Refractory structure of ladle and operation method using ladle with said refractory structure

Abstract

To provide a refractory structure of a ladle which is capable of suppressing heat radiation from a ladle while maintaining refractory properties to improve thermal insulation properties by setting the material or the like of a permanent refractory in the ladle according to regulations, and an operation method using a ladle provided with the refractory structure.SOLUTION: In a ladle 1 where an alumina-magnesia castable wear refractory 4 is applied to a part at the inside of a steel shell 2 of an outer container and filled with molten steel M so as to be contacted, a permanent refractory 3 with a two layer structure is applied to a space between the steel shell 2 and the wear refractory 4. In the permanent refractory 3 with a two layer structure, a main permanent refractory 3a is applied at the side of the steel shell 2, a quasi permanent refractory 3b is applied to the side of the wear refractory 4, and as the main permanent refractory 3a, a refractory having a thermal conductivity λ lower than that of the quasi permanent refractory 3b and with which a boundary temperature between the wear refractory 4 and the quasi permanent refractory 3b reaches above 700°C and less than 1,400°C is adopted.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a refractory structure installed inside a ladle and an operating method using the ladle. [Background technology]

[0002] As is well known, in the steel industry, ladles are used as containers for transporting molten steel. Molten steel is charged into the ladle, where it undergoes secondary refining processes such as removing impurities and adding alloys to the molten steel. Major processes for secondary refining include RH, LF, and CAS. After completing this secondary refining process, the molten steel is transported by the ladle and sent to a continuous casting process or an ingot casting process.

[0003] The inner wall surface (furnace wall) of the ladle into which molten steel is charged is lined with refractories to hold the molten steel in place. The refractories are designed to withstand the high temperatures of the molten steel charged, and are composed of permanent refractories and wear refractories, in that order from the steel shell side (outside) of the ladle. Techniques relating to the structure of such refractories are disclosed in, for example, Patent Documents 1 and 2.

[0004] Patent Document 1 aims to reduce the cost of refractory repair in a molten metal vessel by preventing the dismantling of a sound permanent refractory layer when a wear refractory layer is dismantled. Specifically, the molten metal vessel 100 has a shell 1, two permanent refractory layers 30, 50 formed on the inside of the shell 1, and a wear refractory layer 70 formed on the inside of the permanent refractory layer 50. The shell 1 forms the outer shell of the molten metal vessel 100. Of the permanent refractory layers 30, 50, mortar A2 that bonds the refractory materials 3 that form the permanent refractory layer 30 on the shell side has a stronger bonding strength than mortar B4 that bonds the refractory materials 5 that form the permanent refractory layer 50 on the wear refractory layer 70 side.

[0005] Patent Document 2 aims to prevent buildup of slag on the inner surface of a molten steel vessel such as a ladle. Specifically, the molten steel line 6 on the inner surface of a ladle 1 is lined with a dolomite refractory material. It discloses that the refractory material is made of CaO, MgO, C, and inevitable impurities. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-78105 [Patent Document 2] Patent re-publication No. WO2013 / 180219 Summary of the Invention [Problem to be solved by the invention]

[0007] The refractory material installed on the inner wall of a ladle is damaged and gradually wears out as molten steel is repeatedly charged and tapped. This refractory wear can lead to problems such as holes in the furnace wall. It is also necessary to maintain the temperature of the molten steel in the ladle so as not to affect the steelmaking process, such as during secondary refining and transport of the molten steel. For these reasons, ladles are required to have the ability to retain the heat of the molten steel while suppressing refractory wear.

[0008] The present inventors have conducted extensive research to improve the thermal insulation of refractories. They have found that in order to improve the thermal insulation, it is necessary to control (keep within a predetermined range) the interface temperature between a wear refractory, which comes into contact with molten steel, and an adjacent permanent refractory (semi-permanent refractory). They have found that the interface temperature can be kept within the predetermined range by taking into account the thermal conductivity of the refractory.

[0009] However, Patent Documents 1 and 2 have the following problems. Patent Document 1 has a heat insulating material between the steel shell and the permanent refractory, but when dismantling the worn wear refractory layer, in order to prevent the permanent refractory layer from being dismantled, This document is a technology that specifies the bonding strength of refractories. In other words, it is different from a technology that improves thermal insulation, and therefore the thermal conductivity of the refractory (insulating material), which is important in the present invention, is not described and is unclear. For this reason, it is not possible to calculate the interface temperature between the wear refractory and the permanent refractory (semi-permanent refractory), which is necessary to improve thermal insulation. It is unclear from this document whether the wear refractory has sufficient slag corrosion resistance and thermal shock resistance.

[0010] Furthermore, Patent Document 2 discloses a technology in which an insulating material is provided between the shell and the permanent refractory, but a gap is formed between the insulating material to improve the air permeability during the pre-drying of the monolithic refractory. In other words, since this technology is different from the technology for improving thermal insulation, the thermal conductivity of the refractory (insulating material), which is important in the present invention, is not disclosed and is unclear. For this reason, it is not possible to calculate the interface temperature between the wear refractory and the permanent refractory (semi-permanent refractory), which is necessary to improve thermal insulation. It is unclear from this document whether the wear refractory has sufficient slag corrosion resistance and thermal shock resistance.

[0011] In view of the above problems, the present invention aims to provide a refractory structure for a ladle in which a permanent refractory structure is installed between the steel shell and the wear refractory of a ladle, and in which the material, arrangement, thickness, etc. of the refractory are set in accordance with regulations, thereby suppressing heat radiation from the ladle while maintaining the properties of the refractory, thereby improving heat insulation, and enabling the heat insulation performance to be maintained for a long period of time, such as several years, and an operating method using a ladle equipped with the refractory structure. [Means for solving the problem]

[0012] In order to achieve the above object, the present invention provides the following technical means. The refractory structure of the ladle according to the present invention is a ladle in which an alumina-magnesia castable wear refractory is installed inside the steel shell of the outer vessel and at a location where the ladle is filled with molten steel and comes into contact with the steel shell. After the molten steel is charged into the ladle and the charged molten steel is subjected to secondary refining, the molten steel after the secondary refining is discharged. put out The operation of repeating the above charge is regarded as one charge, and the charge is repeated. In the charge, the temperature of the molten steel charged into the ladle is set to 1650°C or more and 1700°C or less. The temperature inside the furnace rises from the time the molten steel is charged until the molten steel is completely discharged, and after the molten steel is completely discharged, Next Single charge of molten steel of The ladle is used in an operating environment where the temperature inside the furnace drops until charging begins, and a two-layer permanent refractory is installed between the shell and the wear refractory, and the two-layer permanent refractory is configured such that the silica-based permanent refractory is installed on the shell side and an alumina-based semi-permanent refractory is installed on the wear refractory side, and the permanent refractory has a thermal conductivity λ lower than that of the semi-permanent refractory, and the interface temperature between the wear refractory and the semi-permanent refractory, estimated based on the following formula (1), is such that the minimum temperature during operation exceeds 700°C and the maximum temperature during operation is less than 1400°C. [Formula (1)] The internal energy change of the wear refractory in contact with the molten steel and the semi-permanent refractory in contact with the wear refractory is calculated by one-dimensional unsteady heat transfer calculation only in the thickness direction of the ladle, and is given by equation (A), TIFF0007802608000001.tif20170 The change in internal energy of the refractory or steel shell in contact with the atmosphere is calculated by one-dimensional unsteady heat transfer calculation only in the thickness direction of the ladle, as shown in formula (B). TIFF0007802608000002.tif17170 The change in internal energy of the refractory or steel shell in contact with the refractory or steel shell is calculated by one-dimensional unsteady heat transfer calculation only in the thickness direction of the ladle, as shown in formula (C), TIFF0007802608000003.tif16170 The temperature at the boundary between the wear refractory and the semi-permanent refractory is estimated by substituting the initial temperature of the wear refractory, the initial temperature of the steel shell, the atmospheric temperature inside the ladle, the atmospheric temperature outside the ladle, the heat transfer coefficient, and the emissivity into equations (A), (B), and (C). however, TIFF0007802608000004.tif145170

[0013] In the method of operation using a ladle according to the present invention, when a ladle having a refractory structure is used, when the charge is the first, the operation is carried out so that t≦193 min is satisfied, where t (min) is the time from the completion of discharge of molten steel from the ladle to the completion of charging of molten steel for the next charge, and when the charge is the second or subsequent charge, the operation is carried out so that t≦210 min is satisfied, t≦193 or If t≦210 is not satisfied, The charge following the current charge is again considered the first charge, and the time t until the charging of the charge following the first charge is completed is The method is characterized in that the operation is performed so that t≦193, and thereby the interface temperature from the start of the secondary refining treatment to the completion of discharge of the molten steel in the ladle exceeds 700°C at the lowest temperature during the operation and is less than 1400°C at the highest temperature during the operation. [Effects of the Invention]

[0014] According to the present invention, in the structure of the permanent refractory installed between the steel shell and the wear refractory of the ladle, the material, arrangement, thickness, etc. of the refractory are set in accordance with regulations, so that the heat radiation from the ladle can be suppressed and the heat insulating performance can be improved while maintaining the properties of the refractory, and further, the heat insulating performance can be maintained for a long period of time, for example, several years. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 2 is a diagram schematically illustrating the structure of a refractory material applied to the inner wall of a ladle. [Figure 2]1 is a graph showing the relationship between NOld (times) at which the interface temperature between the wear refractory and the semi-permanent refractory reaches 700°C and t (min). [Figure 3] FIG. 1 is a diagram showing an example of calculation results of the transition of the interface temperature (° C.) between a wear refractory and a semi-permanent refractory. [Figure 4] 1 is a flowchart showing the concept of increasing the number of times N that molten steel is charged into a ladle. [Figure 5] This figure shows the lining structure patterns (I, II, III) installed inside the ladle considered in one-dimensional unsteady heat transfer calculations. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, embodiments of a refractory structure for a ladle according to the present invention and an operating method using a ladle having the refractory structure will be described with reference to the drawings. The embodiment described below is an example of a specific embodiment of the present invention, and the configuration of the present invention is not limited to this specific example. The present invention relates to a refractory 3 structure (lining structure) applied to the inner wall of a ladle 1 used in the steel manufacturing industry, and an operating method using a ladle 1 equipped with the refractory 3 structure. The structure of the refractory 3 applied to the inner wall of the ladle 1 is specified so as to have excellent thermal insulation properties while maintaining refractory properties such as abrasion resistance and thermal shock resistance.

[0017] That is, in the present invention, in a ladle 1 in which an alumina-magnesia castable is applied to a wear refractory 4 at a portion where the ladle 1 is filled with and comes into contact with molten steel M, a permanent refractory 3 is applied to the outside of the wear refractory 4, and the permanent refractory 3 is composed of an outer permanent refractory 3a and an inner semi-permanent refractory 3b, the thermal conductivity λ of the permanent refractory 3a being lower than the thermal conductivity λ of the semi-permanent refractory 3b, and the material, arrangement and thickness of the semi-permanent refractory 3b are set so that the interface temperature between the wear refractory 4 and the adjacent semi-permanent refractory 3b is in a temperature range exceeding 700°C and lower than 1400°C.

[0018] The structure of the refractory material 3 of the ladle 1 of the present invention and the operating method using the ladle 1 having the refractory material 3 structure will be specifically described. The present invention is directed to a ladle 1 in which an alumina-magnesia castable is applied to the wear refractory 4 at the portion where molten steel M is filled. As is well known, in the steel industry, a ladle 1 is used as a container for transporting molten steel M. Molten steel is charged into the ladle 1, and secondary refining processes such as removing impurities from the molten steel M and adding alloys to the molten steel M are carried out. Major processing methods for secondary refining include, for example, RH, LF, and CAS. After such secondary refining, the molten steel M is transported by the ladle 1 and subjected to a continuous casting process or an ingot-making process.

[0019] FIG. 1 shows a detailed schematic diagram of the structure (lining structure) of the refractory material 3 applied to the inner wall of the ladle 1. As shown in Fig. 1, a refractory material 3 is installed on the inner wall surface (furnace wall) of a ladle 1 into which molten steel M is charged in order to hold the molten steel M. The refractory material 3 is capable of withstanding the high temperature of the charged molten steel M, and is composed of a permanent refractory material 3 and a wear refractory material 4, in that order from the shell 2 side (outside) of the ladle 1.

[0020] The permanent refractory 3 is intended to prevent steel leakage from the ladle 1 due to infiltration of the base metal (molten steel M melting the steel shell 2 of the ladle 1 and leaking to the outside during secondary refining, etc.), and is mainly made of dense bricks. When the permanent refractory 3 is formed in two layers, for example, they are called the permanent refractory 3a and the semi-permanent refractory 3b, in that order from the shell 2 side. In the following description, the permanent refractory 3a may be referred to as the "permanent refractory 3a," and the semi-permanent refractory 3b may be referred to as the "semi-permanent refractory 3b."

[0021] The Perm 3a is a silica-based refractory, and the Semi-Perm 3b is an alumina-based refractory. The wear refractory 4 is a refractory material that is placed on the innermost surface of the ladle 1 and that is in direct contact with the molten steel M and slag. This wear refractory 4 is required to be made of a material that has excellent slag corrosion resistance and thermal shock resistance. In addition, magnesia-carbon bricks, which have good slag corrosion resistance, are installed in the area that is in direct contact with the slag (slag line).

[0022] In this embodiment, an alumina-magnesia castable refractory, which has excellent slag corrosion resistance and thermal shock resistance, is applied to the portion (wear refractory 4) that comes into direct contact with the molten steel M. The alumina-magnesia castable is a pourable material based on alumina and made of alumina cement, primarily composed of MgO, SiO2, and CaO·Al2O3. The pourable material is a material made by adding water to powder and granules, mixing it, pouring it into a mold like concrete, and drying it before use.

[0023] The ladle 1 of this embodiment has a two-layered refractory 3 between the shell 2 and the wear refractory 4 . In this embodiment, the purpose is to improve the thermal insulation of the ladle 1, but if the refractory 3 has a single layer structure, only dense bricks are used, and it is not possible to use a refractory with a low thermal conductivity λ (described later) in combination with the refractory 3. In other words, it is difficult to improve the thermal insulation with a single layer structure of the refractory 3.

[0024] Furthermore, when castable is used for the wear refractory 4, the castable requires time to dry, so if the refractory 3 has a three-layer structure, construction takes time, reducing productivity. For the above reasons, in the present invention, a two-layered permanent refractory 3 is provided between the shell 2 and the wear refractory 4.

[0025] In the ladle 1 of this embodiment, in order to suppress heat radiation from the ladle 1, a refractory having a lower thermal conductivity λ than the semi-permanent refractory 3b, which is the refractory on the wear refractory 4 side, is placed on the permanent refractory 3a, which is the refractory on the steel shell 2 side, of the two-layer refractory 3. The reason why a refractory material with a low thermal conductivity λ is placed in the permanent 3a is that the temperature of the refractory material with a low thermal conductivity λ can be kept low, and therefore the heat insulating performance can be maintained for a long period of time, for example, for more than two years.

[0026] For this reason, for the present permanent 3a, a refractory material is used that has a lower thermal conductivity λ than that of the semi-permanent 3b (λ of the present permanent 3a < λ of the semi-permanent 3b is satisfied) and the interface temperature between the wear refractory material 4 and the semi-permanent 3b exceeds 700°C and is less than 1400°C during operation. In this embodiment, the charging time from the completion of discharging the molten steel M in the ladle 1 to the completion of charging the molten steel M of the next charge is defined as t (min).

[0027] When the charging time t is short, the amount of heat released from the steel shell 2 and the wear refractory 4 of the ladle 1 is small, so the amount of heat stored in the ladle 1 is large, and when the next charge of molten steel M is received, the amount of heat released from the molten steel M to the ladle 1 is small, improving the heat retention of the molten steel M. In other words, the temperature drop of the molten steel M can be suppressed. On the other hand, if the charging time t is long, the amount of heat released from the steel shell 2 and the wear refractory 4 of the ladle 1 is large, so the amount of heat stored in the ladle 1 is small, and when the next charge of molten steel M is received, the amount of heat released from the molten steel M to the ladle 1 is large, which reduces the heat retention of the molten steel M. In other words, this accelerates the temperature drop of the molten steel M.

[0028] In this embodiment, the number of times molten steel is charged into the ladle 1 in the pre-charge is set to N Old The number of times molten steel is charged into the ladle 1 for the charge is N New Let's say. N New =N Old The condition for +1 is: N Old When = 1, t ≦ 193 min, N Old If ≥ 2, t ≤ 210 min, If the above is not met, N New =1.

[0029] Number of times molten steel is charged into the charge NNew When is 1, heat storage in the ladle 1 by holding the molten steel M in the previous charge cannot be obtained. Therefore, the charging time t and the number of molten steel charging times N New This changes the heat storage condition of the ladle 1, which affects the interface temperature between the wear refractory 4 and the semi-perm 3b, which will be described later. Therefore, in the present invention, in order to clarify the heat storage state of the ladle 1, the condition for increasing the number of molten steel charging times N is determined from the charging time t.

[0030] Figure 2 shows the N Old This shows the relationship between (times) and t(min). As shown in FIG. 2, the lining (refractory structure) of "Experiment No. 1" in this example (see Table 4 shown later) which has the lowest refractory temperature was used, and the charging time t at which the interface temperature between the wear refractory 4 and the semi-perm 3b at the start of the secondary refining treatment reaches 700°C was set as the implementation conditions (details will be described later). ) was obtained from a one-dimensional unsteady heat transfer calculation.

[0031] From Figure 2, the number of molten steel charging times for the charge, N New The conditions for increasing are (1) and (2) below. (1)N Old When = 1, t≦193 min is satisfied. (2)N Old If ≧2, t≦210min is satisfied. The case where molten steel M is charged for the first time after the completion of construction (for example, repairs, etc.) of ladle 1 is called N. New =1.

[0032] As described above, under the above conditions, the interface temperature between the wear refractory 4 and the semi-perm 3b satisfies the condition of less than 1400°C in any of the present examples. In this embodiment, N New The operation is carried out so that the interface temperature between the wear refractory 4 and the semi-permanent refractory 3b exceeds 700°C and is less than 1400°C from the start of the secondary refining process ≧2 until the discharge of the molten steel M from the ladle 1 is completed.

[0033] The reason why the interface temperature is set to exceed 700° C. is as follows. According to a report by Ishikawa et al. shown in the references, alumina-magnesia castables show a maximum thermal stress at 700°C (reference: Ishikawa et al.: Refractories, 51(3) (1999), pp. 144-148). For this reason, when the temperature of the wear refractory 4 is 700°C or lower, the alumina-magnesia castable expands thermally, causing a crumbling crack, and slag penetrates from the crack into the semi-perm 3b. The slag reacts with the semi-perm 3b, reducing its refractoriness and potentially causing steel leakage.

[0034] The reason why the interface temperature is set to less than 1400° C. is as follows. According to a report by Nagai et al., anorthite is formed in alumina-magnesia castables at temperatures above 1400°C (reference: Nagai et al.: Refractories, 40(5)(1988), p284-289). For this reason, if the interface temperature between the wear refractory 4 and the quasi-perm 3b becomes 1400°C or higher, anorthite may be generated at the interface between the wear refractory 4 and the quasi-perm 3b. As a result, anorthite, which is a low-melting point substance, may infiltrate the quasi-perm 3b, reducing the refractoriness of the quasi-perm 3b and possibly causing steel leakage.

[0035] From the above, it has been found that it is appropriate to set the interface temperature between the wear refractory 4 and the semi-perm 3b to be more than 700°C and less than 1400°C after the start of the secondary refining process for preparing slag. FIG. 3 shows an example of the results of calculating the transition of the interface temperature (° C.) between the wear refractory 4 and the semi-perm 3b.

[0036] As shown in FIG. 3, after the charging of the molten steel M is completed, the secondary refining process is started and the discharge of the molten steel M is completed. OldDuring this time, the interface temperature rises from about 550°C to about 1000°C. Thereafter, the interface temperature drops to about 750°C before the next charge of molten steel M is received. Next, N New During this time, the interface temperature rises to about 750°C and about 1000°C. New ≧2), the interface temperature is in the range of more than 700°C and less than 1400°C.

[0037] Figure 4 shows a flowchart of how to increase the number of times N that molten steel is charged into the ladle 1. Here, N is the number of times that molten steel is charged into the ladle, and X is a natural number of 2 or more. As shown in Figure 4, after work on ladle 1 (for example, repairs) is completed, molten steel M is charged for the first time (N=1). If t≦193 min is satisfied, proceed to the next step. If t>193 min, reheat ladle 1 using a burner or similar device. The next charge of molten steel M is received (N=2). If t≦210 min is satisfied, proceed to the next step. If t>210 min, reheat ladle 1 using a burner or similar device. This process is repeated.

[0038] Table 1 shows the definitions of the parameters used in this embodiment.

[0039] [Table 1]

[0040] [Example] Below, we will explain the structure of the refractory material 3 installed in the ladle 1 of the present invention, examples carried out in accordance with an operating method using the ladle 1 equipped with the refractory material 3 structure, and comparative examples carried out for comparison with the present invention. The conditions for carrying out this example are as follows.

[0041] The interface temperature (°C) between the wear refractory 4 and the semi-perm 3b was calculated using one-dimensional unsteady heat transfer calculations. The method for calculating the above interface temperature (°C) is shown below. When the refractory 3 (lining structure) shown in this example and comparative examples (see Table 4 below) was installed, the temperature change over time from the wear refractory 4 to the shell 2 when molten steel M was being held was calculated by one-dimensional unsteady heat transfer calculation. Similarly, the temperature change over time from the wear refractory 4 to the shell 2 when molten steel M was not being held was calculated by one-dimensional unsteady heat transfer calculation. Using these results, the transition of the interface temperature between the wear refractory 4 and the quasi-perm 3b was determined.

[0042] The internal energy change Q(W) of an object can be expressed by the following equation (1).

[0043]

number

[0044] Moreover, V is shown in the following formula (2).

[0045]

number

[0046] However, the following definitions apply.

[0047]

number

[0048] If the heat flux generated by heat transfer is q1, it is expressed by the following equation (3).

[0049]

number

[0050] Furthermore, if the heat flux generated by thermal conduction is q2, it is expressed by the following equation (4).

[0051]

number

[0052] Furthermore, if the heat flux generated by thermal radiation is q3, it is expressed by the following equation (5).

[0053]

number

[0054] However, the following definitions apply.

[0055]

number

[0056] In the present invention, since one-dimensional heat transfer calculation is performed, dy=1, dz=1 will be used hereinafter. Figure 5 shows patterns (I, II, III) of the lining structure (structure of the refractory 3) applied to the inner wall of the ladle 1 considered in one-dimensional unsteady heat transfer calculations. As shown in FIG. 5, for the ladle 1, calculations are performed for each of the lining structure conditions shown in (I) to (III).

[0057] (I): The change in internal energy of the refractories 3 and 4 in contact with the molten steel M is shown in equation (6).

[0058]

number

[0059] (II): The internal energy change of the refractories 3, 4 or the steel shell 2 in contact with the atmosphere is shown in equation (7).

[0060]

number

[0061] (III): The changes in internal energy of the refractory 4 in contact with the refractory 3, the refractories 3 and 4 in contact with the shell 2, and the shell 2 in contact with the refractories 3 and 4 are shown in equation (8).

[0062]

number

[0063] However, the following definitions apply.

[0064]

number

[0065] The calculation for the wear refractory 4 was divided into 10 parts, and the calculation for the other refractories 3 and the iron shell 2 was divided into 2 parts. Table 2 shows the initial conditions such as the initial temperature, the heat transfer coefficient h, and the emissivity ε used in the calculations in this example and comparative examples (see Table 4 shown later).

[0066] [Table 2]

[0067] Table 3 shows the physical properties of the refractories 3 and 4 and the steel shell 2 used in the calculations in the present example and comparative examples.

[0068] [Table 3]

[0069] In addition, with regard to the interface temperature between the wear refractory 4 and the semi-perm 3b described in the present embodiment and comparative examples, the start time of the secondary refining process is assumed to be 55 minutes after the completion of charging of the molten steel M into the ladle 1, and the minimum temperature (°C) and the maximum temperature (°C) during the period from the start of the secondary refining process to the completion of discharging of the molten steel M into the ladle 1 are described. Table 4 shows examples carried out in accordance with the structure of the refractory material 3 installed in the ladle 1 of the present invention and the operating method using the ladle 1 equipped with the refractory material 3 structure, as well as comparative examples carried out for comparison with the present invention.

[0070] [Table 4]

[0071] The comparative example, experiment number 19, had a three-layer structure consisting of a permanent hair 3a, a first layer of semi-permanent hair 3b, and a second layer of semi-permanent hair 3b, in that order from the iron shell. As shown in Table 4, "Experiment Nos. 1 to 17" are the present examples, and "Experiment Nos. 18 to 25" are comparative examples. In the present examples, the permanent refractory 3 between the steel shell 2 and the wear refractory 4 has a two-layer structure of permanent refractory 3a and semi-permanent refractory 3b. On the other hand, the comparative examples include one in which the permanent refractory 3 has a single layer structure (No. 18) and one in which the permanent refractory 3 has a three-layer structure (No. 19).

[0072] Regarding the thermal conductivity λ of the permanent refractory 3, in this example, "thermal conductivity λ of permanent 3a < thermal conductivity λ of semi-permanent 3b" is satisfied. On the other hand, the comparative examples include those (numbers 18 to 19, 22 to 24) that do not satisfy "thermal conductivity λ of permanent 3a < thermal conductivity λ of semi-permanent 3b." Molten steel charging times N New In this embodiment, New ≧2. On the other hand, in the comparative example, N New Includes those that do not satisfy ≧2 (numbers 20-21, 25).

[0073] Regarding the interface temperature between the wear refractory 4 and the semi-permanent refractory 3b, in this example, the interface temperature between the wear refractory 4 and the semi-permanent refractory 3b satisfies the condition "exceeding 700°C and less than 1400°C." On the other hand, in all of the comparative examples, the interface temperature does not satisfy the condition "exceeding 700°C and less than 1400°C." That is, the permanent refractory 3 has a two-layer structure of the permanent refractory 3a and the semi-permanent refractory 3b, and the thermal conductivity λ of the permanent refractory 3a is less than the thermal conductivity λ of the semi-permanent refractory 3b. The charging time of the molten steel M is set to a specified time t (min). New If the temperature at the interface between the wear refractory 4 and the semi-permanent refractory 3b is set to be greater than 700°C and less than 1400°C, the wear of the wear refractory 4 is suppressed, and the amount of heat radiation is suppressed, resulting in the ladle 1 having excellent thermal insulation properties.

[0074] The present invention can be summarized as follows. The refractory structure of the ladle of the present invention comprises a ladle 1 having an alumina-magnesia castable wear refractory 3 installed inside the shell 2 of the outer vessel and at a location where the ladle 1 comes into contact with the molten steel M when the ladle 1 is filled with the molten steel M, and a two-layer permanent refractory 3 is installed between the shell 2 and the wear refractory 4. Of the two-layer permanent refractory 3, the permanent refractory 3a is installed on the shell 2 side, and the semi-permanent refractory 3b is installed on the wear refractory 4 side. The permanent refractory 3a has a lower thermal conductivity λ than the semi-permanent refractory 3b, and the interface temperature between the wear refractory 4 and the semi-permanent refractory 3b exceeds 700°C and is lower than 1400°C during operation.

[0075] In addition, in the operating method using the ladle of the present invention, when operating using the ladle 1 having the above-mentioned structure of the refractory 3, the time from the completion of discharging the molten steel M in the ladle 1 to the completion of charging the molten steel M of the next charge is defined as t (min), and the number of times molten steel is charged into the ladle 1 in the previous charge is defined as N Old The number of times molten steel is charged into the ladle 1 for the charge is N New year, N New =N Old The condition for +1 is: N Old When = 1, t ≦ 193 min, N Old If ≥ 2, t ≤ 210 min, If the above conditions are not met, New =1, NNew The operation is carried out so that the interface temperature between the wear refractory 4 and the semi-permanent refractory 3b exceeds 700°C and is less than 1400°C from the start of the secondary refining process ≧2 until the discharge of the molten steel M from the ladle 1 is completed.

[0076] As described above, according to the present invention, the amount of heat radiation from the ladle 1 can be reduced while suppressing wear of the wear refractory 4, and excellent heat insulation is provided, thereby improving the heat retention of the ladle 1. In addition, the rate of temperature drop of the molten steel M is reduced. That is, according to the present invention, in the structure of the permanent refractory 3 installed between the steel shell 2 and the wear refractory 4 of the ladle 1, the material, arrangement, thickness, etc. of the refractory 3 are set in accordance with regulations, so that the heat radiation from the ladle 1 can be suppressed and the heat insulating performance can be improved while maintaining the characteristics of the refractory 3, and further, the heat insulating performance can be maintained for a long period of time, for example, several years.

[0077] It should be noted that the embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. In particular, in the embodiments disclosed herein, matters not explicitly stated, such as operating conditions, operating conditions, various parameters, dimensions, weights, volumes of components, etc., do not deviate from the scope of ordinary practice by a person skilled in the art, and values ​​that can be easily assumed by a person ordinary skilled in the art are used. [Explanation of symbols]

[0078] 1 ladle 2 Ironhide 3 Permanent refractories 3a Permanent refractory (permanent) 3b Semi-permanent refractories (semi-permanent) 4. Ware Refractories M Molten steel

Claims

1. A ladle in which an alumina-magnesia castable wear refractory is installed inside the steel shell of an outer vessel and at a location where the ladle comes into contact with molten steel when filled, the ladle being used when repeatedly charging molten steel into the ladle, subjecting the charged molten steel to secondary refining, and then discharging the molten steel after secondary refining, each of which constitutes one charge, the temperature of the molten steel charged into the ladle being 1650°C or higher and 1700°C or lower, the temperature inside the furnace rising from the time the molten steel is charged until the molten steel is completely discharged, and then decreasing from the time the molten steel is completely discharged until the charging of the next charge of molten steel begins, A two-layer permanent refractory is installed between the steel shell and the wear refractory, In the two-layered permanent refractory, a silica-based permanent refractory is applied to the shell side, and an alumina-based semi-permanent refractory is applied to the wear refractory side, The permanent refractory has a thermal conductivity λ lower than that of the semi-permanent refractory, and the interface temperature between the wear refractory and the semi-permanent refractory is estimated based on the following formula (1), and the minimum temperature during operation is greater than 700°C, and the maximum temperature during operation is less than 1400°C. Refractory structure of a ladle characterized by: [Formula (1)] The change in internal energy of the wear refractory in contact with the molten steel and the semi-permanent refractory in contact with the wear refractory is calculated by one-dimensional unsteady heat transfer calculation only in the thickness direction of the ladle, and is given by formula (A), The change in internal energy of the refractory or steel shell in contact with the atmosphere is calculated by one-dimensional unsteady heat transfer calculation only in the thickness direction of the ladle, as shown in formula (B), The change in internal energy of the refractory or the steel shell in contact with the refractory or the steel shell is calculated by one-dimensional unsteady heat transfer calculation only in the thickness direction of the ladle, and is given by formula (C), The temperature at the boundary between the wear refractory and the semi-permanent refractory is estimated by substituting the initial temperature of the wear refractory, the initial temperature of the steel shell, the atmospheric temperature inside the ladle, the atmospheric temperature outside the ladle, the heat transfer coefficient, and the emissivity into Equations (A), (B), and (C). however,

2. When operating a ladle having the refractory structure according to claim 1, When the charge is the first time, the time from when the discharge of the molten steel in the ladle is completed to when the charging of the next charge of molten steel is completed is set to t (min). Doing business, When the charge is the second or subsequent charge, the operation is carried out so that t≦210. If t≦193 or t≦210 is not satisfied, the next charge after the current charge is treated as the first charge again, and operation is carried out so that the time t until the charging of the molten steel of the next charge after the next charge is completed is t≦193. The operation is performed so that the interface temperature from the start of the secondary refining process to the completion of the discharge of the molten steel from the ladle exceeds 700°C at the lowest temperature during the operation and is less than 1400°C at the highest temperature during the operation.

1. A method of operating a ladle using the method of claim 1.

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