Austenitic spheroidizing annealing process control method of full hydrogen bell-type annealing furnace

Abstract

The application relates to the technical field of annealing, and discloses a subcritical zone spheroidizing annealing process control method of a full-hydrogen bell-type annealing furnace, which comprises the following steps: obtaining basic information of a steel coil to be treated through a computer control system, wherein the basic information comprises steel coil material parameters, steel coil state parameters and steel coil specifications, the steel coil material parameters include mass percentages of Si, Mn and Cr elements, the steel coil state parameters are pickling coils or cold hard coils, and the steel coil specifications include thickness and outer diameter. Relying on accurate control of a subcritical zone spheroidizing interval, combining real-time cold-hot spot temperature difference monitoring and automatic correction, the steel coil temperature in the furnace is ensured to be uniform, the spheroidizing unevenness problem is avoided, and in view of the characteristics of rolling oil residue, the hydrogen flow rate is monitored in a specific temperature interval, so that the surface of the steel coil after annealing is bright and free of oxidation color. Finally, the annealed steel coil has uniform structure, can adapt to downstream cold rolling, stamping and other processing requirements, defects are not prone to occur in the processing process, and the requirements of customers on product process performance are met.

Description

Technical Field

[0001] This invention relates to the field of annealing technology, specifically to a method for controlling the sub-temperature spheroidizing annealing process in a full-hydrogen bell-type annealing furnace. Background Technology

[0002] The sub-zero spheroidizing annealing process in a full-hydrogen bell-type annealing furnace is one of the key processes in the extended processing of special steel strips. It is mainly used for heat treatment of special steel coils in different states, such as pickled coils and cold-hardened coils. This process, by controlling parameters such as annealing temperature, holding time, and protective gas atmosphere, promotes the transformation of carbides inside the steel coil into spherical or granular shapes, thereby reducing the hardness of the steel coil and improving its mechanical properties. This provides a suitable raw material for subsequent cold rolling, stamping, shearing, and other processing steps, and is widely used in the upstream steel strip processing of end products such as chain links, scissors, and hardware accessories.

[0003] In current industrial production, the sub-critical spheroidizing annealing process using a full hydrogen bell-type annealing furnace has gradually replaced the traditional nitrogen / nitrogen-hydrogen mixed gas bell-type annealing process. The industry typically sets the sub-critical annealing range roughly based on the phase transformation characteristics of the steel grade. Heating is achieved within the furnace through a heating bell, and a circulating fan drives the circulation of protective gases such as hydrogen for heat transfer. The cooling stage often employs a segmented approach: heating bell cooling – cooling bell air cooling – spray cooling.

[0004] However, the application of this process under existing technology still has significant drawbacks: First, it is difficult to ensure the uniformity of temperature inside the furnace. The radial direction of the steel coil (the core and the outer ring) is prone to large temperature differences due to uneven heat transfer, resulting in inconsistent spheroidization of carbides. Some steel coils exhibit under-spheroidization or over-spheroidization, affecting subsequent processing performance. Second, regarding the problem of residual rolling oil on the surface of the steel coil, there is a lack of a hydrogen flow rate control scheme coupled with temperature. Incomplete evaporation of rolling oil or insufficient hydrogen protection can easily lead to defects such as oxidation color and spots on the surface of the steel coil. Third, the compatibility with multiple steel grades is poor. It is difficult to accurately set annealing parameters according to the differences in phase transformation points of different steel grades. After annealing, the uniformity of the microstructure and the surface quality of some steel coils cannot meet the requirements of downstream cold rolling, stamping and other processing, which restricts the stability of the quality of special steel strip products. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for controlling the sub-temperature spheroidizing annealing process in a full-hydrogen bell-type annealing furnace, which solves the problems of uneven annealing temperature, surface defects, and poor compatibility among various steel grades for special steel strips.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for controlling the sub-temperature spheroidizing annealing process in a full-hydrogen bell-type annealing furnace, comprising the following steps:

[0007] S1. The computer control system acquires the basic information of the steel coil to be processed. The basic information includes the material parameters, state parameters and specifications of the steel coil. The material parameters include the mass percentage of Si, Mn and Cr elements. The state parameters are pickled coil or cold-hardened coil. The specifications include thickness and outer diameter. The computer control system establishes the expected process reference based on the basic information.

[0008] S2. The computer control system calculates the phase transformation point A of the steel coil based on the material parameters of the steel coil. c1 Temperature, according to A c1 The temperature range for sub-temperature spheroidizing annealing is determined to be A. c1 Reduce temperature by 20°C to A c1 Reduce by 10℃;

[0009] S3. The computer control system generates a standard process curve containing heating parameters, soaking parameters, and cooling parameters based on the steel coil state parameters, sub-temperature spheroidizing annealing range, and expected process benchmark. The heating parameters include the heating rate and segmented temperature nodes, the soaking parameters include the holding time and hydrogen flow rate threshold, and the cooling parameters include the cooling rate and temperature switching nodes.

[0010] S4. The computer control system sends control commands to the actuators of the all-hydrogen bell-type annealing furnace to start the process. At the same time, it activates the real-time monitoring module and continuously collects the cold and hot temperatures of the steel coil as actual operating data through distributed temperature sensors inside the furnace. It also collects hydrogen flow rate, furnace power and other operating parameters simultaneously.

[0011] S5. During the heating stage, the real-time monitoring module continuously detects the deviation between the actual operating data and the standard process curve. When it determines that the temperature difference between the hot and cold spots of the steel coil exceeds the preset first fault threshold (5°C), the automatic correction subroutine is triggered. The deviation is corrected by adjusting the power output of the corresponding heating area until the temperature difference is detected to be within the first fault threshold. The occurrence time, correction process and result of the deviation event are recorded in the fault log.

[0012] S6. When the cold point temperature of the steel coil reaches the lower limit of the sub-temperature spheroidizing annealing range, the computer control system determines that the process has entered the heat soaking and heat preservation stage, continuously checks whether the furnace temperature is stable within the sub-temperature spheroidizing annealing range, and checks whether the hydrogen flow rate matches the threshold in the heat soaking parameters. If any indicator does not match, an early warning signal is issued.

[0013] S7. After the heat soaking and heat preservation stage, the computer control system controls the furnace to enter the cooling stage. The furnace temperature is controlled to drop from the sub-temperature range to below 200℃ according to the cooling parameters of the standard process curve. During this period, the real-time monitoring module continuously detects the matching between the cooling rate and the hydrogen flow rate.

[0014] S8. Throughout the entire process, the computer control system continuously records furnace temperature, hydrogen flow rate, steel coil temperature difference, and other key performance indicators at each stage for fault detection. If any indicator deviates from the standard process curve by more than the second fault threshold, the system will detect such deviations. The second fault threshold includes furnace temperature deviations of ±3℃ and hydrogen flow rate deviations of ±2m. 3 / h, automatically executes the fault diagnosis module, determines the period as an anomaly by comparing with the historical fault database, and generates a diagnostic report containing speculation on the cause of the anomaly and correction suggestions. The speculation on the cause of the anomaly covers sensor drift, valve jamming, and power fluctuation.

[0015] Preferably, in step S2, A c1 The formula for calculating temperature is:

[0016] A c1 =723 + 25 × Si% - 7 × Mn% + 15 × Cr%, where Si%, Mn%, and Cr% are the mass percentages of the corresponding elements in the steel coil; the computer control system has a built-in material and phase transformation point calibration database, and automatically calls historical A values ​​of the same steel grade from the database after calculation. c1 The measured value is corrected for deviation, and after correction, A c1 The temperature error range is ≤ ±2℃, and the correction result serves as the core parameter for the expected process reference.

[0017] Preferably, the parameter setting rules for the standard process curve in step S3 are as follows:

[0018] The computer control system calls the pre-stored steel coil status-parameter mapping table and automatically matches differentiated process parameters based on the steel coil status parameters and specifications.

[0019] Among them, the heating rate set for pickled rolls is lower than the heating rate set for cold-hardened rolls, and the heat soaking time set for pickled rolls is longer than the heat soaking time set for cold-hardened rolls.

[0020] The generated standard process curve serves as a benchmark for comparing actual operating data.

[0021] Preferably, in step S4, the distributed temperature sensor includes at least three sets of thermocouples arranged radially along the steel coil, which respectively collect the temperature at the center, half radius, and surface of the steel coil. After the computer control system performs filtering and noise reduction processing on the data from each set of sensors, the lowest value is determined as the cold point temperature and the highest value is determined as the hot point temperature. The processed data is used as the core input of the actual operation data.

[0022] Preferably, the automatic correction subroutine in step S5 uses a power regulation algorithm based on temperature difference feedback to achieve power regulation: the computer control system outputs the regulation amount according to the temperature difference value ΔT, where ΔT is the hot spot temperature minus the cold spot temperature. When ΔT exceeds the first fault threshold but is within the first interval, the heating power of the hot spot area is reduced; when ΔT exceeds the first interval, the heating power of the hot spot area is reduced and the heating power of the cold spot area is increased; the regulation response time is ≤30 seconds, and the regulation process ensures continuous process execution through a fault tolerance mechanism.

[0023] Preferably, the verification process in the heat soaking and heat preservation stage of step S6 is as follows:

[0024] The computer control system performs periodic verification by continuously collecting the temperature of hot and cold spots and the hydrogen flow rate three times. If the temperature difference is ≤5℃ and the hydrogen flow rate is within the threshold range, the verification is deemed to be qualified.

[0025] If any data is not met, the automatic correction subroutine in step S5 is triggered to deal with excessive temperature difference, or an abnormal flow rate warning is issued to deal with excessive hydrogen flow rate. The verification result is updated to the fault log in real time.

[0026] Preferably, the hydrogen flow rate and temperature switching process in the cooling stage of step S7 is as follows:

[0027] The real-time monitoring module controls the hydrogen flow rate based on the temperature switching nodes in the cooling parameters.

[0028] When the furnace temperature is not lower than the temperature corresponding to the temperature switching node, the hydrogen flow rate is controlled to be within the first cooling flow rate range; when the furnace temperature is lower than the temperature corresponding to the temperature switching node, the hydrogen flow rate is controlled to switch to a second cooling flow rate range lower than the first cooling flow rate range.

[0029] When the flow rate deviates from the corresponding range, the computer control system corrects it by adjusting the opening of the hydrogen inlet valve.

[0030] Preferably, the operation of the fault diagnosis module in step S8 is as follows:

[0031] Anomaly detection: The difference between the real-time collected key performance indicators and the standard process curve is calculated. If the difference exceeds the second fault threshold for 30 seconds, it is marked as an anomaly.

[0032] Cause speculation: The historical fault database is accessed, and the abnormal parameter characteristics are matched with the fault modes in the database to output the most probable possible cause.

[0033] Report generation: Automatically generates diagnostic reports that include abnormal periods, parameter deviation values, suspected causes, correction steps, and prevention suggestions. It supports exporting via human-machine interface or remote push.

[0034] Preferably, in step S4, when the real-time monitoring module detects that the furnace temperature is in the range of 400°C to 450°C during the heating stage, it automatically increases the monitoring frequency of hydrogen flow rate; at the same time, it presets a higher hydrogen flow rate benchmark value based on the oil stain level on the steel coil surface, and the real-time monitoring module includes the deviation between the actual flow rate and the benchmark value in the first fault threshold judgment range.

[0035] Preferably, the diagnostic report generated in step S8 also includes process parameter optimization suggestions. The computer control system analyzes the abnormal repair records of similar steel coils in the historical fault database to extract the optimal correction parameters. The optimal correction parameters include the heating power adjustment range and the hydrogen flow rate compensation value. When the same type of steel coil enters the annealing process again, the optimal correction parameters are automatically preloaded into the standard process curve to achieve self-iterative optimization of process parameters.

[0036] This invention provides a method for controlling the sub-temperature spheroidizing annealing process in a full-hydrogen bell-type annealing furnace. It has the following beneficial effects:

[0037] 1. This invention relies on precise control of the sub-temperature spheroidizing annealing zone, combined with real-time monitoring and automatic correction of hot and cold spot temperature differences, to ensure uniform temperature of the steel coil in the furnace and avoid uneven spheroidization. Simultaneously, addressing the characteristics of rolling oil residue, it enhances hydrogen flow rate monitoring within a specific temperature range to ensure a bright, oxide-free surface on the annealed steel coil. The resulting annealed steel coil exhibits a uniform microstructure, adaptable to downstream cold rolling and stamping processes, and is less prone to defects during processing, thus meeting customer requirements for product performance.

[0038] 2. This invention completes the entire process of steel coil information collection, process curve generation, and real-time parameter monitoring through a computer control system. It requires minimal manual intervention, can automatically diagnose process anomalies, infer the causes of anomalies based on historical data and provide correction suggestions, and can iteratively optimize process parameters. This not only reduces reliance on operator experience but also reduces process anomalies, ensuring continuous and stable annealing production.

[0039] 3. This invention utilizes integrated high-efficiency heating equipment technology, combined with a segmented heating strategy for steel coils in different states, to accelerate heat transfer efficiency within the furnace and shorten the total annealing time. During the cooling stage, temperature and hydrogen flow rate are coupled and controlled to ensure effective cooling while rationally adjusting the hydrogen flow rate. The overall process improves production efficiency while achieving reasonable energy consumption control, balancing high-efficiency production with cost optimization, thus meeting the needs of large-scale production. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the all-hydrogen bell-type annealing furnace structure of the present invention;

[0041] Figure 2 This is a schematic diagram showing the position of the insert thermocouple of the present invention;

[0042] Figure 3 The figure shows the test results of the inserts in the all-hydrogen bell-type annealing furnace of the present invention;

[0043] Figure 4 This is a schematic diagram of the all-hydrogen hood-type annealing process of the present invention;

[0044] Figure 5 This is a graph showing the evaporation rate of the rolling oil according to the present invention.

[0045] Figure 6 Figure a shows the metallographic structure of the pickled 65Mn roll at different temperatures according to the present invention;

[0046] Figure 7 Figure b shows the metallographic structure of the pickled 65Mn roll at different temperatures according to the present invention;

[0047] Figure 8 Figure c shows the metallographic structure of the pickled 65Mn roll at different temperatures according to the present invention.

[0048] Figure 9 The image shows the metallographic structure of the pickled 65Mn roll at different temperatures according to the present invention.

[0049] Figure 10 This is a schematic diagram of the pickling and annealing process of the present invention. Detailed Implementation

[0050] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of 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.

[0051] Please see the appendix Figures 1-10 This invention provides a method for controlling the sub-temperature spheroidizing annealing process in a full-hydrogen bell-type annealing furnace. It is based on a full-hydrogen bell-type annealing furnace unit equipped with a φ950 high-temperature variable frequency circulating fan, distributed thermocouples, and a hydrogen / nitrogen supply system. The core of this method is a computer control system integrating a real-time monitoring module, a fault diagnosis module, and a historical fault database. This system enables precise control and fault management of the entire sub-temperature spheroidizing annealing process. The following detailed description is provided with reference to four typical embodiments:

[0052] Example 1: Sub-temperature spheroidizing annealing of pickled 50 steel coils

[0053] 1.1 Implementation of Basic Information

[0054] The steel coils are 50 steel hot-rolled pickled coils, with specifications of 3.0×1130mm (thickness 3.0mm, outer diameter 1730mm), and a single coil weight of 19.63t. A total of 4 coils are stacked. During stacking, ensure that the steel coil with the larger outer diameter is at the bottom and that the thickness difference between each coil does not exceed 2mm. During stacking, a 0.2mm thick oil-free high-temperature resistant pad is placed between every two layers of steel coils, covering the entire width of the steel coil to prevent the steel coils from sticking together or scratching the surface. After stacking the 4 steel coils, the gap between the overall outer diameter and the inner wall of the inner shroud is controlled at 50-80mm to ensure that hydrogen gas flows evenly along the gap between the steel coils in the furnace and avoids the formation of local temperature dead zones. The material parameters, by mass percentage, are C 0.61%, Mn 0.61%, Si 0.21%, Cr 0.14%, S≤0.008%, P≤0.015%, and the steel coil condition is pickled coil.

[0055] The equipment parameters utilize a No. 2 furnace platform with a full hydrogen bell-type annealing furnace. The distributed temperature sensors consist of three sets of WRNK-191 thermocouples arranged radially along the steel coil, collecting temperatures at the center half radius and the surface of the coil. The computer control system incorporates a material-phase transition point calibration database containing historical data for 50 steel. c1 The measured value was 726.3℃.

[0056] 1.2 Process Execution

[0057] S1: Basic Information Acquisition and Expected Process Benchmark Establishment: The computer control system inputs the material parameters, status, and specifications of the steel coils through the human-machine interface. After automatically calling the stacking rule library to determine the matching of the specifications of the four steel coils, the expected process benchmark is established with the core objective of the spheroidization rate conforming to GB / T1299-2014 level 2.0-3.0 and not less than 95%, and the temperature difference between hot and cold spots not exceeding 5℃.

[0058] S2: A c1 Temperature calculation and sub-temperature range determination:

[0059] According to the formula:

[0060] A c1 =723+25×Si%-7×Mn%+15×Cr%

[0061] A was calculated c1 =723 + 25 × 0.21 - 7 × 0.61 + 15 × 0.14 = 726.5℃. The computer retrieves the historical data of 50 steel from the database. c1 The measured value of 726.3℃ was corrected, and A was finally determined. c1 The temperature was 726.4℃, based on this A c1 The temperature range for sub-temperature spheroidizing annealing is determined to be 726.4℃ minus 20℃ to 726.4℃ minus 10℃, which is the actual controlled range of 706℃ to 716℃.

[0062] S3: Standard Process Curve Generation: The computer automatically matches the pre-stored steel coil state-parameter mapping table based on the state of the steel coil being pickled, generating a standard process curve. The heating parameters include a heating rate of 55℃ / h and segmented temperature nodes of 300℃, 500℃, and 600℃. The homogenization parameters include a holding time of 23h and a hydrogen flow rate threshold of 9m. 3 The cooling parameters are: cooling rate 35℃ / h, temperature switching node 300℃.

[0063] S4: Process Start-up and Real-time Data Acquisition: The computer sends control commands to the actuator of furnace #2 for nitrogen purging of the inner shroud and closing of the heating shroud. The inner shroud sealing test pressure is 0.05 MPa, and the nitrogen purging flow rate is 72 m³ / h. 3 During nitrogen purging, the computer monitors the oxygen content inside the furnace in real time. When the oxygen content is ≤50ppm, the purging is deemed successful, and nitrogen supply is stopped. If the oxygen content is >50ppm, the purging time is extended, and 10m³ of nitrogen is added. 3 This process is repeated until the oxygen content reaches the standard to prevent oxidation of the steel coil surface during subsequent heating. Simultaneously, the real-time monitoring module is activated. Before introducing hydrogen, the computer verifies the purity sensor data of the hydrogen supply system to ensure that the purity of the hydrogen introduced into the furnace is ≥99.999%, preventing impurities (such as oxygen and moisture) from affecting the surface smoothness of the steel coil and the uniformity of carbide spheroidization. The hydrogen flow rate acquisition accuracy is ±0.5m. 3 The furnace power acquisition accuracy is ±1kW, and the thermocouple acquisition frequency is 1 time / 30 seconds, simultaneously acquiring hydrogen flow rate and furnace power. The hydrogen flow rate acquisition accuracy is ±0.5m. 3 The furnace power acquisition accuracy is ±1kW. When heating to 400℃, the computer automatically increases the hydrogen flow rate monitoring frequency to once every 10 seconds. The detected oil content on the steel coil surface is 0.04g / m. 2 The preset flow velocity baseline value is 19m. 3 / h, real-time comparison of actual flow velocity with reference value, with deviation not exceeding 1m. 3 The condition is considered normal when / h is reached.

[0064] S5: Heating Stage Deviation Detection and Correction: When heating to 500℃, the real-time monitoring module detects a core temperature of 495℃ (cold point temperature) and a surface temperature of 501℃ (hot point temperature). (Based on system calculations, the current lowest temperature (core) is 495℃ (cold point temperature), and the highest temperature (surface) is 501℃ (hot point temperature). The temperature difference of 6℃ exceeds the first fault threshold of 5℃. The computer triggers an automatic correction subroutine that uses a power adjustment algorithm based on temperature difference feedback. According to the temperature difference value ΔT=6℃ (i.e., 5℃<ΔT≤8℃), the output adjustment amount reduces the power of the corresponding heating area on the surface by 7%. The adjustment response time is 25 seconds. After correction, the temperature difference is detected to drop to 4.5℃ within 10 seconds, which is no more than 5℃. The computer automatically records the occurrence time, temperature difference value, and adjustment range of the deviation event to the fault log.

[0065] S6: Heat soaking and heat preservation stage verification: When the temperature reaches 706℃, which is the lower limit of the sub-temperature range, the computer determines that the heat soaking stage has begun. Verification is performed periodically every 15 minutes, continuously collecting the hot and cold spot temperatures and hydrogen flow rate three times. The three collected data points are: furnace temperature 710℃, hydrogen flow rate 8.8 m³ / s. 3 / h temperature difference 4℃ furnace temperature 712℃ hydrogen flow rate 9.1m 3 / h temperature difference 4.2℃ furnace temperature 711℃ hydrogen flow rate 8.9m 3 The temperature difference was 3.8℃ / h. All three data points met the criteria of a temperature difference not exceeding 5℃ and hydrogen flow rate within the threshold range, indicating that the verification was qualified. No warning was triggered during the 23h heat equalization period.

[0066] S7: Cooling Stage Flow Rate and Temperature Coupling Control: After the homogenization phase, the computer controls the cooling stage, reducing the temperature at a rate of 35℃ / h. Real-time monitoring of the furnace temperature and hydrogen flow rate matching is performed. When the furnace temperature is not lower than 300℃, the hydrogen flow rate is maintained at 16m. 3 / h, when the furnace temperature drops to 298℃, the hydrogen flow rate is automatically switched to 9m. 3 / h, the flow rate was measured at 8.8m when the temperature was lowered to 200℃. 3 There was no deviation in / h, no correction operation was performed during the cooling phase, and the data was synchronously recorded to the actual running database.

[0067] In this embodiment, the hydrogen flow rate is controlled in stages according to temperature during the cooling phase. The theoretical basis is the simplified formula of the convective heat transfer coefficient between the protective gas and the steel coil in the all-hydrogen bell furnace:

[0068]

[0069] In the formula:

[0070] Convection heat transfer coefficient (unit: W / (m²)) 2 •K)), This is the inherent constant of the equipment (measured at 0.85 for this furnace). Hydrogen gas flow rate (unit: m) 3 / h), The thermal conductivity of hydrogen gas increases with increasing temperature. The density of hydrogen gas (decreases as temperature increases). This refers to the isobaric specific heat capacity of hydrogen (which increases with increasing temperature). The velocity influence coefficient is 0.7.

[0071] As can be seen from the formula, the convective heat transfer coefficient is closely related to the hydrogen flow rate and the thermophysical parameters of hydrogen: when the furnace temperature is ≥300℃, the combined λ / ρ / cp of hydrogen decreases, requiring the flow rate to be increased to 15-18m. 3 / h to maintain sufficient h; when the furnace temperature is <300℃, the thermophysical properties of hydrogen rise, and the flow rate drops to 8-10m. 3 The heat exchange efficiency can still be guaranteed at a rate of / h, while reducing hydrogen consumption.

[0072] S8: Full-process fault diagnosis and report generation: The computer continuously records data at each stage, with the maximum deviation of furnace temperature from the sub-temperature range not exceeding +2℃ and ±3℃, and the maximum deviation of hydrogen flow rate not exceeding -1.2m. 3 / h not exceeding ±2m 3 / h No abnormal point markers are found. The fault diagnosis module calls a historical fault database containing 200 sets of data from the past 50 steel pickled coils. This historical fault database contains four sets of related data: fault type, abnormal parameter characteristics, repair measures, and corresponding steel grade / state. For example, a heating tube fault corresponds to a sudden temperature rise of 5℃ / min while the furnace power remains unchanged. The repair measure is to shut down the machine and replace the heating tube. This is associated with the pickled / cold-hardened coil status of 50 steel / 65Mn steel. The database data source is the annealing process data of the same type of steel coil from the past 3 years (a total of 520 sets, including 480 sets of normal data and 40 sets of fault data). According to the data, it is updated quarterly to include new fault cases; fault matching uses the Euclidean distance algorithm to calculate the similarity between real-time parameters and fault parameters in the database. When the similarity is ≥85%, the corresponding fault type and probability are output (e.g., sensor drift probability 92%) to ensure the accuracy of cause inference. Matching the current unbiased parameter features generates a diagnostic report containing screenshots of process curves showing no abnormal causes and optimization suggestions. The optimization suggestion is to shorten the soaking time to 22.5h for the next steel coil of the same specification. After the report is exported, the computer automatically sets the current heating rate of 55℃ / h and the hydrogen flow rate threshold of 9m. 3 Optimal parameters such as / h are preloaded into the 50 steel pickled coil parameter library.

[0073] 1.3 Implementation Results

[0074] The spheroidization rate was tested using the following method: Metallographic samples of 10mm × 10mm were cut from the head, middle, and tail of the steel coil (a total of 3 groups to ensure representativeness); the samples were polished stepwise with 400#-2000# sandpaper, etched with 4% nitric acid alcohol solution for 5 seconds, and observed under a metallographic microscope (500x magnification); the spheroidization rate was calculated according to the granular pearlite area ratio method in Appendix A of GB / T1299-2014, and the average value of the 3 groups of samples was taken as the final result; the judgment standard was: spheroidization grade 2.0 corresponds to the granular pearlite area ratio. ≥95%, with grade 3.0 corresponding to a proportion of ≥90%. The metallographic structure of the outer and inner rings of the steel coil is granular pearlite with a spheroidization level of 2.0-3.0 and a spheroidization rate of 96.5% or less. The mechanical properties are tensile strength of 508-573MPa, elongation of 30.0%-34.0%, and hardness of 144-163HB. During the process, only one deviation correction was triggered during the heating stage, and the correction success rate was 100% with no other faults. After longitudinal shearing, the steel coil is cold-rolled to 1.8mm with a total reduction of 1.2mm and no edge breakage or cracking.

[0075] Example 2: Sub-temperature spheroidizing annealing of 50 steel cold-rolled coils

[0076] 2.1 Implementation of Basic Information

[0077] The steel coil parameters are: 50 steel cold-rolled coil, specifications 1.38×1250mm (thickness 1.38mm), outer diameter 1680mm, single coil weight 19.79t, 4 coils stacked together, with the thickness difference between each coil not exceeding 0.6mm, material parameters consistent with Example 1, steel coil state is cold-rolled coil. Assume...

[0078] The thermocouple arrangement of the 17# furnace platform full hydrogen hood annealing furnace is the same as in Example 1. The computer control system calls the steel coil status-parameter mapping table corresponding to the cold-hardened coil.

[0079] 2.2 Process Execution and Results

[0080] The process for determining the sub-temperature range in S2 is consistent with that in Example 1, i.e., the sub-temperature spheroidizing annealing range is 706℃ to 716℃. The standard process curve parameters generated in S3 are: heating rate 75℃ / h, segmented temperature nodes 400℃ and 600℃, soaking time 15h, and hydrogen flow rate threshold 11m. 3 The cooling rate is 45℃ / h. The operation logic from S4 to S8 is the same as in Example 1. In S5, when heating to 450℃, the temperature difference is detected to be 5.5℃. The computer reduces the power of the hot spot area by 9% and increases the power of the cold spot area by 4%. After 18 seconds, the temperature difference drops to 4.8℃. In stage S9, the oil content on the surface of the steel coil is 0.03g / m in the 400-450℃ range. 2 The preset flow velocity baseline value is 18.5m. 3 / h No-deviation triggering.

[0081] The results showed that the spheroidization level of the steel coil was 2.5-3.0, with a spheroidization rate of 98.2% or less. The mechanical properties were tensile strength of 513-533 MPa, elongation of 28.5%-33.5%, and hardness of 140-161 HV. When the steel coil was cold-rolled to 0.5 mm with a total reduction of 0.88 mm, the rolling current was stable and there was no cracking.

[0082] Example 3: Sub-temperature spheroidizing annealing of pickled 65Mn steel coils

[0083] 3.1 Implementation of Basic Information

[0084] The steel coil parameters are 65Mn steel pickled coils, specifications 2.75×1100mm (thickness 2.75mm), outer diameter 1737mm, single coil weight 18.25t, 4 coils stacked together. Material parameters, by mass percentage, are C 0.67%, Mn 0.97%, Si 0.21%, Cr 0.14%, and the steel coil condition is pickled coil. Equipment parameters are consistent with Example 1. The computer control system has a built-in 65Mn steel historical A... c1 The measured value was 724.3℃.

[0085] 3.2 Process Execution and Results

[0086] S2 calculates A according to the formula. c1 =723 + 25 × 0.21 - 7 × 0.97 + 15 × 0.14 = 722.7℃. After correcting using the historical measured value of 724.3℃, A is determined. c1 The temperature is 723.5℃. The sub-temperature spheroidizing annealing range is 723.5℃ minus 20℃ to 723.5℃ minus 10℃, i.e., 703.5℃ to 713.5℃. The standard process curve parameters generated by S3 are: heating rate 58℃ / h, soaking time 24h, hydrogen flow rate threshold 9.5m. 3 The cooling rate is 38°C / h, and the operation logic from S4 to S8 is the same as in Example 1.

[0087] The results showed that the spheroidization level of the steel coil was 2.0-3.0 with a spheroidization rate of 95.8%, and the mechanical properties were tensile strength of 567-597 MPa and elongation of 31.5%-36.5%. The steel coil with a smooth surface and a total reduction of 0.95 mm when cold-rolled to 1.8 mm met the processing requirements.

[0088] Example 4: Sub-temperature spheroidizing annealing of 65Mn steel cold-rolled coils

[0089] 4.1 Implementation of Basic Information

[0090] The steel coil parameters are 65Mn steel cold-hardened coil, specifications 1.6×1200mm (thickness 1.6mm), outer diameter 1689mm, single coil weight 18.48t, a total of 4 coils stacked together. The material parameters are the same as in Example 3, and the steel coil state is cold-hardened coil. The equipment parameters are the same as in Example 2.

[0091] 4.2 Process Execution and Results

[0092] The process for determining the sub-temperature range in S2 is the same as in Example 3, i.e., 703.5℃ to 713.5℃. The standard process curve parameters generated in S3 are: heating rate 78℃ / h, homogenization time 16h, and hydrogen flow rate threshold 11.5m. 3 The cooling rate is 48℃ / h. During the S7 cooling stage, the hydrogen flow rate is adjusted to 17m / h when the furnace temperature is not lower than 300℃, based on historical data. 3 / h shortens the cooling time by 1.5h, and the operation logic of S4 to S6 and S8 is the same as in Example 2.

[0093] The results showed that the spheroidization level of the steel coil was 2.5-3.0 with a spheroidization rate of 98.5%, and the mechanical properties were tensile strength of 610-639 MPa and elongation of 25.5%-30.5%. No cracking was observed when the steel coil was cold-rolled to 0.6 mm with a total reduction of 1.0 mm.

[0094] 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 method for controlling the sub-temperature spheroidizing annealing process in a full-hydrogen bell-type annealing furnace, characterized in that, Includes the following steps: S1. The computer control system acquires the basic information of the steel coil to be processed. The basic information includes the material parameters, state parameters and specifications of the steel coil. The material parameters include the mass percentage of Si, Mn and Cr elements. The state parameters are pickled coil or cold-hardened coil. The specifications include thickness and outer diameter. The computer control system establishes the expected process reference based on the basic information. S2. The computer control system calculates the phase transformation point A of the steel coil based on the material parameters of the steel coil. c1 Temperature, according to A c1 The temperature range for sub-temperature spheroidizing annealing is determined to be A. c1 Reduce temperature by 20°C to A c1 Reduce by 10℃; S3. The computer control system generates a standard process curve containing heating parameters, soaking parameters, and cooling parameters based on the steel coil state parameters, sub-temperature spheroidizing annealing range, and expected process benchmark. The heating parameters include the heating rate and segmented temperature nodes, the soaking parameters include the holding time and hydrogen flow rate threshold, and the cooling parameters include the cooling rate and temperature switching nodes. S4. The computer control system sends control commands to the actuators of the all-hydrogen bell-type annealing furnace to start the process. At the same time, it activates the real-time monitoring module and continuously collects the cold and hot temperatures of the steel coil as actual operating data through distributed temperature sensors inside the furnace. It also collects hydrogen flow rate, furnace power and other preset operating parameters. S5. During the heating stage, the real-time monitoring module continuously detects the deviation between the actual operating data and the standard process curve. When it determines that the temperature difference between the hot and cold spots of the steel coil exceeds the preset first fault threshold (5°C), the automatic correction subroutine is triggered. The deviation is corrected by adjusting the power output of the corresponding heating area until the temperature difference is detected to return to within the first fault threshold. The occurrence time, correction process, and result of the deviation event where the temperature difference between the hot and cold spots exceeds the first fault threshold are recorded in the fault log. S6. When the cold point temperature of the steel coil reaches the lower limit of the sub-temperature spheroidizing annealing range, the computer control system determines that the process has entered the heat soaking and heat preservation stage, continuously checks whether the furnace temperature is stable within the sub-temperature spheroidizing annealing range, and checks whether the hydrogen flow rate matches the threshold in the heat soaking parameters. If any indicator does not match, an early warning signal is issued. S7. After the heat soaking and heat preservation stage, the computer control system controls the furnace to enter the cooling stage. The furnace temperature is controlled to drop from the sub-temperature range to below 200℃ according to the cooling parameters of the standard process curve. During this period, the real-time monitoring module continuously detects the matching between the cooling rate and the hydrogen flow rate. S8. Throughout the entire process, the computer control system continuously records furnace temperature, hydrogen flow rate, steel coil temperature difference, and other key performance indicators at each stage for fault detection. If any indicator deviates from the standard process curve by more than the second fault threshold, the system will detect such deviations. The second fault threshold includes furnace temperature deviations of ±3℃ and hydrogen flow rate deviations of ±2m. 3 / h, automatically executes the fault diagnosis module, and determines the time period corresponding to the deviation of the index from the standard process curve exceeding the second fault threshold by comparing with the historical fault database as the abnormal point, and generates a diagnostic report containing the abnormal cause speculation and correction suggestions. The abnormal cause speculation covers sensor drift, valve jamming and power fluctuation.

2. The method for controlling the sub-temperature spheroidizing annealing process in a full-hydrogen bell-type annealing furnace according to claim 1, characterized in that, In step S2, A c1 The formula for calculating temperature is: A c1 =723 + 25 × Si% - 7 × Mn% + 15 × Cr%, where Si%, Mn%, and Cr% are the mass percentages of the corresponding elements in the steel coil; the computer control system has a built-in material and phase transformation point calibration database, and automatically calls historical A values ​​of the same steel grade from the database after calculation. c1 The measured value is corrected for deviation, and after correction, A c1 The temperature error range is ≤ ±2℃, and the correction result serves as the core parameter for the expected process reference.

3. The method for controlling the sub-temperature spheroidizing annealing process in a full-hydrogen bell-type annealing furnace according to claim 1, characterized in that, The parameter setting rules for the standard process curve in step S3 are as follows: The computer control system calls the pre-stored steel coil status-parameter mapping table and automatically matches differentiated process parameters based on the steel coil status parameters and specifications. Among them, the heating rate set for pickled rolls is lower than the heating rate set for cold-hardened rolls, and the heat soaking time set for pickled rolls is longer than the heat soaking time set for cold-hardened rolls. The generated standard process curve serves as a benchmark for comparing actual operating data.

4. The method for controlling the sub-temperature spheroidizing annealing process in a full-hydrogen bell-type annealing furnace according to claim 1, characterized in that, In step S4, the distributed temperature sensor includes at least three sets of thermocouples arranged radially along the steel coil, which respectively collect the temperature at the center, half radius, and surface of the steel coil. After the computer control system performs filtering and noise reduction processing on the data from each set of sensors, the lowest value is determined as the cold point temperature and the highest value is determined as the hot point temperature. The processed data is used as the core input of the actual operation data.

5. The method for controlling the sub-temperature spheroidizing annealing process in a full-hydrogen bell-type annealing furnace according to claim 1, characterized in that, In step S5, the automatic correction subroutine uses a power regulation algorithm based on temperature difference feedback to achieve power regulation: the computer control system outputs the regulation amount according to the temperature difference value ΔT, where ΔT is the hot spot temperature minus the cooling point temperature.

6. The method for controlling the sub-temperature spheroidizing annealing process in a full-hydrogen bell-type annealing furnace according to claim 1, characterized in that, The verification process in the heat soaking and heat preservation stage of step S6 is as follows: The computer control system performs periodic verification by continuously collecting the temperature of hot and cold spots and the hydrogen flow rate three times. If the temperature difference is ≤5℃ and the hydrogen flow rate is within the threshold range, the verification is deemed to be qualified. If any data is not met, the automatic correction subroutine in step S5 is triggered to deal with excessive temperature difference, or an abnormal flow rate warning is issued to deal with excessive hydrogen flow rate. The verification result is updated to the fault log in real time.

7. The method for controlling the sub-temperature spheroidizing annealing process in a full-hydrogen bell-type annealing furnace according to claim 1, characterized in that, The hydrogen flow rate and temperature switching process in the cooling stage of step S7 is as follows: The real-time monitoring module controls the hydrogen flow rate based on the temperature switching nodes in the cooling parameters. When the furnace temperature is not lower than the temperature corresponding to the temperature switching node, the hydrogen flow rate is controlled to be within the first cooling flow rate range; when the furnace temperature is lower than the temperature corresponding to the temperature switching node, the hydrogen flow rate is controlled to switch to a second cooling flow rate range lower than the first cooling flow rate range. When the flow rate deviates from the corresponding range, the computer control system corrects it by adjusting the opening of the hydrogen inlet valve.

8. The method for controlling the sub-temperature spheroidizing annealing process in a full-hydrogen bell-type annealing furnace according to claim 1, characterized in that, The working process of the fault diagnosis module in step S8 is as follows: Anomaly detection: The difference between the real-time collected key performance indicators and the standard process curve is calculated. If the difference exceeds the second fault threshold for 30 seconds, it is marked as an anomaly. Cause speculation: The historical fault database is accessed, and the abnormal parameter characteristics are matched with the fault modes in the database to output the most probable possible cause. Report generation: Automatically generates diagnostic reports that include abnormal periods, parameter deviation values, suspected causes, correction steps, and prevention suggestions. It supports exporting via human-machine interface or remote push.

9. The method for controlling the sub-temperature spheroidizing annealing process in a full-hydrogen bell-type annealing furnace according to claim 1, characterized in that, In step S4, when the furnace temperature is detected to be in the range of 400°C to 450°C during the heating stage, the real-time monitoring module automatically increases the monitoring frequency of hydrogen flow rate; at the same time, it presets a higher reference value of hydrogen flow rate based on the level of oil contamination on the surface of the steel coil, and the real-time monitoring module includes the deviation between the actual flow rate and the reference value in the first fault threshold judgment range.

10. The method for controlling the sub-temperature spheroidizing annealing process in a full-hydrogen bell-type annealing furnace according to claim 1, characterized in that, The diagnostic report generated in step S8 also includes process parameter optimization suggestions. The computer control system analyzes the abnormal repair records of similar steel coils in the historical fault database and extracts the optimal correction parameters. The optimal correction parameters include the heating power adjustment range and the hydrogen flow rate compensation value. When the same type of steel coil enters the annealing process again, the optimal correction parameters are automatically preloaded into the standard process curve to achieve self-iterative optimization of process parameters.

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