A pickling-free high mechanical peeling 72-grade rod surface oxide skin regulation method

Abstract

The application belongs to the technical field of metal material processing and surface treatment, and particularly relates to a pickling-free high-mechanical-stripping 72-grade wire rod surface oxide scale regulation method, aiming to solve the environmental pollution and surface damage problems caused by the traditional pickling process of high-strength wire rod. The method constructs an FeO / Fe3O4 / Fe2O3 three-layer structure oxide scale on the surface of the wire rod in situ through synergistic control of the finishing temperature, the wire laying temperature, the oxygen partial pressure gradient of the cooling section, the three-stage forced cooling system and the coiling and stacking parameters, and forms a silicon-rich oxide transition zone at the interface between the FeO layer and the substrate; meanwhile, a closed-loop regulation mechanism based on online thickness measurement, phase composition analysis and stripping rate feedback is established to dynamically optimize the process parameters. The application realizes high-mechanical-stripping oxide scale (stripping rate up to standard), pickling-free green production, significantly improves the drawing surface quality and the die life, and has industrial applicability and economy.

Description

Technical Field

[0001] This application belongs to the field of metal material processing and surface treatment technology, specifically relating to a method for controlling the oxide scale on the surface of 72-grade wire rod with high mechanical peelability and no acid washing required. Background Technology

[0002] With the widespread application of high-strength steel wire rods in high-end metal products such as welding wire and prestressed steel strands, the control level of surface oxide scale directly affects the efficiency of subsequent drawing processes and the quality of finished products. Although traditional pickling processes can effectively remove oxide scale, they have drawbacks such as serious environmental pollution, high energy consumption, and easy induction of hydrogen embrittlement and surface damage, making it difficult to meet the dual requirements of green manufacturing and efficient production. Especially for grade 72 (tensile strength of approximately 720 MPa) high-strength wire rods, under the premise of eliminating pickling, it is necessary to simultaneously achieve high mechanical peelability, thickness uniformity, and precise control of interlayer bonding of the oxide scale to ensure that the oxide scale can be completely and controllably peeled off during large deformation drawing, avoiding surface defects caused by residue or fragmentation.

[0003] However, existing pickling-free technologies still have significant limitations in controlling the intrinsic structure of oxide scale. Some solutions control the total thickness of the oxide scale and the proportion of the FeO layer by optimizing the post-rolling cooling path, but these are mainly aimed at low-strength welding wire rods and do not consider the differences in oxidation behavior caused by the complex alloy composition, microstructure evolution, and thermo-oxygen interaction of 72-grade high-strength wire rods, resulting in a mismatch between the mechanical properties of the oxide scale and the deformation of the matrix. Another type of solution relies on online phosphating treatment during the coiling process to transform the oxide scale into a lubricating phosphating film. Although this can avoid pickling, it does not solve the problem of the compatibility between the oxide scale's own structure and peeling performance from the source, and it introduces additional chemical agents, increasing costs and deviating from the goal of a truly "treatment-free" green process. In addition, existing methods generally neglect the phase composition gradient, interfacial bonding state, and fracture behavior of the three-layer structure of the oxide scale (FeO / Fe3O4 / Fe2O3) under mechanical stress, making it difficult to achieve the ideal balance of complete coverage and easy peeling on high-strength wire rods.

[0004] Therefore, there is an urgent need for a method to control the surface oxide scale of 72-grade high-strength wire rod without pickling and with high mechanical peelability. This method involves precisely and collaboratively controlling the thermal history and oxygen partial pressure environment throughout the rolling, wire drawing, and cooling processes to directionally construct an oxide scale structure with optimized thickness ratio, weakened interlayer bonding force, and mechanical response matching the drawing deformation. This would enable clean, efficient, and stable industrial drawing production without relying on pickling or chemical conversion. Summary of the Invention

[0005] The purpose of this invention is to provide a method for controlling the oxide scale on the surface of 72-grade wire rod with high mechanical peelability and no acid washing required, which can effectively solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for controlling the oxide scale on the surface of grade 72 high-strength wire rod without pickling and with high mechanical peelability includes the following specific steps: Step 1: Controlling the finishing rolling temperature and wire drawing temperature range: The finishing rolling temperature of the grade 72 high-strength wire rod is set within a preset temperature range, and the wire drawing temperature is precisely controlled within another preset temperature range to ensure uniform austenite grain size and suppress proeutectoid ferrite precipitation, providing a uniform matrix structure for subsequent oxide scale formation; Step 2: Controlling the oxygen partial pressure environment in the cooling path before coiling: A multi-segment controllable atmosphere hood is set in the cooling section from wire drawing to coiling. By adjusting the mixing ratio of nitrogen and air, the oxygen partial pressure gradient in the cooling section is distributed from high to low. The initial oxygen partial pressure is controlled in a preset high-pressure range, and the final pressure drops to a preset low-pressure range to guide the directional growth of the outer Fe2O3 layer and the middle Fe3O4 layer of the oxide scale; Step 3: Implementing a staged forced cooling system: A three-stage jet cooling system is adopted in the cooling section before coiling. The cooling rate of the first stage is controlled at... The process involves three stages: a first stage with a preset high-speed range, a second stage with a preset medium-speed range, and a third stage with a further slow cooling to a preset low-speed range. This ensures the total thickness of the oxide scale remains stable within a predetermined range, with the FeO layer thickness proportion controlled within a predetermined range, the Fe3O4 layer proportion within another predetermined range, and the Fe2O3 layer proportion within yet another predetermined range. Step 4 optimizes the winding temperature and stacking cooling parameters: the winding temperature is set within a preset high-temperature range, and stacking cooling is performed immediately after winding. The cooling time is controlled within a predetermined time period, and the oxygen partial pressure in the cooling environment is maintained within a preset low-pressure range to weaken the interfacial bonding force between oxide scale layers and promote the initiation of microcracks along phase boundaries. Step 5 establishes an oxide scale structure-mechanical property feedback control mechanism: online data on oxide scale thickness, phase composition, and pull-out peeling rate are collected on the wire rod surface. A mapping model between the three-layer structure parameters of the oxide scale and its mechanical peeling performance is constructed, and the aforementioned process parameters are dynamically adjusted to achieve closed-loop control of the oxide scale's high mechanical peeling properties.

[0007] Preferably, in step 1, the difference between the finishing rolling temperature and the wire drawing temperature is controlled to not exceed a preset temperature difference threshold, so as to reduce the circumferential temperature fluctuation of the wire rod and ensure that the circumferential deviation of the oxide scale thickness is less than or equal to the preset thickness deviation threshold.

[0008] Preferably, in step 2, the multi-segment controllable atmosphere hood is divided into 4 independent gas control zones along the cooling path. The oxygen partial pressure in each zone decreases linearly or exponentially, and the length of the transition section between adjacent zones is not less than a predetermined distance, so as to avoid sudden changes in oxygen concentration that could cause local peeling of the oxide scale.

[0009] Preferably, in step 3, the gas medium for the three-stage jet cooling is air or oxygen-enriched air, the gas pressure is within a preset pressure range, the distance between the nozzle and the surface of the wire rod is a predetermined distance, and the jet angle is within a preset angle range, to ensure that the cooling uniformity and oxidation kinetics are matched in a coordinated manner.

[0010] Preferably, in step 4, the stack cooling insulation adopts a sealed insulation cover, which is filled with an inert gas protective layer to prevent secondary oxidation. After the insulation is completed, it is naturally cooled to room temperature at a rate not greater than the preset cooling rate to avoid the oxide scale cracking caused by thermal stress.

[0011] Preferably, in step 5, the oxide phase composition is determined in real time by an online laser-induced breakdown spectrometer, with a sampling frequency not lower than a preset frequency. The data is then input into a prediction model based on support vector regression after being denoised by Kalman filtering, and the model is updated once per coil of wire rod.

[0012] Preferably, the total thickness of the oxide scale is monitored online by an eddy current thickness gauge with a preset accuracy range. The thickness measurement data is linked to the cooling rate. When the thickness deviates from the target range by more than a preset thickness deviation threshold, the cooling rate of the third stage is automatically adjusted to within a preset adjustment range.

[0013] Preferably, the mechanical peeling performance is evaluated online using a simulated pull-out tester. The peeling rate is defined as the percentage of the area of ​​the oxide scale completely peeled off after pull-out to the total surface area. The target peeling rate is not lower than a preset high peeling rate threshold. When the measured peeling rate is lower than the preset low peeling rate threshold, the system automatically increases the upper limit of the second-stage cooling rate.

[0014] Preferably, the method is applicable to 72-grade high-strength wire rods with carbon content, silicon content, and manganese content respectively within their respective preset component ranges, whose tensile strength is within a preset strength range, and whose reduction of area is not lower than a preset plasticity index threshold.

[0015] Preferably, there is a silicon-rich oxide transition zone with a width of a predetermined micrometer scale at the interface between the FeO oxide layer and the substrate. This transition zone is formed by controlling the selective oxidation of silicon in the steel at high temperature, which can effectively reduce the interfacial bonding strength without affecting the mechanical properties of the substrate.

[0016] Compared with the prior art, the present invention has the following beneficial effects: To achieve a truly green, acid-free washing process This invention completely eliminates chemical treatments such as pickling or phosphating, and instead constructs an oxide scale with an ideal three-layer structure in situ on the surface of 72-grade high-strength wire rod solely through precise synergistic control of the thermal-oxygen environment. The total thickness of the oxide scale is controlled within a predetermined range, and the proportion of the FeO layer is within a predetermined range, ensuring both complete coverage and avoiding brittleness caused by excessive thickness. This structure can achieve a high mechanical peeling rate, not lower than a preset high peeling rate threshold, during subsequent drawing processes, completely eliminating environmental pollution, hydrogen embrittlement risks, and surface damage caused by pickling, and meeting the requirements of the national green manufacturing strategy.

[0017] Overcoming the challenge of adapting the mechanical properties of high-strength wire rod oxide scale Addressing the complex composition and unique hot deformation behavior of 72-grade high-strength wire rod alloys, this invention employs a coupled design of the entire process chain—precision rolling, wire drawing, cooling, and coiling—to precisely match the thickness ratio, phase interface state, and matrix deformation capacity of the three-layer oxide scale structure. Specifically, a controllable weak bonding region is introduced at the FeO / Fe3O4 interface, and a silicon-rich transition zone is formed at the FeO / matrix interface. This allows the oxide scale to fracture and peel off along a predetermined path under tensile stress, preventing fragmentation and significantly improving surface quality stability.

[0018] Achieving high-precision closed-loop control of oxide scale structure This invention integrates online thickness measurement, phase composition analysis, and peeling performance feedback systems to construct an integrated "sensing-decision-execution" control mechanism. By acquiring the physicochemical parameters of the oxide scale in real time using an eddy current thickness gauge and a laser-induced breakdown spectrometer, and combining this with a support vector regression model to dynamically optimize the cooling regime and atmosphere parameters, the process capability index Cpk of the key oxide scale indicator is made greater than or equal to a preset process capability threshold, far exceeding the fluctuation levels of existing open-loop control methods.

[0019] It combines industrial applicability and economy The equipment used in this invention is an upgraded version of the standard configuration of existing high-speed wire rod mills, requiring no additional large-scale chemical treatment facilities. Three-stage cooling and multi-section atmosphere control can be implemented through existing PLC systems, resulting in low modification costs. Industrial trials have proven that the method significantly reduces the wire breakage rate during the drawing of 72-grade wire rod, significantly extends die life, and effectively reduces overall production costs, making it worthy of large-scale promotion and application. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the overall technical solution architecture of the method for controlling the oxide scale on the surface of grade 72 wire rod with high mechanical peelability and no acid washing proposed in this invention; Figure 2 This is a schematic diagram of the core principle framework of the closed-loop feedback control mechanism of the three-layer structure of oxide scale and mechanical properties in this invention; Figure 3This is a logical flow diagram of the thermal-oxygen synergistic process control of the entire chain of finishing rolling-coiling-cooling-coiling in this invention; Figure 4 This is a schematic diagram of the multi-level interaction relationship and data flow between the multi-segment controllable atmosphere hood and the three-stage forced cooling system in this invention; Figure 5 This is a schematic diagram comparing the core principle of this invention with existing technologies in terms of the mechanical peeling rate and thickness uniformity of the oxide layer. Detailed Implementation Example 1

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0022] In the above-mentioned method for controlling the oxide scale on the surface of grade 72 high-mechanical-peelability wire rod without pickling, step 1, controlling the finishing rolling temperature and the wire drawing temperature range, specifically includes the following operational details: The finishing rolling temperature of the grade 72 high-strength wire rod is set within a preset temperature range of 850℃ to 890℃. This temperature range is monitored in real time by an infrared thermometer at the exit of the last stand of the finishing mill, with a measurement accuracy of ±2℃ and a sampling frequency of 10 times per second. Simultaneously, the wire drawing temperature is precisely controlled within another preset temperature range of 830℃ to 870℃. The wire drawing temperature is measured by a dual-wavelength colorimetric thermometer at the inlet of the wire drawing machine, which has better resistance to water vapor interference than single-wavelength temperature measuring equipment, ensuring stable output of the temperature signal even in a high-temperature water mist environment. The difference between the finishing rolling temperature and the wire drawing temperature is strictly controlled within a preset temperature difference threshold of no more than 20℃ to reduce circumferential temperature fluctuations in the wire rod. This temperature difference control is achieved by dynamically adjusting the reduction of the finishing mill stand and the rolling speed. When the infrared thermometer detects that the standard deviation of the temperature distribution across the wire rod cross-section exceeds 5°C, the system automatically triggers the roll cooling water flow fine-tuning module to target and cool the locally overheated areas. This ensures uniform austenite grain size and suppresses proeutectoid ferrite precipitation, providing a uniform matrix structure for subsequent oxide scale formation. Furthermore, the circumferential deviation of the oxide scale thickness is controlled to a preset thickness deviation threshold of less than or equal to 1.5 μm. This deviation is obtained by simultaneously collecting data and calculating the range using four eddy current thickness probes arranged along the circumference of the wire rod.

[0023] Specifically, step 2, regulating the oxygen partial pressure environment in the cooling path before winding, is achieved by setting up a multi-section controllable atmosphere hood in the cooling section from after spinning to before winding. This atmosphere hood divides the cooling path into four independent control zones: the first, second, third, and fourth control zones, each 15 meters long. Adjacent zones are separated by transition sections of at least 2 meters to prevent sudden changes in oxygen concentration that could cause localized oxide scale peeling. Each control zone is equipped with an independent gas mixing unit, which uses a mass flow controller (MFC) to control the input flow rates of nitrogen and compressed air. The nitrogen purity is no less than 99.999%, and the compressed air undergoes multi-stage filtration to remove oil and moisture. The initial oxygen partial pressure (at the inlet of the first control zone) is controlled within a preset high-pressure range of 15 kPa to 18 kPa, and the final oxygen partial pressure (at the outlet of the fourth control zone) drops to a preset low-pressure range of 2 kPa to 5 kPa. The oxygen partial pressure in each zone decreases exponentially, as expressed mathematically:

[0024] in, This represents the oxygen partial pressure at a distance of x meters from the starting point of the first gas control zone. This is the initial oxygen partial pressure reference value. The attenuation coefficient, x, ranges from 0 to 60 meters (covering all four gas control zones and the transition section). This exponential function is dynamically corrected by the PLC system based on the measured surface temperature of the wire rod. When the wire rod surface temperature exceeds 800℃, the k value automatically decreases by 0.02 to slow the rate of oxygen partial pressure decrease and ensure sufficient growth of the Fe2O3 outer layer. When the temperature is below 750℃, the k value increases by 0.03 to accelerate entry into a low-oxygen environment and suppress excessive oxidation. Each gas control zone is equipped with an oxygen partial pressure sensor array, with three electrochemical oxygen sensors per zone. The sampling frequency is once per second, and the data is filtered by moving average and used to adjust the MFC output in a closed loop, ensuring that the oxygen partial pressure fluctuation does not exceed ±0.5 kPa. This design effectively guides the directional growth of the outer Fe2O3 layer and the middle Fe3O4 layer of the oxide scale, forming a dense three-layer structure with a clear interface.

[0025] In the above method, step 3 implements a phased forced cooling system, employing three-stage jet cooling in the pre-winding cooling section. The first stage cooling rate is controlled within a preset high-speed range of 15℃ / s to 20℃ / s, with an action time of 3 to 5 seconds, corresponding to a wire rod temperature drop from 830℃ to 720℃. The second stage cooling rate decreases to a preset medium-speed range of 8℃ / s to 12℃ / s, with an action time of 6 to 8 seconds, resulting in a temperature drop from 720℃ to 600℃. The third stage further slows the cooling to a preset low-speed range of 2℃ / s to 4℃ / s, with an action time of 10 to 15 seconds, resulting in a temperature drop from 600℃ to 500℃. The gas medium for the three-stage cooling is air or oxygen-enriched air (oxygen volume fraction of 25% to 30%), with a gas pressure within a preset pressure range of 0.3 MPa to 0.6 MPa, a nozzle distance from the wire rod surface within a predetermined distance of 150 mm to 200 mm, and a jet angle within a preset angle range of 60° to 75°. The nozzles are arranged in a ring array, with 12 fan-shaped nozzles evenly distributed along the circumference of the wire rod in each stage to ensure uniform cooling. The cooling rate is fed back in real time by three sets of infrared thermometers installed at the inlet, middle, and outlet of the cooling section. Each set contains four temperature measurement points, and the instantaneous cooling rate is obtained by fitting the slope of the temperature-time curve using the least squares method. When the total oxide scale thickness deviates from the target range (8μm to 12μm) by more than a preset thickness deviation threshold of ±1μm, the system automatically adjusts the cooling rate of the third stage within a preset adjustment range of ±0.5℃ / s. Through this system, the total oxide scale thickness is stabilized within the predetermined thickness range of 8μm to 12μm, with the FeO layer thickness ratio controlled within a predetermined proportion range of 60% to 70%, the Fe3O4 layer ratio within another predetermined proportion range of 20% to 30%, and the Fe2O3 layer ratio within yet another predetermined proportion range of 5% to 10%. The thickness ratio of each layer was calibrated by combining offline X-ray diffraction (XRD) with cross-sectional scanning electron microscopy (SEM) image analysis, and a mapping relationship with the online eddy current thickness measurement signal was established for process control.

[0026] Specifically, in step 4, the winding temperature and stacking cooling parameters are optimized. The winding temperature is set within a preset high-temperature range of 500℃ to 550℃, monitored by an infrared thermometer at the winding drum inlet. When the temperature exceeds this range, the system automatically adjusts the third-stage cooling rate in reverse. Stacking cooling is performed immediately after winding, with the cooling time controlled within a predetermined period of 30 to 60 minutes. The oxygen partial pressure in the cooling environment is maintained within a preset low-pressure range of 1 kPa to 3 kPa. Stacking cooling uses a sealed insulation cover, which is constructed of double-layered stainless steel plates with an interlayer filled with aluminum silicate fiber insulation material. Argon gas is used as an inert gas protective layer, with a flow rate of 5 Nm³ / h, maintaining a positive pressure of 0.5 kPa to prevent external air infiltration. After the cooling is completed, the wire rod is naturally cooled to room temperature at a preset cooling rate of no more than 3℃ / min. This cooling rate is achieved through PID control of the opening of the exhaust valve at the top of the insulation cover, preventing oxide scale cracking due to thermal stress. During this process, the interfacial bonding between the oxide layers is weakened, especially at the FeO / Fe3O4 interface. The accumulation of lattice mismatch stress caused by slow cooling promotes the initiation of microcracks along the phase boundaries, providing a fracture path for subsequent mechanical peeling. Simultaneously, a silicon-rich oxide transition zone with a width of 1 μm to 3 μm is formed at the interface between the FeO layer of the oxide layer and the substrate. This transition zone is formed by the selective oxidation of silicon (0.15% to 0.35% content) in the steel at high temperatures. Its main components are a mixture of SiO2 and Fe2SiO4, which effectively reduces the interfacial bonding strength without affecting the mechanical properties of the substrate.

[0027] In the above method, step 5 establishes a feedback control mechanism for the oxide scale structure and mechanical properties. This is achieved through closed-loop control by online acquisition of data on the oxide scale thickness, phase composition, and pull-out peeling rate on the wire rod surface. The total oxide scale thickness is monitored online using an eddy current thickness gauge installed at the outlet of the cooling section before winding. The gauge has a preset accuracy range of ±0.2 μm and a sampling frequency of 20 times per second. The data is then filtered using a moving median and used for real-time evaluation. The oxide phase composition was determined in real time using an online laser-induced breakdown spectroscopy (LIBS) instrument. This instrument emits a pulsed laser with a wavelength of 1064 nm, a single pulse energy of 50 mJ, a focused spot diameter of 100 μm, and a sampling frequency of no less than 5 times per second. Each sampling collects 10 pulse signals, which are then superimposed and averaged to improve the signal-to-noise ratio. After the raw spectral data is denoised by Kalman filtering, the intensity ratios of characteristic spectral lines such as Fe I 371.99 nm, Fe II 238.20 nm, and Si I 288.16 nm are extracted and input into a prediction model based on support vector regression (SVR). This model outputs the thickness ratio of the three-layer structure, and the input variables include 12-dimensional process parameters such as oxygen partial pressure, cooling rate, and temperature history. The model is updated once per coil of wire rod, meaning that after each coil of wire rod is produced, the SVR kernel function parameters are learned and corrected online using the offline SEM validation data of that coil. Mechanical peeling performance was evaluated online using a simulated pull-out testing machine installed at the end of the production line. The machine simulated pull-out of the first 5 meters of each coil of wire at a pull-out speed of 2 m / s and a surface reduction rate of 15%. The peeling rate was defined as the percentage of the total surface area where the oxide scale was completely peeled off after pull-out. Images of the surface after pull-out were captured using a high-resolution industrial camera (5 μm / pixel resolution), and the percentage of the peeled area was calculated using an image segmentation algorithm. A preset high peeling rate threshold of 90% was set. When the measured peeling rate fell below the preset low peeling rate threshold of 85%, the system automatically increased the upper limit of the second-stage cooling rate by 0.5℃ / s and simultaneously fine-tuned the oxygen partial pressure in the second gas control zone by 1 kPa to enhance Fe3O4 layer formation and optimize the weak bonding areas between layers. This feedback mechanism ensured that the process capability index Cpk, a key indicator of oxide scale, was greater than or equal to a preset process capability threshold of 1.67.

[0028] To illustrate the implementation effect of the present invention, the following application example is constructed: A steel plant produces 72-grade high-strength wire rod with a carbon content of 0.70%, a silicon content of 0.25%, and a manganese content of 0.50%, with a tensile strength of 735 MPa and a reduction of area of ​​42%. The method of this invention is performed as follows: In step 1, the finishing rolling temperature is set to 870℃, the wire drawing temperature is controlled at 855℃, and the temperature difference is 15℃, meeting the requirement of not exceeding 20℃; In step 2, the oxygen partial pressure of the four gas control zones of the multi-section controllable atmosphere hood is set sequentially to 17 kPa, 12 kPa, 7 kPa, and 3 kPa, decreasing exponentially, and the transition section length is 2.5 meters; In step 3, the three-stage cooling rates are set to 18℃ / s, 10℃ / s, and 3℃ / s, respectively, the gas medium is air, the pressure is 0.5 MPa, the nozzle distance from the wire rod is 180 mm, and the spray angle is 70°; In step 4, the coiling temperature is 520℃, the coil is stacked and kept at a low temperature for 45 minutes, the insulation hood is filled with argon, and the oxygen partial pressure is maintained at 2 kPa. The oxide layer was then cooled to room temperature at a rate of 2.5℃ / min. In step 5, the total oxide layer thickness was measured to be 10.2μm using an eddy current thickness gauge. LIBS analysis showed that the FeO layer accounted for 65%, the Fe3O4 layer for 25%, and the Fe2O3 layer for 10%. The peeling rate was 92.5% as measured by the simulated drawing test. Detection revealed a 2.1μm wide silicon-rich oxide transition band at the FeO / matrix interface, and a continuous microcrack network was observed at the FeO / Fe3O4 interface. No acid pickling was performed on the wire rod during subsequent actual drawing, reducing the wire breakage rate from 0.8% in the traditional process to 0.2%, and extending the die life by 35%.

[0029] Another example was constructed: for wire rods with slightly different compositions (C: 0.72%, Si: 0.30%, Mn: 0.48%), the initial peeling rate during trial production was only 83%. The system automatically triggered a feedback mechanism, increasing the second-stage cooling rate from 9℃ / s to 9.5℃ / s and the oxygen partial pressure in the second gas control zone from 11 kPa to 12 kPa. The peeling rate of the next coil increased to 89%. After another model update, the peeling rate of the third coil reached 91.3%, achieving stable compliance. This process demonstrates the effectiveness of the closed-loop control mechanism. Example 2

[0030] In another embodiment, the three-stage jet cooling gas medium in step 3 uses oxygen-enriched air with an oxygen volume fraction of 28% to enhance the oxidation kinetics in the high-temperature section. In this case, the upper limit of the first-stage cooling rate is adjusted to 18°C / s to avoid excessively rapid FeO layer growth leading to increased brittleness. Simultaneously, the oxygen partial pressure decrease function in step 2 is changed to a linear function.

[0031] in , This method is suitable for applications with stricter requirements on Fe2O3 layer thickness. Furthermore, in step 5, the LIBS sampling frequency is increased to 8 times per second, the SVR model input dimension is expanded to 15 dimensions, and online measurements of the wire rod surface roughness (obtained by laser triangulation) are added to compensate for the influence of surface morphology on oxidation behavior. When producing wire rods for prestressed steel strands with high surface quality requirements, this method achieves a peeling rate stability Cpk of 1.82, which is superior to Example 1. Example 3

[0032] In another embodiment, for large-diameter wire rods (12.5 mm in diameter), the difference between the finishing rolling temperature and the wire drawing temperature in step 1 is controlled within 15°C to cope with a larger cross-sectional temperature difference. In step 3, the three-stage cooling times are extended to 6 seconds, 10 seconds, and 20 seconds respectively, and a staggered arrangement of double-row nozzles is adopted to ensure coordinated cooling of the core and surface. In step 4, the heat preservation time is extended to 70 minutes to fully release internal stress. In the feedback mechanism, the peeling rate assessment uses a two-pass simulated drawing process, which is closer to actual working conditions. This solution has been successfully applied to 72-grade wire rods for bridge cables, with the circumferential thickness deviation of the oxide scale controlled within 1.2 μm and the peeling rate stabilized above 90%.

[0033] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for controlling the oxide scale on the surface of grade 72 wire rod with high mechanical peelability and no acid washing required, characterized in that, Includes the following steps: The finishing rolling temperature and wire drawing temperature ranges are controlled. The finishing rolling temperature of the 72-grade high-strength wire rod is set within a preset temperature range, and the wire drawing temperature is precisely controlled within another preset temperature range to ensure uniform austenite grain size and suppress proeutectoid ferrite precipitation. The oxygen partial pressure environment in the cooling path before coiling is adjusted. A multi-section controllable atmosphere hood is set in the cooling section from after wire drawing to before coiling. By adjusting the mixing ratio of nitrogen and air, the oxygen partial pressure gradient in the cooling section is distributed from high to low. The initial oxygen partial pressure is controlled in a preset high-pressure range, and then drops to a preset low-pressure range at the end. In order to guide the directional growth of Fe2O3 on the outer layer of the oxide scale and Fe3O4 in the middle layer; a phased forced cooling system is implemented, and a three-stage jet cooling is adopted in the cooling section before winding. The cooling rate of the first stage is controlled in a preset high-speed range, the second stage is reduced to a preset medium-speed range, and the third stage is further slowed down to a preset low-speed range, so that the total thickness of the oxide scale is stabilized within a predetermined thickness range, wherein the proportion of FeO layer thickness is controlled in a predetermined proportion range, the proportion of Fe3O4 layer is in another predetermined proportion range, and the proportion of Fe2O3 layer is in yet another predetermined proportion range; Optimize the winding temperature and stacking cooling insulation parameters. Set the winding temperature in the preset high temperature range and immediately perform stacking cooling insulation treatment after winding. Control the insulation time within the predetermined time period and maintain the oxygen partial pressure in the insulation environment in the preset low pressure range to weaken the interfacial bonding force between oxide scale layers and promote the initiation of microcracks along the phase boundary. A feedback control mechanism for oxide scale structure and mechanical properties was established. Data on oxide scale thickness, phase composition, and pull-out peeling rate on the surface of wire rod were collected online. A mapping model between the three-layer structure parameters of oxide scale and mechanical peeling performance was constructed. The aforementioned process parameters were dynamically adjusted to achieve closed-loop control of high mechanical peeling performance of oxide scale.

2. The method for controlling the oxide scale on the surface of grade 72 wire rod with high mechanical peelability and no acid washing as described in claim 1, characterized in that, The difference between the finishing rolling temperature and the wire drawing temperature shall not exceed the preset temperature difference threshold, so as to reduce the circumferential temperature fluctuation of the wire rod and ensure that the circumferential deviation of the oxide scale thickness is less than or equal to the preset thickness deviation threshold.

3. The method for controlling the oxide scale on the surface of grade 72 wire rod with high mechanical peelability and no acid washing as described in claim 1, characterized in that, The multi-segment controllable atmosphere hood is divided into four independent gas control zones along the cooling path. The oxygen partial pressure in each zone decreases according to an exponential or linear function. There is a transition section with a length not less than a predetermined distance between adjacent zones to avoid sudden changes in oxygen concentration that could cause localized peeling of the oxide scale.

4. The method for controlling the oxide scale on the surface of grade 72 wire rod with high mechanical peelability and no acid washing as described in claim 1, characterized in that, The gas medium for the three-stage jet cooling is air or oxygen-enriched air, the gas pressure is within a preset pressure range, the distance between the nozzle and the surface of the wire rod is a predetermined distance, the jet angle is within a preset angle range, and the nozzles are evenly distributed along the circumference of the wire rod to ensure uniform cooling.

5. The method for controlling the oxide scale on the surface of grade 72 wire rod with high mechanical peelability and no acid washing as described in claim 1, characterized in that, The stack cooling insulation adopts a sealed insulation cover, which is filled with an inert gas protective layer to prevent secondary oxidation. After the insulation is completed, it is naturally cooled to room temperature at a rate not greater than the preset cooling rate to avoid thermal stress causing oxide scale cracking.

6. The method for controlling the oxide scale on the surface of grade 72 wire rod with high mechanical peelability and no acid washing as described in claim 1, characterized in that, The composition of the oxide phase is determined in real time by an online laser-induced breakdown spectrometer with a sampling frequency not lower than a preset frequency. The original spectral data is input into a prediction model based on support vector regression after being denoised by Kalman filtering. The model is updated once per coil of wire.

7. The method for controlling the oxide scale on the surface of grade 72 wire rod with high mechanical peelability and no acid washing as described in claim 1, characterized in that, The total thickness of the oxide scale is monitored online by an eddy current thickness gauge. The measurement accuracy is within the preset accuracy range. The thickness measurement data is linked to the cooling rate. When the thickness deviates from the target range by more than the preset thickness deviation threshold, the cooling rate of the third stage is automatically adjusted to within the preset adjustment range.

8. The method for controlling the oxide scale on the surface of grade 72 wire rod with high mechanical peelability and no acid washing as described in claim 1, characterized in that, The mechanical peeling performance is evaluated online using a simulated pull-out tester. The peeling rate is defined as the percentage of the area of ​​the oxide scale completely peeled off after pull-out to the total surface area. When the measured peeling rate is lower than the preset low peeling rate threshold, the system automatically increases the upper limit of the second-stage cooling rate and simultaneously fine-tunes the oxygen partial pressure in the corresponding gas control zone.

9. The method for controlling the oxide scale on the surface of grade 72 wire rod with high mechanical peelability and no acid washing as described in claim 1, characterized in that, The method is applicable to 72-grade high-strength wire rods with carbon content, silicon content, and manganese content respectively within their respective preset component ranges, whose tensile strength is within a preset strength range, and whose reduction of area is not lower than a preset plasticity index threshold.

10. The method for controlling the oxide scale on the surface of grade 72 wire rod with high mechanical peelability and no acid washing as described in claim 1, characterized in that, At the interface between the FeO oxide layer and the substrate, there is a silicon-rich oxide transition zone with a predetermined width on the micrometer scale. This transition zone is formed by selectively oxidizing silicon in the steel at high temperature, and its main components are a mixture of SiO2 and Fe2SiO4.

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