Method for controlling segregation of high carbon high alloy steel in continuous casting

Abstract

The application provides a high-efficiency continuous casting high-carbon high-alloy 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; the segregation control condition comprises that 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; when the segregation control condition is met, low cooling rate is ensured to be formed at the solidification front during the solidification process of the casting blank, and heavy pressing is carried out before and after 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 the condition of high pulling 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 high-efficiency high-carbon high-alloy 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, high-alloy steel produced by continuous casting. Background Technology

[0002] High-carbon high-alloy steel is more prone to segregation in continuously cast billets due to its high carbon content. Furthermore, the interaction between elements can increase segregation. Therefore, controlling segregation, especially center segregation, is the most critical quality requirement in the continuous casting process. If center segregation is not well controlled, it will result in severe banded and network carbon structures in the final material, affecting 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 control of center segregation in high-carbon steel and high-alloy steel mainly employs techniques such as 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, once the solidification end reaches the horizontal section after the distance from the intersection of the vertical line from the center point of the casting machine's arc and the outer arc of the casting machine to the liquid surface in the crystallizer stops increasing and feeding reaches its limit, 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, negating the improvement effect on center segregation. Single-roll heavy pressure can eliminate shrinkage cavities, but its control over segregation is limited. Therefore, existing single technologies are insufficient to achieve stable control of center segregation in high-carbon and high-alloy 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 high-alloy steel through 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 and the outer arc of the casting machine to the liquid surface of the crystallizer, it is difficult to achieve stable control of center segregation in high-carbon high-alloy steel using a single technique.

[0006] This invention provides a method for controlling segregation in high-carbon, high-alloy steel produced by 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, a low cooling rate is ensured at the solidification front during the solidification process of the billet, and heavy pressure is applied before and after 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 low cooling rate at the solidification front during the solidification process of the billet include: a secondary cooling process water volume of less than 1.2 L / kg.

[0013] Furthermore, a preferred embodiment is that the process conditions for ensuring a low cooling rate at the solidification front during the solidification process of the billet include: a superheat of less than 25°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 includes applying heavy pressure before and after the critical point where the liquid core flow of the cast billet completely disappears, comprising:

[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 and after the critical pressure position.

[0018] Furthermore, a preferred approach is to apply heavy pressure to the billet using a single-roller, sufficient pressing process both before and after the critical point when the liquid flow in the billet completely disappears.

[0019] Furthermore, in a preferred embodiment, the amount of reduction under heavy pressure is not less than 7 mm; and the sum of the reduction amounts under heavy pressure at the positions before and after the critical point where the liquid core flow of the billet completely disappears is not less than 15 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 made of high-carbon alloy steel or high-alloy steel.

[0022] As can be seen from the above technical solution, the efficient continuous casting segregation control method for high-carbon high-alloy steel 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 low cooling rate is ensured at the front edge during the billet solidification process, while overall segregation process control is implemented under heavy pressure before and after 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 and implementing a low cooling rate at the solidification front edge during the continuous casting process, and simultaneously applying heavy pressure before and after the critical point where the liquid core flow disappears, the method achieves stable control of the center segregation effect of high-carbon steel under efficient continuous casting. This provides technical guidance for the efficient continuous casting production of high-carbon high-alloy steel. Based on the stable control of center segregation in efficient continuous casting of high-carbon steel, it reduces the difficulty of controlling superheat, which is beneficial for 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 a high-efficiency continuous casting method for controlling segregation in high-carbon, high-alloy steel 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 center segregation in high-carbon high-alloy steel using a single technology, a method for controlling segregation in high-carbon high-alloy steel using 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 segregation control method for continuous casting of high-carbon, high-alloy steel provided by this invention. Figure 1 The flowchart of a method for controlling segregation in high-carbon high-alloy steel by continuous casting 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 continuously cast high-carbon high-alloy steel 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, a low cooling rate is ensured at the solidification front during the solidification process of the billet, and heavy pressure is applied before and after the critical point when the liquid core flow of the billet completely disappears.

[0036] When the length of the solidification end of the billet exceeds the distance from the intersection of the vertical line from the center point of the continuous casting machine's arc and the outer arc of the machine to the liquid surface in the crystallizer, it enters the horizontal section. At this point, 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-efficiency continuous casting of high-carbon and high-alloy steel. For example, for a 160x160mm small square billet using a full-arc casting machine with an arc radius of 10m, the distance from the intersection of the vertical line from the center point of the continuous casting machine's arc and the outer arc to the liquid surface in the crystallizer is approximately 16m. If the casting speed for 70# steel reaches 3.3m / min, the solidification end will be approximately 24m, far exceeding the distance from the intersection of the vertical line from the center point of the continuous casting machine's arc and the outer arc to the liquid surface in the crystallizer. Therefore, effectively controlling segregation in high-efficiency continuous casting of high-carbon and high-alloy steel requires overall process control. The process control strategy is to ensure a low cooling rate at the leading edge during billet solidification, thereby making the microstructure more uniform, and to apply heavy pressure before and after the critical point where the liquid core flow of the billet completely disappears.

[0037] High-carbon high-alloy steel refers to both high-carbon alloy steel and high-alloy steel.

[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 a low cooling rate is formed at the front edge during the solidification process of the billet, and to apply heavy pressure before and after 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 with a low cooling rate at the solidification front edge in the continuous casting process, and applying heavy pressure before and after 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 and high alloy 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 at the same time simplifies the layout of the straightening machine.

[0039] As a preferred embodiment of the present invention, the segregation control conditions also include 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. After multiple experimental verifications, it has been found that when both 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 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 met, the overall process control segregation method that ensures a low cooling rate at the leading edge during the solidification process of the billet, and applies heavy pressure before and after the critical point where the liquid core flow of the billet completely disappears, is more applicable and yields better segregation control results. Of course, if only the condition that 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 is met, 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 met, the overall process control method provided in the embodiments of the present invention can also be applied, 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 low cooling rate at the solidification front during the solidification process of the billet include: a secondary cooling process water volume of less than 1.2 L / kg. A secondary cooling process water volume of less than 1.2 L / kg can help the billet form a low cooling rate at the solidification front during the solidification process.

[0041] As a preferred embodiment of the present invention, the process conditions for ensuring a low cooling rate at the solidification front during the solidification process of the cast billet include: a superheat of less than 25°C. A superheat of less than 25°C helps the cast billet to form a low cooling rate at the solidification front during the solidification process. The superheat can preferably be any temperature below 25°C, such as 10°C, 15°C, or 20°C.

[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 and after 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 pressure before and after the critical pressure position.

[0046] The location of the critical point where the liquid core flow of the billet completely disappears is determined by the central solid fraction 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, it is more suitable to adopt an overall process control that ensures a low cooling rate at the leading edge during the solidification process of the billet, and applies heavy pressure before and after the critical point where the liquid core flow of the billet completely disappears, resulting in better segregation control.

[0047] As a preferred embodiment of the present invention, the heavy pressure process is carried out before and after the critical point when the liquid core flow of the billet completely disappears.

[0048] Before and after the critical point where the liquid core flow of the billet completely disappears, a single-roll, full-volume reduction process is used to heavily reduce the billet. This single-roll, full-volume reduction process, combined with a low cooling rate, allows for better control of center segregation in high-carbon, high-alloy steel billets.

[0049] In a preferred embodiment of the present invention, the reduction under heavy pressure is not less than 7 mm; and the sum of the reduction under heavy pressure at positions before and after the critical point where the liquid wicking of the billet completely disappears is not less than 15 mm. Specifically, the reduction of each roller at positions before and after the critical point where the liquid wicking of the billet completely disappears is not less than 7 mm; for example, 8 mm, 9 mm, 10 mm, etc. The sum of the weights under heavy pressure from each roller at positions before and after the critical point where the liquid wicking of the billet completely disappears is not less than 15 mm. When using single-roller heavy pressure, a front pressure roller is installed before the critical point where the liquid wicking of the billet completely disappears, and a rear pressure roller is installed after the critical point where the liquid wicking of the billet completely disappears. The reduction of both the front and rear pressure rollers is not less than 7 mm, and the sum of the reduction under heavy pressure from the two pressure rollers is not less than 15 mm.

[0050] 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.

[0051] In a preferred embodiment of the present invention, the billet is made of high-carbon alloy steel or high-alloy steel. The carbon content of high-carbon alloy steel is generally between 0.65% and 1.35%; high-alloy steel refers to alloy steel containing more than 10% alloying elements. The efficient continuous casting segregation control method for high-carbon and high-alloy steel provided by the present invention is mainly aimed at the efficient continuous casting production of high-carbon and high-alloy steels, including spring steel (60Si2Mn), bearing steel GCr15, and high-alloy tool steels such as T91 and P91.

[0052] To better illustrate the efficient method for controlling segregation in continuous casting of high-carbon, high-alloy steel provided by this invention, the following example is given:

[0053] Example 1

[0054] Taking the continuous casting production of small square billets in a domestic factory as an example, the cross-section is 160X160mm, the machine is a full arc type with an arc radius of 10m, and the distance between the perpendicular line from the center point of the arc of the continuous casting machine and the intersection point of the outer arc of the continuous casting machine and the liquid surface of the crystallizer is about 16m (that is, the process judgment distance is 16m). If 60Si2Mn steel is produced and the casting speed reaches 3.3m / min, then the solidification end of the billet is about 24.6m, 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 central solid fraction of 0.65, is about 23.7m, 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 20℃ and a secondary cooling water ratio of 0.8L / kg was adopted to ensure that a low cooling rate was formed at the front edge during the solidification process of the billet. A single roll was pressed down by 9mm on a straightening machine at a height of 22.6m, which is less than the critical point where the liquid core flow completely disappears, and at the same time, a single roll was pressed down by 8mm on a straightening machine at a height of 23.9m, which is greater than the critical point where the liquid core flow completely disappears. The center segregation index was stably controlled within 1.09.

[0055] It should be noted that this specific embodiment is merely a detailed description of the efficient continuous casting segregation control method for high-carbon high-alloy steel provided by the present invention in practical applications, and does not limit the technical solution provided by the present invention.

[0056] As can be seen from the above specific embodiments, the high-efficiency continuous casting segregation control method for high-carbon and high-alloy steel 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 low cooling rate is ensured at the front edge during the billet solidification process, while overall segregation process control is implemented under heavy pressure before and after 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 and implementing a low cooling rate at the solidification front edge during the continuous casting process, and simultaneously applying heavy pressure before and after 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 and high-alloy 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, which is beneficial for production control and simplifies the layout of the straightening machine.

[0057] The efficient method for controlling segregation in continuous casting of high-carbon, high-alloy steel 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 method for controlling segregation in continuous casting of high-carbon, high-alloy steel according to 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, high-alloy steel produced by 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, a low cooling rate is ensured at the solidification front during the solidification process of the billet, and heavy pressure is applied before and after the critical point when the liquid core flow of the billet completely disappears; wherein, the process conditions for ensuring a low cooling rate at the solidification front during the solidification process of the billet include: the secondary cooling process water volume is less than 1.2 L / kg; and the superheat is less than 25°C.

2. The method for controlling segregation in high-carbon, high-alloy 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, high-alloy 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, high-alloy steel through efficient continuous casting according to claim 3, characterized in that, The process of applying heavy pressure before and after the critical point where the liquid core flow of 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 and after the critical pressure position.

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

6. The method for controlling segregation in high-carbon, high-alloy steel through efficient continuous casting according to claim 1, characterized in that, The compression under the heavy pressure is not less than 7 mm; and... The sum of the pressure reduction under heavy pressure at the positions before and after the critical point where the liquid core flow of the billet completely disappears shall not be less than 15 mm.

7. The method for controlling segregation in high-carbon, high-alloy 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.

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