Low-sulfur steel preparation method based on BOF-CAS

Abstract

The invention provides a low-sulfur steel preparation method based on BOF-CAS, and belongs to the field of steelmaking. The method comprises the following steps: adding alloy and slag charge in a converter tapping process to obtain modified molten steel; the modified molten steel is subjected to first desulfurization treatment, and first desulfurized molten steel is obtained; transferring the first desulfurized molten steel to a CAS, and carrying out second desulfurization treatment to obtain second desulfurized molten steel; and the second desulfurized molten steel is refined, and the low-sulfur steel is obtained. Ladle slag is modified and subjected to first desulfurization treatment by fully utilizing good dynamic conditions in the converter tapping process, and meanwhile, second desulfurization treatment is carried out in cooperation with good dynamic conditions such as large argon in the CAS station-entering argon pre-blowing process. Therefore, the low-sulfur steel grade is produced based on efficient desulfurization of the CAS method.

Description

Technical Field

[0001] The present application relates to the technical field of steelmaking, and in particular to a method for preparing low-sulfur steel based on BOF-CAS. Background Art

[0002] Sulfur in steel can form compounds with iron, which damages the texture at the grain boundary, leading to intergranular fracture. Sulfur can also reduce the ductility of steel, affecting the plasticity and tensile strength of steel. Sulfur reduces the tensile properties and impact toughness of steel. Too high sulfur content will increase the brittleness of steel, which is not conducive to the use of steel.

[0003] After the CAS hood of the sealed argon blowing alloy composition adjustment method (CAS method, Composition Adjustment by Sealed Argon Bubbling) is lowered, the steel slag mixing is not obvious, so the conventional CAS has no desulfurization ability and cannot produce low-sulfur steel grades. At the same time, the traditional CAS treatment of feeding the cored wire for desulfurization in the later stage will increase the CAS cycle, and the molten steel in the later stage of CAS is low, which is not suitable for desulfurization. The method of slagging after CAS desulfurization and then slag making treatment avoids resulfurization, but it is not suitable for high-rhythm CAS production, especially single-station CAS. Therefore, how to produce low-sulfur steel grades based on the CAS method with efficient desulfurization is a technical problem that urgently needs to be solved. Summary of the invention

[0004] The present application provides a method for preparing low-sulfur steel based on BOF-CAS to solve the following technical problem: how to produce low-sulfur steel by efficient desulfurization based on the CAS method.

[0005] The present application provides a method for preparing low-sulfur steel based on BOF-CAS, the method comprising:

[0006] In the process of tapping steel from the converter, alloy and slag are added to obtain modified molten steel;

[0007] The modified molten steel is subjected to a first desulfurization treatment to obtain a first desulfurized molten steel;

[0008] Transferring the first desulfurized steel liquid to CAS and performing a second desulfurization treatment to obtain a second desulfurized steel liquid;

[0009] The second desulfurized steel liquid is subjected to refining treatment to obtain low-sulfur steel.

[0010] Optionally, the first desulfurization treatment time is 2 minutes to 6 minutes, and the second desulfurization treatment time is 2 minutes to 5 minutes.

[0011] Optionally, during the first desulfurization treatment, the exposed area of ​​the molten steel is greater than 0.2 m 2During the second desulfurization treatment, the exposed area of ​​molten steel is greater than 0.5m 2 .

[0012] Optionally, the desulfurization rate of the first desulfurization treatment is ≥35%, and the desulfurization rate of the second desulfurization treatment is ≥42%.

[0013] Optionally, the sulfur content in the first desulfurized steel liquid is ≤1.5S by mass fraction. max , where S max It is the upper limit of sulfur content in low sulfur steel.

[0014] Optionally, the slag material is a high-basicity slag-forming agent, the addition amount of the high-basicity slag-forming agent is 4kg / t steel to 12kg / t steel, and the particle size of the high-basicity slag-forming agent is 5mm to 15mm.

[0015] Optionally, the chemical composition of the high basicity slag-forming agent includes, by mass fraction: CaO: 50% to 60%, SiO2: 5% to 10%, Al2O3: 10% to 20%, and CaF2: 10% to 20%.

[0016] Optionally, the aluminum content in the modified steel liquid is 0.035% to Al max , where Al max The aluminum content of low sulfur steel is 0.02% or more above the upper limit.

[0017] Optionally, the molar basicity of the ladle slag of the modified molten steel is 6 to 12, wherein the molar basicity is the molar ratio of CaO to SiO2 in the ladle slag; and the sum of the contents of TFe and TMn in the ladle slag is ≤3% in terms of mass fraction.

[0018] Optionally, the temperature of the converter tapping steel satisfies the following relationship:

[0019] T=T1+T2,

[0020] Wherein, T is the temperature of the converter tapping steel, T1 is the liquidus temperature, and T2 is 140°C to 200°C.

[0021] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0022] The present application provides a method for preparing low-sulfur steel based on BOF-CAS, including: adding alloy and slag during the process of steel tapping from a converter to obtain a modified steel liquid; subjecting the modified steel liquid to a first desulfurization treatment to obtain a first desulfurized steel liquid; transferring the first desulfurized steel liquid to CAS and subjecting it to a second desulfurization treatment to obtain a second desulfurized steel liquid; subjecting the second desulfurized steel liquid to a refining treatment to obtain low-sulfur steel. By making full use of the good kinetic conditions during steel tapping from a converter, the ladle slag is modified and subjected to a first desulfurization treatment, and the second desulfurization treatment is carried out in cooperation with the good kinetic conditions such as large argon gas during the CAS station pre-purging argon. It is only necessary to control the steel tapping temperature and add an appropriate amount of high-basicity slag-making agent to create a high-basicity, low-oxidizing, low-melting-point ladle slag, providing good thermodynamic conditions for the first desulfurization treatment and the second desulfurization treatment, solving the problem of efficient desulfurization by CAS, without the need to increase the CAS cycle, and realizing efficient and fast production of low-sulfur steel grades by CAS. Thus, low-sulfur steel grades are produced based on efficient desulfurization by CAS method. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0024] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0025] Figure 1 A schematic flow chart of a method for preparing low-sulfur steel based on BOF-CAS provided in an embodiment of the present application. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0027] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be understood as a rigid limitation on the scope of the present application; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numerical values ​​within the range. For example, the range description from 1 to 6 should be considered to have specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which apply regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0028] In addition, in the description of the specification of the present application, the terms "including", "comprising", etc. mean "including but not limited to". In this article, relational terms such as "first" and "second", etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this article, "and / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. Wherein A and B can be singular or plural. In this article, "at least one" means one or more, and "plurality" means two or more. "At least one", "at least one of the following" or similar expressions refer to any combination of these items, including any combination of singular or plural items. For example, "at least one of a, b, or c", or "at least one of a, b and c", can both mean: a, b, c, ab (i.e. a and b), ac, bc or abc, where a, b, c can be single or plural, respectively.

[0029] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0030] CAS (Composition Adjustment by Sealed Argon Bubbling) is a sealed argon blowing alloy composition adjustment method. CAS has the following functions: sealed argon blowing in the ladle, fine-tuning of composition, uniform composition and temperature of molten steel, chemical heating by adding aluminum and blowing, calcium treatment, and removal of large inclusions in molten steel. CAS has the following characteristics: low equipment investment and low process cost. After the molten steel enters the CAS, a large flow of argon gas is required to be blown from the bottom to uniform the composition and temperature. At the same time, the slag surface of the ladle is blown open, and the CAS cover is lowered to insert the molten steel to isolate the ladle slag outside the cover. After the cover is lowered, the molten steel is protected by the argon gas in the CAS cover, which reduces the secondary oxidation of the molten steel.

[0031] After the CAS hood is lowered, the slag mixing is not obvious, so conventional CAS has no desulfurization ability and cannot produce low-sulfur steel. Traditional CAS treatment of feeding cored wire desulfurization at the later stage will increase the CAS cycle. At the same time, the molten steel at the later stage of CAS is low, which is not suitable for desulfurization. The method of slag removal after CAS desulfurization and then slag making treatment avoids resulfurization, but it is not suitable for CAS high-rhythm production, especially single-station CAS.

[0032] This application makes full use of the good kinetic conditions in the converter steel-tapping process to modify the ladle slag and perform the first desulfurization treatment, and at the same time cooperates with the good kinetic conditions such as large argon gas in the CAS station pre-blowing process to perform the second desulfurization treatment. It only needs to control the steel-tapping temperature and add an appropriate amount of high-basicity slag-making agent to create high-basicity, low-oxidizing, low-melting-point ladle slag, which provides good thermodynamic conditions for the first desulfurization treatment and the second desulfurization treatment, solves the problem of CAS efficient desulfurization, does not need to increase the CAS cycle, and realizes CAS efficient and fast production of low-sulfur steel grades with lower production costs.

[0033] The technical solution provided by the embodiment of the present invention is to solve the above technical problems, and the overall idea is as follows:

[0034] Figure 1 A schematic flow chart of a method for preparing low-sulfur steel based on BOF-CAS provided in an embodiment of the present application.

[0035] According to a typical implementation of the present invention, see Figure 1 The present application provides a method for preparing low-sulfur steel based on BOF-CAS, the method comprising:

[0036] S1. Adding alloy and slag during the process of tapping steel from a converter to obtain modified molten steel;

[0037] In some embodiments, the slag material is a high-basicity slag-forming agent, the addition amount of the high-basicity slag-forming agent is 4kg / t steel to 12kg / t steel, and the particle size of the high-basicity slag-forming agent is 5mm to 15mm.

[0038] As an optional implementation, the reason for adding a high-basicity slag-forming agent during the steel-making process in step S1 is to provide high-basicity ladle slag for "double-step desulfurization" to achieve efficient and fast desulfurization of CAS.

[0039] As an optional embodiment, the reason why the high-basicity slag-forming agent is added in an amount of 4kg / t steel to 12kg / t steel in step S1 is: if the amount of high-basicity slag-forming agent added is too small, the amount of ladle slag and basicity cannot be guaranteed, which is not conducive to the desulfurization reaction; if the amount of high-basicity slag-forming agent added is too large, the temperature of the molten steel will drop too much, and there will be hidden dangers of oxygen blowing, heating and sulfur regeneration. Exemplarily, the amount of the high-basicity slag-forming agent added can be 4kg / t steel, 6kg / t steel, 8kg / t steel, 10kg / t steel, 11kg / t steel, 12kg / t steel, etc.

[0040] As an optional embodiment, the reason why the particle size of the high basicity slag-forming agent in step S1 is 5mm to 15mm is: if the particle size is too large, it will affect the melting speed of the high basicity slag-forming agent; if the particle size is too small, the high basicity slag-forming agent will be sucked by the dust removal equipment during the feeding process, affecting the slag modification and the first desulfurization treatment effect. Exemplarily, the particle size of the high basicity slag-forming agent can be 5mm, 7mm, 9mm, 10mm, 12mm, 14mm, 15mm, etc.

[0041] In some embodiments, the chemical composition of the high basicity slag-forming agent includes, by mass fraction: CaO: 50% to 60%, SiO2: 5% to 10%, Al2O3: 10% to 20%, and CaF2: 10% to 20%.

[0042] As an optional embodiment, the high basicity slag-making agent composition in step S1: CaO: 50% to 60%, SiO2: 5% to 10%, Al2O3: 10% to 20%, CaF2: 10% to 20% reason: it is conducive to maintaining good reducibility and fluidity of ladle slag and increasing the desulfurization effect. Exemplarily, the content of CaO can be 50%, 52%, 54%, 56%, 58%, 60%, etc., the content of SiO2 can be 5%, 6%, 7%, 8%, 9%, 10%, etc., the content of Al2O3 can be 10%, 12%, 14%, 16%, 18%, 20%, etc., and the content of CaF2 can be 10%, 12%, 14%, 16%, 18%, 20%, etc.

[0043] In some embodiments, the total aluminum content in the modified steel liquid is 0.035% to Al max , where Al max The aluminum content of low sulfur steel is 0.02% or more above the upper limit.

[0044] As an optional implementation, the range of total aluminum Alt in the molten steel after steelmaking in step S1 is: 0.035%~Al max Reasons: If the total aluminum Alt in the molten steel after tapping is too low, it will affect the reduction of the oxidation of the ladle slag and the desulfurization effect; if the total aluminum Alt in the molten steel after tapping is too high, it will cause the CAS to end and the finished product aluminum to be high, and the composition will be abnormal.

[0045] As an optional implementation, in step S1, Al in the molten steel after tapping max The reason for setting the aluminum content of the steel grade above the upper limit of 0.02% is: keeping the aluminum content in the molten steel at a high level is beneficial to slag modification and molten steel desulfurization, while taking into account the aluminum loss of the molten steel during the first desulfurization treatment and the second desulfurization treatment.

[0046] In some embodiments, the molar basicity of the ladle slag of the modified molten steel is 6 to 12, wherein the molar basicity is the molar ratio of CaO to SiO2 in the ladle slag; in terms of mass fraction, the sum of the contents of TFe and TMn in the ladle slag is ≤3%.

[0047] As an optional embodiment, the reason why the molar basicity of the ladle slag for modifying the molten steel in step S1 is 6 to 12 is that if the molar basicity of the ladle slag is too low, the desulfurization effect of the molten steel is affected; if the molar basicity of the ladle slag is too high, the melting point of the ladle slag is affected, and the desulfurization effect is also affected. Exemplarily, the molar basicity of the ladle slag can be 6, 7, 8, 9, 10, 11, 12, etc.

[0048] As an optional implementation, the reason why TFe+TMn≤3% in the ladle slag of the modified molten steel in step S1 is: if the TFe+TMn in the ladle slag is too large, the ladle slag has strong oxidizing property, which affects the desulfurization effect.

[0049] In some embodiments, the temperature of the steel tapping from the converter satisfies the following relationship: T=T1+T2, wherein T is the temperature of the steel tapping from the converter, T1 is the liquidus temperature, and T2 is 140°C to 200°C.

[0050] As an optional implementation manner, the reason why the steel tapping temperature in step S1 is 140-200°C higher than the liquidus is: adding desulfurizer and bottom blowing stirring can reduce the temperature of the molten steel. If the tapping temperature is too low, the CAS process temperature will be low, and the oxygen blowing and temperature increase will affect the desulfurization efficiency and cause the molten steel to resulfurize; if the tapping temperature is too high, the erosion of the converter refractory material will be aggravated.

[0051] S2, subjecting the modified molten steel to a first desulfurization treatment to obtain a first desulfurized molten steel;

[0052] In some embodiments, the first desulfurization treatment lasts for 2 minutes to 6 minutes.

[0053] As an optional embodiment, the first desulfurization treatment time in step S2 is 2 minutes to 6 minutes because: if the first desulfurization treatment time is too short, the first desulfurization treatment effect of the molten steel will be affected; if the first desulfurization treatment time is too long, the ladle will wait for desulfurization after the furnace, affecting the fast-paced production of low-sulfur steel. Exemplarily, the first desulfurization treatment time can be 2 minutes, 3 minutes, 4 minutes, 5 minutes, 6 minutes, etc.

[0054] In some embodiments, during the first desulfurization treatment, the exposed area of ​​the molten steel is greater than 0.2 m 2 .

[0055] As an optional embodiment, the exposed area of ​​the molten steel during the first desulfurization treatment in step S2 is greater than 0.2m 2 Reason: If the exposed area of ​​molten steel during the first desulfurization treatment is too small, the ladle bottom blowing flow rate is small or the ladle bottom blowing effect is poor, the first desulfurization treatment effect of the molten steel will be affected.

[0056] In some embodiments, the sulfur content in the first desulfurized steel liquid is ≤1.5S by mass fraction. max , where S max It is the upper limit of sulfur content in low sulfur steel.

[0057] As an optional implementation, the reason why the sulfur content in the first desulfurization treated steel liquid in step S2 is less than 1.5 times the upper limit of the steel grade determination is: if the sulfur content in the first desulfurization treated steel liquid is too high, the second CAS desulfurization treatment will be difficult, increasing the CAS cycle and temperature drop.

[0058] S3, transferring the first desulfurized steel liquid to CAS, and performing a second desulfurization treatment to obtain a second desulfurized steel liquid;

[0059] The reason for adopting "double-step desulfurization" is: to make full use of the good kinetic conditions in the converter steelmaking process to modify the ladle slag, create high-basicity, low-oxidizing slag, and complete the first desulfurization treatment after the furnace; at the same time, use the CAS inlet argon pre-blowing to uniformly achieve the good kinetic conditions of composition, temperature and slag discharge under the hood for the second desulfurization treatment. "Double-step desulfurization" realizes the efficient and fast production of low-sulfur steel.

[0060] In some embodiments, the second desulfurization treatment lasts for 2 minutes to 5 minutes.

[0061] As an optional embodiment, the reason why the second desulfurization treatment time in step S2 is 2 to 5 minutes is: if the second desulfurization treatment time is too short, the second desulfurization treatment effect of the molten steel is affected, and the uniform composition and temperature effect are also affected; if the second desulfurization treatment time is too long, it is necessary to wait for the desulfurization to be completed before slag removal and lowering the cover, which affects the fast-paced production of low-sulfur steel CAS. Exemplarily, the second desulfurization treatment time can be 2 minutes, 2.5 minutes, 3.0 minutes, 4 minutes, 4.5 minutes, 5 minutes, etc.

[0062] In some embodiments, during the second desulfurization treatment, the exposed area of ​​the molten steel is greater than 0.5 m 2 .

[0063] As an optional embodiment, in the second desulfurization process in step S2, the exposed area of ​​molten steel is greater than 0.5m 2 Reasons: If the exposed area of ​​molten steel during the second desulfurization treatment is too small, the ladle bottom blowing flow rate is small or the ladle bottom blowing effect is poor, the second desulfurization treatment effect of the molten steel will be affected; at the same time, it will affect the CAS slag discharge under the hood, resulting in a large amount of ladle slag in the CAS hood, affecting the cleanliness of the low-sulfur steel and the slag sticking to the CAS hood.

[0064] In some embodiments, the desulfurization rate of the first desulfurization treatment is ≥35%, and the desulfurization rate of the second desulfurization treatment is ≥42%.

[0065] S4. Refining the second desulfurized steel liquid to obtain low-sulfur steel.

[0066] This application makes full use of the good kinetic conditions in the converter steel-tapping process to modify the ladle slag and perform the first desulfurization treatment, and at the same time cooperates with the good kinetic conditions such as large argon gas in the CAS station pre-blowing process to perform the second desulfurization treatment. It only needs to control the steel-tapping temperature and add an appropriate amount of high-basicity slag-making agent to create high-basicity, low-oxidizing, low-melting-point ladle slag, which provides good thermodynamic conditions for the first desulfurization treatment and the second desulfurization treatment, solves the problem of CAS efficient desulfurization, does not need to increase the CAS cycle, and realizes CAS efficient and fast production of low-sulfur steel grades with lower production costs.

[0067] The present application will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are intended only to illustrate the present application and are not intended to limit the scope of the present application. The experimental methods for which specific conditions are not specified in the following examples are usually measured according to industry standards. If there is no corresponding industry standard, then the conditions recommended by the manufacturer are followed.

[0068] The following is a detailed description of a method for preparing low-sulfur steel based on BOF-CAS provided by the present application in combination with examples, comparative examples and experimental data. The method comprises:

[0069] S11, adding alloy and slag during the process of tapping steel from the converter to obtain modified molten steel;

[0070] S21, subjecting the modified molten steel to a first desulfurization treatment to obtain a first desulfurized molten steel;

[0071] S31, transferring the first desulfurized steel liquid to CAS, and performing a second desulfurization treatment to obtain a second desulfurized steel liquid;

[0072] S41. The second desulfurized steel liquid is subjected to refining treatment to obtain low-sulfur steel. The process parameters of each embodiment and each comparative example are shown in Table 1 and Table 2.

[0073] Table 1 Process parameters of low sulfur steel preparation method

[0074]

[0075] Table 2 Process parameters of low sulfur steel preparation method

[0076]

[0077] From the data in Table 1 and Table 2, we can see that:

[0078] In Comparative Example 1, the tapping temperature is 90° C. higher than the liquidus line. The low tapping temperature causes low temperatures after the furnace and in the CAS process, and low desulfurization efficiency.

[0079] In Comparative Example 2, the amount of high-basicity slag-forming agent added is 2 kg / t steel, the amount of high-basicity slag-forming agent added is small, and the molar basicity of the ladle slag is 3. Low basicity is not conducive to the desulfurization reaction.

[0080] In Comparative Example 3, the amount of high-basicity slag-forming agent added is 20kg / t steel. The amount of high-basicity slag-forming agent added is too much, resulting in excessive temperature drop of the molten steel, poor melting effect of the slag-forming agent, and is not conducive to desulfurization.

[0081] In Comparative Example 4, the Alt content of the molten steel after steel tapping is 0.014%. The total aluminum Alt in the molten steel after steel tapping is too low, which affects the reduction of the oxidation property of the ladle slag and the desulfurization effect.

[0082] In Comparative Example 5, the molar basicity of the ladle slag of the modified molten steel is 3, and the molar basicity of the ladle slag is too low, which affects the desulfurization effect of the molten steel.

[0083] In Comparative Example 6, the TFe+TMn content of the ladle slag of the modified molten steel is 5.8%, the ladle slag has strong oxidizing property, and the desulfurization effect is poor.

[0084] In Comparative Example 7, the first desulfurization treatment was not performed, resulting in a high pressure in the second desulfurization treatment of CAS, which easily leads to a high sulfur content in the finished product.

[0085] In Comparative Example 8, the exposed area of ​​molten steel during the first desulfurization treatment was 0, the ladle bottom blowing effect was poor, the ladle slag modification effect was poor, and the first desulfurization treatment effect was poor.

[0086] In Comparative Example 9, the second desulfurization treatment was not performed, and the sulfur content in the molten steel was relatively high.

[0087] In the second desulfurization process in Comparative Example 10, the exposed area of ​​molten steel is 0.2 m 2 , the ladle bottom blowing effect is poor, affecting the normal smelting, uniform composition, uniform temperature and desulfurization of CAS.

[0088] In Examples 1 to 3, the good kinetic conditions in the converter steel-tapping process are fully utilized to modify the ladle slag and perform the first desulfurization treatment, and the second desulfurization treatment is performed in cooperation with the good kinetic conditions such as large argon gas in the CAS station pre-purging argon process. It is only necessary to control the steel-tapping temperature and add an appropriate amount of high-basicity slag-making agent to create high-basicity, low-oxidizing, low-melting-point ladle slag, which provides good thermodynamic conditions for the first desulfurization treatment and the second desulfurization treatment, solves the problem of efficient desulfurization of CAS, and realizes efficient and fast production of low-sulfur steel grades by CAS, with lower production costs, and does not occupy the normal smelting cycle of CAS.

[0089] The above description is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest range consistent with the principles and novel features applied for herein.

Claims

1. A method for preparing low-sulfur steel based on BOF-CAS, characterized in that: The method comprises: In the process of tapping steel from the converter, alloy and slag are added to obtain modified molten steel; The modified molten steel is subjected to a first desulfurization treatment to obtain a first desulfurized molten steel; Transferring the first desulfurized steel liquid to CAS and performing a second desulfurization treatment to obtain a second desulfurized steel liquid; The second desulfurized steel liquid is subjected to refining treatment to obtain low-sulfur steel.

2. The method according to claim 1, characterized in that: The time of the first desulfurization treatment is 2 minutes to 6 minutes, and the time of the second desulfurization treatment is 2 minutes to 5 minutes.

3. The method according to claim 2, characterized in that During the first desulfurization treatment, the exposed area of ​​molten steel is greater than 0.2 m 2 During the second desulfurization treatment, the exposed area of ​​molten steel is greater than 0.5m 2 .

4. The method according to claim 3, characterized in that The desulfurization rate of the first desulfurization treatment is ≥35%, and the desulfurization rate of the second desulfurization treatment is ≥42%.

5. The method according to claim 1, characterized in that The sulfur content in the first desulfurized steel liquid is ≤1.5S by mass fraction. max , where S max It is the upper limit of sulfur content in low sulfur steel.

6. The method according to claim 1, characterized in that The slag material is a high-basicity slag-forming agent, the addition amount of the high-basicity slag-forming agent is 4kg / t steel to 12kg / t steel, and the particle size of the high-basicity slag-forming agent is 5mm to 15mm.

7. The method according to claim 6, characterized in that Calculated by mass fraction, the chemical composition of the high basicity slag-forming agent includes: CaO: 50% to 60%, SiO2: 5% to 10%, Al2O3: 10% to 20%, and CaF2: 10% to 20%.

8. The method according to claim 1, characterized in that In terms of mass fraction, the aluminum content in the modified steel liquid is 0.035% to Al max , where Al max The aluminum content of low sulfur steel is 0.02% or more above the upper limit.

9. The method according to claim 8, characterized in that The molar basicity of the ladle slag of the modified molten steel is 6 to 12, wherein the molar basicity is the molar ratio of CaO to SiO2 in the ladle slag; in terms of mass fraction, the sum of the contents of TFe and TMn in the ladle slag is ≤3%.

10. The method according to claim 1, characterized in that The temperature of the converter tapping steel satisfies the following relationship: T=T1+T2, Wherein, T is the temperature of the converter tapping steel, T1 is the liquidus temperature, and T2 is 140°C to 200°C.

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