Method for controlling segregation of high carbon steel in continuous casting

Abstract

The application provides a high-efficiency continuous casting high-carbon steel segregation control method, which comprises the following steps: taking the intersection of the vertical line of the center point of the arc of the continuous casting machine and the outer arc of the continuous casting machine as a process judgment point; taking the distance between the process judgment point and the liquid surface of the crystallizer as a process judgment distance; setting a segregation control condition according to the process judgment distance; wherein the segregation control condition comprises: the length of the solidification end of the casting blank is greater than the process judgment distance and enters the horizontal section of the continuous casting machine; in the high-efficiency continuous casting production, when the segregation control condition is met, the high cooling rate is ensured to be formed at the front end of the casting blank in the solidification process, and the heavy pressing is carried out before the critical point at which the liquid core flow of the casting blank disappears completely. The application can solve the problem that in the prior art, under high speed, for the case that the length of the solidification end is greater than the distance from the intersection of the vertical line of the center point of the arc of the continuous casting machine and the outer arc of the continuous casting machine to the liquid surface of the crystallizer, it is difficult to obtain stable control of the center segregation of the high-efficiency high-carbon steel by using a single technology.

Description

Technical Field

[0001] This invention relates to the field of continuous casting technology, and more specifically, to a method for controlling segregation in high-carbon steel through efficient continuous casting. Background Technology

[0002] High-carbon steel is more prone to segregation in continuously cast billets due to its high carbon content. Therefore, controlling segregation, especially center segregation, is the most critical quality requirement in the continuous casting process. If center segregation cannot be well controlled, it will result in severe banded and network carbon in the final material structure, affecting the material properties.

[0003] Especially as the casting speed increases, the solidification end lengthens, the two-phase region lengthens, and when the increase in static pressure head slows down or even stops increasing with the lengthening of the liquid core, the feeding capacity decreases, and the quality of the billet core, including porosity and segregation, increases rapidly, and central segregation deteriorates rapidly.

[0004] Currently, the main methods for controlling center segregation in high-carbon steel include reducing casting speed, reducing superheat, increasing stirring, and applying light or heavy pressure. These methods can effectively control center segregation. However, at high casting speeds, the length of the solidification end exceeds the distance from the intersection of the casting machine's vertical line and the outer arc of the casting machine to the liquid surface in the crystallizer. After entering the horizontal section, the static pressure head no longer increases, the feeding reaches its limit, and the center segregation of the billet increases sharply. Existing methods cannot effectively control center segregation. The effect of stirring is limited, and light or heavy pressure can easily introduce cracks, thus negating the effect of improving center segregation. Single-roll heavy pressure can eliminate shrinkage cavities, but its control over segregation is limited. Therefore, it is difficult for existing single technologies to achieve stable and efficient control of center segregation in high-carbon steel. Summary of the Invention

[0005] In view of the above problems, the purpose of this invention is to provide a method for controlling segregation in high-carbon steel through high-efficiency continuous casting, so as to solve the problem in the prior art that, under high casting speed, when the length of the solidification end is greater than the distance from the intersection of the perpendicular line from the center point of the casting machine's arc to the liquid surface of the crystallizer, it is difficult to achieve stable control of center segregation in high-carbon steel using a single technique.

[0006] This invention provides a method for controlling segregation in high-carbon steel through continuous casting, comprising the following steps:

[0007] The intersection of the perpendicular line from the center point of the arc of the continuous casting machine and the outer arc of the continuous casting machine is taken as the process judgment point;

[0008] The distance between the process judgment point and the liquid surface in the crystallizer is taken as the process judgment distance;

[0009] Segregation control conditions are set according to the process judgment distance; wherein, the segregation control conditions include: the length of the solidification end of the billet is greater than the process judgment distance and it enters the horizontal section of the continuous casting machine;

[0010] In high-efficiency continuous casting production, when the segregation control conditions are met, it is ensured that a high cooling rate is formed at the leading edge of the billet during solidification, and heavy pressure is applied before the critical point when the liquid core flow of the billet completely disappears.

[0011] Furthermore, in a preferred embodiment, the segregation control conditions also include the fact that the position of the critical point at which the liquid core flow of the billet completely disappears is greater than the process judgment distance.

[0012] Furthermore, a preferred embodiment is that the process conditions for ensuring a high cooling rate at the front edge during the solidification process of the billet include: a secondary cooling process water volume of not less than 1.2 L / kg.

[0013] Furthermore, a preferred embodiment is that the process conditions for ensuring a high cooling rate at the front edge during solidification of the billet include a superheat of 25–55°C.

[0014] Furthermore, a preferred embodiment is that the central solid fraction at the critical point where the liquid core flow of the billet completely disappears is 0.65 to 0.75.

[0015] Furthermore, a preferred embodiment is that the heavy pressure applied before the critical point where the liquid core flow of the cast billet completely disappears includes:

[0016] The location of the critical point at which the liquid core flow of the billet completely disappears is determined based on the central solid fraction standard, and this location is taken as the critical pressure position.

[0017] The billet is subjected to heavy pressure before the critical pressure position.

[0018] Furthermore, a preferred approach is to use a single-roller, sufficient pressing process to press the billet under heavy pressure before the critical point when the liquid core flow of the billet completely disappears.

[0019] Furthermore, a preferred embodiment is that the compression under heavy pressure is greater than 14 mm.

[0020] Furthermore, a preferred embodiment is that the length of the solidification end of the billet is related to the cross-sectional dimensions of the billet and the casting speed.

[0021] Furthermore, a preferred embodiment is that the billet is a high-carbon steel billet.

[0022] As can be seen from the above technical solution, the high-efficiency continuous casting high-carbon steel segregation control method provided by this invention uses the intersection of the perpendicular line from the center point of the continuous casting machine's arc and the outer arc of the continuous casting machine as the process judgment point; the distance between the process judgment point and the liquid surface of the crystallizer as the process judgment distance; and sets segregation control conditions. For cases where the length of the solidification end of the billet exceeds the process judgment distance and enters the horizontal section of the continuous casting machine, a high cooling rate is ensured at the front edge of the billet during solidification, while overall segregation process control is implemented under heavy pressure before the critical point where the liquid core flow of the billet completely disappears. Based on the segregation mechanism and extensive practical experience in individual technical engineering, by designing a high cooling rate process at the solidification front edge during continuous casting, and simultaneously applying heavy pressure before the critical point where the liquid core flow disappears, the method achieves stable control of the center segregation effect of high-carbon steel under high-efficiency continuous casting. This provides technical guidance for the high-efficiency continuous casting production of high-carbon steel. On the basis of stable control of center segregation in high-efficiency continuous casting of high-carbon steel, it reduces the difficulty of controlling superheat, facilitates production control, and simplifies the layout of the straightening machine.

[0023] To achieve the foregoing and related objectives, one or more aspects of the invention include the features that will be described in detail below. The following description and accompanying drawings illustrate certain exemplary aspects of the invention. However, these aspects indicate only a few of the various ways in which the principles of the invention can be used. Furthermore, the invention is intended to encompass all such aspects and their equivalents. Attached Figure Description

[0024] Other objects and results of the invention will become more apparent and readily understood with reference to the following description taken in conjunction with the accompanying drawings. In the drawings:

[0025] Figure 1 A flowchart of an efficient continuous casting high-carbon steel segregation control method according to an embodiment of the present invention;

[0026] Figure 2 This is a schematic diagram of the intersection point of the perpendicular line from the center point of the arc of the continuous casting machine and the outer arc of the continuous casting machine according to an embodiment of the present invention. Detailed Implementation

[0027] In the following description, numerous specific details are set forth for illustrative purposes and to provide a thorough understanding of one or more embodiments. However, it will be apparent that these embodiments may also be implemented without these specific details.

[0028] In response to the aforementioned problem in the existing technology that, under high casting speeds, when the length of the solidification end is greater than the distance from the intersection of the perpendicular line from the center point of the casting machine's arc to the liquid surface of the crystallizer, it is difficult to achieve stable control of high-carbon steel center segregation using a single technology, a method for controlling segregation in high-carbon steel through high-efficiency continuous casting is proposed.

[0029] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0030] To illustrate the efficient method for controlling segregation in continuous casting of high-carbon steel provided by this invention. Figure 1 The flowchart of an efficient method for controlling segregation in continuous casting of high-carbon steel according to an embodiment of the present invention is shown; Figure 2 The diagram shows the intersection of the perpendicular line from the center point of the arc of the continuous casting machine and the outer arc of the continuous casting machine according to an embodiment of the present invention.

[0031] like Figure 1 Combination Figure 2 As shown in the figure, the efficient method for controlling segregation in high-carbon steel continuous casting provided by the present invention includes the following steps:

[0032] S1. The intersection of the perpendicular line from the center point of the arc of the continuous casting machine and the outer arc of the continuous casting machine is taken as the process judgment point.

[0033] S2. The distance between the process judgment point and the liquid surface of the crystallizer is taken as the process judgment distance;

[0034] S3. Set segregation control conditions based on the process judgment distance; among which, the segregation control conditions include: the length of the solidification end of the billet is greater than the process judgment distance and enters the horizontal section of the continuous casting machine;

[0035] S4. In high-efficiency continuous casting production, when the segregation control conditions are met, ensure that the billet forms a high cooling rate at the front edge during the solidification process, and at the same time, apply heavy pressure before the critical point when the liquid core flow of the billet completely disappears.

[0036] Among them, the "front edge" in ensuring that the billet forms a high cooling rate at the front edge during the solidification process refers to the front edge of the billet solidification.

[0037] When the solidification end of the billet exceeds the process judgment distance and enters the horizontal section, the static pressure head stops increasing, while the liquid core continues to lengthen. This is the reason for the sharp increase in center segregation in high-carbon steel produced by efficient continuous casting. For example, for a 160x160mm small square billet using a full-arc mill with an arc radius of 10m, the process judgment distance is approximately 16m. If producing No. 70 steel at a casting speed of 3.3m / min, the solidification end of the billet will be around 24m, far exceeding the process judgment distance. In this case, effective control of high-carbon steel segregation requires overall process control. The process control strategy is to ensure a high cooling rate at the leading edge during billet solidification and to apply heavy pressure before the critical point when the liquid core flow completely disappears.

[0038] By using the intersection of the perpendicular line from the center point of the continuous casting machine's arc and the outer arc of the continuous casting machine as the process judgment point, and the distance between the process judgment point and the liquid surface of the crystallizer as the process judgment distance, and setting segregation control conditions, for cases where the length of the solidification end of the billet exceeds the process judgment distance and enters the horizontal section of the continuous casting machine, a process control method is adopted to ensure that the billet forms a high cooling rate at the front edge during solidification, and to apply heavy pressure before the critical point where the liquid core flow of the billet completely disappears. Based on the segregation mechanism and a large amount of practical experience in individual technical engineering, by designing a process to achieve a high cooling rate at the solidification front edge in the continuous casting process, and applying heavy pressure before the critical point where the liquid core flow disappears, the center segregation effect of high carbon steel under high-efficiency continuous casting is stably controlled. This provides technical guidance for the high-efficiency continuous casting production of high carbon steel. On the basis of stably controlling the center segregation of high carbon steel in high-efficiency continuous casting, the difficulty of controlling superheat is reduced, which is conducive to the realization of production control and simplifies the layout of the straightening machine.

[0039] As a preferred embodiment of the present invention, the segregation control condition further includes that the position of the critical point where the liquid core flow of the billet completely disappears is greater than the process judgment distance. That is, the distance between the position of the critical point where the liquid core flow of the billet completely disappears and the liquid surface of the crystallizer is greater than the process judgment distance. Multiple experiments have verified that when both the length of the solidification end of the billet entering the horizontal section of the continuous casting machine is greater than the process judgment distance and the position of the critical point where the liquid core flow of the billet completely disappears is greater than the process judgment distance are simultaneously satisfied, the overall process control method that ensures a high cooling rate at the leading edge of the billet during solidification and applies heavy pressure before the critical point where the liquid core flow of the billet completely disappears is more applicable, resulting in better segregation control. Of course, if only the condition that the length of the solidification end of the billet enters the horizontal section of the continuous casting machine is satisfied, but the condition that the position of the critical point where the liquid core flow of the billet completely disappears is greater than the process judgment distance is not satisfied, the overall process control method provided in this embodiment of the present invention is also applicable, but the segregation control effect is not as good as when both of the above conditions are met.

[0040] As a preferred embodiment of the present invention, the process conditions that ensure a high cooling rate at the front edge of the cast billet during solidification include: a secondary cooling process water concentration of not less than 1.2 L / kg. A secondary cooling process water concentration greater than 1.2 L / kg can help the cast billet form a high cooling rate at the front edge during solidification.

[0041] As a preferred embodiment of the present invention, the process conditions that ensure a high cooling rate at the front edge of the casting during solidification include a superheat of 25–55°C. A superheat of 25–55°C helps the casting achieve a high cooling rate at the front edge during solidification. Preferably, 25°C, 40°C, or 55°C are used. Of course, any temperature between 25 and 55°C can also be selected.

[0042] As a preferred embodiment of the present invention, the standard for the central solid fraction of the critical point at which the liquid core flow completely disappears in the cast billet is 0.65 to 0.75. The location of the critical point at which the liquid core flow completely disappears can be determined by the central solid fraction standard, which is generally between 0.65 and 0.75.

[0043] As a preferred embodiment of the present invention, the heavy pressure applied before the critical point at which the liquid core flow of the cast billet completely disappears includes:

[0044] The location of the critical point at which the liquid core flow of the billet completely disappears is determined based on the central solid fraction standard, and this location is taken as the critical pressure position.

[0045] The billet is subjected to heavy reduction before reaching the critical reduction position.

[0046] The location of the critical point where the liquid core flow of the billet completely disappears is determined by the central solids ratio standard. This location can be used to determine the position for applying heavy pressure to the billet, and also to determine whether the segregation control condition is met, i.e., whether the location of the critical point where the liquid core flow of the billet completely disappears is greater than the process judgment distance. When both the length of the solidification end of the billet is greater than the process judgment distance and it enters the horizontal section of the continuous casting machine, and the location of the critical point where the liquid core flow of the billet completely disappears is greater than the process judgment distance, the overall process control of ensuring that the billet forms a high cooling rate at the leading edge during solidification and applying heavy pressure before the critical point where the liquid core flow of the billet completely disappears is more suitable and the segregation control effect is better.

[0047] As a preferred embodiment of the present invention, during the heavy pressing process before the critical point where the liquid core flow of the billet completely disappears, a single-roll, sufficient pressing process is used to press the billet. By using a single-roll, sufficient pressing process to press the billet, combined with a high cooling rate, better control of center segregation in the billet can be achieved.

[0048] In a preferred embodiment of the present invention, the compression amount under heavy pressure is greater than 14 mm. This is a preferred embodiment, wherein the compression amount can be 15 mm, 16 mm, 17 mm, etc., as long as it is greater than 14 mm.

[0049] In a preferred embodiment of the present invention, the length of the solidification end of the billet is related to the cross-sectional dimensions of the billet and the casting speed. Based on the cross-sectional dimensions of the billet and the casting speed, the length of the solidification end of the billet can be obtained, thereby determining whether the billet in the current high-efficiency continuous casting production meets the segregation control conditions.

[0050] As a preferred embodiment of the present invention, the billet is a high-carbon steel billet. Although the method provided in the embodiments of the present invention can also be applied to other types of billets, extensive practice and experimental verification have shown that it is more suitable for high-carbon steel billets.

[0051] To better illustrate the efficient continuous casting high-carbon steel segregation control method provided by this invention, the following example is given:

[0052] Example 1

[0053] Taking the continuous casting production of small square billets in a domestic plant as an example, the cross-section is 160X160mm, the machine is a full-arc type with an arc radius of 10m, and the distance from the perpendicular line from the center point of the arc of the continuous casting machine to the intersection point of the outer arc of the continuous casting machine to the liquid surface of the crystallizer is about 16m (i.e., the process judgment distance is 16m). If 70# steel is produced and the casting speed reaches 3.3m / min, the length of the solidification end is about 24m, which is much greater than the process judgment distance. Among them, the critical point where the liquid core flow completely disappears, determined according to the standard of 0.65 of the central solids fraction, is about 22.8m, which is also much greater than the process judgment distance. Therefore, in order to control the center segregation of the billet, a cooling process with a superheat of 45℃ and a secondary cooling water ratio of 1.3L / kg is adopted to ensure that a high cooling rate is formed at the front edge during the solidification process of the billet. At the same time, a single roll is pressed down by 15mm on a 22.5m straightening machine, and the center segregation index is stably controlled within 1.1.

[0054] Example 2

[0055] Another domestic factory uses a continuous casting machine for small square billets with a cross-section of 165x165mm. The machine is a full-arc type with an arc radius of 10m. The distance from the perpendicular line from the center point of the arc of the continuous casting machine to the intersection point of the outer arc of the machine is approximately 16m from the liquid surface in the crystallizer (i.e., the process judgment distance is 16m). If producing 65# steel at a casting speed of 2.8m / min, the length of the solidification end is approximately 20.7m, far exceeding the process judgment distance. The critical point at which the liquid core flow completely disappears, determined according to the standard of 0.65 for the central solids fraction, is approximately 19.7m, also far exceeding the process judgment distance. Therefore, to control the central segregation of the billet, a cooling process with a superheat of 45℃ and a secondary cooling water ratio of 1.5L / kg is adopted to ensure a high cooling rate at the leading edge during billet solidification. A single roll is used to reduce the central segregation by 15mm on an 18.2m straightening machine, and the average central segregation index is stably controlled below 1.08.

[0056] It should be noted that this specific embodiment is merely a detailed description of the efficient continuous casting high-carbon steel segregation control method provided by the present invention in practical applications, and does not limit the technical solution provided by the present invention.

[0057] As can be seen from the above specific embodiments, the high-efficiency continuous casting high-carbon steel segregation control method provided by the present invention uses the intersection of the perpendicular line from the center point of the continuous casting machine's arc and the outer arc of the continuous casting machine as the process judgment point; the distance between the process judgment point and the liquid surface of the crystallizer as the process judgment distance; and sets segregation control conditions. For cases where the length of the solidification end of the billet exceeds the process judgment distance and enters the horizontal section of the continuous casting machine, a high cooling rate is ensured at the front edge of the billet during solidification, while overall segregation process control is implemented under heavy pressure before the critical point where the liquid core flow of the billet completely disappears. Based on the segregation mechanism and extensive practical experience in individual technical engineering, by designing a high cooling rate process at the solidification front edge during continuous casting, and simultaneously applying heavy pressure before the critical point where the liquid core flow disappears, the method achieves stable control of the center segregation effect of high-carbon steel under high-efficiency continuous casting. This provides technical guidance for the high-efficiency continuous casting production of high-carbon steel. Based on the stable control of center segregation in high-efficiency continuous casting of high-carbon steel, it reduces the difficulty of controlling superheat, facilitates production control, and simplifies the layout of the straightening machine.

[0058] The efficient continuous casting high-carbon steel segregation control method proposed according to the present invention has been described above by way of example with reference to the accompanying drawings. However, those skilled in the art should understand that various modifications can be made to the efficient continuous casting high-carbon steel segregation control method proposed by the present invention without departing from the scope of the invention. Therefore, the scope of protection of the present invention should be determined by the contents of the appended claims.

Claims

1. A method for controlling segregation in high-carbon steel through continuous casting, characterized in that, Includes the following steps: The intersection of the perpendicular line from the center point of the arc of the continuous casting machine and the outer arc of the continuous casting machine is taken as the process judgment point; The distance between the process judgment point and the liquid surface in the crystallizer is taken as the process judgment distance; Segregation control conditions are set according to the process judgment distance; wherein, the segregation control conditions include: the length of the solidification end of the billet is greater than the process judgment distance and it enters the horizontal section of the continuous casting machine; In high-efficiency continuous casting production, when the segregation control conditions are met, it is ensured that a high cooling rate is formed at the leading edge of the billet during solidification, and heavy pressure is applied before the critical point when the liquid core flow of the billet completely disappears; wherein, the process conditions for ensuring that a high cooling rate is formed at the leading edge of the billet during solidification include: the secondary cooling process water volume is not less than 1.2 L / kg; and the superheat is 25~55℃.

2. The method for controlling segregation in high-carbon steel through efficient continuous casting according to claim 1, characterized in that, The segregation control conditions also include the fact that the position of the critical point where the liquid core flow of the billet completely disappears is greater than the process judgment distance.

3. The method for controlling segregation in high-carbon steel through efficient continuous casting according to claim 1, characterized in that, The standard for the central solid fraction at the critical point where the liquid core flow of the billet completely disappears is 0.65~0.

75.

4. The method for controlling segregation in high-carbon steel through efficient continuous casting according to claim 3, characterized in that, The process of applying heavy pressure before the critical point when the liquid core flow in the cast billet completely disappears includes: The location of the critical point at which the liquid core flow of the billet completely disappears is determined based on the central solid fraction standard, and this location is taken as the critical pressure position. The billet is subjected to heavy pressure before the critical pressure position.

5. The method for controlling segregation in high-carbon steel through efficient continuous casting according to claim 1, characterized in that, During the process of applying heavy pressure before the critical point when the liquid core flow of the cast billet completely disappears, The billet is subjected to heavy pressing using a single-roll, full-volume pressing process.

6. The method for controlling segregation in high-carbon steel through efficient continuous casting according to claim 1, characterized in that, The compression under the heavy pressure is greater than 14 mm.

7. The method for controlling segregation in high-carbon steel through efficient continuous casting according to claim 1, characterized in that, The length of the solidification end of the billet is related to the cross-sectional dimensions of the billet and the casting speed.

8. The method for controlling segregation in high-carbon steel through efficient continuous casting according to claim 1, characterized in that, The billet is a high-carbon steel billet.

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