JP7597019B2 - Steelmaking container and method for operating the same - Google Patents

Description

The present invention relates to a steelmaking vessel used in a high-temperature process, in which a carbon-containing unburned brick refractory is used as the work refractory, and to a method for operating the steelmaking vessel.

In the conventional steelmaking process, molten iron discharged from a blast furnace is transported to the steelmaking process in a molten iron transport vessel such as a torpedo car or a molten iron ladle. After that, it is refined in a steelmaking refining vessel such as a converter or an electric furnace, and the refined molten steel is transferred to a vessel such as a ladle and transported to the next process such as secondary refining or continuous casting. Among these, steelmaking refining vessels such as converters and electric furnaces (one example of steelmaking vessels) not only perform decarburization refining, but also play an important role in regulating the molten steel temperature. In addition, molten iron transport vessels such as a molten iron ladle (blast furnace ladle) installed in a torpedo car (one example of steelmaking vessels) not only transport molten iron from a blast furnace to a steelmaking plant, but also play an important role in reducing the cost of refining by performing desiliconization, dephosphorization, and desulfurization treatments (hot metal pretreatment) during transportation.

In steelmaking processes, each of the multiple refining processes is often a batch process, and therefore the equipment periodically absorbs and releases heat. When refractory equipment is repeatedly subjected to thermal loads, the thermal stress generated in the refractory fluctuates accordingly. This causes cracks to form in the refractory, leading to its destruction. Therefore, if the toughness of the refractory can be improved to improve its durability, the lifespan of refractory equipment in the steelmaking process can be extended, and costs associated with equipment repairs can be reduced.

For example, in converters, such as top and bottom blown converters, a method of decarburization refining by supplying oxidizing gas into a reaction vessel such as a converter is used as a known technology. Oxidizing gas (mainly oxygen gas) is supplied into the furnace through a top blowing lance, and as shown in the following formula (3), a reaction in which carbon in the molten steel reacts with the oxygen gas to generate carbon monoxide (CO) (hereinafter referred to as primary combustion) is promoted to decarburize the molten iron.

C + 1/2O ₂ = CO...Equation (3)

At the same time, the molten iron is stirred and gas (mainly inert gas) is supplied to the molten iron from the bottom of the furnace to increase the reaction efficiency. In the bottom-blown converter called Q-BOP, oxidizing gas is supplied to the furnace from the tuyere located at the bottom of the furnace to perform decarburization and refining. These tuyere refractories are made of metal pipes with refractory applied. The tuyere refractory receives enormous heat energy from the molten iron (molten steel) and supplies high-speed gas from the metal pipe to the molten iron (molten steel), so a very high thermal gradient is generated in the tuyere refractory. In addition, there is a possibility that the tuyere refractory will come into contact with slag containing iron oxide when steel is tapped from the converter. For this reason, tuyere refractories are required to have thermal shock resistance (thermal spalling resistance) and corrosion resistance, and from the above viewpoints, MgO-C bricks are used. The work refractory layer on the side wall is also required to be resistant to thermal shock and mechanical shock.

In addition, Al ₂ O ₃ -SiC-C bricks are used for the workpiece refractory of the molten pig iron transport vessel. The workpiece refractory may come into contact with iron oxide-containing slag during molten pig iron transport and molten pig iron pretreatment. In addition, considering the absorption and release of heat in the molten pig iron transport vessel, the workpiece refractory is in a high temperature state when the molten pig iron is filled, and heat is released after the molten pig iron is discharged, so that heat is repeatedly input and output, and accordingly, thermal stress is repeatedly generated in the workpiece refractory. This repeatedly generated thermal stress causes thermal fatigue failure. Therefore, the workpiece refractory of the molten pig iron transport vessel is required to have thermal shock resistance (thermal spalling resistance) and corrosion resistance.

One method for improving the toughness of refractories is to prevent the initiation and propagation of cracks that cause destruction within the material. One method for preventing the initiation and propagation of cracks is to add materials with high aspect ratios, such as fibrous materials, to the refractory to strengthen bridging.

In recent years, many carbon nanomaterials have been discovered, such as carbon black, carbon nanotubes (hereinafter sometimes referred to as "CNT"), carbon nanofibers (hereinafter sometimes referred to as "CNF"), fullerenes, and graphene, and many technologies have been used to improve mechanical properties, especially spalling resistance, by adding these nanomaterials. For example, Patent Document 1 discloses a technology in which mesophase pitch + thermosetting resin is added to a refractory material, and carbon nanofibers (diameter: maximum 500 nm, length: 100 μm) are generated by thermal decomposition (1000°C or less) of the mesophase pitch + thermosetting resin, thereby improving corrosion resistance and thermal shock resistance. Patent Document 2 discloses a technology in which fullerenes are added to a refractory material in a range of 5% or less to improve spalling resistance. The principle is that fullerenes react with the binder phenolic resin at high temperatures (heat treatment: up to 1500°C), producing carbon nanofibers (CNF). These CNFs act as a bridging effect, improving spalling resistance. One type of spalling resistance is heat spalling resistance.

Patent Document 3 discloses a technology for improving the toughness of refractories by kneading an organic binder, a colloidal or suspension-like solution or dispersion of transition metals or transition metal salts in which fine particles with a particle size of 1000 nm or less are dispersed in a solvent, and refractory raw materials, and heat treating the mixture at a temperature of 600°C to 1200°C to produce a dispersion of fine particles containing a carbon fiber structure and transition metals or transition metal salts with a particle size of 1000 nm or less.

Patent Document 4 also discloses a technology that uses a catalyst-coated refractory raw material, in which the surface of the refractory raw material is coated with one or more metals selected from the group consisting of V, Fe, Co, Ni, Cu, Mo, Pd, Rh, W, and Pt as a catalyst, and an organic polymer resin or its precursor as raw materials, and heat-treats the refractory material to uniformly disperse nanocarbon tubes in the structure and improve toughness.

Furthermore, Patent Document 5 discloses a technology for providing a refractory material with excellent strength and fracture resistance by applying a refractory material made of a refractory material whose surface is coated with CNT or CNF.

These technologies all aim to prevent the growth of cracks that occur in the refractory due to mechanical loads by introducing fibrous materials into the structure of the refractory and using the bridging effect of the fibrous materials. The above-mentioned conventional technologies can be applied not only to low-carbon bricks, but also to bricks with a relatively high carbon content, and contribute to further increasing the strength of the refractory or further improving its spalling resistance.

JP 2005-139062 A JP 2006-8504 A Patent No. 4641316 Patent No. 4856513 Patent No. 5192774

However, in the case of Patent Document 1, the added substance is mesophase pitch, which is relatively expensive, and there is a problem in terms of production costs. In the case of Patent Document 2, the added substance is fullerene, which is relatively expensive, and this may lead to an increase in the production costs of the refractory material.

In addition, in the case of Patent Document 3, a colloidal or liquid substance is newly added along with the liquid organic binder. At this time, the fluidity of the kneaded material increases excessively, making it very difficult to mold the refractory material. This results in a restriction on the amount of colloidal substance or suspension added to the binder, which places great restrictions on the manufacture of refractories. Furthermore, the technologies disclosed in Patent Documents 4 and 5 both apply coating technology. This coating technology normally uses a deposition method such as CVD, but this method also has the problem of being very expensive and very difficult to coat in large quantities. Therefore, these technologies cannot be said to be necessarily effective.

The present invention was made in consideration of the above circumstances, and aims to provide a steelmaking vessel and an operating method for the steelmaking vessel that can improve the thermal spalling resistance of the refractory by applying a refractory to the steelmaking vessel and then preheating the vessel.

The gist and configuration of the present invention to solve the above problems are as follows.
[1] A steelmaking vessel used in steelmaking, which is composed of a work refractory, a permanent refractory, and an iron shell from the inside out, in that order, and at least a part of the work refractory uses a carbon-containing unburned brick refractory containing a mixed raw material including the following (1), (2), and (3):
(1) Refractory raw material; (2) Graphite raw material; (3) A mixture in which a transition metal or a transition metal compound containing a transition metal, the average particle size of which is 1 μm or less, is mixed with a liquid binder made of an organic substance. [2] The iron-making vessel described in [1] is an iron-making refining vessel that holds molten iron inside and has a gas injection port for injecting gas into the molten iron from the bottom of the furnace, and the carbon-containing unburned brick refractory is used for at least the portion of the work refractory having the gas injection port arranged in the bottom of the furnace.
[3] The steelmaking vessel described in [1] is a molten iron transport vessel for steelmaking, for transporting molten iron or for performing preliminary treatment on the molten iron while transporting the molten iron.
[4] The refractory raw material is composed of at least one compound of Al ₂ O ₃ and MgO, and the compound has a particle size range of 5 to 40 mass% of average particle diameter of 3 mm or more, 10 to 45 mass% of average particle diameter of 1 mm or more but less than 3 mm, 15 to 30 mass% of average particle diameter of 0.15 mm or more but less than 1 mm, and 5 to 45 mass% of average particle diameter of less than 0.15 mm.
[5] The ironmaking vessel described in any one of [1] to [4], wherein the mass of the binder is 2 mass% or more and 5 mass% or less, with the exception of the total mass of the refractory raw material and the graphite raw material.
[6] The container for iron making described in any one of [1] to [5], wherein the transition metal compound is a compound containing Fe or Ni.
[7] The container for iron-making according to [6], wherein the compound containing Fe or Ni is any one of Fe ₂ O ₃ , Fe ₃ O ₄ , FeO, NiCO ₃ , and NiO.
[8] A container for ironmaking described in any one of [1] to [7], wherein the total mass of the transition metal and the transition metal compound is 0.1 mass% or more and 8.0 mass% or less relative to the mass of the binder.
[9] A method for operating an iron-making vessel used in iron making, comprising a preheating step of preheating the inside of the iron-making vessel to fire the carbon-containing unburned brick refractory before operation of the iron-making vessel, the work refractory being at least partly made of a carbon-containing unburned brick refractory containing a mixed raw material including the following (1), (2), and (3), thereby producing carbon nanotubes from the mixture of (3) below.
(1) Refractory raw material (2) Graphite raw material (3) A mixture of transition metals or transition metal compounds containing transition metals with an average particle size of 1 μm or less, mixed with a liquid binder made of an organic substance.

According to the present invention, by applying a refractory material to a steelmaking vessel and then subjecting the steelmaking vessel to a preheating treatment, it becomes possible to efficiently generate fibrous material in the refractory material. This in turn makes it possible to improve the heat spalling resistance of the refractory material.

FIG. 2 is a cross-sectional schematic diagram showing a refractory lining structure of a steel refining vessel. FIG. 2 is a cross-sectional schematic diagram showing a refractory lining structure of a molten iron transport vessel for steelmaking. FIG. 2 is a diagram showing a heating temperature pattern of a mixture of a binder and a transition metal (transition metal compound). FIG. 1 is a diagram showing a TEM photograph of a phenol resin dry distillation product (CNT) in the case where a transition metal compound (Fe ₂ O ₃ ) is used. FIG. 1 is a TEM photograph of a phenol resin dry distillation product (CNT) when a transition metal compound (NiCO ₃ ) is used. 1 is a graph showing the relationship between load and displacement in normal bricks and _NiCO3- added bricks. 1 is a graph showing the static elastic modulus of normal bricks and _NiCO3- added bricks. FIG. 1 is a schematic diagram showing a CNT production mechanism when FeO is added as a transition metal to a phenol resin.

The present invention will be described below through the embodiments of the present invention. In the present invention, "unfired brick refractory" refers to a brick refractory prior to the firing step, as opposed to a brick refractory manufactured by carrying out a molding step in which refractory raw materials, graphite raw materials, binder, etc. are mixed and molded, and a firing step in which the product molded in the molding step is fired. The molding step may include a treatment for thermally curing the binder as necessary (for example, a treatment (curing treatment) in which the molded product is held at about 150 to 300°C for a long period of time (24 to 72 hours)).

<About steelmaking containers>
First Embodiment
The case where the steelmaking vessel according to the present invention is a steelmaking refining vessel such as a converter will be described with reference to FIG. 1. FIG. 1 is a schematic cross-sectional view showing a refractory lining structure of the steelmaking refining vessel. The steelmaking refining vessel 10 holds molten iron inside and has a gas injection tuyere 4 for injecting gas into the molten iron from the bottom of the furnace. The steelmaking refining vessel 10 is configured from the inside to the work refractory 3, the permanent refractory 2, and the steel shell 1 in that order. The permanent refractory 2 is provided so as to contact the steel shell 1 of the steelmaking refining vessel 10, and the work refractory 3 is provided inside the permanent refractory 2. As the permanent refractory 2, for example, MgO bricks are used. As the work refractory 3, a carbon-containing unburned brick refractory described later is applied. In this embodiment, it is preferable that at least the work refractory 3 in the portion (around the tuyere) having the gas injection tuyere 4 arranged at the bottom of the steel refining vessel 10, which is particularly susceptible to thermal load, is made of a carbon-containing unburned brick refractory, but the work refractory 3 in the portion other than the portion having the gas injection tuyere 4 may also be made of a carbon-containing unburned brick refractory.

As shown in FIG. 1, molten steel 8 and slag 7 are held inside an iron-making refining vessel 10 such as a converter. A top-blowing lance 5 is provided to blow oxygen gas 6 into the molten iron from above, and bottom-blowing stirring gas 9 is also blown into the furnace bottom.

The steel refining vessel 10 is characterized by having a preheating process before operation. Specifically, after constructing the steel refining vessel 10 by installing the permanent refractory 2 and the work refractory 3 inside the steel shell 1 of the steel refining vessel 10, the steel refining vessel 10 is preheated (800 to 1200°C) to fire the carbon-containing unburned brick refractory. As a result, a reaction occurs in the carbon-containing unburned brick refractory according to the mechanism shown in Figure 8, which will be described later, and carbon nanotubes (CNTs) are uniformly generated inside the refractory from the mixture (mixed raw materials) contained in at least a portion of the carbon-containing unburned brick refractory. The bridging effect of the generated CNTs greatly improves the toughness of the refractory, achieving an improvement in the refractory life.

Second Embodiment
Next, a case where the steelmaking vessel according to the present invention is a molten pig iron transport vessel for steelmaking mounted on a torpedo car will be described with reference to FIG. 2. FIG. 2 is a schematic cross-sectional view of a refractory lining structure of a molten pig iron transport vessel for steelmaking. In this embodiment, as shown in FIG. 2, a case where the steelmaking vessel is a molten pig iron transport vessel for steelmaking 20 will be described. The molten pig iron transport vessel for ironmaking 20 holds molten iron inside and is used for transporting molten pig iron and for decarburization refining (molten pig iron preliminary treatment) during transport. The molten pig iron transport vessel for ironmaking 20 is composed of a work refractory 13, a permanent refractory 12, and a steel shell 11 in this order from the inside. The permanent refractory 2 is provided so as to contact the steel shell 1 of the molten pig iron transport vessel for ironmaking 20, and the work refractory 3 is provided inside the permanent refractory 2. As the permanent refractory 2, for example, an Al ₂ O ₃ -SiO ₂ -based fired brick is used. As the work refractory 3, a carbon-containing unburned brick refractory, which will be described later, is applied.

The hot metal transport vessel 20 for ironmaking is characterized by having a preheating process before operation. Specifically, the hot metal transport vessel 20 for ironmaking is constructed by installing the permanent refractory 2 and the work refractory 3 inside the steel shell 1 of the hot metal transport vessel 20 for ironmaking, and then the hot metal transport vessel 20 for ironmaking is preheated (800 to 1200°C) to fire the carbon-containing unburned brick refractory. As a result, a reaction occurs in the carbon-containing unburned brick refractory according to the mechanism shown in Figure 8, which will be described later, and carbon nanotubes (CNTs) are uniformly generated inside the refractory from the mixture (mixed raw materials) contained in at least a part of the carbon-containing unburned brick refractory. The bridging effect of the generated CNTs greatly improves the toughness of the refractory, thereby achieving an improvement in the refractory life.

<Carbon-containing unburned brick refractories>
The thermal spalling resistance of refractories is not as high as that of metals or other ductile materials. One method to improve the thermal spalling resistance is to introduce fibrous materials into the structure of the refractory, and to prevent the propagation of cracks generated in the refractory by mechanical loads through the bridging effect of the fibrous materials.

Refractories such as MgO-C bricks and Al ₂ O ₃ -SiC-C bricks are composed of refractory raw materials such as aggregate and fine powder, graphite raw material (flake-like graphite), liquid binders made of organic substances such as phenolic resins, and various additives. When the liquid binder made of organic substances is heated, volatiles are removed and carbon substances such as amorphous carbon are generated. If nano-fibrous substances such as carbon nanotubes can be generated during heating using the binder as a raw material, it is possible to generate fibrous substances in the refractory at a lower cost and solve various problems. Therefore, the inventors have investigated whether or not carbon nano-fibrous substances can be generated when a binder material (for example, organic resins such as tar, phenolic resin, and pitch) is heated.

It is known that when fine particles of Fe or Ni are present, nanotubes are generated and grow from these particles as nuclei. Therefore, the inventors added Fe and Ni oxides to the binder material and conducted observations, aiming to generate nanotubes from the Fe and Ni particles generated by reduction with the binder material components during heating. The details of the investigation experiment are described below.

The raw materials used were powdered Fe ₂ O ₃ or NiCO ₃ as a transition metal compound, and phenolic resin as a binder. 10 g of phenolic resin was added to a carbon crucible, and then powdered Fe ₂ O ₃ or NiCO ₃ was added to the crucible. The amount added and the experimental level are shown in Table 1. In each condition, the phenolic resin and the powdered transition metal compound were thoroughly mixed in the crucible and heated in an Ar atmosphere with the temperature pattern shown in FIG. 3. Then, the sample after cooling was observed with a TEM (transmission electron microscope). TEM photographs under each condition are shown in FIGS. 4 and 5. FIG. 4 shows a TEM photograph of CNT, which is an example of a phenolic resin dry distillation product when a transition metal compound (Fe ₂ O ₃ ) is used. FIG. 5 shows a TEM photograph of CNT, which is an example of a phenolic resin dry distillation product when a transition metal compound (NiCO ₃ ) is used. 4 and 5, the presence of pseudo-fibrous substances of sub-μm size was confirmed.

Based on the results of the investigation and experiment, powdered NiCO ₃ was added to the binder in an amount of 1 mass % to prepare a binder in which the binder and powdered NiCO ₃ were premixed, and the mixture was mixed with a refractory raw material and a graphite raw material to form a molded product, which was then heat-treated to produce a prototype MgO-10%C brick. Here, "MgO-10%C brick" refers to a brick made by mixing magnesia (MgO) and 10 mass % graphite raw material (C). The bending strength (σ: MPa) and static elastic modulus (E: MPa) of the brick were evaluated by a three-point bending test (JIS R2213:2005 Test method for bending strength of refractory bricks). Here, the static elastic modulus (E) was evaluated using the following formula (1). Here, L is the distance between the supports (m), B is the width of the sample (m), W is the height of the sample (m), Δu is the deflection (mm), and ΔP is the maximum load in the linear range (N).

The results are shown in Figures 6 and 7. The static elastic modulus was almost the same as that of normal MgO-C bricks without added _NiCO3 , and the bending strength was improved. This suggests that the thermal shock fracture resistance R (unit: K) defined by the following formula (2) is improved by using a binder with added nano- _NiCO3 . In formula (2), ν is Poisson's ratio (dimensionless number (here, 0.3)), and α is the thermal expansion coefficient of the material (1/K). In fact, when comparing the thermal shock fracture resistance R of the two, R was 22 for the normal brick and R was 34 for the bricks with added _NiCO3 , and the thermal shock fracture resistance R was greatly increased.

Here, the CNT generation mechanism of the present invention will be described with reference to FIG. 8, taking the case where FeO is added as a transition metal as an example. First, as shown in FIG. 8(a), reducing gas (CxHy, H ₂ , CO) is volatilized from the phenolic resin (resin) by the heat treatment. Then, as shown in FIG. 8(b), the reducing gas and FeO cause an oxidation-reduction reaction to generate metallic Fe. After that, as shown in FIG. 8(c), the reducing gas volatilized from the phenolic resin is decomposed on the surface of metallic Fe, and carbon is generated and diffused with metallic Fe as a nucleus. In response to this, as shown in FIG. 8(d), the carbon diffused on the surface of metallic Fe is bonded (C-C bond) by the catalytic action of metallic Fe, and is generated and grown as CNT.

By utilizing the reaction that occurs during this heat treatment, it is possible to efficiently generate and grow CNTs within the refractory. Taking the construction and operation of a converter as an example, construction is carried out in the same way as for normal refractories, and during preheating of the converter (800-1200°C), a reaction occurs according to the mechanism shown in Figure 8, and CNTs are generated uniformly inside the refractory. The bridging effect of the generated CNTs greatly improves the toughness of the refractory, thereby achieving an improvement in its lifespan.

Here, the additive used in the present invention should be a transition metal having an average particle size of 1 μm or less, or a transition metal compound (oxide, carbonate, or other compound) containing a transition metal. This is because particles having an average particle size exceeding 1 μm are difficult to generate CNT. In this case, transition metal particles are most preferable, but they are relatively expensive and require sufficient attention to safety when handling. Therefore, it is preferable to add a transition metal compound (oxide, carbonate, or other compound) in the sense that safety when handling can be ensured and the same effect can be obtained. The compound preferably contains Fe or Ni, and more preferably NiCO ₃ , Fe ₂ O ₃ , Fe ₃ O ₄ , FeO, NiO, etc. In addition, when used as a transition metal, Fe or Ni is preferable. And, the additive to the binder may be a mixture of a transition metal and a transition metal compound (for example, a mixture of Fe and FeO), or a mixture of transition metal compounds (for example, a mixture of Fe ₃ O ₄ and FeO).

In addition, it is preferable to mix transition metals or transition metal compounds (oxides, carbonates, and other compounds) with an average particle size of 1 μm or less with a liquid binder made of an organic substance in advance, and then add the mixture to the refractory raw material and graphite raw material to prepare a mixed raw material, since this ensures dispersibility within the refractory and makes it easier to generate CNTs. Note that the mixing method can be performed in various ways, such as using a stirrer such as a mixer or a kneader, and the method is not limited.

Furthermore, it is desirable to add transition metals or transition metal compounds (oxides, carbonates, and other compounds) with an average particle size of 1 μm or less in an amount of 0.1% to 8.0% by mass relative to the liquid binder made of an organic substance. If the amount is less than 0.1% by mass, the amount of CNT generated will be suppressed, and if the amount is more than 8.0% by mass, the effect will be the same as that of 8.0% by mass, and excessive effects cannot be expected. Conversely, this is not desirable because it will affect the close packing of the refractory structure.

The mass of the binder added should desirably be between 2% and 5% by mass relative to the total mass of the refractory raw material and the graphite raw material. If it is less than 2% by mass, it will not act as a sufficient binder, and if it is more than 5% by mass, there will be too much binder and it may seep out during the molding of the refractory material.

The present invention can be applied to various carbon-containing bricks such as MgO-C, Al ₂ O ₃ -C, and Al ₂ O ₃ -MgO-C. When at least one compound of Al ₂ O ₃ and MgO is used as the refractory raw material, the particle size range of Al ₂ O ₃ and MgO is preferably 5 to 40 mass% of 3 mm or more, 10 to 45 mass% of 1 mm or more and less than 3 mm, 15 to 30 mass% of 0.15 mm or more and less than 1 mm, and 5 to 45 mass% of less than 0.15 mm in terms of average particle size. Of course, it is not at all problematic to add antioxidants such as Al and Si to these refractories. Rather, since Al and the like contribute to the generation of whiskers, a higher effect can be fully expected. The present invention can also be applied to refractories to which SiC has been added.

The refractory raw materials used in the present invention can be any of the following: electrically fused products, sintered products, and natural materials (including seawater MgO, band shale, chamotte, and rosewood). SiC can be used in any grade, particle size, or blend, depending on various design concepts. In addition, various graphite raw materials can be used, such as scaly graphite, carbon black, and thin graphite.

Example 1
Tuyere bricks made of MgO-C were installed at the tuyere of a weakly stirred top-and-bottom blown converter with a heat size of 320 t/ch. The carbon concentration in the brick was set to 20 mass%. The composition of the reference MgO-C brick is shown in Table 2. The MgO-C brick with the composition shown in Table 2 is an example shown as Comparative Example 1 in Tables 3 and 4 described below.

A list of the invention examples and comparative examples is shown in Table 3. In invention example 1, _CoCO3 was added as an additive having an average particle size of 1 μm or less at a ratio of 9.0 mass% to the binder by mixing it in advance. In invention example 2, NiO was added as an additive having an average particle size of 1 μm or less at a ratio of 8.0 mass% to the binder by mixing it in advance.

In contrast, in Comparative Example 1, the materials were mixed according to the composition shown in Table 2, and no additives were added. In Comparative Example 2, the composition was revised, and the graphite content was set to 25.0 mass%. In Comparative Example 3, the composition was the same as in Comparative Example 1, but 1.0 mass% of pitch was added as an additive. In Comparative Example 4, the composition was the same as in Comparative Example 2, but 1.0 mass% of pitch was added as an additive. In Comparative Example 5, NiCO ₃ was added separately from the binder at a ratio of 10.0 mass% relative to the binder as an additive having an average particle size of 1 μm or less. In Comparative Example 6, Fe ₂ O ₃ was added separately from the binder at a ratio of 8.5 mass% as an additive having an average particle size of 1 μm or less. Here, "added separately from the binder" in Comparative Examples 5 and 6 means that metal particles are added directly to the refractory raw material.

Here, decarburization blowing was performed for the refractories of the invention example and the comparative example for a predetermined period (approximately 3,000 furnace uses) until the refractories reached their wear limit, and the wear rate of the tuyere refractory and the furnace life at that point were compared and evaluated. The results of the comparison of the refractories of the invention example and the comparative example are shown in Table 4.

Here, the wear rate shown in Table 4 means the difference in thickness of the refractory before and after use (mm) divided by the number of uses (number of charges (Ch)). The furnace life means the number of times the refractory can be used (number of charges (Ch)). The unit cost index means a value defined as the product of the refractory unit cost (amount of refractory used per ton of molten steel (unit: kg/t-steel)) and the unit price of the refractory (price of refractory per unit weight (unit: yen/kg)), and indicates the cost per unit weight of molten steel. In the examples of this application, the increase or decrease when Comparative Examples 1 and 9 are set to "1.00" is referred to as the unit cost index.

Invention Examples 1 and 2, which added a transition metal compound with an average particle size of 1 μm or less, had improved thermal shock fracture resistance R, reduced wear rate, and improved furnace life compared to Comparative Examples 1 and 2. Comparative Examples 3 and 4 had a lower wear rate than Comparative Examples 1 and 2, but were more expensive and had a high unit cost index (when Comparative Example 1 is set to "1"). In contrast, the unit cost index of Invention Examples 1 and 2 was lower than that of Comparative Example 1.

Furthermore, when comparing the results of surface observation of bricks after operation with a focus on thermal spalling resistance, no cracks were observed on the refractory surface in Invention Examples 1 and 2, but large cracks were observed in Comparative Example 1, and fine cracks were observed in Comparative Examples 2 to 4. This shows almost the same tendency as the higher thermal shock fracture resistance R value of the Invention Examples compared to the Comparative Examples. Furthermore, Comparative Examples 5 and 6, in which the metal compound was added separately from the binder, did not achieve an improvement in wear rate or thermal shock fracture resistance R compared to the Invention Examples, due to insufficient dispersion of the metal compound.

Example 2
Next, tuyere bricks made of MgO-C were installed on the side wall of the straight body of a weakly stirred top-and-bottom blown converter with a heat size of 320 t/ch. The carbon concentration in the bricks was set to 15.0 mass%. The composition of the reference MgO-C brick is shown in Table 5. The MgO-C brick with the composition shown in Table 5 is an example shown as Comparative Example 7 in Tables 6 and 7 described below.

Table 6 shows a list of invention examples and comparative examples. In invention example 3, FeO was added as an additive with an average particle size of 1 μm or less by premixing it with the binder at a ratio of 8.0 mass% relative to the binder. In invention example 4, metallic Fe was added as an additive with an average particle size of 1 μm or less by premixing it with the binder at a ratio of 4.0 mass% relative to the binder.

In contrast, in Comparative Example 7, MgO-15% C bricks mixed as shown in Table 5 were used. In Comparative Example 8, 1.0 mass% pitch was added to the bricks of the Comparative Example 7 composition.

Here, decarburization blowing was performed for the refractories of the invention example and the comparative example for a predetermined period (approximately 1,000 furnace uses) until the refractories reached their wear limit, and the wear rate of the sidewall refractories at that point was compared and evaluated. The results of the comparison of the refractories of the invention example and the comparative example are shown in Table 7.

As shown in Table 7, Examples 3 and 4 of the invention, which contained a transition metal or transition metal compound with an average particle size of 1 μm or less, showed a reduced wear rate compared to Comparative Examples 7 and 8.

Example 3
Next, work bricks made of Al ₂ O ₃ -SiC-C were applied to a molten iron ladle-type vessel with a heat size of 280 t/ch. The carbon concentration in the bricks was set to 10.0 mass%. The composition of the reference Al ₂ O ₃ -SiC-C brick is shown in Table 8. The Al ₂ O ₃ -SiC-C brick with the composition shown in Table 8 is an example shown as Comparative Example 9 in Tables 9 and 10 described below.

A list of the invention examples and comparative examples is shown in Table 9. In invention example 5, _CoCO3 was added as an additive having an average particle size of 1 μm or less at a ratio of 9.0 mass% to the binder. In invention example 6, NiO was added as an additive having an average particle size of 1 μm or less at a ratio of 8.0 mass% to the binder.

In contrast, in Comparative Example 9, the materials were mixed according to the composition shown in Table 8, and no additives were added. In Comparative Example 10, the composition was revised, and the graphite content was set to 15.0 mass%. In Comparative Example 11, the composition was the same as in Comparative Example 9, but 1.0 mass% of pitch was added as an additive. In Comparative Example 12, the composition was the same as in Comparative Example 10, but 1.0 mass% of pitch was added as an additive. In Comparative Example 13, _NiCO3 was added separately from the binder at a ratio of 10.0 mass% relative to the _binder as an additive having an average particle size of 1 μm or less. In Comparative Example 14, _Fe2O3 was added separately from the binder at a ratio of 8.5 mass% as an additive having an average particle size of 1 μm or less.

Here, for the refractories according to the invention example and the comparative example, molten iron transportation and molten iron pretreatment (dephosphorization, desulfurization treatment) were carried out until the refractories reached their wear limit (approximately 1,000 furnace uses), and the wear rate and crack condition of the work refractories at that point were compared and evaluated. The results of the comparison of the refractories according to the invention example and the comparative example are shown in Table 10.

Invention Examples 5 and 6, which contained a transition metal compound with an average particle size of 1 μm or less, the thermal shock fracture resistance R was improved and the wear rate was reduced compared to Comparative Examples 9 and 10. Comparative Examples 11 and 12 had a lower wear rate than Comparative Examples 9 and 10, but because of their higher costs, the unit cost index (when Comparative Example 9 is set to 1) was higher. The unit cost index in Invention Examples 5 and 6 was lower than that of Comparative Examples 9 and 10.

Furthermore, when comparing the results of surface observation of bricks after operation with a focus on thermal spalling resistance, no cracks were observed on the refractory surface in either invention examples 5 and 6, but large cracks were observed in comparative example 9, and fine cracks were observed in comparative examples 10 to 12. This shows almost the same tendency as the thermal shock fracture resistance R value of the invention examples being higher than that of the comparative examples. Furthermore, in comparative examples 13 and 14, in which the metal compound was added separately from the binder, the dispersion of the metal compound was insufficient, and therefore the wear rate and thermal shock fracture resistance R were not improved compared to the invention examples.

From the above, by utilizing the steelmaking vessel and the method of operating the steelmaking vessel according to the present invention, and applying a carbon-containing unburned brick refractory to the steelmaking vessel and then preheating the steelmaking vessel, it is possible to efficiently generate fibrous material in the refractory. It has also become clear that this has an excellent effect on the thermal shock fracture resistance, i.e., thermal spalling resistance, of the carbon-containing brick refractory.

1, 11 Steel shell 2, 12 Permanent refractory 3, 13 Work refractory 4 Gas blowing tuyere 5 Top blowing lance 6 Oxygen gas 7 Slag 8 Molten steel 9 Bottom blowing stirring gas 10 Steelmaking refining vessel 19 Torpedo car 20 Molten pig iron transport vessel for steelmaking

Claims (8)

A method for operating a steelmaking vessel used in steelmaking, comprising the steps of:
Before the operation of the steelmaking vessel having therein a work refractory material at least partially using a carbon-containing unburned brick refractory material containing a mixed raw material including the following (1), (2), and (3),
A method for operating a vessel for steelmaking, comprising a preheating step of preheating the inside of the vessel for steelmaking to fire the carbon-containing unburned brick refractory material, thereby producing carbon nanotubes from the mixture of (3) below.
(1) Refractory raw material (2) Graphite raw material (3) A mixture in which a powdered transition metal or a transition metal compound containing a transition metal, the powdered transition metal or transition metal compound having an average particle size of 1 μm or less, is mixed with a liquid binder made of an organic substance (however, this does not include a mixture in which the transition metal or the transition metal compound containing a transition metal is added to the liquid binder in a state of being suspended in a solvent). The steelmaking vessel is a steelmaking refining vessel that holds molten iron therein and has a gas injection port for injecting gas into the molten iron from a bottom of the furnace,
2. The method for operating an iron-making vessel according to claim 1, wherein the carbon-containing unburned brick refractory is used as the work refractory at least in a portion having the gas-blowing tuyere arranged in the bottom of the furnace. 2. The method for operating a vessel for ironmaking according to claim 1, wherein the vessel for ironmaking is a molten iron transport vessel for transporting molten iron or for subjecting the molten iron to preliminary treatment during transportation. The refractory raw material is composed of at least one compound selected from the group consisting of Al ₂ O ₃ and MgO,
The compound has an average particle size range of 5 to 40% by mass of 3 mm or more, 10 to 45% by mass of 1 mm or more and less than 3 mm, 15 to 30% by mass of 0.15 mm or more and less than 1 mm, and 5 to 45% by mass of less than 0.15 mm.
A method for operating a vessel for iron-making according to any one of claims 1 to 3. The method for operating a vessel for ironmaking according to any one of claims 1 to 4, wherein the mass of the binder is 2 mass% or more and 5 mass% or less with respect to the total mass of the refractory raw material and the graphite raw material . The method for operating a vessel for iron-making according to any one of claims 1 to 5, wherein the transition metal compound is a compound containing Fe or Ni. The method for operating a vessel for iron-making according to claim 6, wherein the compound containing _Fe or Ni is any one of _{Fe2O3 , Fe3O4} , FeO, _NiCO3 , and NiO. The method for operating a vessel for iron-making according to any one of claims 1 to 7, wherein the total mass of the transition metal and the transition metal compound is 0.1 mass% or more and 8.0 mass% or less with respect to the mass of the binder.

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