Rolling and annealing treatment process for copper-steel composite strip

Abstract

The invention discloses a rolling and annealing treatment process for a copper-steel composite strip, and relates to the technical field of material rolling, the process comprises the following steps: selecting a high-purity copper plate and a stainless steel plate, and depositing a nano nickel / graphene composite transition layer through a magnetron sputtering technology; the stainless steel layer is promoted to deform through front-section low-speed high-pressure rolling, and the copper layer interface bonding force is improved through rear-section high-speed low-pressure rolling; performing short-time local annealing by using a high-frequency induction coil; honeycomb-shaped micro-pits are formed in the stainless steel surface through the laser micro-texture technology, and the interface bonding force is improved in combination with the nano-nickel / graphene layer. Copper layer hardening is eliminated through low-temperature annealing, stainless steel recrystallization is promoted through medium-temperature annealing, and a nanometer precipitated phase is fixed through rapid water cooling; the heating rate is controlled, and nitrogen-hydrogen mixed gas is used for preventing oxidation; the rolling process and the annealing process are seamlessly connected, and the temperature, the stress and the atmosphere are detected in real time through an online monitoring system. The mechanical property, the corrosion resistance and the machining stability of the copper-steel composite strip are remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of material rolling, and particularly to a rolling and annealing process for copper-steel composite strips. Background Art

[0002] In recent years, due to their excellent mechanical and electrical conductivity, copper-steel composite materials have been widely used in industries such as electricity, electronics, aerospace, etc. Copper-steel composite strips are mainly used to manufacture materials with high strength, high temperature resistance, and good electrical conductivity in these fields. However, in the production process of existing copper-steel composite materials, problems such as insufficient interfacial bonding force, uneven material properties, and interfacial delamination often occur, which limit their further development in high-end applications.

[0003] Traditional production processes for copper-steel composite strips usually adopt conventional rolling and heat treatment techniques. Although these techniques can effectively form copper-steel composite strips, due to the large difference in thermal expansion coefficients of different materials and the easy generation of residual stress and interfacial delamination problems during rolling, the overall performance of the materials is difficult to meet the high requirements of usage standards. In addition, traditional annealing processes are usually relatively single and cannot effectively control the heat treatment requirements of different metal layers, further affecting the mechanical properties and thermal stability of the composite materials.

[0004] In view of the above problems, the present invention provides a rolling and annealing process for copper-steel composite strips, aiming to improve the interfacial bonding force, mechanical properties, and corrosion resistance of copper-steel composite strips. Summary of the Invention

[0005] The present invention addresses the above problems and provides a rolling and annealing process for copper-steel composite strips to solve the problems of insufficient interfacial bonding force, uneven material properties, residual stress and work hardening, poor mechanical properties, and low production efficiency in the prior art during the production process.

[0006] To solve the above technical problems, the present invention provides the following technical solution: A rolling and annealing process for copper-steel composite strips, comprising the following steps: Step S1, select high-purity copper plates and stainless steel plates, perform pickling, degreasing, and polishing treatments, and deposit a nano-nickel / graphene composite transition layer on the surface of the stainless steel through magnetron sputtering technology; Among them, in step S1, the following sub-steps are further included: S1-1, select oxygen-free copper with a purity of more than 99.9% for the copper plate, and select austenitic stainless steel for the stainless steel plate; The copper plate is soaked in a 10% sulfuric acid solution for 3 - 5 minutes to remove the surface oxide layer; it is rinsed with flowing pure water and dried with hot air to prevent secondary oxidation; the stainless steel plate is sandblasted to increase the surface roughness for facilitating the adhesion of the subsequent nano-layer; it is cleaned with a dilute nitric acid mixed solution to further remove the residual oxides on the surface; a thin layer of activator is coated on the treated stainless steel surface to enhance the adhesion of the subsequent nano-transition layer; S1-2, introducing a nano nickel / graphene composite transition layer at the copper-stainless steel interface; nickel has good metal compatibility with both copper and stainless steel, which can effectively reduce the difference in interface thermal expansion coefficients and relieve thermal stress; graphene has extremely high thermal conductivity, which can promote interface heat conduction, enhance atomic diffusion during the rolling process, and form a firm interface bonding structure at the same time; Using a DC magnetron sputtering device, the vacuum degree is controlled below Pa; high-purity nickel targets and graphene composite targets are selected as the targets; a "nickel-graphene-nickel" three-layer structure is adopted to enhance the chemical bonding and mechanical strength of the interface.

[0007] Step S2, by adjusting the roller speed difference of the rolling mill, low-speed and high-pressure rolling in the front section promotes the deformation of the stainless steel layer, high-speed and low-pressure rolling in the rear section improves the interface bonding force of the copper layer, and controlling the rolling temperature promotes interface diffusion to avoid delamination; Among them, in step S2, the following sub-steps are also included: S2-1, adjusting the rotational speed of the upper roller to be slightly higher than that of the lower roller to form a speed difference; the speed difference requires the rotational speed of the upper roller to be 5 - 10% faster than that of the lower roller to control the interface shear stress and reduce delamination; controlling the roll gap, according to the thickness difference between the copper and steel layers, adjusting the roll gap of the rolling mill to make the rolling pressure distribution of the two layers of materials uniform; controlling the reduction rate during the rolling process to ensure good bonding of the two layers of materials; determining the rolling parameters by calculating the roller speed difference of the rolling mill, specifically as shown in formula (1): Formula (1) Among them, is the strain rate, and are the speeds of the upper and lower rollers respectively, is the strip thickness; S2-2, low-speed and high-pressure rolling in the front section, low-speed and high-pressure rolling is adopted in the front section, focusing on making the stainless steel layer produce plastic deformation first; by controlling the rolling parameters, preferentially promoting the plastic deformation of the stainless steel rather than the copper layer to enhance the initial bonding strength of the copper-steel composite material; S2-3, high-speed and low-pressure rolling in the rear section, during the rear section rolling process, high-speed and low-pressure are adopted, and the high ductility of the copper layer is used to achieve close fitting between the two layers of metals and reduce work hardening.

[0008] Step S3: Perform short-time local annealing using a high-frequency induction coil to eliminate work hardening, reduce residual stress, and optimize the hardness-plasticity balance of the material. In step S3, the following sub-steps are further included: S3-1: Install a high-frequency induction coil at the mill outlet to provide local short-time annealing for the composite strip, eliminating work hardening and reducing residual stress. The induction heating device is positioned to install a high-frequency induction coil near the mill outlet, heating the surface of the composite strip through electromagnetic induction. According to the thickness and material properties of the strip, adjust the operating frequency of the induction coil to achieve efficient heating. Control the heating depth within the range of the surface to a few millimeters to avoid overheating the internal structure and maintain the strength of the material. S3-2: Control the annealing temperature and time to adjust the microstructure of the material, avoiding excessive grain growth and deterioration of mechanical properties during the heat treatment process. Control the annealing temperature between 300 - 500 °C. This temperature range can effectively eliminate work hardening in the material while maintaining good strength. The annealing time is controlled within 10 - 30 seconds, enabling the completion of heat treatment in a very short time and avoiding grain coarsening caused by overheating. Calculate the heat transfer efficiency of the material using the heat conduction formula, specifically as shown in Equation (2): Equation (2) Where, is the heat conducted, is the thermal conductivity of the material, is the heat conduction area, is the temperature on the heating side, is the temperature on the cooling side, is the length of the heat conduction path; S3-3: Through real-time online monitoring and adjustment of the parameters of induction annealing, ensure that the material does not generate excessive residual stress during the rolling process, thereby guaranteeing the overall performance of the composite strip. Use an online stress sensor or X-ray stress analyzer to monitor the residual stress state in the material in real time. The stress monitoring system can be linked with the control system to provide real-time feedback of data and adjust the heating power or heating duration of the induction annealing device. Calculate the residual stress, specifically as shown in Equation (3): Equation (3) Where, is the residual stress, is the stress generated during rolling or heating, is the cross-sectional area of the strip.

[0009] Step S4, form honeycomb micro-pits on the stainless-steel surface using laser micro-texturing technology to enhance mechanical interlocking and chemical bonding, combine with the nano-nickel / graphene layer, and improve the interfacial bonding strength and the mechanical properties of the composite strip; In step S4, the following sub-steps are further included: S4-1, laser micro-texturing treatment, fabricate honeycomb micro-pits on the stainless-steel surface through laser micro-texturing technology to form a special microstructure; Use a high-power laser beam and adopt a dot matrix scanning method to process a honeycomb micro-pit structure with a diameter of 20 - 50 μm and a depth of 5 - 10 μm on the stainless-steel surface; precisely adjust the laser power and scanning speed to ensure the uniformity of the micro-pit morphology, and ensure that the depth and diameter of each pit reach the predetermined value; control the arrangement density and distribution pattern of the micro-pits by adjusting the laser processing parameters to optimize the mechanical interlocking effect; S4-2, further improve the chemical bonding strength and atomic diffusivity at the interface by introducing a nano-nickel / graphene composite transition layer at the copper-steel interface; combine with the honeycomb micro-pits processed by laser micro-texturing to form a dual-enhancement mechanism of mechanical interlocking and chemical bonding, and further optimize the interfacial bonding strength.

[0010] Step S5, annealing is divided into three stages: low-temperature annealing eliminates the hardening of the copper layer, medium-temperature annealing promotes the recrystallization of the stainless steel, and rapid water cooling fixes the nano-precipitation phase to improve the microstructure and enhance the strength of the stainless steel; In step S5, the following sub-steps are further included: S5-1, the first-stage low-temperature short-time annealing, by eliminating the work hardening of the copper layer, improves its plasticity and electrical conductivity, while the stainless-steel layer maintains a certain plasticity; control the annealing temperature within the recrystallization temperature range of the copper layer to ensure effective softening of the copper layer without affecting the strength of the stainless-steel layer; Specific steps: set the annealing temperature to 400 °C and the holding time to 10 minutes; use a nitrogen-hydrogen mixed gas ( ) as the protective atmosphere to avoid oxidation of the copper layer, and at the same time provide a reducing atmosphere, which helps to remove surface oxides and improve the electrical conductivity of the copper layer. The relationship between the annealing temperature and hardness is specifically as shown in Equation (4): Equation (4) Where, is the hardness at temperature, is the initial hardness, is the hardness temperature coefficient, is the annealing temperature, is the initial temperature; S5-2, Medium-temperature gradient annealing in the second stage. During the medium-temperature stage, through gradient temperature control, the recrystallization of the stainless steel layer is promoted, its plasticity is restored, and the grains are refined; during this stage, the copper layer needs to inhibit excessive grain growth and maintain its high strength. Through the grain growth model, specifically as shown in Equation (5): Equation (5) Wherein, is the average diameter of the grains after annealing, is the initial grain diameter, is the grain growth constant, is the annealing time; The annealing temperature is controlled in three zones, specifically 600°C, 650°C, and 700°C, and the holding time for each temperature zone is 20 minutes; by adopting the three-zone temperature control technology, the temperature can be gradually adjusted to achieve the optimal balance between the recrystallization of the stainless steel layer and the grain inhibition of the copper layer; S5-3, Rapid water cooling treatment in the third stage. Through rapid water cooling, the nano-precipitation phase formed during the annealing process is fixed, the strength of the stainless steel layer is further improved, the coarsening phenomenon of the precipitation phase is prevented, and the composite material is ensured to have good mechanical properties and thermal stability; Specific steps: The cooling rate of the rapid water cooling treatment is set to >50°C / s; water is used as the cooling medium to quickly remove heat, ensuring that the cooling rate is high enough to fix the precipitation phase. The cooling rate calculation is specifically as shown in Equation (6): Equation (6) Wherein, is the heat released during the cooling process, is the mass of the cooling medium, is the specific heat capacity of the cooling medium, is the temperature change.

[0011] In step S6, the heating rate is controlled at ≤50°C / min to ensure uniform temperature, avoid thermal stress concentration, use a nitrogen-hydrogen mixed gas to prevent oxidation, optimize the reduction effect, and improve the surface quality and corrosion resistance; Among them, in step S6, the following sub-steps are also included: S6-1, Heating rate control. The heating rate has an important impact on the microstructure and stress distribution of the composite material. The heating rate is controlled at ≤50°C / min to ensure uniform temperature distribution during the heating process and minimize the thermal stress during the temperature rise, avoiding stress concentration or cracks caused by rapid heating; S6-2, Using a nitrogen-hydrogen mixed gas ( ) as the annealing protective atmosphere; during the annealing process, the hydrogen content is adjusted in a timely manner according to the surface state of the material to optimize the reduction effect and prevent the formation of an oxide layer.

[0012] Step S7: Seamlessly connect the rolling and annealing processes, and use an on-line monitoring system to detect the temperature, stress, and atmosphere in real time to ensure the stability of the annealing process.

[0013] In step S7, the following sub-steps are further included: S7-1: After rolling is completed, the copper-steel composite strip directly enters the annealing furnace for on-line annealing, enabling seamless connection between the rolling process and the annealing process, reducing the time for intermediate cooling and reheating, and improving the continuity of the production line. S7-2: Use a high-precision temperature sensor to monitor the temperature change in the annealing furnace in real time, monitor the key parameters during the annealing process in real time, ensure that the process parameters are within the specified range, and adjust the deviation during the annealing process; detect the residual stress of the copper-steel composite strip in real time through a stress sensor, and adjust the annealing process parameters to eliminate internal stress; on-line monitor the ratio of nitrogen-hydrogen atmosphere in the annealing furnace to ensure the accuracy and stability of the atmosphere and prevent the formation of oxide layers.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: Through gradient asynchronous rolling, nano-nickel / graphene composite transition layer, and laser micro-texture technology, the present invention effectively enhances the interfacial bonding force of the copper-steel composite strip, avoiding problems such as interfacial delamination and peeling.

[0015] The present invention adopts dynamic induction annealing technology to eliminate work hardening and residual stress in real time, improving the plasticity and subsequent processability of the material.

[0016] Through multi-stage zone temperature control annealing and rapid water cooling technology, the present invention inhibits excessive grain growth, fixes nano-precipitates, and significantly improves the strength and corrosion resistance of the stainless steel layer of the composite strip.

[0017] By seamlessly connecting the rolling and annealing processes, the present invention reduces the process interval and heat loss, significantly improving production efficiency and reducing energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the embodiments. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.

[0019] Figure 1 is the production process flow chart of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but is merely for the selected embodiments of the present invention.

[0021] Please refer to Figure 1 which is a schematic diagram of the rolling and annealing treatment process of a copper-steel composite strip provided by an embodiment of the present invention, including the following steps: S1. Select high-purity copper plates and stainless steel plates, perform pickling, degreasing, and polishing treatments, and deposit a nano nickel / graphene composite transition layer on the surface of the stainless steel through magnetron sputtering technology; S1-1. Select oxygen-free copper with a purity of more than 99.9% for the copper plate, and select austenitic stainless steel for the stainless steel plate; Immerse the copper plate in a 10% sulfuric acid solution for 3-5 minutes to remove the surface oxide layer; rinse with flowing pure water and dry with hot air to prevent secondary oxidation; perform sandblasting on the stainless steel plate to increase the surface roughness for facilitating the subsequent attachment of the nano layer; clean with a dilute nitric acid mixed solution to further remove the residual oxides on the surface; coat a thin layer of activator on the treated stainless steel surface to enhance the adhesion of the subsequent nano transition layer; S1-2. Introduce a nano nickel / graphene composite transition layer at the copper-stainless steel interface; nickel has good metal-intermediate compatibility with both copper and stainless steel, which can effectively reduce the difference in the coefficient of thermal expansion at the interface and relieve thermal stress; graphene has extremely high thermal conductivity, which can promote interface heat conduction, enhance atomic diffusion during the rolling process, and at the same time form a firm interface bonding structure; Use a DC magnetron sputtering device, and control the vacuum degree at below Pa; select high-purity nickel targets and graphene composite targets for the targets; adopt a "nickel-graphene-nickel" three-layer structure to enhance the chemical bonding and mechanical strength at the interface.

[0022] It should be noted that for the promotion of atomic diffusion, the high thermal conductivity of graphene helps to quickly and uniformly heat up, promoting atomic diffusion at the copper and stainless steel interface; for the relief of interface stress, the nano nickel layer forms a flexible transition zone between copper and stainless steel, reducing the residual stress generated due to the difference in thermal expansion; for the enhancement of corrosion resistance, graphene has excellent chemical inertness, which can improve the corrosion resistance of the composite material.

[0023] S2. By adjusting the speed difference of the rolling mill rolls, low-speed and high-pressure rolling in the front section promotes the deformation of the stainless steel layer, while high-speed and low-pressure rolling in the rear section improves the interfacial bonding force of the copper layer. Controlling the rolling temperature promotes interfacial diffusion and avoids delamination phenomena. S2-1. Adjust the rotational speed of the upper roll slightly higher than that of the lower roll to form a speed difference. The speed difference requires the rotational speed of the upper roll to be 5 - 10% faster than that of the lower roll to control the interfacial shear stress and reduce delamination phenomena. Control the roll gap. According to the thickness difference between the copper and steel layers, adjust the roll gap of the rolling mill to make the rolling pressure distribution of the two layers of materials uniform. Ensure good bonding of the two layers of materials by controlling the reduction rate during the rolling process. Determine the rolling parameters by calculating the speed difference of the rolling mill rolls, specifically as shown in Equation (1): Equation (1) where is the strain rate, and are the speeds of the upper and lower rolls respectively, is the strip thickness. S2-2. Low-speed and high-pressure rolling in the front section. In the front section rolling, use low speed and high pressure, focusing on making the stainless steel layer undergo plastic deformation first. By controlling the rolling parameters, preferentially promote the plastic deformation of the stainless steel rather than the copper layer to enhance the initial bonding strength of the copper-steel composite material. S2-3. High-speed and low-pressure rolling in the rear section. During the rear section rolling process, use high speed and low pressure to utilize the high ductility of the copper layer to achieve close fitting between the two layers of metal and reduce work hardening.

[0024] It should be noted that for the specific steps of low-speed and high-pressure rolling in the front section, control the rolling speed between 10 - 20 m / min, and use the method of low speed and high pressure to ensure sufficient plastic deformation of the stainless steel layer. At a reduction rate of 20%, ensure that the stainless steel layer can be fully plastically deformed to improve its interfacial bonding with the copper layer. Keep the temperature of the copper-steel strip within the range of normal temperature to 300 °C in this stage to ensure that the stainless steel layer can effectively form plastic deformation without excessive work hardening.

[0025] The specific steps of high-speed and low-pressure rolling in the rear section are as follows: increase the rolling speed in the rear section to 30 - 50 m / min, which significantly speeds up the rolling process. At a reduction rate of 10%, ensure that the copper layer can be fully extended and the ductility of the copper layer is fully utilized to achieve close bonding of the copper-steel interface. Maintain a moderate rolling temperature to avoid excessive softening of the copper layer due to too high a temperature. The low-pressure setting enables the copper layer to be uniformly extended, avoiding excessive compression of the copper layer and maintaining its good electrical conductivity and ductility.

[0026] S3. Use a high-frequency induction coil for short-time local annealing to eliminate work hardening, reduce residual stress, and optimize the hardness and plasticity balance of the material. S3-1. Install a high-frequency induction coil at the mill exit to provide local short-time annealing for the composite strip, eliminate work hardening, and reduce residual stress. The induction heating device is located near the mill exit to install a high-frequency induction coil, and the surface of the composite strip is heated by electromagnetic induction. According to the thickness and material properties of the strip, the operating frequency of the induction coil is adjusted to achieve efficient heating. The heating depth is controlled within the range from the surface to several millimeters to avoid overheating the internal structure and maintain the strength of the material. S3-2. Control the annealing temperature and time to adjust the microstructure of the material and avoid excessive grain growth and deterioration of mechanical properties during the heat treatment process. Control the annealing temperature between 300 - 500 °C. This temperature range can effectively eliminate work hardening in the material while maintaining good strength. The annealing time is controlled within 10 - 30 seconds, which can complete the heat treatment in a very short time and avoid grain coarsening caused by overheating. Use the heat conduction formula to calculate the heat transfer efficiency of the material, specifically as shown in Equation (2): Equation (2) Where, is the heat conducted, is the thermal conductivity of the material, is the heat conduction area, is the temperature on the heating side, is the temperature on the cooling side, is the length of the heat conduction path; S3-3. Through real-time on-line monitoring and adjustment of the parameters of induction annealing, ensure that the material does not generate excessive residual stress during the rolling process, thereby guaranteeing the overall performance of the composite strip. Use an on-line stress sensor or X-ray stress analyzer to monitor the residual stress state in the material in real time. The stress monitoring system can be linked with the control system to feedback data in real time and adjust the heating power or heating duration of the induction annealing device. The calculation of residual stress is specifically as shown in Equation (3): Equation (3) Where, is the residual stress, is the stress generated during rolling or heating, is the cross-sectional area of the strip.

[0027] It should be noted that dynamic induction annealing removes the work hardening generated due to plastic deformation in real time during the rolling process, improving the ductility and formability of the material. Through local short-time heating, the annealing effect eliminates the residual stress in the material under the condition of avoiding overheating, ensuring the shape stability of the strip. According to the stress detection results, adjust the power output of the induction coil or the rolling parameters to achieve an ideal stress distribution state; in some cases, the heating time and temperature of induction annealing can be slightly adjusted to ensure that excessive stress does not occur.

[0028] S4. On the stainless-steel surface, use laser micro-texturing technology to form honeycomb-shaped micro-pits, enhance mechanical interlocking and chemical bonding, and combine with a nano-nickel / graphene layer to improve the interfacial bonding force and the mechanical properties of the composite strip. S4-1. Laser micro-texturing treatment: Through laser micro-texturing technology, make honeycomb-shaped micro-pits on the stainless-steel surface to form a special micro-structure. Use a high-power laser beam and adopt a dot matrix scanning method to process a honeycomb-shaped micro-pit structure with a diameter of 20 - 50 μm and a depth of 5 - 10 μm on the stainless-steel surface; precisely adjust the laser power and scanning speed to ensure that the morphology of the micro-pits is uniform and consistent, and ensure that the depth and diameter of each pit reach the predetermined value; by adjusting the laser processing parameters, control the arrangement density and distribution pattern of the micro-pits to optimize the mechanical interlocking effect. S4-2. By introducing a nano-nickel / graphene composite transition layer at the copper-steel interface, further improve the chemical bonding force and atomic diffusivity at the interface; combine with the honeycomb-shaped micro-pits processed by laser micro-texturing to form a dual-enhancement mechanism of mechanical interlocking and chemical bonding, and further optimize the interfacial bonding force.

[0029] It should be noted that the mechanical interlocking mechanism uses the honeycomb-shaped micro-pits formed by laser micro-texturing technology, enabling the copper layer to better embed into the micro-structure on the surface of the stainless-steel layer during the rolling process, enhancing the mechanical interlocking effect.

[0030] Design of the nano-nickel / graphene composite transition layer: Deposit a nano-nickel / graphene composite transition layer on the stainless-steel surface using magnetron sputtering technology, and control the thickness of the composite layer between 50 - 200 nm; utilize the high thermal conductivity of graphene and the good diffusivity of nickel to promote atomic diffusion at the copper-steel interface, thereby enhancing the interfacial bonding strength.

[0031] Through the combination of the deposition of the nickel / graphene composite layer and micro-texturing technology, a stable chemical bond can be formed between the copper layer and the stainless-steel layer, reducing the interfacial delamination phenomenon; the nano-scale graphene structure helps to reduce the interfacial energy at the interface, making the interfacial bonding more compact.

[0032] Combining the chemical bonding effect of the nano-nickel / graphene composite transition layer and the mechanical interlocking effect brought by laser micro-texturing, the dual enhancement of interfacial bonding is thus achieved; improving interfacial stability: The introduction of the nano-composite layer enhances the heat resistance and corrosion resistance of the interface, and it performs more stably especially in high-temperature and harsh environments.

[0033] Through the chemical bonding of the nickel / graphene composite layer and the mechanical interlocking effect brought by the micro-texture, the interfacial bonding force is significantly enhanced, avoiding the problems of interfacial peeling and delamination.

[0034] S5. The annealing is divided into three stages: low-temperature annealing eliminates the hardening of the copper layer, medium-temperature annealing promotes the recrystallization of stainless steel, and rapid water cooling fixes the nano-precipitates, improving the organizational structure and enhancing the strength of stainless steel. S5-1. In the first stage of low-temperature short-time annealing, by eliminating the work hardening of the copper layer, its plasticity and electrical conductivity are improved, while the stainless steel layer maintains a certain plasticity. The annealing temperature is controlled within the recrystallization temperature range of the copper layer to ensure effective softening of the copper layer without affecting the strength of the stainless steel layer. Specific steps: The annealing temperature is set at 400 °C and the holding time is 10 minutes. A nitrogen-hydrogen mixed gas ( ) is used as the protective atmosphere to avoid oxidation of the copper layer and at the same time provide a reducing atmosphere, which helps to remove surface oxides and improve the electrical conductivity of the copper layer. The relationship between annealing temperature and hardness is specifically as shown in Equation (4): Equation (4) Where, is the hardness at temperature, is the initial hardness, is the hardness temperature coefficient, is the annealing temperature, is the initial temperature; S5-2. In the second stage of medium-temperature gradient annealing, through gradient temperature control in the medium-temperature stage, the recrystallization of the stainless steel layer is promoted to restore its plasticity and refine the grains. The copper layer needs to inhibit excessive grain growth during this stage and maintain its high strength. Through the grain growth model, it is specifically as shown in Equation (5): Equation (5) Where, is the average diameter of the grains after annealing, is the initial grain diameter, is the grain growth constant, is the annealing time; The annealing temperature is controlled in three zones, specifically 600 °C, 650 °C, and 700 °C, and the holding time in each temperature zone is 20 minutes. The three-zone temperature control technology is adopted, which can gradually adjust the temperature to achieve the optimal balance between the recrystallization of the stainless steel layer and the grain inhibition of the copper layer. S5-3. In the third stage of rapid water cooling treatment, the nano-precipitates formed during the annealing process are fixed through rapid water cooling, further enhancing the strength of the stainless steel layer, preventing the coarsening of the precipitates, and ensuring that the composite material has good mechanical properties and thermal stability. Specific steps: The cooling rate of the rapid water cooling treatment is set to >50 °C / s; water is used as the cooling medium to quickly remove heat, ensuring that the cooling rate is high enough to fix the precipitated phase. The cooling rate calculation is as shown in Equation (6): Equation (6) Where is the heat released during the cooling process,[[]]END]] is the mass of the cooling medium,[[]]END]] is the specific heat capacity of the cooling medium,[[]]END]] is the temperature change.[[]]END]]

[0035] It should be noted that through the recrystallization of stainless steel in the medium-temperature annealing stage, the grains of the stainless steel layer are refined, and while the strength is improved, good plasticity is maintained; by suppressing the excessive growth of the grains in the copper layer, the grain size of the copper layer is effectively controlled, and high strength and electrical conductivity are maintained; after the nano-precipitated phase is fixed, the strength of the stainless steel layer is significantly improved, and the material properties are more excellent; rapid cooling reduces the formation of oversized grains, enabling the composite material to still maintain good performance in a high-temperature environment.[[]]END]]

[0036] S6. Control the heating rate to ensure uniform temperature and avoid thermal stress concentration. Use a nitrogen-hydrogen mixed gas to prevent oxidation, optimize the reduction effect, improve the surface quality and corrosion resistance; S6-1. Heating rate control: The heating rate has an important impact on the microstructure and stress distribution of the composite material. The heating rate is controlled at ≤50 °C / min to ensure uniform temperature distribution during the heating process and minimize the thermal stress during the temperature rise, avoiding stress concentration or cracks caused by rapid heating; S6-2. Use a nitrogen-hydrogen mixed gas ( ) as the annealing protective atmosphere; during the annealing process, adjust the hydrogen content in a timely manner according to the surface state of the material to optimize the reduction effect and prevent the formation of an oxide layer.[[]]END]]

[0037] It should be noted that by controlling the heating rate, the internal stress concentration caused by non-uniform temperature is avoided, thereby improving the overall quality and durability of the material.[[]]END]]

[0038] Heating rate control can effectively maintain the microstructure stability of the material during the annealing process, ensuring the mechanical properties and processing accuracy of the composite strip; by precisely managing the nitrogen-hydrogen ratio in the atmosphere, while ensuring anti-oxidation, oxides are effectively removed, and the surface quality of the composite material is optimized; the nitrogen-hydrogen atmosphere can effectively prevent oxidation, ensuring that there is no oxide interference at the copper-steel interface and the surface, thereby improving the mechanical properties and corrosion resistance of the composite strip.[[]]END]]

[0039] S7 seamlessly connects the rolling and annealing processes, and uses an on-line monitoring system to detect temperature, stress and atmosphere in real time to ensure the stability of the annealing process.

[0040] S7-1, after rolling is completed, the copper-steel composite strip directly enters the annealing furnace for on-line annealing, enabling seamless connection between the rolling process and the annealing process, reducing the time for intermediate cooling and reheating, and improving the continuity of the production line; S7-2, uses high-precision temperature sensors to monitor the temperature changes in the annealing furnace in real time, and monitors key parameters during the annealing process, such as temperature, stress and atmosphere, to ensure that the process parameters are within the specified range and adjust the deviations during the annealing process; detects the residual stress of the copper-steel composite strip in real time through stress sensors and adjusts the annealing process parameters to eliminate internal stress; on-line monitors the ratio of nitrogen-hydrogen atmosphere in the annealing furnace to ensure the accuracy and stability of the atmosphere and prevent the formation of oxide layers.

[0041] It should be noted that on-line annealing and continuous processing are one of the important innovations in the present invention. By seamlessly connecting the rolling and annealing processes, the cooling and reheating times caused by process intervals in the traditional process are eliminated, thereby improving production efficiency and reducing energy consumption. At the same time, an integrated on-line monitoring system is used to monitor key parameters such as temperature, stress and atmosphere during the annealing process in real time, ensuring the high quality and consistency of the copper-steel composite strip. This innovation improves the automation level of the process, optimizes the production process, and significantly improves production efficiency and product quality.

[0042] On-line annealing technology: This technology organically combines the rolling and annealing processes, making the entire process flow more efficient and stable. On-line annealing avoids the energy loss caused by common process intervals and cooling and reheating in the traditional process.

[0043] On-line monitoring technology: The present invention integrates an on-line monitoring system during the annealing process to track key parameters in real time, timely discover and correct potential problems, and ensure the consistency and stability of the product.

[0044] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, various changes and modifications can be made to the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A rolling and annealing process for copper-steel composite strip, characterized in that, It includes the following steps: Step S1: Select high-purity copper plates and stainless steel plates, perform pickling, degreasing, and polishing treatments, and deposit a nano nickel / graphene composite transition layer on the stainless steel surface through magnetron sputtering technology; Step S2: By adjusting the roller speed difference of the rolling mill, low-speed and high-pressure rolling in the front section promotes the deformation of the stainless steel layer, high-speed and low-pressure rolling in the rear section improves the interfacial bonding force of the copper layer, and controlling the rolling temperature promotes interfacial diffusion to avoid delamination; Step S3: Use a high-frequency induction coil for short-time local annealing to eliminate work hardening, reduce residual stress, and optimize the hardness-plasticity balance of the material; Step S4: Use laser micro-texturing technology on the stainless steel surface to form honeycomb-shaped micro-pits, enhance mechanical interlocking and chemical bonding, combine with the nano nickel / graphene layer, and improve the interfacial bonding force and mechanical properties of the composite strip; Step S5: The annealing is divided into three stages: low-temperature annealing eliminates the hardening of the copper layer, medium-temperature annealing promotes the recrystallization of the stainless steel, and rapid water cooling fixes the nano-precipitated phase to improve the microstructure and enhance the strength of the stainless steel; Step S6: The heating rate is controlled at ≤50°C / min to ensure temperature uniformity, avoid thermal stress concentration, use a nitrogen-hydrogen mixed gas to prevent oxidation, optimize the reduction effect, and improve the surface quality and corrosion resistance; Step S7: Seamlessly connect the rolling and annealing processes, and use an on-line monitoring system to detect the temperature, stress, and atmosphere in real time to ensure the stability of the annealing process.

2. A rolling and annealing treatment process for a copper-steel composite strip according to claim 1, characterized in that: Wherein in step S1, the following sub-steps are further included: S1-1: Select oxygen-free copper with a purity of more than 99.9% for the copper plate, and select austenitic stainless steel for the stainless steel plate; The copper plate is soaked in a 10% sulfuric acid solution for 3-5 minutes to remove the surface oxide layer; it is rinsed with flowing pure water and dried with hot air to prevent secondary oxidation; the stainless steel plate is treated by sandblasting to increase the surface roughness for subsequent nano-layer adhesion; it is cleaned with a dilute nitric acid mixed solution to further remove the surface residual oxides; a thin layer of activator is coated on the treated stainless steel surface to enhance the adhesion of the subsequent nano-transition layer; S1-2: Introduce a nano nickel / graphene composite transition layer at the copper-stainless steel interface; nickel has good metal compatibility with both copper and stainless steel, which can effectively reduce the difference in interfacial thermal expansion coefficients and relieve thermal stress; graphene has extremely high thermal conductivity, which can promote interfacial heat conduction, enhance atomic diffusion during rolling, and at the same time form a firm interfacial bonding structure; Using a DC magnetron sputtering device, the vacuum degree is controlled at below Pa; the target materials are a high-purity nickel target and a graphene composite target; a "nickel-graphene-nickel" three-layer structure is adopted to enhance the chemical bonding and mechanical strength of the interface.

3. A rolling and annealing treatment process for a copper-steel composite strip according to claim 1, characterized in that: Wherein in step S2, the following sub-steps are further included: S2-1: Adjust the rotational speed of the upper roller to be slightly higher than that of the lower roller to form a speed difference; the speed difference requires the rotational speed of the upper roller to be 5-10% faster than that of the lower roller to control the interfacial shear stress and reduce delamination; Control of the roll gap: According to the thickness difference between the copper and steel layers, adjust the roll gap of the rolling mill to make the rolling pressure distribution of the two layers of materials uniform; control the reduction rate during rolling to ensure good bonding of the two layers of materials; determine the rolling parameters by calculating the roll speed difference of the rolling mill, specifically as shown in formula (1): Formula (1) Among them, is the strain rate, and are the speeds of the upper and lower rollers respectively, is the strip thickness; S2-2. In the first stage of low-speed and high-pressure rolling, low-speed and high-pressure rolling is adopted in the first stage, focusing on causing plastic deformation of the stainless-steel layer first; by controlling the rolling parameters, the plastic deformation of the stainless steel is preferentially promoted rather than that of the copper layer, enhancing the initial bonding strength of the copper-steel composite material. S2-3. In the second stage of high-speed and low-pressure rolling, during the second-stage rolling process, high-speed and low-pressure rolling is adopted, and the high ductility of the copper layer is utilized to achieve close bonding between the two metal layers and reduce work hardening.

4. A rolling and annealing treatment process for a copper-steel composite strip according to claim 1, characterized in that: In step S3, the following sub-steps are further included: S3-1. Install a high-frequency induction coil at the exit of the rolling mill to provide local short-time annealing for the composite strip, eliminate work hardening and reduce residual stress; The induction heating device is located by installing a high-frequency induction coil near the exit of the rolling mill to heat the surface of the composite strip through electromagnetic induction; according to the thickness and material properties of the strip, the operating frequency of the induction coil is adjusted to achieve efficient heating; the heating depth is controlled within the range from the surface to several millimeters to avoid overheating the internal structure and maintain the strength of the material. S3-2. Control the annealing temperature and time to adjust the microstructure of the material and avoid excessive grain growth and deterioration of mechanical properties during the heat treatment process; The annealing temperature is controlled between 300-500 °C. This temperature range can effectively eliminate work hardening in the material while maintaining good strength; the annealing time is controlled within 10-30 seconds, which can complete the heat treatment in a very short time and avoid grain coarsening caused by overheating; the heat transfer efficiency of the material is calculated using the heat conduction formula, specifically as shown in Equation (2): Formula (2) Among them, is the heat conducted, is the thermal conductivity of the material, is the heat conduction area, is the temperature on the heating side, is the temperature on the cooling side, is the length of the heat conduction path; S3-3. Through real-time online monitoring and adjustment of the parameters of induction annealing, ensure that excessive residual stress does not occur in the material during the rolling process, thereby ensuring the overall performance of the composite strip; Use an online stress sensor or X-ray stress analyzer to monitor the residual stress state in the material in real time; the stress monitoring system can be linked with the control system to feedback data in real time and adjust the heating power or heating duration of the induction annealing device. The calculation of residual stress is specifically as shown in Equation (3): Formula (3) Among them, is the residual stress, is the stress generated during rolling or heating, is the cross-sectional area of the strip.

5. A rolling and annealing treatment process for a copper-steel composite strip according to claim 1, characterized in that: In step S4, the following sub-steps are further included: S4-1. Laser micro-texturing treatment, through laser micro-texturing technology, honeycomb-shaped micro-pits are made on the surface of the stainless steel to form a special micro-structure; Use a high-power laser beam and adopt a dot matrix scanning method to process a honeycomb-shaped micro-pit structure with a diameter of 20-50 μm and a depth of 5-10 μm on the surface of the stainless steel; precise adjustment of the laser power and scanning speed ensures that the morphology of the micro-pits is uniform and consistent, and ensures that the depth and diameter of each pit reach the predetermined value; by adjusting the laser processing parameters, the arrangement density and distribution pattern of the micro-pits are controlled to optimize the mechanical interlocking effect. S4-2. By introducing a nano-nickel / graphene composite transition layer at the copper-steel interface, the chemical bonding force and atomic diffusivity of the interface are further improved; combined with the honeycomb micro-pits processed by laser micro-texturing, a dual enhancement mechanism of mechanical interlocking and chemical bonding is formed to further optimize the interface bonding force.

6. A rolling and annealing treatment process for a copper-steel composite strip according to claim 1, characterized in that: In step S5, the following sub-steps are further included: S5-1. Low-temperature and short-time annealing in the first stage. By eliminating the work hardening of the copper layer, its plasticity and electrical conductivity are improved, while the stainless steel layer maintains a certain plasticity; the annealing temperature is controlled within the recrystallization temperature range of the copper layer to ensure that the copper layer is effectively softened without affecting the strength of the stainless steel layer. Specific steps: The annealing temperature is set at 400 °C and the holding time is 10 minutes; a nitrogen-hydrogen mixed gas, 95% N2 and 5% H2, is used as the protective atmosphere to avoid oxidation of the copper layer and at the same time provide a reducing atmosphere, which helps to remove surface oxides and improve the electrical conductivity of the copper layer. The relationship between the annealing temperature and hardness is specifically as shown in formula (4): Formula (4) Among them, is the hardness at temperature, is the initial hardness, is the hardness temperature coefficient, is the annealing temperature, is the initial temperature; S5-2. Medium-temperature gradient annealing in the second stage. In the medium-temperature stage, through gradient temperature control, the recrystallization of the stainless steel layer is promoted to restore its plasticity and refine the grains; the copper layer needs to inhibit excessive grain growth in this stage and maintain its high strength, through the grain growth model, specifically as shown in formula (5): Formula (5) Among them, is the average diameter of the grains after annealing, is the initial grain diameter, is the grain growth constant, is the annealing time; The annealing temperature is controlled in three zones, specifically 600 °C, 650 °C, and 700 °C, and the holding time for each temperature zone is 20 minutes; the three-zone temperature control technology is adopted to gradually adjust the temperature to achieve the optimal balance between the recrystallization of the stainless steel layer and the grain inhibition of the copper layer. S5-3. Rapid water cooling treatment in the third stage. By rapidly water cooling to fix the nano-precipitation phase formed during the annealing process, the strength of the stainless steel layer is further improved, the coarsening phenomenon of the precipitation phase is prevented, and the composite material is ensured to have good mechanical properties and thermal stability. Specific steps: The cooling rate of the rapid water cooling treatment is set at >50 °C / s; water is used as the cooling medium to quickly remove heat and ensure that the cooling rate is high enough to fix the precipitation phase. The calculation of the cooling rate is specifically as shown in formula (6): Formula (6) Among them, is the heat released during the cooling process, is the mass of the cooling medium, is the specific heat capacity of the cooling medium, is the temperature change.

7. A rolling and annealing treatment process for a copper-steel composite strip according to claim 1, characterized in that: In step S6, the following sub-steps are further included: S6-1. Heating rate control. The heating rate has an important influence on the microstructure and stress distribution of the composite material. The heating rate is controlled at ≤50 °C / min to ensure uniform temperature distribution during the heating process and minimize the thermal stress during the temperature rise, avoiding stress concentration or cracks caused by rapid heating. S6-2. Use a nitrogen-hydrogen mixed gas as the annealing protective atmosphere, and adjust the hydrogen content in a timely manner according to the surface state of the material during the annealing process to optimize the reduction effect and prevent the formation of an oxide layer.

8. A rolling and annealing treatment process for a copper-steel composite strip according to claim 1, characterized in that: In step S7, the following sub-steps are further included: S7-1. After rolling is completed, the copper-steel composite strip directly enters the annealing furnace for on-line annealing, enabling seamless connection between the rolling process and the annealing process, reducing the time for intermediate cooling and reheating, and improving the continuity of the production line. S7-2. Use high-precision temperature sensors to monitor the temperature changes in the annealing furnace in real time, monitor the key parameters during the annealing process in real time, ensure that the process parameters are within the specified range, and adjust the deviations during the annealing process. Detect the residual stress of the copper-steel composite strip in real time through stress sensors, and adjust the annealing process parameters to eliminate internal stress; on-line monitor the ratio of nitrogen-hydrogen atmosphere in the annealing furnace to ensure the accuracy and stability of the atmosphere and prevent the formation of oxide layers.

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