A method for controlling inner loop indentation of a high-strength steel coil

Abstract

The application discloses a high-strength steel coil inner circle indentation control method. The high-strength steel slab to be processed is subjected to hot rolling treatment to obtain a hot-rolled strip; the hot-rolled strip is subjected to ultra-fast cooling treatment to obtain a first cooling strip; the first cooling strip is subjected to laminar flow cooling treatment to obtain a second cooling strip; in the laminar flow cooling treatment, the laminar flow cooling treatment comprises first cooling treatment applied to a preset length region of the head of the first cooling strip and second cooling treatment applied to other regions of the first cooling strip; according to the hydraulic pressure increment of the pinch roll and the real-time roll gap increment, the biting time of the pinch roll is determined, and then the biting operation of the winding drum on the second cooling strip and the step control operation of the winding roll are performed, the winding treatment of the second cooling strip is completed, and a high-strength steel coil is obtained. According to the application, the inner circle indentation in the winding treatment process can be effectively eliminated.

Description

Technical Field

[0001] This application belongs to the field of hot rolling in metallurgy, and particularly relates to a method for controlling the indentation on the inner ring of high-strength steel coils. Background Technology

[0002] High-strength steel for engineering machinery is a key material for equipment such as cranes and heavy trucks. As downstream industries continue to upgrade, users' requirements for its surface quality have risen to a near "zero-defect" level, with standards approaching those of automotive exterior panels.

[0003] However, during the conventional hot-rolling coiling process, a periodic indentation defect, known in the industry as "tongue marks," is unavoidable on the inner ring of the steel coil. These slight indentations, lacking tactile depth and only showing color difference, can be up to 100 meters long. This defect directly forces companies to cut the affected steel coil sections, resulting in significant yield losses and severely impacting production efficiency and cost control due to the additional cutting process. Summary of the Invention

[0004] This application provides a method for controlling the inner ring indentation of high-strength steel coils, which can largely avoid the generation of inner ring indentations during hot rolling and coiling, thereby reducing the yield loss caused by defect removal, and improving product surface quality, production efficiency and customer satisfaction.

[0005] This application provides a method for controlling the indentation on the inner ring of a high-strength steel coil, the method comprising: The high-strength steel slab to be treated is hot-rolled to obtain hot-rolled strip steel; Hot-rolled strip steel is subjected to ultra-fast cooling treatment to obtain single-cooled strip steel. The cooling rate of ultra-fast cooling treatment is 50-100℃ / s, and the target cooling temperature is 750-820℃. A laminar flow cooling process is applied to a primary cooled strip to obtain a secondary cooled strip. The laminar flow cooling process includes a first cooling process applied to a predetermined length region at the head of the primary cooled strip, and a second cooling process applied to other regions of the primary cooled strip. The first cooling target temperature for the predetermined length region at the head is 380-480℃, and the second cooling target temperature for other regions is 400-500℃. The first cooling target temperature is lower than the second cooling target temperature, and the temperature difference between the first cooling target temperature and the second cooling target temperature is 20-50℃. The first cooling rate for the first cooling process is 15-45℃ / s, and the second cooling rate for the second cooling process is 10-40℃ / s. The first cooling rate is greater than the second cooling rate. The secondary cooled strip steel is coiled by the pinch rolls, auxiliary coiling rolls, and coil drum of the coiler to obtain high-strength steel coils. In this step, the bite time of the pinch rolls is determined according to the commanded pressure increment and the executed pressure increment of the pinch rolls, as well as the real-time roll gap increment of the pinch rolls. Based on the bite time, the coil drum bites into the secondary cooled strip steel and the auxiliary coiling rolls step control operation is executed to complete the coiling process of the secondary cooled strip steel and obtain high-strength steel coils.

[0006] The beneficial effects of the high-strength steel coil inner ring indentation control method according to an embodiment of this application are described below: After hot rolling, high-strength steel slabs are processed to obtain hot-rolled strip. The hot-rolled strip is then subjected to ultra-rapid cooling and laminar flow cooling sequentially. The ultra-rapid cooling rate is controlled at 50-100℃ / s, with a target cooling temperature of 750-820℃. After ultra-rapid cooling, the hot-rolled strip is rapidly and intensely cooled to an intermediate temperature of 750-820℃ to refine the grains, laying the foundation for obtaining a high-strength fine-grained microstructure in subsequent processes. The laminar flow cooling first cooling process has a cooling rate controlled at 15-45℃ / s, with a target cooling temperature of 380-480℃. The cooling rate of the second cooling process is 10-40℃ / s, and the target cooling temperature is 400-500℃, enabling coiling at a lower temperature. It is understood that after the first and second cooling processes, the cold head temperature (380-480℃) of the hot-rolled strip is even lower than the middle temperature (400-500℃). Therefore, the strength and hardness of the strip in the cold head area are greatly improved. This allows the secondary-cooled strip to effectively resist external pressure and reduce the risk of surface indentation when the coiling roller presses on the secondary-cooled strip to bend it and establish tension during the coiling process. Before the actual winding, pinch rolls are needed to assist in threading the strip. This application uses multi-dimensional information such as the hydraulic pressure increment of the pinch rolls and the real-time roll gap increment of the pinch rolls to determine whether the pinch rolls are biting the steel and to obtain the biting time. The determination of whether the pinch rolls are biting the steel by combining multi-dimensional information has very good sensitivity and will not cause misjudgment due to common problems in production such as strip deviation during secondary cooling or irregular head shape. The determination accuracy is very high, so the biting time obtained is very accurate, which can improve the accuracy of head tracking when the auxiliary winding roll steps during winding and avoid the indentation caused by high pressure impact on the head.

[0007] In summary, this application achieves higher strength and hardness at the head of the secondary cooled strip by adjusting the cooling modes of ultra-fast cooling and laminar flow cooling, laying a solid foundation for indentation control. Furthermore, by using multi-dimensional information to determine the biting condition of the pinch rolls before coiling, the subsequent coiling rollers can accurately track the head and achieve step control, effectively preventing indentations caused by the coiling rollers impacting the head. This improves product surface quality and customer satisfaction, while also reducing yield loss due to indentation defect removal. Attached Figure Description

[0008] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly introduced below. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0009] Figure 1 This is a schematic flowchart of a method for controlling the indentation on the inner ring of a high-strength steel coil according to an embodiment of this application; Figure 2 This is a graph showing the relationship between temperature and strength of the secondary-cooled strip steel; Figure 3 This is a schematic diagram of the winding process provided in one embodiment of this application; Figure 4 This is a flowchart illustrating step S420 in one embodiment of this application. Detailed Implementation

[0010] The features and exemplary embodiments of various aspects of this application will be described in detail below. To make the objectives, technical solutions, and advantages of this application clearer, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only intended to explain this application and not to limit it. For those skilled in the art, this application can be implemented without some of these specific details. The following description of the embodiments is merely to provide a better understanding of this application by illustrating examples.

[0011] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising..." does not exclude the presence of additional identical elements in the process, method, article, or apparatus that includes said element.

[0012] Inner coil indentation refers to periodic dents, scratches, embossing, and color differences that appear on the surface of the innermost coils during the process of coiling strip into a coil. This defect usually occurs at the beginning of the coiling process.

[0013] For example, if the winding tension is too high at the beginning of the winding process, the huge pressure will press the surface of the innermost strip steel into the gaps, protrusions or scratches of the winding machine's drum or jaws, thus forming an indentation.

[0014] When the strip head wraps around the drum once, overlap occurs. As the number of wraps increases, auxiliary roll step control technology is required to prevent the overlapping portion of the strip head from being crushed. If the auxiliary roll step control is poor after the winding process begins, the auxiliary roll may not lift up in time or the lifting height may be insufficient during the jump-over process. This can cause relative sliding or continuous contact between the auxiliary roll surface and the strip surface, forming friction indentations. More seriously, the auxiliary roll may crush the overlapping portion of the strip head, forming a crescent-shaped head indentation on the upper and lower surfaces of the strip. Coils with head indentations must be cut off, resulting in quality loss. Especially as the strip thickness decreases and the winding speed increases significantly, the allowable error of the winding process and the step time window shrink drastically, making the requirements for step control precision even more stringent.

[0015] Even after the auxiliary winding roller is opened, the raised section of the strip can easily produce color difference indentations on the surface of the strip under the action of winding tension. As the coil diameter gradually increases, the color difference indentations disappear.

[0016] In order to solve existing technical problems, such as Figure 1 As shown in the embodiment of this application, a method for controlling the indentation on the inner ring of a high-strength steel coil is provided. This method may include: Step S100: Hot rolling is performed on the high-strength steel slab to be processed to obtain hot-rolled strip steel.

[0017] Hot rolling generally includes three processes: heat treatment, rough rolling, and finish rolling.

[0018] Step S200: The hot-rolled strip is subjected to ultra-fast cooling treatment to obtain a single-cooled strip.

[0019] The ultra-fast cooling process has a cooling rate of 50-100℃ / s and a target cooling temperature of 750-820℃.

[0020] Ultrafast cooling treatment achieves a cooling rate far exceeding that of traditional laminar flow cooling. It typically utilizes densely packed nozzles with high water pressure, high impact force, and extremely small impact angles to instantly break the vapor film on the strip surface, resulting in explosive heat exchange. As soon as the strip exits the finishing mill, it undergoes ultrafast cooling treatment, rapidly (50-100℃ / s) to a predetermined intermediate temperature of 750-820℃. The purpose is to refine the grains, laying the foundation for obtaining a high-strength, fine-grained microstructure in subsequent processes.

[0021] Step S300: Perform laminar flow cooling on the primary cooled strip to obtain secondary cooled strip.

[0022] The laminar flow cooling process includes a first cooling process applied to a predetermined length region at the head of the primary cooling strip, and a second cooling process applied to other regions of the primary cooling strip.

[0023] The first target cooling temperature for the predetermined length region of the head is 380-480℃, and the second target cooling temperature for the remaining regions is 400-500℃. The first target cooling temperature is lower than the second target cooling temperature, and the temperature difference between the two is 20-50℃. The first cooling rate for the first cooling process is 15-45℃ / s, and the second cooling rate for the second cooling process is 10-40℃ / s, preferably 13-40℃ / s. The first cooling rate is greater than the second cooling rate. Figure 2 The figure shows the relationship between temperature and strength of the strip after secondary cooling. It can be seen that within the 380-480℃ range, the strength of the head section within the preset length is higher, which is beneficial for controlling the inner ring indentation during coiling. The first cooling target temperature is lower than the second cooling target temperature to specifically improve the strength and hardness of the strip head, avoiding indentation during step control. If the first cooling target temperature is too low, it will hinder the bending of the strip head and subsequent coiling tension; furthermore, it will produce waviness, affecting the strip shape.

[0024] As can be seen, this application employs a composite cooling process of ultra-fast cooling treatment + laminar flow cooling treatment to cool hot-rolled strip steel. Laminar flow cooling treatment, through a gentler and more controllable cooling method than ultra-fast cooling treatment, precisely and differentially adjusts the temperature of the pre-set length region at the head of the strip steel and the remaining regions to the target temperature required for subsequent coiling processing.

[0025] Because the first target cooling temperature of the pre-set length region at the head is lower than the second target cooling temperature of the remaining regions, this pre-set length region at the head can be simply referred to as the cold head. Assuming the cold head length is 50m, the first cooling process targets a fixed length (50m) of strip extending backward from the starting point of the strip head, with a target cooling temperature of 380-480℃. When the strip region outside the cold head is reached, the first cooling process switches to the second cooling process, targeting the remaining regions, with a target cooling temperature of 400-500℃. Under precisely controlled temperatures, the strip completes the final transformation from austenitic to bainitic + ferrite microstructure, especially achieving a higher bainite content and higher strength in the cold head section. This improves the overall strength and hardness of the strip while specifically enhancing the strength and hardness of the cold head without adversely affecting the shape of the high-strength steel sheet. Specifically, after laminar flow cooling, the microstructure of the cold head of the strip includes 15%-30% ferrite and 70-85% bainite by volume, while the microstructure of the remaining areas of the strip includes 20-35% ferrite and 65-80% bainite by volume. Within the same strip section, the bainite content in the microstructure of the cold head is higher than that in the other areas.

[0026] It is worth noting that by using differentiated cooling treatments at the front and rear sections, the length of the cold head section is specifically set, and the strength and hardness of the strip steel in the cold head area are improved. As a result, when the coiling roller presses on the strip steel to make it bend and establish tension, the strip steel can effectively resist external pressure and reduce the probability of surface indentation.

[0027] In step S400, the secondary cooled strip steel is coiled using the pinch rollers, auxiliary coiling rollers, and coil drum of the coiler to obtain a high-strength steel coil.

[0028] The method described in this embodiment can effectively control the indentation of the inner coil, meet the surface quality requirements of high-strength engineering machinery steel for panel applications, improve production efficiency, reduce the yield loss (approximately 8.7%) caused by defect removal, and improve product surface quality and customer satisfaction.

[0029] Figure 3 This is a flowchart illustrating the winding process, as shown below. Figure 3 As shown, step S400 may include: Step S410: Determine the steel biting moment of the pinch roll based on the hydraulic pressure increment of the pinch roll and the real-time roll gap increment of the pinch roll.

[0030] Step S420: Based on the biting moment, the winding drum bites into the secondary cooled strip and the stepping control operation of the auxiliary winding roller is performed to complete the winding process of the secondary cooled strip and obtain a high-strength steel coil.

[0031] Before the actual winding begins, pinch rollers are needed to assist in threading the strip. The secondary cooled strip from the laminar flow cooling treatment unit is first firmly gripped by the pinch rollers and guided to the actual winding area. When the head of the secondary cooled strip reaches the winding area, the assist rollers press down, guiding and forcing the head to bend and wind onto the drum. With the assist rollers' pressure assistance (step control), the secondary cooled strip tightly winds around the drum several times, forming a solid core. At this point, the assist rollers have completed their task and are fully lifted and withdrawn. Afterward, the pinch rollers and the drum work together to maintain tension until the entire secondary cooled strip is wound. It is important to note that when the drum bites into the secondary cooled strip, the assist rollers need to press the head together; in subsequent processes, the assist rollers must avoid the overlapping portion corresponding to the head.

[0032] During the coiling process, it is necessary to ensure that the coiling drum accurately bites into the head of the secondary cooled strip and to avoid indentation defects caused by poor step control of the auxiliary coiling rollers, which could result in crushing the overlapping portion corresponding to the head. Therefore, this method improves the accuracy and sensitivity of the pinch roll bite judgment before formal coiling, thereby enhancing the precision of the coiling drum biting into the strip during formal coiling and the accuracy of head tracking during the step control of the auxiliary coiling rollers. This prevents the auxiliary coiling rollers from lifting in a timely manner, lifting too low, or even directly crushing the overlapping portion corresponding to the head with high pressure.

[0033] Specifically, this method comprehensively determines whether the pinch roll is biting the steel by using the hydraulic pressure increment of the pinch roll and the real-time roll gap increment of the pinch roll, and thus determines the biting moment of the pinch roll.

[0034] The gap between the upper and lower pinch rolls refers to the distance between them. Generally, pinch rolls have two control modes: gap control mode and pressure control mode. In gap control mode, the operator or control system first sets an initial gap value, which is slightly smaller than the strip thickness, to ensure the strip head is smoothly guided in and prevent impact or jamming. After the strip head is successfully guided in, the system switches to pressure control mode. In this mode, the gap between the pinch rolls decreases slightly to ensure sufficient friction between the pinch rolls and the strip, thereby reliably conveying the strip and establishing tension. From a macroscopic perspective, the gap decreases after the pinch rolls bite the strip. However, the inventors observed that at the instant the pinch rolls bite the strip, when the strip head "collides" into the gap at a certain speed and angle, the impact force is not uniformly applied along the entire length of the roll. Because the strip may slightly deviate or tilt upwards, the impact force is initially concentrated on one side of the pinch roll (usually the operating side). This sudden, localized impact force causes a slight torsional deformation of the pinch roll, resulting in a momentary upward bounce-like motion on the operating side. The roll gap sensor installed on the operating side immediately detects this upward bounce signal. In other words, the real-time roll gap increment of the pinch roll is calculated based on the initial roll gap value mentioned above. The hydraulic pressure can be detected by the pressure sensor of the pinch roll hydraulic cylinder. If, within the expected pinch roll biting time window, the hydraulic pressure increment detected by the pressure sensor on the rod or piston side of the hydraulic cylinder exceeds the set pressure increment threshold, then biting can be determined.

[0035] In summary, using one or more parameters from the real-time roll gap increment of the pinch roll and the pressure increment on the rod side or piston side of the upper pinch roll hydraulic cylinder for steel bite determination offers high accuracy and sensitivity, ensuring timely and accurate issuance of the steel bite signal, thereby determining the precise steel bite moment. It is worth noting that the tracking time window is a crucial constraint, meaning that the above three parameters are only recognized within the short period expected to arrive at the strip head, fundamentally eliminating false triggering caused by interference in other time periods. In one embodiment, the pinch roll hydraulic pressure increment in step S410 is detected by the pinch roll hydraulic cylinder pressure sensor within the tracking time window of the secondary cooled strip head. The real-time roll gap increment of the pinch roll in step S410 is detected by the pinch roll hydraulic cylinder position sensor within the tracking time window of the secondary cooled strip head.

[0036] The pinch roll hydraulic cylinder generally refers to the upper pinch roll hydraulic cylinder. The hydraulic pressure can be the rod-side pressure detected by the pressure sensor on the piston side of the pinch roll hydraulic cylinder, or the piston-side pressure detected by the pressure sensor on the piston side of the pinch roll hydraulic cylinder.

[0037] In one embodiment, step S410, determining the steel-biting moment of the pinch roll based on the hydraulic pressure increment of the pinch roll and the real-time roll gap increment of the pinch roll, may include: 1) When the hot metal detector detects the head of the secondary cooled strip, and within the head tracking time window, the pressure increment on the piston side or rod side of the pinch roll hydraulic cylinder exceeds the first preset pressure threshold, the coiler determines that the pinch roll has bitten the steel and issues a biting signal. The biting time is determined based on the biting signal. Although the absolute pressure values ​​measured by the pressure sensors on the piston side and rod side of the pinch roll hydraulic cylinder are different, this embodiment sets the preset pressure threshold for the pressure increment of both to be the same. When the pressure increment measured by the pressure sensor on either the piston side or rod side of the hydraulic cylinder exceeds the first preset pressure threshold, a biting is determined.

[0038] 2) When the hot metal detector detects the head of the secondary cooled strip and the real-time roll gap increment of the pinch roll exceeds the first preset roll gap threshold within the head tracking time window, it is determined that the pinch roll of the coiler is biting the steel and a biting signal is issued. The biting time is determined based on the biting signal.

[0039] 3) When the hot metal detector detects the head of the secondary cooled strip, and within the head tracking time window, the pressure increment on the piston side or rod side of the pinch roll hydraulic cylinder does not exceed the first preset pressure threshold, but exceeds the second preset pressure threshold, and at the same time, the real-time roll gap increment of the pinch roll does not exceed the first preset roll gap threshold, but exceeds the second preset roll gap threshold, it is determined that the pinch roll of the coiler is biting the steel and a biting signal is issued. The biting time is determined based on the biting signal.

[0040] It can be seen that the first preset pressure threshold is greater than the second preset pressure threshold, and the first preset roll gap threshold is greater than the second preset roll gap threshold. Specifically, the first preset pressure threshold can be 0.5 MPa, the second preset pressure threshold can be 0.3 MPa, the first preset roll gap threshold can be 0.6 mm, and the second preset roll gap threshold can be 0.4 mm. It is worth noting that the real-time roll gap increment or hydraulic pressure increment of the pinch roll can be the roll gap increment or pressure increment on either the operating side or the drive side of the pinch roll.

[0041] A steel bite signal is a structured event message data packet that can contain the following: 1) Event type: pinch roll bites steel.

[0042] 2) Event time: The moment when the pinch roll bites the steel, which is equivalent to a timestamp and can be accurate to the millisecond level.

[0043] 3) Event location: pinch roller, which may also include the position coordinates of the pinch roller on the production line.

[0044] 4) Trigger source: Record which sensor(s) data triggered the steel bite detection, which is helpful for subsequent analysis and diagnosis.

[0045] 5) Strip markings: information such as strip thickness.

[0046] The three pinch roll bite detection logics described above can be used to handle complex working conditions, ensuring timely and accurate bite detection. For example, they are highly accurate in detecting misjudgments caused by common production phenomena such as strip misalignment and irregular strip head shape. When everything is normal, all signals arrive almost simultaneously, and the bite detection is completed by the signal with the fastest response.

[0047] Figure 4 This is a flowchart illustrating step S420 in one embodiment, as shown below. Figure 4 As shown, step S420 may include: Step S421: Calculate the real-time head position of the secondary cooling strip based on the bite time, the position of the pinch rolls, and the running speed of the secondary cooling strip.

[0048] Step S422: When the real-time head position is equal to the preset bite position of the drum on the secondary cooling strip, control the drum to perform the bite operation, and control the auxiliary roll to perform the step control operation according to the real-time head position.

[0049] At the moment of steel biting, the head of the secondary cooling strip is located between the upper and lower pinch rolls. The position of the pinch rolls in the production line can be regarded as the starting position of the head of the secondary cooling strip. Knowing the starting position and the corresponding steel biting moment, combined with the running speed of the secondary cooling strip, the head position of the secondary cooling strip can be calculated continuously in real time.

[0050] In the coiler's control program, a pre-set bite trigger position P-bite is established. When the head of the secondary cooled strip is calculated to be about to reach P-bite, the control system typically sends a pre-command to the coiler, instructing the auxiliary coiling rollers to enter the final preparation state. The instant the calculated real-time head position of the secondary cooled strip equals P-bite, the control system immediately issues the final command to execute the bite operation. At this point, the relevant auxiliary coiling rollers, with the set roll gap and pressure, press down, bending the strip head and forcibly pressing it against the continuously rotating drum surface, thus completing the bite operation. Subsequently, the real-time head position of the secondary cooled strip can still be calculated based on the drum's rotation speed. This allows the auxiliary coiling rollers to be raised precisely when the head and its corresponding overlapping portion are about to reach the auxiliary coiling rollers after one revolution around the drum, achieving precise step control of the auxiliary coiling rollers.

[0051] In one embodiment, step 422 may further include: The indentation risk assessment area is defined based on the real-time head position. Within the indentation risk assessment area, the indentation risk of the secondary cooling strip is assessed based on the pressure jump and roll gap change when the auxiliary roll performs step control operation.

[0052] It is known that indentations mostly occur the instant the strip head passes under the coiling roller. Therefore, 24-hour continuous monitoring is unnecessary. Risk assessment only needs to be initiated within a brief time interval—the period between the strip head approaching, passing under, and just leaving the coiling roller—which constitutes the aforementioned indentation risk assessment area. This area can be defined using the real-time head position. It can be seen that, based on the high accuracy of the pinch roller's bite timing, the delineation of the coiling roller's indentation risk assessment area is also more precise. This allows for indentation detection and alarm, enabling timely detection and prevention of indentation defects caused by equipment malfunctions.

[0053] Pressure jump refers to the actual pressure change of the winding roller. Roll gap change refers to the actual physical position change of the winding roller. The roll gap of the winding roller is the gap between the roller surface and the surface of the top layer of steel coil on the drum.

[0054] The pressure jump variable indicates whether the coiling roller, during its step control operation, achieves the preset transition from high pressure to low pressure and back to high pressure. The roll gap change indicates whether the coiling roller, during its step control operation, achieves the action of pressing down, lifting (stepping), and pressing down again. Ideally, within the indentation risk assessment area, the pressure and roll gap change synchronously and sufficiently. Under risk conditions, within the indentation risk assessment area: 1) an excessively large pressure jump variable indicates inaccurate timing of the coiling roller lifting, potentially resulting in head indentation; 2) an excessively large roll gap change indicates insufficient lifting height or inaccurate timing of the coiling roller lifting, causing compression of the overlapping portion corresponding to the strip head.

[0055] In summary, an indentation risk alarm will only be triggered if the pressure jump of the coiling roller exceeds the pressure threshold or the roll gap change exceeds the roll gap threshold within the indentation risk assessment area. Otherwise, no alarm will be triggered. Subsequently, technicians can analyze the alarm data to further determine whether indentation exists, thus preventing defective steel coils from being released and reducing steel coil quality disputes.

[0056] In one embodiment, before the hot rolling process of the high-strength steel slab, the following may be included: High-strength steel is obtained by refining molten steel and casting it into a high-strength steel slab.

[0057] Refined steel comprises the following components by mass percentage: C: 0.15-0.19%, Si: 0.1-0.3%, Mn: 1.0-1.5%, S: ≤0.010%, P: ≤0.020%, Als: 0.025-0.060%, Nb: 0.01-0.03%, Ti: 0.01-0.03%, Ni: 0.2-0.5%, Cr: 0.2-0.5%, B: 0.0010-0.0030%, with the remainder being Fe and unavoidable impurities during steelmaking. The thickness of high-strength steel slabs can be 230-240mm.

[0058] In one embodiment, during the hot rolling process of the high-strength steel slab, the final rolling temperature is 850-900°C. The final rolling temperature refers to the instantaneous temperature of the high-strength steel slab as it leaves the last finishing mill. At this temperature, the hot-rolled strip is in an austenitic state, extremely soft, and unable to build tension. Direct contact with the pinch rolls or coiling rollers would result in severe sticking and failure to maintain the coil shape. Therefore, a subsequent cooling process is required to cool the hot-rolled strip to the target coiling temperature, causing austenite to transform into ferrite and bainite phases on the surface and inside of the strip, increasing its strength and hardness, and ensuring that the strip can withstand coiling tension and coiling roller pressure.

[0059] In one embodiment, the step of hot-rolling a high-strength steel slab to obtain hot-rolled strip includes: The high-strength steel slab to be treated is heated to obtain a heated high-strength steel slab.

[0060] The heated high-strength steel slab is subjected to rough rolling to obtain an intermediate slab. The rough rolling process is performed in 5 or 7 passes.

[0061] The intermediate slab is subjected to finish rolling to obtain hot-rolled strip steel. The finish rolling process is a 7-stand continuous finish rolling process.

[0062] In one embodiment, the heat treatment time for the high-strength steel slab can be 150-300 min, and the target temperature for the heat treatment can be 1200-1260℃.

[0063] In one embodiment, the thickness of the high-strength steel coil is 3.0-8.0 mm. It can be seen that this solution can achieve control over the inner ring indentation of ultra-thin strip steel coils.

[0064] Example 1 Step S1: Place the 230mm thick high-strength steel slab to be treated in a heating furnace for heating treatment to obtain the heated high-strength steel slab. The heating treatment time is 180 minutes, and the target heating temperature is 1220℃. The chemical composition of the high-strength steel slab to be treated, by mass fraction, is: C: 0.179%, Si: 0.15%, Mn: 1.1%, S: ≤0.010%, P: ≤0.020%, Als: 0.028%, Nb: 0.023%, Ti: 0.018%, Ni: 0.35%, Cr: 0.25%, B: 0.0015%, with the remainder being Fe and unavoidable impurities during smelting.

[0065] Step S2: The heated high-strength steel slab is subjected to 7 passes of rough rolling to obtain an intermediate slab. The intermediate slab is then subjected to 7 stands of continuous finish rolling to obtain hot-rolled strip steel. The final rolling temperature is 890℃.

[0066] Step S3: The hot-rolled strip is subjected to ultra-rapid cooling treatment to obtain a single-cooled strip. The cooling rate of the ultra-rapid cooling treatment is 100℃ / s, and the target cooling temperature is 820℃.

[0067] Step S4: Perform laminar flow cooling on the primary cooled strip to obtain a secondary cooled strip with a 50m long cold head. The laminar flow cooling process includes a first cooling process and a second cooling process. The first cooling process has a first cooling rate of 27.0℃ / s and a first cooling target temperature of 420℃. The second cooling process has a second cooling rate of 24.5℃ / s and a second cooling target temperature of 450℃.

[0068] Step S5: When the head of the secondary cooled strip is detected by the hot metal detector and the real-time roll gap increment on the operating side of the pinch roll is 0.8mm within the head tracking time window, it is determined that the pinch roll bites the steel and the bite time is determined. Based on the bite time, the winding drum bites the secondary cooled strip and the step control operation of the auxiliary winding roll is performed to complete the winding process of the secondary cooled strip and obtain a 4.0mm thick high-strength steel coil without inner ring indentation.

[0069] Example 2 Step S1: Place the 230mm thick high-strength steel slab to be treated in a heating furnace for heat treatment to obtain the heated high-strength steel slab. The heat treatment time is 210 minutes, the target temperature is 1240℃, and the chemical composition of the high-strength steel slab to be treated, by mass fraction, is: C: 0.19%, Si: 0.25%, Mn: 1.3%, S: ≤0.010%, P: ≤0.020%, Als: 0.025%, Nb: 0.020%, Ti: 0.015%, Ni: 0.30%, Cr: 0.35%, B: 0.0020%, with the remainder being Fe and unavoidable impurities during smelting.

[0070] Step S2: The heated high-strength steel slab is subjected to 7 passes of rough rolling to obtain an intermediate slab. The intermediate slab is then subjected to 7 stands of continuous finish rolling to obtain hot-rolled strip steel. The final rolling temperature is 870℃.

[0071] Step S3: The hot-rolled strip is subjected to ultra-rapid cooling treatment to obtain a single-cooled strip. The cooling rate of the ultra-rapid cooling treatment is 70℃ / s, and the target cooling temperature is 780℃.

[0072] Step S4: Perform laminar flow cooling on the primary cooled strip to obtain a secondary cooled strip with a 50m long cold head. The laminar flow cooling process includes a first cooling process and a second cooling process. The first cooling process has a first cooling rate of 20.0℃ / s and a first cooling target temperature of 450℃. The second cooling process has a second cooling rate of 17.0℃ / s and a second cooling target temperature of 490℃.

[0073] Step S5: When the head of the secondary cooled strip is detected by the hot metal detector and within the head tracking time window, the pressure increment measured by the pressure sensor on the piston side of the pinch roll is 0.6 MPa. It is determined that the pinch roll bites the steel and the biting moment is determined. Based on the biting moment, the winding drum bites the secondary cooled strip and the stepping control operation of the auxiliary winding roller is performed to complete the winding process of the secondary cooled strip and obtain a 5.0 mm thick high-strength steel coil without inner ring indentation.

[0074] Example 3 Step S1: Place the 230mm thick high-strength steel slab to be treated in a heating furnace for heating treatment to obtain the heated high-strength steel slab. The heating treatment time is 200 minutes, and the target heating temperature is 1248℃. The chemical composition of the high-strength steel slab to be treated, by mass fraction, is: C: 0.17%, Si: 0.20%, Mn: 1.2%, S: ≤0.010%, P: ≤0.020%, Als: 0.035%, Nb: 0.025%, Ti: 0.022%, Ni: 0.35%, Cr: 0.45%, B: 0.0022%, with the remainder being Fe and unavoidable impurities during smelting.

[0075] Step S2: The heated high-strength steel slab is subjected to 7 passes of rough rolling to obtain an intermediate slab. The intermediate slab is then subjected to 7 stands of continuous finish rolling to obtain hot-rolled strip steel. The final rolling temperature is 870℃.

[0076] Step S3: The hot-rolled strip is subjected to ultra-rapid cooling treatment to obtain a single-cooled strip. The cooling rate of the ultra-rapid cooling treatment is 50℃ / s, and the target cooling temperature is 760℃.

[0077] Step S4: Perform laminar flow cooling on the primary cooled strip to obtain a secondary cooled strip with a 50m long cold head. The laminar flow cooling process includes a first cooling process and a second cooling process. The first cooling process has a first cooling rate of 16.5℃ / s and a first cooling target temperature of 430℃. The second cooling process has a second cooling rate of 14.0℃ / s and a second cooling target temperature of 480℃.

[0078] Step S5: When the head of the secondary cooled strip is detected by the hot metal detector and the pressure increment measured by the pressure sensor on the side of the pinch roll is 0.7 MPa within the head tracking time window, it is determined that the pinch roll bites the steel and the bite moment is determined. Based on the bite moment, the winding drum bites the secondary cooled strip and the step control operation of the auxiliary winding roller is performed to complete the winding process of the secondary cooled strip and obtain a 7.0 mm thick high-strength steel coil without inner ring indentation.

[0079] Example 4 Ignoring step S5, the only difference between Example 4 and Example 1 is that in step S3, the cooling rate of the ultrafast cooling process is 80℃ / s, the target cooling temperature is 770℃, the first cooling rate of the laminar flow cooling process is 24.0℃ / s, the first target cooling temperature is 380℃, the second cooling rate is 23.0℃ / s, and the second target cooling temperature is 400℃.

[0080] Example 5 Ignoring step S5, the only difference between Example 4 and Example 1 is that in step S3, the cooling rate of the ultrafast cooling process is 90℃ / s, the target cooling temperature is 810℃, the first cooling rate of the laminar flow cooling process is 22.0℃ / s, the first target cooling temperature is 480℃, the second cooling rate is 20.6℃ / s, and the second target cooling temperature is 500℃.

[0081] Comparative Example 1 Ignoring step S5, the difference between Comparative Example 1 and Example 5 is that both the first cooling target temperature and the second cooling temperature are 580°C. The first cooling target temperature of 580°C is higher than the upper limit of the 380-480°C range defined in this application, resulting in insufficient strength and hardness of the cold head, making it prone to stepping and imprinting during the winding process.

[0082] As shown in Table 1, process parameters for ultrafast cooling and laminar flow cooling of Examples 1-5 and Comparative Example 1 are provided.

[0083] Table 2 shows the microstructure of the cold head and other areas of the secondary cooled strip steel in Examples 1-5 and Comparative Example 1, as well as the indentation condition after coiling.

[0084] To illustrate the present invention, the present invention has been appropriately and sufficiently described above through embodiments. The above embodiments are only for illustrating the present invention and are not intended to limit the present invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Any modifications, equivalent substitutions, improvements, etc., should be included within the protection scope of the present invention. The patent protection scope of the present invention should be defined by the claims.

Claims

1. A method for controlling the indentation on the inner ring of a high-strength steel coil, characterized in that, The method includes: The high-strength steel slab to be treated is hot-rolled to obtain hot-rolled strip steel; The hot-rolled strip steel is subjected to ultra-fast cooling treatment to obtain a single-cooled strip steel. The cooling rate of the ultra-fast cooling treatment is 50-100℃ / s, and the target cooling temperature is 750-820℃. The primary cooled strip is subjected to laminar flow cooling to obtain a secondary cooled strip. The laminar flow cooling includes a first cooling treatment applied to a predetermined length region at the head of the primary cooled strip, and a second cooling treatment applied to other regions of the primary cooled strip. The first target cooling temperature for the predetermined length region at the head is 380-480℃, and the second target cooling temperature for the other regions is 400-500℃. The first target cooling temperature is lower than the second target cooling temperature, and the temperature difference between the first and second target cooling temperatures is 20-50℃. The first cooling rate for the first cooling treatment is 15-45℃ / s, and the second cooling rate for the second cooling treatment is 10-40℃ / s. The first cooling rate is greater than the second cooling rate. The secondary cooled strip steel is coiled using the pinch rolls, assist rolls, and coil drum of a coiler to obtain a high-strength steel coil. In this step, the bite time of the pinch roll is determined based on the hydraulic pressure increment of the pinch roll and the real-time roll gap increment of the pinch roll. Based on the bite time, the coil drum performs a biting operation on the secondary cooled strip steel, and the assist roll performs a stepping control operation to complete the coiling process of the secondary cooled strip steel and obtain a high-strength steel coil.

2. The method for controlling the indentation on the inner ring of a steel coil according to claim 1, characterized in that, The hydraulic pressure increment of the pinch roll is detected by the pressure sensor of the pinch roll hydraulic cylinder within the tracking time window of the head of the secondary cooling strip. The real-time roll gap increment of the pinch roll is detected by the position sensor of the pinch roll hydraulic cylinder within the tracking time window of the head of the secondary cooling strip.

3. The method for controlling the indentation on the inner ring of a steel coil according to claim 1, characterized in that, The step of determining the steel-biting moment of the pinch roll based on the commanded pressure increment, the executed pressure increment, and the real-time roll gap increment of the pinch roll includes: When the hot metal detector detects the head of the secondary cooled strip, and within the head tracking time window, the pressure increment on the piston side or rod side of the pinch roll hydraulic cylinder exceeds the first preset pressure threshold, it is determined that the pinch roll of the coiler is biting the steel and a biting signal is issued. The biting time is determined based on the biting signal. When the head of the secondary cooled strip is detected by the hot metal detector, and the real-time roll gap increment of the pinch roll exceeds the first preset roll gap threshold within the head tracking time window, it is determined that the pinch roll of the coiler is biting the steel and a biting signal is issued. The biting time is determined based on the biting signal. When the hot metal detector detects the head of the secondary cooled strip, and within the head tracking time window, the pressure increment on the piston side or rod side of the pinch roll hydraulic cylinder does not exceed the first preset pressure threshold but exceeds the second preset pressure threshold, and at the same time, the real-time roll gap increment of the pinch roll does not exceed the first preset roll gap threshold but exceeds the second preset roll gap threshold, it is determined that the pinch roll of the coiler is biting the steel and a biting signal is issued. The biting time is determined based on the biting signal.

4. The method for controlling the indentation on the inner ring of a steel coil according to claim 1, characterized in that, The step-by-step control operation of the coiling drum on the secondary cooled strip and the step-by-step control operation of the auxiliary coiling roller, based on the bite-off time, includes: Based on the bite moment, the position of the pinch roll, and the running speed of the secondary cooling strip, the real-time head position of the secondary cooling strip is calculated. When the real-time head position is equal to the preset bite position of the drum on the secondary cooling strip, the drum is controlled to perform a bite operation, and the auxiliary winding roller is controlled to perform a stepping control operation according to the real-time head position.

5. The method for controlling the indentation on the inner ring of a steel coil according to claim 4, characterized in that, The method further includes: The pressure mark risk assessment area is defined based on the real-time head position; Within the indentation risk assessment area, the indentation risk of the secondary cooling strip is assessed based on the pressure jump and roll gap change when the auxiliary coiling roll performs step control operation.

6. The method for controlling the indentation on the inner ring of a steel coil according to claim 1, characterized in that, Before the step of hot rolling the high-strength steel slab to be processed, the method further includes: The refined molten steel for providing high-strength steel comprises the following components by mass percentage: C: 0.15-0.19%, Si: 0.1-0.3%, Mn: 1.0-1.5%, S: ≤0.010%, P: ≤0.020%, Als: 0.025-0.060%, Nb: 0.01-0.03%, Ti: 0.01-0.03%, Ni: 0.2-0.5%, Cr: 0.2-0.5%, B: 0.0010-0.0030%, with the remainder being Fe and unavoidable impurities during steelmaking; The refined molten steel is cast to obtain a high-strength steel slab; Optionally, the thickness of the high-strength steel slab is 230-240 mm.

7. The method for controlling the indentation on the inner ring of a steel coil according to claim 1, characterized in that, In the step of hot rolling the high-strength steel slab, the final rolling temperature of the hot rolling process is 850-900℃.

8. The method for controlling the indentation on the inner ring of a steel coil according to claim 1, characterized in that, The step of hot-rolling the high-strength steel slab to be processed to obtain hot-rolled strip steel includes: The high-strength steel slab to be processed is heated to obtain a heated high-strength steel slab. The heated high-strength steel slab is subjected to rough rolling to obtain an intermediate slab. The rough rolling process is performed in 5 or 7 passes. The intermediate slab is subjected to finish rolling to obtain hot-rolled strip steel. The finish rolling process is a 7-stand continuous finish rolling process.

9. The method for controlling the indentation on the inner ring of a steel coil according to claim 8, characterized in that, In the step of heat treatment of the high-strength steel slab, the heat treatment time is 150-300 minutes. Optionally, the target temperature for the heat treatment is 1200-1260℃.

10. The method for controlling the indentation on the inner ring of a steel coil according to claim 1, characterized in that, The thickness of the high-strength steel coil is 3.0-8.0 mm.

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