A method of heat treatment to eliminate anisotropy in a stamped part

Abstract

This invention relates to the field of high-performance steel heat treatment equipment technology, and discloses a heat treatment method for eliminating anisotropy in stamped parts, comprising five stages: pretreatment, gradient temperature-controlled annealing, magnetic field-assisted regulation, integrated cooling, and post-treatment. This invention innovatively employs thickness-layered gradient temperature control, pulsed magnetic field-assisted grain boundary regulation, a micron-level high-precision temperature control system, and integrated closed-loop control of annealing and cooling to achieve precise control of the microstructure: the average grain size of the steel is ≤2μm, grain uniformity is ≥92%, tensile strength is ≥1200MPa / 950MPa, elongation is ≥25%, and the strength-ductility matching coefficient is improved by more than 40% compared to traditional processes; process repeatability error is ≤3%, microstructure recovery and softening rate is ≤5%, and residual stress elimination rate is ≥95%; achieving synergistic optimization of strength and ductility, it can be widely applied in high-end equipment manufacturing fields such as aerospace, nuclear fusion devices, and extreme cold environment engineering.

Description

Technical Field

[0001] This invention relates to the field of high-performance steel heat treatment equipment technology, specifically a heat treatment method for eliminating anisotropy in stamped parts. Background Technology

[0002] High-performance steels such as austenitic stainless steel and high-strength alloy steel have become core materials in high-end manufacturing fields due to their excellent corrosion resistance and high strength. The service performance of these materials is highly dependent on their microstructure, including grain size, grain boundary state, twin orientation, and the uniformity and rationality of precipitate distribution. Heat treatment is a key means of controlling the microstructure.

[0003] The synergistic improvement of the strength and ductility of steel is a core technological requirement for high-end manufacturing; however, existing annealing equipment and processes have significant technical shortcomings. During the stamping process, the metal material undergoes plastic flow under strong stress, forming obvious metal streamlines. The presence of streamlines causes the grains to be elongated along the deformation direction, forming texture, which makes the mechanical properties of the material exhibit obvious directionality. This anisotropy will cause the workpiece to have inconsistent performance in different stress directions, and it is prone to cracking or fatigue failure along the streamline direction during service.

[0004] Traditional stress-relief annealing can reduce residual stress, but it is difficult to eliminate the directionality of grain morphology and cannot fundamentally solve the anisotropy problem; forging and other processes can break the flow lines, but they are energy-intensive, inefficient and poorly adaptable to thin-walled or complex-shaped workpieces.

[0005] However, traditional heat treatment processes have four major defects that severely restrict the performance improvement and application expansion of high-performance steel.

[0006] 1. Traditional annealing equipment uses overall temperature control, which cannot achieve gradient temperature control along the material thickness direction, making it difficult to accurately regulate and resulting in poor microstructure uniformity; 2. Lacking a magnetic field synergistic mechanism, it is impossible to regulate grain boundary migration and twin orientation through magneto-stress, resulting in low regulation efficiency and limited improvement in material strength and toughness; 3. Insufficient temperature control accuracy, unable to match the sensitive dependence on temperature, resulting in poor process repeatability; 4. The annealing process is disconnected from the subsequent cooling stage. The microstructure after low-temperature control is prone to recovery and softening during the cooling process, and there is a lack of effective real-time monitoring and feedback control mechanisms. Summary of the Invention

[0007] This invention provides a heat treatment method for eliminating anisotropy in stamped parts, relating to the technical field of high-performance steel heat treatment equipment. It is applicable to the precise control of the microstructure of metal materials such as austenitic stainless steel and high-strength alloy steel, achieving synergistic optimization of strength and ductility, and can be widely used in high-end equipment manufacturing fields such as aerospace, nuclear fusion devices, and extreme cold environment engineering.

[0008] This invention provides the following technical solution: a heat treatment method for eliminating anisotropy in stamped parts, comprising five stages: pretreatment, gradient temperature-controlled annealing, magnetic field synergistic regulation, integrated cooling, and post-treatment. The specific steps are as follows: Step 1: Pre-treatment stage: Laser cleaning or pickling passivation, vacuum drying and preheating treatment are performed on high-performance steel to remove surface impurities and eliminate residual processing stress. Step 2: Gradient temperature control annealing stage: A layered gradient temperature control annealing furnace is used, which is divided into surface layer, transition layer and core layer along the thickness direction of the steel. Differentiated temperature curves are set, the heating rate is 15℃ / min, the holding time is 60-90 minutes, the temperature gradient in the thickness direction is ≤5℃ / mm, and the temperature fluctuation is ≤±1℃. Step 3: Magnetic field coordinated control stage: The annealing furnace is integrated with the pulse magnetic field generator. The magnetic field strength is controlled within the range of 0.5-2T, the pulse frequency is 10-50Hz, and the magnetic field direction is at a 45° angle to the steel rolling direction. Grain boundary migration and twin orientation are controlled by magnetostrictive stress. A pulsed magnetic field was initiated under a 600℃ holding condition, with the magnetic field strength increasing in a stepwise manner from 0.5T to 1T to 1.5T to 2T, with each step lasting 15 minutes. The pulse frequency increased synchronously with the magnetic field strength from 10Hz to 20Hz to 30Hz to 50Hz. During the control process, the grain boundary migration rate was monitored in real time using EBSD, with a target rate ≤0.1μm / s, and the twin orientation distribution was monitored, with the preferred orientation accounting for ≥85%. The magnetic field parameters were dynamically adjusted accordingly. Step 4: Integrated Cooling Stage: Staged cooling using a mixture of nitrogen and argon gases. Cooling rate is 5℃ / min for 600-400℃ with a magnetic field strength of 0.8T. Cooling rate is 10℃ / min for 400-200℃ with a magnetic field strength of 0.5T. Cooling rate is 15℃ / min for 200-80℃ with no magnetic field. Microstructure recovery and softening are suppressed through real-time monitoring and feedback. Step 5: Post-processing stage: Plasma nitriding or gas carburizing treatment is performed. An online residual stress detector is used for testing, with an accuracy of ±5MPa. Full-area stress testing is conducted on the slowly cooled stamped parts, and the data is automatically uploaded to the control system. If localized stress concentration exists, when the stress value >100MPa, a secondary short-term heat preservation is automatically initiated at 650℃ for 30 minutes. After passing the inspection, simple finishing is performed, including removing minor burrs from the surface of the stamped parts. After finishing, the parts directly proceed to the subsequent assembly process.

[0009] The selected high-performance steels include austenitic stainless steel and high-strength alloy steel, with a workpiece thickness range of 5-20mm.

[0010] Specifically, in the pretreatment stage, the laser cleaning power is 300-500W, and the cleaning time is 10-30s; the pickling and passivation uses a mixture of nitric acid and hydrofluoric acid in a ratio of 5:1, the pickling temperature is controlled at 25-30℃, and the pickling time is 10-15 minutes; the vacuum drying temperature is 80±5℃, and the vacuum degree is ≤5Pa; the preheating temperature is 200℃, and the holding time is 20 minutes.

[0011] The target temperatures for the gradient temperature-controlled annealing stage are as follows: 1050-1140℃ for austenitic stainless steel and 880-970℃ for high-strength alloy steel; the transition layer temperature lags behind the surface layer by 10-20℃, and the core temperature lags behind the surface layer by 20-40℃.

[0012] In the selected magnetic field coordinated control stage, the magnetic field strength is increased in a stepwise manner from 0.5T to 1T to 1.5T to 2T, with each step lasting 15 minutes, and the pulse frequency is simultaneously increased to 10-50Hz; the proportion of twin preferred orientation is ≥85%, and the grain boundary migration rate is ≤0.1μm / s.

[0013] In the selected integrated cooling stage, the mixed gas volume ratio is 7:3. During the cooling process, the microstructure is monitored in real time by EBSD, and the recovery and softening rate is ≤5%. If signs of softening appear, the cooling rate is automatically reduced and the 0.3T low-intensity magnetic field is restarted.

[0014] Specifically, in the post-treatment stage, the plasma nitriding temperature is 450℃, the time is 2 hours, and the nitriding layer thickness is 5-8μm; the gas carburizing temperature is 920℃, the time is 3 hours, and the carburized layer thickness is 0.8-1.2mm. The corrosion resistance meets the requirement of no rust after ≥100 hours of neutral salt spray test.

[0015] The present invention has the following beneficial effects: 1. This invention innovatively adopts thickness-layer gradient temperature control, which transforms the oriented grains after stamping into equiaxed grains and disperses the second-phase particles, completely solving the problem of uneven microstructure. It achieves a temperature deviation of ≤5℃ between the surface, transition layer and core of the steel, a grain uniformity of ≥92%, and an average grain size of ≤2μm. This completely solves the defect of uneven microstructure in the thickness direction in traditional processes and lays the foundation for strong ductility synergistic optimization.

[0016] 2. This invention effectively regulates grain boundary migration through the synergistic effect of pulsed magnetic field and temperature field, with a migration rate ≤0.1μm / s and a preferred ratio of twin orientation ≥85%. This results in high-strength alloy steel with tensile strength ≥1200MPa and elongation ≥25%, and austenitic stainless steel with tensile strength ≥950MPa and elongation ≥30%. The strength-ductility matching coefficient is improved by more than 40% compared with traditional processes, breaking through the efficiency bottleneck of single temperature field regulation.

[0017] 3. This invention uses a micron-level high-precision temperature control system to match the temperature-sensitive requirements of materials, combined with a real-time monitoring and feedback mechanism. The process repeatability error is ≤3%, which is a huge improvement compared to the ≥15% error of traditional processes. The mechanical property deviation of the same batch of products is ≤2%, which meets the mass production requirements of high-end manufacturing.

[0018] 4. This invention achieves seamless integration of annealing and cooling stages, with gradient cooling and continuous magnetic field action synergistically suppressing microstructure recovery and softening. The recovery and softening rate is ≤5%, significantly reducing the anisotropy of stamped parts compared to ≥20% in traditional processes. Real-time monitoring and dynamic feedback ensure full controllability of the microstructure, with a residual stress elimination rate ≥95%, a global residual stress standard deviation ≤20MPa, and a product deformation rate ≤0.5%, far lower than traditional processes, resulting in significantly improved product service stability.

[0019] 5. This invention is adaptable to various high-performance steels such as austenitic stainless steel and high-strength alloy steel, and can restore and soften workpieces with a thickness range of 5-20mm. Whether it is a simple plate or a complex cross-section structure, it can achieve precise control of the microstructure. The process chain only requires 5 core processes of restoration and softening, which reduces the restoration and softening processes by 3-5 processes compared to forging and forging routes, shortening the production cycle by more than 60%. The equipment modification cost is low, fully meeting the needs of mass production. The process is highly compatible with existing production lines, requiring only the addition of a magnetic field generating device and monitoring module, without large-scale equipment modification. It has significant advantages in terms of short process chain and ease of implementation. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the crystal structure of the stamped part after processing according to the present invention; Figure 2This is a schematic diagram of the crystal structure of the stamped part after semi-processing according to the present invention; Figure 3 This is a schematic diagram of the crystal structure of the stamped part of the present invention before semi-processing. Detailed Implementation

[0021] The technical solutions in the embodiments of this invention are clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0022] A heat treatment method for eliminating anisotropy in stamped parts includes five stages: pretreatment, gradient temperature-controlled annealing, magnetic field-assisted regulation, integrated cooling, and post-treatment. The specific steps are as follows: Step 1: Pre-treatment stage: Laser cleaning, vacuum drying and preheating treatment are performed on high-performance steel to remove surface impurities and eliminate residual processing stress; Laser cleaning removes oxide scale, oil stains, and processing residues from the workpiece surface, preventing impurities from affecting the evolution of the microstructure. The laser cleaning power is 300-500W, and the cleaning time is 10-30 seconds. No chemical reagents are required, avoiding interference with subsequent homogenization processes. The cleaning parameters are automatically matched according to the surface area of ​​the stamped parts. For austenitic stainless steel, additional pickling and passivation pretreatment is performed; a mixture of nitric acid and hydrofluoric acid is used with a mixing ratio of 5:1, the pickling temperature is controlled at 25-30℃, and the pickling time is 10-15 minutes to improve the corrosion resistance of the stamped parts surface. After cleaning, the workpiece is placed in a vacuum oven with a vacuum degree ≤5Pa and dried at 80±5℃ for 30 minutes to remove surface moisture. Then, it is preheated to 200℃ at a rate of 10℃ / min and held for 20 minutes to eliminate residual processing stress. Eliminating residual processing stress is to ensure uniform temperature control in the subsequent process. The stamped parts are directly fixed to the conveying device to ensure stable position during subsequent heat treatment and avoid uneven temperature control caused by displacement. Step 2: Gradient temperature control annealing stage: A layered gradient temperature control annealing furnace is used, which is divided into surface layer, transition layer and core along the thickness direction of the steel. Differentiated temperature curves are set, the heating rate is 15℃ / min, the holding time is 60-90 minutes, the temperature gradient in the thickness direction is ≤5℃ / mm, and the temperature fluctuation is ≤±1℃. A layered gradient temperature control annealing furnace is adopted, with three independent heating units set along the thickness direction in the furnace chamber, corresponding to the surface layer, transition layer and core respectively. It is equipped with a high-precision infrared thermometer and multi-point thermocouples to realize independent control and real-time monitoring of the temperature in the thickness direction. Gradient temperature control parameters: Heating stage: The surface layer is heated to the target temperature at a rate of 15℃ / min, where the target temperature for austenitic stainless steel is 1050-1140℃, the target temperature for high-strength alloy steel is 880-970℃, the transition layer lags the surface layer by 10-20℃, the core lags the surface layer by 20-40℃, and the temperature difference in the thickness direction is controlled at ≤40℃. Insulation stage: The surface layer, transition layer and core are insulated for 60-90 minutes respectively. The austenitic stainless steel stamping parts are insulated for 90 minutes and the high-strength alloy steel stamping parts are insulated for 60 minutes. During this period, the heating unit dynamically replenishes the temperature and the gradient temperature control avoids the problem of overheating of the core and overcooling of the surface. While ensuring the recrystallization of grains, it lays the foundation for magnetic field-coordinated homogenization and initially breaks the structure of oriented grain arrangement. Pre-cooling stage: Cool to 600℃ synchronously at a rate of 8℃ / min, hold for 30 minutes, in preparation for magnetic field coordinated control; Step 3: Integrate the annealing furnace with a pulsed magnetic field generator. The magnetic field strength can be adjusted from 0.5 to 2T, the pulse frequency is 10 to 50Hz, and the magnetic field direction is at a 45° angle to the steel rolling direction. Grain boundary migration and twin orientation are controlled by magnetostrictive stress. A pulsed magnetic field was initiated under a 600℃ holding condition, with the magnetic field strength increasing in a stepwise manner from 0.5T to 1T to 1.5T to 2T, with each step lasting 15 minutes. The pulse frequency increased synchronously with the magnetic field strength from 10Hz to 20Hz to 30Hz to 50Hz. During the control process, the grain boundary migration rate was monitored in real time using EBSD, with a target rate ≤0.1μm / s, and the twin orientation distribution was monitored, with the preferred orientation accounting for ≥85%. The magnetic field parameters were dynamically adjusted accordingly. Step 4: Integrated Cooling Stage: Staged cooling using a mixture of nitrogen and argon gases. Cooling rate is 5℃ / min for 600-400℃ with a magnetic field strength of 0.8T. Cooling rate is 10℃ / min for 400-200℃ with a magnetic field strength of 0.5T. Cooling rate is 15℃ / min for 200-80℃ with no magnetic field. Microstructure recovery and softening are suppressed through real-time monitoring and feedback. Cooling system: It adopts inert gas, which is a mixture of nitrogen and argon in a volume ratio of 7:3. Forced convection cooling is used, and it is equipped with a staged cooling unit to achieve precise control of the cooling rate.

[0023] The first stage temperature is 600-400℃, the cooling rate is 5℃ / min, and a 0.8T pulsed magnetic field is continuously applied to suppress the recovery growth of ultrafine grains. The second stage temperature is 400-200℃: the cooling rate is 10℃ / min, the magnetic field strength is reduced to 0.5T, and the twin structure and precipitated phase distribution are stabilized; The third stage temperature is 200-80℃: cooling rate is 15℃ / min, magnetic field is turned off to avoid residual low-temperature magneto-stress; Real-time monitoring and feedback: During the cooling process, the microstructure evolution is monitored in real time by EBSD, including grain size, twin integrity and precipitated phase state. The cooling rate is monitored by infrared thermometer. If signs of recovery and softening are found, indicating that the grain size growth is ≥0.2μm, the cooling rate is automatically reduced and a low-intensity magnetic field is restarted. The magnetic field strength is temporarily set at 0.3T to ensure the stability of the microstructure. After annealing, the inert gas slow cooling system is started, and the cooling rate is controlled at 5-10℃ / min to slowly reduce the temperature from the annealing temperature to room temperature of 25-30℃. During the cooling process, the magnetic field module is kept running at a low intensity, with a magnetic field strength of 0.2-0.3T, to assist in the orderly diffusion of residual stress. This step seamlessly integrates with the existing stamping production line's conveying system. The slow cooling channel directly connects to the annealing furnace outlet, eliminating the need to remove the stamped parts from the tooling and avoiding secondary stress during transport, thus ensuring the uniformity of residual stress redistribution.

[0024] Step 5: Post-processing stage: Plasma nitriding or gas carburizing treatment is performed. In the post-treatment stage, the plasma nitriding temperature is 450℃ and the time is 2 hours, with a nitriding layer thickness of 5-8μm; the gas carburizing temperature is 920℃ and the time is 3 hours, with a carburized layer thickness of 0.8-1.2mm. The corrosion resistance meets the requirement of no rust after ≥100 hours of neutral salt spray test. An online residual stress detector is used for testing, with a testing accuracy of ±5MPa. The stamped parts are subjected to full-area stress testing after slow cooling, and the test data is automatically uploaded to the control system. If there is local stress concentration, when the stress value is >100MPa, a second short-term heat preservation is automatically started. The heat preservation temperature is 650℃ and the heat preservation time is 30min. After passing the test, a simple finishing process is performed, which includes removing small burrs from the surface of the stamped parts. After finishing, the parts can directly enter the subsequent assembly process.

[0025] Gradient temperature control parameters for austenitic stainless steel stamping parts: Thickness of stamped parts (mm): 5-10; Gradient temperature control range (surface / transition layer / core, °C): 1050 / 1060 / 1070; Heating time (h): 1-1.5; Magnetic field strength (T): 0.5-2. Stamping thickness (mm): 10-15; its gradient temperature control range (surface / transition layer / core, °C): 1070 / 1085 / 1100; heat preservation time (h): 1.5-2; magnetic field strength (T): 0.5-2. Stamping thickness (mm): 15-20; its gradient temperature control range (surface / transition layer / core, °C): 1100 / 1120 / 1140; heat preservation time (h): 2-2.5; magnetic field strength (T): 0.5-2. Gradient temperature control parameters for high-strength alloy steel stamping parts: Stamping thickness (mm): 5-10; its gradient temperature control range (surface / transition layer / core, °C): 880 / 890 / 900; heat preservation time (h): 1-1.5; magnetic field strength (T): 0.5-2. Stamping part thickness (mm): 10-15; its gradient temperature control range (surface / transition layer / core, °C): 900 / 915 / 930; holding time (h): 1.5-2; magnetic field strength (T): 0.5-2; Stamping part thickness (mm): 15-20; its gradient temperature control range (surface / transition layer / core, °C): 930 / 950 / 970; holding time (h): 2-2.5; magnetic field strength (T): 0.5-2; 1. Pretreatment: Laser cleaning power: 350W, cleaning time: 20s; use a mixture of nitric acid and hydrofluoric acid in a ratio of 5:1, acid pickling temperature controlled at 228℃ for 12 minutes; vacuum drying at 80℃ for 30 minutes, vacuum degree: 4Pa; preheating at 200℃ for 20 minutes.

[0026] 2. Gradient temperature controlled annealing: surface layer is heated to 1070℃, transition layer to 1060℃, core to 1050℃, held for 90 minutes, temperature fluctuation ≤±1℃; pre-cooled at 600℃ for 30 minutes. 3. Pulsed magnetic field coordinated control: 0.5T (10Hz) - 1T (20Hz) - 1.5T (30Hz) - 2T (50Hz), with a dwell time of 15 minutes per stage; EBSD monitoring showed that the twin preferred orientation ratio was 90%; 4. Integrated cooling: 600-400℃, cooling rate of 5℃ / min, magnetic field strength of 0.8T; 400-200℃, cooling rate of 10℃ / min, magnetic field strength of 0.5T; 200-80℃, cooling rate of 15℃ / min, no magnetic field; real-time monitoring shows no recovery or softening. 5. Post-treatment: Hold at 140℃ for 90 minutes; plasma nitriding at 450℃ for 2 hours, resulting in a nitrided layer thickness of 6μm.

[0027] Test results: average grain size 1.5μm, grain uniformity 95%; tensile strength 980MPa, elongation 32%; residual stress relief rate 97%; process repeatability error 2.2%; no rust after 150 hours of neutral salt spray test, meeting the requirements for core components of precision instruments. 1. Pretreatment: Laser cleaning power: 400W, cleaning time: 15s; vacuum drying at 80℃ for 30 minutes, vacuum degree: 3Pa; preheating at 200℃ for 20 minutes.

[0028] 2. Gradient temperature controlled annealing: The surface layer is heated to 900℃, the transition layer to 890℃, and the core to 880℃. The temperature is maintained for 60 minutes with a fluctuation of ≤±1℃. The surface layer is then pre-cooled at 600℃ for 30 minutes. 3. Pulsed magnetic field coordinated control: 0.5T (10Hz) - 1T (20Hz) - 1.5T (30Hz) - 2T (50Hz), with a dwell time of 15 minutes per stage; EBSD monitoring showed that the twin preferred orientation ratio was 88%; 4. Integrated cooling: Cooling rate of 5℃ / min for 600-400℃, magnetic field strength of 0.8T; cooling rate of 10℃ / min for 400-200℃, magnetic field strength of 0.5T; cooling rate of 15℃ / min for 200-80℃, no magnetic field; real-time monitoring shows no recovery or softening. 5. Post-treatment: Hold at 130℃ for 90 minutes; gas carburizing temperature is 920℃, carburizing time is 3 hours, and carburized layer thickness is 1.0mm.

[0029] Test results: average grain size 1.8μm, grain uniformity 93%; tensile strength 1280MPa, elongation 28%; residual stress relief rate 96%; process repeatability error 2.5%; no rust after 120 hours of neutral salt spray test, meeting the service requirements of aerospace structural components. The traditional uniform temperature annealing process is adopted: the whole body is heated to 880℃, held for 90 minutes, and then air-cooled to room temperature; there is no magnetic field control or real-time monitoring.

[0030] Test results: average grain size 6.8 μm, grain uniformity 65%; tensile strength 920 MPa, elongation 18%; residual stress relief rate 70%; process repeatability error 18%; recovery and softening rate 22%.

[0031] Comparative conclusion: Compared with the traditional process, the method of the present invention improves grain uniformity by 43%, tensile strength by 39.1%, elongation by 55.6%, reduces process repeatability error by 86.1%, and reduces recovery and softening rate by 77.3%, demonstrating significant comprehensive performance advantages.

[0032] 1. This invention innovatively adopts thickness-layer gradient temperature control, which transforms the oriented grains after stamping into equiaxed grains and disperses the second-phase particles, completely solving the problem of uneven microstructure. It achieves a temperature deviation of ≤5℃ between the surface, transition layer and core of the steel, a grain uniformity of ≥92%, and an average grain size of ≤2μm. This completely solves the defect of uneven microstructure in the thickness direction in traditional processes and lays the foundation for strong ductility synergistic optimization.

[0033] 2. This invention effectively regulates grain boundary migration through the synergistic effect of pulsed magnetic field and temperature field, with a migration rate ≤0.1μm / s and a preferred ratio of twin orientation ≥85%. This results in high-strength alloy steel with tensile strength ≥1200MPa and elongation ≥25%, and austenitic stainless steel with tensile strength ≥950MPa and elongation ≥30%. The strength-ductility matching coefficient is improved by more than 40% compared with traditional processes, breaking through the efficiency bottleneck of single temperature field regulation.

[0034] 3. This invention uses a micron-level high-precision temperature control system to match the temperature-sensitive requirements of materials, combined with a real-time monitoring and feedback mechanism. The process repeatability error is ≤3%, which is a huge improvement compared to the ≥15% error of traditional processes. The mechanical property deviation of the same batch of products is ≤2%, which meets the mass production requirements of high-end manufacturing.

[0035] 4. This invention achieves seamless integration of annealing and cooling stages, with gradient cooling and continuous magnetic field action synergistically suppressing microstructure recovery and softening. The recovery and softening rate is ≤5%, significantly reducing the anisotropy of stamped parts compared to ≥20% in traditional processes. Real-time monitoring and dynamic feedback ensure full controllability of the microstructure, with a residual stress elimination rate ≥95%, a global residual stress standard deviation ≤20MPa, and a product deformation rate ≤0.5%, far lower than traditional processes, resulting in significantly improved product service stability.

[0036] 5. This invention is adaptable to various high-performance steels such as austenitic stainless steel and high-strength alloy steel, and can restore and soften workpieces with a thickness range of 5-20mm. Whether it is a simple plate or a complex cross-section structure, it can achieve precise control of the microstructure. The process chain only requires 5 core processes of restoration and softening, which reduces the restoration and softening processes by 3-5 processes compared to forging and forging routes, shortening the production cycle by more than 60%. The equipment modification cost is low, fully meeting the needs of mass production. The process is highly compatible with existing production lines, requiring only the addition of a magnetic field generating device and monitoring module, without large-scale equipment modification. It has significant advantages in terms of short process chain and ease of implementation.

[0037] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A heat treatment method for eliminating anisotropy in stamped parts, characterized in that: It includes five stages: pretreatment, gradient temperature-controlled annealing, magnetic field-assisted regulation, integrated cooling, and post-treatment. The specific steps are as follows: Step 1: Pre-treatment stage: Laser cleaning or pickling passivation, vacuum drying and preheating treatment are performed on high-performance steel to remove surface impurities and eliminate residual processing stress. Step 2: Gradient temperature control annealing stage: A layered gradient temperature control annealing furnace is used, which is divided into surface layer, transition layer and core layer along the thickness direction of the steel. Differentiated temperature curves are set, the heating rate is 15℃ / min, the holding time is 60-90 minutes, the temperature gradient in the thickness direction is ≤5℃ / mm, and the temperature fluctuation is ≤±1℃. Step 3: Magnetic field coordinated control stage: The annealing furnace is integrated with the pulse magnetic field generator. The magnetic field strength is controlled within the range of 0.5-2T, the pulse frequency is 10-50Hz, and the magnetic field direction is at a 45° angle to the steel rolling direction. Grain boundary migration and twin orientation are controlled by magnetostrictive stress. A pulsed magnetic field was initiated under a 600℃ holding condition, with the magnetic field strength increasing in a stepwise manner from 0.5T to 1T to 1.5T to 2T, with each step lasting 15 minutes. The pulse frequency increased synchronously with the magnetic field strength from 10Hz to 20Hz to 30Hz to 50Hz. During the control process, the grain boundary migration rate was monitored in real time using EBSD, with a target rate ≤0.1μm / s, and the twin orientation distribution was monitored, with the preferred orientation accounting for ≥85%. The magnetic field parameters were dynamically adjusted accordingly. Step 4: Integrated Cooling Stage: Staged cooling using a mixture of nitrogen and argon gases. Cooling rate is 5℃ / min for 600-400℃ with a magnetic field strength of 0.8T. Cooling rate is 10℃ / min for 400-200℃ with a magnetic field strength of 0.5T. Cooling rate is 15℃ / min for 200-80℃ with no magnetic field. Microstructure recovery and softening are suppressed through real-time monitoring and feedback. Step 5: Post-processing stage: Plasma nitriding or gas carburizing treatment is performed. An online residual stress detector is used for testing, with an accuracy of ±5MPa. Full-area stress testing is conducted on the slowly cooled stamped parts, and the data is automatically uploaded to the control system. If localized stress concentration exists, when the stress value >100MPa, a secondary short-term heat preservation is automatically initiated at 650℃ for 30 minutes. After passing the inspection, simple finishing is performed, including removing minor burrs from the surface of the stamped parts. After finishing, the parts directly proceed to the subsequent assembly process.

2. The heat treatment method for eliminating anisotropy of stamped parts according to claim 1, characterized in that: The high-performance steels include austenitic stainless steel and high-strength alloy steel, with a workpiece thickness ranging from 5 to 20 mm.

3. The heat treatment method for eliminating anisotropy of stamped parts according to claim 1, characterized in that: In the pretreatment stage, the laser cleaning power is 300-500W and the cleaning time is 10-30s; the pickling and passivation uses a mixture of nitric acid and hydrofluoric acid in a ratio of 5:1, the pickling temperature is controlled at 25-30℃, and the pickling time is 10-15 minutes; the vacuum drying temperature is 80±5℃ and the vacuum degree is ≤5Pa; the preheating temperature is 200℃ and the holding time is 20 minutes.

4. The heat treatment method for eliminating anisotropy of stamped parts according to claim 1, characterized in that: The target temperatures for the gradient temperature-controlled annealing stage are: 1050-1140℃ for austenitic stainless steel and 880-970℃ for high-strength alloy steel; the transition layer temperature lags behind the surface layer by 10-20℃, and the core temperature lags behind the surface layer by 20-40℃.

5. The heat treatment method for eliminating anisotropy of stamped parts according to claim 1, characterized in that: During the magnetic field coordinated control stage, the magnetic field strength is increased in a stepwise manner from "0.5T-1T-1.5T-2T", with each step lasting for 15 minutes, and the pulse frequency is simultaneously increased to 10-50Hz; the proportion of twin preferred orientation is ≥85%, and the grain boundary migration rate is ≤0.1μm / s.

6. The heat treatment method for eliminating anisotropy of stamped parts according to claim 1, characterized in that: In the integrated cooling stage, the volume ratio of the mixed gas is 7:

3. During the cooling process, the microstructure is monitored in real time by EBSD, and the recovery and softening rate is ≤5%. If signs of softening appear, the cooling rate is automatically reduced and the 0.3T low-intensity magnetic field is restarted.

7. The heat treatment method for eliminating anisotropy of stamped parts according to claim 1, characterized in that: In the post-treatment stage, the plasma nitriding temperature is 450℃, the time is 2 hours, and the nitriding layer thickness is 5-8μm; the gas carburizing temperature is 920℃, the time is 3 hours, and the carburized layer thickness is 0.8-1.2mm. The corrosion resistance meets the requirement of no rust after ≥100 hours of neutral salt spray test.

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