Annealing thin steel strip shape control process

Abstract

The present invention provides a process method for controlling the shape of an annealed thin steel strip, comprising: performing a straightening process on the thin steel strip before the tail rolling pass, so that the internal stress of the thin steel strip tends to be uniform; performing a gradient annealing process on the thin steel strip that has completed the straightening process to eliminate the uniformly distributed internal stress inside the thin steel strip; performing tail rolling on the thin steel strip after the gradient annealing process; performing a second straightening process on the thin steel strip after the tail rolling process to obtain a finished steel strip. The process method for controlling the shape of an annealed thin steel strip provided by the present invention performs a straightening process on the thin steel strip before the tail rolling pass, so that the uneven internal stress in the thin steel strip is uniformed, and then performs a gradient annealing process on the thin steel strip whose internal stress tends to be uniform, thereby forming an annealing time difference for different positions of the thin steel strip, which can improve the flatness while eliminating the internal stress of the thin steel strip, and has a significant effect on the edge wave control of the thin steel strip.

Description

Technical Field

[0001] The invention belongs to the technical field of stainless steel thin strip processing, and in particular relates to a process method for controlling the shape of an annealed thin steel strip. Background Art

[0002] Stainless steel thin strips are often used in electronic components such as computer parts, mobile phone parts, and vehicle parts. They are usually processed by cold rolling. The current specific process flow of stainless steel thin strips is mostly to subject the strip to rough rolling, finish rolling, cleaning, annealing, straightening, longitudinal shearing and other steps in sequence to obtain the finished product.

[0003] Stainless steel strips are subjected to the dual effects of tensioning and rolling during the cold rolling process, so there are complex internal stresses inside the steel strips, which makes it difficult to control the quality of product forming. In particular, the edge ripple defect problem has always been a pain point in the industry. Although the use of stress relief annealing in the process can have a certain effect, it cannot achieve the truly expected effect. Summary of the invention

[0004] The embodiment of the present invention provides a method for controlling the shape of an annealed thin steel strip, aiming to optimize the annealing process of the thin steel strip and improve the quality of the product shape.

[0005] To achieve the above object, the technical solution adopted by the present invention is: to provide a method for controlling the shape of an annealed thin steel strip, comprising:

[0006] Step S100, before the thin steel strip is subjected to a tail rolling pass, the thin steel strip is subjected to a straightening process to make the internal stress of the thin steel strip uniform;

[0007] Step S200, performing gradient annealing on the thin steel strip that has been straightened once to eliminate the internal stress uniformly distributed inside the thin steel strip;

[0008] Step S300, performing tail rolling on the thin steel strip after gradient annealing in a tail rolling pass;

[0009] Step S400, performing secondary straightening on the thin steel strip after the tail rolling to obtain a finished steel strip.

[0010] In a possible implementation, step S200 includes:

[0011] Step S201, dividing the range of gradient annealing regions on the width of the thin steel strip, wherein the divided range of gradient annealing regions at least includes a middle annealing region and side annealing regions located on both sides of the middle annealing region;

[0012] Step S202, heating the middle annealing zone and the side annealing zone;

[0013] Step S203, cooling the side annealing zone to a first temperature;

[0014] Step S204, cooling the middle annealing zone and the side annealing zone together to a second temperature lower than the first temperature, and then taking them out of the furnace and air cooling them.

[0015] In some embodiments, step S201 includes:

[0016] Step S2011, determining the width of the corrugated area appearing on both side edges of the thin steel strip based on a visual inspection system, and determining the width of the side annealing zone as the width of the corrugated area;

[0017] Step S2012, adjusting the cooling manifold passages of the laminar cooling system according to the width of the corrugated area, so that the laminar cooling system forms a middle manifold group corresponding to the middle annealing zone and an edge manifold group corresponding to the side annealing zone.

[0018] Exemplarily, step S202 includes:

[0019] Step S2021, heating the middle annealing zone and the side annealing zone to a third temperature at the same time;

[0020] Step S2022, heating the side annealing zone to a fourth temperature higher than the third temperature.

[0021] For example, the first temperature is 150-180° C. lower than the third temperature.

[0022] In a possible implementation, the fourth temperature is 17-30° C. higher than the third temperature, and in step S2022 , the fourth temperature gradually decreases from the edge of the side annealing zone toward the middle annealing zone.

[0023] In some embodiments, the edge manifold group includes multiple sections of laminar flow manifolds with adjustable flow rates that are sequentially distributed along the width direction of the thin steel strip; wherein, in step S203, the middle manifold group is closed, and the flow rates of each section of the laminar flow manifolds that are sequentially distributed away from the middle manifold group gradually increase.

[0024] Exemplarily, in step S204, the intermediate header group is opened, and the flow rates of the laminar flow headers that are sequentially distributed away from the intermediate header group are equal or gradually decrease.

[0025] For example, the elongation of thin steel strip after one-time straightening is 0.32% to 0.36%, and the elongation of thin steel strip after two-time straightening is 0.42% to 0.49%; the thickness of the finished steel strip is 0.06 to 0.08 mm.

[0026] In some embodiments, the inlet tension of the tail rolling is 280-420 KN, the outlet tension is 210-330 KN, the rolling force is 8100-8600 KN, and the rolling speed is 160-240 m / min.

[0027] The beneficial effect of the annealing thin steel strip plate shape control process method provided by the present invention is that: compared with the prior art, the annealing thin steel strip plate shape control process method of the present invention performs a stretching and straightening on the thin steel strip before entering the tail rolling pass to uniformize the uneven internal stress in the thin steel strip, and then performs a gradient annealing treatment on the thin steel strip with uniform internal stress, thereby forming an annealing temperature difference and time difference according to the deformation amount at different positions of the thin steel strip, which can improve the flatness while eliminating the internal stress of the thin steel strip, especially for the edge wave control effect of the thin steel strip. After the gradient annealing treatment is completed, tail rolling is performed again to reduce the unevenness of the thin steel strip caused by the internal stress after tail rolling, and a secondary stretching and straightening is performed after the tail rolling is completed to further improve the flatness, thereby improving the plate shape quality of the finished steel strip. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 A flowchart of a thin steel strip annealing shape control process method provided by an embodiment of the present invention;

[0029] Figure 2 A flowchart of a process for performing gradient annealing in an embodiment of the present invention;

[0030] Figure 3 A flowchart of a process for dividing the range of gradient annealing regions in an embodiment of the present invention;

[0031] Figure 4 It is a flowchart of the process of annealing and heating a thin steel strip in an embodiment of the present invention. DETAILED DESCRIPTION

[0032] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0033] It should be noted that it should be understood that the orientation or positional relationship indicated by the terms "length", "width", "upper", "lower", "front", "back", "top", "bottom", "inside", "outside", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application. The terms "first", "second", "third", and "fourth" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first", "second", "third", and "fourth" may explicitly or implicitly include one or more of the features. In the description of the present application, the meanings of "multiple" and "several" refer to two or more, unless otherwise clearly and specifically limited in quantity.

[0034] See also Figure 1 The annealing thin steel strip shape control process method provided by the present invention is now described. The annealing thin steel strip shape control process method comprises:

[0035] Step S100, before the thin steel strip is subjected to a tail rolling pass, the thin steel strip is subjected to a straightening process to make the internal stress of the thin steel strip uniform;

[0036] Step S200, performing gradient annealing on the thin steel strip that has been straightened once to eliminate the internal stress uniformly distributed inside the thin steel strip;

[0037] Step S300, performing tail rolling on the thin steel strip after gradient annealing in a tail rolling pass;

[0038] Step S400, performing secondary straightening on the thin steel strip after the tail rolling to obtain a finished steel strip.

[0039] It should be noted that the thin steel strip in this embodiment is cold-rolled using a cold-rolled strip with a thickness of 0.8 to 1.5 mm. The cold rolling process is the same as the existing process of cold-rolled thin steel strip before tail rolling, including conventional processes such as strip annealing, rough rolling, cleaning, stress relief annealing, finishing rolling, cleaning, and straightening. The above-mentioned tail rolling can be specifically understood as a set of rolling passes added after finishing rolling.

[0040] Taking into account that the internal grain distribution of the thin steel strip is mixed after rough rolling and finish rolling, resulting in extremely uneven internal stress distribution, if the stress relief annealing method is directly adopted, the thin steel strip will be deformed due to the release of internal stresses of different sizes in different position areas, especially the appearance of corrugated edge waves on the two side positions of the thin steel strip; in this embodiment, by adding a straightening process before tail rolling, the grain area inside the thin steel strip is parallelized along the length direction of the thin steel strip through a straightening process, so that the uneven internal stress inside the thin steel strip tends to be uniform, and then annealing is performed to release the uniform internal stress inside the thin steel strip. On this basis, the annealed thin steel strip is tail-rolled again, so that the internal grains of the thin steel strip are more stable under the action of tail rolling, and the internal stress distribution of the thin steel strip during the tail rolling process is relatively uniform based on the internal grains tending to be consistent in direction, and a secondary straightening is performed after tail rolling to further improve the plate quality of the final finished steel strip.

[0041] It should be explained that the gradient annealing treatment in this embodiment can be understood as controlling the order, temperature and time of annealing at each position according to the deformation amount at each position after the thin steel strip is straightened once. Specifically, a lower annealing temperature can be used for the middle area of ​​the thin steel strip with small deformation, and a relatively higher annealing temperature can be used for the side area with large deformation, thereby forming a gradient in temperature; a longer holding time can be used for the middle area of ​​the thin steel strip with small deformation, and a relatively shorter holding time can be used for the side area with large deformation, so that the side area is annealed and cooled before the middle area, thereby forming a gradient in annealing time.

[0042] Compared with the prior art, the annealed thin steel strip shape control process method provided in the present embodiment performs a straightening process on the thin steel strip before entering the tail rolling pass to even out the uneven internal stress in the thin steel strip, and then performs a gradient annealing treatment on the thin steel strip with uniform internal stress, thereby forming an annealing temperature difference and time difference according to the deformation amount at different positions of the thin steel strip, which can improve the flatness while eliminating the internal stress of the thin steel strip, especially for the edge wave control effect of the thin steel strip. Tail rolling is performed after the gradient annealing treatment is completed, which can reduce the unevenness of the thin steel strip caused by the internal stress after tail rolling, and a secondary straightening process is performed after the tail rolling is completed to further improve the flatness, thereby improving the shape quality of the finished steel strip.

[0043] As a specific implementation of the above step S200, please refer to Figure 2 , step S200 includes:

[0044] Step S201, divide the range of gradient annealing areas on the width of the thin steel strip, and the divided range of gradient annealing areas at least includes the middle annealing area and the side annealing areas on both sides of the middle annealing area. From the perspective of the thin steel strip structure and the rolling force, the side of the thin steel strip within a certain width range is an area that is more easily deformed, and the rest of the middle part is relatively stable. Therefore, in this embodiment, the area is divided in the width direction from the perspective of the amount of deformation. Specifically, the thin steel strip can be divided into the range of gradient annealing areas on the width based on the actual empirical data of the finished steel strip, or the division boundary of the gradient annealing area can be determined in real time based on the detection data of the thin steel strip in the actual production process. It should be understood that after the gradient annealing area is divided, the deformation of the middle annealing zone is smaller than that of the side annealing zone.

[0045] Step S202, heating the middle annealing zone and the side annealing zone. Here, the middle annealing zone and the side annealing zone can be heated simultaneously or in different time periods. The heating method can be electromagnetic heating or electric heating tube heating. The heating temperatures of the two can be the same or different. If the heating temperatures are different, it is preferred that the heating temperature of the side annealing zone is higher than that of the middle annealing zone. At the same time, in order to avoid the temperature difference being too large and causing the product to have different characteristics such as hardness, yield strength, etc. at different positions, the temperature difference between the middle annealing zone and the side annealing zone does not exceed 30°C.

[0046] Step S203, cooling the side annealing zone to the first temperature. After heating, the side annealing zone is first slowly cooled, so that the edge waves of the side annealing zone gradually shrink and flatten during the cooling process to the first temperature, thereby improving the edge wave shape.

[0047] Step S204, cool the middle annealing zone and the side annealing zone to a second temperature below the first temperature, and then take the steel strip out of the furnace for air cooling. After the side annealing zone is cooled to the first temperature and the edge waves are basically eliminated, the thin steel strip is cooled as a whole, and after the temperature drops to the second temperature, the thin steel strip is taken out of the furnace for air cooling as a whole. Here, the side annealing zone is first cooled to improve the edge waves, and then the thin steel strip is cooled as a whole synchronously. On the one hand, the efficiency can be improved, and on the other hand, the overall plate quality of the thin steel strip after the final annealing is controlled through synchronous cooling to reduce unevenness.

[0048] For some possible implementations, see Figure 3 , step S201 includes:

[0049] Step S2011, based on the visual inspection system, the width of the corrugated area appearing on the two side edges of the thin steel strip is determined, and the width of the side annealing zone is determined as the width of the corrugated area. The visual inspection system is an existing automated inspection technology that uses industrial cameras instead of human eyes to complete the functions of identification, measurement, positioning, etc., and here the viewing angles of several industrial cameras can be aligned with the side position of the thin steel strip, specifically, the side horizontal alignment of the thin steel strip edge can be used to detect the height of the edge wave, and the vertical alignment of the thin steel strip edge area can be used to detect the width of the edge wave, thereby determining the width of the corrugated area of ​​the thin steel strip.

[0050] Step S2012, according to the width of the corrugated area, the cooling manifold passage of the laminar cooling system is adjusted so that the laminar cooling system forms an intermediate manifold group corresponding to the intermediate annealing zone and an edge manifold group corresponding to the side annealing zone. The laminar cooling system is a process for online controlled cooling of the strip steel after rolling by introducing laminar water flow through the laminar manifold. Specifically, the manifolds for introducing laminar water flow are allocated to the corresponding intermediate annealing zone and the side annealing zone, so that the intermediate manifold group cools the intermediate annealing zone and the edge manifold group cools the side annealing zone, thereby meeting the gradient annealing cooling requirements.

[0051] Specifically, Figure 4 As shown, in this embodiment, the above step S202 includes:

[0052] Step S2021, heating the middle annealing zone and the side annealing zone to a third temperature at the same time;

[0053] Step S2022, heating the side annealing zone to a fourth temperature higher than the third temperature.

[0054] The thin steel strip is synchronously heated by the heating tubes in the annealing furnace, wherein the distribution of the heating tubes is also individually controlled corresponding to the middle annealing zone and the side annealing zone. In the early stage of heating, the heating tubes in the middle annealing zone and the side annealing zone work simultaneously to make the thin steel strip synchronously heated to the third temperature over the entire width, and then the heating tubes corresponding to the middle annealing zone are turned off, and the heating tubes corresponding to the side annealing zone work alone to further heat the side annealing zone to the fourth temperature, thereby forming a temperature gradient between the side annealing zone and the middle annealing zone, and smoothing the edge waves of the side annealing zone by using a relatively high heating temperature and a preferential cooling method, thereby improving the plate quality of the final finished steel strip.

[0055] Exemplarily, in this embodiment, the first temperature is 170-200°C lower than the third temperature. After the side annealing zone is slowly cooled to the first temperature, the intermediate annealing zone is slowly cooled, and finally the thin steel strip is cooled to the second temperature in the annealing furnace as a whole, and then air-cooled out of the furnace, wherein the side annealing zone is cooled to 170-200°C below the third temperature before the intermediate annealing zone, so that the edge wave defects of the thin steel strip can be shrunk and flattened in advance during the cooling process, and then the thin steel strip is cooled synchronously and uniformly over the entire width, thereby improving the plate unevenness of the annealed thin steel strip.

[0056] Specifically, the first temperature is 780-835°C; the second temperature is 410-435°C; the third temperature is 980-1005°C; and the fourth temperature is 995-1035°C.

[0057] On the basis of the above, the fourth temperature in this embodiment is 15 to 30°C higher than the third temperature, and in step S2022, the fourth temperature gradually decreases from the edge of the side annealing zone to the direction close to the middle annealing zone. The annealing temperature of the side annealing zone is set to be 15 to 30°C higher than that of the middle annealing zone, so that the internal stress of the side annealing zone with larger deformation can be released more fully, and at the same time, the side annealing zone can be cooled from a higher annealing temperature to the first temperature to achieve shrinkage and flattening of the side waves, thereby improving the overall plate quality of the thin steel strip after annealing; in addition, establishing a temperature difference gradient of no more than 30°C between the side annealing zone and the middle annealing zone can avoid the temperature difference being too large, which leads to obvious differences in metal properties after annealing in the two zones, thereby ensuring the consistency of the overall forming quality of the thin steel strip.

[0058] Further considering that the closer the thin steel strip is to the edge, the greater the edge wave fluctuation is, and the cooling rate is faster near the edge during the actual cooling process, the final heating temperature of the side annealing zone can be made to present a gradual temperature that gradually decreases from the edge to the side close to the middle annealing zone within the setting range of the fourth temperature. Specifically, the temperature of the side annealing zone at the edge of the thin steel strip can be made higher than the third temperature by 30°C, and the temperature at the junction of the side annealing zone and the middle annealing zone can be made higher than the third temperature by 15°C. In this way, the difference in deformation amount in the width of the side annealing zone and the difference in cooling rate can be corresponded through the gradual difference in heating temperature, so that the side annealing zone can better eliminate the edge wave defects when it is cooled to the first temperature.

[0059] Please note that, see Figure 1The above-mentioned edge manifold group includes multiple sections of laminar flow manifolds with adjustable flow rates that are sequentially distributed along the width direction of the thin steel strip; wherein, in step S203, the intermediate manifold group is closed, and the flow rates of the various sections of laminar flow manifolds that are sequentially distributed away from the intermediate manifold group gradually increase; in step S204, the intermediate manifold group is opened, and the flow rates of the various sections of laminar flow manifolds that are sequentially distributed away from the intermediate manifold group are equal or gradually decrease.

[0060] The flow of the laminar manifold can be adjusted by an electromagnetic flow valve. When cooling is performed in step S203, the flow of the intermediate manifold group is first closed, and the laminar manifold of the edge manifold group is opened to a gradually decreasing opening from the outer edge to the inside, thereby increasing the cooling rate of the edge position of the side annealing zone away from the intermediate annealing zone, so that the side edge position with the largest deformation can shrink and flatten at a faster cooling rate, and finally the side annealing zone is flattened by proportional matching of the cooling rate and the deformation in the width direction. After the side annealing zone is cooled to the first temperature, the intermediate manifold group is opened to start synchronous cooling of the intermediate annealing zone, and finally the intermediate annealing zone and the side annealing zone are cooled together to the second temperature and can be taken out of the furnace for air cooling.

[0061] Optionally, in this embodiment, the elongation of the thin steel strip after the first straightening is 0.32% to 0.36%, and the elongation of the thin steel strip after the second straightening is 0.42% to 0.49%; the thickness of the finished steel strip is 0.06 to 0.08 mm. In the first straightening, the grain distribution inside the thin steel strip is mainly combed by rolling the thin steel strip. Since the thin steel strip itself is in a high hardness state after fine rolling, a relatively low elongation is adopted. After the first straightening is completed and the gradient annealing is performed, the second straightening is mainly performed to target the internal stress generated by the thin steel strip during the tail rolling process. The role of the tail rolling is mainly to ensure the final thickness of the finished steel strip, and at the same time, the tail rolling is used to make the grain state inside the thin steel strip more stable, and then the second straightening is performed to ensure the flatness of the finished steel strip on the entire width, so as to avoid the rebound of edge wave defects in the later stage.

[0062] For example, the entrance tension of tail rolling is 280~420KN, the exit tension is 210~330 KN, the rolling force is 8100~8600KN, and the rolling speed is 160~240m / min.

[0063] The annealed thin steel strip shape control process method provided in this embodiment can specifically adopt the following parameters: the thin steel strip obtained after rough rolling and finish rolling with a 0.6mm cold-rolled strip is first subjected to a straightening machine at an elongation of 0.32% before entering the tail rolling, and the uneven internal stress is uniformed by the straightening, and then enters the annealing furnace, and the width of the corrugated area appearing on the two side edges of the thin steel strip is detected by a visual inspection system in the annealing furnace (although the straightening makes the internal stress uniform and promotes the weakening of the edge waves, it cannot completely eliminate the edge waves, so the corrugated effect is still presented visually), and then the width size data of the side annealing zone and the middle annealing zone to be divided are obtained, and then the power parameters of the corresponding electromagnetic heating elements or electric heating tubes, as well as the flow parameters of the corresponding middle manifold group and edge manifold group are adjusted according to the width of the side annealing zone and the middle annealing zone.

[0064] The middle annealing zone and the side annealing zone are heated to the third temperature of 980°C at the same time, and then the middle annealing zone stops heating, and the side annealing zone continues to be heated to a fourth temperature of 995-1015°C (the side close to the middle annealing zone is heated to 995°C, and the side away from the middle annealing zone is heated to 1015°C, and the fourth temperature is made to present a gradual gradient by controlling the power of the corresponding electromagnetic heating elements or electric heating tubes at different positions), and then after the whole is kept warm in the annealing furnace for thirty seconds, the middle annealing zone continues to be kept warm, and the side annealing zone begins to slowly cool down to the first temperature of 780°C, and the cooling takes ten seconds (equivalent to the middle annealing zone being kept warm for forty seconds), and then the middle annealing zone starts to be cooled synchronously for thirty seconds, and finally the middle annealing zone and the side annealing zone are cooled to the second temperature of 410°C in the annealing furnace, and then taken out of the furnace and air-cooled to complete the annealing.

[0065] After annealing, the thin steel strip enters the tail rolling process. The entrance tension of the tail rolling is set to 280KN, the exit tension is set to 210KN, the rolling force is set to 8100KN, and the rolling speed is set to 160m / min. After the tail rolling is completed, secondary straightening is carried out with an elongation of 0.42% to obtain a finished steel strip with a thickness of 0.06mm.

[0066] The annealing thin steel strip shape control process method provided in this embodiment can also specifically adopt the following parameters: the thin steel strip obtained after rough rolling and finish rolling of a 1.2 mm cold-rolled strip is first stretched and straightened once in a straightening machine at an elongation of 0.36% before entering the annealing furnace. In the annealing furnace, a visual inspection system is used to detect the width of the corrugated area appearing on both side edges of the thin steel strip, and then the width dimension data of the side annealing zone and the middle annealing zone to be divided are obtained, and then the power parameters of the corresponding electromagnetic heating elements or electric heating tubes, as well as the flow parameters of the corresponding middle manifold group and edge manifold group are adjusted according to the width of the side annealing zone and the middle annealing zone.

[0067] The middle annealing zone and the side annealing zone are heated to the third temperature of 1005°C at the same time, and then the middle annealing zone stops heating, and the side annealing zone continues to be heated to the fourth temperature of 1015-1035°C (it takes no more than two seconds, the side close to the middle annealing zone is heated to 1015°C, and the side away from the middle annealing zone is heated to 1035°C, showing a gradual temperature gradient), and then after the whole is kept warm in the annealing furnace for sixty seconds, the middle annealing zone continues to be kept warm, and the side annealing zone begins to slowly cool down to the first temperature of 835°C, and the cooling takes twenty seconds (equivalent to keeping the middle annealing zone warm for eighty seconds), and then the middle annealing zone starts to cool synchronously, and finally the middle annealing zone and the side annealing zone are cooled to the second temperature of 435°C in the annealing furnace, and then taken out of the furnace and air-cooled to complete the annealing.

[0068] After annealing, the thin steel strip enters the tail rolling process. The entrance tension of the tail rolling is set to 420KN, the exit tension is set to 330KN, the rolling force is set to 8600KN, and the rolling speed is set to 240m / min. After the tail rolling is completed, secondary straightening is carried out with an elongation of 0.49% to obtain a finished steel strip with a thickness of 0.08mm.

[0069] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A process for controlling the shape of annealed thin steel strip, characterized in that: include: Step S100, performing a tension straightening on the thin steel strip before the tail rolling pass, so that the internal stress of the thin steel strip tends to be uniform; Step S200, performing gradient annealing treatment on the thin steel strip that has been straightened once to eliminate the internal stress uniformly distributed inside the thin steel strip; Step S300, performing tail rolling on the thin steel strip after gradient annealing in the tail rolling pass; Step S400, performing secondary straightening on the thin steel strip after tail rolling to obtain a finished steel strip; Wherein, the step S200 includes: Step S201, dividing the range of gradient annealing regions on the width of the thin steel strip, wherein the divided range of gradient annealing regions at least includes a middle annealing region and side annealing regions located on both sides of the middle annealing region; Step S202, heating the middle annealing zone and the side annealing zone, including: step S2021, heating the middle annealing zone and the side annealing zone to a third temperature at the same time; step S2022, heating the side annealing zone to a fourth temperature above the third temperature; Step S203, cooling the side annealing zone to a first temperature; Step S204, cooling the middle annealing zone and the side annealing zone together to a second temperature lower than the first temperature, and then taking them out of the furnace and air cooling them.

2. The annealing thin steel strip shape control process method according to claim 1, characterized in that: The step S201 includes: Step S2011, determining the width of the corrugated area appearing on both side edges of the thin steel strip based on a visual inspection system, and determining the width of the side annealing zone as the width of the corrugated area; Step S2012, adjusting the cooling manifold passages of the laminar cooling system according to the width of the corrugated area, so that the laminar cooling system forms an intermediate manifold group corresponding to the intermediate annealing zone and an edge manifold group corresponding to the side annealing zone.

3. The annealing thin steel strip shape control process method according to claim 1, characterized in that: The first temperature is 170-200° C. lower than the third temperature.

4. The annealing thin steel strip shape control process method according to claim 1, characterized in that: The fourth temperature is 15-30° C. higher than the third temperature, and in the step S2022 , the fourth temperature gradually decreases from the edge of the side annealing zone toward the middle annealing zone.

5. The annealing thin steel strip shape control process method according to claim 4, characterized in that: The edge manifold group includes multiple sections of laminar flow manifolds with adjustable flow rates that are sequentially distributed along the width direction of the thin steel strip; wherein, in step S203, the intermediate manifold group is closed, and the flow rates of the laminar flow manifolds of each section that is sequentially distributed away from the intermediate manifold group are gradually increased.

6. The annealing thin steel strip shape control process method according to claim 5, characterized in that: In the step S204, the intermediate header group is opened, and the flow rates of the laminar flow headers in each section that is sequentially distributed away from the intermediate header group are equal or gradually decrease.

7. The annealing thin steel strip shape control process method according to any one of claims 1 to 6, characterized in that: The elongation of the thin steel strip after primary straightening is 0.32% to 0.36%, and the elongation of the thin steel strip after secondary straightening is 0.42% to 0.49%; the thickness of the finished steel strip is 0.06 to 0.08 mm.

8. The annealing thin steel strip shape control process method according to any one of claims 1 to 6, characterized in that: The inlet tension of the tail rolling is 280-420 KN, the outlet tension is 210-330 KN, the rolling force is 8100-8600 KN, and the rolling speed is 160-240 m / min.

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