Rolling stress relief and plate shape flatness coordinated optimization method in strip steel annealing process

Abstract

The invention provides a rolling stress relief and plate shape flatness coordinated optimization method in a strip steel annealing process, which comprises the following steps of: performing segmented dynamic tension control, dual-frequency electromagnetic field temperature control, gradient pulse stress reconstruction and electromagnetic-pulse multi-target coupling optimization; the problems that heat conduction lags behind, residual stress release is not thorough and flatness control is insufficient in a traditional process are solved, and the method has the advantages that stress elimination and plate shape control are synchronously optimized, recrystallization uniformity is improved, and residual stress is reduced.

Description

Technical Field

[0001] The present invention relates to the field of stainless steel annealing processes, and particularly to a method for coordinating and optimizing the elimination of rolling stress and the flatness of strip shape in a strip annealing process. Background Art

[0002] The core contradiction in the current stress-strip shape coordinated control lies in the coordinated regulation of the internal stress gradient distribution and grain recrystallization. Traditional annealing processes have made some progress through the optimization of the tension system and the regulation of the temperature field, but there are still some limitations. First, the thermal conduction lag effect leads to a large temperature difference in the thickness direction, causing non-uniform recrystallization. Second, the residual stress remains at a relatively high level after traditional annealing, and the stress release is incomplete. In addition, the control accuracy of the elongation of the existing temper mill is insufficient, affecting the strip shape control effect. Electromagnetic-assisted annealing can break through the traditional thermal conduction limit and improve the grain boundary migration rate through the dislocation movement induced by the Lorentz force and the Joule heat effect. In view of the above problems, the existing technology urgently needs to be improved. Summary of the Invention

[0003] In order to solve the above technical problems, the purpose of the present invention is to provide a method for coordinating and optimizing the elimination of rolling stress and the flatness of strip shape in a strip annealing process, which has the advantages of synchronously optimizing stress elimination and strip shape control, improving the uniformity of recrystallization, and reducing residual stress.

[0004] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0005] The present application provides a method for coordinating and optimizing the elimination of rolling stress and the flatness of strip shape in a strip annealing process. The technical solution is as follows: The annealing furnace is divided into a preheating section, a soaking section, and a cooling section. Independent tensiometers and speed sensors are set in each section, and the tension is dynamically adjusted to be controlled within 13.4 - 16.8 N / mm 2 ; A transverse magnetic inductor array is installed at the entrance of the annealing furnace. By using a dual-frequency electromagnetic field combined with a precise temperature control model, the temperature difference between the edge and the middle of the strip is controlled within ±5°C; A gradient pulse power supply is used, and a slow cooling system is used to realize the internal stress reconstruction of the strip; An electromagnetic-pulse coupling control is established, and the electromagnetic field distribution and pulse parameters are multi-objectively optimized.

[0006] Further, the present application also proposes that in step (a), the tension is dynamically adjusted through the formula:

[0007]

[0008] Where: E is the elastic modulus, H is the strip thickness, B0 is the strip width, ν is the Poisson's ratio, and Δε is the strain difference.

[0009] Further, the present application also proposes that in step (b), the dual-frequency electromagnetic field is 50 Hz for the low frequency and 20 kHz for the high frequency.

[0010] Furthermore, the present application also proposes that in step (b), the precise temperature control model is as follows: the coupling relationship between the Maxwell equation and the Fourier heat conduction equation is solved by the finite element method, and the Joule heat distribution of the low-frequency electromagnetic field and the skin effect heat source of the high-frequency electromagnetic field are mainly calculated. Among them,

[0011] Low-frequency field heat source density: Q L =σ|E L | 2 (σ is the conductivity, and E is the electric field strength)

[0012] High-frequency field heat source density: (μ is the magnetic permeability, ω is the angular frequency, and δ is the skin depth)

[0013] The three-dimensional temperature field simulation is realized through COMSOL software to predict the temperature difference distribution law between the strip edge and the middle part.

[0014] Furthermore, the present application also proposes that in step (c), the frequency of the gradient pulse power supply is adjustable from 1 to 100 Hz, and the duty cycle is 10-90%.

[0015] Furthermore, the present application also proposes that in step (d), the electromagnetic-pulse coupling control includes: integrating the Maxwell equations and the heat conduction equation, adopting the finite element-phase field coupling algorithm to realize the dynamic interaction simulation of the electromagnetic field and the pulse energy density. Among them, the Bayesian inversion algorithm is introduced into the electromagnetic field module to correct the magnetic field distribution in real time according to the material conductivity σ to solve the edge-center field strength difference caused by the skin effect. The pulse module adopts the Landauer formalization method to establish a non-linear mapping between the pulse energy density and the dislocation migration rate, and optimizes the pulse waveform through time series analysis.

[0016] Furthermore, the present application also proposes that the multi-objective optimization includes at least the optimization of the recrystallization efficiency η and the optimization of the grain size d.

[0017] Furthermore, the present application also proposes that in step (c), the slow cooling system realizes the cooling rate gradually decreasing from 100 °C / s to 1 °C / s through a multi-stage air cooling or water cooling device, promoting the rearrangement of dislocations to form a stable network structure.

[0018] Furthermore, the present application also proposes that in step (a), there are three sections: the preheating section (200-600 °C), the soaking section (700-850 °C), and the cooling section (50-300 °C). Each section is independently equipped with the following systems: a tensiometer: a piezomagnetic tension sensor is selected and installed downstream of the outlet roll group of each section; a speed encoder: a 2048-line incremental encoder is adopted to monitor the strip running speed in real time; a temperature sensor: a combination of an infrared thermometer and a K-type thermocouple is used to monitor the strip temperature gradient.

[0019] As can be seen from the above, a coordinated optimization method for rolling stress elimination and strip shape flatness in a strip annealing process provided by the present application overcomes the problems of heat conduction lag, incomplete release of residual stress, and insufficient flatness control in traditional processes through segmented dynamic tension control, dual-frequency electromagnetic field temperature control, gradient pulse stress reconstruction, and electromagnetic-pulse multi-objective coupling optimization. It has the advantages of synchronously optimizing stress elimination and strip shape control, improving the uniformity of recrystallization, and reducing residual stress. Description of the Drawings

[0020] Figure 1 It is a flowchart of the steps of a coordinated optimization method for rolling stress elimination and strip shape flatness in a strip annealing process according to the present invention. Detailed Embodiments

[0021] The following details the embodiments of the present invention. The examples of the embodiments are shown in the drawings, where the same or similar reference numerals represent the same or similar elements or elements with the same or similar functions throughout. The embodiments described below with reference to the drawings are exemplary and are only used to explain the present invention and should not be construed as a limitation of the present invention.

[0022] In the description of the present invention, it should be understood that if there are terms such as "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. indicating the orientation or positional relationship, they are based on the orientation or positional relationship shown in the drawings. This is only for the convenience of describing the present invention 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. Therefore, it should not be construed as a limitation of the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes and should not be construed as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of the said features. In the description of the present invention, "a plurality" means two or more, unless otherwise specifically defined.

[0023] In the description of the present invention, it should be noted that unless otherwise clearly defined and limited, the terms "installed", "connected", and "coupled" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection. It can be a mechanical connection or an electrical connection. It can be directly connected or indirectly connected through an intermediate medium, and it can be the internal communication of two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0024] As Figure 1 shown, in the prior art, the field of strip annealing process has long faced the difficult problem of difficult coordination and optimization between rolling stress elimination and flatness of strip shape. Traditional methods rely on tension regime adjustment and temperature field control. However, due to the thermal conduction lag effect, a significant temperature gradient is easily formed in the thickness direction of the strip, resulting in uneven recrystallization process. After conventional annealing, the residual stress retention ratio is relatively high. At the same time, the control accuracy of the elongation rate in the leveling process is limited, making it difficult to meet the processing requirements of high-precision sheets. During the operation of the continuous annealing production line, the thermodynamic state difference between the strip edge and the central region easily causes wavy defects.

[0025] To solve the above problems, during the R & D process, the correlation between residual stress and shape defects was first observed, and it was found that the traditional single-section control could not balance the contradiction between stress release and tissue reconstruction. By analyzing the phase transformation kinetics characteristics, the influence law differences of different temperature ranges on material plasticity and phase transformation rate were found. Based on the principle of electromagnetic heat effect and mechanical energy coupling, the idea of combining electromagnetic field regulation and pulsed energy injection was proposed, and an attempt was made to intervene in energy input during the thermodynamic softening stage to promote dislocation recombination. The synergistic action mechanism of the composite energy field was verified through multi-physics field coupling simulation.

[0026] Therefore, this application proposes an optimization method for strip annealing process including the following steps: dividing the annealing furnace into a preheating section, a soaking section and a cooling section, setting independent tensiometers and speed sensors in each section for dynamic adjustment of tension control; installing a transverse magnetic inductor array at the entrance of the annealing furnace, using a dual-frequency electromagnetic field combined with a precise temperature control model; using a gradient pulse power supply in cooperation with a slow cooling system; establishing electromagnetic-pulse coupling control and conducting multi-objective optimization.

[0027] Among them, the independent tensiometer and speed sensor refer to the mechanical parameter monitoring devices configured in sub-regions, which can be specifically implemented by combining a piezomagnetic sensor and an incremental encoder, and are used to obtain the stress state and strip running parameters of each section in real time. The transverse magnetic inductor array refers to the electromagnetic generating device arranged along the width direction of the strip, which can be specifically implemented by the parallel structure of multiple groups of Helmholtz coils, and compensates for the edge heat loss by adjusting the coil spacing and the excitation current distribution. The dual-frequency electromagnetic field refers to the electromagnetic energy application method of composite frequencies, which can be specifically implemented by the superposition mode of a low-frequency electromagnetic field and a high-frequency electromagnetic field. The low-frequency component generates uniform Joule heat, and the high-frequency component enhances the skin effect. The gradient pulse power supply refers to the electric energy conversion device with adjustable output characteristics, which can be specifically implemented by combining an IGBT module and an LC filter circuit, and adjusts the stress wave penetration depth by changing the pulse frequency and duty cycle. The slow cooling system refers to the cooling device with a controllable rate, which can be specifically implemented by the alternating arrangement structure of multi-stage air cooling and water cooling, and realizes gradient cooling by adjusting the flow rate of the cooling medium. The electromagnetic-pulse coupling control refers to the multi-physical field joint optimization system, which can be specifically implemented by coupling a finite element algorithm and a phase field model, and reversely solves the correlation function of the field strength distribution and the energy density.

[0028] Specifically, after the annealing furnace is set in sections, a lower tension is adopted in the preheating section to avoid damage to the oxide layer, the tension is increased in the soaking section to promote the migration of recrystallization grain boundaries, and the tension is gradually reduced in the cooling section to inhibit the accumulation of residual stress. When the transverse magnetic inductor array applies a composite electromagnetic field, the low-frequency component compensates for the edge heat radiation loss, the high-frequency component enhances the eddy current effect in the central region, and the transverse temperature difference control is realized by combining the three-dimensional temperature field simulation prediction. The gradient pulse power supply injects energy in stages during the slow cooling stage, and promotes the reconstruction of the dislocation network through the stress wave superposition effect. The coupling optimization of the electromagnetic field and pulse parameters seeks the optimal balance point between the recrystallized grain size and the dislocation density by establishing a multi-objective function.

[0029] Compared with the prior art, the traditional single-section control cannot adapt to the phase transformation characteristic differences of materials in different temperature ranges, while this solution realizes the optimal matching of process parameters through sub-region dynamic adjustment. Conventional electromagnetic annealing only uses a single-frequency field and cannot take into account the heat compensation requirements of the edge and the center. This solution breaks through the heat conduction lag limit through the dual-frequency superposition mode. Existing pulse processing mostly has fixed parameter inputs, and this solution realizes the dynamic coordination of stress waves and cooling rates through gradient adjustment.

[0030] Through the above technical solutions, this application realizes the coordinated optimization of the rolling stress and the shape quality during the strip annealing process, effectively inhibits the non-uniform recrystallization phenomenon, significantly reduces the residual stress level, and improves the flatness control accuracy of the sheet. The heat conduction lag effect is effectively compensated, the temperature distribution uniformity of the strip cross-section is significantly improved, and the controllability of the dislocation recombination process is significantly enhanced.

[0031] The present application further proposes to set up independent tension meters and speed sensors in each section of the annealing furnace, and dynamically adjust the tension through the formula:

[0032]

[0033] Among them, the elastic modulus refers to the ability of a material to resist elastic deformation when subjected to force. It can be achieved by interpolating the measured temperature through the JMatPro material database to establish a quantitative relationship between tension and material stiffness. The thickness of the strip refers to the size of the strip in the vertical direction. Its cubic relationship reflects the sensitivity of the bending stiffness to thickness changes and can be monitored in real time by a laser thickness gauge. Bandwidth refers to the transverse width of the strip. As the basis for calculating the transverse cross-sectional area, a visual measurement system is used for online detection. Poisson's ratio refers to the ratio of the transverse strain to the longitudinal strain of the material. As a typical value for steel, it takes a fixed parameter and needs to be fine-tuned according to the alloy composition. The strain difference refers to the strain gradient per unit length. It is obtained by measuring the speed difference of adjacent roller groups with a laser velocimeter and converting it to quantify the degree of uneven deformation inside the strip.

[0034] Specifically, a closed-loop control model is constructed by comprehensively calculating the material characteristic parameters and the real-time detected strain gradient. The elastic modulus is dynamically adjusted according to the annealing temperature to compensate for the softening effect of the material at high temperature; the cubic operation of the strip thickness strengthens the sensitivity of thickness fluctuations to tension control; the bandwidth parameter ensures that the lateral dimensional changes are accurately incorporated into the calculation system; the fixed value of the Poisson's ratio simplifies the calculation complexity while retaining the factors affecting the lateral deformation of the material; the real-time detection of the strain difference enables the tension adjustment to directly correspond to the actual deformation state. Each parameter is synchronously collected through multi-sensor fusion technology, and the dynamic tension setting value is output after matrix operation by an industrial computer, driving the hydraulic servo system to achieve precise adjustment of the roller group pressure.

[0035] Compared with the existing technology, the traditional method uses empirical formulas or a single parameter to adjust the tension, which does not consider the dynamic response of material properties with temperature changes, and cannot effectively associate the strain gradient with the tension control amount. This solution establishes a multi-parameter coupled physical model to achieve the coordinated calculation of material stiffness, geometric dimensions and deformation state, so that the tension control has a clear physical meaning and quantitative basis.

[0036] Through the above technical solution, this application solves the problem of incomplete elimination of strain difference caused by insufficient tension control accuracy in the traditional annealing process, and realizes the directional release of residual stress. By accurately matching material properties and deformation state, the stress gradient inside the strip is effectively reduced, creating a uniform stress environment for the subsequent grain recrystallization process, thereby improving the control accuracy of plate flatness.

[0037] This application further proposes to install a transverse magnetic inductor array at the entrance of the annealing furnace, and adopt a dual-frequency electromagnetic field combined with a precise temperature control model, where the dual-frequency electromagnetic field is 50 Hz for low frequency and 20 kHz for high frequency.

[0038] Among them, the 50 Hz low-frequency electromagnetic field refers to an alternating magnetic field with a working frequency of 50 Hz, which can be specifically realized by using a power frequency power supply and a toroidal coil. Its large penetration depth enables a uniform Joule heat effect to be formed in the thickness direction of the strip steel, realizing overall basic heating. The 20 kHz high-frequency electromagnetic field refers to an alternating magnetic field with a working frequency of 20 kHz, which can be specifically realized by using an IGBT inverter and a planar coil. Its skin effect enables the electromagnetic energy to be concentrated on the surface layer of the strip steel, especially strengthening the induction heating of the edge area.

[0039] Specifically, the low-frequency electromagnetic field forms a volume heating inside the strip steel through hysteresis loss and eddy current effect, effectively reducing the temperature gradient in the thickness direction; the high-frequency electromagnetic field performs directional energy compensation for the edge area through the skin distribution of the surface layer current. The superposition of the two forms a spatially differentiated heat source distribution. The low-frequency component maintains the balance of the matrix temperature field, and the high-frequency component actively offsets the edge temperature drop caused by heat dissipation. The electromagnetic field energy is partitioned and distributed according to frequency bands on the cross-section of the strip steel. The low-frequency component covers the entire cross-section depth, and the high-frequency component focuses on specific surface areas, achieving a breakthrough in the heat conduction lag effect through the coupling control of the frequency domain - spatial domain.

[0040] Compared with the prior art, the traditional annealing process uses a single-frequency electromagnetic field or a conventional heat conduction heating method, which cannot simultaneously meet the requirements of overall temperature uniformity and edge heat compensation. This solution solves the technical contradiction that a single heating mode cannot take into account the overall and local heat balance by means of the energy coupling mechanism of the dual frequency band, while maintaining the stability of the matrix thermal field, implementing high-frequency energy supplementation for the edge area prone to heat dissipation.

[0041] Through the above technical solutions, this application realizes the dynamic balance control of the temperature field on the cross-section of the strip steel, controls the temperature difference between the edge and the middle within the set threshold range, effectively inhibits the non-uniform recrystallization phenomenon caused by heat conduction lag, and provides stable thermodynamic conditions for subsequent stress elimination and shape control.

[0042] This application further proposes that when installing a transverse magnetic inductor array at the entrance of the annealing furnace, a precise temperature control model is used to control the temperature difference between the edge and the middle of the strip steel. This model solves the coupling relationship between the Maxwell equation and the Fourier heat conduction equation by the finite element method, and calculates the Joule heat distribution generated by the low-frequency electromagnetic field and the skin effect heat source generated by the high-frequency electromagnetic field respectively. Among them, the heat source density of the low-frequency field: Q L =σ|E L | 2 (σ is the conductivity, E is the electric field strength), the heat source density of the high-frequency field: (μ is magnetic permeability, ω is angular frequency, and δ is skin depth), and COMSOL software is used to perform three-dimensional temperature field simulation.

[0043] Among them, the Joule heat distribution of the low-frequency electromagnetic field refers to the body heat source generated by the conductor material under the action of the low-frequency current. Specifically, it can be achieved by using a copper winding induction coil with a 50Hz AC power supply. This heat source provides basic energy input for the overall heating of the strip. The skin effect heat source of the high-frequency electromagnetic field refers to the thermal effect generated on the surface of the conductor under the action of a high-frequency alternating magnetic field. Specifically, it can be achieved by using a graphite electrode array with a 20kHz high-frequency power supply. This heat source strengthens the rapid heating of the surface of the strip. Three-dimensional temperature field simulation refers to the numerical solution of the spatial temperature distribution of the strip through the finite element discretization method. Specifically, it can be achieved by using the COMSOL multi-physics field coupling module. This simulation can accurately capture the temperature gradient change law in the thickness direction of the strip.

[0044] Specifically, by constructing a bidirectional coupling model of electromagnetic field and temperature field, the electromagnetic energy distribution calculated by the Maxwell equations is used as the heat source term input of the Fourier equation, and the material parameter changes caused by temperature changes are fed back to the electromagnetic field calculation module. The Joule heat calculation of the low-frequency electromagnetic field uses the body heat source integration method to accurately characterize the overall heating state of the strip; the skin effect calculation of the high-frequency electromagnetic field uses the boundary layer heat source loading method to accurately describe the transient heating process of the surface of the strip. During the three-dimensional simulation process, a multi-layer grid division strategy is set, and the grid encryption processing is performed in the edge area of the strip. The mobile grid technology is combined to simulate the continuous motion state of the strip, and finally the three-dimensional temperature field cloud map in the traveling direction, transverse direction and thickness direction of the strip is output.

[0045] Compared with the existing technology, the traditional annealing process only predicts the temperature field through a single heat conduction equation, ignoring the direct impact of electromagnetic energy conversion on the heat source distribution, resulting in a temperature gradient calculation error of more than 20% in the thickness direction. This solution establishes an electromagnetic-thermal multi-field coupling model, directly embeds the electromagnetic field energy conversion process into the heat conduction calculation, and improves the temperature field prediction accuracy to an engineering applicable level. The two-dimensional simplified model used in the existing technology cannot reflect the lateral temperature difference caused by the edge effect of the strip. The three-dimensional full-scale simulation of this solution can accurately capture the temperature anomaly area caused by the electromagnetic field distortion at the edge.

[0046] Through the above technical solution, the present application effectively solves the problem of temperature difference in the thickness direction caused by heat conduction lag during the annealing process of the strip, and realizes the precise control of the temperature distribution of the strip cross section. Through the synergistic effect of low-frequency electromagnetic field and high-frequency electromagnetic field, the temperature gradient between the surface and the core is precisely controlled while ensuring uniform heating of the strip as a whole. The establishment of a three-dimensional temperature field simulation model provides a reliable basis for the optimization of process parameters, so that the maximum temperature difference between the edge and the middle of the strip is stably controlled within the process allowable range.

[0047] The present application further proposes that the frequency adjustment range of the gradient pulse power supply is 1 to 100 Hz, and the duty cycle adjustment range is 10% to 90%.

[0048] Among them, the gradient pulse power supply refers to a power supply device that can output a pulse waveform with a parameter gradient change. Specifically, it can be achieved by using a multi-stage inverter circuit and a digital signal processor for coordinated control, and dynamic energy input can be achieved by adjusting the pulse waveform parameters.

[0049] Among them, the frequency adjustment range of 1 to 100 Hz means that the number of periodic changes of the pulse current can be adjusted within this range, which can be specifically achieved by using a variable frequency thyristor trigger circuit. The low frequency band corresponds to the relaxation time constant of the macroscopic stress relaxation of the strip, and the high frequency band matches the vibration frequency of the microscopic dislocation motion.

[0050] Among them, the duty cycle adjustment range of 10% to 90% means that the ratio of the on-time to the total period in a single pulse cycle is adjustable, which can be achieved by controlling the on-off timing of the insulated gate bipolar transistor through a pulse width modulation chip, and realizing nonlinear control of the dislocation migration rate by changing the energy input density.

[0051] Specifically, the stress relaxation response frequency band related to the thickness of the strip is selected by adjusting the pulse frequency. The low frequency band acts on the internal stress gradient in the millimeter-level thickness direction, and the high frequency band excites dislocation slip inside the micron-level grains. Duty cycle adjustment is used to balance pulse energy accumulation and heat dissipation requirements. A higher duty cycle accelerates dislocation migration but requires cooling rate control. A lower duty cycle prolongs the thermal relaxation time to avoid overheating of the grain boundaries. The combined adjustment of the two forms an energy gradient distribution in the space-time dimension, so that the residual stresses at different depths of the strip are dynamically reconstructed in turn, breaking through the stress release threshold limit caused by traditional fixed parameter pulse processing.

[0052] Compared with the existing technology, the traditional annealing process uses a fixed frequency pulse power supply and the duty cycle is not adjustable, which leads to a mismatch between the energy input and the material stress relaxation characteristics, and cannot adapt to strip steels of different thicknesses and materials. This solution solves the technical defect of insufficient residual stress release in the traditional process by constructing a wide range of adjustable pulse parameter windows to dynamically match the pulse energy distribution with the internal stress gradient of the material.

[0053] Through the above technical scheme, the present application realizes multi-scale regulation of residual stress inside the strip, which significantly improves the completeness of stress release, while avoiding the problem of abnormal grain growth caused by energy input mismatch, and provides a basic guarantee for plate flatness control.

[0054] This application further proposes electromagnetic-pulse coupling control, which includes integrating Maxwell's equations and heat conduction equations, and using a finite element-phase field coupling algorithm to realize the dynamic interaction simulation of electromagnetic fields and pulse energy density. Among them, the Bayesian inversion algorithm is introduced in the electromagnetic field module to correct the magnetic field distribution in real time according to the material conductivity, and the Landauer formalism is used in the pulse module to establish a nonlinear mapping between the pulse energy density and the dislocation migration rate and optimize the pulse waveform through time series analysis.

[0055] Among them, the finite element-phase field coupling algorithm refers to a computational method for jointly modeling the electromagnetic field distribution and the evolution process of the material microstructure. Specifically, data interaction can be realized through the software interface of ANSYS and MICRESS, and the cross-scale coupling problem of electromagnetic field thermal effects and dislocation motion can be solved by synchronously iterating the solution of Maxwell's equation and the phase field control equation. The Bayesian inversion algorithm refers to a parameter optimization method based on probability statistics. Specifically, Markov chain Monte Carlo sampling can be used to realize the real-time correction of the electromagnetic field distribution, and the magnetic field intensity distribution model can be dynamically updated by online obtaining the change data of the strip conductivity, eliminating the field strength difference between the edge and the central region caused by the skin effect. The Landauer formalism refers to a theoretical framework for establishing the relationship between energy transfer and microscopic defect motion. Specifically, the dislocation migration barrier can be calculated by density functional theory, and a nonlinear function relationship between energy density and dislocation rate can be constructed in combination with the pulse current waveform parameters, providing a quantitative basis for pulse parameter optimization.

[0056] Specifically, the electromagnetic field module solves the three-dimensional transient electromagnetic field distribution by the finite element method, takes the calculated Joule heat distribution as the heat source term and inputs it into the heat conduction equation, and at the same time the phase field module calculates the change of dislocation density according to the evolution of the temperature field; the pulse module extracts the characteristic parameters of the current waveform through time series analysis, combines the Landauer model to predict the dislocation migration rate under different pulse parameters, and feeds the optimized pulse waveform parameters back to the power supply control system. The Bayesian inversion algorithm dynamically adjusts the boundary conditions of the finite element model by real-time collecting the strip surface impedance measurement values during the electromagnetic field solution process, effectively compensating for the field strength distortion caused by the uneven distribution of material conductivity. Thus, a multi-field coupling closed-loop control system of electromagnetic field-temperature field-microstructure field is formed to realize the collaborative optimization configuration of electromagnetic parameters and pulse parameters.

[0057] Compared with the existing technology, the traditional electromagnetic annealing technology uses a fixed-frequency magnetic field, resulting in serious attenuation of the edge magnetic field, and the static pulse parameter setting is difficult to meet the dislocation motion requirements of strip steel with different thicknesses. This solution eliminates the edge effect by dynamically correcting the magnetic field distribution, and at the same time establishes an accurate mapping relationship between the pulse energy and the dislocation rate, overcoming the regulation blind area brought by single-parameter optimization. In the existing technology, the electromagnetic field and pulse control belong to independent systems. This solution realizes the analysis of the interaction mechanism between the two through multi-physics field coupling modeling, providing a theoretical support for collaborative control.

[0058] Through the above technical solutions, the present application can dynamically compensate for the difference in electromagnetic field strength between the strip edge and the central region, ensuring the uniformity of the field strength distribution in the thickness direction; accurately establish the quantitative relationship between the pulse energy density and the dislocation migration rate, and achieve targeted optimization of the pulse waveform parameters; through the real-time interactive adjustment of the electromagnetic field and pulse parameters, a closed-loop control mechanism is formed to effectively coordinate the process of stress elimination and grain structure reconstruction inside the strip.

[0059] The present application further proposes that the multi-objective optimization at least includes the optimization of the recrystallization efficiency and the optimization of the grain size.

[0060] Among them, the optimization of the recrystallization efficiency refers to achieving stress elimination by regulating the dislocation migration rate and the grain boundary movement efficiency. Specifically, it can be realized by the synergistic effect of adjusting the annealing temperature gradient and the pulse frequency. By dynamically matching the electromagnetic field strength with the material phase transformation activation energy, the reconstruction of the dislocation network is accelerated.

[0061] The optimization of the grain size refers to forming a uniform microstructure by balancing the dynamic relationship between the nucleation rate and the growth rate. Specifically, it can be realized by combining the gradient cooling rate control with the adaptive adjustment of the pulse energy density. Using the phase field model to predict the grain growth kinetic trajectory to suppress abnormal grain growth.

[0062] Specifically, by establishing a multi-objective coupling optimization model, the thermodynamic driving factors and the grain evolution kinetic conditions of the recrystallization process are synchronously regulated during the annealing process. The improvement of the recrystallization efficiency depends on the dislocation motion strengthening effect induced by the electromagnetic field, which shortens the recrystallization completion time by enhancing the grain boundary migration driving force; the grain size control is achieved through the coordinated adjustment of the pulse energy input and the slow cooling rate, while suppressing secondary recrystallization, maintaining the uniformity of the grain size distribution. This coupling mechanism realizes dynamic feedback through the finite element-phase field joint algorithm, ensuring the synergistic optimization of the stress elimination efficiency and the microstructure stability.

[0063] Compared with the prior art, the traditional method only adjusts the recrystallization process through a single temperature field or tension system, and cannot solve the contradiction between the stress release efficiency and the grain coarsening at the same time. This solution realizes the decoupled control of dislocation motion and grain growth under the action of the electromagnetic-pulse composite energy field by constructing a two-dimensional optimization target, overcoming the defects of stress residue or tissue inhomogeneity caused by single-parameter regulation.

[0064] Through the above technical solutions, the present application can achieve the synchronous optimization of the stress elimination rate and the material microstructure during the strip annealing process, effectively reduce the residual stress level and maintain the grain size stability, avoid the problem of abnormal grain growth caused by excessive pursuit of stress release efficiency, and at the same time prevent the phenomenon of incomplete stress elimination caused by simply controlling grain refinement.

[0065] The present application further proposes a technical solution for achieving a phased reduction in cooling rate by using a multi-stage cooling device in the strip annealing process, wherein the cooling rate is gradually reduced from 100°C / second to 1°C / second, and a multi-stage air cooling or water cooling device is used to cause the internal dislocations of the strip to be rearranged to form a stable network structure.

[0066] Among them, the multi-stage air cooling device refers to multiple groups of independently controlled fan arrays arranged along the production line. It can be specifically implemented by a combination of axial flow fans and centrifugal fans. The cooling intensity of different areas can be controlled by adjusting the fan speed and air supply angle.

[0067] Among them, the multi-stage water cooling device refers to a cooling system with a segmented spray structure, which can be specifically realized by combining a high-pressure atomizing nozzle with a low-pressure water curtain nozzle, and the linear adjustment of the cooling rate can be achieved by adjusting the water pressure and flow rate.

[0068] Among them, cooling rate gradient control refers to real-time monitoring of strip surface temperature changes through a temperature feedback system. Specifically, a PID control algorithm can be used to dynamically adjust the cooling medium flow rate so that the cooling rate presents an exponential attenuation curve.

[0069] Specifically, when the strip enters the cooling stage after annealing, high-intensity cooling is used in the initial stage to quickly reduce the surface temperature. At this time, the fan or spray system operates at maximum power, and the cooling rate can reach 100°C / second. As the temperature drops to the critical transition point, the control system gradually reduces the cooling intensity, and the cooling rate decreases in steps by adjusting the fan speed or the number of nozzles opened in stages. In the low-temperature stage, it switches to low-speed cooling mode, and the cooling rate is reduced to 1°C / second by reducing the wind pressure or reducing the water flow. This process continues until the strip reaches room temperature. In this process, the atomic migration rate inside the strip forms a dynamic balance with the cooling rate, which causes dislocations to move in an orderly manner along the grain boundary direction and form a three-dimensional network cross-linked structure.

[0070] Compared with the existing technology, the traditional annealing process usually adopts a single cooling rate or a fixed cooling medium, which leads to non-uniform thermal stress inside the material. This solution solves the problem of dislocation accumulation caused by rapid cooling by constructing a multi-stage cooling device and a gradient control strategy, while avoiding grain boundary cracking caused by sudden temperature changes. In the existing technology, the water cooling system often produces temperature fluctuations due to medium switching, while this solution achieves a continuous and smooth transition of the cooling process by using a combination of media and coordinated parameter adjustment.

[0071] Through the above technical solution, the present application can effectively eliminate the residual stress inside the strip steel, promote the formation of a stable three-dimensional network distribution of the dislocation structure, and enhance the anti-deformation ability of the material. The gradient change of the cooling rate provides a sufficient time window for atomic diffusion, avoiding lattice distortion caused by rapid cooling. The combined use of the multi-stage cooling device can adapt to the cooling requirements of strip steels with different thicknesses, ensuring the uniformity and controllability of stress release.

[0072] The present application further proposes to divide the annealing furnace into three temperature zones: a preheating zone, a soaking zone, and a cooling zone. The temperature ranges of each zone are set to 200 - 600 °C, 700 - 850 °C, and 50 - 300 °C respectively, and a piezomagnetic tension sensor, an incremental velocity encoder, and a combined temperature sensor system are independently configured in each zone. Among them, the piezomagnetic tension sensor is installed downstream of the outlet roll group in each zone. The velocity encoder has a resolution of 2048 lines, and the temperature monitoring system consists of an infrared thermometer and a K-type thermocouple.

[0073] Among them, the temperature range of 200 - 600 °C in the preheating zone refers to the heating temperature range of the strip steel in this interval. Specifically, it can be achieved by a radiant tube heater cooperating with a proportional-integral-derivative controller. This temperature range can promote the transformation of the material from elastic deformation to plastic deformation. The soaking zone of 700 - 850 °C refers to the core recrystallization temperature range of the strip steel. Specifically, it can be achieved by an induction heating coil array cooperating with a temperature feedback system. This temperature range is conducive to full recrystallization of grains. The cooling zone of 50 - 300 °C refers to the slow cooling control temperature range of the strip steel. Specifically, it can be achieved by a multi-stage air cooling device cooperating with a flow regulating valve. This gradient cooling process can avoid the generation of residual stress. The piezomagnetic tension sensor refers to a force measurement device based on the magnetostriction principle. Specifically, it can be achieved by a Fe-Co alloy sensitive element cooperating with a Hall effect detection circuit. Its non-contact characteristic can avoid mechanical vibration interference. The 2048-line incremental encoder refers to a speed detection device with 2048 pulse signals per revolution. Specifically, it can be achieved by an optoelectronic encoder cooperating with an orthogonal decoding circuit. Its high resolution can accurately feedback the running speed of the strip steel. The combination of the infrared thermometer and the K-type thermocouple refers to a composite system for rapid surface temperature detection and internal temperature gradient monitoring. Specifically, it can be achieved by a short-wave infrared detector and an armored thermocouple array. The data fusion of the two can eliminate the single detection blind area.

[0074] Specifically, the annealing furnace is divided into three processing sections with distinct temperature boundaries, and different temperature control targets are set for each section according to the material phase transformation law. In the preheating stage, the strip is gradually heated to the critical temperature of plastic deformation. At this time, the piezomagnetic sensor continuously monitors the tension change, the speed encoder synchronously tracks the running state of the strip, and the combined temperature sensor forms the temperature distribution data in the thickness direction through the combination of surface infrared scanning and internal thermocouple detection. After entering the soaking stage, the system dynamically adjusts the heating power according to the temperature gradient data collected in real time to ensure that the entire cross-section of the strip reaches the temperature conditions required for recrystallization. The cooling stage adopts a hierarchical cooling strategy. By the feedback of the strip position information from the speed encoder, the air volume distribution in each area of the air-cooling device is coordinated to make the cooling rate match the process of material stress release. The data of each detection device is transmitted to the central controller through the fieldbus to form a closed-loop control of the temperature field, stress field and speed field.

[0075] Compared with the prior art, the traditional annealing process usually adopts a single temperature zone or a rough segmented temperature control method, resulting in a significant temperature gradient in the thickness direction of the strip. In the prior art, temperature detection mostly relies on a single type of sensor and cannot capture the surface temperature distribution and internal heat conduction state at the same time. This solution realizes the real-time reconstruction of the three-dimensional temperature field of the strip by accurately dividing three characteristic temperature sections and configuring a multi-dimensional sensing system, overcoming the temperature control deviation caused by the thermal lag effect in the traditional method.

[0076] Through the above technical solutions, this application can effectively reduce the temperature gradient fluctuation of the strip during annealing. Through the fusion processing of multi-source sensing data, the temperature difference in the thickness direction is controlled within the range allowed by the material phase transformation, and at the same time, the speed-tension-temperature parameters in each processing stage are coordinated and matched, ultimately realizing the uniform control of the internal stress distribution of the strip.

[0077] This application further proposes a technical solution of dividing the annealing furnace into three temperature intervals: a preheating section, a soaking section and a cooling section, and respectively setting a piezomagnetic tension sensor, an incremental speed encoder and a combined temperature monitoring device in each interval.

[0078] Among them, the temperature range of the preheating section is set in the range of 200 - 600 °C and is used for the initial heating stage of the strip. The temperature gradient monitoring system is composed of an infrared thermometer and a K-type thermocouple. The former measures the surface temperature distribution of the strip in a non-contact manner, and the latter is embedded inside the strip to obtain the deep temperature data. This combined temperature measurement method can construct a three-dimensional temperature field model in the thickness direction to identify the temperature deviation caused by heat conduction lag.

[0079] Specifically, the piezomagnetic tension sensor is arranged downstream of the outlet roll group of each section to directly detect the actual stress state of the strip steel. This installation position can effectively avoid the interference of the mechanical vibration of the roll group on the measured value and ensure the accuracy of the tension feedback data. The speed encoder is designed with a resolution of 2048 lines, and the frequency of its pulse signal generation is linearly related to the running speed of the strip steel, providing real-time speed reference parameters for the tension control system. The temperature monitoring system arranges multiple detection points in the width direction of the strip steel. By comparing the temperature change rates of the edge and the central region, the heating power distribution can be dynamically adjusted.

[0080] Compared with the prior art, the traditional annealing process usually adopts single-temperature interval control, and the temperature monitoring means is limited to single-point surface temperature measurement. Through dividing the process sections with clear temperature gradients and combining multi-dimensional sensing technologies, this solution realizes the precise control of the thermal history of the strip steel in the thickness direction. Especially in the cooling section, a combined temperature measurement device is set up to synchronously obtain the difference in the cooling rates of the surface layer and the core, providing data support for eliminating residual stress.

[0081] Through the above technical solutions, this application effectively reduces the temperature gradient difference in the thickness direction of the strip steel, making the recrystallization process inside the material tend to be uniform. The synergistic effect of the combined sensing system improves the response speed of the process parameter adjustment, ensuring that the strip steel obtains stable mechanical properties during the phase change process. The synchronous monitoring mechanism of the temperature field and the stress field creates controllable process conditions for eliminating residual stress and improving the flatness of the sheet shape.

[0082] It should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the embodiments, for those skilled in the art, they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features. However, any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A coordinated optimization method for rolling stress elimination and strip shape flatness in a strip annealing process, characterized in that, It includes the following steps: (a) Divide the annealing furnace into a preheating section, a soaking section, and a cooling section. Install independent tensiometers and speed sensors in each section to dynamically adjust the tension to be controlled within 13.4 - 16.8 N / mm 2 ; (b) Install a transverse magnetic inductor array at the entrance of the annealing furnace, and adopt a dual-frequency electromagnetic field combined with a precise temperature control model to control the temperature difference between the strip edge and the middle within ±5°C; (c) Adopt a gradient pulse power supply and cooperate with a slow cooling system to realize the internal stress reconstruction of the strip; (d) Establish an electromagnetic-pulse coupling control and perform multi-objective optimization on the electromagnetic field distribution and pulse parameters.

2. The method for coordinating and optimizing the rolling stress elimination and strip shape flatness in the strip annealing process according to claim 1, wherein In the step (a), the tension is dynamically adjusted through the formula: where: E is the elastic modulus, H is the strip thickness, B0 is the strip width, ν is the Poisson's ratio, and Δε is the strain difference.

3. The method for coordinated optimization of rolling stress elimination and strip shape flatness in the strip annealing process according to claim 1, characterized in that, In the step (b), the dual-frequency electromagnetic field is 50 Hz for the low frequency and 20 kHz for the high frequency.

4. The method for coordinating and optimizing the rolling stress elimination and strip shape flatness in the strip annealing process according to claim 1, characterized in that, In the step (b), the precise temperature control model adopted is: The finite element method is used to solve the coupling relationship between the Maxwell equation and the Fourier heat conduction equation, and the Joule heat distribution of the low-frequency electromagnetic field and the skin effect heat source of the high-frequency electromagnetic field are mainly calculated. Among them, Low-frequency field heat source density: Q L = σ|E L | 2 (where σ is the conductivity and E is the electric field strength) High-frequency field heat source density: (where μ is the magnetic permeability, ω is the angular frequency, and δ is the skin depth) The three-dimensional temperature field simulation is realized through COMSOL software to predict the temperature difference distribution law between the strip edge and the middle.

5. The method for coordinating and optimizing the rolling stress elimination and strip shape flatness in the strip annealing process according to claim 1, characterized in that In the step (c), the frequency of the gradient pulse power supply is adjustable from 1 to 100 Hz, and the duty cycle is 10-90%.

6. The method for coordinated optimization of rolling stress elimination and strip shape flatness in the strip annealing process according to claim 1, characterized in that In the step (d), the electromagnetic-pulse coupling control includes: Integrate the Maxwell equations and the heat conduction equation, and adopt a finite element-phase field coupling algorithm to realize the dynamic interaction simulation of the electromagnetic field and the pulse energy density. Among them, The Bayesian inversion algorithm is introduced into the electromagnetic field module, and the magnetic field distribution is corrected in real time according to the material conductivity σ to solve the edge-center field strength difference caused by the skin effect. The pulse module adopts the Landauer formalism method to establish a non-linear mapping between the pulse energy density and the dislocation migration rate, and optimizes the pulse waveform through time series analysis.

7. The method for coordinated optimization of rolling stress elimination and strip shape flatness in the strip annealing process according to claim 6, characterized in that, The multi-objective optimization at least includes the optimization of the recrystallization efficiency η and the optimization of the grain size d.

8. The method for coordinated optimization of rolling stress elimination and flatness of strip shape in the strip annealing process according to claim 1, characterized in that, In the step (c), the slow cooling system realizes the cooling rate gradually decreasing from 100°C / s to 1°C / s through a multi-stage air cooling or water cooling device, and promotes the dislocation to rearrange to form a stable network structure.

9. The method for coordinated optimization of rolling stress elimination and strip shape flatness in the strip annealing process according to claim 1, characterized in that, In the step (a), There are three sections: a preheating section (200-600°C), a soaking section (700-850°C), and a cooling section (50-300°C). Each section is independently equipped with the following systems: Tension meter: A piezomagnetic tension sensor is selected and installed downstream of the outlet roll group of each section. Speed encoder: A 2048-line incremental encoder is adopted to monitor the strip running speed in real time. Temperature sensor: A combination of an infrared thermometer and a K-type thermocouple is used to monitor the strip temperature gradient.

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