Smelting method of bake-hardened steel

Abstract

The invention provides a smelting method of bake-hardened steel, and belongs to the field of steel smelting. The method comprises the following steps: performing RH decarburization on converter molten steel to obtain decarburized molten steel; the content of Al, Mn and P in the decarburized molten steel is adjusted, the content of Ti, the content of Nb and the content of excess carbon [C] eff in the decarburized molten steel are adjusted according to the content of C and the content of N in the decarburized molten steel, the decarburized molten steel is alloyed, and alloyed molten steel is obtained; and pure circulation treatment is conducted on the alloyed molten steel for set time, and the molten steel for continuous casting is obtained. Based on the RH decarburization end point C content, the content of alloy elements such as [Ti] and [Nb] is dynamically adjusted, accurate control over excess carbon is achieved, it is ensured that the carbon content of a final finished product is controlled to be 0.0013%-0.0025%, and the strict requirement of bake-hardened steel for the low carbon content is met.

Description

Technical Field

[0001] This application relates to the technical field of steel smelting, and particularly to a smelting method for bake hardening steel. Background Art

[0002] Bake Hardening Steel is developed on the basis of the composition of IF steel (C ≤ 0.0030%, N ≤ 0.0040%). Due to its good deep drawing performance, Nb and Ti are added simultaneously to solidify N atoms. At the same time, there is excess carbon, which hardens during the baking process, improving the strength and having good dent resistance. Therefore, it is widely used in the production of automotive outer panels.

[0003] However, compared with IF steel, due to the composition, especially the narrow control range of the content of excess carbon [C]eff, which is generally required to be controlled within the range of 0.0005% - 0.0013%, and the content of excess carbon [C] eff is affected by the contents of various elements such as C, N, Nb, and Ti in the molten steel, its control strategy has become a difficult point in the smelting process. Summary of the Invention

[0004] This application provides a smelting method for bake hardening steel to solve the following technical problem: how to ensure that the content of excess carbon ([C] eff ) in the bake hardening steel is accurately controlled within the range of 0.0005% - 0.0013% through the control of the steelmaking process.

[0005] The embodiment of this application provides a smelting method for bake hardening steel, and the method includes:

[0006] Subjecting the converter molten steel to RH decarburization to obtain decarburized molten steel;

[0007] Adjusting the contents of Al, Mn, and P in the decarburized molten steel, and adjusting the contents of Ti, Nb, and the content of excess carbon [C] in the decarburized molten steel according to the C content and N content in the decarburized molten steel eff to carry out alloying treatment on the decarburized molten steel to obtain alloyed molten steel; and

[0008] Subjecting the alloyed molten steel to pure circulation treatment for a set time to obtain molten steel for continuous casting.

[0009] Optionally, in terms of mass fraction, in the decarburized molten steel, the C content ≤ 0.0030%.

[0010] Optionally, in terms of mass fraction, in the alloyed molten steel, the Al content is 0.020% - 0.050%.

[0011] Optionally, by mass fraction, in the alloyed molten steel, the Mn content is 0.60% - 0.70%.

[0012] Optionally, by mass fraction, in the alloyed molten steel, the P content is 0.030% - 0.040%.

[0013] Optionally, by mass fraction, when the C content in the decarburized molten steel ≤ 0.0020%, the Ti and Nb contents in the alloyed molten steel satisfy the following relationship:

[0014] [Ti] ≤ 3.43·[N], and [Nb] = 7.75·([C] - [C] eff )

[0015] In the formula, [Ti] represents the Ti content in the alloyed molten steel; [Nb] represents the Nb content in the alloyed molten steel; [N] represents the N content in the decarburized molten steel and the predicted nitrogen increase in the molten steel during the RH to continuous casting process; [C] eff represents the target excess carbon content in the alloyed molten steel, [C] eff is 0.0005% - 0.0013%; [C] represents the C content in the decarburized molten steel.

[0016] Optionally, by mass fraction, when the C content in the decarburized molten steel > 0.0020%, the Ti and Nb contents in the alloyed molten steel satisfy the following relationship:

[0017] [Ti] > 3.43·[N], and [Nb] = 7.75·([Ti] / 4 - [N] / 1.17) - ([C] - [C] eff )

[0018] In the formula, [Ti] represents the Ti content in the alloyed molten steel; [Nb] represents the Nb content in the alloyed molten steel; [N] represents the N content in the decarburized molten steel and the predicted nitrogen increase in the molten steel during the RH to continuous casting process; [C] eff represents the target excess carbon content in the alloyed molten steel, [C] eff is 0.0005% - 0.0013%; [C] represents the C content in the decarburized molten steel.

[0019] Optionally, the time for the pure circulation treatment is 4 min - 10 min.

[0020] Optionally, the method uses a carbon - free ladle to control the ladle carbon increase amount ≤ 0.0003%.

[0021] Optionally, the carbon increase amount of the molten steel for continuous casting in the continuous casting process refractory material ≤ 0.0003%.

[0022] The above technical solution provided by the embodiments of the present application has the following advantages compared with the prior art:

[0023] The embodiments of the present application provide a smelting method for bake hardening steel, and the method includes: subjecting converter molten steel to RH decarburization to obtain decarburized molten steel; adjusting the contents of Al, Mn, and P in the decarburized molten steel, and adjusting the contents of Ti, Nb, and excess carbon content [C] in the decarburized molten steel according to the C content and N content in the decarburized molten steel eff , so as to alloy the decarburized molten steel to obtain alloyed molten steel; and subjecting the alloyed molten steel to a pure circulation treatment for a set time to obtain molten steel for continuous casting. First, through the RH decarburization process, it is beneficial to the overall control of the C content of the steel grade; secondly, based on the C content at the end point of RH decarburization, the contents of alloying elements such as [Ti] and [Nb] are dynamically adjusted to achieve precise control of excess carbon, ensuring that the carbon content of the final product is controlled within 0.0013% to 0.0025%, meeting the strict requirements of bake hardening steel for low carbon content; finally, through the pure circulation of molten steel, the composition and inclusion control of the molten steel can be ensured to be qualified. Thus, through the control of the steelmaking process, the excess carbon content ([C] eff ) of the bake hardening steel is accurately controlled within the range of 0.0005% to 0.0013%. Description of the Drawings

[0024] The drawings here are incorporated into the specification and form a part of this specification, showing the embodiments that conform to the present application, and are used together with the specification to explain the principles of the present application.

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0026] Figure 1 It is a schematic flow chart of a smelting method for bake hardening steel provided by the embodiments of the present application. Detailed Embodiments

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the drawings in the embodiments of the present application. Obviously, the described examples are part of the embodiments of the present application, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative efforts belong to the scope of protection of the present application.

[0028] The various embodiments of the present application may exist 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 construed as a rigid limitation on the scope of the present application; therefore, it should be considered that the description of the range has specifically disclosed all possible sub-ranges and individual values within that range. For example, it should be considered that the description of the range from 1 to 6 has 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., and individual numbers within that range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Additionally, whenever a numerical range is indicated herein, it means including any recited number (fraction or integer) within the indicated range.

[0029] In addition, in the description of the specification of the present application, terms such as "including" and "comprising" mean "including but not limited to". In this text, relational terms such as "first" and "second" 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 text, "and / or" describes the associated relationship of associated objects, indicating that three relationships may exist. For example, A and / or B may represent: A exists alone, A and B exist simultaneously, and B exists alone. Where A and B may be singular or plural. In this text, "at least one" means one or more, and "a plurality" means two or more. "At least one kind", "at least one of the following (items)" or similar expressions refer to any combination of these items, including any combination of single item (s) or plural items (s). For example, "at least one of a, b, or c", or, "at least one of a, b, and c" can both represent: a, b, c, a - b (i.e., a and b), a - c, b - c, or a - b - c, where a, b, and c can be single or multiple respectively. The "parts representation method" such as parts by weight and parts by mass represents the proportional relationship between each component. In the proportional relationship involved in this text, the parameters that need to be described by proportion should be understood as the antecedents of the proportion formula in the order of description, and the proportional numbers should be understood as the consequents of the proportion formula. For example, if the mass ratio of substance A, substance B, and substance C is 1:2:3, then substance A, substance B, and substance C should correspond one by one with the proportional numbers in the proportion formula in the order of description, that is, the mass of substance A: the mass of substance B: the mass of substance C = 1:2:3.

[0030] Unless otherwise specifically stated, various raw materials, reagents, instruments, and equipment used in the present application can be obtained through market purchase or can be prepared by existing methods.

[0031] Figure 1 It is a schematic flow diagram of a smelting method for bake - hardening steel provided for the embodiments of the present application.

[0032] As Figure 1 shown, the present application provides a smelting method for bake hardening steel, and the method includes:

[0033] S1. Decarburize the converter molten steel by RH to obtain decarburized molten steel;

[0034] In some embodiments, by mass fraction, in the decarburized molten steel, the C content ≤ 0.0030%.

[0035] RH decarburization is mainly based on the chemical reaction that carbon in steel reacts with hydrogen or oxygen at high temperature to generate methane or carbon monoxide. During this process, oxygen diffuses into the steel, and at the same time, carbon in the steel diffuses outwards, thereby achieving decarburization. Limiting the C content in the molten steel after RH decarburization to ≤ 0.0030% can control the C content in the molten steel at a low level, which is beneficial to the overall control of the C content of the steel grade. Exemplarily, the C content in the decarburized molten steel can be 0.0010%, 0.0015%, 0.0020%, 0.0025%, 0.0030%, etc.

[0036] S2. Adjust the contents of Al, Mn, and P in the decarburized molten steel, and adjust the contents of Ti, Nb, and excess carbon content [C] in the decarburized molten steel according to the C content and N content in the decarburized molten steel eff , so as to perform alloying treatment on the decarburized molten steel to obtain alloyed molten steel;

[0037] In some embodiments, by mass fraction, in the alloyed molten steel, the Al content is 0.020% - 0.050%.

[0038] In some embodiments, by mass fraction, in the alloyed molten steel, the Mn content is 0.60% - 0.70%.

[0039] In some embodiments, by mass fraction, in the alloyed molten steel, the P content is 0.030% - 0.040%.

[0040] By adjusting the Al content, on the one hand, the O content in the molten steel is reduced, and the recovery rate of other alloying elements is increased. On the other hand, the Al content is ensured to reach the steel grade control target. At the same time, other elements such as Mn and P are adjusted to meet the requirements of the steel grade. Exemplarily, in the alloyed molten steel, the Al content can be 0.020%, 0.025%, 0.030%, 0.040%, 0.045%, 0.050%, etc., the Mn content can be 0.60%, 0.62%, 0.64%, 0.66%, 0.68%, 0.70%, etc., and the P content can be 0.030%, 0.032%, 0.034%, 0.036%, 0.038%, 0.040%, etc.

[0041] Adjusting the [C], [Nb], and [Ti] contents of molten steel. When the contents of other steel elements have been adjusted, adjusting the contents of alloying elements such as [Nb] and [Ti] in molten steel is conducive to accurately controlling the excess carbon content [C]. eff .

[0042] In some embodiments, when the C content in the decarburized molten steel is ≤0.0020% by mass, the Ti and Nb contents in the alloyed molten steel satisfy the following relationship:

[0043] [Ti]≤3.43·[N], and [Nb]=7.75·([C]-[C] eff )

[0044] In the formula, [Ti] represents the Ti content in the alloyed steel water; [Nb] represents the Nb content in the alloyed steel water; [N] represents the N content in the decarburized steel water; [C] eff represents the target excess carbon content in the alloyed molten steel, [C] eff It is 0.0005% to 0.0013%; [C] represents the C content in the decarburized molten steel.

[0045] According to the precipitation order of C and N compounds in steel during solidification: TiN→AlN→TiC→NbC, therefore, the alloy order is adjusted according to the C content in the decarburized molten steel at the end point of RH decarburization. If the C content of the decarburized molten steel is ≤0.0020% at this time, the Ti content of the molten steel is adjusted according to the N content of the decarburized molten steel and the predicted amount of nitrogen increase in the molten steel during RH to continuous casting. Controlling [Ti]≤3.43·[N] can ensure that all Ti in the decarburized molten steel can be combined with N, ensuring that there is no excess Ti, and the remaining N can be combined with Al; on this basis, the excess carbon [C] is adjusted through Nb eff , making it equal to [C]-([Nb] / 7.75), achieving [C] eff Precise control.

[0046] In some embodiments, when the C content in the decarburized molten steel is greater than 0.0020% by mass, the Ti and Nb contents in the alloyed molten steel satisfy the following relationship:

[0047] [Ti]>3.43·[N], and [Nb]=7.75·([Ti] / 4-[N] / 1.17)-([C]-[C] eff )

[0048] In the formula, [Ti] represents the Ti content in the alloyed steel water; [Nb] represents the Nb content in the alloyed steel water; [N] represents the N content in the decarburized steel water; [C] effRepresents the target excess carbon content in the alloyed molten steel, [C] eff is 0.0005% - 0.0013%; [C] represents the C content in the decarburized molten steel.

[0049] If the C content in the decarburized molten steel at the end of RH decarburization > 0.0020%, at this time [C] eff has insufficient adjustable space and must adopt the mode of multi-alloy composite adjustment to adjust [C] eff , in order to finally meet eff the need for precise control. Under this condition, combined with the precipitation sequence of carbonitrides in steel during solidification, first adjust with Ti according to the upper and middle limits, control [Ti] > 3.43[N], then the remaining [Ti] combined by [N] can consume a part of [C], and then adjust [Nb] to meet eff =[C] - ([Ti] / 4 - [N] / 1.17) - ([Nb] / 7.75), [C] eff is controlled within the range of 0.0005% - 0.0013%.

[0050] S3. Carry out pure circulation treatment on the alloyed molten steel for a set time to obtain molten steel for continuous casting.

[0051] In some embodiments, the time of the pure circulation treatment is 4 min - 10 min.

[0052] After alloying, the pure circulation time of the alloyed molten steel is 4 min - 10 min, so as to ensure that the steel liquid composition and inclusion control are qualified. Exemplarily, the pure circulation time of the alloyed molten steel can be 4 min, 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, etc.

[0053] In some embodiments, the method uses a carbon-free ladle to control the ladle carbon increase amount ≤ 0.0003%.

[0054] In some embodiments, the carbon increase amount of the refractory material during continuous casting of the molten steel for continuous casting ≤ 0.0003%.

[0055] During the production process, a carbon-free ladle is used to control the ladle carbon increase amount ≤ 0.0003%, and the carbon increase amount of the refractory material during continuous casting is controlled ≤ 0.0003% to avoid excessive excess carbon. Through the implementation of the above method, the C content of the final product is controlled to 0.0013% - 0.0025%.

[0056] In summary, the smelting method of a bake hardening steel provided by the embodiment of the present application has the following significant advantages:

[0057] (1) Low-carbon precise control: Through the RH decarburization process, the carbon content in the decarburized molten steel is strictly controlled within the range of ≤0.0030%, providing a good basis for subsequent alloying treatment. At the same time, according to the carbon content in the decarburized molten steel, the contents of alloying elements Ti and Nb are precisely adjusted to control the excess carbon content [C]. eff Within the precise range of 0.0005% - 0.0013%, it ensures that the carbon content of the final product is controlled within 0.0013% - 0.0025%, meeting the strict requirements of bake hardening steel for low carbon content.

[0058] (2) Alloying element optimization: By adjusting the contents of elements such as Al, Mn, P, etc., not only the oxygen content in the molten steel is reduced, the recovery rate of other alloying elements is improved, but also the steel grade composition meets specific requirements. Precisely controlling the contents of Ti and Nb not only optimizes the microstructure of the steel, but also improves the bake hardening performance and strength of the steel.

[0059] (3) High-efficiency pure circulation treatment: The alloyed molten steel is subjected to pure circulation treatment for 4 min - 10 min, effectively ensuring the uniformity of the molten steel composition and the control of inclusions, and improving the quality of the molten steel.

[0060] (4) Strict control of carburization amount: Carbon-free ladles are used, and the carburization amount of refractory materials during continuous casting is strictly controlled, avoiding the problem of excessive excess carbon and ensuring that the carbon content of the final product is controlled within the target range.

[0061] (5) Process flexibility and controllability: This method is not only applicable to the production of extra-low carbon steel, but also the contents of alloying elements can be adjusted according to specific requirements to meet the requirements of different steel grades. By precisely controlling various process parameters, such as decarburization time, alloying element content, pure circulation treatment time, etc., precise control of the molten steel composition and performance is achieved.

[0062] (6) Improving production efficiency and reducing costs: The optimized smelting process shortens the production cycle and improves production efficiency. By precisely controlling the contents of alloying elements, unnecessary addition of alloying elements is reduced, and production costs are lowered.

[0063] The following will further elaborate on this application in combination with specific embodiments. It should be understood that these embodiments are only used to illustrate this application and not to limit the scope of this application. The experimental methods without specific conditions noted in the following embodiments are usually determined according to industry standards. If there is no corresponding industry standard, they are carried out according to general international standards, conventional conditions, or conditions recommended by the manufacturer.

[0064] Example 1

[0065] The nominal capacity of the converter in this example is 210 t.

[0066] 1) The carbon content at the end of the converter is 0.040%, and the molten steel at the end of blowing enters the RH for decarburization;

[0067] 2) After the RH decarburization, the [C] of the molten steel is 0.0018% and the [N] is 0.0022%;

[0068] 3) The control targets for the alloying elements [Al], [Mn], and [P] in the molten steel are 0.020% - 0.050%, 0.60% - 0.70%, and 0.030% - 0.040% respectively. By adding alloying agents, the actual adjustments of the alloying elements [Al], [Mn], and [P] in the molten steel are 0.034%, 0.62%, and 0.036% respectively;

[0069] 4) The control targets for the alloying elements [Ti], [C] eff , [Nb] in the molten steel are 0.0020% - 0.0080%, 0.0005% - 0.0013%, and 0.0060% - 0.0100% respectively. According to the relational formula of the Ti and Nb contents and the control targets of the [Ti], [C] eff , [Nb] alloying elements, alloying operations are carried out. The actual adjustments of the [Ti], [C] eff , [Nb] alloying elements in the molten steel are 0.0070%, 0.0010%, and 0.0062% respectively;

[0070] The pure circulation of the molten steel is 6 minutes, and it is sent to continuous casting;

[0071] 5) The carbon increase Δ[C]1 of the carbon-free ladle is 0.0002%, and the carbon increase Δ[C]2 of the refractory material during continuous casting is 0.0003%;

[0072] 6) The final [C] content of the molten steel is equal to the sum of [C] eff , Δ[C]1, and Δ[C]2, which is 0.0015%.

[0073] Example 2

[0074] The nominal capacity of the converter in this example is 210t.

[0075] 1) The carbon content at the end of the converter is 0.043%, and the molten steel at the end of blowing enters the RH for decarburization;

[0076] 2) After the RH decarburization, the [C] of the molten steel is 0.0024% and the [N] is 0.0020%;

[0077] 3) The control targets for the alloying elements [Al], [Mn], and [P] in the molten steel are 0.020% - 0.050%, 0.60% - 0.70%, and 0.030% - 0.040% respectively. By adding alloying agents, the actual adjustments of the alloying elements [Al], [Mn], and [P] in the molten steel are 0.039%, 0.65%, and 0.033% respectively;

[0078] 4) The control targets for the alloying elements [Ti], [C] eff , and [Nb] in the molten steel are 0.0020% - 0.0080%, 0.0005% - 0.0013%, and 0.0060% - 0.0100% respectively. And according to the relational formula of the Ti and Nb contents and the control targets of the alloying elements [Ti], [C] eff , and [Nb], alloying operations are carried out. The actual adjustments of the alloying elements [Ti], [C] eff , and [Nb] in the molten steel are 0.0072%, 0.0012%, and 0.0086% respectively;

[0079] 5) The pure circulation of the molten steel is 8 minutes, and then it is fed into continuous casting;

[0080] 6) The carbon increase Δ[C]1 by using a carbon-free ladle is 0.0001%, and the carbon increase Δ[C]2 by refractories during continuous casting is 0.0003%;

[0081] 7) The final [C] content in the molten steel is equal to the sum of [C] eff , Δ[C]1, and Δ[C]2, which is 0.0016%.

[0082] Example 3

[0083] The nominal capacity of the converter in this example is 300t.

[0084] 1) The carbon content at the end of the converter blowing is 0.037%, and the molten steel after the blowing ends enters RH for decarburization;

[0085] 2) After the RH decarburization ends, the [C] of the molten steel is 0.0020% and the [N] is 0.0025%;

[0086] 3) The control targets for the alloying elements [Al], [Mn], and [P] in the molten steel are 0.020% - 0.050%, 0.60% - 0.70%, and 0.030% - 0.040% respectively. By adding alloying agents, the actual adjustments of the alloying elements [Al], [Mn], and [P] in the molten steel are 0.041%, 0.67%, and 0.038% respectively;

[0087] 4) The alloying elements [Ti], [C] effThe control targets for alloying elements [Ti], [Nb] are 0.0020% - 0.0080%, 0.0005% - 0.0013%, 0.0060% - 0.0100% respectively, and according to the relational expressions of the contents of Ti and Nb and [Ti], [C] eff and the control targets for alloying elements [Ti], [Nb], alloying operations are carried out, and the actual adjustments of [Ti], [C] eff and [Nb] in the molten steel are 0.0078%, 0.0008%, 0.0093% respectively;

[0088] 5) The molten steel is purely circulated for 9 min and then fed into continuous casting;

[0089] 6) The carbon addition Δ[C]1 in the carbon-free ladle is 0.0003%, and the carbon addition Δ[C]2 from refractory materials during continuous casting is 0.0003%;

[0090] 7) The final [C] content in the molten steel is equal to the sum of [C] eff , Δ[C]1, and Δ[C]2, which is 0.0014%.

[0091] In addition, one or more technical solutions in the embodiments of the present application at least have the following technical effects or advantages:

[0092] In the embodiments of the present application, through strict control of the RH refining process and the like, high-quality smelting of bake hardening steel is achieved, and the [C] content of the finished product is controlled to be 0.0013% - 0.0025%.

[0093] In the embodiments of the present application, based on the [C] content at the end point of RH decarburization, the contents of alloying elements such as [Ti] and [Nb] are dynamically adjusted to achieve precise control of excess carbon, and the excess carbon [C] eff content is controlled to be 0.0005% - 0.0013%.

[0094] The above are only specific embodiments of the present application, enabling those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be obvious 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 these embodiments shown herein, but will conform to the broadest scope consistent with the principles and novel features claimed herein.

Claims

1. A smelting method for bake hardening steel, the method comprising: Performing RH decarburization on converter molten steel to obtain decarburized molten steel; Adjust the contents of Al, Mn, and P in the decarburized molten steel, and adjust the contents of Ti, Nb, and excess carbon content [C] in the decarburized molten steel according to the C content and N content in the decarburized molten steel. eff , so as to perform alloying treatment on the decarburized molten steel to obtain alloyed molten steel; And Performing a pure circulation treatment on the alloyed molten steel for a set time to obtain molten steel for continuous casting.

2. The method according to claim 1, wherein By mass fraction, in the decarburized molten steel, the C content is ≤0.0030%.

3. The method according to claim 1, wherein By mass fraction, in the alloyed molten steel, the Al content is 0.020% - 0.050%.

4. The method according to claim 1, wherein By mass fraction, in the alloyed molten steel, the Mn content is 0.60% - 0.70%.

5. The method according to claim 1, characterized in that, By mass fraction, in the alloyed molten steel, the P content is 0.030% - 0.040%.

6. The method according to claim 1, wherein By mass fraction, when the C content in the decarburized molten steel is ≤0.0020%, the Ti and Nb contents in the alloyed molten steel satisfy the following relationship: [Ti] ≤ 3.43·[N], and [Nb] = 7.75·([C] - [C] eff ) In the formula, [Ti] represents the Ti content in the alloyed molten steel; [Nb] represents the Nb content in the alloyed molten steel; [N] represents the N content in the decarburized molten steel; [C] eff represents the target excess carbon content in the alloyed molten steel, [C] eff is 0.0005% to 0.0013%; [C] represents the C content in the decarburized molten steel.

7. The method according to claim 1, characterized in that By mass fraction, when the C content in the decarburized molten steel is >0.0020%, the Ti and Nb contents in the alloyed molten steel satisfy the following relationship: [Ti] > 3.43·[N], and [Nb] = 7.75·([Ti] / 4 - [N] / 1.17) - ([C] - [C] eff ) In the formula, [Ti] represents the Ti content in the alloyed molten steel; [Nb] represents the Nb content in the alloyed molten steel; [N] represents the N content in the decarburized molten steel; [C] eff represents the target excess carbon content in the alloyed molten steel, [C] eff is 0.0005% to 0.0013%; [C] represents the C content in the decarburized molten steel.

8. The method according to claim 1, wherein The time of the pure circulation treatment is 4 min - 10 min.

9. The method according to claim 1, wherein The method uses a carbon-free ladle to control the ladle carbon increase amount ≤0.0003%.

10. The method according to claim 1, characterized in that, During continuous casting, the refractory carbon increase amount of the molten steel for continuous casting is ≤0.0003%.

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