How to use iron sources

Abstract

To provide a method for utilizing an iron source capable of suppressing an increase in refining load when steelmaking slag is used as the iron source.SOLUTION: A method for utilizing an iron source includes: an addition step of adding granular metal obtained by crushing steelmaking slag and magnetic force sorting to hot metal; and a desulfurization step of subjecting the hot metal to hot metal desulfurization treatment after the addition step. The granular metal contains CaO and S.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for utilizing an iron source. [Background technology]

[0002] In the steelmaking process, a cold iron source is added to molten iron in order to improve iron yield. For example, Patent Document 1 provides a technique that can add a cold iron source to a molten iron ladle while suppressing the amount of metal adhering to the molten iron ladle. Also, Patent Document 2 provides a technique that reduces heat loss by placing a cold iron source in an empty molten iron ladle. In addition, various slags are generated during the steelmaking process, and these slags contain impurities (oxides of Si, P, S, Mn, Al, etc.) and iron. This iron is recovered and reused as an iron source. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-189841 [Patent Document 2] Japanese Patent Application Laid-Open No. 2007-113055 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the technology of Patent Document 1 does not mention the components of the cold iron source to be added, and there is a possibility that the cost of auxiliary materials will increase significantly if impurities are removed after the cold iron source is dissolved in the molten iron.Furthermore, the technology of Patent Document 2 also does not mention the components, and there is a possibility that the cost of auxiliary materials will increase in the next process. Furthermore, when steelmaking slag is added to molten iron, the refining costs are expected to increase because steelmaking slag contains many impurities. In particular, S cannot be removed by oxidation reactions, which causes a significant increase in refining costs.

[0005] Therefore, the present invention has been made in light of the above-mentioned problems, and aims to provide a method for utilizing an iron source that can suppress an increase in the refining load when steelmaking slag is used as an iron source. [Means for solving the problem]

[0006] (1) According to one aspect of the present invention, there is provided a method for utilizing an iron source, the method comprising: an adding step of adding, to molten iron, powdered or granular ingots obtained by crushing steelmaking slag and magnetically separating the ingots; and a desulfurization step of subjecting the molten iron to a hot metal desulfurization treatment after the adding step, wherein the powdered or granular ingots contain CaO and S. (2) In the above-mentioned configuration (1), in the adding step, the powdered metal is added to the molten iron charged in a molten iron ladle. (3) In the above-mentioned configuration (1) or (2), the components of the granular ingot satisfy the following: CaO is 15 mass% or more and 35 mass% or less, T.Fe is 20 mass% or more and 40 mass% or less, M.Fe is 10 mass% or more, and basicity is 2.5 or more. (4) In any one of the above (1) to (3), the components of the powdery ingot satisfy the condition that S is 0.001% or more and 0.05% or less. (5) In any one of the above (1) to (4), the particle size of the granular metal ingot satisfies the range of 0.5 mm to 5 mm. (6) In any one of the configurations (1) to (5) above, the amount of the molten iron ladle filled is 200 tons or more and 400 tons or less, and the components of the molten iron satisfy the following: Si is 0.01 mass% or more and 1.0 mass% or less, and C is 4.0 mass% or more and 5.3 mass% or less. [Effects of the Invention]

[0007] According to one aspect of the present invention, a method for utilizing an iron source is provided that can suppress an increase in refining load when steelmaking slag is used as an iron source. [Brief explanation of the drawings]

[0008] [Figure 1]FIG. 2 is a schematic diagram showing an addition step in one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0009] In the following detailed description, embodiments of the present invention will be described with reference to the drawings. In the description of the drawings, identical or similar parts are designated by identical or similar reference numerals, and redundant explanations will be omitted. The drawings are schematic and may differ from the actual product. Furthermore, the embodiments shown below exemplify devices and methods for embodying the technical concept of the present invention, and the technical concept of the present invention does not specify the materials, structure, arrangement, etc. of component parts as described below. The technical concept of the present invention can be modified in various ways within the technical scope defined by the claims.

[0010] <How to use iron sources> A method for utilizing an iron source according to one embodiment of the present invention will be described with reference to Fig. 1. In this embodiment, an adding step is performed in which powdered or granular ingots obtained by pulverizing steelmaking slag and magnetically separating them are added to molten pig iron, followed by a desulfurization step in which the molten pig iron is desulfurized. Note that no other refining processes are performed between the adding step and the desulfurization step.

[0011] In the addition process, as shown in Figure 1, granular metal ingots 3 are added by free-falling from above into molten pig iron 2 filled in a molten pig iron ladle 1. The granular metal ingots 3 are obtained by crushing and magnetically separating steelmaking slag generated in a converter or the like, and contain CaO and S. By including CaO in the granular metal ingots 3, the CaO contained therein acts as a desulfurization agent in the desulfurization process, thereby suppressing an increase in the amount of desulfurization agent due to the pickup of S in the granular metal ingots 3 during the desulfurization process.

[0012] The components of the granular ingot 3 preferably satisfy a CaO content of 15 mass% to 35 mass% and a basicity of 2.5 or more, and more preferably a CaO content of 15 mass% to 30 mass% and a basicity of 2.5 or more. By making the CaO content of the granular ingot 3 15 mass% or more and a basicity of 2.5 or more, the granular ingot 3 can fully fulfill its role as a desulfurization agent in the desulfurization process and suppress an increase in the amount of desulfurization agent. The basicity is the ratio of the SiO2 content (mass%) to the CaO content (mass%) in the components of the granular ingot 3. In other words, the granular ingot 3 also contains SiO2 as a component depending on the CaO content and basicity. Furthermore, if the CaO content of the granular ingot 3 exceeds 35 mass%, the iron content in the granular ingot 3 decreases, thereby reducing the effect of improving iron yield. This increases the impact of heat loss (reduction in molten iron temperature) on the improvement of iron yield, resulting in increased production costs.

[0013] The metal powder 3 preferably has a total iron content (T.Fe) of 40 mass% or less and a metallic iron content (M.Fe) of 10 mass% or more. The metal powder 3 obtained from steelmaking slag contains iron oxides such as FeO and Fe2O3 in addition to metallic iron. As the T.Fe content of the metal powder 3 increases, the iron oxide content also increases. This raises the concern that the addition of the metal powder 3 will increase the oxygen concentration in the molten pig iron 2, thereby reducing the desulfurization efficiency in the desulfurization process. Therefore, if the T.Fe content exceeds 40 mass%, the iron oxide content also increases, reducing the desulfurization efficiency in the desulfurization process. Therefore, the T.Fe content of the metal powder 3 is preferably 40 mass% or less. As the M.Fe content of the metal powder 3 is less than 10 mass%, the impact of heat loss on the improvement of iron yield increases, resulting in increased production costs.

[0014] Furthermore, the components of the metal powder 3 preferably satisfy the following: S content is 0.001 mass% or more and 0.05 mass% or less. If the S content of the metal powder 3 exceeds 0.05 mass%, the amount of S picked up from the metal powder 3 to the molten pig iron 2 increases, and the variation in the amount picked up also increases, so the effect of reducing the amount of desulfurization agent in the desulfurization process decreases. Furthermore, the particle size of the powdered metal 3 is 0.5 mm or more and 5 mm or less. If the particle size of the powdered metal 3 is less than 0.5 mm, there is a high risk of dust generation. On the other hand, if the particle size of the powdered metal 3 is more than 5 mm, there is a risk that the unmelted powdered metal 3 will damage the refractories in the molten iron ladle 1 during the desulfurization process.

[0015] The components of the molten pig iron 2 preferably satisfy the following: Si is 0.01 mass% or more and 1.0 mass% or less, and C is 4.0 mass% or more and 5.3 mass% or less. The amount of molten pig iron 2 charged into the molten pig iron ladle 1, i.e., the amount of molten pig iron 2 that can be contained in the molten pig iron ladle 1, is preferably 200 t or more and 400 t or less. In the desulfurization step, the molten pig iron 2 to which the fine or granular ingots 3 have been added is subjected to desulfurization. The desulfurization method in the desulfurization step is not particularly limited, but for example, a mechanical stirring type desulfurization method can be used.

[0016] <Modification> Although the present invention has been described above with reference to specific embodiments, it is not intended that the invention be limited by these descriptions. By referring to the description of the present invention, other embodiments of the present invention that include various modifications in addition to the disclosed embodiments will be apparent to those skilled in the art. Therefore, it should be understood that the embodiments of the invention set forth in the claims also encompass embodiments that include these modifications described herein, either alone or in combination. For example, in the above embodiment, the method of adding the powdery ingot 3 is to charge the powdery ingot 3 from above the molten pig iron 2, but the present invention is not limited to this example. The method of adding the powdery ingot 3 is not particularly limited, and other methods may be used, such as injecting the powdery ingot 3 into the molten pig iron 2 using an injection lance.

[0017] In the above embodiment, the fine and granular ingots 3 are added to the molten pig iron 2 charged in the hot metal ladle 1 in the adding step, and the desulfurization step is performed immediately after the adding step. However, the present invention is not limited to this example. For example, the fine and granular ingots 3 may be added to the molten pig iron 2 before desulfurization, and may be added to the molten pig iron 2 contained in another hot metal vessel such as a torpedo, or to the molten pig iron 2 tapped from a blast furnace during casthouse desiliconization. Note that if the fine and granular ingots 3 are placed in the hot metal vessel beforehand and then the molten pig iron 2 is charged into the hot metal vessel, dust may be generated during the charging of the molten pig iron, which may cause operational problems or a decrease in yield. However, adding the fine and granular ingots 3 to the molten pig iron 2 contained in the hot metal vessel can reduce this risk. [Example]

[0018] Next, an example conducted by the present inventors will be described. In this example, the addition process and desulfurization process of the above embodiment were performed, and the amount of desulfurization agent used in the desulfurization process was evaluated. The amount of the hot metal ladle 1 filled was 200 tons or more and 400 tons or less. The components of the hot metal 2 were 0.01 mass% to 1.0 mass% Si and 4.0 mass% to 5.3 mass% C. The components of the granular ingot 3 added in the addition process were 15 mass% to 35 mass% CaO, 0.001 mass% to 0.05 mass% S, 20 mass% to 40 mass% T.Fe, 10 mass% or more M.Fe, and a basicity of 2.5 or more. The particle size of the granular ingot 3 was 0.5 mm to 5 mm. The amount of the fine metal particles 3 added is 2.5 kg or more and 7.0 kg or less per ton of molten iron.

[0019] In the examples, the reduction in the amount of desulfurization agent was evaluated by comparing the actual amount of desulfurization agent used in the desulfurization process with the amount of desulfurization agent used (taking into account the amount of desulfurization agent pickup) in the case where the S content in the molten pig iron 2 increases due to S contained in the fine or granular ingots 3. As a result, it was confirmed that the actual amount of desulfurization agent used can be reduced by 38% compared to the amount taking into account the amount of desulfurization agent pickup. In other words, it was confirmed that the method for using an iron source according to the above embodiment can suppress an increase in the refining load when steelmaking slag is used as the iron source. [Explanation of symbols]

[0020] 1 molten iron ladle 2. Molten iron 3 Powdered metal

Claims

1. an adding step of adding powdered metal obtained by crushing steelmaking slag and magnetically separating it to molten iron; a desulfurization step of subjecting the molten iron to a molten iron desulfurization treatment after the adding step; Equipped with The powdered metal contains CaO and S, The components of the powdery or granular ingot satisfy the following: CaO is 15 mass% or more and 35 mass% or less, T.Fe is 40 mass% or less, M.Fe is 10 mass% or more, and basicity is 2.5 or more; A method for utilizing an iron source, wherein no other refining process is carried out between the adding step and the desulfurizing step.

2. The method for using an iron source according to claim 1 , wherein the adding step includes adding the powdered or granular ingot to the molten iron charged in a molten iron ladle.

3. 3. The method for utilizing an iron source according to claim 1, wherein the components of the powdery or granular ingot satisfy a S content of 0.001 mass% or more and 0.05 mass% or less.

4. 4. The method for utilizing an iron source according to claim 3, wherein the particle size of the granular metal ingot satisfies 0.5 mm to 5 mm.

5. The amount of the molten iron ladle filled is 200 tons or more and 400 tons or less, 3. The method for using an iron source according to claim 2, wherein the molten iron contains 0.01 mass% or more and 1.0 mass% or less of Si and 4.0 mass% or more and 5.3 mass% or less of C.

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