Method for controlling non-pressing length of billet tail and pressing method of continuous casting billet

Abstract

The invention provides a method for controlling the non-reduction length of a billet tail and a reduction method of a continuous casting billet, and belongs to the technical field of continuous casting, and the method comprises the following steps: setting a tail billet non-reduction interval at the billet tail of the continuous casting billet; in the process that the continuous casting billet enters the tail billet, when the front end of the non-pressing section of the tail billet sequentially reaches the position of the withdrawal and straightening machine of the pressing section in the billet drawing direction, the pressing work of the corresponding withdrawal and straightening machine is correspondingly stopped in sequence, so that the withdrawal and straightening machine of the pressing section gradually stops the pressing work until the last withdrawal and straightening machine of the pressing section stops the pressing work, and the final withdrawal and straightening machine of the pressing section stops the pressing work. And the blank tail non-pressing length is controlled to be located in the tail blank non-pressing interval. By means of the method, the problem that in the prior art, an effective scheme capable of effectively controlling the length of the continuous casting billet with the billet tail not pressed down so as to reduce the remelting cost of the continuous casting billet without pressing down does not exist can be solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of continuous casting, more particularly, to a method for controlling the length of a non-press-down billet tail and a press-down method for a continuous casting billet. BACKGROUND

[0002] From the process effect, the press-down technology has a significant effect on the improvement of the internal quality of the continuous casting billet, and the press-down technology has been widely applied in various billet types. In the process of the tail billet of each pouring, due to the reduction of the drawing speed and the capping operation, the tail billet is very hard, the drawing straightening machine is lifted during the control of the tail billet passing through the drawing straightening machine, and therefore the tail billet is not pressed down. In addition, due to the reduction or even stop of the drawing speed, the solidification end of the billet is shortened, the press-down interval is shortened, and the tail billet is not pressed down for a long time. Therefore, the press-down technology must be used to improve the internal quality of the steel, and the steel is usually a high-grade product steel or a special steel. The continuous casting billet that is not pressed down can only be treated by re-melting, and therefore the waste of the continuous casting billet is caused, and the yield and the profit are reduced.

[0003] When the continuous casting pouring is quickly finished, the molten steel entering the crystallizer from the tundish is stopped, the casting flow enters the tail billet process, and the drawing speed is quickly reduced or even returned to zero, so as to perform the capping operation. This process generally needs 5-10 minutes. After the temperature of the tail billet is reduced, the drawing speed is started to be increased, and gradually increased to the normal production drawing speed. During the tail billet process, the drawing speed is once returned to zero, and the press-down cannot be stopped, otherwise the drawing accident will be caused. In addition, during the tail billet process, the drawing speed is lower than the normal production drawing speed. Due to the reduction of the drawing speed, the solidification end is shortened, and the press-down interval is reduced. Even the first drawing straightening machine position is less than the press-down interval, so that the press-down cannot be performed. Even if the tail billet process meets the press-down condition, the press-down is ended after the first drawing straightening machine is not pressed down, so that the tail billet is not pressed down for a long time.

[0004] Through a large number of field statistics, the length of the tail billet that is not pressed down is related to the arrangement of the drawing straightening machine, and is about 12-18 m. For a bloom, such as a 250x300 mm bloom, the waste is more serious. In addition, the tail billet that is not pressed down needs to be re-melted, the cost is increased, and the larger the section, the greater the influence, and even unacceptable.

[0005] In summary, in the prior art, there is no effective scheme for effectively controlling the length of the tail billet that is not pressed down, so as to reduce the re-melting cost of the tail billet that is not pressed down. SUMMARY

[0006] In view of the above problems, the present application aims to provide a method for controlling the length of the non-press-down tail of a continuous casting billet and a press-down method for a continuous casting billet, so as to solve the problem in the prior art that there is no effective solution to effectively control the length of the non-press-down tail of a continuous casting billet to reduce the cost of recycling the non-press-down continuous casting billet.

[0007] The present application provides a method for controlling the length of the non-press-down tail of a continuous casting billet, comprising the following steps:

[0008] Setting a tail billet non-press-down interval in the tail of the continuous casting billet;

[0009] After the continuous casting billet enters the tail billet process, along the direction of the billet drawing, when the front end of the tail billet non-press-down interval reaches the position of the press-down section of the withdrawal-straightening machine in sequence, the press-down work of the corresponding withdrawal-straightening machine is stopped in sequence, so that the press-down work of the withdrawal-straightening machine of the press-down section is stopped in sequence until the last withdrawal-straightening machine of the press-down section stops the press-down work, so as to control the length of the non-press-down tail of the continuous casting billet to be located in the tail billet non-press-down interval.

[0010] In addition, preferably, the method further comprises: after the continuous casting billet enters the tail billet process, the drawing speed of the continuous casting billet is not returned to zero.

[0011] In addition, preferably, the method further comprises:

[0012] In the tail billet process at a lower normal drawing speed, by increasing the press-down process for the low solidification end in the preset secondary press-down process table, when the front end of the tail billet non-press-down interval passes the first withdrawal-straightening machine of the press-down section, the press-down process for the low solidification end makes the first withdrawal-straightening machine perform press-down; wherein the length of the low solidification end is smaller than the preset process solidification end in the secondary press-down process table.

[0013] In addition, preferably, in the process of increasing the press-down process for the low solidification end in the preset secondary press-down process table,

[0014] The press-down process for the low solidification end is set to be a press-down process using a single roller.

[0015] In addition, preferably, the method further comprises:

[0016] After the continuous casting billet enters the tail billet process, the drawing speed of the continuous casting billet is reduced to 0.25-0.35 m / min for capping, and the time for the drawing speed to be reduced to the normal production drawing speed and then to be increased to the normal production drawing speed is within 3 minutes.

[0017] In addition, preferably, the drawing speed of the continuous casting billet is reduced to 0.3 m / min for capping.

[0018] In addition, preferably, the method further comprises:

[0019] In the process of entering the tail strand, the casting speed of the continuous casting billet is reduced to the top sealing, and the casting speed of the continuous casting billet is increased in the process of increasing the speed of the casting billet again, the casting speed of the continuous casting billet after the speed increasing is greater than or equal to the normal production speed.

[0020] In addition, preferably, the method further comprises:

[0021] The length of the continuous casting billet produced in the low-speed time period in the tail strand tracking record is recorded as a suspicious length, and the continuous casting billet with the suspicious length is marked as a quality-suspected continuous casting billet.

[0022] In addition, preferably, the tail strand non-pressing interval is set according to actual process requirements.

[0023] The application also provides a continuous casting billet pressing method, in which the method for controlling the tail strand non-pressing length is used to control the tail strand non-pressing length in the process of pressing the continuous casting billet.

[0024] From the above technical solutions, it can be seen that the method for controlling the tail strand non-pressing length and the continuous casting billet pressing method provided by the application set a tail strand non-pressing interval in the tail strand of the continuous casting billet; then, in the process of entering the tail strand, when the front end of the tail strand non-pressing interval reaches the position of the press-down machine of the press-down section along the direction of the casting billet, the corresponding press-down work of the corresponding press-down machine is stopped in sequence, so that the press-down work of the press-down machine of the press-down section is stopped in sequence, until the last press-down machine of the press-down section stops the press-down work, to control the tail strand non-pressing length to be located in the tail strand non-pressing interval; by the above gradual press-down stopping, the control of the length of the tail strand non-pressing interval is realized, so that the limit of the tail strand non-pressing length in the tail strand is reduced, thereby reducing the waste product continuous casting billet, and reducing the cost of waste continuous casting billet re-melting.

[0025] To the accomplishment of the foregoing and related ends, one or more aspects of the application comprise the features hereinafter fully described and illustrated in the accompanying drawings. These and other aspects, features, and advantages of the application will become apparent to those of ordinary skill in the art from a review of the following description, especially when considered in a context of the drawings and the associated descriptions. Understanding that these aspects, features and advantages of the application can be susceptible to numerous BRIEF DESCRIPTION OF DRAWINGS

[0026] Other objects and results of the application will become more fully understood and appreciated only upon a reading of the following detailed description, with reference where appropriate to the accompanying drawings.

[0027] Figure 1 A flow chart of the method for controlling the tail strand non-pressing length according to the embodiment of the application;

[0028] Figure 2 A schematic diagram of the position of the press-down machine and the original calibration according to Comparative Example 1 of the application;

[0029] Figure 3 Fig. 1 is a schematic diagram of the change of the casting speed in the tail strand process according to the embodiment 1 of the present application;

[0030] Fig. 2 is a schematic diagram of the tail strand low casting speed strand interval and the tail strand non-pressing interval discontinuity according to the embodiment 1 of the present application. Figure 4 DETAILED DESCRIPTION

[0031] In the following description, for the purpose of providing a comprehensive understanding of one or more embodiments, a number of specific details are set forth. It is apparent, however, to one skilled in the art that these embodiments can be practiced without these specific details.

[0032] In view of the foregoing existing technology, there is a lack of an effective solution to effectively control the length of the tail strand non-pressing strand to reduce the cost of the tail strand non-pressing strand, and a method for controlling the length of the tail strand non-pressing strand and a pressing method of the continuous casting strand are provided.

[0033] The specific embodiments of the present application will be described in detail below with reference to the accompanying drawings.

[0034] In order to illustrate the method for controlling the length of the tail strand non-pressing strand provided by the present application, Figure 1 Fig. 1 shows the flow of the method for controlling the length of the tail strand non-pressing strand according to the embodiment of the present application; Figure 1 Fig. 1 shows the flow of the method for controlling the length of the tail strand non-pressing strand according to the embodiment of the present application; Figure 2 Fig. 2 shows the position of the withdrawal and straightening machine and the original calibration according to the comparative example 1 of the present application; Figure 3 Fig. 1 shows the change of the casting speed in the tail strand process according to the embodiment 1 of the present application; Figure 4 Fig. 2 shows the tail strand low casting speed strand interval and the tail strand non-pressing interval discontinuity according to the embodiment 1 of the present application.

[0035] As shown in Figure 1 The method for controlling the length of the tail strand non-pressing strand provided by the present application comprises the following steps:

[0036] Step S1, setting a tail strand non-pressing interval at the tail of the continuous casting strand.

[0037] Specifically, the tail strand non-pressing interval is set at the tail of the continuous casting strand, one end of the tail strand non-pressing interval is the rear end of the tail, and the tail strand non-pressing interval is calibrated on the continuous casting strand. The tail strand or tail in the present application refers to the rear part of the casting strand during the casting process of the continuous casting strand, and the length thereof is determined by the actual process or steel grade.

[0038] As a preferred scheme of the present application, the tail strand non-pressing interval is set according to the actual process requirement.

[0039] Specifically, the tail blank non-pressing interval in the technical scheme of the present application is set according to actual process requirements and is generally set by process personnel.

[0040] In step S2, after the continuous casting blank enters the tail blank process, along the direction of the blank drawing, when the front end of the tail blank non-pressing interval reaches the position of the press-down section of the pull-straightening machine in sequence, the corresponding pull-straightening machine is stopped from pressing down in sequence, so that the pull-straightening machine of the press-down section is stopped from pressing down in sequence until the last pull-straightening machine of the press-down section is stopped from pressing down, so as to control the tail blank non-pressing length to be located in the tail blank non-pressing interval.

[0041] Specifically, according to the set tail blank non-pressing interval, when the tail blank non-pressing interval just reaches the first pull-straightening machine and the first pull-straightening machine is executing pressing down, only the first pull-straightening machine is stopped, and obviously, the pull-straightening machines behind are still pressing down at this time; when the tail blank non-pressing interval just reaches the second pull-straightening machine and the pull-straightening machine is executing pressing down, the pull-straightening machine is stopped from pressing down; in this way, the gradual stop of pressing down of all pull-straightening machines is completed until the last pull-straightening machine executing pressing down is stopped from pressing down, so as to shorten the tail blank non-pressing length. Through program tracking, it can be known that the front end of the tail blank non-pressing interval reaches the position of the pull-straightening machine.

[0042] As a preferred scheme of the present application, the method for controlling the tail blank non-pressing length further comprises:

[0043] After the continuous casting blank enters the tail blank process, the drawing speed of the continuous casting blank is not returned to zero.

[0044] Specifically, from the operation, in the tail blank process, the drawing speed cannot be returned to zero, because once the drawing speed is returned to zero, the pressing down is necessarily stopped, and in the case of re-drawing speed, the blank drawing accident will be caused.

[0045] As a preferred scheme of the present application, the method for controlling the tail blank non-pressing length further comprises:

[0046] In the tail blank process with a lower normal drawing speed, by adding the pressing down process of the low solidification end in the preset secondary pressing down process table, when the front end of the tail blank non-pressing interval passes the first pull-straightening machine of the press-down section, the pressing down process of the low solidification end makes the first pull-straightening machine execute pressing down; wherein the length of the low solidification end is smaller than the preset process solidification end in the secondary pressing down process table.

[0047] Specifically, from the process, in the tail blank process with a reduced drawing speed, the natural solidification end will be shortened, and if the residence time is long enough, the normal pressing down interval requirement will not be met, and the pressing down may be directly exited, therefore, by adding the corresponding pressing down process of the low solidification end in the secondary pressing down process table, the pressing down after the solidification of the tail blank process is moved forward can still be executed.

[0048] As a preferred scheme of the present application, in the process of increasing the reduction process for the low solidification end in the preset two-stage reduction process table,

[0049] The reduction process for the low solidification end is set as a single-roller reduction process.

[0050] As a preferred scheme of the present application, the method for controlling the length of the non-reduction tail piece further comprises:

[0051] After the continuous casting billet enters the tail piece process, the casting speed of the continuous casting billet is reduced to 0.25-0.35 m / min for capping, and the time for the speed reduction to the normal production speed is within 3 min.

[0052] Although the gradual reduction stopping scheme can realize the non-reduction length in the tail piece process as short as possible within the preset tail piece non-reduction interval, it does not mean that the quality of the continuously cast billet in the tail piece process can meet the same quality level as the normal speed. Therefore, in order to ensure the quality and identify the interval of the reduced quality, the speed of the continuous casting billet is reduced to 0.25-0.35 m / min for capping after the continuous casting billet enters the tail piece process, and the time for the speed reduction to the normal production speed is within 3 min.

[0053] As a preferred scheme of the present application, the speed of the continuous casting billet is reduced to 0.3 m / min for capping.

[0054] It should be noted that the speed of the continuous casting billet is reduced to 0.3 m / min for capping, which is only a preferred scheme of the present application.

[0055] As a preferred scheme of the present application, the method for controlling the length of the non-reduction tail piece further comprises:

[0056] In the process of increasing the speed of the continuous casting billet after the speed of the continuous casting billet is reduced to the capping speed in the tail piece process, the speed of the continuous casting billet after the speed increase is greater than or equal to the normal production speed.

[0057] Specifically, after the capping of the tail piece is completed, the speed of the continuous casting billet is increased (raised), and the speed can be higher than the normal production speed, so as to ensure that the solidification end is maintained to the solidification end of the normal speed.

[0058] As a preferred scheme of the present application, the method for controlling the length of the non-reduction tail piece further comprises:

[0059] The length of the continuous casting billet generated in the low speed time interval in the tail piece process is recorded as a suspicious length, and the continuous casting billet with the suspicious length is marked as a quality suspicious continuous casting billet, i.e., a tail piece low speed continuous casting billet interval.

[0060] Specifically, after the critical solidification end is reached, the continuously cast billet that has undergone the pressing of the withdrawal straightening machine is tracked cumulatively to form a billet tail low withdrawal speed billet interval, the quality of the billet in this interval is suspicious, thereby realizing accurate positioning of the quality error, and the billet can be processed separately in the later stage.

[0061] The method for tracking the length of the continuously cast billet in the low withdrawal speed time period during the billet tail process can use the following formula:

[0062] L t = V*Delta t

[0063] L = L pre + L t ,

[0064] Wherein, L t is the length of the billet in the period; V is the withdrawal speed in the period; Delta t is the period time; L is the length of the billet produced in the low withdrawal speed time period; L pre is the length of the billet produced in the low withdrawal speed time period before the current time. The length of the billet produced in the low withdrawal speed time period can be calculated cumulatively by setting the period time, for example, 3s, 4s, 5s, etc.

[0065] In the tail billet process, as the withdrawal speed decreases and increases, even increases to above the normal withdrawal speed, the solidification end decreases and recovers, and the solidification end can be smaller than the critical solidification end first and larger than the critical solidification end after a period of time during the process, therefore, the tracked billet tail low withdrawal speed billet interval can not be continuous with the billet tail non-pressing interval, at this time, the billets can be distributed according to the billet tail low withdrawal speed billet interval, or all the continuously cast billets from the tail billet low withdrawal speed billet interval to the tail billet non-pressing interval can be processed as downgraded. The critical solidification end is related to the solidification end corresponding to the position of the withdrawal straightening machine and the normal pressing process, and needs to be verified by test. The billet tail low withdrawal speed billet interval is obtained by program tracking.

[0066] The method for pressing the continuously cast billet provided by the application controls the billet tail non-pressing length by using the method for controlling the billet tail non-pressing length as described above during the pressing process of the continuously cast billet.

[0067] The tail billet non-pressing interval is set in the billet tail of the continuously cast billet, then when the front end of the tail billet non-pressing interval reaches the position of the withdrawal straightening machine of the pressing section in sequence along the direction of the billet withdrawal during the process of the continuously cast billet entering the tail billet process, the pressing work of the corresponding withdrawal straightening machine is stopped in sequence, so that the withdrawal straightening machines of the pressing section stop the pressing work one by one until the last withdrawal straightening machine of the pressing section stops the pressing work, thereby controlling the billet tail non-pressing length to be located in the tail billet non-pressing interval, and gradually stopping the pressing work is realized to control the length of the billet tail non-pressing interval, so that the limit of the billet tail non-pressing length is reduced in the tail billet process, thereby reducing the waste billet, and reducing the cost of recycling the waste billet.

[0068] In order to better illustrate the method for controlling the non-pressing length of the tail of the billet and the pressing method of the continuous casting billet, examples are given as follows:

[0069] Comparative Example 1

[0070] Taking a 250X300mm bloom caster of a certain steel plant as an example, the main steel grade of the caster is bearing steel GCr15, and there are 6 withdrawal straighteners, which are arranged as shown in Figure 2 In the existing original program logic, the start of the tail of the billet process will cause the withdrawal speed to return to zero, and the low withdrawal speed duration of the tail of the billet process is greater than 5min, thus causing the entire tail of the billet to be not pressed, so that at least 17m of the tail of the billet is not pressed, as shown in Figure 2 When the tail of the billet non-pressing interval reaches the first withdrawal straightener and the first withdrawal straightener performs pressing, the pressing is stopped, which causes at least 8m of the billet to be not pressed, and a large amount of waste billets are accumulated after long-term production, which greatly increases the cost.

[0071] Example 1

[0072] The method for controlling the non-pressing length of the tail of the billet provided by the present application is applied to the certain steel plant in Comparative Example 1, and taking a 250X300mm bloom caster as an example, the main steel grade of the caster is also bearing steel GCr15, and there are 6 withdrawal straighteners.

[0073] The tail of the billet non-pressing interval is set to 2m, as shown in Figure 2 When the tail of the billet non-pressing interval reaches the first withdrawal straightener and the first withdrawal straightener performs pressing, the pressing is stopped, which causes at least 8m of the billet to be not pressed, and a large amount of waste billets are accumulated after long-term production, which greatly increases the cost.

[0074] As shown in Figure 3 , the withdrawal speed change of the tail of the billet process in the present example, in the tail of the billet process, the withdrawal speed is rapidly reduced to the capping withdrawal speed, about 0.3m / min, after the capping is completed, the withdrawal speed is increased, the normal production withdrawal speed is 0.8m / min, and the withdrawal speed is increased to 0.85-0.9m / min, so that the solidification end in the entire process is not less than 17.0m, so that the tail of the billet low withdrawal speed billet interval is not generated.

[0075] In order to enable pressing in the entire tail of the billet process except the tail of the billet non-pressing interval, a specific processing method is adopted, the program is set to perform single-roller 15mm pressing of the 1# roller when the solidification end is greater than 8m, and the critical solidification end is 17.0m. In the tail of the billet process, the solidification end is reduced and recovered with the reduction and increase of the withdrawal speed, but since the low withdrawal speed time is slightly long and is increased to be greater than the normal production withdrawal speed, the solidification end in the process may be less than the critical solidification end first, and then greater than the critical solidification end after a period of time, so that the tracked tail of the billet low withdrawal speed billet interval may not be continuous with the tail of the billet non-pressing interval, as shown inFigure 4 As shown, at this time, the billets can be processed according to the low speed casting billet section of the billet tail, or the tail billet low speed casting section can be directly processed to the tail billet non-press-down section.

[0076] It should be noted that the embodiment is only for the detailed description of the method for controlling the length of the non-press-down billet tail in the actual application, and does not limit the technical solutions provided by the present application.

[0077] As can be seen from the above specific embodiments, the method for controlling the length of the non-press-down billet tail and the press-down method of the continuous casting billet provided by the present application sets a tail billet non-press-down section at the tail of the continuous casting billet; then, during the tail billet process, along the direction of the billet drawing, when the front end of the tail billet non-press-down section reaches the position of the press-down section of the puller-straightener in sequence, the corresponding press-down work of the puller-straightener is stopped in sequence, so that the puller-straightener of the press-down section stops the press-down work in sequence, until the last puller-straightener of the press-down section stops the press-down work, so as to control the length of the tail billet non-press-down section to be located in the tail billet non-press-down section; by the above gradual press-down, the control of the length of the tail billet non-press-down section is realized, so as to reduce the limit of the length of the tail billet non-press-down section during the tail billet process, thereby reducing the waste product casting billet, and reducing the cost of the waste casting billet.

[0078] The method for controlling the length of the non-press-down billet tail and the press-down method of the continuous casting billet according to the present application are described above with reference to the accompanying drawings in an exemplary manner. However, those skilled in the art should understand that various improvements can be made to the above-mentioned method for controlling the length of the non-press-down billet tail and the press-down method of the continuous casting billet provided by the present application without departing from the content of the present application. Therefore, the protection scope of the present application should be determined by the content of the appended claims.

Claims

1. A method for controlling the length of the billet tail that is not pressed down, characterized in that, Includes the following steps: A non-pressurized section is set at the tail of the continuously cast billet; After the continuously cast billet enters the tail billet process, along the billet pulling direction, when the front end of the tail billet non-pressurized section reaches the position of the straightening machine in the pressing section in sequence, the pressing operation of the corresponding straightening machine is stopped in sequence, so that the straightening machine in the pressing section stops pressing operation one by one until the last straightening machine in the pressing section stops pressing operation, so as to control the non-pressurized length of the billet tail to be within the tail billet non-pressurized section.

2. The method for controlling the unpressed length of the billet tail according to claim 1, characterized in that, The method further includes: After the continuously cast billet enters the tailing process, the casting speed of the continuously cast billet is prevented from returning to zero.

3. The method for controlling the unpressed length of the billet tail according to claim 1, characterized in that, The method further includes: During the tail billet process at a lower than normal drawing speed, a low solidification end reduction process is added to the preset two-stage reduction process table so that when the front end of the non-reduced section of the tail billet passes the first tension leveler of the reduction section, the low solidification end reduction process causes the first tension leveler to perform reduction; wherein, the length of the low solidification end is less than the preset process solidification end in the two-stage reduction process table.

4. The method for controlling the unpressed length of the billet tail according to claim 3, characterized in that, In the process of adding a reduction process for the low solidification end to the preset two-stage reduction process table, The pressing process for the low solidification end is set to a single-roller pressing process.

5. The method for controlling the unpressed length of the billet tail according to claim 1, characterized in that, The method further includes: After the continuously cast billet enters the tailing process, the casting speed of the continuously cast billet is reduced to 0.25-0.35 m / min for capping, and the time from deceleration to acceleration to normal production casting speed is within 3 minutes.

6. The method for controlling the unpressed length of the billet tail according to claim 5, characterized in that, The casting speed of the continuously cast billet is reduced to 0.3 m / min for capping.

7. The method for controlling the unpressed length of the billet tail according to claim 1, characterized in that, The method further includes: During the process of the continuously cast billet entering the tail section and the process of the continuously cast billet being pulled down to the top speed, and then the speed of the billet being increased again, the speed of the continuously cast billet after the speed increase is greater than or equal to the normal production speed.

8. The method for controlling the unpressed length of the billet tail according to claim 1, characterized in that, The method further includes: The length of the continuously cast billet generated during the low casting speed period at the billet tail is recorded as the questionable length, and the billet with the questionable length is marked as a continuously cast billet with questionable quality.

9. The method for controlling the unpressed length of the billet tail according to claim 1, characterized in that, The unpressed section of the tail billet is set according to actual process requirements.

10. A method for reducing a continuously cast billet, characterized in that, During the continuous casting billet reduction process, the non-reduced length of the billet tail is controlled by the method described in any one of claims 1-9.

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