Method for cooling decarburized slag, method for manufacturing steel materials, and coolant for decarburized slag
By using a coolant from steelmaking slag with iron, CaO, and SiO2 to cool and solidify decarburized slag, the method addresses high melting point issues and bumping phenomena, ensuring safe and efficient refining with maintained product quality and iron recycling.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- JFE STEEL CORP
- Filing Date
- 2023-01-04
- Publication Date
- 2026-05-26
AI Technical Summary
The high basicity of decarburized slag leads to increased melting point, causing poor remeltable properties and potential bumping phenomena during the refining process, which can result in incomplete phosphorus removal and decreased product quality.
A method involving the use of a coolant derived from steelmaking slag, containing iron as a main component and CaO and SiO2, to cool and solidify decarburized slag by mixing and oscillating the container, thereby preventing bumping and maintaining appropriate melting point.
The method enhances operational safety, ensures proper execution of refining steps, and maintains product quality by preventing boiling over and controlling the slag's melting point, while also promoting iron source recycling.
Smart Images
Figure 0007865214000002 
Figure 0007865214000003 
Figure 0007865214000004
Abstract
Description
Technical Field
[0001] The present invention relates to a method for cooling decarburized slag, a method for manufacturing steel, and a coolant for decarburized slag.
Background Art
[0002] The refining process includes, for example, a desiliconization and dephosphorization treatment for removing silicon (Si) and phosphorus (P) from hot metal charged into a converter, a decarburization treatment for removing carbon (C) from molten steel after the desiliconization and dephosphorization treatment, and a tapping treatment for discharging the molten steel after the decarburization treatment. Note that in the desiliconization and dephosphorization treatment, it is not always necessary to remove Si, and only the dephosphorization treatment may be performed.
[0003] Conventionally, in order to reduce the energy loss of hot metal and also reduce the fixed costs (equipment costs and labor costs) of the processes before and after the converter, these processes of the refining process have been integrated into the converter.
[0004] For example, Patent Documents 1 to 3 disclose that new hot metal is charged into the converter with the decarburized slag generated in the previous refining process remaining, and the above desiliconization and dephosphorization treatment to tapping treatment are repeatedly performed.
[0005] By the way, the decarburized slag contains iron oxide such as FeO. In Patent Document 1, the molten decarburized slag is reused. The oxygen contained in the iron oxide may react with the carbon contained in the hot metal. Therefore, when the hot metal is charged or at the initial stage of the refining process, the carbon and oxygen in the hot metal may react rapidly, and there is a risk of a so-called boiling-over phenomenon occurring.
[0006] In order to avoid such a boiling-over phenomenon, in Patent Document 2, the decarburized slag is cooled with an inert gas such as nitrogen. However, if the decarburized slag is excessively cooled by this inert gas, there is a problem that the treatment time of the desiliconization and dephosphorization treatment becomes long because it takes time for remelting.
[0007] Patent Document 3 discloses cooling decarburized slag using a coolant containing a large amount of iron oxide. However, similar to Patent Document 1, there is a risk that a sudden reaction between the carbon and oxygen in the molten iron may occur when the molten iron is charged or in the initial stages of the refining process, causing a bumping phenomenon.
[0008] To suppress such bumping phenomena, Patent Document 4 discloses the use of pre-cooled decarburized slag. [Prior art documents] [Patent Documents]
[0009] [Patent Document 1] Japanese Patent Application Publication No. 4-72007 [Patent Document 2] Japanese Patent Application Publication No. 8-199218 [Patent Document 3] Patent No. 4065097 [Patent Document 4] Japanese Patent Publication No. 2014-169492 [Overview of the project] [Problems that the invention aims to solve]
[0010] Incidentally, the melting point of decarburized slag changes depending on its basicity. Figure 8 shows the relationship between the basicity (CaO / SiO2) of decarburized slag and its melting point. As shown in Figure 8, the melting point increases with increasing basicity of the decarburized slag. Generally, the basicity of decarburized slag is around 3.
[0011] Decarburized slag contains components that increase its basicity. Therefore, as described in Patent Document 4, if a large amount of decarburized slag is left in the converter, the basicity of the decarburized slag increases, leading to a problem of a higher melting point. In other words, when the basicity of decarburized slag increases, its melting point rises, which leads to a problem of poor remeltable properties of the decarburized slag. If the remeltable properties of decarburized slag deteriorate, for example, it may not completely dissolve at the processing temperature for Si-de-P-de-treatment. As a result, it may not be possible to remove sufficient phosphorus from the molten steel, which may lead to a decrease in product quality.
[0012] The present invention has been made in view of the above problems, and aims to provide a method for cooling decarburized slag, a method for manufacturing steel, and a coolant for decarburized slag that can suppress the occurrence of bumping phenomena in the refining process and maintain the quality of the product. [Means for solving the problem]
[0013] [1] A method for cooling decarburized slag, comprising a mixing step of mixing a coolant for decarburized slag obtained by magnetically attaching steelmaking slag with the decarburized slag. [2] The method for cooling decarburized slag according to [1], wherein the mixing step is performed by shaking the container after a coolant for the decarburized slag has been introduced into the container containing the decarburized slag. [3] The decarburization process involves removing molten iron from the raw materials, A method for manufacturing steel, comprising: a cooling step of cooling the decarburized slag generated in the decarburization step using a coolant for decarburized slag obtained by magnetically attaching steelmaking slag. [4] A supply process that supplies raw materials containing at least molten iron into a container, The process includes a Si-de-P step in which the raw material is subjected to Si-de-treatment and P-de-treatment, The method for manufacturing steel according to [3], wherein the supply step, the Si-de-P step, and the decarburization step are performed sequentially after the cooling step is completed. [5] A coolant for decarburized slag, which contains iron as a main component, contains at least one of CaO and SiO2, and each of these components is derived from steelmaking slag. [6] A method for producing a coolant for decarburized slag, comprising a collecting step of collecting a component containing iron from steelmaking slag using a magnetic force.
Advantages of the Invention
[0014] According to the method for cooling decarburized slag of the present invention, since the decarburized slag is cooled using a coolant for decarburized slag that contains iron as a main component and contains at least one of CaO and SiO2 as a component, it is possible to prevent boiling over. Therefore, it is possible to enhance the safety of the operation. Further, since the refining process can be performed while maintaining the melting point of the decarburized slag in an appropriate state, each step of the refining process can be appropriately executed, and it is possible to maintain the quality of the product.
Brief Description of the Drawings
[0015] [Figure 1] It is a flowchart showing each step of the refining process. [Figure 2] It is an explanatory diagram showing the mode of the supply step in FIG. 1. [Figure 3] It is an explanatory diagram showing the mode of the desiliconization and dephosphorization step in FIG. 1. [Figure 4] It is an explanatory diagram showing the mode of the first discharge step in FIG. 1. [Figure 5] It is an explanatory diagram showing the mode of the decarburization step in FIG. 1. [Figure 6] It is an explanatory diagram showing the mode of the second discharge step in FIG. 1. [Figure 7] It is an explanatory diagram showing the mode of the cooling step in FIG. 1. [Figure 8] It is a ternary diagram showing the relationship between the composition and melting point of decarburized slag.
Modes for Carrying Out the Invention
[0016] The following describes an example in which the decarburized slag cooling method of the present invention is used in the refining process, which is a steel manufacturing process. Figure 1 shows each step of the refining process. As shown in Figure 1, the refining process begins with a supply step (step S101) in which molten iron is supplied to a converter, which is a container.
[0017] Next, a desilicon and dephosphorussing step (step S102) is performed to remove silicon (Si) and phosphorus (P) from the molten iron supplied to the converter. A first discharge step (step S103) is performed to discharge the slag generated in the desilicon and dephosphorussing step (step S102) out of the converter.
[0018] Next, a decarburization process (step S104) is performed to remove carbon (C) from the molten iron after the first discharge process in step S103 has been carried out. A second discharge process (step S105) is performed to discharge the molten steel that has undergone the decarburization process in step S104 out of the converter. Finally, a cooling process (step S106) is performed to cool the slag generated in the decarburization process. In this way, the molten iron produced in the blast furnace becomes molten steel through the sequentially performed processes from the supply process in step S101 to the cooling process in step S106.
[0019] Figure 2 shows the configuration of the supply process in step S101. In this embodiment, an example in which a converter is used as an example of a refining vessel will be described. In the supply process of step S101, as shown in Figure 2, first, iron scrap 10 is charged into the converter 20. Molten iron 30 produced in a blast furnace (not shown) is stored in a molten iron ladle 40. The molten iron 30 in the molten iron ladle 40 is charged into the converter 20.
[0020] Iron scrap can include, for example, block-shaped scrap iron obtained by finely crushing used cast iron products, as defined in the "Unified Standards for Inspection and Acceptance of Iron Scrap" of the Japan Iron and Steel Association, and pig iron shavings, which are cutting waste generated during the production of cast iron products.
[0021] Iron scrap is not an essential material for the refining process. Iron scrap can be used as appropriate depending on the method of implementation. Furthermore, it is preferable to use molten iron 30 in which the concentrations of Si (silicon), P (phosphorus), and S (sulfur) have been reduced to predetermined concentrations, but it is not limited to this.
[0022] Figure 3 shows the configuration of the Si-de-P process in step S102. As shown in Figure 3, in the Si-de-P process, an upper blowing lance 50 is inserted into the converter 20 from above, and oxygen is supplied from this upper blowing lance 50. Oxygen is supplied until the concentrations of Si and P in the molten iron fall below predetermined concentrations.
[0023] Furthermore, the Si and P concentrations in the molten iron 30 are measured, for example, by emission spectroscopy. That is, the top-blowing lance 50 stops supplying oxygen and is withdrawn from the converter 20 when the Si and P concentrations in the molten iron reach predetermined values.
[0024] Figure 4 shows the configuration of the first discharge step in step S103. As shown in Figure 4, in the first discharge step, the converter 20 is tilted from an upright position. The slag generated in the Si-de-P-de-step in step S102 is discharged from the converter 20 to a slag pot (not shown).
[0025] Figure 5 shows the configuration of the decarburization process in step S104. As shown in Figure 5, in the decarburization process, the converter 20 is moved from a tilted position to an upright position. Next, an upper blowing lance 50 is charged into the converter 20, and oxygen is supplied from this upper blowing lance 50. The supply of oxygen continues until the carbon content of the molten iron 30 falls below a predetermined concentration. Note that the supply of oxygen in the decarburization process is not limited to this configuration and may also be carried out by so-called bottom blowing.
[0026] Furthermore, the carbon concentration of the molten iron 30 is measured, for example, by emission spectroscopy. That is, the top-blowing lance 50 stops supplying oxygen and is withdrawn from the converter 20 when the carbon concentration of the molten iron reaches a predetermined value.
[0027] Figure 6 shows the configuration of the second discharge process in step S105. In the second discharge process, the converter 20 is tilted from an upright position. Molten steel is tapped into the molten steel ladle 60 from the discharge port 21 provided on the side wall of the converter 20.
[0028] Figure 7 shows the configuration of the cooling process in step S106. In the cooling process, the decarburized slag 80 generated in the decarburization process in step S105 is cooled and solidified in the converter 20.
[0029] The cooling process begins with a mixing step in which the coolant 70 of the decarburized slag is mixed with the decarburized slag 80. Specifically, in the mixing step, the coolant 70 of the decarburized slag is introduced into the converter 20 containing the decarburized slag 80.
[0030] Here, the coolant 70 of the decarburized slag is required to be less prone to bumping during the charging of molten iron 30. That is, the occurrence of bumping can be reduced by reducing the reactivity between the decarburized slag 80 and the carbon in the molten iron 30. Furthermore, it is preferable that the coolant 70 of the decarburized slag is quickly remelted in the Si-de-P-de-step S102.
[0031] In other words, it is preferable that the coolant 70 does not contain excess FeO as a component and does not cause an increase in the melting point of the decarburized slag 80. Such a coolant 70 is preferably derived from steelmaking slag.
[0032] When the coolant 70 for decarburized slag is derived from steelmaking slag, the coolant 70 is manufactured, for example, by using magnetism to extract iron-containing components from the steelmaking slag (hereinafter also referred to as magnetic deposition). A lifting magnet can be used when extracting these components from the steelmaking slag. In other words, the coolant 70 for decarburized slag used in the cooling process is obtained by magnetic deposition of steelmaking slag.
[0033] Furthermore, the particle size of iron magnetized from steelmaking slag is typically less than 100 mm. Therefore, heat transfer from the decarburized slag 80 to the coolant 70 is expected to proceed easily. By using the components magnetized from steelmaking slag as the coolant 70, it becomes possible to achieve iron source recycling within the steelmaking process.
[0034] The steelmaking slag is not particularly limited, but it is preferable that it has a low sulfur content. This is to avoid increasing the sulfur content of the molten iron 30 when it melts in the Si-de-P de-process in step S102. Specifically, it is preferable that the slag produced when desulfurization is performed before charging into the converter 20 is not used as a coolant raw material because it has a high sulfur content.
[0035] The coolant 70 obtained by magnetically attaching steelmaking slag contains iron as its main component and at least one of CaO and SiO2 as a component. The coolant 70 preferably contains 20 to 60% by mass of iron. The coolant 70 more preferably contains 30 to 60% by mass of iron, and even more preferably contains 40 to 50% by mass.
[0036] The coolant 70 preferably contains 10 to 40% by mass of CaO, and more preferably 20 to 30% by mass.
[0037] The coolant 70 preferably contains 5 to 15% by mass of SiO2, and more preferably contains 5 to 10% by mass.
[0038] In the mixing process, after the coolant 70 is introduced into the converter 20 as described above, the converter 20 is oscillated. By oscillating the converter 20 in this way, the entire decarburized slag 80 can be cooled, and thus the decarburized slag 80 can be solidified uniformly.
[0039] In the decarburized slag cooling method of the present invention, it is preferable that the decarburized slag 80 solidified as described above is left in the converter 20, and that the steps from the supply step S101 to the cooling step S106 are performed sequentially. That is, it is preferable to return to the supply step S101, again charge the next batch of molten iron 30 and scrap iron 10 into the converter 20, and repeat the steps up to the cooling step S106.
[0040] As described above, the decarburized slag cooling method uses a coolant made of decarburized slag that contains iron as its main component and at least one of CaO and SiO2 as components, thus preventing bumping.
[0041] Therefore, it is possible to improve safety during the work. In addition, since the refining process can be carried out while maintaining the melting point of the decarburized slag at an appropriate level, each step of the refining process can be executed properly, and the quality of the product can be maintained. Furthermore, because the coolant for decarburized slag of the present invention has a lower FeO content compared to the ore, it can effectively suppress the phenomenon of bumping.
[0042] Furthermore, for example, by using a coolant made from decarburized slag produced by magnetic attachment from fine-grained steelmaking slag generated in casting or converters, the iron source generated during steelmaking can be utilized efficiently.
[0043] In this embodiment, the process was described in a manner that includes steps such as a Si-decarbonization and P-decarbonization step. However, as long as a decarburization step and a cooling step for cooling the decarburized slag generated in the decarburization step are included, other steps can be performed as desired. [Examples]
[0044] A solid coolant was added to the molten decarburized slag contained in the converter to cool and solidify it. The converter used was a top-bottom blowing type with a capacity of 375 tons of molten iron. 3 to 10 tons of decarburized slag were used. 1 to 6 tons of coolant were used.
[0045] Specifically, ten examples (Tests No. 1-10) were tested, varying the amount of decarburized slag, the amount of coolant, and the type of coolant. The amounts of decarburized slag, coolant, and coolant for Tests No. 1-10 are shown in Table 1.
[0046] Regarding the coolant, for the decarburized slag in Tests No. 1 to 7 (Inventive Examples), a metal obtained by magnetically attaching steelmaking slag was used as the coolant. For the decarburized slag in Tests No. 8 to 10 (Comparative Examples), calcined lime (CaO) and limestone (CaCO3) were used as the coolants.
[0047] Next, after the iron scrap was charged into the converter, molten iron that had been adjusted to the specified composition in the molten iron pretreatment process was charged into the converter. Subsequently, a Si-de-P-de-process was carried out on the molten iron in the converter.
[0048] The evaluation involved checking for the occurrence of bumping phenomena from the supply process where molten iron is charged until the completion of the Si-P-decomposition process. The results are shown in Table 1. Specifically, those without bumping phenomena were considered acceptable and are indicated with (○) in Table 1. Those with bumping phenomena were considered unacceptable and are indicated with (×) in Table 1.
[0049] [Table 1]
[0050] As shown in Table 1, in all cases, no bumping occurred when the molten iron was charged in Tests No. 1 to 7 (Inventive Examples), and therefore all were evaluated as (○). This is thought to be because the decarburized slag coolant in Tests No. 1 to 7 (Inventive Examples) did not contain enough oxygen to react with the carbon in the molten iron, and therefore carbon dioxide was not produced.
[0051] In tests No. 8 and 9 (comparative examples), no bumping occurred when the molten iron was charged. This is thought to be because the coolant in the decarburized slag of tests No. 8 and 9 (comparative examples) did not contain enough oxygen to react with the carbon in the molten iron, and therefore no carbon dioxide was produced.
[0052] In tests No. 8-9 (comparative examples), as shown in the three-phase diagram in Figure 8, the melting point increases as the amount of calcined lime (CaO) in the slag increases. This leads to problems with the melting properties of the coolant. Furthermore, using calcined lime incurs additional costs for auxiliary materials and utilities, resulting in poor economic efficiency.
[0053] In Test No. 10 (Comparative Example), a sudden boiling phenomenon occurred during oxygen blowing in the Si-P-de-process. The limestone (CaCO3) used as a coolant in Test No. 10 (Comparative Example) contains oxygen atoms. It is thought that these oxygen atoms in the limestone reacted with carbon to produce carbon dioxide.
[0054] From the above results, it was confirmed that the molten steel manufacturing method of the present invention suppresses the bumping phenomenon when molten iron is charged into the converter. Furthermore, the coolant for the decarburized slag in Tests No. 1 to 7 (Inventive Examples) does not increase the basicity of the decarburized slag, thus maintaining the melting point of the decarburized slag. This makes it possible to maintain the quality of the product. Moreover, by using this coolant, it was possible to recycle the iron source. [Explanation of symbols]
[0055] 10 Iron scrap 20 Converter 30 molten iron 40 molten iron pots 50 Upward-blowing lance 60 molten steel pots
Claims
1. The process includes a mixing step of mixing a coolant, which is decarburized slag obtained by magnetically attaching steelmaking slag and has a particle size of less than 100 mm, with the decarburized slag. The method for cooling decarburized slag, wherein the coolant contains 20 to 60% by mass of iron, 10 to 40% by mass of CaO, and 5 to 15% by mass of SiO₂.
2. The method for cooling decarburized slag according to claim 1, wherein the mixing step is performed by shaking the container after a coolant for the decarburized slag has been introduced into the container containing the decarburized slag.
3. A method for manufacturing steel using the decarburized slag cooling method described in claim 1 or 2, The decarburization process involves removing molten iron from the raw materials, A method for manufacturing steel, comprising: a cooling step of cooling the decarburized slag generated in the decarburization step using a coolant for decarburized slag obtained by magnetically attaching steelmaking slag.
4. A supply process that supplies raw materials containing at least molten iron into a container, The process includes a Si-de-P step in which the raw material is subjected to Si-de-treatment and P-de-treatment, The method for manufacturing steel according to claim 3, wherein the supply step, the Si-de-P step, and the decarburization step are performed sequentially after the cooling step is performed.
5. A coolant for decarburized slag, which is used in the decarburized slag cooling method described in claim 1 or 2, It contains iron as its main component, and also contains CaO and SiO ２ It contains at least one of the above, and each of these components is derived from steelmaking slag. A coolant made from decarburized slag containing 20-60% by mass of iron, 10-40% by mass of CaO, and 5-15% by mass of SiO₂.
6. A method for producing a coolant for decarburized slag, using the decarburized slag cooling method described in claim 1 or 2, A method for producing a coolant from decarburized slag, comprising a sampling step of extracting iron-containing components from steelmaking slag using magnetic force.