A production method for controlling the flatness of ultra-thick plates using TMCP process with a strength of 420 MPa or higher.

Abstract

This invention relates to a production method for controlling the flatness of ultra-thick plates produced by TMCP process with a strength of 420 MPa or higher, comprising the following steps: (1) The reduction amount of finishing rolling passes, except for the last pass, is evenly distributed and gradually reduced, the sled coefficient is controlled within the range of +5~10%, the biting speed is controlled within the range of 0.7~0.8 m / s for low-speed biting, the sled action length is controlled within the range of 0.5 m~0.8 m, and the reduction amount of the last finishing rolling pass is ≤4 mm; (2) The pre-straightening machine is set to an automatic three-pass reciprocating straightening machine. The process involves the steel plate entering the pre-straightening machine for one pass of forward straightening, then automatically undergoing one pass of reverse straightening, followed by another pass of forward straightening. As the straightening passes continue, the straightening reduction increases with each pass. During the first pass of forward straightening and the second pass of reverse straightening, the steel plate does not undergo cooling in the ACC rapid cooling zone. Cooling only occurs when the plate re-enters the ACC rapid cooling zone after the third pass of forward straightening. Steel plates with a thickness of 65mm or more produced using this method have a flatness of less than 2mm / m.

Description

Technical Field

[0001] This invention relates to the field of steel rolling technology, and in particular to a production method for controlling the flatness of ultra-thick plates using the TMCP process with a strength of 420 MPa or higher. Background Technology

[0002] The TMCP process produces high-strength, high-toughness steel plates without adding excessive alloying elements or requiring complex heat treatment. It is a cost-effective process that improves the mechanical properties of steel plates. As the thickness of products produced using the TMCP process continues to increase, its biggest advantage over hot-rolling is that the steel plate, after being cooled by a large volume of water in an ACC rapid cooling unit at a relatively higher initial cooling temperature, achieves better mechanical properties at a relatively lower reheating temperature. If the steel plate has poor shape or insufficient flatness before cooling, uneven cooling during the rapid water cooling process will result in different internal structures and severe deformation of the steel plate.

[0003] Currently, when using the TMCP process to produce steel plates with a strength of 420 MPa and above and a thickness of 65 mm and above, the low initial rolling temperature and long intermediate billet temperature control time during the finishing rolling of high-strength steel plates result in a lower temperature on the lower surface of the steel plate compared to the upper surface. During rolling, the steel plate head severely buckles, causing it to impact the roller table during high-speed rolling, forming small waves or "S"-shaped bends at both ends. After cooling, when the red-hot temperature is below 450°C, it is difficult to straighten this high-strength, low-red-hot-temperature steel plate using a hot straightener after ACC (Adjustable Temperature). This is due to the high yield strength and high deformation resistance at low temperatures. Even with multiple straightening methods using a hot straightener, it is difficult to flatten this type of high-strength, low-red-hot-temperature steel plate. Furthermore, using the TMCP + high-temperature tempering straightening process to salvage the shape of this high-strength, ultra-thick steel plate can lead to insufficient tensile strength and other mechanical properties.

[0004] Therefore, it is necessary to develop a method for controlling the shape of high-strength ultra-thick plates before cooling based on TMCP technology, so as to avoid the problems of poor initial plate shape, deformation due to uneven temperature during rapid cooling, and low temperature after cooling, which prevents the hot straightener from leveling the plate. Summary of the Invention

[0005] The technical problem to be solved by this invention is: for high-strength ultra-thick plates under the TMCP process, the poor plate shape before cooling affects the uniformity of the cooling temperature of the steel plate and causes further deformation. At the same time, after the steel plate is cooled, at low temperature, the high yield strength and high deformation resistance of the steel plate make it impossible for the hot straightener to flatten the steel plate. The invention provides a production method for controlling the flatness of ultra-thick plates with a strength of 420 MPa or above under the TMCP process.

[0006] This invention discloses a production method for controlling the flatness of ultra-thick plates produced using the TMCP process with a strength of 420 MPa or higher. The method includes precision rolling pass control, pre-straightening, and ACC rapid cooling. The conveyor rollers of the pre-straightening machine are connected to the conveyor rollers of the ACC rapid cooling zone. The pre-straightened steel plate directly enters the ACC rapid cooling zone, wherein: (1) Except for the last pass, the reduction of the finishing rolling pass is evenly distributed and gradually reduced. The sled coefficient is controlled within the range of +5~10%. The biting speed is controlled within the range of 0.7~0.8m / s for low-speed biting. The sled action length is controlled within the range of 0.5m~0.8m. The reduction of the last finishing rolling pass is ≤4mm. (2) The pre-straightening machine is set to automatic three-pass reciprocating straightening, that is, after the steel plate enters the pre-straightening machine for one pass of forward straightening, it automatically reverses to perform one pass of reverse straightening, and then automatically performs one pass of forward straightening. As the straightening passes are carried out, the straightening pressure increases with each pass, thereby achieving the purpose of fully straightening the steel plate in the pre-straightening machine. During the first pass of forward straightening and the second pass of reverse straightening, the steel plate does not undergo cooling in the ACC rapid cooling zone. Instead, the steel plate is cooled when it enters the ACC rapid cooling zone again after the third pass of forward straightening.

[0007] Furthermore, in step (2) above, as the straightening passes are carried out, the straightening reduction amount increases with each pass, with the reduction amount increasing by 0.5~1mm per pass.

[0008] Furthermore, in step (2) above, in order to ensure that the cooling flow rate meets the process requirements when the steel plate enters the ACC rapid cooling zone, after the steel plate leaves the mill after finishing rolling, the valves of the ACC cooling device start to operate. At the same time, when the steel plate enters the ACC device for the first two straightening passes in the pre-straightening machine, it is not cooled with water. In addition, the control of the straightening speed is not transferred to the ACC for the first two straightening passes. When the third straightening pass begins, the control of the straightening speed is transferred to the ACC. When the steel plate enters the ACC rapid cooling zone, it is cooled with water.

[0009] The method of this invention is applicable to high-strength ultra-thick steel plates with a thickness of 65 mm or more rolled by the TMCP process.

[0010] The technological principle of this invention is as follows: (1) The reduction of finishing rolling passes, except for the last pass, is evenly distributed. The sled coefficient is controlled within the range of +5~10%. The biting speed is controlled within the range of 0.7~0.8m / s for low-speed biting. The sled working length is controlled within the range of 0.5m~0.8m. The reduction of finishing rolling at the last pass is ≤4mm. To ensure a slight tilt at the head of the steel plate during the finishing rolling process and prevent small waves caused by the head impacting the roller table, the head and tail shape of the steel plate are improved by adjusting the reduction amount, sled coefficient, and bite speed during the finishing rolling process. The reduction amount is evenly distributed across the finishing rolling passes to avoid the head tilting down due to insufficient reduction in any particular pass. The sled coefficient is controlled within the range of +5% to 10%, and the bite speed is controlled within the range of 0.7 to 0.8 m / s for low-speed bite to prevent the steel plate from failing to perform its proper sled function when the bite motor speed decreases. At the same time, the sled action length is controlled within the range of 0.5 m to 0.8 m to avoid "S" shaped bends. The final pass is adjusted to a small reduction amount of ≤4 mm to avoid the head tilting of the steel plate caused by excessive reduction in the final pass, ensuring that the final pass mainly serves a leveling function to improve the rolled plate shape.

[0011] (2) The pre-straightening machine is set to automatic three-pass reciprocating straightening, that is, after the steel plate enters the pre-straightening machine for one pass of forward straightening, it automatically reverses for one pass of reverse straightening, and then automatically performs one pass of forward straightening. As the straightening passes, the straightening reduction increases with each pass, thereby achieving the purpose of fully straightening the steel plate in the pre-straightening machine. During the first pass of forward straightening and the second pass of reverse straightening, the steel plate does not undergo cooling in the ACC rapid cooling zone. Instead, the steel plate is cooled when it re-enters the ACC rapid cooling zone after the third pass of forward straightening. In traditional TMCP process production, the steel plate is only straightened once in the pre-straightening machine. Due to the close proximity of the pre-straightening machine and the ACC device (within 3m), the straightening speed of the steel plate in the pre-straightening machine is controlled by the ACC cooling speed to ensure that the cooling of the steel plate hits the target. Therefore, under the condition of a large ACC speed and one pass of straightening, it is difficult to achieve sufficient bending and straightening of high-strength ultra-thick plates. To further improve the straightness of the steel plate before cooling, a multi-pass automatic straightening function is added to the pre-straightening machine before the ACC rapid cooling device. This involves automatically straightening the steel plate three times in a reciprocating motion within the pre-straightening machine, gradually increasing the reduction in pressure with each pass. This ensures the steel plate is fully bent and straightened during the high-temperature, low-deformation-resistance stage before cooling. Furthermore, the straightening speed control is not transferred to the ACC during the first two passes; it is only transferred to the ACC when the third straightening pass begins. Water cooling is applied when the steel plate enters the ACC rapid cooling zone, thus ensuring that the cooling parameters of the steel plate meet the target.

[0012] The beneficial effects of this invention are as follows: (1) Using the method of the present invention, the steel plate is in a high temperature state before cooling, and its deformation resistance is small. The steel plate is straightened multiple times before cooling, which can effectively improve the flatness of the steel plate. At the same time, before cooling, the initial plate shape of the steel plate is effectively improved, ensuring the temperature uniformity of the steel plate during the rapid cooling process of the TMCP process with a large amount of water.

[0013] (2) The method of the present invention effectively solves the technical bottleneck problem that the flatness of ultra-thick plates under the existing TMCP process is not up to standard, and the resistance strength is insufficient when straightening after high temperature tempering in heat treatment. Detailed Implementation

[0014] To better explain the technical solution of the present invention, the technical solution of the present invention will be further described below with reference to specific embodiments. The following embodiments are merely illustrative of the technical solution of the present invention and do not limit the present invention in any way. The sequence numbers of the following embodiments are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0015] Example 1 This embodiment uses a rolled steel plate Q500qD with a finished thickness of 66mm as an example to explain the present invention in detail. The strength of the steel plate in this embodiment is 500MPa.

[0016] A production method for controlling the flatness of ultra-thick plates processed by TMCP with a strength of 420 MPa or higher includes control of finishing rolling passes, pre-straightening, and ACC rapid cooling. The conveyor rollers of the pre-straightening mill are connected to the conveyor rollers of the ACC rapid cooling zone. The pre-straightened steel plate directly enters the ACC rapid cooling zone, wherein: (1) Except for the last pass, the reduction in the finishing rolling passes is evenly distributed and gradually reduced. The sled coefficient is controlled within the range of +5 to 10%, the bite speed is controlled within the range of 0.7 to 0.8 m / s for low-speed bite, the sled working length is controlled within the range of 0.5 m to 0.8 m, and the reduction in the last finishing rolling pass is ≤4 mm; the initial thickness of the finishing rolling steel plate is 130 mm. In this embodiment, the specific rolling parameters are set as shown in Table 1 below: Table 1. List of process parameters for the steel plate finishing rolling process in Example 1

[0017] (2) The pre-straightening machine is set to automatic three-pass reciprocating straightening. That is, after the steel plate enters the pre-straightening machine for one pass of forward straightening, it automatically performs one pass of reverse straightening, and then automatically performs one pass of forward straightening. As the straightening passes, the straightening reduction increases with each pass, thereby achieving the purpose of fully straightening the steel plate in the pre-straightening machine. During the first pass of forward straightening and the second pass of reverse straightening, the steel plate does not undergo cooling in the ACC rapid cooling zone. Instead, it is cooled when the steel plate re-enters the ACC rapid cooling zone after the third pass of forward straightening. The specific straightening and cooling process is as follows: When the inlet grating of the pre-straightener detects the steel plate, the front and rear roller conveyors of the straightener control the steel plate to start the first pass of forward straightening at a speed of 1 m / s. The inlet reduction of the pre-straightener is set to 3.5 mm, and the outlet reduction is set to 0.5 mm. The straightening force is >600 tons. When the tail of the steel plate leaves the outlet grating of the pre-straightener or the straightening force F <1 ton, the signal indicates that the steel plate has completed the first pass of straightening. The inlet and outlet roller gap values ​​of the straightener are automatically switched and adjusted, and the reduction is increased by 0.5 mm on each side. That is, during the second pass of reverse straightening, the reduction at the outlet of the straightener (original straightener inlet) is 4.0 mm, and the reduction at the inlet (original straightener outlet) is 1 mm. The straightening force is >700 tons, and the outlet roller conveyor of the straightener is automatically controlled to start the second pass of reverse straightening at a speed of 1 m / s. Once the inlet grating or straightener force F is less than 1 ton, the steel plate is considered to have completed the second pass of straightening. At this point, the ACC rapid cooling device's cooling mode lock signal is released, and the rapid cooling device's cooling valves open according to process cooling requirements, including flow valves and side spray valves. Simultaneously, the pre-straightening inlet and outlet roller gaps are swapped and adjusted again, increasing the reduction by 0.5mm on top of the second pass's reduction. Therefore, for the third pass, the straightener inlet reduction is 4.5mm, and the outlet reduction is 1mm. The third pass straightening force is greater than 800 tons, and the steel plate begins the third pass straightening at a speed of 1m / s. A steel plate detection grating is added at the rapid cooling inlet. Once the rapid cooling inlet grating detects the steel plate, the speed control of the pre-straightening machine and outlet roller conveyor is transferred to the ACC rapid cooling device to ensure that the straightening speed S = cooling speed S. acc This is to meet the process requirements for the cooling rate of the steel plate.

[0018] In this embodiment, a pre-straightening anti-straightening function button is added to the pre-straightening machine's operating interface. After the steel plate is rolled on the finishing mill, this button is manually clicked to activate the pre-straightening machine's anti-straightening function, transmitting its trigger signal to the ACC fast cooling device PLC control system. Upon receiving the signal, the ACC fast cooling device PLC locks the fast cooling device's cooling mode. In non-cooling mode, all cooling valves are closed, and the control of the ACC roller conveyor is completely handed over to the pre-straightening machine. When the steel plate leaves the pre-straightening machine's inlet grating for the second straightening pass or the straightening machine force F < 1 ton, it is determined that the steel plate has completed the second straightening pass. At this time, the ACC fast cooling device's cooling mode lock signal is released, and the fast cooling device's cooling valves open according to the process cooling requirements, including flow valves and side spray valves. The steel plate begins its third straightening pass at a speed of 1 m / s. A steel plate detection grating is added at the ACC fast cooling zone inlet. When the fast cooling inlet grating detects the steel plate, the speed control of the pre-straightening machine and the outlet roller conveyor is handed over to the fast cooling device, ensuring that the straightening speed S = cooling speed S. acc This is to meet the process requirements for the cooling rate of the steel plate.

[0019] After being rolled, straightened, and cooled using the above methods, the finished steel plate in this embodiment has a thickness of 66mm, a strength of 500MPa, and a flatness of 1mm / m, meeting the technical requirements of 5mm / m for railway bridge steel and 8mm / m for national standards.

[0020] Example 2 This embodiment uses a rolled steel plate Q500qD with a finished thickness of 78mm as an example to explain the present invention in detail. The strength of the steel plate in this embodiment is 500MPa.

[0021] A production method for controlling the flatness of ultra-thick plates processed by TMCP with a strength of 420 MPa or higher includes control of finishing rolling passes, pre-straightening, and ACC rapid cooling. The conveyor rollers of the pre-straightening mill are connected to the conveyor rollers of the ACC rapid cooling zone. The pre-straightened steel plate directly enters the ACC rapid cooling zone, wherein: (1) Except for the last pass, the reduction in the finishing rolling passes is evenly distributed and gradually reduced. The sled coefficient is controlled within the range of +5~10%, the bite speed is controlled within the range of 0.7~0.8m / s for low-speed bite, the sled working length is controlled within the range of 0.5m~0.8m, and the reduction in the last finishing rolling pass is ≤4mm; the starting thickness of the finishing rolling steel plate is 130mm. In this embodiment, the specific rolling parameters are set as shown in Table 2 below: Table 2. List of process parameters for the steel plate finishing rolling process in Example 2

[0022] (2) The pre-straightening machine is set to automatic three-pass reciprocating straightening. That is, after the steel plate enters the pre-straightening machine for one pass of forward straightening, it automatically performs one pass of reverse straightening, and then automatically performs one pass of forward straightening. As the straightening passes, the straightening reduction increases with each pass, thereby achieving the purpose of fully straightening the steel plate in the pre-straightening machine. During the first pass of forward straightening and the second pass of reverse straightening, the steel plate does not undergo cooling in the ACC rapid cooling zone. Instead, it is cooled when the steel plate re-enters the ACC rapid cooling zone after the third pass of forward straightening. The specific straightening and cooling process is as follows: When the inlet grating of the pre-straightener detects the steel plate, the front and rear roller conveyors of the straightener control the steel plate to start the first pass of forward straightening at a speed of 1 m / s. The inlet reduction of the pre-straightener is set to 2.5 mm, and the outlet reduction is set to 0.5 mm. The straightening force is >600 tons. When the tail of the steel plate leaves the outlet grating of the pre-straightener or the straightening force F <1 ton, the signal indicates that the steel plate has completed the first pass of straightening. The inlet and outlet roller gap values ​​of the straightener are automatically switched and adjusted, and the reduction is increased by 0.5 mm on each side. That is, during the second pass of reverse straightening, the reduction at the outlet of the straightener (original straightener inlet) is 3 mm, and the reduction at the inlet (original straightener inlet) is 1 mm. The straightening force is >700 tons, and the outlet roller conveyor of the straightener is automatically controlled to start the second pass of reverse straightening at a speed of 1 m / s. When the steel plate leaves the pre-straightener... Once the inlet grating or straightener force F is less than 1 ton, the steel plate is considered to have completed the second straightening pass. At this point, the ACC rapid cooling device's cooling mode lock signal is released, and the rapid cooling device's cooling valves, such as the flow valve and side spray valve, are opened according to the process cooling requirements. Simultaneously, the pre-straightening inlet and outlet roller gaps are swapped and adjusted again, increasing the reduction by 0.5mm on top of the second straightening reduction. That is, for the third straightening pass, the straightener inlet reduction is 3.5mm, and the outlet reduction is 1mm. The third straightening force is greater than 800 tons, and the steel plate begins the third straightening pass at a speed of 1m / s. A steel plate detection grating is added at the rapid cooling inlet. Once the rapid cooling inlet grating detects the steel plate, the speed control of the pre-straightener and outlet roller conveyor is transferred to the ACC rapid cooling device to ensure that the straightening speed S = cooling speed S. acc This is to meet the process requirements for the cooling rate of the steel plate.

[0023] In this embodiment, a pre-straightening anti-straightening function button is added to the pre-straightening machine's operating interface. After the steel plate is rolled on the finishing mill, this button is manually clicked to activate the pre-straightening machine's anti-straightening function, transmitting its trigger signal to the ACC fast cooling device PLC control system. Upon receiving the signal, the ACC fast cooling device PLC locks the fast cooling device's cooling mode. In non-cooling mode, all cooling valves are closed, and the control of the ACC roller conveyor is completely handed over to the pre-straightening machine. When the steel plate leaves the pre-straightening machine's inlet grating for the second straightening pass or the straightening machine force F < 1 ton, it is determined that the steel plate has completed the second straightening pass. At this time, the ACC fast cooling device's cooling mode lock signal is released, and the fast cooling device's cooling valves open according to the process cooling requirements, including flow valves and side spray valves. The steel plate begins its third straightening pass at a speed of 1 m / s. A steel plate detection grating is added at the ACC fast cooling zone inlet. When the fast cooling inlet grating detects the steel plate, the speed control of the pre-straightening machine and the outlet roller conveyor is handed over to the fast cooling device, ensuring that the straightening speed S = cooling speed S. acc This is to meet the process requirements for the cooling rate of the steel plate.

[0024] After being rolled, straightened, and cooled by the above method, the finished steel plate of this embodiment has a thickness of 78mm, a strength of 500MPa, and a flatness of 1mm / m, which meets the technical requirements of 5mm / m for railway bridge steel and 8mm / m for national standards.

[0025] The above embodiments are merely specific examples exemplified to explain the present invention and do not limit the present invention in any way. Any non-substantial changes made by any person based on the above content and form that do not depart from the scope of protection of the claims of the present invention should be considered to fall within the scope of protection of the claims of the present invention. The present invention is not limited to the specific embodiments described above.

Claims

1. A production method for controlling the flatness of ultra-thick plates processed by TMCP with a strength of 420 MPa or higher, comprising finishing rolling pass control, pre-straightening, and ACC rapid cooling, wherein the conveyor rollers of the pre-straightening machine are connected to the conveyor rollers of the ACC rapid cooling zone, and the pre-straightened steel plate directly enters the ACC rapid cooling zone, characterized in that: (1) Except for the last pass, the reduction of the finishing rolling pass is evenly distributed and gradually reduced. The sled coefficient is controlled within the range of +5~10%. The biting speed is controlled within the range of 0.7~0.8m / s for low-speed biting. The sled action length is controlled within the range of 0.5m~0.8m. The reduction of the last finishing rolling pass is ≤4mm. (2) The pre-straightening machine is set to automatic three-pass reciprocating straightening, that is, after the steel plate enters the pre-straightening machine for one pass of forward straightening, it automatically reverses to perform one pass of reverse straightening, and then automatically performs one pass of forward straightening. As the straightening passes are carried out, the straightening pressure increases with each pass, thereby achieving the purpose of fully straightening the steel plate in the pre-straightening machine. During the first pass of forward straightening and the second pass of reverse straightening, the steel plate does not undergo cooling in the ACC rapid cooling zone. Instead, the steel plate is cooled when it enters the ACC rapid cooling zone again after the third pass of forward straightening.

2. The production method for controlling the flatness of ultra-thick plates using TMCP process with a strength of 420 MPa or higher, as described in claim 1, is characterized in that: As the straightening passes continue, the straightening reduction increases with each pass, increasing by 0.5~1mm per pass.

3. The production method for controlling the flatness of ultra-thick plates using TMCP process with a strength of 420 MPa or higher, as described in claim 1, is characterized in that: To ensure that the cooling flow rate meets process requirements when the steel plate enters the ACC rapid cooling zone, the valves of the ACC cooling device start to operate after the steel plate leaves the mill after finishing rolling. At the same time, the steel plate does not receive water cooling when it enters the ACC device during the first two straightening passes in the pre-straightening mill, and the control of the straightening speed is not transferred to the ACC during the first two straightening passes. When the third straightening pass begins, the control of the straightening speed is transferred to the ACC. Water cooling is performed when the steel plate enters the ACC rapid cooling zone.

4. The production method for controlling the flatness of ultra-thick plates using TMCP process with a strength of 420 MPa or higher, as described in claim 1, is characterized in that: The thickness of the finished ultra-thick steel plate is 65mm or more.

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