A method for processing a surface of a nickel material

Abstract

The application provides a processing method for surface heat treatment of nickel materials, and comprises the following steps: S1, a pretreatment stage: ultrasonic cleaning of nickel strip raw materials; S2, a hot air preheating stage: the pretreated nickel strip is sent to a preheating zone; the atmosphere is a mixed gas of argon and hydrogen; S3, a core heat treatment stage: the preheated nickel strip is sent to a core heat treatment zone for constant temperature treatment; the atmosphere is a mixed gas of argon, hydrogen and carbon monoxide; S4, the nickel strip is cooled by using a four-stage gradient; S5, surface passivation treatment is performed on the cooled nickel strip, and then blow drying and winding are performed. Therefore, the application mainly adopts a stepwise atmosphere mode of "preheating argon + low-concentration hydrogen" -> "core argon + hydrogen + carbon monoxide", which can not only avoid the problems of low-temperature invalidation and carbon residue of carbon monoxide in the preheating stage, but also can form a dense protective film with high matching degree of the nickel matrix by "hydrogen impurity removal and carbon monoxide film formation" in the core stage, so as to block the diffusion of oxygen atoms along the grain boundary.

Description

Technical Field

[0001] This invention relates to the field of nickel processing technology, and more specifically to a method for heat treatment of nickel surface. Background Technology

[0002] With the rapid development of the new energy vehicle industry, the demand for new energy batteries is also increasing. Nickel and its alloys (such as Ni-Cu and Ni-Fe) are widely used in new energy batteries due to their excellent corrosion resistance, high-temperature strength, and electromagnetic properties. In this application, the surface cleanliness, microstructure (such as grain size and grain boundary state), and resistance to surface oxidation of the material are key factors that determine its final performance and reliability.

[0003] Traditional nickel strip heat treatment often employs box furnaces or continuous protective atmosphere furnaces. However, when heat treating thin, high-purity nickel strips, this method suffers from limitations. Because thin, high-purity nickel strips contain fewer impurity elements, these impurities cannot effectively "block" the grain boundary diffusion channels. Therefore, under hot air heating, even trace amounts of oxygen partial pressure can cause oxygen atoms to diffuse along the grain boundaries at a rate reaching 10³-10⁻¹⁰ within the grain. 4 The thin nickel strip (thickness ≤ 50 μm) preferentially forms a grain boundary oxide layer, thereby destroying the grain boundary integrity; and the thin nickel strip has a very small heat capacity and a fast temperature response. Uneven hot air flow rate and small fluctuations in temperature change rate will cause significant temperature gradients in the thickness and width directions, which in turn will generate residual stress gradients. Existing technologies for improving nickel strip heat treatment mainly focus on enhancing the uniformity of heating temperature and controlling the concentration of protective atmosphere. Although hydrogen and carbon monoxide have been used as reducing atmospheres for metal heat treatment, existing technologies use them crudely as general oxidation inhibitors: for example, simply increasing the hydrogen concentration to enhance the reducing ability, while ignoring that high concentrations of hydrogen will accelerate the growth of high-purity nickel strip grains (leading to a decrease in plasticity).

[0004] Therefore, developing a heat treatment method that can precisely adapt to thin-gauge high-purity nickel strips and simultaneously suppress grain boundary oxidation and stress gradient is of great significance for improving the quality of high-end nickel strip products and expanding their application in harsh environments. Summary of the Invention

[0005] The purpose of this invention is to provide a heat treatment method for nickel materials that does not have any of the disadvantages mentioned above.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for heat treatment of nickel material surface, comprising the following steps: S1. Pretreatment stage: Ultrasonic cleaning of nickel strip raw material; S2. Hot air preheating stage: The pretreated nickel strip is sent into the preheating zone and heated in a three-stage gradient manner, with each gradient stage held for 5-8 minutes; the hot air flow rate is 1.5-2.0 m / s; and a laminar flow jetting method is used, with the jetting direction at an angle of 30°-45° to the surface of the nickel strip; the atmosphere is a mixture of argon and hydrogen, with hydrogen comprising 5-8% and a pressure of 0.105-0.11 MPa; S3, Core Heat Treatment Stage: The preheated nickel strip is sent into the core heat treatment zone for constant temperature treatment and held for 10-15 minutes; hot air is sprayed symmetrically in both directions at a flow rate of 2.5-3.0 m / s, with the spray direction at an angle of 60°-75° to the surface of the nickel strip; the atmosphere is a mixture of argon, hydrogen, and carbon monoxide, with a hydrogen volume fraction of 8-10%, a carbon monoxide volume fraction of 0.5-1.0%, and a pressure of 0.11-0.12 MPa; The core heat treatment area is equipped with a grain boundary oxidation monitoring module to monitor the oxide layer thickness d in real time, and to increase the volume fraction of carbon monoxide in the atmosphere when d≥0.1μm. S4. Gradient Cooling Stage: The core heat-treated nickel strip is sent into the cooling zone and a four-stage gradient cooling is adopted. The cooling rate of each cooling stage is 30-50℃ / min. The hot air flow rate is gradually reduced from 2.0m / s to 0.8m / s. The atmosphere is pure argon and the pressure is 0.105-0.11MPa. S5. Post-processing stage: The cooled nickel strip is surface passivated, then dried and wound up.

[0007] Furthermore, S1 also includes a plasma activation treatment, wherein the plasma activation treatment uses low-pressure argon plasma and the treatment time is 1-3 minutes.

[0008] Furthermore, in S2, the target temperature of the three-stage gradient heating is set according to the subsequent core heat treatment temperature, the gradient increases sequentially from low temperature to high temperature, and the temperature difference between adjacent gradients is 150-250℃.

[0009] Furthermore, in S4, the target temperature of the four-stage gradient cooling decreases sequentially from high temperature to low temperature, and the end temperature of each cooling stage is set as follows: the first stage to 70-80% of the core heat treatment temperature, the second stage to 40-50%, the third stage to 20-30%, and the fourth stage to below 80°C.

[0010] Furthermore, in S5, the passivation solution used in the surface passivation treatment is a potassium dichromate solution with a concentration of 5-8 g / L, and the treatment time is 2-3 min.

[0011] Furthermore, in S3, the flow equalization plate and temperature compensation module ensure that the hot air temperature fluctuation is ≤±2℃.

[0012] Furthermore, in S3, the grain boundary oxidation monitoring module employs one of a laser interferometric thickness gauge, an elliptic polarization thickness gauge, or an X-ray fluorescence thickness gauge.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The present invention adopts a pretreatment method that combines ultrasonic cleaning and plasma activation, which can not only thoroughly remove impurities such as oil and oxide scale from the surface of nickel strip, but also form active sites through argon plasma bombardment, significantly improving the adsorption efficiency of the subsequent protective atmosphere, providing clean and highly active surface conditions for the reduction and film formation in the core stage, effectively avoiding the interference of impurity residues on film formation, and improving the stability of the overall process. 2. To address the different needs of "gentle heating" in preheating and "efficient reaction" in the core stage, differentiated hot air jet angles are adopted (30-45° for preheating and 60-75° for the core stage). During the preheating stage, the smaller angle ensures laminar flow stability, achieving uniform heating of the nickel strip and initial gentle reduction, avoiding initial stress generation. In the core stage, the larger angle enhances hot air scouring and atmosphere contact, accelerating the removal of reduction products and improving the uniformity of the carbon monoxide protective film formation. 3. This invention employs a three-stage gradient heating stage in the preheating phase and a four-stage gradient cooling stage in the cooling phase. This precisely adapts to the thermally sensitive and low-heat-capacity characteristics of thin-gauge high-purity nickel strips, avoiding thermal shock and stress concentration caused by rapid temperature changes. In the core stage, bidirectional symmetrical hot air jetting, combined with flow equalization and temperature compensation devices, ensures temperature fluctuations ≤ ±2℃, significantly reducing the temperature gradient in the thickness and width directions of the nickel strip. After treatment, the residual stress in the nickel strip is effectively reduced, and the uniformity of stress distribution is stably improved, thereby solving the problems of cracking and warping in subsequent precision machining. This invention employs a stepped atmosphere method of "preheating argon + low-concentration hydrogen" → "core argon + hydrogen + carbon monoxide". This method avoids the problems of low-temperature failure of carbon monoxide and carbon residue in the preheating stage, and can form a dense protective film with high matching degree with nickel substrate through "hydrogen impurity removal and carbon monoxide film formation" in the core stage, thereby blocking the diffusion of oxygen atoms along the grain boundary. Attached Figure Description

[0014] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 This is a schematic diagram of the processing technology in this invention. Detailed Implementation

[0016] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0017] Example Traditional nickel strip heat treatment often employs box furnaces or continuous protective atmosphere furnaces. However, when heat treating thin, high-purity nickel strips, this method suffers from limitations. Because thin, high-purity nickel strips contain fewer impurity elements, these impurities cannot effectively "block" the grain boundary diffusion channels. Therefore, under hot air heating, even trace amounts of oxygen partial pressure can cause oxygen atoms to diffuse along the grain boundaries at a rate reaching 10³-10⁻¹⁰ within the grain. 4 The thin nickel strip (thickness ≤ 50 μm) preferentially forms a grain boundary oxide layer, thereby destroying the grain boundary integrity; and the thin nickel strip has a very small heat capacity and a fast temperature response. Uneven hot air flow rate and small fluctuations in temperature change rate will cause significant temperature gradients in the thickness and width directions, which in turn will generate residual stress gradients. Existing technologies for improving nickel strip heat treatment mainly focus on enhancing the uniformity of heating temperature and controlling the concentration of protective atmosphere. Although hydrogen and carbon monoxide have been used as reducing atmospheres for metal heat treatment, existing technologies use them crudely as general oxidation inhibitors: for example, simply increasing the hydrogen concentration to enhance the reducing ability, while ignoring that high concentrations of hydrogen will accelerate the growth of high-purity nickel strip grains (leading to a decrease in plasticity).

[0018] Based on the above issues, please refer to Figure 1 A method for heat treating the surface of nickel materials, comprising the following steps: S1. Pretreatment stage: The nickel strip raw material is surface cleaned to remove oil, oxide scale and impurities. The surface cleaning adopts a combined treatment of ultrasonic cleaning and plasma activation. The ultrasonic cleaning power is 800-1200W, the cleaning medium is anhydrous ethanol, and the cleaning time is 10-20min. The plasma activation uses argon as the working gas, the gas flow rate is 10-20cm³ / min, the output power of the plasma generator is 300-500W, and the processing time is 1-3min. The argon plasma bombards the material surface to form deeper and denser micro-nano pits and active sites, thereby slightly improving the surface roughness and thus increasing the contact area for subsequent gas adsorption.

[0019] S2. Hot air preheating stage: The pretreated nickel strip is sent into the preheating zone of the hot air heat treatment furnace. A three-stage gradient temperature rise is adopted to adapt to the heat-sensitive characteristics of the thin strip and avoid thermal shock caused by rapid temperature rise. The preheating zone is set with three temperature gradient sections: the first gradient section is 400-450℃, the second gradient section is 550-600℃, and the third gradient section is 650-700℃. Each gradient section is held for 5-8 minutes. The hot air flow rate is controlled at 1.5-2.0 m / s, and a laminar flow injection method is adopted, with the injection direction at an angle of 30-45° to the nickel strip surface. This allows the nickel strip to be heated gently and evenly. Within this angle range, the hot air can flow smoothly along the surface of the nickel strip, forming a stable laminar flow heating environment. This ensures that the heat is evenly transferred to all areas of the nickel strip, avoiding local overheating that would lead to uneven contact between the nitrogen-hydrogen atmosphere and the nickel strip surface. At the same time, the gentle airflow can drive the nitrogen-hydrogen mixed atmosphere in the preheating zone to fully cover the surface of the nickel strip, allowing the low-concentration hydrogen (5-8%) to efficiently complete the "gentle reduction", that is, only removing trace amounts of oxide impurities on the surface without causing excessive reduction. Meanwhile, nitrogen, as the inert main gas, can quickly fill the furnace cavity with the help of a stable airflow, blocking oxygen penetration. If the angle is too large (>45°), the hot air impact will disrupt the laminar flow, causing local turbulence in the nitrogen-hydrogen atmosphere. This will not only prevent uniform reduction but may also cause vibration of the thin nickel strip, generating initial stress. If the angle is too small (<30°), the airflow will be slow, the contact efficiency between the nitrogen-hydrogen atmosphere and the nickel strip surface will decrease, and the reduction products will easily accumulate, affecting the effect of the atmosphere in the subsequent core stage. Therefore, the preheating stage in this invention mainly focuses on "gently heating and initially removing impurities" from the nickel strip, rather than directly forming a protective film. Thus, a mixture of argon and hydrogen is used. Argon, as the inert main gas, can quickly fill the furnace cavity and expel air, preventing oxygen from reacting with the nickel strip surface to form an initial oxide layer (especially suitable for the easily oxidized grain boundaries of high-purity nickel strips). It also creates a slightly positive pressure environment (0.105-0.11 MPa) to block external oxygen penetration. Low-concentration hydrogen (5-8%) can achieve "gentle reduction," removing only trace amounts of residual oxide impurities on the nickel strip surface (such as oxide debris not completely removed after pretreatment), avoiding excessive reduction that leads to excessively high surface activity of the nickel strip and uneven gas adsorption in the subsequent core stage. More importantly, if carbon monoxide is added at this stage, the low preheating temperature (400-700℃) will result in insufficient carbon monoxide activity, preventing the formation of a dense protective film. Instead, carbon residue may be produced due to carbon monoxide decomposition, adhering to the nickel strip surface and affecting the film formation quality in the subsequent core stage.

[0020] S3, Core Heat Treatment Stage: The preheated nickel strip is sent to the core heat treatment zone for constant temperature treatment. The heat treatment temperature is adjusted according to the material: 850-900℃ for high-purity nickel strip (to avoid abnormal grain growth caused by excessive temperature), 800-850℃ for Ni-Cu nickel alloy strip, and 820-870℃ for Ni-Fe nickel alloy strip; the holding time is 10-15 minutes to adapt to the rapid heat conduction characteristics of the thin strip and avoid excessive oxidation caused by excessive holding time; the hot air adopts a bidirectional symmetrical spray structure, with the flow velocity on both sides being consistent (2.5-3.0m / s), and the spray direction is at a 60-75° angle to the surface of the nickel strip. With the help of a flow equalization plate and a temperature compensation device, the hot air temperature fluctuation is ensured to be ≤±2℃. The core purpose of setting an angle of 60-75° here is to enhance the scouring effect of hot air on the nickel strip surface while ensuring a uniform temperature field, accelerating the removal of surface reduction reaction products, and promoting full contact between the precisely proportioned mixed atmosphere and the nickel strip surface, thereby improving the uniform film formation efficiency of the carbon monoxide protective film. If the angle is too large (>75°), the impact force of the hot air on the nickel strip surface will be too strong, which may cause local shaking or deformation of thin nickel strips, damaging the integrity of the film layer. At the same time, it will also increase the energy loss of hot air and reduce the stability of the temperature field. If the angle is too small (<60°), the scouring force of the hot air will be insufficient, and the reduction products will easily adhere to the nickel strip surface to form impurities. In addition, the contact efficiency between the atmosphere and the surface will be reduced, which will not be able to ensure uniform coverage of the protective film and affect the grain boundary oxidation inhibition effect. The atmosphere is a mixture of argon, hydrogen, and trace amounts of carbon monoxide. The hydrogen volume fraction is 8-10%, which can completely reduce surface impurities without promoting grain growth. The carbon monoxide volume fraction is 0.5-1.0%, which can form a dense carbon oxide protective film with a thickness of 0.05-0.1μm. The atmosphere pressure is 0.11-0.12MPa. Therefore, hydrogen preferentially reduces trace oxide impurities on the surface, and carbon monoxide forms a protective film on the clean surface with a high degree of matching with the elastic modulus of the nickel substrate. It is precisely embedded in the grain boundary defect channel, thereby blocking the high-speed diffusion of oxygen atoms and mitigating thermal stress impact. In addition, a grain boundary oxidation monitoring module is set up in the core heat treatment area to monitor the oxide layer thickness d in real time using a laser interferometer, elliptic polarization thickness gauge, or X-ray fluorescence thickness gauge. This monitoring module adopts a multi-point scanning monitoring mode, which can cover key areas in the width direction of the nickel strip, ensuring the comprehensiveness and accuracy of the monitoring data. When the grain boundary oxide layer thickness at any monitoring point exceeds 0.1 μm, the atmosphere parameter adjustment program is immediately triggered, automatically increasing the volume fraction of carbon monoxide in the mixed atmosphere by 0.2-0.3 percentage points. By increasing the supply of carbon monoxide, the carbon oxide protective film on the surface of the nickel strip is quickly replenished and thickened, further enhancing the sealing effect on the grain boundary diffusion channels and preventing the continuous expansion of oxidation defects. At the same time, the volume fraction ratio of argon and hydrogen is kept constant during the adjustment process to ensure the stability of the reducing environment and prevent the film layer on the surface of the nickel strip from peeling off or abnormal grain growth caused by sudden changes in the concentration of a single gas.

[0021] It is worth mentioning that the differentiated design of the hot air injection angle in this invention during the preheating stage (30-45°) and the core heat treatment stage (60-75°) is not an independent parameter optimization, but rather an adaptive design based on the phased atmosphere requirements of "pretreatment with a nitrogen + hydrogen mixed atmosphere followed by core treatment with a nitrogen + hydrogen + trace carbon monoxide mixed atmosphere." There is a correlation between the two: "the atmosphere target determines the angle parameter, and angle optimization ensures the atmosphere's effectiveness." Therefore, the design of the angle difference is of great significance. From the perspective of the phased atmosphere objectives, the core purpose of using a nitrogen + hydrogen mixed atmosphere in the preheating stage is "gentle reduction and the creation of an inert environment." Low-concentration hydrogen (5-8%) needs to initially remove trace oxide impurities from the nickel strip surface under undisturbed conditions. Simultaneously, nitrogen, as the primary inert gas, needs to quickly fill the furnace cavity to prevent oxygen penetration. Therefore, the hot air injection in the preheating stage must focus on "stable laminar flow and uniform contact," hence the use of a small-angle injection design of 30-45°. At this angle, the hot air can flow smoothly along the nickel strip surface, avoiding the initial stress caused by airflow impact on the thin-gauge nickel strip, while also ensuring the nitrogen-hydrogen mixed atmosphere uniformly covers the nickel strip surface. This ensures sufficient reaction between the low-concentration hydrogen and oxide impurities, while allowing nitrogen to efficiently build a stable inert environment, laying a clean and stable surface foundation for subsequent core processing. If a large angle, typical of core processing, were used in this stage, it would disrupt the laminar flow, causing localized atmospheric turbulence. This would not only fail to achieve uniform reduction but could also induce initial stress in the nickel strip due to airflow impact, violating the "gentle adaptation" objective of the preheating stage. Entering the core heat treatment stage, the atmosphere is switched to a mixture of nitrogen, hydrogen, and trace amounts of carbon monoxide. The core objective shifts to "complete reduction and precise film formation." The hydrogen concentration is increased to 8-10% to achieve complete impurity reduction, while the trace amount of carbon monoxide (0.5-1.0%) needs to form a dense protective film on the clean nickel strip surface, precisely embedding into grain boundary defect channels to block oxygen atom diffusion. This objective requires the hot air jet to simultaneously "enhance scouring and promote diffusion," necessitating a large-angle jet design of 60-75°. At this angle, the scouring effect of the hot air on the nickel strip surface is significantly enhanced, quickly removing trace products generated by hydrogen reduction and preventing residual impurities from interfering with carbon monoxide film formation. Simultaneously, the strong airflow promotes the uniform mixing and rapid diffusion of the three gases (nitrogen, hydrogen, and carbon monoxide), ensuring that the trace amount of carbon monoxide precisely covers the nickel strip surface and forms a protective film with extremely high compatibility with the nickel substrate. Meanwhile, the nitrogen can maintain a stable environment within the furnace through symmetrical airflow, preventing localized atmospheric concentration fluctuations from affecting film quality. If the small angle of the preheating stage is used in this stage, the insufficient airflow scouring force will lead to the accumulation of reduction products, a decrease in atmosphere contact and diffusion efficiency, and an inability to ensure uniform coverage of the protective film. Ultimately, the core goal of "precisely sealing the boundary and inhibiting grain boundary oxidation" cannot be achieved.

[0022] Therefore, the difference in hot air jet angle is a precise adaptation to the staged atmosphere treatment target. The two angles are matched to the needs of different atmospheres, forming a solution of "small angle for gentle reduction and large angle for precise film formation". If the angle difference is eliminated, whether it is a small angle or a large angle throughout the process, it is impossible to meet the atmosphere requirements of the two stages at the same time. This would prevent the advantages of the staged atmosphere solution from being realized, and ultimately fail to achieve simultaneous suppression of grain boundary oxidation and stress gradient. Therefore, the difference in hot air jet angle based on the staged atmosphere treatment method can ensure the overall heat treatment process effect and adapt to the processing of thin high-purity nickel strips.

[0023] S4. Gradient Cooling Stage: The core heat-treated nickel strip is sent to the cooling zone. Due to the small heat capacity and sensitive temperature response of thin high-purity nickel strips, rapid cooling can easily cause severe thermal expansion and contraction, which in turn exacerbates the residual stress gradient and may even lead to deformation and cracking of the strip. Therefore, this stage adopts a four-stage gradient cooling method to adapt to the thermally sensitive characteristics of the thin strip, achieving a smooth temperature transition and gradual stress release. The cooling zone is specifically set with four temperature gradient sections, from high to low: the first cooling section is 595-720℃, the second cooling section is 340-450℃, the third cooling section is 170-270℃, and the fourth cooling section is 50-80℃. That is, the first cooling section reaches 70-80% of the core heat treatment temperature, the second cooling section reaches 40-50%, the third cooling section reaches 20-30%, and the fourth cooling section cools to below 80℃. This rate range is determined by precisely matching the thermal conductivity of the thin strip, which can ensure a certain cooling efficiency, avoid excessive heat preservation leading to abnormal grain growth, and effectively suppress stress concentration caused by sudden temperature drops. To further ensure cooling uniformity... The hot air flow rate is gradually adjusted from an initial 2.0 m / s to 0.8 m / s. In the initial cooling stage, a high flow rate is used to quickly remove a large amount of heat from the strip surface. As the strip temperature decreases, the flow rate is gradually reduced to avoid local overcooling of the strip due to excessive flow rate in the later low-temperature stage. Pure argon is used in the cooling stage, and the pressure is maintained at a slightly positive pressure of 0.105-0.11 MPa. Pure argon can prevent other gases from reacting with the nickel strip surface during the cooling process. At the same time, the slightly positive pressure environment can effectively block external air from seeping into the furnace cavity and prevent secondary oxidation of the strip during the cooling stage. In addition, the hot air in the cooling zone adopts a closed-loop recycling design. The recycled hot air is dried by a drying module to remove moisture (to avoid moisture residue affecting the subsequent hot air heating effect and the surface quality of the strip). The dried hot air is then sent back to the hot air generator for heating and reuse. This design not only recovers the waste heat carried by the hot air and reduces the overall energy consumption of the process, but also reduces the environmental impact of hot air emissions, significantly improving the green economy and sustainability of the process.

[0024] S5. Post-processing stage: The cooled nickel strip is surface passivated, then dried and wound up. The surface passivation treatment uses a potassium dichromate solution with a concentration of 5-8 g / L as the passivation solution. Potassium dichromate can form a dense chromate conversion film on the surface of the nickel strip. This film can be tightly adsorbed on the surface of the nickel strip and the previously formed carbon oxide protective film, forming a "double protection system". This significantly enhances the nickel strip's resistance to atmospheric corrosion and electrochemical corrosion, preventing oxidation and rust during storage, transportation and subsequent processing. The passivation temperature is controlled at 30-40℃. This temperature range ensures a moderate passivation reaction rate, guaranteeing rapid and dense uniform film formation, while avoiding excessively high temperatures that lead to a rough and loose film with reduced adhesion, or excessively low temperatures that result in insufficient passivation reaction and insufficient film thickness. The passivation time is set to 2-3 minutes, based on the synergistic adaptation of the passivation solution concentration and temperature. This ensures that the film thickness is controlled within the optimal range of 0.5-1.0 μm, providing effective protection without affecting subsequent welding, stamping and other processing performance due to excessive film thickness.

[0025] After passivation, the strip is first dried with clean hot air at a temperature of 60-80℃ and a flow rate of 1.0-1.5m / s to prevent water droplets from forming or causing localized corrosion. After drying, the strip is wound up with a tension of 5-8N. This tension range ensures a smooth winding of the thin nickel strip (5-50μm) due to its low stiffness. It avoids both insufficient tension causing loosening and wrinkles and excessive tension causing stretching deformation and grain distortion. Ultimately, the wound nickel strip has a uniform diameter, no scratches or wrinkles, and its dimensional accuracy meets the stringent requirements of high-end applications.

[0026] Furthermore, to verify the performance advantages of the heat treatment method of the present invention compared with the traditional hot air heat treatment method, nickel strips / nickel alloy strips of the same specifications and materials were selected as experimental samples in this invention. The method of the present invention (experimental group) and the traditional hot air heat treatment method (control group) were used for treatment respectively. The core difference between the two groups lies in the method of using the protective atmosphere; other basic parameters (such as core heating temperature, holding time, and basic hot air flow rate) remain consistent. The specific parameter settings are as follows: Experimental group (method of this invention): The protective atmosphere is precisely adapted in stages. In the preheating stage, a nitrogen + hydrogen mixed atmosphere is used (nitrogen gas fraction 92-95%, hydrogen gas fraction 5-8%). In the core heat treatment stage, the atmosphere is switched to a nitrogen + hydrogen + carbon monoxide mixed atmosphere (nitrogen gas fraction 89-91.5%, hydrogen gas fraction 8-10%, carbon monoxide volume fraction 0.5-1.0%). It is equipped with ultrasonic cleaning + plasma activation pretreatment, three-stage gradient heating, four-stage gradient cooling, differentiated hot air angle (preheating 30-45°, core 60-75°) and bidirectional symmetrical spray design. Control group (traditional method): The entire process uses a mixed atmosphere of nitrogen, carbon monoxide and hydrogen (nitrogen gas volume fraction 85%, hydrogen gas volume fraction 12%, carbon monoxide volume fraction 3%), without staged switching; no plasma activation synergistic pretreatment, no gradient heating / cooling, and constant temperature heating + air cooling; the hot air jet angle is fixed at 90°.

[0027] The key performance indicators of the two groups of samples were tested and compared, and the results are shown in the table below:

[0028] The data above shows that, compared with the traditional hot air heat treatment method, the nickel strip / nickel alloy strip treated by the method of this invention achieves significant improvements in core performance indicators. Specifically, ① the control group used a single concentration of nitrogen + carbon monoxide + hydrogen mixed atmosphere throughout the process, without considering the differences in process objectives at different stages. In the low-temperature stage (corresponding to the preheating stage of the experimental group), the carbon monoxide activity was insufficient, which easily decomposed and produced carbon residues adhering to the surface of the nickel strip. Moreover, the high concentration of hydrogen easily led to excessive reduction of the nickel strip surface, resulting in a harsh film formation environment in the subsequent core stages. In contrast, the experimental group first used a nitrogen + hydrogen mixed atmosphere for pretreatment and preheating, which could gently remove trace oxidation impurities on the surface and improve surface activity without the interference of carbon monoxide, providing a clean foundation for subsequent film formation. Therefore, the thickness of the grain boundary oxide layer was 12.9%-15.4% of that of the traditional method, effectively solving the problem of severe grain boundary oxidation in the traditional method. ② The control group lacked gradient temperature control and differentiated hot air angle design, and suffered from the drawbacks of using a single atmosphere throughout the process. This made it unsuitable for the heat-sensitive characteristics of thin nickel strips, resulting in significantly higher residual stress. In contrast, the present invention uses a staged atmosphere with synergistic gradient temperature control, resulting in lower residual stress in the nickel strip after treatment, a 3-5 times increase in the number of bends, and significantly enhanced plasticity in subsequent processing. ③ The experimental group precisely controlled the addition of trace amounts of carbon monoxide (0.5-1.0%) in the core stage. The resulting dense protective film did not affect conductivity but enhanced corrosion resistance, increasing conductivity by 10%-13.6%. The corrosion resistance improvement rate was 2.8-3.4 times that of traditional methods, extending the product's service life.

[0029] It should be noted that when a component is said to be "fixed to" another component, it can be directly attached to the other component or there may be an intervening component. When a component is said to be "connected to" another component, it can be directly connected to the other component or there may be an intervening component. The terms "upper," "lower," "left," "right," "front," "back," and similar expressions used in this document are for illustrative purposes only.

[0030] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for heat treating the surface of nickel materials, characterized in that, Includes the following steps: S1. Pretreatment stage: Ultrasonic cleaning of nickel strip raw material; S2. Hot air preheating stage: The pretreated nickel strip is sent into the preheating zone and a three-stage gradient heating is adopted. Each gradient stage is held for 5-8 minutes. The hot air flow rate is 1.5-2.0 m / s. The atmosphere is a mixture of argon and hydrogen, with hydrogen gas fraction of 5-8% and pressure of 0.105-0.11 MPa. S3, Core Heat Treatment Stage: The preheated nickel strip is sent into the core heat treatment zone for constant temperature treatment and held for 10-15 minutes; the flow rate is 2.5-3.0 m / s, the atmosphere is a mixture of argon, hydrogen and carbon monoxide, the hydrogen volume fraction is 8-10%, the carbon monoxide volume fraction is 0.5-1.0%, and the pressure is 0.11-0.12 MPa; The core heat treatment area is equipped with a grain boundary oxidation monitoring module to monitor the oxide layer thickness d in real time, and to increase the volume fraction of carbon monoxide in the atmosphere when d≥0.1μm. S4. Gradient Cooling Stage: The core heat-treated nickel strip is sent into the cooling zone and a four-stage gradient cooling is adopted. The cooling rate of each cooling stage is 30-50℃ / min. The hot air flow rate is gradually reduced from 2.0m / s to 0.8m / s. The atmosphere is pure argon and the pressure is 0.105-0.11MPa. S5. Post-processing stage: The cooled nickel strip is surface passivated, then dried and wound up.

2. The processing method for heat treatment of nickel material surface according to claim 1, characterized in that, In S2, the hot air is sprayed in a laminar flow manner, with the spray direction at an angle of 30°-45° to the nickel strip surface; in S3, the hot air is sprayed symmetrically in both directions, with the spray direction at an angle of 60°-75° to the nickel strip surface.

3. The processing method for heat treatment of nickel material surface according to claim 1, characterized in that, S1 also includes plasma activation treatment, which uses low-pressure argon plasma and takes 1-3 minutes.

4. The processing method for heat treatment of nickel material surface according to claim 1, characterized in that, In S2, the target temperature of the three-stage gradient heating is set according to the subsequent core heat treatment temperature. The gradient increases sequentially from low temperature to high temperature, and the temperature difference between adjacent gradients is 150-250℃.

5. The processing method for heat treatment of nickel material surface according to claim 1, characterized in that, In S4, the target temperature of the four-stage gradient cooling decreases sequentially from high temperature to low temperature. The end temperature of each cooling stage is set as follows: the first stage reaches 70-80% of the core heat treatment temperature, the second stage reaches 40-50%, the third stage reaches 20-30%, and the fourth stage cools to below 80°C.

6. The processing method for heat treatment of nickel material surface according to claim 1, characterized in that, In S5, the passivation solution used in the surface passivation treatment is a potassium dichromate solution with a concentration of 5-8 g / L, and the treatment time is 2-3 min.

7. The processing method for heat treatment of nickel material surface according to claim 1, characterized in that, In S3, the flow equalization plate and temperature compensation module are used to ensure that the hot air temperature fluctuation is ≤±2℃.

8. The processing method for heat treatment of nickel material surface according to claim 1, characterized in that, In S3, the grain boundary oxidation monitoring module employs one of the following: a laser interferometric thickness gauge, an elliptic polarization thickness gauge, or an X-ray fluorescence thickness gauge.

Images