Method for adding deoxidizing agents and lime

Abstract

This disclosure aims to provide a method for adding a deoxidizing agent and lime that can easily improve the desulfurization effect of molten steel that has been tapped. [Solution] A method for adding a deoxidizing agent and lime according to one aspect of the present disclosure comprises the steps of receiving molten steel tapped from a converter or electric furnace in a ladle, and adding a deoxidizing agent and lime to the molten steel being received in the ladle, wherein T is the time from the start to the end of receiving the steel in the ladle, the addition of the deoxidizing agent is started within 0.10T, and the addition of lime is finished within 0.50T.

Description

[Technical Field]

[0001] The present disclosure relates to a method for adding a deoxidizer and lime to molten steel. [Background Art]

[0002] In general, since sulfur in steel reduces the properties of the steel, it is desirable to keep the concentration of sulfur low. In the production of low-sulfur steel, in addition to desulfurization treatment of molten iron tapped from a blast furnace, desulfurization treatment may also be performed at the molten steel stage. A low-cost desulfurization method for performing desulfurization treatment at the molten steel stage is known (Japanese Patent Application Laid-Open No. 10-102135). [Prior Art Literature] [Patent Literature]

[0003] [Patent Literature 1] Japanese Patent Application Laid-Open No. 10-102135 [Summary of the Invention] [Problem to be Solved by the Invention]

[0004] In the desulfurization method disclosed in Patent Document 1, a deoxidizer is added to molten steel being tapped into a ladle such that sol.Al in the molten steel in the ladle reaches a predetermined value, and after the addition of the deoxidizer is completed, a lime-based desulfurizing agent is added to the molten steel being tapped. It is stated that by adding the deoxidizer in advance to sufficiently reduce the oxygen potential in the molten steel, sufficient desulfurization can be achieved even when an inexpensive lime-based desulfurizing agent is used. Some types of lime contain calcium carbonate (CaCO₃). When such lime is added to the tapping stream, carbon dioxide gas is generated during dissolution, which easily causes slag forming, and slag removal may be required in some cases. Furthermore, since the stirring energy in the ladle from tapping decreases as time elapses from the start of tapping, if the lime is added after the completion of the addition of the deoxidizer, sufficient stirring cannot be performed, and there is a possibility that a desired desulfurization effect cannot be obtained.

[0005] In view of the circumstances described above, this disclosure aims to provide a deoxidizing agent and a method for adding lime that can easily improve the desulfurization effect of molten steel. [Means for solving the problem]

[0006] A method for adding a deoxidizing agent and lime according to one aspect of the present disclosure for solving the above problems comprises the steps of receiving molten steel tapped from a converter or electric furnace in a ladle, and adding a deoxidizing agent and lime to the molten steel being received in the ladle, wherein T is the time from the start to the end of receiving the steel in the ladle, the addition of the deoxidizing agent is started within 0.10T, and the addition of lime is finished within 0.50T. [Effects of the Invention]

[0007] The method of adding the deoxidizing agent and lime can easily improve the desulfurization effect of the molten steel that has been tapped. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a graph showing the relationship between the timing of lime addition and the desulfurization rate. [Modes for carrying out the invention]

[0009] [Description of Embodiments in this Disclosure] First, the embodiments of this disclosure will be listed and described.

[0010] (1) A method for adding a deoxidizing agent and lime according to one aspect of the present disclosure comprises the steps of receiving molten steel tapped from a converter or electric furnace in a ladle, and adding a deoxidizing agent and lime to the molten steel being received in the ladle, wherein the time from the start to the end of receiving the steel in the ladle is T, the addition of the deoxidizing agent is started within 0.10T, and the addition of lime is finished within 0.50T.

[0011] In this method of adding the deoxidizing agent and lime (hereinafter also simply referred to as the "addition method"), the deoxidizing agent and lime are added to the molten steel being received in the ladle. Therefore, even if the lime contains calcium carbonate, slag forming can be suppressed, and steel can be obtained efficiently. Furthermore, in this addition method, the addition of the lime is completed within 0.50T of the time T from the start to the end of receiving the steel in the ladle. That is, the lime is added in the first half of the tapping process when the stirring energy in the ladle is high. As a result, the lime can be sufficiently stirred, and the desulfurization effect of the molten steel tapped into the ladle can be easily improved.

[0012] (2) In the above addition step in (1), the addition of the deoxidizing agent may be started before the addition of the lime. The desulfurization effect can be improved by starting the addition of the deoxidizing agent before the addition of the lime.

[0013] (3) In (1) or (2) above, the amount of lime added per ton of molten steel may be 0.0075 tons or more and 0.0140 tons or less. By setting the amount of lime added within the above range, the slag in the molten steel can be made to have a composition that has desulfurization ability, and the desulfurization effect can be further improved.

[0014] (4) In any of (1) to (3) above, an alloy that adjusts the composition of the molten steel may be added in the addition step, and the addition of the alloy may be started before the addition of lime. Starting the addition of the alloy before the addition of lime can improve the certainty of adjusting the composition of the molten steel.

[0015] (5) In any of (1) to (4) above, the desulfurization rate D in the following formula 1 may be 10% or more. A desulfurization rate D of 1 in the following formula 1 is 10% or more, which facilitates secondary refining in subsequent processes. D={1-(S1 / S2)}×100 (1) In Formula 1 above, "S1" represents the sulfur content [mass%] in molten steel after the completion of lime addition, and "S2" represents the sulfur content [mass%] in molten steel before the start of lime addition.

[0016] [Detailed Description of Embodiments of the Present Disclosure] Hereinafter, one embodiment of the addition method will be described.

[0017] The addition method comprises: a step of receiving molten steel tapped from a converter or an electric arc furnace in a ladle; and a step of adding a deoxidizer and lime to the molten steel received by the ladle, wherein letting T be the time from the start to the end of steel receiving in the ladle, the addition of the deoxidizer is started within 0.10T, and the addition of lime is completed after 0.50T.

[0018] [Steel Receiving Step] In the steel receiving step, the converter or electric arc furnace is tilted to pour the stored molten steel into the ladle. The converter, electric arc furnace and ladle are not particularly limited, and may be any known converter, electric arc furnace and ladle. The molten steel contains sulfur (S). The sulfur content S2 in the molten steel is not particularly limited, and for example, may be 0.0020 mass% or more and 0.0150 mass% or less.

[0019] [Adding Step] The deoxidizer added to the molten steel received by the ladle is not particularly limited, and examples thereof include aluminum (Al), ferrosilicon (FeSi) alloy, silicomanganese (SiMn) alloy, and the like. A plurality of types of deoxidizers may be added to the molten steel.

[0020] The lime added to the molten steel received by the ladle is not particularly limited as long as its main component is calcium oxide (CaO), and may contain CaCO3. Note that the main component refers to the component with the highest content, for example, it means a component with a content of 50 mass% or more.

[0021] Let the time from the start to the end of steel receiving in the ladle be T, the addition of the deoxidizer starts within 0.10T, and the addition of the lime ends within 0.50T. Both the deoxidizer and the lime are added to the molten steel in the ladle. That is, neither the deoxidizer nor the lime is added to the tapped steel stream (the molten steel flowing from the converter to the ladle). By not adding them to the tapped steel stream, slag foaming can be suppressed even if the lime contains CaCO₃.

[0022] The deoxidizer preferably starts to be added before the addition of the lime is started. By starting the addition of the deoxidizer before the addition of the lime is started, the oxygen potential (dissolved oxygen concentration) in the molten steel in the ladle can be reduced. For this reason, the reliability of the desulfurization effect achieved by the subsequently added lime can be improved.

[0023] With respect to the addition start timing of the deoxidizer in the time T from the start to the end of steel receiving in the ladle (hereinafter simply referred to as "steel receiving time T"), it may be within 0.09T, may be within 0.07T, or may be within 0.05T. The addition of the deoxidizer may start simultaneously with the start of the steel receiving (0.00T). By setting the addition start of the deoxidizer to the above timing, the deoxidizer can be effectively dissolved by the stirring energy from steel tapping, and the dissolved oxygen concentration can be easily and reliably reduced.

[0024] The addition of the deoxidizer preferably ends before the addition of the lime ends, more preferably before the addition of the lime is started, or during the addition of the lime. As the addition end timing of the deoxidizer, for example, it may be within 0.48T, or may be within 0.45T.

[0025] The amount of the deoxidizing agent added per ton of molten steel is not particularly limited, but for example, the lower limit of the amount of the deoxidizing agent added may be 0.50 ton or 0.75 ton. The upper limit of the amount of the deoxidizing agent added may be 1.40 ton or 1.35 ton. By setting the amount of the deoxidizing agent added within the above range, the desulfurization effect by lime can be promoted. Note that if multiple types of deoxidizing agents are added, the amount of the deoxidizing agent added is the total amount.

[0026] In the above-mentioned addition process, an alloy for adjusting the composition of the molten steel may be further added. The addition of the alloy should preferably begin before the addition of lime. The timing of the start of the addition of the alloy may be at the same time as the start of the addition of the deoxidizing agent, or it may be after the start of the addition of the deoxidizing agent. The timing of the end of the addition of the alloy is preferably before the end of the addition of lime, and may be at the same time as the end of the addition of the deoxidizing agent, or it may be before or after the end of the addition of the deoxidizing agent. The alloy is not particularly limited, and may be a known alloy for adjusting the composition of molten steel, such as a ferromanganese (FeMn) alloy or a ferrochrome (FeCr) alloy.

[0027] The completion time for adding lime is within 0.50T. The completion time for adding lime may also be within 0.45T or within 0.40T. It is preferable that the addition of lime be completed after the addition of the deoxidizing agent and the alloy is completed, for example, after 0.20T, or after 0.25T or after 0.30T. By completing the addition of lime at the above time, the stirring energy from the steel tapping can be efficiently utilized, and desulfurization can be performed easily and reliably.

[0028] The addition of lime should ideally begin after the addition of the deoxidizing agent. In other words, the addition of lime should ideally begin at a concentration greater than 0.10T. The addition of lime may begin at 0.15T or later, or at 0.20T or later, or at 0.25T or later. When adding the alloy, the addition of lime should begin after the addition of the alloy. If the addition of lime begins before the addition of the deoxidizing agent and the alloy, the added lime may form a film on the surface of the molten steel in the ladle, preventing the dissolution of the added deoxidizing agent and alloy in the molten steel from being promoted, which may reduce the effectiveness of deoxidation (reduction of dissolved oxygen concentration) and the reliability of component adjustment. By starting the addition of lime after the addition of the deoxidizing agent and the alloy, the reduction of dissolved oxygen concentration in the molten steel and the reliability of component adjustment can be improved, as can the reliability of the desulfurization effect due to the reduction of dissolved oxygen concentration.

[0029] The amount of lime added per ton of molten steel is preferably between 0.0075 tons and 0.0140 tons. The lower limit of the amount of lime added may be 0.0077 tons or 0.0079 tons. The upper limit of the amount of lime added may be 0.0135 tons or 0.0130 tons. By setting the amount of lime added within the above range, the slag in the molten steel can be made to have a composition with high desulfurization ability, and the desulfurization effect can be further improved.

[0030] The desulfurization rate D of the molten steel produced by this additive method should be 10% or more. The desulfurization rate D is expressed by the following formula 1. D={1-(S1 / S2)}×100 (1) In Formula 1 above, "S1" is the sulfur content [mass%] in the molten steel after the addition of lime has been completed, and "S2" is the sulfur content [mass%] in the molten steel before the addition of lime has been started.

[0031] The lower limit of the desulfurization rate D may be 10.5%, 11.0%, or 11.5%. The upper limit of the desulfurization rate D is not particularly limited and may be, for example, 25.0%. By having a desulfurization rate equal to or greater than the lower limit, the ease of secondary refining of the molten steel after the additive process can be improved, thereby improving the ease and certainty of obtaining steel material with desired properties.

[0032] <Other Embodiments> The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is not limited to the configurations of the embodiments described above, but is indicated by the claims, and all modifications within the meaning and scope equivalent to the claims are intended to be included. [Examples]

[0033] The present disclosure will be described in more detail below with reference to examples, but the present disclosure is not limited to these examples.

[0034] The differences in desulfurization rate D were compared by adding a deoxidizing agent, alloy, and lime to molten steel being received in a ladle. The conditions and results for each test example are shown in Table 1. The above deoxidizing agent and alloy (hereinafter also referred to as "the above deoxidizing agent, etc.") were added simultaneously with the start of receiving the steel (0.00T). The temperature of the molten steel in the converter to which the steel was tapped into the ladle was between 1679°C and 1690°C in all cases.

[0035] [Table 1]

[0036] In each test example, samples with a desulfurization rate D of 10% or more were classified as good products (A), and those with a rate of less than 10% were classified as defective products (B). In Test Examples 1 to 5, where lime addition was completed within 0.50T, the evaluation was A, indicating that desulfurization was effective. In Test Examples 6 to 8, where lime addition was completed more than 0.50T, the evaluation was B, indicating that the desired desulfurization effect was not obtained. Figure 1 shows the results of each test example plotted and an approximation line drawn. From the above approximation line, it can be seen that the desulfurization rate D can be increased to 10% or more by completing lime addition within 0.50T. [Industrial applicability]

[0037] As explained above, this additive method can effectively desulfurize molten steel and is therefore suitable for use in the manufacture of steel materials.

Claims

1. The process of receiving molten steel tapped from a converter or electric furnace into a ladle, The process involves adding a deoxidizing agent and lime to the molten steel receiving the ladle mentioned above. Equipped with, Let T be the time from the start to the end of steeling in the ladle described above. Start by adding the above deoxidizing agent at a dose of 0.10 T or less. A deoxidizing agent and a method for adding lime, wherein the addition of lime is completed within 0.50 T.

2. The addition method according to claim 1, wherein the addition of the deoxidizing agent is started before the addition of the lime in the addition step described above.

3. The addition method according to claim 1, wherein the amount of lime added per ton of molten steel is 0.0075 tons or more and 0.0140 tons or less.

4. In the above additive step, an alloy is further added to adjust the composition of the molten steel. The addition method according to claim 1, wherein the addition of the alloy is started before the addition of the lime.

5. The additive method according to any one of claims 1 to 4, wherein the desulfurization rate D in the following formula 1 is 10% or more. D={1-(S1 / S2)}×100 (1) In Formula 1 above, "S1" is the sulfur content [mass%] in the molten steel after the addition of lime has been completed, and "S2" is the sulfur content [mass%] in the molten steel before the addition of lime has been started.

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