Molten iron holding furnace, molten iron holding method, and use of refractory material

Abstract

According to the present invention, when molten iron having a carbon concentration less than the saturation concentration is held in a molten iron holding furnace, the occurrence of thermal spalling or structural spalling in a refractory material brought into contact with the molten iron is suppressed. A molten iron holding furnace according to the present disclosure holds molten iron having a carbon concentration less than the saturation concentration. At least a portion of a site of the molten iron holding furnace brought into contact with the molten iron is lined with a refractory material containing a refractory raw material and 2-10 mass% of free carbon.

Description

Molten iron holding furnace, molten iron holding method and use of refractories

[0001] The present application discloses a molten iron holding furnace, a method for holding molten iron, and the use of refractories.

[0002] In a molten iron holding furnace, molten iron may be stored and held for the production of molten iron, preliminary treatment, etc. The portion of the molten iron holding furnace that comes into contact with the molten iron is lined with a refractory material. Refractories with various chemical compositions are known for lining molten iron holding furnaces. For example, Patent Documents 1 and 2 disclose refractories containing alumina, silicon carbide, and carbon that can be used to line molten iron holding furnaces.

[0003] JP-A-6-001650 JP-A-1-257164

[0004] Thermal spalling due to temperature changes of the molten iron and structural spalling due to infiltration of the molten iron are likely to occur in the refractory lining of a molten iron holding furnace at a portion that comes into contact with the molten iron. Meanwhile, an iron source with a low carbon concentration, such as scrap, may be used as the iron source for the molten iron held in the molten iron holding furnace. In this case, the carbon concentration of the molten iron held in the molten iron holding furnace becomes unsaturated. In the prior art, there is room for improvement in suppressing the occurrence of thermal spalling and structural spalling in the refractory that comes into contact with the molten iron when the molten iron is held in a molten iron holding furnace with a carbon concentration below the saturated concentration.

[0005] The present application discloses the following multiple aspects as means for solving the above-mentioned problems. <Aspect 1> A molten iron holding furnace for holding molten iron having a carbon concentration below the saturation concentration, wherein at least a portion of the portion of the molten iron holding furnace that comes into contact with the molten iron is lined with a refractory material containing refractory raw materials and 2 to 10 mass % free carbon. <Aspect 2> The molten iron holding furnace of Aspect 1, wherein the carbon concentration of the molten iron is lower by 1.0 mass % or more than the saturation concentration. <Aspect 3> The molten iron holding furnace of Aspect 1 or 2, wherein the molten iron holding furnace has a heating mechanism for heating the molten iron. <Aspect 4> The molten iron holding furnace of Aspect 3, wherein the refractory lining the portion of the molten iron holding furnace that comes into contact with the molten iron contains refractory raw materials and 2 to 10 mass % free carbon, at least in a portion closest to the heating mechanism. <Aspect 5> A method for holding molten iron, comprising holding molten iron having a carbon concentration below a saturation concentration in a molten iron holding furnace, wherein the molten iron holding furnace is lined with a refractory containing refractory raw materials and 2% by mass to 10% by mass of free carbon in at least a portion of a region in contact with the molten iron. <Aspect 6> The method for holding molten iron of Aspect 5, wherein the carbon concentration of the molten iron is lower by 1.0% by mass or more than the saturation concentration. <Aspect 7> The method for holding molten iron of Aspect 5 or 6, wherein the molten iron holding furnace is equipped with a heating mechanism for heating the molten iron. <Aspect 8> The method for holding molten iron of Aspect 7, wherein the refractory lining the region of the molten iron holding furnace in contact with the molten iron contains refractory raw materials and 2% by mass to 10% by mass of free carbon in at least a region closest to the heating mechanism. <Aspect 9> Use of a refractory in at least a part of a portion of a molten iron holding furnace that comes into contact with molten iron, wherein the molten iron has a carbon concentration less than a saturation concentration, and the refractory contains a refractory raw material and 2% by mass or more and 10% by mass or less of free carbon.

[0006] According to the technology disclosed herein, when molten iron with a carbon concentration below the saturation concentration is held in a molten iron holding furnace, thermal spalling and structural spalling are unlikely to occur in refractories that come into contact with the molten iron.

[0007] FIG. 1 schematically shows an example of a molten iron holding furnace. FIG. 2 schematically shows an example of the configuration of a pig iron storage furnace as a molten iron holding furnace. FIG. 3 schematically shows an example of the configuration of a cross section taken along the line III-III of FIG. 2. FIG. 4 schematically shows another example of the configuration of a cross section taken along the line III-III of FIG. 2. FIG. 5 schematically shows another example of the configuration of a cross section taken along the line III-III of FIG. 2. FIG. 6 schematically shows another example of the configuration of a cross section taken along the line III-III of FIG. 2. FIG. 7 schematically shows an example of the configuration of an electric melting furnace as a molten iron holding furnace. FIG. 8 schematically shows another example of the configuration of an electric melting furnace as a molten iron holding furnace.

[0008] Hereinafter, a molten iron holding furnace, a molten iron holding method, and use of a refractory material according to embodiments will be described with reference to the drawings, but the technology of the present disclosure is not limited to the following embodiments.

[0009] 1. Molten Iron Holding Furnace FIG. 1 schematically illustrates a cross-sectional configuration of a molten iron holding furnace 100 according to one embodiment. As shown in FIG. 1, the molten iron holding furnace 100 according to one embodiment holds molten iron 10 having a carbon concentration below the saturation concentration. At least a portion of the molten iron holding furnace 100 that comes into contact with the molten iron 10 is lined with a refractory material 20 containing refractory raw materials and 2% to 10% by mass of free carbon. As shown in FIG. 1, the molten iron holding furnace 100 according to one embodiment may include a furnace body 30. The furnace body 30 has a space therein for holding the molten iron 10. The furnace body 30 may have a shell 31, and the refractory material 20 described above may line the inside of the shell 31.

[0010] In this application, the term "molten iron holding furnace" refers to a container capable of holding molten iron, and includes furnaces for holding molten iron produced in a previous process, furnaces for holding molten iron produced in a previous process while adding a solid iron source to the molten iron to melt the solid iron source, furnaces into which a solid iron source is charged and which produce molten iron by melting the solid iron source with a heating mechanism, furnaces for pre-treating the molten iron while holding the molten iron, as well as furnaces for transporting molten iron (for example, torpedo cars).

[0011] In this application, "a portion that comes into contact with molten iron" includes not only a portion that comes into contact with the molten iron while the molten iron is being held in the molten iron holding furnace, but also a portion that comes into contact with the molten iron when the molten iron is being tapped, etc. In this application, "at least a portion of the portion of the molten iron holding furnace that comes into contact with the molten iron is lined with a refractory material" means that at least a portion of the portion of the hearth or furnace wall that comes into contact with the molten iron is made of a refractory material for the purpose of extending the life of the furnace, etc.

[0012] 1.1 Molten Iron The carbon concentration of the molten iron 10 held in the molten iron holding furnace 100 is less than the saturated concentration. Whether the carbon concentration of the molten iron 10 is saturated or unsaturated can be determined experimentally or theoretically from the chemical composition and temperature of the molten iron 10 held in the molten iron holding furnace 100. In this application, the saturated carbon concentration of the molten iron is calculated by the following formula. The actual carbon concentration of the molten iron 10 can be determined by sampling the molten iron 10 and analyzing it in accordance with JIS G 1211-3:2018.

[0013] [Saturated carbon concentration (mass%)] = 1.34 + 0.00254 × [molten iron temperature (°C)] - 0.4 × [Si] - 0.33 × [Mn] - 0.33 × [P] (where [Si], [Mn], and [P] are the Si concentration (mass%), Mn concentration (mass%), and P concentration (mass%) in the molten iron.)

[0014] The carbon concentration of the molten iron 10 held in the molten iron holding furnace 100 may be lower than the saturated concentration by more than 0 mass%, 0.1 mass% or more, 0.2 mass% or more, 0.3 mass% or more, 0.4 mass% or more, 0.5 mass% or more, 0.6 mass% or more, 0.7 mass% or more, 0.8 mass% or more, 0.9 mass% or more, 1.0 mass% or more, 1.1 mass% or more, 1.2 mass% or more, 1.3 mass% or more, 1.4 mass% or more, or 1.5 mass% or more. It is believed that the lower the carbon concentration of the molten iron 10 is relative to the saturated carbon concentration, the faster the corrosion rate of the refractory, and the greater the effect of applying the technology of the present disclosure. In particular, when the carbon concentration of the molten iron 10 is lower by 1.0 mass% or more than the above-mentioned saturated concentration (i.e., when the difference between the saturated carbon concentration of the molten iron 10 and the actual carbon concentration of the molten iron 10 is 1.0 mass% or more), the effect of achieving both heat spalling resistance and structural spalling resistance by the technology of the present disclosure becomes more remarkable. The lower limit of the carbon concentration of the molten iron 10 is not particularly limited. For example, the carbon concentration of the molten iron 10 may be more than 0 mass%, 0.5 mass% or more, 1.0 mass% or more, 1.5 mass% or more, 2.0 mass% or more, 2.5 mass% or more, 3.0 mass% or more, or 3.5 mass% or more.

[0015] The chemical composition of the molten iron 10 held in the molten iron holding furnace 100 is not particularly limited as long as the carbon concentration of the molten iron 10 does not reach the saturation concentration. The molten iron 10 may contain Si, Mn, P, S, and the like in addition to carbon and Fe. The molten iron 10 is obtained, for example, by melting an iron source. Specifically, the molten iron 10 may be obtained by (1) melting one or more iron sources having a carbon concentration lower than the saturation concentration when formed into molten iron, (2) melting one or more iron sources having a carbon concentration lower than the saturation concentration when formed into molten iron into molten pig iron (molten iron having a carbon concentration of the saturation concentration), or (3) melting one or more iron sources having a carbon concentration lower than the saturation concentration when formed into molten iron together with a carbon-containing material. Examples of iron sources having a carbon concentration lower than the saturation concentration when formed into molten iron include one or both of scrap and reduced iron.

[0016] The temperature of the molten iron 10 held in the molten iron holding furnace 100 is not particularly limited as long as the carbon concentration of the molten iron 10 does not reach the saturated concentration. The temperature of the molten iron 10 may be, for example, 1160°C or higher and 1650°C or lower.

[0017] 1.2 Refractories Refractories that come into contact with molten iron are prone to cracks and thermal spalling due to temperature changes in the molten iron, etc. Increasing the thermal conductivity of the refractory is effective in suppressing thermal spalling. For example, adding free carbon to the refractory improves the heat spalling resistance of the refractory. On the other hand, if the carbon concentration of the molten iron is below the saturation concentration, carbon is likely to leach from the working surface of the refractory that comes into contact with the molten iron into the molten iron. When carbon leach from the working surface of the refractory into the molten iron, voids form in the surface layer of the refractory (the working surface and its vicinity), which can cause structural spalling. According to the inventor's new findings, excellent heat spalling resistance and structural spalling resistance are likely to be ensured when the amount of free carbon contained in the refractory is 2% by mass or more and 10% by mass or less. That is, in the molten iron holding furnace 100, the refractory 20 lining at least a part of the area that comes into contact with the molten iron 10 contains refractory raw materials and 2% by mass to 10% by mass of free carbon.

[0018] 1.2.1 Refractory Raw Materials The refractory 20 includes refractory raw materials. The refractory raw materials may be any known refractory raw materials used in refractories for molten iron holding furnaces. For example, the refractory raw materials may include one or more of alumina, magnesia, silica, silicon carbide, silicon nitride, zirconia, and chromium oxide. In one embodiment, the refractory raw materials may include alumina, magnesia, or a combination of alumina and magnesia.

[0019] The proportion of the refractory raw material in the entire refractory 20 may be, for example, 70% by mass or more, 80% by mass or more, or 90% by mass or more, or 98% by mass or less, 97% by mass or less, 96% by mass or less, or 95% by mass or less. In one embodiment, the refractory 20 may contain 70% by mass or more and 98% by mass or less of alumina, 70% by mass or more and 98% by mass or less of magnesia, or 70% by mass or more and 98% by mass or less of a combination of alumina and magnesia.

[0020] The shape and size of the refractory raw material are not particularly limited. The shape of the refractory raw material may be, for example, particulate or lumpy. The refractory raw material may have a maximum diameter of, for example, 10 μm or more and 5 mm or less.

[0021] 1.2.2 The free carbon refractory 20 contains 2% by mass or more and 10% by mass or less of free carbon. The free carbon may be derived from elemental carbon or from a carbon compound. In other words, the refractory 20 contains a carbon material, and the content of free carbon derived from the carbon material is 2% by mass or more and 10% by mass or less. The type of carbon material that can become the free carbon is not particularly limited, and may be, for example, one or more of graphite, anthracite, carbon black, phenolic resin, tar, and pitch. The shape and size of the free carbon are also not particularly limited. When the free carbon is derived from graphite, the free carbon may be particles having a particle diameter D50 of 500 μm or less. When the free carbon is derived from anthracite, the free carbon may be particles having a particle diameter D50 of 500 μm or less. When the free carbon is derived from carbon black, the free carbon may be particles having a particle diameter D50 of 1 μm or less. When the free carbon is derived from a phenolic resin, the free carbon may be particles having a particle diameter D50 of 1 μm or less. When the free carbon is derived from tar, the free carbon may be particles having a particle diameter D50 of 1 μm or less. When the free carbon is derived from pitch, the free carbon may be particles having a particle diameter D50 of 1 μm or less. The free carbon may be particles having a particle diameter D50 of 0.1 μm or less, such as residual carbon in an organic binder. Note that the particle diameter D50 of free carbon referred to in this application is the particle diameter (median diameter) at 50% cumulative value in a volume-based particle size distribution determined by spherical approximation using a laser diffraction / scattering method.

[0022] The proportion of free carbon in the entire refractory 20 is 2% by mass or more and 10% by mass or less. When the proportion of free carbon in the entire refractory 20 is 2% by mass or more, the refractory 20 has excellent thermal conductivity, and as a result, the heat spalling resistance of the refractory 20 is ensured. On the other hand, when the proportion of free carbon in the entire refractory 20 is 10% by mass or less, even if carbon elutes from the refractory 20 into the molten iron 10 and voids are formed in the surface layer of the refractory 20, the surface layer of the refractory 20 does not peel off and maintains its structure, and as a result, the structural spalling resistance of the refractory 20 is ensured. The proportion of free carbon in the entire refractory 20 may be 3% by mass or more, 4% by mass or more, or 5% by mass or more, or may be 9% by mass or less, 8% by mass or less, or 7% by mass or less. The free carbon content of the refractory 20 is determined in accordance with JIS R 2011:2007.

[0023] Carbon volume fraction r in the refractory 20 ｃ may be, for example, more than 0.01 and less than 0.19, 0.02 or more and 0.14 or less, or 0.06 or more and 0.10 or less. In particular, the carbon volume fraction r ｃ When the carbon volume fraction r is 0.02 or more and 0.14 or less, the heat resistance and structural spall resistance of the refractory 20 are likely to be compatible at a higher level. ｃ is calculated based on the following formula: ｃ = [bulk specific gravity of refractory] × [proportion of free carbon in the entire refractory (mass%)] / 100 / [specific gravity of graphite] In the above formula, the "bulk specific gravity of the refractory" can be determined by measurement in accordance with JIS R 2205:1992. Furthermore, the "proportion of free carbon in the refractory" is quantified in accordance with JIS R 2011:2007, as described above. Furthermore, since it is difficult to measure the bulk specific gravity of free carbon in a refractory, the above formula uses the "specific gravity of graphite" as a value representing the specific gravity of carbon. In the present application, the "specific gravity of graphite" is deemed to be 2.26.

[0024] 1.2.3 Other Materials The refractory 20 may contain other materials in addition to the above-mentioned refractory raw materials and free carbon. The proportion of the other materials in the refractory 20 may be, for example, 25 mass % or less, 20 mass % or less, 15 mass % or less, 13 mass % or less, 11 mass % or less, 9 mass % or less, 7 mass % or less, or 5 mass % or less. Examples of the other materials include metal powder and impurities. Examples of the impurities include mineral-derived impurities and binder-derived impurities. Specifically, the refractory 20 may contain TiO as the other material. ２ , Na ２ O, Fe ２ O ３ , SiO ２ , CaO and MnO ２ It may include one or more of the following:

[0025] 1.2.4 Refractory Lining Portion The refractory 20 may line at least a portion of the portion of the molten iron holding furnace 100 that comes into contact with the molten iron 10. For example, the refractory 20 may line the entire portion of the portion that comes into contact with the molten iron 10. Alternatively, the refractory 20 may line only a portion of the portion that comes into contact with the molten iron 10, and the other portion of the portion that comes into contact with the molten iron 10 may be lined with a refractory 21 other than the refractory 20. Furthermore, the molten iron holding furnace 100 may also be lined with a refractory in a portion that does not come into contact with the molten iron 10, and the refractory lining the portion that does not come into contact with the molten iron 10 may be the refractory 20 described above or a refractory 21 other than the refractory 20. The "refractory 21 other than the refractory 20" may be, for example, a refractory containing a refractory raw material and no free carbon, a refractory containing a refractory raw material and more than 0 mass % but less than 2 mass % free carbon, or a refractory containing a refractory raw material and more than 10 mass % free carbon. The refractory raw material and free carbon are as described above. By using the refractory 20 in combination with the refractory 21 other than the refractory 20, it is possible to expect effects such as facilitating the absorption of thermal expansion differences and mechanical shocks, suppressing the occurrence of cracks and peeling, and improving structural stability.

[0026] 2 to 6 schematically show an example of the configuration of a pig iron storage furnace as a molten iron holding furnace 100. FIG. 2 shows the external configuration of the pig iron storage furnace when viewed from above, and FIGS. 3 to 6 show the configuration of a cross section taken along the line III-III in FIG. 2. As shown in FIG. 3, the refractory 20 may line the entire area that comes into contact with the molten iron 10. Alternatively, as shown in FIGS. 4 to 6, the refractory 20 may line only a portion of the area that comes into contact with the molten iron 10, and the remaining area that comes into contact with the molten iron 10 may be lined with a refractory 21 other than the refractory 20. For example, as shown in FIG. 4, the refractory 20 may be lined near an induction heating mechanism as a heating mechanism 40 provided in the molten iron holding furnace 100. Details of the case where the refractory 20 is lined near the heating mechanism 40 will be described later. Alternatively, as shown in Fig. 5, the refractory material 20 may be provided as a lining on a portion that contacts the interface between the molten iron 10 and the slag 15. Alternatively, as shown in Fig. 6, the refractory material 20 may be provided as a lining on a wall surface that defines a tap hole 36 provided in the storage furnace.

[0027] 7 to 9 are schematic diagrams showing an example of the configuration of an electric melting furnace as a molten iron holding furnace 100. Each of FIGS. 7 to 9 shows a cross-sectional structure of an electric melting furnace. As shown in FIG. 7, the refractory 20 may line the entire area that comes into contact with the molten iron 10. Alternatively, as shown in FIGS. 8 and 9, the refractory 20 may line only a portion of the area that comes into contact with the molten iron 10, and the remaining area of ​​the area that comes into contact with the molten iron 10 may be lined with a refractory 21 other than the refractory 20. For example, as shown in FIG. 8, the refractory 20 may line the vicinity of an electrode (near the electrode when an arc is generated from the electrode, for example, directly below the electrode) that serves as a heating mechanism 40 provided in the molten iron holding furnace 100. Alternatively, as shown in FIG. 9, the refractory 20 may line the area that comes into contact with the interface between the molten iron 10 and the slag 15. Alternatively, the refractory material 20 may be used to line the wall surface that defines a tap hole (not shown) provided in the electric melting furnace.

[0028] The refractory material 20 is preferably provided to line a portion of the molten iron holding furnace 100 that comes into contact with the molten iron 10, particularly a portion where thermal spalling is likely to occur. Examples of portions where thermal spalling is likely to occur include a portion near the heating mechanism 40 or a portion near the tap hole 36 provided in the molten iron holding furnace 100. That is, in one embodiment, the refractory material 20 lining the portion of the molten iron holding furnace 100 that comes into contact with the molten iron 10 may contain refractory raw materials and 2% by mass to 10% by mass of free carbon at least in the portion closest to the heating mechanism 40. Alternatively, in one embodiment, the refractory material 20 may line at least the portion closest to the heating mechanism 40 of the molten iron holding furnace 100 that comes into contact with the molten iron 10. Alternatively, in one embodiment, among the refractories lining the molten iron holding furnace 100 at a portion in contact with the molten iron 10, the refractory 20 lining the portion closest to the heating mechanism 40 may contain refractory raw materials and 2% to 10% by mass of free carbon. More specifically, when the molten iron holding furnace 100 is a pig iron storage furnace, as shown in Fig. 3 or 4, among the refractories lining the molten iron 10 at a portion in contact with the molten iron 10, the refractory 20 lining the portion closest to the induction heating device serving as the heating mechanism 40 may contain refractory raw materials and 2% to 10% by mass of free carbon. Alternatively, when the molten iron holding furnace 100 is an electric melting furnace, as shown in Fig. 7 or 8, among the refractories lining the molten iron 10 at a portion closest to the electrode serving as the heating mechanism 40, the refractory 20 lining the portion closest to the electrode serving as the heating mechanism 40 may contain refractory raw materials and 2% to 10% by mass of free carbon.

[0029] 1.2.5 Other Matters Regarding the Refractory The refractory 20 may be lined as a shaped refractory such as a brick, or as an unshaped refractory such as a castable, sprayed material, stamped material, precast block, or rammed material. The shaped refractory is produced, for example, by dry or wet mixing the above-mentioned refractory raw material, a carbon material capable of becoming free carbon, and optionally other materials to obtain a mixture, and then molding and firing the mixture. The unshaped refractory is produced, for example, by mixing the above-mentioned refractory raw material, a carbon material capable of becoming free carbon, and optionally other materials.

[0030] 1.3 Relationship between carbon concentration of molten iron and free carbon content in refractory In a molten iron holding furnace, the lower the carbon concentration of the molten iron, the faster the wear rate of the refractory, that is, the more likely it is that the effect of lining the refractory 20 in at least a part of the area in contact with the molten iron 10 is enhanced. １ (X １ (mass%) = saturated carbon concentration of molten iron 10 - actual carbon concentration of molten iron 10) and the ratio of free carbon in the entire refractory 20 X ２ (mass%) and the ratio X １ / X ２ may be 0.07 or more and 2.50 or less, 0.13 or more and 0.83 or less, or 0.15 or more and 0.75 or less.

[0031] 1.4 Other Matters Regarding the Molten Iron Holding Furnace The molten iron holding furnace 100 is not particularly limited in configuration as long as it holds the molten iron 10 described above and is lined with the refractory material 20 on at least a portion of the area that comes into contact with the molten iron 10. An example of other configurations that may be provided in the molten iron holding furnace 100 will be described below.

[0032] 1.4.1 Furnace Body As shown in FIGS. 2 to 6, the molten iron holding furnace 100 may be a pig iron storage furnace. In this case, the molten iron holding furnace 100 may be, for example, a furnace body 30 supported by a support 50. The furnace body 30 has a space therein for holding the molten iron 10. The furnace body 30 may have the heating mechanism 40 described above. The furnace body 30 may be one in which at least a portion of the inside of the steel shell 31 is lined with a refractory 20. A refractory material different from the refractory 20 may be lined between the steel shell 31 and the refractory 20. The furnace body 30 may be equipped with, for example, a charging port 32 for molten iron or the like and a charging port 33 for an iron source or the like, and each of the charging ports 32, 33 may be equipped with an open / close lid 34, 35. The furnace body 30 may also be equipped with, for example, a tapping port 36 for the molten iron 10. The surface of the molten iron 10 held inside the furnace body 30 may be covered with slag 15 .

[0033] Alternatively, as shown in FIGS. 7 to 9 , the molten iron holding furnace 100 may be an electric melting furnace that uses an arc to heat the molten iron and melt the iron source. In this case, the heating mechanism 40 provided in the molten iron holding furnace 100 includes electrodes and the like. When the molten iron holding furnace 100 is an electric melting furnace, the molten iron holding furnace 100 includes, for example, a furnace body 30. The furnace body 30 has a space therein for holding the molten iron 10. The furnace body 30 may have a shell 31 whose inside is at least partially lined with a refractory 20. A refractory material different from the refractory 20 may be lined between the shell 31 and the refractory 20. The furnace body 30 may include, for example, a charging port for molten iron or the like and a charging port for the iron source or the like, and each charging port may be provided with an open / close lid. The furnace body 30 may also include, for example, an outlet for discharging the molten iron 10. The furnace body 30 may also be provided with, for example, a slag discharge port for discharging slag. The surface of the molten iron 10 held inside the furnace body 30 may be covered with slag 15.

[0034] 1.3.2 Heating Mechanism As described above, thermal spalling of refractories in contact with molten iron is likely to occur due to temperature changes of the molten iron, etc. For example, when the temperature of the molten iron is increased by a heating mechanism, thermal spalling of the refractory is likely to occur. In contrast, according to the technology disclosed herein, the refractory 20 in contact with the molten iron 10 contains 2 mass% or more of free carbon, thereby providing excellent thermal conductivity and making the refractory 20 less susceptible to thermal spalling even when the temperature of the molten iron 10 increases rapidly. In other words, according to the technology disclosed herein, the molten iron holding furnace 100 includes a heating mechanism 40 that heats the molten iron 10, and thermal spalling of the refractory 20 can be suppressed even when the molten iron 10 is heated by the heating mechanism 40. The heating mechanism 40 may be, for example, a mechanism that heats the molten iron 10 by induction heating, a mechanism that heats the molten iron 10 by arc heating, or another heating mechanism that heats the molten iron 10. For example, as shown in Figures 2 to 6, the molten iron holding furnace 100 may have an induction heating mechanism (induction heater) as the heating mechanism 40. Alternatively, as shown in Figures 7 to 9, the molten iron holding furnace 100 may have a mechanism including electrodes that generate arcs as the heating mechanism 40.

[0035] 2. Molten Iron Holding Method The technology disclosed herein includes not only the molten iron holding furnace described above, but also a molten iron holding method. The molten iron holding method includes holding molten iron 10 having a carbon concentration below the saturation concentration in a molten iron holding furnace 100. In this embodiment, the molten iron holding furnace 100 is lined with a refractory 20 containing refractory raw materials and 2% to 10% by mass of free carbon on at least a portion of a portion that comes into contact with the molten iron 10. Details of the molten iron 10, the refractory 20, and the molten iron holding furnace 100 are as described above. For example, in one embodiment of the molten iron holding method, the carbon concentration of the molten iron 10 may be 1.0% or more by mass lower than the saturation concentration. In another embodiment of the molten iron holding method, the molten iron holding furnace 100 may include a heating mechanism 40 that heats the molten iron 10. In addition, in the method for holding molten iron according to one embodiment, the refractory 20 lining the portion of the molten iron holding furnace 100 that comes into contact with the molten iron 10 may contain refractory raw materials and 2% by mass to 10% by mass of free carbon at least in a portion closest to the heating mechanism 40. Alternatively, in the method for holding molten iron according to one embodiment, the refractory 20 may line at least a portion of the portion of the molten iron holding furnace 100 that comes into contact with the molten iron 10 that is closest to the heating mechanism 40. Alternatively, in the method for holding molten iron according to one embodiment, the refractory 20 lining the portion of the refractory lining the portion of the molten iron holding furnace 100 that comes into contact with the molten iron 10 that is closest to the heating mechanism 40 may contain refractory raw materials and 2% by mass to 10% by mass of free carbon.

[0036] 3. Manufacturing Method of Molten Iron In addition to the above-described molten iron holding furnace and molten iron holding method, the technology disclosed herein also includes a manufacturing method of molten iron. The manufacturing method of molten iron includes melting an iron source in a molten iron holding furnace 100 to obtain molten iron 10 having a carbon concentration below the saturation concentration. Here, the molten iron holding furnace 100 is lined with a refractory 20 containing a refractory raw material and 2 mass % to 10 mass % of a carbon material on at least a portion of a portion that comes into contact with the molten iron 10. For example, a manufacturing method of molten iron according to one embodiment may include charging molten iron into the molten iron holding furnace 100 and dissolving an iron source (e.g., reduced iron or scrap) having a carbon concentration below the saturation concentration when formed into molten iron into the molten iron. Alternatively, a manufacturing method of molten iron according to one embodiment may include charging an iron source (e.g., reduced iron or scrap) having a carbon concentration below the saturation concentration when formed into molten iron into the molten iron holding furnace 100 and melting the iron source. Alternatively, a method for producing molten iron according to one embodiment may include charging an iron source (reduced iron, scrap, etc.) that has a carbon concentration lower than the saturation concentration when turned into molten iron into the molten iron holding furnace 100, and melting the iron source together with a carbon material as an auxiliary raw material. The melting of the iron source and the carbon material may be performed, for example, by heating the iron source and the carbon material using the heating mechanism described above.

[0037] 4. Use of Refractory The technology disclosed herein includes the use (method of use) of a refractory in addition to the above-described molten iron holding furnace, molten iron holding method, and molten iron manufacturing method. That is, the use of the refractory disclosed herein is the use of a refractory 20 in at least a portion of a molten iron holding furnace 100 that comes into contact with molten iron 10, the molten iron 10 having a carbon concentration less than the saturation concentration, and the refractory 20 containing refractory raw materials and 2% by mass to 10% by mass of free carbon. Details of the molten iron 10, refractory 20, and molten iron holding furnace 100 are as described above, and will not be described here.

[0038] 5. Effects As described above, according to the technology disclosed herein, when the molten iron 10 having a carbon concentration below the saturation concentration is held in the molten iron holding furnace 100, at least a portion of the portion of the molten iron holding furnace 100 that comes into contact with the molten iron 10 is lined with the refractory material 20 containing refractory raw materials and 2% by mass to 10% by mass of free carbon, which makes it easy to ensure excellent heat spalling resistance and structural spalling resistance in the refractory material 20. As a result, the life of the molten iron holding furnace 100 is extended.

[0039] The effects of the technology of the present disclosure will be described in more detail below with reference to examples, but the technology of the present disclosure is not limited to the following examples.

[0040] 1. Operating conditions and evaluation conditions In the molten iron holding furnace shown in Figures 1 and 2, molten iron was charged and scrap melted repeatedly to hold and produce molten iron with a specified carbon saturation. Here, during the holding and production of molten iron, the operation was carried out with the maximum induction heating output applied. The "carbon saturation" of molten iron is defined by the following formula; the lower the actual carbon concentration relative to the saturated carbon concentration of the molten iron, the larger the negative value of the carbon saturation. Carbon saturation (mass%) = carbon concentration of sampled molten iron - saturated carbon concentration

[0041] When the induction heating device was replaced every six months after the start of operation of the molten iron holding furnace, the damage condition of the refractory present in the area in contact with the molten iron was visually inspected, and the structural spalling resistance and heat spalling resistance of the refractory were evaluated according to the following criteria: C: Severe damage such as cracks and chips making continued use impossible B: Minor cracks were observed, but the damage was minor and did not interfere with continued use A: No cracks were observed and continued use was not affected

[0042] In this example, the above-described operation and evaluation were carried out for a plurality of molten iron holding furnaces (Examples 1 to 3, Comparative Examples 1 and 2) lined with different refractories.

[0043] 2. Evaluation Results Table 1 below shows the carbon saturation degree of the molten iron held in the molten iron holding furnace, the components of the refractory lining the molten iron holding furnace, the evaluation results of the heat spalling resistance of the refractory, and the evaluation results of the structural spalling resistance of the refractory. Note that "carbon" among the components of the refractory means simple carbon. In this example, the carbon content in the refractory is equal to the free carbon content in the refractory. Furthermore, "others" refers to TiO ２ , Na ２ O, Fe ２ O ３ , SiO ２ , CaO, MnO ２ means.

[0044]

[0045] The results shown in Table 1 reveal the following.

[0046] The refractory of the molten iron holding furnace according to Comparative Example 1 had insufficient heat spalling resistance. In the molten iron holding furnace according to Comparative Example 1, the amount of free carbon contained in the refractory in contact with the molten iron was as low as 1 mass %, so sufficient thermal conductivity was not ensured in the refractory, and the temperature of the refractory became uneven when the temperature of the molten iron changed, causing large cracks and chips in the refractory.

[0047] The refractory structural spalling resistance was insufficient in the molten iron holding furnace of Comparative Example 2. In the molten iron holding furnace of Comparative Example 2, the carbon content in the refractory in contact with the molten iron was as high as 15 mass %, so carbon eluted from the refractory, forming excessive voids in the refractory, causing peeling on the working surface of the refractory and significant damage to the refractory.

[0048] In contrast, the molten iron holding furnaces according to Examples 1 to 3 exhibited both good heat-resistant spalling properties and good structural spalling properties of the refractory. In the molten iron holding furnaces according to Examples 1 to 3, the refractory in contact with the molten iron contained a carbon content of 2% by mass or more, which gave the refractory excellent thermal conductivity, and as a result, it is believed that the heat-resistant spalling properties of the refractory were ensured. Furthermore, since the carbon content of the refractory was 10% by mass or less, even if carbon eluted from the refractory into the molten iron and voids were formed in the surface layer of the refractory, the voids did not become excessive, and the surface layer of the refractory maintained its structure without peeling, and as a result, it is believed that the structural spalling properties of the refractory were ensured.

[0049] In the above examples, the refractory lining the molten iron holding furnace is an alumina-carbonaceous refractory, an alumina-silicon carbide-carbonaceous refractory, a magnesia-carbonaceous refractory, or a magnesia-silicon carbide-carbonaceous refractory, but the refractory raw materials constituting the refractory are not limited to alumina, magnesia, or silicon carbide. Even when other refractory raw materials are used, as long as the amount of carbon material contained in the refractory is 2% by mass or more and 10% by mass or less, it can be said that both heat spalling resistance and structural spalling resistance are ensured by the above-mentioned mechanism.

[0050] In the above embodiment, a molten iron holding furnace having an induction heating mechanism is lined with a predetermined refractory material, but the configuration of the molten iron holding furnace is not limited to this. Even if a molten iron holding furnace having a heating mechanism other than an induction heating mechanism (for example, an arc heating mechanism) is used, or even if a molten iron holding furnace having no heating mechanism is used, the same effect can be expected by lining it with a predetermined refractory material.

[0051] 3. Summary As described above, when a molten iron holding furnace holds molten iron whose carbon concentration is below the saturated concentration, lining at least a portion of the portion of the molten iron holding furnace that comes into contact with the molten iron with a refractory containing a refractory raw material and 2% by mass to 10% by mass of a carbon material makes it easy to ensure the heat spalling resistance and structural spalling resistance of the refractory.

[0052] 100 Molten iron holding furnace 10 Molten iron 15 Slag 20 Refractory material 30 Furnace body 31 Iron shell 32, 33 Charging port 34, 35 Opening and closing cover 36 Tap hole 40 Heating mechanism 50 Support

Claims

1. A molten iron holding furnace for holding molten iron whose carbon concentration is below the saturated concentration, wherein at least a portion of the area of ​​the molten iron holding furnace that comes into contact with the molten iron is lined with a refractory material containing refractory raw materials and 2% by mass to 10% by mass of free carbon.

2. A molten iron holding furnace according to claim 1, wherein the carbon concentration of the molten iron is lower than the saturated concentration by 1.0 mass % or more.

3. A molten iron holding furnace according to claim 1 or 2, comprising a heating mechanism for heating the molten iron.

4. A molten iron holding furnace as claimed in claim 3, wherein the refractory lining at the portion of the molten iron holding furnace that comes into contact with the molten iron contains refractory raw materials and 2% by mass or more and 10% by mass or less of free carbon, at least in the portion closest to the heating mechanism.

5. A method for holding molten iron, comprising holding molten iron having a carbon concentration below a saturation concentration in a molten iron holding furnace, wherein the molten iron holding furnace is lined with a refractory material containing refractory raw materials and 2% by mass or more and 10% by mass or less of free carbon, in at least a portion of a region that comes into contact with the molten iron.

6. A method for holding molten iron according to claim 5, wherein the carbon concentration of the molten iron is lower than the saturated concentration by 1.0 mass % or more.

7. A method for holding molten iron according to claim 5 or 6, wherein the molten iron holding furnace has a heating mechanism for heating the molten iron.

8. A method for holding molten iron as set forth in claim 7, wherein the refractory lining at the portion of the molten iron holding furnace that comes into contact with the molten iron contains refractory raw materials and 2% by mass or more and 10% by mass or less of free carbon, at least in the portion closest to the heating mechanism.

9. Use of a refractory in at least a portion of a portion of a molten iron holding furnace that comes into contact with molten iron, wherein the molten iron has a carbon concentration less than the saturation concentration, and the refractory contains refractory raw materials and 2% by mass or more and 10% by mass or less of free carbon.