Methods for controlling the protective atmosphere and cooling inside a vertical furnace to enhance the gloss of stainless steel

Abstract

This invention discloses a method and system for controlling the protective atmosphere and cooling in a vertical furnace to improve the gloss of stainless steel, relating to the field of metal material heat treatment technology. The method is applied to a vertical furnace having a heating section, a soaking section, a slow cooling section, and a rapid cooling section. It includes: introducing a hydrogen-containing first protective atmosphere in the heating and soaking sections; introducing hydrocarbons in the slow cooling section to form a second protective atmosphere to repair the surface of the stainless steel strip; stopping the introduction of the aforementioned atmosphere in the rapid cooling section and switching to the introduction of a non-oxidizing gas for high-speed jet cooling; and adjusting the jet parameters of the non-oxidizing gas in real time according to the steel strip specifications and speed during cooling. This invention also discloses a system for implementing this method. This invention solves the problems of low gloss and unstable quality during stainless steel heat treatment, effectively repairs the chromium-depleted layer on the surface, avoids hydrogen embrittlement, and improves product surface quality and production stability.

Description

Technical Field

[0001] This invention relates to the field of heat treatment technology for metallic materials, and in particular to a method and system for controlling the protective atmosphere and cooling inside a vertical furnace to improve the gloss of stainless steel. Background Technology

[0002] To achieve excellent mechanical properties and surface quality, stainless steel strip typically requires bright annealing. A vertical continuous bright annealing furnace is the key equipment for this process. In existing technologies, a hydrogen-containing protective atmosphere (such as a hydrogen-nitrogen mixture) is usually introduced into the annealing furnace to prevent the stainless steel from oxidizing at high temperatures.

[0003] However, this traditional process has the following drawbacks: First, the reducing power of a low-concentration hydrogen atmosphere is limited, making it difficult to completely prevent the stainless steel surface from reacting with residual oxygen and water vapor in the furnace, resulting in poor surface gloss of the final product; second, during the high-temperature homogenization process, chromium on the stainless steel surface is prone to selective oxidation or volatilization, forming a chromium-depleted layer, which not only reduces the material's corrosion resistance but also causes uneven surface gloss; finally, for stainless steel strips of different thicknesses, widths, and grades, it is difficult to guarantee consistent cooling effects and product quality using fixed process parameters, leading to unstable product quality. Summary of the Invention

[0004] The main objective of this invention is to provide a method and system for controlling the protective atmosphere and cooling in a vertical furnace to improve the gloss of stainless steel. This aims to solve the technical problems in the prior art of stainless steel heat treatment, such as insufficient reducing ability of the protective atmosphere, easy formation of a chromium-depleted layer on the surface at high temperatures, and poor adaptability of the cooling process, which result in low surface gloss and unstable quality of the final product.

[0005] To achieve the above objectives, this invention provides a method for controlling the protective atmosphere and cooling in a vertical furnace to enhance the gloss of stainless steel. The method is applied to a vertical furnace having a heating section, a soaking section, a slow cooling section, and a rapid cooling section arranged sequentially along the running direction of the stainless steel strip. The method includes the following steps: in the heating section and soaking section of the stainless steel strip, a first protective atmosphere containing hydrogen is introduced into the furnace; in the slow cooling section of the stainless steel strip, a hydrocarbon is introduced into the furnace to form a second protective atmosphere for repairing the surface of the stainless steel strip; in the rapid cooling section of the stainless steel strip, the introduction of the first protective atmosphere and the hydrocarbon is stopped, and a non-oxidizing gas is introduced instead, using the non-oxidizing gas to perform high-speed airflow jet cooling on the stainless steel strip; during the cooling process, the jet speed and / or flow rate of the non-oxidizing gas are adjusted in real time according to the specifications and running speed of the stainless steel strip.

[0006] Optionally, the hydrogen content of the first protective atmosphere is 75%-95%.

[0007] Optionally, the hydrocarbon is methane, propane, or acetylene.

[0008] Optionally, in the step of using the non-oxidizing gas for high-speed airflow jet cooling, the jet velocity of the non-oxidizing gas is 100-150 m / s.

[0009] Optionally, after the rapid cooling section, a final cooling step is also included to cool the stainless steel strip to below 80°C.

[0010] Optionally, in the step of adjusting the injection speed and / or flow rate of the non-oxidizing gas in real time, the adjustment is based on the thickness and / or width of the stainless steel strip.

[0011] The present invention also provides a vertical annealing furnace system for processing stainless steel strips, comprising: a furnace body, internally divided into a heating section, a soaking section, a slow cooling section, and a rapid cooling section; an atmosphere supply device configured to supply a first protective atmosphere containing hydrogen to the heating section and the soaking section, and to supply hydrocarbons to the slow cooling section; a cooling device disposed in the rapid cooling section, comprising a high-speed nozzle for injecting a non-oxidizing gas, and configured with a valve group for stopping the supply of the first protective atmosphere and hydrocarbons and switching to supplying the non-oxidizing gas; and a control system connected to the atmosphere supply device and the cooling device, the control system being configured to adjust the speed and / or flow rate of the non-oxidizing gas injected by the cooling device in real time according to the specifications and operating speed of the stainless steel strip.

[0012] Optionally, the atmosphere supply device is configured to supply a first protective atmosphere with a hydrogen content of 75%-95%.

[0013] Optionally, the high-speed nozzle of the cooling device is configured to inject the non-oxidizing gas at a speed of 100-150 m / s.

[0014] Optionally, the control system includes: a sensor module for monitoring the specifications and operating speed of the stainless steel strip; a central controller for making decisions based on a preset control algorithm; and an actuator module for adjusting the speed and / or flow rate of the non-oxidizing gas.

[0015] The beneficial effects of this invention are as follows: 1. By employing a high-hydrogen-content first protective atmosphere for strong reduction protection in the heating and soaking zones, and introducing hydrocarbons for surface repair in the slow cooling zone, this invention can effectively suppress high-temperature oxidation and repair the chromium-depleted layer on the surface, thereby significantly improving the surface gloss and uniformity of stainless steel strips.

[0016] 2. By switching to a non-oxidizing gas for high-speed jet cooling in the rapid cooling section, the stainless steel strip can quickly pass through the oxidation-sensitive temperature range, solidify the bright surface, and prevent secondary oxidation. On the other hand, it fundamentally avoids the risk of hydrogen embrittlement that may be caused by the presence of hydrogen, thereby improving the mechanical properties and safety of the product.

[0017] 3. By adjusting the injection parameters of non-oxidizing gas in real time according to the specifications and operating speed of the stainless steel strip, this invention achieves process adaptability to products of different specifications, ensuring a high degree of consistency and stability of product quality in mass production. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments 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.

[0019] Figure 1 This is a schematic flowchart of a method for controlling the protective atmosphere and cooling inside a vertical furnace to improve the gloss of stainless steel according to an embodiment of the present invention.

[0020] Figure 2 This is a schematic diagram of a vertical annealing furnace system for processing stainless steel strips according to an embodiment of the present invention.

[0021] Figure 3 This is a structural block diagram of a control system according to an embodiment of the present invention.

[0022] Explanation of reference numerals in the attached drawings: 10: Vertical annealing furnace; 11: Heating section; 12: Soaking section; 13: Slow cooling section; 14: Rapid cooling section; 15: Final cooling section; 20: Stainless steel strip; 131: Hydrocarbon inlet; 141: High-speed gas nozzle; 310: Sensor module; 311: Laser thickness gauge; 312: Speed ​​encoder; 313: Infrared thermometer; 320: Central controller PLC; 330: Actuator module; 331: Mass flow controller; 332: Variable frequency fan. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings. The described embodiments should not be regarded as limitations on the present invention. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Unless otherwise defined, all technical and scientific terms used in the embodiments of this invention have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used in the embodiments of this invention is for descriptive purposes only and is not intended to limit the invention.

[0025] Before providing a further detailed description of the embodiments of the present invention, some of the nouns and terms involved in the embodiments of the present invention will be explained, and the nouns and terms involved in the embodiments of the present invention shall be interpreted as follows.

[0026] (1) First protective atmosphere: refers to the protective gas introduced into the heating and soaking sections of the vertical annealing furnace to suppress oxidation of the stainless steel strip during heating and holding. In some embodiments of the present invention, it may be a hydrogen-nitrogen mixture with a hydrogen content of 75%-95%, which has strong reducing properties, can effectively remove oxides on the surface of the stainless steel strip, and prevent it from oxidizing again at high temperatures, thus laying the foundation for obtaining a high-gloss surface.

[0027] (2) Hydrocarbons: These are substances introduced during the slow cooling section that can form a micro-carburizing atmosphere on the surface of the stainless steel strip to repair the chromium-depleted layer. During high-temperature homogenization, chromium on the stainless steel surface is prone to selective oxidation or volatilization, forming a chromium-depleted layer that affects corrosion resistance and surface gloss. The purpose of introducing these hydrocarbons is to replenish the lost chromium or form fine carbides through controlled surface reactions, thereby repairing this defect. In some embodiments of the present invention, the hydrocarbons may be methane, propane, or acetylene.

[0028] (3) Non-oxidizing gas: refers to the gas used in the rapid cooling section for high-speed airflow jet cooling of stainless steel strip. It has stable chemical properties and will not react with stainless steel strip at high temperatures, thus protecting the bright surface formed in the previous process. In some embodiments of the present invention, it may be high-purity nitrogen or an inert gas, such as argon.

[0029] (4) Vertical annealing furnace system: refers to a physical device for performing the method described in this invention, which includes at least a furnace body with specific functional zones, an atmosphere supply device for supplying different gases, a cooling device for rapid cooling, and a control system for automated process control. This system constitutes the complete physical carrier for implementing the method of this invention.

[0030] To better understand the technical solution of the present invention, a detailed description will be provided below in conjunction with the accompanying drawings and specific embodiments. Please refer to... Figure 1 This illustration shows a schematic flow diagram of a method for controlling the protective atmosphere and cooling inside a vertical furnace to improve the gloss of stainless steel, according to an embodiment of the present invention. The method is applied to a vertical furnace having a heating section, a soaking section, a slow cooling section, and a rapid cooling section arranged sequentially along the running direction of the stainless steel strip, for example... Figure 2 The vertical annealing furnace 10 shown.

[0031] like Figure 2 As shown, in a specific application scenario, the stainless steel strip 20 runs vertically within a vertical annealing furnace 10, sequentially passing through a heating section 11, a soaking section 12, a slow cooling section 13, a rapid cooling section 14, and an optional final cooling section 15 within the furnace body. The method of this invention achieves excellent surface quality and product performance through coordinated control of the atmosphere and cooling conditions in different sections.

[0032] Reference Figure 1 The method specifically includes the following steps. First, a strong reducing heating step S100 is performed. In this step, when the stainless steel strip 20 reaches the heating section 11 and the soaking section 12, a first protective atmosphere containing hydrogen is introduced into the furnace. This first protective atmosphere has strong reducing properties, which can effectively remove any slight oxide film that may exist on the surface of the stainless steel strip 20 before it enters the furnace, and continuously inhibit its reaction with residual oxygen, water vapor, and other oxidizing substances in the furnace throughout the high-temperature heating and holding stages. This protects the metallic color of the stainless steel from the source, laying a key foundation for finally obtaining a high-gloss surface quality.

[0033] Next, the surface repair slow cooling step S200 is performed. After the stainless steel strip 20 leaves the soaking zone 12 and enters the slow cooling zone 13, hydrocarbons are introduced into the furnace. These hydrocarbons decompose at high temperatures, forming a second protective atmosphere with the existing atmosphere in the furnace to repair the surface of the stainless steel strip 20. The technical principle is that stainless steel is prone to selective volatilization or oxidation of chromium at high temperatures, resulting in a chromium-depleted layer on the surface, which reduces the material's corrosion resistance and causes uneven gloss. By introducing hydrocarbons, a controlled micro-carburizing reaction can be initiated on the steel strip surface. The generated fine carbides or altered surface electrochemical potential can effectively repair the chromium-depleted layer, restoring the surface composition to uniformity, thereby significantly improving the gloss uniformity and corrosion resistance of the final product. The hydrocarbons can be introduced through the hydrocarbon inlet 131 located in the slow cooling zone 13.

[0034] Subsequently, the hydrogen-free rapid cooling step S300 is performed. A critical transition occurs when the stainless steel strip 20 enters the rapid cooling section 14. At this point, the introduction of the first protective atmosphere (i.e., hydrogen supply is stopped) and hydrocarbons is immediately halted, and the process is quickly switched to introducing a non-oxidizing gas into the furnace. Simultaneously, this non-oxidizing gas is used to perform high-speed air jet cooling on the stainless steel strip 20. This step serves a dual purpose: firstly, the high-speed airflow allows the steel strip to rapidly pass through the oxidation-sensitive temperature range of 450℃-800℃ at an extremely high cooling rate, effectively solidifying the bright surface formed in the previous process and preventing secondary oxidation; secondly, completely stopping the hydrogen supply fundamentally avoids the risk of hydrogen embrittlement caused by hydrogen penetrating into the steel strip matrix during cooling, ensuring the mechanical properties and safety of the product. This high-speed air jet is achieved through high-speed gas nozzles 141 installed within the rapid cooling section 14.

[0035] During the hydrogen-free rapid cooling step S300, a dynamic coupling control step S400 is executed in parallel. Specifically, during the cooling process, the injection speed and / or flow rate of the non-oxidizing gas need to be adjusted in real time according to the specifications of the stainless steel strip 20 (e.g., thickness, width) and the operating speed of the production line. Different specifications of steel strips have different heat capacities and heat dissipation characteristics, and fixed cooling parameters are difficult to guarantee consistent quality. Through dynamic adjustment, a suitable cooling curve can be obtained regardless of whether the plate is thick or thin, or whether the production is high-speed or low-speed, thereby ensuring a high degree of stability and consistency in product quality during mass production.

[0036] In one specific embodiment, the material being processed is a SUS304 austenitic stainless steel strip 20 with a thickness of 1.0 mm and a width of 1219 mm. In the strong reduction heating step S100, a hydrogen-nitrogen mixture with a hydrogen content of 85% is introduced into the heating section 11 and the soaking section 12 as a first protective atmosphere, and the dew point inside the furnace is strictly controlled below -60°C. The stainless steel strip 20 is heated to 1050°C and subjected to soaking treatment. This high-hydrogen, low-dew-point atmosphere provides excellent reducing power.

[0037] Next, in the surface repair slow cooling step S200, after the stainless steel strip 20 enters the slow cooling section 13, a small amount of methane gas is additionally introduced as a hydrocarbon inlet 131, in addition to the original atmosphere. The methane decomposes at high temperature and reacts with the steel strip surface, effectively repairing the surface chromium depletion that may have occurred due to high-temperature homogenization and improving the chemical uniformity of the surface.

[0038] Subsequently, in the hydrogen-free rapid cooling step S300, when the stainless steel strip 20 enters the rapid cooling section 14, the atmosphere supply system immediately activates, stopping the supply of all hydrogen and methane and switching to high-purity nitrogen (99.999%) as a non-oxidizing gas. Simultaneously, the cooling system drives the high-speed gas nozzles 141 installed in the rapid cooling section 14 to powerfully spray and cool the steel strip surface at an average speed of 120 m / s.

[0039] Throughout the cooling process, the dynamic coupling control step S400 remains operational. The control system maintains a spray rate of 120 m / s based on the current 1.0 mm thickness and the set production line speed. If subsequent production plans switch to processing 1.5 mm thick stainless steel strip 20, the control system will automatically increase the spray rate to 140 m / s according to a preset process model to match the greater cooling intensity required for the thicker steel strip, thereby ensuring consistent cooling performance for different product specifications.

[0040] In a preferred embodiment, such as Figure 1 and Figure 2 As shown, after the rapid cooling section 14, a final cooling section 15 can be set up, and a final cooling step S500 is performed. In this step, after leaving the rapid cooling section, the stainless steel strip 20 enters the final cooling section 15, where it is finally cooled using a low-speed fan or other gentle methods until the strip temperature drops below 80°C (e.g., 70°C), and then leaves the vertical annealing furnace 10. This step ensures that the stainless steel strip is at a safe temperature when it exits the furnace, facilitating subsequent winding, handling, and other operations, and is a useful supplement to the complete industrial production process.

[0041] The technical advantage of this invention lies in the fact that, through the synergistic effect of the above steps, the treated SUS304 stainless steel strip 20 exhibits a high surface finish with no observed oxidation color. Its gloss test value is more than 20% higher compared to the traditional low-hydrogen atmosphere, no-repair-step process. Simultaneously, mechanical property testing revealed no hydrogen embrittlement, demonstrating excellent ductility and strength, thus improving both product quality and safety.

[0042] In another preferred embodiment, the method of the present invention is also applicable to different types of materials and process gases, demonstrating its broad applicability. For example, the material to be processed can be a 0.8 mm thick SUS430 ferritic stainless steel strip. In this case, the first protective atmosphere in the strong reduction heating step S100 can be a hydrogen-nitrogen mixture with a hydrogen content of 75%, which can achieve effective reduction, and the heating temperature is adjusted to 850°C according to the material characteristics.

[0043] In the surface repair slow cooling step S200 of this embodiment, the introduced hydrocarbon can be propane gas, which is introduced into the slow cooling section 13 through the hydrocarbon inlet 131. As a common hydrocarbon, propane can also effectively form a micro-carburizing atmosphere, repairing surface defects that are more likely to occur in ferritic stainless steel at high temperatures.

[0044] In the hydrogen-free rapid cooling step S300, high-purity argon can be used as the non-oxidizing gas. As a completely inert gas, argon has better chemical stability than nitrogen and can provide superior cooling protection in certain special applications where surface purity is extremely important. Meanwhile, for thin steel strips of 0.8mm, the dynamic coupling control step S400 can set the injection speed at a relatively low level of 100m / s, which meets the cooling requirements while saving energy.

[0045] Furthermore, to address the needs of special products requiring extremely high surface quality, such as ultra-thin precision SUS316L stainless steel strips with a thickness of 0.5 mm, the process parameters of this invention can be adjusted within their optimized range to achieve superior technical results. In such applications, the strong reduction heating step S100 can employ a first protective atmosphere with a hydrogen content of up to 95% to provide the strongest reduction capability, ensuring high surface purity at a high temperature of 1100°C.

[0046] Accordingly, in the surface repair slow cooling step S200, acetylene can be selected as the hydrocarbon. Acetylene has a higher carbon potential, enabling the surface repair process to be completed more efficiently in the extremely short time it takes for the steel strip to pass through the slow cooling section 13 at high speed. In the hydrogen-free rapid cooling step S300, in order to achieve instantaneous quenching of the ultra-thin strip steel to minimize grain growth and facilitate rapid passage through the brittle zone, a maximum speed of 150 m / s (the upper limit of the parameters) can be used to spray and cool the steel strip through a high-speed gas nozzle 141. The combined application of these limiting parameters fully demonstrates the adjustable range and processing capacity of the process of this invention, providing strong support for the rationality of the numerical range.

[0047] The present invention also provides a vertical annealing furnace system for implementing the above-described method. For example... Figure 2 and Figure 3 As shown, this system is the physical carrier for implementing the aforementioned control method. The vertical annealing furnace system includes a furnace body 10, an atmosphere supply device, a cooling device, and a control system.

[0048] Specifically, the furnace body 10 has a vertical structure, and its internal space is physically or technologically divided into a heating section 11, a soaking section 12, a slow cooling section 13, and a rapid cooling section 14 along the running path of the stainless steel strip 20. This functional zoning is the basis for achieving segmented atmosphere and temperature control.

[0049] The atmosphere supply unit is configured to perform multiple functions. First, it is capable of supplying a first protective atmosphere containing hydrogen to the heating section 11 and the soaking section 12. Second, it is capable of supplying hydrocarbons to the slow cooling section 13, for example, through a piping and valve system connected to the hydrocarbon inlet 131. This unit is crucial for achieving strong reducing protection and surface repair.

[0050] The cooling device is located in the rapid cooling section 14, and its core component includes a high-speed gas nozzle 141 for injecting non-oxidizing gas. In addition, the device is equipped with a valve assembly for switching the atmosphere between different process stages. This valve assembly is capable of precisely executing the operation of "stopping the supply of the first protective atmosphere and hydrocarbons and switching to the supply of non-oxidizing gas," and is a key actuator for achieving the hydrogen-free rapid cooling step S300.

[0051] The control system is the core control unit of the entire vertical annealing furnace system. It is electrically connected to and controls the operation of the atmosphere supply device and the cooling device. The control system is configured to adjust the speed and / or flow rate of the non-oxidizing gas injected by the cooling device in real time according to the specifications (such as thickness and width) and operating speed of the stainless steel strip 20, thereby realizing the dynamic coupling control step S400.

[0052] In a preferred embodiment, the atmosphere supply device is configured to precisely control the hydrogen content of the supplied first protective atmosphere within the range of 75% to 95%. This allows the system to flexibly select the optimal hydrogen concentration based on the reduction requirements and cost considerations of different stainless steel grades.

[0053] In another preferred embodiment, the high-speed gas nozzle 141 in the cooling device and its drive system (such as a variable frequency fan) are configured to inject non-oxidizing gas at speeds ranging from 100 to 150 m / s. This wide adjustable speed range ensures that the system can handle both thin-gauge products requiring gentle cooling and thick-gauge or special-grade products requiring intensive cooling.

[0054] To gain a deeper understanding of how control systems work, please refer to [link / reference needed]. Figure 3 In one specific embodiment, the control system can be structurally decomposed into three core modules: a sensor module 310, a central controller PLC 320, and an actuator module 330. These three modules constitute a closed-loop control logic of "perception-decision-execution".

[0055] The sensor module 310 is responsible for real-time monitoring of key parameters in the process. For example, it may include a laser thickness gauge 311 located at the production line entrance for accurately measuring the thickness of the stainless steel strip 20 entering the furnace; a speed encoder 312 distributed along the production line for providing feedback on the real-time running speed of the steel strip; and a multi-point infrared thermometer 313 located at key locations such as the rapid cooling section 14 for non-contact monitoring of the steel strip's surface temperature. The data collected by these sensors forms the basis for achieving precise control.

[0056] The central controller, PLC320, is the core of the control system and is typically a programmable logic controller (PLC) or an industrial computer. It receives real-time monitoring data from the sensor module 310. Internally, it stores control algorithms and a process database based on heat transfer models and extensive experimental data. This database pre-sets standard cooling curves and corresponding cooling gas flow / speed reference values ​​for stainless steel strips of different grades, thicknesses, and widths at different production line speeds.

[0057] Actuator module 330 is the final executor of control commands. It includes a mass flow controller 331 for regulating the total flow rate of non-oxidizing gas, and a variable frequency fan 332 or pressure regulating valve for regulating the gas injection speed. The central controller PLC 320 issues control commands to these actuators based on its decision results.

[0058] The control system operates as follows: When a new roll of stainless steel strip 20 enters the production line, sensors such as the laser thickness gauge 311 immediately read its specifications and transmit them to the central controller PLC 320. Based on the read specifications, the steel strip grade input by the operator, and the real-time speed feedback from the speed encoder 312, the PLC 320 retrieves the corresponding target cooling curve and basic control parameters from its built-in database. When the steel strip passes through the rapid cooling section 14, the infrared thermometer 313 feeds back the real-time temperature to the PLC 320. The PLC 320 compares the actual temperature with the target cooling curve, calculates the deviation using PID (proportional-integral-derivative) control algorithms, and immediately generates adjustment commands to send to the actuator module 330. The mass flow controller 331 and the variable frequency fan 332 then adjust their outputs, dynamically changing the total volume and speed of the injected gas, ensuring that the actual cooling curve of the steel strip always closely matches the target curve. This system achieves closed-loop control of the cooling process, improving the automation level and yield of production.

[0059] In a preferred embodiment, the method and system of the present invention can be configured to process ultra-thin precision stainless steel strips (such as SUS316L) with the most stringent requirements. In this scenario, various technical features are combined to achieve maximum synergy. First, in the heating section 11 and the soaking section 12, a first protective atmosphere with a hydrogen content of up to 95% is used to create a strong reducing environment, ensuring that the steel strip surface reaches an ideal state free of any oxides before entering the slow cooling section 13. Next, in the slow cooling section 13, high-carbon-potential acetylene is introduced as a hydrocarbon, utilizing its highly efficient reaction characteristics to complete the repair of potential surface micro-defects in a short time as the steel strip passes through at high speed. Subsequently, in the rapid cooling section 14, the system switches to high-purity nitrogen and drives the variable frequency fan 332 to its maximum power, causing the high-speed gas nozzle 141 to spray at a maximum speed of 150 m / s, achieving instantaneous quenching of the low-heat-capacity ultra-thin steel strip and effectively solidifying its bright surface. The entire process is handled by... Figure 3 The control system shown performs closed-loop monitoring and adjustment to ensure the control accuracy of each link. Through this implementation, the produced stainless steel strip exhibits excellent surface quality, high and uniform gloss, no hydrogen embrittlement was observed, and its mechanical properties and corrosion resistance are significantly improved, enabling the treated stainless steel strip to possess surface quality and performance suitable for precision manufacturing. This embodiment demonstrates the synergistic effect of the various technical features of the present invention.

[0060] Comparison of the Invention Method with Existing Technologies: Experimental Examples To further verify the superiority of the technical solution of the present invention, especially to verify the actual effect of introducing hydrocarbons in the slow cooling section on repairing the chromium-depleted layer on the surface, improving gloss and corrosion resistance, this experimental example selected SUS304 austenitic stainless steel strips of the same batch and specifications (thickness 1.0 mm, width 1219 mm) and conducted a comparative experiment on the same vertical annealing furnace equipment.

[0061] 1. Experimental grouping and process parameter setting Comparative Group 1 (Prior Technology): Using the traditional low-hydrogen atmosphere annealing process.

[0062] Atmosphere of heating / soaking section: hydrogen-nitrogen mixture, with hydrogen content of 15% by volume.

[0063] The atmosphere in the slow cooling section is as follows: no hydrocarbons are introduced, and only residual nitrogen and trace impurities in the furnace are used.

[0064] Rapid cooling section atmosphere: Pure nitrogen is used for jet cooling at a speed of 100 m / s.

[0065] Heating temperature: 1050℃.

[0066] The present invention group (Example 1): adopts the process parameters described in Example 1 of the present invention.

[0067] Atmosphere of heating / soaking section: hydrogen-nitrogen mixture, with hydrogen volume content of 85% and dew point controlled below -60℃.

[0068] Atmosphere in the slow cooling section: a trace amount of methane gas is introduced (the flow rate is controlled to maintain the carbon potential in the furnace within a specific range, such as 0.2%-0.4%).

[0069] Rapid cooling section atmosphere: Hydrogen supply is stopped, and high-purity nitrogen is switched to high-speed injection cooling at a speed of 120 m / s.

[0070] Heating temperature: 1050℃.

[0071] 2. Detection methods and results (1) Surface gloss test Testing standard: According to the gloss test method specified in the appendix of GB / T 13825-2008 Metallic Coatings - Hot-dip galvanized Coatings of Ferrous Metal Materials by Weighing Method of Unit Area Mass, the gloss meter with an incident angle of 60° is used to test the surface of the annealed steel strip. Ten points are randomly selected from each group to calculate the average value.

[0072] Test results: Comparison Group 1 (Low Hydrogen, No Repair): Average Gloss Value 180 GU.

[0073] The invention group (high hydrogen + carbon repair): average gloss value 230 GU.

[0074] Improvement: The gloss of the present invention group was improved by approximately 27.8% compared to the control group 1. This indicates that a high-hydrogen atmosphere combined with hydrocarbon repair can more effectively suppress oxidation and obtain a denser, smoother surface.

[0075] (2) Surface corrosion resistance testing (electrochemical testing) Detection method: The pitting potential of the material in 3.5% NaCl solution was evaluated by potentiodynamic polarization curve testing.

[0076] Testing standard: Based on GB / T 24196-2009 Corrosion of metals and alloys - Electrochemical test methods - Guide to potentiostatic polarization measurement.

[0077] Test results: Comparison Group 1 (low hydrogen, no repair): The average pitting potential was approximately 0.32V (vs. SCE).

[0078] The average pitting potential of this invention group (high hydrogen + carbon remediation) is approximately 0.48V (vs. SCE).

[0079] Improvement: The pitting potential of this invention group was increased by 50% compared to control group 1. A higher pitting potential indicates better pitting corrosion resistance of the material. This demonstrates that hydrocarbon repair effectively mitigates the decline in surface corrosion resistance caused by high-temperature chromium removal.

[0080] (3) Surface composition analysis (XPS photoelectron spectroscopy) Detection method: XPS depth profiling was performed on the surfaces of the two groups of samples to analyze the chromium / iron atomic ratio (Cr / Fe) in the surface layer (within a depth of about 10 nm).

[0081] Purpose of the test: To verify the mechanism of “repairing the chromium-depleted layer”.

[0082] Test results: Comparative Group 1 (low hydrogen, no repair): The surface Cr / Fe atomic ratio is about 0.12 (the theoretical value of the matrix is ​​usually 0.22-0.25), confirming the presence of a significant chromium-depleted layer.

[0083] The present invention group (high hydrogen + carbon repair): the surface Cr / Fe atomic ratio is restored to about 0.21, which is close to the theoretical value of the matrix.

[0084] Analysis: Data confirms that the introduction of hydrocarbons into the slow cooling section altered the surface thermodynamic equilibrium through micro-carburization, inhibiting further chromium volatilization and even promoting chromium back-diffusion or selective oxide reduction, thus successfully repairing the chromium-depleted surface layer formed at high temperatures. This is the fundamental reason for the improved gloss and corrosion resistance.

[0085] 3. Conclusion The comparative experiments described above clearly demonstrate that the "introduction of hydrocarbons in the slow cooling section" described in this invention is not simply an atmosphere adjustment, but rather an effective repair of the inevitably chromium-depleted surface layer generated during high-temperature annealing through precisely controlled micro-carburization. Compared to traditional low-hydrogen, non-repairing processes, this invention can improve the gloss of stainless steel strips by approximately 27% and its pitting corrosion resistance by approximately 50%, significantly enhancing the material's corrosion resistance while improving surface quality, achieving unexpected technical results.

Claims

1. A method for controlling the protective atmosphere and cooling inside a vertical furnace to improve the gloss of stainless steel, applied to a vertical furnace having a heating section, a soaking section, a slow cooling section, and a rapid cooling section arranged sequentially along the running direction of the stainless steel strip, characterized in that, Includes the following steps: In the heating section and soaking section of the stainless steel strip, a first protective atmosphere containing hydrogen is introduced into the furnace. In the slow cooling section of the stainless steel strip, hydrocarbons are introduced into the furnace to form a second protective atmosphere for repairing the surface of the stainless steel strip. In the rapid cooling section of the stainless steel strip, the first protective atmosphere and the hydrocarbon are stopped, and a non-oxidizing gas is introduced to cool the stainless steel strip by high-speed airflow jet cooling. During the cooling process, the injection speed and / or flow rate of the non-oxidizing gas are adjusted in real time according to the specifications and operating speed of the stainless steel strip.

2. The method according to claim 1, characterized in that, The hydrogen content of the first protective atmosphere is 75%-95%.

3. The method according to claim 1 or 2, characterized in that, The hydrocarbon is methane, propane, or acetylene.

4. The method according to claim 1 or 2, characterized in that, In the step of using the non-oxidizing gas for high-speed airflow jet cooling, the jet velocity of the non-oxidizing gas is 100-150 m / s.

5. The method according to claim 1 or 2, characterized in that, Following the rapid cooling section, a final cooling step is also included to cool the stainless steel strip to below 80°C.

6. The method according to claim 1 or 2, characterized in that, In the step of adjusting the injection speed and / or flow rate of the non-oxidizing gas in real time as described in claim 1, the adjustment is based on the thickness and / or width of the stainless steel strip.

7. A vertical annealing furnace system for processing stainless steel strips, used to achieve the vertical furnace protective atmosphere and cooling control method for improving the gloss of stainless steel as described in claim 1, characterized in that, include: The furnace body is internally divided into a heating section, a soaking section, a slow cooling section, and a rapid cooling section; An atmosphere supply device is configured to supply a first protective atmosphere containing hydrogen to the heating section and the soaking section, and to supply hydrocarbons to the slow cooling section; A cooling device, located in the rapid cooling section, includes a high-speed nozzle for injecting non-oxidizing gas and is equipped with a valve group for stopping the supply of the first protective atmosphere and hydrocarbons and switching to supplying the non-oxidizing gas. A control system, connected to the atmosphere supply device and the cooling device, is configured to adjust the speed and / or flow rate of the non-oxidizing gas injected by the cooling device in real time according to the specifications and operating speed of the stainless steel strip.

8. The system according to claim 7, characterized in that, The atmosphere supply device is configured to supply a first protective atmosphere with a hydrogen content of 75%-95%.

9. The system according to claim 7 or 8, characterized in that, The high-speed nozzle of the cooling device is configured to spray the non-oxidizing gas at a speed of 100-150 m / s.

10. The system according to claim 7 or 8, characterized in that, The control system includes: Sensor module used to monitor the specifications and operating speed of the stainless steel strip; A central controller that makes decisions based on a preset control algorithm; and An actuator module for regulating the speed and / or flow rate of the non-oxidizing gas.

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