Current control method of continuous casting blank stirrer

Abstract

The invention relates to a current control method for a continuous casting blank stirrer, and the method comprises the steps: setting control parameters of a variable-frequency controller in an electromagnetic stirrer, enabling an actual current to rise to a target current value, controlling the current to be increased to a current oscillation upper limit value at a certain rate, and then enabling the current to be reduced to a current oscillation lower limit value at a certain rate, and the circulation is repeated, so that the continuous casting electromagnetic stirring current is changed in a periodic sinusoidal waveform. The electromagnetic stirring current is controlled to change in a periodic sinusoidal waveform, so that the carbon segregation of the casting blank is improved, the carbon segregation range of the casting blank is reduced, the internal components of the casting blank are more uniform, and the performance of the casting blank is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of continuous casting, and in particular to a current control method for a continuous casting billet stirrer. Background Art

[0002] Continuous casting is a key step in modern steelmaking. The quality of its ingots directly impacts the smooth progress of subsequent rolling processes and the performance of the final product. Compositional uniformity of the ingots is a key quality indicator. Carbon segregation can lead to uneven composition distribution within the ingots, affecting their mechanical and processability, and consequently, hindering subsequent steel processing and application.

[0003] Currently, to address carbon segregation in cast strands, existing continuous casting machines typically employ strand stirring and end-stage electromagnetic stirring. Strand stirring primarily involves placing a stirring device beneath the mold or at a specific location within the continuous casting machine to agitate the flowing molten steel, ensuring a more uniform mixing of its components. End-stage electromagnetic stirring utilizes the principle of electromagnetic induction to stir the strands at the end of the continuous casting machine. The electromagnetic force promotes flow within the strands, thereby reducing component segregation. While these two stirring methods can improve carbon segregation and enhance strand performance to a certain extent, they still have limitations. Specifically, existing agitators used in cast strands (including strand stirring and end-stage stirring) generally have two stirring modes: continuous and alternating. While the continuous stirring mode provides continuous stirring of the molten steel, its stirring effect is often limited by factors such as the solidification process, making further optimization difficult. While the alternating stirring mode can vary the stirring rhythm to some extent, its relatively fixed stirring pattern may not accurately adapt to the stirring requirements at different stages of the complex and ever-changing continuous casting process, hindering further improvement in stirring effectiveness.

[0004] Therefore, how to accurately control the stirring process without changing the equipment of the continuous casting device to make the internal structure of the ingot more uniform, thereby effectively improving the carbon segregation of the ingot, is a technical problem that needs to be solved at present. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the purpose of the present invention is to provide a current control method for a continuous casting billet stirrer. Compared with the existing technology, the present invention controls the electromagnetic stirring current to change into a periodic sinusoidal waveform, thereby improving the carbon segregation of the billet, reducing the extreme difference in carbon segregation of the billet, and making the internal composition of the billet more uniform, thereby improving the performance of the billet.

[0006] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0007] The present invention provides a current control method for a continuous casting strand stirrer, the current control method comprising the following steps:

[0008] S1, before continuous casting electromagnetic stirring, setting the control parameters of the frequency conversion controller in the electromagnetic stirrer, wherein the control parameters include the target current value, the upper limit value of the current oscillation, the lower limit value of the current oscillation, the increase value of the current oscillation amplitude, and the deceleration value of the current oscillation amplitude;

[0009] S2, start the electromagnetic stirrer and increase the actual current to the target current value;

[0010] S3, after reaching the target current value, gradually increase the current at the set speed increase value until it reaches the current oscillation upper limit;

[0011] S4: After reaching the upper limit of the current oscillation, the current is gradually reduced at the set deceleration value until it reaches the lower limit of the current oscillation;

[0012] Repeat the operations of steps S3-S4 to make the current of the continuous casting electromagnetic stirring change into a periodic sinusoidal waveform until the continuous casting electromagnetic stirring is completed.

[0013] In the current control method provided by the present invention, the current is regularly increased or decreased to alternately oscillate, so that the current of the electromagnetic stirring casting changes in a periodic sinusoidal waveform, which can break the fixed mode of constant current in the traditional stirring mode, and use the periodic current change to generate a periodic electromagnetic stirring force, so as to promote the molten steel inside the ingot to produce a more uniform flow, thereby making the distribution of carbon elements and other components inside the ingot more uniform, effectively reducing the extreme difference of carbon segregation in the ingot, making the internal structure of the ingot more uniform, thereby improving the mechanical properties of the ingot, such as strength and toughness, and reducing the risk of defects such as cracks and fractures in the ingot during subsequent rolling, forging and other processing.

[0014] Preferably, the increasing value of the current oscillation amplitude is the increase in current per second.

[0015] Preferably, the increase rate value of the current oscillation amplitude is 2-4 A / s, for example, it can be 2A / s, 2.2A / s, 2.5A / s, 2.8A / s, 3A / s, 3.2A / s, 3.5A / s, 3.8A / s or 4A / s, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0016] Preferably, the deceleration value of the current oscillation amplitude is the reduction in current per second.

[0017] Preferably, the deceleration value of the current oscillation amplitude is 2-4 A / s, for example, it can be 2A / s, 2.2A / s, 2.5A / s, 2.8A / s, 3A / s, 3.2A / s, 3.5A / s, 3.8A / s or 4A / s, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0018] It is worth noting that the setting of the control parameters in the present invention is mainly based on two considerations: the cross-sectional area of ​​the ingot and the carbon content of the ingot. From the perspective of the cross-sectional area, a higher stirring force is usually required for a larger cross-sectional area to promote sufficient mixing of the entire ingot cross section; from the perspective of the carbon content of the ingot, the higher the carbon content, the greater the possibility of carbon segregation inside the ingot, and therefore a stronger stirring effect is required to improve the carbon distribution.

[0019] In the present invention, for a billet with a diameter of 700-1200 mm and a C content of 25-55%, it is preferred to control the acceleration and deceleration values ​​of the current oscillation amplitude within a specific range, which can further improve the carbon segregation phenomenon and make the carbon distribution inside the billet more uniform.

[0020] Preferably, the difference between the current oscillation upper limit value and the target current value is 20-30A, for example, it can be 20A, 21A, 22A, 23A, 24A, 25A, 26A, 27A, 28A, 29A or 30A, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0021] Preferably, the difference between the target current value and the lower limit of the current oscillation is 20-30A, for example, it can be 20A, 21A, 22A, 23A, 24A, 25A, 26A, 27A, 28A, 29A or 30A, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0022] In the present invention, for a billet with a diameter of 700-1200 mm and a C content of 25-55%, it is preferred to control the difference between the upper limit of the current oscillation and the target current value, and the difference between the target current value and the lower limit of the current oscillation within a specific range, which can further improve the carbon segregation phenomenon and make the carbon distribution inside the billet more uniform.

[0023] Preferably, the diameter of the ingot obtained by the continuous casting electromagnetic stirring is 700-1200 mm, for example, it can be 700 mm, 720 mm, 740 mm, 760 mm, 780 mm, 800 mm, 820 mm, 840 mm, 860 mm, 880 mm, 900 mm, 1000 mm, 1100 mm or 1200 mm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0024] Preferably, the ingot obtained by continuous casting and electromagnetic stirring comprises medium carbon steel.

[0025] Preferably, the C content in the medium carbon steel is 25-55% by mass, for example, 25%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54% or 55%, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0026] In the present invention, the medium carbon steel includes but is not limited to the following steel grades, calculated by mass percentage, C is 0.45-0.47%, Si is 0.25-0.29%, Mn is 0.65-0.69%, P≤0.015%, S≤0.005%, Cr≤0.25%, Ni≤0.25%, Cu≤0.25%, Mo≤0.08%, Al is 0.005-0.015%, and H≤0.0001%.

[0027] In the present invention, continuous casting electromagnetic stirring generally includes at least one of head-end electromagnetic stirring, strand electromagnetic stirring or end-end electromagnetic stirring. It is preferred to use head-end electromagnetic stirring, strand electromagnetic stirring and end-end electromagnetic stirring in sequence; wherein the head-end electromagnetic stirring is mainly used to stir the molten steel in the crystallizer, and generally does not need to be controlled by the current control method provided by the present invention. The current control method provided by the present invention is mainly used for control in strand electromagnetic stirring and end-end electromagnetic stirring.

[0028] Preferably, the superheat of the continuous casting electromagnetic stirring is 15-30°C, for example, it can be 15°C, 16°C, 17°C, 18°C, 19°C, 20°C, 21°C, 22°C, 23°C, 24°C, 25°C, 26°C, 27°C, 28°C, 29°C or 30°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0029] Preferably, the frequency of the continuous casting electromagnetic stirring is 1-2 Hz, for example, 1 Hz, 1.2 Hz, 1.4 Hz, 1.6 Hz, 1.8 Hz or 2 Hz, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0030] Preferably, the current of the electromagnetic stirring at the head end is 260-280A, for example, it can be 260A, 262A, 264A, 266A, 268A, 270A, 271A, 272A, 274A, 276A, 278A or 280A, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0031] Preferably, the target current value of the electromagnetic stirring of the casting strand is 160-170A, for example, it can be 160A, 162A, 164A, 166A, 168A or 170A, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0032] Preferably, the target current value of the end electromagnetic stirring is 260-270A, for example, it can be 260A, 262A, 264A, 266A, 268A or 270A, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0033] As a preferred technical solution of the present invention, the current control method includes the following steps:

[0034] S1, before continuous casting electromagnetic stirring, setting the control parameters of the frequency conversion controller in the electromagnetic stirrer, wherein the control parameters include the target current value, the upper limit value of the current oscillation, the lower limit value of the current oscillation, the increase value of the current oscillation amplitude, and the deceleration value of the current oscillation amplitude;

[0035] S2, start the electromagnetic stirrer and increase the actual current to the target current value;

[0036] S3, after reaching the target current value, gradually increase the current at a set speed increase value of 2-4A / s until it reaches the current oscillation upper limit value, and the difference between the current oscillation upper limit value and the target current value is 20-30A;

[0037] S4, after reaching the current oscillation upper limit, gradually reduce the current at a set deceleration value of 2-4A / s until it reaches the current oscillation lower limit, and the difference between the target current value and the current oscillation lower limit is 20-30A;

[0038] Repeat steps S3-S4 to make the current of the continuous casting electromagnetic stirring change in a periodic sinusoidal waveform until the continuous casting electromagnetic stirring is completed; the diameter of the ingot obtained by the continuous casting electromagnetic stirring is 700-1200 mm, and the C content in the ingot is 25-55% by mass; the superheat of the continuous casting electromagnetic stirring is 15-30°C, and the frequency is 1-2 Hz.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] (1) The current control method provided by the present invention can change the current of the electromagnetic stirring casting into a periodic sinusoidal waveform by regularly increasing or decreasing the current and oscillating alternately. It can break the fixed mode of constant current in the traditional stirring mode, and use the periodic current change to generate a periodic electromagnetic stirring force, so as to promote the steel liquid inside the ingot to produce a more uniform flow, thereby making the distribution of carbon elements and other components inside the ingot more uniform, effectively reducing the extreme difference of carbon segregation in the ingot, making the internal structure of the ingot more uniform, thereby improving the mechanical properties of the ingot and reducing the risk of defects such as cracks and fractures in the ingot during subsequent rolling, forging and other processing.

[0041] (2) Taking the preparation of medium carbon steel with a diameter of 800 mm by the current control method provided by the present invention as an example, under optimal conditions, the extreme difference in carbon segregation in the cross section (excluding the center point) can be reduced to less than 0.094%, and the extreme difference in carbon segregation in the cross section (including the center point) can be reduced to less than 0.096%. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 3 is a waveform diagram of the terminal electromagnetic stirring current in Example 1 of the present invention. DETAILED DESCRIPTION

[0043] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0044] Example 1

[0045] This embodiment provides a current control method for a continuous casting ingot stirrer. Taking the preparation of medium carbon steel with a diameter of 800 mm as an example, the steel comprises, in terms of mass percentage, 0.46% C, 0.27% Si, 0.67% Mn, 0.01% Al, and the remainder Fe. Raw materials are selected according to the above composition, and the raw materials are sequentially subjected to KR pretreatment, converter smelting, LF refining, and VD vacuum to obtain molten steel; the molten steel is subjected to electromagnetic stirring at the head end at a superheat of 20°C, a frequency of 1.5Hz, and a current of 271A; then electromagnetic stirring of the casting strand and electromagnetic stirring of the end are sequentially performed. During the process of electromagnetic stirring of the casting strand and electromagnetic stirring of the end, the current control method provided in this embodiment is respectively used for control, which specifically includes the following steps:

[0046] S1, before continuous casting electromagnetic stirring, setting the control parameters of the frequency conversion controller in the electromagnetic stirrer, wherein the control parameters include the target current value, the upper limit value of the current oscillation, the lower limit value of the current oscillation, the increase value of the current oscillation amplitude, and the deceleration value of the current oscillation amplitude;

[0047] S2, start the electromagnetic stirrer and increase the actual current to the target current value;

[0048] S3, after reaching the target current value, gradually increase the current at the set speed increase value until it reaches the current oscillation upper limit;

[0049] S4: After reaching the upper limit of the current oscillation, the current is gradually reduced at the set deceleration value until it reaches the lower limit of the current oscillation;

[0050] Repeat the operations of steps S3-S4 to make the current of the continuous casting electromagnetic stirring change into a periodic sinusoidal waveform until the continuous casting electromagnetic stirring is completed.

[0051] Taking the end electromagnetic stirring in this embodiment as an example, the waveform of the current is as follows: Figure 1 As shown, from Figure 1 It can be seen that the current of electromagnetic stirring changes in a periodic sinusoidal waveform.

[0052] The target current value, the difference between the upper limit of current oscillation and the target current value, the difference between the target current value and the lower limit of current oscillation, the increase rate of current oscillation amplitude, the deceleration rate of current oscillation amplitude, and the frequency in strand electromagnetic stirring and terminal electromagnetic stirring are shown in Table 1.

[0053] Table 1

[0054]

[0055] Example 2

[0056] This embodiment provides a current control method for a continuous casting strand stirrer. Taking the preparation of the same medium carbon steel as in Example 1 as an example, the molten steel is subjected to electromagnetic stirring at the head end at a superheat of 20°C, a frequency of 1.5 Hz, and a current of 271A. Then, electromagnetic stirring of the strand and electromagnetic stirring of the tail end are sequentially performed. During the strand electromagnetic stirring and the tail end electromagnetic stirring, the current control method provided in this embodiment is used for control, specifically comprising the following steps:

[0057] S1, before continuous casting electromagnetic stirring, setting the control parameters of the frequency conversion controller in the electromagnetic stirrer, wherein the control parameters include the target current value, the upper limit value of the current oscillation, the lower limit value of the current oscillation, the increase value of the current oscillation amplitude, and the deceleration value of the current oscillation amplitude;

[0058] S2, start the electromagnetic stirrer and increase the actual current to the target current value;

[0059] S3, after reaching the target current value, gradually increase the current at the set speed increase value until it reaches the current oscillation upper limit;

[0060] S4: After reaching the upper limit of the current oscillation, the current is gradually reduced at the set deceleration value until it reaches the lower limit of the current oscillation;

[0061] Repeat the operations of steps S3-S4 to make the current of the continuous casting electromagnetic stirring change into a periodic sinusoidal waveform until the continuous casting electromagnetic stirring is completed.

[0062] The target current value, the difference between the upper limit of current oscillation and the target current value, the difference between the target current value and the lower limit of current oscillation, the increase rate of current oscillation amplitude, the deceleration rate of current oscillation amplitude, and the frequency in strand electromagnetic stirring and terminal electromagnetic stirring are shown in Table 2.

[0063] Table 2

[0064]

[0065]

[0066] Example 3

[0067] This embodiment provides a current control method for a continuous casting strand stirrer. Taking the preparation of the same medium carbon steel as in Example 1 as an example, the molten steel is subjected to electromagnetic stirring at the head end at a superheat of 20°C, a frequency of 1.5 Hz, and a current of 271A. Then, electromagnetic stirring of the strand and electromagnetic stirring of the tail end are sequentially performed. During the strand electromagnetic stirring and the tail end electromagnetic stirring, the current control method provided in this embodiment is used for control, specifically comprising the following steps:

[0068] S1, before continuous casting electromagnetic stirring, setting the control parameters of the frequency conversion controller in the electromagnetic stirrer, wherein the control parameters include the target current value, the upper limit value of the current oscillation, the lower limit value of the current oscillation, the increase value of the current oscillation amplitude, and the deceleration value of the current oscillation amplitude;

[0069] S2, start the electromagnetic stirrer and increase the actual current to the target current value;

[0070] S3, after reaching the target current value, gradually increase the current at the set speed increase value until it reaches the current oscillation upper limit;

[0071] S4: After reaching the upper limit of the current oscillation, the current is gradually reduced at the set deceleration value until it reaches the lower limit of the current oscillation;

[0072] Repeat the operations of steps S3-S4 to make the current of the continuous casting electromagnetic stirring change into a periodic sinusoidal waveform until the continuous casting electromagnetic stirring is completed.

[0073] The target current value, the difference between the upper limit of current oscillation and the target current value, the difference between the target current value and the lower limit of current oscillation, the increase rate of current oscillation amplitude, the deceleration rate of current oscillation amplitude, and the frequency in strand electromagnetic stirring and terminal electromagnetic stirring are shown in Table 3.

[0074] Table 3

[0075]

[0076] Example 4

[0077] This embodiment provides a current control method for a continuous casting strand stirrer. The only difference compared with Example 1 is that the acceleration value and deceleration value in the strand electromagnetic stirring and the end electromagnetic stirring are both 1 A / s.

[0078] Example 5

[0079] This embodiment provides a current control method for a continuous casting strand stirrer. The only difference compared with Example 1 is that the acceleration value and deceleration value in the strand electromagnetic stirring and the end electromagnetic stirring are both 5 A / s.

[0080] Example 6

[0081] This embodiment provides a current control method for a continuous casting strand stirrer. The only difference compared with Example 1 is that the difference between the upper limit value of current oscillation and the target current value in the electromagnetic stirring of the casting strand and the end electromagnetic stirring, as well as the difference between the target current value and the lower limit value of current oscillation are both 10A.

[0082] Example 7

[0083] This embodiment provides a current control method for a continuous casting strand stirrer. The only difference compared with Example 1 is that the difference between the upper limit value of current oscillation and the target current value in the electromagnetic stirring of the casting strand and the end electromagnetic stirring, as well as the difference between the target current value and the lower limit value of current oscillation are both 40A.

[0084] Comparative Example 1

[0085] This comparative example provides a current control method for a continuous casting strand stirrer, which differs from Example 1 only in that a constant current is used in both the strand electromagnetic stirring and the end electromagnetic stirring, ie, stirring is performed at the target current value in Table 1.

[0086] The carbon-sulfur analyzer was used to measure the carbon segregation range of the cross section (excluding the center point) and the carbon segregation range of the cross section (including the center point). The results are shown in Table 4.

[0087] Table 4

[0088]

[0089] The following points can be seen from the data in Table 4:

[0090] (1) From the data of Examples 1-3, it can be seen that, taking the preparation of medium carbon steel with a diameter of 800 mm by the current control method provided by the present invention as an example, under optimal conditions, the extreme difference in carbon segregation in the cross section (excluding the center point) can be reduced to less than 0.094%, and the extreme difference in carbon segregation in the cross section (including the center point) can be reduced to less than 0.096%.

[0091] (2) A comprehensive comparison of the data of Example 1 and Examples 4-7 shows that the present invention can further enhance the electromagnetic stirring effect and reduce segregation by preferentially controlling the acceleration value, the deceleration value, and preferentially controlling the difference between the upper limit value of the current oscillation and the target current value, and the difference between the target current value and the lower limit value of the current oscillation.

[0092] (3) A comprehensive comparison of the data of Example 1 and Comparative Example 1 shows that the current control method provided by the present invention can effectively reduce the extreme difference in carbon segregation of the ingot by making the current of the continuous casting electromagnetic stirring change into a periodic sinusoidal waveform compared with a constant current, thereby making the internal structure of the ingot more uniform.

[0093] In summary, the present invention controls the electromagnetic stirring current to change into a periodic sinusoidal waveform, thereby improving the carbon segregation of the ingot and reducing the extreme difference in carbon segregation of the ingot, thereby making the internal composition of the ingot more uniform and improving the performance of the ingot.

[0094] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A current control method for a continuous casting strand stirrer, characterized in that: The current control method comprises the following steps: S1, before continuous casting electromagnetic stirring, setting the control parameters of the frequency conversion controller in the electromagnetic stirrer, wherein the control parameters include the target current value, the upper limit value of the current oscillation, the lower limit value of the current oscillation, the increase value of the current oscillation amplitude, and the deceleration value of the current oscillation amplitude; S2, start the electromagnetic stirrer and increase the actual current to the target current value; S3, after reaching the target current value, gradually increase the current at the set speed increase value until it reaches the current oscillation upper limit; S4: After reaching the upper limit of current oscillation, the current is gradually reduced at the set deceleration value until it reaches the lower limit of current oscillation; Repeat the operations of steps S3-S4 to make the current of the continuous casting electromagnetic stirring change in a periodic sinusoidal waveform until the continuous casting electromagnetic stirring is completed.

2. The current control method according to claim 1, wherein: The increasing value of the current oscillation amplitude is the increase in current per second; Preferably, the increasing speed of the current oscillation amplitude is 2-4 A / s.

3. The current control method according to claim 1 or 2, characterized in that: The deceleration value of the current oscillation amplitude is the reduction in current per second; Preferably, the deceleration value of the current oscillation amplitude is 2-4 A / s.

4. The current control method according to any one of claims 1 to 3, characterized in that: The difference between the current oscillation upper limit value and the target current value is 20-30A.

5. The current control method according to any one of claims 1 to 4, characterized in that: The difference between the target current value and the current oscillation lower limit is 20-30A.

6. The current control method according to any one of claims 1 to 5, characterized in that: The diameter of the ingot obtained by the continuous casting and electromagnetic stirring is 700-1200 mm.

7. The current control method according to any one of claims 1 to 6, characterized in that: The ingot obtained by continuous casting and electromagnetic stirring comprises medium carbon steel.

8. The current control method according to claim 7, characterized in that: The medium carbon steel has a C content of 25-55% by mass.

9. The current control method according to any one of claims 1 to 8, characterized in that: The superheat degree of the continuous casting electromagnetic stirring is 15-30°C; Preferably, the frequency of the continuous casting electromagnetic stirring is 1-2 Hz.

10. The current control method according to any one of claims 1 to 9, characterized in that: The current control method comprises the following steps: S1, before continuous casting electromagnetic stirring, setting the control parameters of the frequency conversion controller in the electromagnetic stirrer, wherein the control parameters include the target current value, the upper limit value of the current oscillation, the lower limit value of the current oscillation, the increase value of the current oscillation amplitude, and the deceleration value of the current oscillation amplitude; S2, start the electromagnetic stirrer and increase the actual current to the target current value; S3, after reaching the target current value, gradually increase the current at a set speed increase value of 2-4A / s until it reaches the current oscillation upper limit value, and the difference between the current oscillation upper limit value and the target current value is 20-30A; S4, after reaching the current oscillation upper limit, gradually reduce the current at a set deceleration value of 2-4A / s until it reaches the current oscillation lower limit, and the difference between the target current value and the current oscillation lower limit is 20-30A; Repeat steps S3-S4 to make the current of the continuous casting electromagnetic stirring change in a periodic sinusoidal waveform until the continuous casting electromagnetic stirring is completed; the diameter of the ingot obtained by the continuous casting electromagnetic stirring is 700-1200 mm, and the C content in the ingot is 25-55% by mass; the superheat of the continuous casting electromagnetic stirring is 15-30°C, and the frequency is 1-2 Hz.

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