing material becomes solid. Since it may be in a liquid mixed state and difficult to handle in operation, it is preferably 25% by mass or less. The water content is a water content in consideration of the water of crystallization component contained in the sedative material. The content can be measured using a general thermal analyzer such as TG-DTA, but the blending ratio is based on the representative values of the added water and the water in the raw material before the addition. It may be calculated from.

The apparent density of the sedative material shall be 1250 kg / m ³ or more. If the apparent density is less than 1250 kg / m ³ , the density will be lower than that of the conventional papermaking waste molded product, and the subduction into the slag will be insufficient. Preferably, the apparent density is 1500 kg / m ³ or more. The apparent density value may be similarly measured by the method described in JIS Z8807: 2012, or may be a value calculated using the values of the shape inside the smelting furnace and the weight of the slag in the furnace. ..

The sedative material added to the slag formed in this embodiment does not necessarily have to be molded, but if a powdery sedative material is added without molding, it affects the safety of workers and the equipment and operations used. It is necessary to add a sedative after careful consideration.

For example, when adding the sedating material as powder without molding, in the actual process, a considerable amount of sedating material is placed in the hopper on the converter, a part of it is cut out, and then the required amount is cut out. Add to the forming slag in the converter. Since the sedative material contains 4% by mass or more of water, if the sedative material remains as a powder, it may stick in the hopper. Further, if the worker tries to add the powder of the sedative material packed in a bag directly into the furnace by hand throwing, there is a safety problem such as damage when a steam explosion occurs. Therefore, it is necessary to provide a certain distance between the operator and the forming slag so that the scattering of the slag due to forming can be safely avoided. For example, when the sedative material is added to the slag pot from the vicinity of the trunnion portion of the converter, the sedative material according to the present embodiment can be added as it is in powder form.

When the sedative material of the present invention is used as a powder without being molded, it is preferable to use the forming slag in a slag pot as a target. This is because when powdery stagnation material is added to the forming slag of the converter, the gas ejected from the furnace mouth and a part of the stagnation material fly out of the furnace as the slag metal reaction in the converter progresses. It may not reach the formed slag, or some of the sedative material may adhere to the furnace wall inside the furnace. This is also because some of the sedative material may not reach the forming slag and may be sucked by the dust collecting equipment on the converter.

Further, when the sedative material was used as it was in the form of powder without being formed, the slag sedating effect was high when the particle size of the refractory powder mixed with slag was 50% by mass or more. When the ratio of 2 mm or less is less than 50% by mass, the amount of water contained in the refractory powder mixed with slag is relatively small, so that when the grains become large, the ability to absorb into the refractory powder mixed with slag is available. It is considered that this is because the amount of gas generated in the forming slag is reduced.

On the other hand, when the refractory powder mixed with slag in the present invention is molded and used, it is preferable to use the forming slag in the converter as a target. This is because by molding, the above-mentioned sedative material can be prevented from scattering and the sedative material can reach the surface of the forming slag.

Further, in the molded product, the ratio of the particle size of 5 mm or more is preferably 50% by mass or more. By setting the ratio of the particle size of 5 mm or more to 50% by mass, the scattering of the sedative material is suppressed, the ratio of reaching the deeper part of the slag is increased, and a higher sedative effect can be obtained. More preferably, the ratio of the particle size of 5 mm or more is 60% by mass or more.

Further, if the particle size is too large, it takes time for the molded body to react in the forming slag, and the forming slag cannot be efficiently sedated. Therefore, the ratio of the particle size of 100 mm or less is 50% by mass or more. It is preferable to use 60% by mass or more, more preferably 60% by mass or more.
Here, the above-mentioned particle size and its distribution can be measured using, for example, a sieve such as JIS Z 8801.

In the case of a molded body, the above-mentioned powder of a refractory material mixed with slag having a particle size of 2 mm or less is 50% by mass or more is used, and the particle size of 5 mm or more is 50% by mass or more. It is more preferable to make a certain molded body. The present inventors have confirmed that the slag soothing effect is enhanced by setting the particle size of the refractory powder mixed with slag used for molding to 50% by mass or more in a proportion of 2 mm or less. When the ratio of 2 mm or less is less than 50% by mass, the amount of water contained in the refractory powder mixed with slag was relatively small. It is thought that this is because the ability to produce is reduced and the amount of gas generated in the forming slag is reduced.

As described above, the sedative material according to the present embodiment is assumed to contain a refractory material, slag, and water in an amount of more than 4% by mass, but may contain other materials. In particular, with respect to water, when the sedating material is combined with not only slag but also other hydrating binders and the water is immobilized in the sedating material as water of crystallization, a better soothing effect of forming can be obtained. That is, by increasing the gas generation volume and further increasing the apparent density by the binder, it is possible to settle the sedative material deeper in the forming slag and further increase the gas generation amount. .. Further, by crystallizing the water contained in the sedative material, it is possible to prevent the sedative materials from sticking to each other in the hopper.

The type of binder for immobilizing water as water of crystallization is not particularly limited, but cement is preferable, for example. Cement has the effect of fixing the water contained in the sedative material as water of crystallization in the forming slag. If the sedative material contains cement, it is possible to prevent the sedative materials from sticking to each other in the hopper and to allow a large amount of water to be contained in the sedative material. Further, by containing cement, it is possible to form the sedative material into a desired shape in a relatively short time and at low cost.

Further, in the sedative material, the ratio of the refractory to the slag is preferably 0.5 times or more and 4 times or less the mass of the refractory with respect to the mass of the slag. This is because slag has the effect of containing a large amount of water, and the refractory has the effect of increasing the apparent density, and each effect works appropriately.

Although the preferred embodiment of the present invention has been described above, the present invention is not limited to such an example. It is clear that a person skilled in the art can come up with various modifications or modifications within the scope of the technical ideas described in the claims, and of course, the technical scope of the present invention also includes them. It is understood that it belongs to.

Next, an example of the present invention will be described. The conditions in the examples are one condition example adopted for confirming the feasibility and effect of the present invention, and the present invention is based on this one condition example. Not limited. The present invention can adopt various conditions as long as the gist of the present invention is not deviated and the object of the present invention is achieved.

(First Example)
After charging 250 tons of hot metal into a 300 ton scale converter and adding flux etc. to perform dephosphorization, the converter is tilted to reduce the forming slag inside the converter to about 10 tons, and the slag pot outside the furnace. It was discharged to. The slag temperature at this time was 1300 to 1450 ° C., and the slag composition was CaO = 30 to 40% by mass, SiO ₂ = 20 to 35% by mass, and T.I. Fe = 10 to 20% by mass, MgO = 5 to 10% by mass, MnO = 5 to 10% by mass, P ₂ O ₅ = 2 to 5% by mass, and Al ₂ O ₃ = 0 to 5% by mass.

At that time, the sedative material was put into the slag in the slag pot under the conditions shown in Table 1, and the slag removal time until the slag from the converter was completed was investigated. If the forming sedation is insufficient, the discharge from the converter is temporarily suspended to prevent the outflow of slag, and the discharge time becomes longer accordingly. In other words, the shorter the slag discharge time, the greater the sedative effect of the forming in the slag pot. Further, in this embodiment, the sedative material packed in a bag is added by hand throwing it directly toward the formed slag, and the sedative material is dropped from the chute by gravity without being put in the bag. Experiments were conducted with two patterns: adding a sedative to the formed slag. The amount of the sedative material to be added was 200 kg, and the sedative material was added at the timing when the worker confirmed the forming condition of the slag and determined that the formed slag might flow out from the slag pot.

In addition, the test No. 1 to No. 6, No. 9, No. The respective sedative materials A to C, I, and J used in No. 10 are fire resistant generated from devices such as tundish, blast furnace slag, converter furnace body, KR (Kanbara Reactor) impeller, and RH type vacuum degassing device, respectively. It is a mixture of refractory powder and slag powder. The sedative material C is formed by adding cement to this mixture, and all other materials are powders. The composition of the slag powder was almost the same as that of the above-mentioned slag. In addition, the test No. 7 and No. The calming material H of No. 8 is a molded product of papermaking waste, and is a columnar column having a diameter of 30 to 50 mm and a height of 30 to 50 mm by mixing papermaking waste: 30 to 50% by mass, moisture: 10% by mass, steelmaking slag, and the like. It is a molded product that is agglomerated into a mass.

As shown in Table 1, Test No. which is an example of the invention. 1 and No. 2 is the test No. 2 which is a reference example. 7 and No. A forming sedative effect almost equivalent to that of No. 8 was obtained. In addition, the test No. 3 and No. 4 is the test No. 4 respectively. 1 and No. Since the water content was higher than that of 2, the amount of gas generated was larger and the slag discharge time was shorter, and the forming sedative effect was higher under each condition. In addition, the test No. 5 and No. No. 6 was molded using cement, and the slag discharge time was even shorter, and the forming sedative effect was higher under each condition.

On the other hand, Test No. which is a comparative example. 9 and No. In No. 10, since the water content was 4.0% by mass or less and the apparent density was less than 1250 kg / m ³ , the scavenging time was longer and the sedative effect of forming was lower than that of the invention example and the reference example. rice field. In addition, in the experimental results in this example, the scavenging time was relatively shorter when the sedative material was added from the shoot than when the sedative material was thrown by hand. It is considered that this is because the sedative material could be stably supplied to a part of the forming slag by adding the sedative material from the chute, and the sedative material could be efficiently penetrated into the forming slag.

(Second Example)
250 tons of hot metal was charged into a 300 ton scale converter, dephosphorized, and then intermediate slag was discharged. After that, oxygen was blown from a top-blown lance to perform decarburization and smelting. Then, the molten iron temperature during decarburization and blowing was measured with a temperature measuring probe, and an experiment was conducted in which 200 kg of the sedative material shown in Table 2 was added from the chute into the converter. The composition of the slag when the sedative was added was CaO: 30 to 60% by mass, SiO ₂ : 10 to 35% by mass, T.I. Fe: 10 to 30% by mass, MgO: 5 to 10% by mass, P ₂ O ₅ : 2 to 5% by mass, and Al ₂ O ₃ : 0 to 5% by mass.

In addition, the test No. 11-No. The respective calming materials D to G and K to M used in 18 are refractory powder and slag powder generated from equipment such as a tundish, a blast furnace gutter, a converter furnace body, a KR, and an RH type vacuum degassing device. It is a molded product in which cement and water are further added and the mixing ratio is changed. The particle size was 50% by mass or more when the particle size was 5 mm or more. The composition of the slag powder was almost the same as that of the above-mentioned slag. Further, the ratio of the refractory to the slag in Table 2 was calculated from the mass balance calculation of CaO using the representative composition of the adhered slag because the refractory does not contain CaO. Test No. The sedative material H of 19 is a papermaking waste material molded product, and is the same as that used in the first embodiment.

Immediately after adding the sedative material, the operator tilted the converter while confirming whether or not slag could flow out from the vicinity of the furnace mouth in order to tilt the converter to eject steel. At that time, the slag extraction angle was investigated. This slag outflow angle indicates the tilt angle of the converter when the outflow of slag starts, and this tilt angle is 0 degrees when the furnace mouth of the converter at the end of smelting is in the vertical direction. , The tilt angle increases with the tilt of the furnace during intermediate slag. That is, the larger the slag outflow angle, the smaller the slag height in the furnace and the greater the slag sedative effect.

As shown in Table 2, Test No. which is an example of the invention. 11-No. Reference numeral 18 is a reference example, Test No. 18. The slag outflow angle was larger than that of 9, and the forming sedative effect was larger in each case. Test No. 11-No. It is probable that all of No. 18 contained cement and most of the water was immobilized as water of crystallization.

In addition, the test No. In No. 18, the apparent density was larger than 1500 kg / m ³ and gas was generated in the deeper part of the forming, so that the sedative effect was shown in Test No. 18. It was larger than 11 and 12. In addition, the test No. In 13, 14, 16 and 17, the apparent density was larger than 1500 kg / m ³ , and the mass of the refractory was 0.5 times or more and 4 times or less the mass of the slag. Therefore, the sedative material was more efficient, and the gas was generated deeper in the slag, so that the forming sedative effect was greater.

Claims (6)

A forming sedative that contains refractory, slag, and more than 4% by mass of water and has an apparent density of 1250 kg / m ³ or more. The forming sedative material according to claim 1, wherein the refractory powder mixed with slag has a particle size of 2 mm or less and a ratio of 50% by mass or more. The forming sedative material according to claim 1, wherein the molded product has a particle size of 5 mm or more and a proportion of 50% by mass or more. The forming sedative material according to any one of claims 1 to 3, further comprising cement as a binder. The forming sedative material according to any one of claims 1 to 4, wherein the apparent density is 1500 kg / m ³ or more. The forming sedative material according to any one of claims 1 to 5, wherein the mass of the refractory is 0.5 times or more and 4 times or less with respect to the mass of the slag.