Method for on-line detection and compensation of local decarburization of high-strength spring steel strip

Abstract

The application provides an online detection and compensation method for local decarburization of high-strength spring steel strips, which comprises the following steps: monitoring oxygen concentration in real time by arranging an oxygen content sensor in a continuous annealing furnace and marking potential decarburization risk sections; scanning the steel strips in the risk sections by infrared thermal imaging to generate a carbon distribution map and locate decarburization zones; performing pulse laser heating on the decarburization zones and introducing a methane-argon mixed gas to realize in-situ carburization; and finally eliminating local thermal stress by high-frequency induction heating. The method realizes dynamic early warning of decarburization risk, accurate positioning of defects, local efficient carburization and stress homogenization control, and significantly improves the surface quality and fatigue performance of the steel strips.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high-strength spring steel strip production, and particularly to an online detection and compensation method for local decarburization of high-strength spring steel strip. BACKGROUND

[0002] In the steel manufacturing industry, high-strength spring steel strips (such as 60Si2MnA) are widely used in key components such as automobile suspensions and mechanical valves due to their excellent elasticity and fatigue performance. The production of such steel strips usually requires heat treatment processes such as continuous annealing, quenching, and tempering to ensure that their mechanical properties meet the requirements. However, during continuous annealing, decarburization easily occurs on the surface of the steel strip, especially when it stays in the high-temperature zone (800-900°C) for a long time. The carbon elements on the surface of the steel strip will react with residual oxygen or water vapor in the furnace, resulting in a decrease in the carbon content of the surface layer and the formation of a decarburized layer. The presence of the decarburized layer not only reduces the surface hardness and wear resistance of the steel strip, but also causes micro-cracks in the subsequent quenching process due to the difference in organizational transformation between the surface layer and the core, which seriously affects the fatigue life and safety of the spring.

[0003] Currently, the industry generally uses protective atmosphere annealing (such as nitrogen or hydrogen-nitrogen mixed gas) to reduce the risk of decarburization, and combines sampling metallographic detection or hardness testing to monitor the decarburization situation. However, these methods still have obvious defects:

[0004] Firstly, although protective atmosphere annealing can reduce the overall decarburization probability, local fluctuations in the furnace atmosphere (such as transient increase in residual oxygen content) may still cause micro-area intermittent decarburization in some sections of the steel strip during continuous production. Traditional sampling detection cannot cover the entire surface of the steel strip, resulting in delayed detection of problems.

[0005] Secondly, even if decarburization is detected, existing compensation methods (such as overall secondary annealing or carburizing) are often inefficient and may affect other properties of the steel strip due to over-treatment.

[0006] Therefore, how to achieve accurate detection and efficient repair of local decarburization has become a key problem in the production of spring steel strips. SUMMARY

[0007] To overcome the defects in the prior art that local atmosphere fluctuations in the continuous annealing furnace make it difficult to detect and accurately repair the decarburization of the steel strip in real time, the present application provides an online detection and compensation method for local decarburization of high-strength spring steel strip, which can realize dynamic early warning of decarburization risk, accurate positioning of defect areas, local efficient carbon compensation, and stress uniformization control, thereby significantly improving the surface quality and fatigue performance of the spring steel strip.

[0008] To solve the above technical problems, the application provides a high-strength spring steel strip local decarburization online detection and compensation method, which comprises the following steps:

[0009] A plurality of oxygen content sensors are arranged in the soaking section and the slow cooling section of the continuous annealing furnace to monitor the oxygen concentration in each region of the furnace in real time; when the oxygen concentration of any one of the oxygen content sensors exceeds a threshold value, the position coordinates of the steel strip in the region are recorded, and the region is marked as a potential decarburization risk section;

[0010] The surface of the steel strip located in the potential decarburization risk section after being discharged from the furnace is scanned by infrared thermal imaging, and a surface carbon distribution map is generated by utilizing the difference in thermal radiation between the decarburization region and the non-decarburization region to locate the position and range of the actual decarburization region;

[0011] For the identified decarburization region, a pulse laser beam is used to locally heat to the austenitizing temperature, and a methane-argon mixed gas is introduced to cause an in-situ carburization reaction in the decarburization region, so that the surface carbon content is restored to the level of the steel strip matrix;

[0012] The carburized steel strip is subjected to overall rapid preheating by a high-frequency induction heating device to eliminate the local thermal stress caused by laser carburization.

[0013] In an embodiment of the application, the oxygen content sensors are arranged as follows:

[0014] The arrangement interval of the plurality of oxygen content sensors is determined according to the length of each section of the annealing furnace, and the interval between the two adjacent oxygen content sensors arranged in the soaking section is not more than 1 / 5 of the length of the section, and the interval between the two adjacent oxygen content sensors arranged in the slow cooling section is not more than 1 / 3 of the length of the section;

[0015] The detection range of each oxygen content sensor covers the full width of the steel strip in the width direction, and at least three detection points are arranged in the width direction;

[0016] When the oxygen concentration of two or more adjacent detection points in the width direction is detected to exceed the threshold value at the same time, the marked region is extended to a region 1 / 8 interval upstream and downstream of the detection range of the oxygen content sensor, and the steel strip at the corresponding position of the region is marked as a potential decarburization risk section.

[0017] In an embodiment of the application, after the potential decarburization risk section is determined, a color-coded laser marker is used to mark the starting position of the risk section on the edge of the steel strip.

[0018] In an embodiment of the application, the specific implementation of the infrared thermal imaging scanning includes:

[0019] A plurality of infrared thermal imaging arrays are arranged in the running direction of the steel strip, each array comprising three thermal imagers at different angles, which are arranged to scan synchronously from directly above the steel strip, 45 degrees to the left side and 45 degrees to the right side;

[0020] The data collected by each thermal imager is processed in three dimensions to generate a surface carbon distribution map, and the surface carbon distribution map is used to determine the thermal radiation difference;

[0021] A corresponding relationship model between the thermal radiation difference and the decarburization depth is established, when the thermal radiation difference is detected to exceed a set threshold, the decarburization area is marked, the area and depth of the decarburization area are calculated, and the decarburization grade is determined;

[0022] Edge recognition and contour extraction are performed on the marked decarburization area to generate an accurate decarburization area contour map.

[0023] In an embodiment of the present application, the methane-argon gas mixture ratio is determined according to the decarburization grade, including the following steps:

[0024] The decarburization grade is divided into three grades, including: mild decarburization: decarburization depth ≤ 0.1mm, moderate decarburization: 0.1mm < decarburization depth ≤ 0.15mm, and severe decarburization: decarburization depth > 0.15mm;

[0025] For different decarburization grades, the methane-argon gas mixture ratio is adjusted: for mild decarburization, the methane-argon gas mixture ratio is 1:9, for moderate decarburization, the methane-argon gas mixture ratio is 1:4, and for severe decarburization, the methane-argon gas mixture ratio is 1:2.

[0026] In an embodiment of the present application, the laser spot diameter and power density are adjusted according to the area and depth of the decarburization area, wherein:

[0027] For a decarburization area with an area less than 10mm², a small spot high power density mode with a diameter of 1-2mm is used;

[0028] For a decarburization area with an area of 10-50mm², a medium spot scanning mode with a diameter of 3-5mm is used;

[0029] For a decarburization area with an area greater than 50mm², a multi-spot collaborative processing mode is used.

[0030] In an embodiment of the present application, the temperature of the pulsed laser beam is set to be 50-80℃ above the austenitizing temperature, the real-time temperature during the heating of the steel strip is monitored, the flow rate of the methane-argon gas mixture is adjusted according to the real-time temperature ratio of the steel strip, and when the steel strip is heated to the austenitizing temperature, the flow rate of the methane-argon gas mixture reaches a maximum value.

[0031] In an embodiment of the present application, during the in-situ carburization reaction in the decarburization area, an online spectrum analyzer is used to monitor the surface carbon concentration change, when the carbon concentration is detected to reach 95% of the matrix level, the holding stage is entered, and the local heating by the pulsed laser beam and the supply of the methane-argon gas mixture are stopped;

[0032] The holding time is calculated according to the decarburization area at 5s / mm2, and the surface carbon concentration conversion value is continuously detected until the surface carbon content reaches the level of the steel strip substrate.

[0033] In one embodiment of the present application, when the supply of the methane-argon mixed gas is stopped, the supply is stopped in a gradual manner of reducing the gas flow, and the proportion of the methane-argon mixed gas is gradually adjusted, and the argon protection is maintained until the temperature is reduced to a safe range.

[0034] In one embodiment of the present application, the specific process steps of overall rapid preheating by the high-frequency induction heating device include:

[0035] A plurality of groups of induction coils are arranged in the width direction of the steel strip, the power of each group of coils is independently adjustable, the transverse temperature distribution of the steel strip is monitored in real time by an infrared thermal imager, and when the detected temperature deviation exceeds ±15℃, the power of the corresponding position coil is adjusted.

[0036] In the initial stage, the temperature is raised at a rate of 30-50℃ / s to 300-350℃, in the intermediate stage, the temperature is raised at a rate of 15-20℃ / s to 450-500℃, and in the final stage, the temperature is raised at a rate of 5-10℃ / s to the target temperature of 550-600℃.

[0037] The target temperature is maintained for 30-60 seconds to fully release the thermal stress, and the stress change is monitored in real time by a laser ultrasonic detection device, when the residual stress is reduced below a safe threshold, the cooling process is entered, and in the process of cooling, the steel strip is stretched in a tension state.

[0038] The above technical method of the present application has the following advantages compared with the prior art:

[0039] The core of the online detection and compensation method for local decarburization of the high-strength spring steel strip is to organically combine dynamic monitoring, infrared imaging, laser recarburization and high-frequency induction homogenization processes to form a closed loop control.

[0040] Firstly, by arranging oxygen content sensors in the soaking and slow cooling sections of the continuous annealing furnace, the furnace atmosphere fluctuations are captured in real time, and the potential decarburization risk section is marked to provide accurate positioning basis for subsequent detection, which solves the randomness and hysteresis problems of traditional sampling detection. Subsequently, the steel strip surface in the risk section is scanned using infrared thermal imaging technology, and based on the thermal radiation difference between the decarburization zone (mainly ferrite) and the non-decarburization zone (mainly pearlite), a carbon distribution map is quickly generated to realize non-destructive positioning of the decarburization micro-zone. Compared with destructive metallographic detection, this method not only has higher efficiency, but also can cover the full length of the steel strip to avoid missed detection. In the repair link, the traditional whole carburizing or secondary annealing is abandoned, and instead, a pulsed laser beam is used to locally heat the decarburization zone, while a mixture of methane and argon gas is introduced to allow carbon elements to infiltrate the surface layer of the steel strip in situ. The high energy density of the laser ensures the carburizing efficiency, and the local treatment avoids the energy waste and organizational performance fluctuations caused by overall heating. Finally, the carbon compensation zone is preheated quickly by high-frequency induction heating to homogenize the thermal stress introduced by laser treatment and prevent cracks caused by stress concentration during subsequent quenching. The synergistic effect of these steps not only realizes real-time discovery and accurate repair of decarburization defects, but also significantly improves the overall quality stability of the steel strip.

[0041] From the technical principle, the beneficial effects of this method mainly reflect in three aspects: first, through the linkage of oxygen sensors and infrared imaging, early range warning and accurate positioning of decarburization risk are realized, avoiding the judgment blind area of traditional methods; second, the local treatment method of laser carburizing takes into account efficiency and energy consumption, only the defect area is repaired without affecting the performance of the steel strip; third, the high-frequency induction homogenization process eliminates local thermal stress to ensure the process stability of subsequent quenching. These improvements work together to systematically solve the decarburization problem of high-strength spring steel strips, thereby improving the fatigue life and reliability of the final product and meeting the demanding needs of high-end application scenarios. BRIEF DESCRIPTION OF DRAWINGS

[0042] In order to make the content of the present application more easily understood, the following further detailed description of the present application is made according to specific embodiments of the present application and in conjunction with the accompanying drawings, in which:

[0043] Figure 1 is a step flow chart of the online detection and compensation method for local decarburization of high-strength spring steel strips of the present application;

[0044] Figure 2 is a step flow chart of the arrangement method of the oxygen content sensor of the present application;

[0045] Figure 3 is a step flow chart of the specific implementation of the infrared thermal imaging scanning of the present application;

[0046] Figure 4is a surface carbon distribution map obtained by three-dimensional fusion processing of the present application;

[0047] Figure 5 is a step flow chart of the present application for determining the proportion of methane-argon gas mixture according to the decarburization grade;

[0048] Figure 6 is a step flow chart of the present application for adjusting the laser spot diameter and power density according to the area and depth of the decarburization zone;

[0049] Figure 7 is a step flow chart of the specific process of the present application for overall rapid preheating by a high-frequency induction heating device. DETAILED DESCRIPTION

[0050] The present application will be further described below in conjunction with the drawings and specific embodiments, so that those skilled in the art can better understand the present application and implement it, but the embodiments are not limiting to the present application.

[0051] Referring to Figure 1 The online detection and compensation method of the present application for local decarburization of high-strength spring steel strip includes the following steps:

[0052] A plurality of oxygen content sensors are arranged in the soaking and slow cooling sections of the continuous annealing furnace to monitor the oxygen concentration in each region of the furnace in real time. When the oxygen concentration of any one of the oxygen content sensors exceeds the threshold value, the coordinates of the steel strip at that region are recorded and marked as a potential decarburization risk section.

[0053] It should be noted that because the decarburization of the steel strip is mainly caused by the oxidation reaction of carbon elements with oxygen in a high-temperature environment, when the oxygen concentration exceeds the threshold value, it indicates that there is an oxidizing atmosphere in that region, which will accelerate the loss of carbon elements on the surface of the steel strip. Therefore, the coordinates of the steel strip at that position need to be recorded and marked as a potential decarburization risk section. This real-time monitoring method can provide an early warning of decarburization risk and provide a basis for subsequent targeted detection, avoiding the randomness and lagging problems of traditional sampling detection. At the same time, determining the decarburization zone of the steel strip can reduce the decarburization range of the steel strip and reduce the subsequent workload.

[0054] Specifically, the threshold value of oxygen concentration is essentially based on the coupling relationship between material science and heat treatment process. For high-strength spring steel strip (such as 60Si2MnA), the critical decarburization oxygen concentration threshold value is determined by a process database established through experiments. Specifically, in a laboratory environment simulating the actual working conditions of the annealing furnace, the variation of the decarburization depth of the steel strip surface with time (1-30 minutes) under different oxygen concentrations (5-500 ppm gradient) is tested, and the critical oxygen concentration value that leads to significant decarburization (>0.05 mm) is determined by combining metallographic analysis and microhardness testing.

[0055] The threshold value is not a fixed value, but is dynamically associated with three key parameters: first, the current annealing furnace temperature zone of the steel strip (the holding segment threshold value is set to be 20-30% lower than the slow cooling segment), second, the running speed of the steel strip (the threshold value is lowered by 5% for every 10 m / min increase in speed), and third, the thickness of the steel strip (the threshold value is raised by 3% for every 0.1 mm increase in thickness).

[0056] The surface of the steel strip located in the potential decarburization risk segment after being discharged is scanned by infrared thermal imaging, and a surface carbon distribution map is generated by utilizing the difference in thermal radiation between the decarburization zone and the non-decarburization zone, thereby locating the position and range of the actual decarburization zone.

[0057] It should be noted that since the main component of the decarburization zone is ferrite, its thermal emissivity is lower than that of the normal region dominated by pearlite. This difference can be clearly presented by infrared imaging, thereby generating an accurate surface carbon distribution map. This method not only accurately locates the position and range of the actual decarburization zone, but also realizes non-contact and full-surface detection. Compared with destructive metallographic detection, this method is not only more efficient, but also covers the entire length of the potential decarburization risk segment, thereby avoiding missed detection.

[0058] For the identified decarburization zone, a pulsed laser beam is used to locally heat it to the austenitizing temperature, while a mixture of methane and argon gas is introduced to cause in-situ carburization of the decarburization zone, thereby restoring the surface carbon content to the level of the steel strip matrix.

[0059] It should be noted that this technology discards the traditional overall carburization or secondary annealing, and instead uses a pulsed laser beam to locally heat the decarburization zone while introducing a mixture of methane and argon gas to allow carbon elements to be in-situ carburized into the surface layer of the steel strip. The high energy density of the laser ensures the carburization efficiency, and local processing avoids the energy waste and organizational performance fluctuations caused by overall heating.

[0060] The austenitizing temperature is the temperature range at which the solubility of carbon in steel is the highest. At this temperature, the crystal structure of the steel is most conducive to the diffusion and solid solution of carbon atoms. In steel strip heat treatment, the specific value of the austenitizing temperature depends on the chemical composition of the steel (especially the carbon content and alloying elements). Taking a typical high-strength spring steel (such as 60Si2MnA) as an example, its austenitizing temperature range is usually 850-920℃ (the specific value needs to be adjusted according to the steel grade).

[0061] The active carbon atoms produced by the decomposition of methane at high temperatures can quickly penetrate into the surface layer of the steel strip, while argon gas acts as a protective gas to prevent secondary oxidation. This local processing method realizes in-situ carburization repair of the decarburization zone, ensuring the carburization effect while avoiding energy waste and organizational performance fluctuations caused by overall processing.

[0062] The carburized steel strip is then subjected to overall rapid preheating through a high-frequency induction heating device to eliminate the local thermal stress caused by laser carburization.

[0063] It should be noted that, since laser carbon compensation will form a temperature gradient in the local area, resulting in thermal stress concentration, high-frequency induction heating uniformly heats the whole steel strip through electromagnetic induction principle, prompting the internal stress to redistribute to achieve a balanced state, which effectively eliminates the local thermal stress and prevents cracking risk caused by uneven stress in the subsequent quenching process, ensuring the quality stability of the final product.

[0064] The method of the embodiment realizes the whole-process control from early warning, detection to repair through the organic cooperation of each step, and significantly improves the surface quality and fatigue performance of the spring steel strip.

[0065] Referring to Figure 2 As shown in the figure, according to the actual use requirements, in order to solve the detection blind area problem and the risk of misjudgment that may exist in the traditional arrangement mode, the oxygen content sensor arrangement mode is optimized and designed in this embodiment: in the specific implementation process, first, according to the structure characteristics of each section of the annealing furnace, the differential arrangement is carried out, since the soaking section is the high-risk area of decarburization, the distance between the adjacent two groups of oxygen content sensors is controlled to be not more than 1 / 5 of the length of this section, which ensures that a continuous detection coverage area can be formed in the running direction of the steel strip, avoiding the monitoring blank; while in the slow cooling section, since the decarburization risk is relatively reduced, the distance is relaxed to not more than 1 / 3 of the length of this section, which optimizes the number of sensor configurations while ensuring the detection effect.

[0066] Each group of oxygen content sensors is provided with at least three detection points in the width direction of the steel strip, and this multi-point arrangement can effectively capture the uneven oxygen concentration distribution in the transverse direction of the steel strip, overcoming the defect that the single-point detection may miss the edge area.

[0067] When the oxygen concentration of two or more adjacent detection points in the width direction is detected at the same time, the length direction is extended to mark the area, this design is based on the physical property that oxygen concentration anomalies usually diffuse along the running direction of the steel strip under the action of air flow, through the extension mark of 1 / 8 interval upstream and downstream, which not only ensures the complete coverage of the potential risk area, but also avoids the waste of resources caused by excessive marking. This intelligent area expansion algorithm is particularly suitable for dynamic detection scenes on continuous production lines, through the establishment of spatial correlation judgment mechanism, the accuracy of risk marking is significantly improved.

[0068] The oxygen content sensor arrangement method disclosed in the embodiment realizes all-around and dead-angle-free monitoring of the oxygen concentration distribution in the annealing furnace by combining fine division in the spatial dimension and real-time monitoring in the time dimension, and provides a reliable early warning basis for subsequent decarburization detection and compensation; from the technical effect, on the one hand, the arrangement method ensures the continuity of detection through reasonable spacing setting, and on the other hand, improves the reliability of detection through multi-point detection and intelligent expansion mechanism, and finally realizes high-precision positioning of the potential decarburization risk section, and provides accurate data support for subsequent steps of the whole method.

[0069] Specifically, when the method of the embodiment detects the potential decarburization risk section of the steel strip, the steel strip is continuously running in the annealing furnace, in order to mark the detected potential decarburization risk section for subsequent accurate positioning, when the oxygen content sensor detects an anomaly and determines the potential decarburization risk section, a color mark laser marker is triggered to mark the edge of the steel strip immediately, this marking method utilizes the principle of interaction between laser and steel strip surface material, through accurate control of laser parameters, stable and durable color marks are formed on the surface without affecting the performance of the steel strip, compared with traditional inkjet or mechanical scribing marking, laser marking has higher accuracy and environmental adaptability, can work stably on the high-temperature and high-speed production line, and the marks will not disappear due to subsequent process treatment.

[0070] The selection of the marking position at the edge of the steel strip is based on two important considerations: one is to avoid affecting the main use area of the steel strip, and the other is to facilitate the rapid positioning of the potential decarburization risk section in the subsequent process, wherein: the selection of the color mark considers high contrast with the steel strip matrix to ensure that it can be accurately identified under various lighting conditions.

[0071] From the technical mechanism, this marking method changes the oxidation state of the steel strip surface at the microscopic level through non-contact laser action to produce color difference, without introducing foreign pollutants or causing mechanical damage, completely meeting the cleanliness requirements of steel production, and the whole marking method realizes data linkage with other detection equipment on the production line, when the oxygen content sensor detects an anomaly, the position coordinates can be transmitted to the marking device in real time, ensuring the timeliness and accuracy of the marking, and establishing a reliable position reference for the whole decarburization detection and compensation process.

[0072] Referring to Figure 3 On the basis of the above embodiment, the present application further deepens and refines the infrared thermal imaging scanning step, and constructs a complete method for identifying the decarburization area by using infrared thermal imaging scanning, realizing accurate detection and quantitative evaluation of the decarburization defects on the surface of the steel strip.

[0073] In the implementation process, first, a plurality of groups of infrared thermal imagers with special configurations are arranged in the running direction of the steel strip, each group of arrays is composed of three thermal imagers with a specific spatial distribution, and the thermal radiation data of the steel strip surface is synchronously collected from three directions of directly above, left side 45 degrees and right side 45 degrees. The design of this multi-angle synchronous scanning is based on an important material science phenomenon: the decarburized area and the non-decarburized area will show different thermal radiation characteristics under different observation angles, and this multi-dimensional data can effectively eliminate the interference caused by the steel strip surface oxidation film, slight warping or contaminants when detected at a single angle; referring to Figure 4 The collected multi-source data are transmitted to the central processing system in real time for three-dimensional fusion processing, the thermal images at different angles are accurately superimposed through a spatial registration algorithm, and a high-resolution surface carbon distribution map is generated, wherein: the decarburized area is a ferrite enrichment area with low thermal emissivity, showing a banded low-temperature dark area; the non-decarburized area is a mixture of pearlite and austenite with high emissivity, showing a uniform bright background.

[0074] After obtaining the carbon distribution map, based on the inherent relationship between the thermal physical properties and the carbon content of the material, the thermal radiation difference value of each area is calculated. This step utilizes the essential differences in specific heat capacity, thermal conductivity and thermal emissivity between the decarburized area (mainly ferrite) and the normal area (mainly pearlite), and realizes the leap from qualitative detection to quantitative analysis by establishing a corresponding relationship model between the thermal radiation difference and the decarburization depth. The model is trained by a large amount of experimental data and can accurately calculate the decarburization depth according to the numerical value of the thermal radiation difference. When the detection value exceeds the set threshold value, it is marked as a decarburized area, and the key parameters such as decarburization area ratio and maximum depth are calculated to determine the decarburization grade and provide accurate quantitative basis for subsequent compensation processing.

[0075] In this embodiment, standard samples with different decarburization depths (0.01-0.5mm gradient) are prepared in the laboratory, and the quantitative relationship between decarburization depth and mechanical properties is established by microhardness testing and electron probe analysis; experiments show that when the decarburization depth exceeds 0.08mm, the fatigue life of 60Si2MnA spring steel decreases by more than 30%, and this critical value is determined as the lowest detection threshold.

[0076] After completing the decarburized area identification and grading, the edge recognition algorithm is started to extract the contour of the decarburized area. This step uses advanced image processing technology to accurately distinguish the boundary between the decarburized area and the normal area, and generates a decarburized area contour map with sub-millimeter precision. This accurate contour information is crucial for the subsequent laser recarburization process, as it ensures that the recarburization process can completely cover the decarburized area while minimizing the impact on the normal area.

[0077] The whole method realizes the all-around and high-precision detection of the decarburization defects on the steel strip surface through the organic combination of multi-angle data acquisition, three-dimensional information fusion, quantitative model analysis and accurate contour extraction, and provides reliable technical support for the whole decarburization online detection and compensation method. From the technical effect, the multi-angle three-dimensional scanning method has obvious advantages compared with the traditional single-angle detection: firstly, the limitation of single detection angle is effectively eliminated through space multi-source data fusion; secondly, the quantitative analysis model based on the thermal physical properties of materials greatly improves the accuracy of the detection result; finally, the accurate contour extraction creates necessary conditions for the subsequent local compensation processing, thereby ensuring that the processing precision and efficiency of the whole method are optimal.

[0078] Referring to Figure 5 As shown in the figure, after determining the decarburization grade according to the decarburization area ratio and the maximum depth, the application further establishes a scientific corresponding relationship between the decarburization grade and the carburizing gas ratio, and optimizes the carbon compensation efficiency through a grading processing mechanism.

[0079] In specific implementation, first, according to the determined decarburization depth data, the defects are divided into three process grades: when the decarburization depth is not more than 0.1 mm, it is classified as mild decarburization, at this time, the carbon loss of the steel strip matrix is less, and a 1:9 methane-argon mixed ratio is adopted, this low concentration carburizing gas can not only ensure the recovery of the surface layer carbon content, but also avoid the formation of brittle phase caused by excessive carburizing; for moderate decarburization of 0.1-0.15 mm, a medium concentration ratio of 1:4 is switched to, the carbon atom diffusion is accelerated by increasing the methane ratio to compensate for the deeper carbon loss layer; when the detected decarburization depth exceeds 0.15 mm, a high concentration ratio of 1:2 is adopted, at this time, argon mainly plays a role of carrier gas and protection, and the active carbon atoms generated by the decomposition of high-density methane can quickly fill the deep decarburization area.

[0080] This grading control mechanism is based on the carbon diffusion kinetics principle, and different ratios correspond to different carbon potential gradients: the carbon flux required for mild decarburization is low, and thin gas can be used to accurately control the carburized layer; moderate decarburization needs to establish a moderate carbon concentration gradient to ensure that carbon atoms can penetrate the ferrite layer; severe decarburization needs to form a steep carbon potential difference to drive carbon atoms to diffuse to a deeper layer. In the implementation process, the temperature field distribution of the laser heating area is monitored in real time, and the gas flow is dynamically adjusted to keep the methane decomposition rate and the austenite carbon absorption capacity balanced, avoiding the formation of carbon black or insufficient carburizing.

[0081] From the technical effect, this intelligent ratio method realizes three breakthroughs: first, through the accurate mapping of defect grade and process parameters, the process risks of "over-treatment" or "insufficient treatment" are avoided; second, the grading gas ratio significantly improves the carbon atom utilization rate, and reduces gas consumption compared with the traditional fixed ratio process; third, the dynamic adjustment mechanism ensures that different depth decarburization areas can all obtain uniform and consistent carbon compensation.

[0082] Referring to Figure 6 As shown in the determination of decarburization zone geometry, the application also provides an adaptive laser processing method, which realizes intelligent matching of laser parameters and decarburization zone morphology, and solves the problems of uneven energy distribution or low processing efficiency in traditional laser processing by establishing a dynamic response mechanism of decarburization zone area and laser beam parameters.

[0083] In specific implementation, first, the generated decarburization zone contour map is analyzed, the projected area and maximum depth of the decarburization zone are accurately calculated, and the optimal processing mode is automatically selected according to the area threshold: when a micro decarburization zone with an area less than 10 mm² is detected, a small spot with a diameter of 1-2 mm is used in combination with a high power density mode. This configuration can concentrate energy in a small area, quickly establish austenite phase transition conditions through short-time high-temperature action, and at the same time, high energy density can ensure that carbon atoms diffuse sufficiently within a limited action time, avoiding the diffusion of the heat-affected zone to the normal area; for medium-area decarburization zones with an area of 10-50 mm², a scanning mode with a 3-5 mm spot is switched to, at which time the laser beam performs full-coverage scanning on the decarburization zone with a specific trajectory, and the scanning speed and overlap rate are controlled to maintain a stable temperature field. This mode not only ensures processing efficiency, but also makes the energy distribution more uniform; when a large-area decarburization zone with an area exceeding 50 mm² is encountered, a multi-spot collaborative working mode is started, the target area is divided into several sub-areas, and multiple laser heads are used for synchronous processing. The action areas of the spots are set with an overlap of 10-15% to ensure seamless connection. This distributed processing strategy effectively overcomes the problem of temperature unevenness caused by edge cooling in single-spot systems during large-area processing.

[0084] From the technical mechanism, this hierarchical adjustment method is based on three key characteristics of laser and material interaction: first, the spot size determines the energy action range, which needs to match the geometric size of the decarburization zone to avoid energy waste or insufficient coverage; second, the power density affects the austenitizing speed and depth, which needs to be dynamically adjusted according to the decarburization depth; third, multi-spot collaboration can achieve interference enhancement effect through phase control, improving the energy utilization rate of large-area regions. During implementation, the molten pool morphology and temperature distribution are monitored in real time, and the laser parameters are dynamically adjusted through closed-loop feedback to ensure consistent processing quality for decarburization zones of different sizes.

[0085] The technical advantages of this method are reflected in three aspects: first, adaptive parameter matching enables laser energy to act precisely on the target area, controlling the heat-affected zone to the minimum range; second, the multi-mode switching mechanism takes into account both processing accuracy and efficiency, ensuring optimal speed for small-area repair and large-area processing; finally, the collaborative processing mode avoids the problem of power density decline caused by the expansion of traditional single-beam through spatial energy distribution, perfectly achieving the process goal of "precise repair, minimal intervention", and providing reliable protection for the uniformity of steel strip quality.

[0086] Specifically, in the process of heating the steel strip with a pulsed laser beam, the target temperature of the pulsed laser beam is first set to a superheat interval of 50-80℃ above the austenitizing temperature. This temperature window is set based on two key scientific principles: on the one hand, moderate superheating can accelerate the austenite transformation process and shorten the organizational transformation time; on the other hand, the remaining 50-80℃ can compensate for the heat loss caused by heat conduction during laser heating, ensuring that the actual action temperature always remains above the austenitizing critical point.

[0087] After the laser starts to act, a high-precision infrared temperature sensor is used to monitor the temperature change curve of the steel strip heating area in real time with a millisecond-level sampling frequency. When the temperature is detected to rise to the 70% interval of the austenitizing temperature, the gradual introduction of methane-argon mixed gas is started. At this time, the gas flow increases linearly according to the temperature rise ratio. This early intervention gas supply strategy allows a uniform gas cover layer to be formed on the surface of the steel strip at the moment it reaches the austenitizing temperature. As the temperature continues to rise to the austenitizing critical point, the gas flow reaches the preset maximum value at the same time. At this time, the austenite lattice on the surface of the steel strip is fully expanded, and the carbon solubility reaches a peak. The active carbon atoms produced by the decomposition of high-flow mixed gas can quickly dissolve into the austenite lattice. This temperature-flow linkage mechanism is based on the diffusion kinetics of carbon in austenite: during the warming-up stage, the diffusion coefficient of carbon increases exponentially with temperature, and the flow increment ensures that the carbon supply rate matches the diffusion capacity; during the austenitizing plateau period, the maximum flow ensures that the surface carbon potential reaches saturation, forming a concentration gradient that drives diffusion towards the center.

[0088] From a technical effect point of view, this dynamic control method realizes a triple breakthrough: first, the superheat design ensures the rapid start of the austenitizing process; second, the flow proportional adjustment mechanism to temperature avoids ineffective gas supply at low temperatures and gas supply lag at high temperatures; finally, the precise synchronization of maximum flow and austenitizing temperature ensures the full absorption of carbon atoms in the most active stage of the lattice.

[0089] In the specific implementation process, after the laser-induced carburizing reaction is started, a high-sensitivity online spectrum analyzer is used to monitor the carbon concentration gradient of the treated area at a sampling frequency of 20 times per second. Its working principle is to use the emission intensity difference of steels with different carbon contents in the characteristic spectral band to convert the spectral signal into real-time carbon concentration values through a calibration curve. When the critical point of the surface carbon concentration is detected to recover to 95% of the base level, the process conversion program is triggered immediately: first, the energy supply of the pulsed laser beam is cut off, and the austenitizing process is stopped; simultaneously, the methane-argon mixed gas valve is closed, and the carbon source input is terminated. This dual shutdown mechanism is based on the accurate control of material phase transformation dynamics, and the 95% threshold setting ensures the full recovery of the main carbon content and reserves an appropriate amount for the carbon homogenization in the subsequent holding stage.

[0090] After entering the holding stage, the holding time is automatically calculated according to the projected area of the decarburization zone, and is dynamically adjusted according to the proportional relationship of 5 s / mm2. This parameter is derived from a carbon diffusion model established based on a large amount of experimental data, and can ensure that carbon atoms in decarburization zones of different sizes have sufficient time to complete redistribution. During the holding period, the spectral analyzer continues to work, and the change in carbon concentration is tracked in real time until the matrix level is reached. This continuous monitoring mechanism effectively solves the problem of uneven carbon distribution caused by local temperature fluctuations.

[0091] From the technical mechanism analysis, this method has three scientific advantages: first, online spectral monitoring breaks through the lag of traditional post-detection, realizing real-time closed-loop control of the process; second, intelligent judgment of the 95% threshold avoids energy waste caused by blindly extending the main carburizing stage; and finally, the holding time design according to the area proportion conforms to the diffusion law of Fick's second law, so that defects of different sizes can be optimally homogenized. In practical application, especially for large-sized decarburization zones (> 50 mm2), through precise holding time control, the traditional "edge carbon-poor" phenomenon is successfully eliminated, providing a reliable guarantee for the quality consistency of high-strength spring steel strips.

[0092] On the basis of the above-mentioned embodiments, the present application further optimizes the termination stage control process of the carburizing process, and effectively solves the surface quality defect problem caused by the traditional sudden gas cut-off by establishing a gradual gas supply exit mechanism. The core of this technical method is to construct a collaborative decay curve of gas flow and temperature field, and to realize smooth transition of process parameters.

[0093] In the specific implementation process, when the online spectral analyzer detects the conversion condition that the carbon concentration reaches 95% of the matrix level, the gas valve will not be closed immediately, but the intelligent gas reduction program will be started: first, gradually reduce the total gas flow at a rate of 5% reduction per second, and this stage lasts for 8-10 seconds to complete 90% flow reduction; at the same time, the proportion of methane and argon in the mixed gas is adjusted, and the methane proportion is linearly reduced to zero within the first 5 seconds, and pure argon is supplied for the last 3-5 seconds. This phased exit strategy is based on the coupling principle of gas dynamics and surface reaction: gradual flow reduction avoids disturbance of the molten pool caused by sudden changes in gas pressure, maintaining the stability of surface reaction; preferential reduction of the methane proportion ensures that the supply of active carbon atoms precedes the exit of the protective gas, preventing non-equilibrium carburizing at the end; the pure argon maintenance stage effectively suppresses the secondary oxidation of the high-temperature steel strip surface through inert gas coverage.

[0094] In terms of temperature control, the cooling curve is monitored in real time, and argon protection is completely terminated only when the temperature drops below the safety threshold of 600°C, which is lower than the apparent oxidation initiation temperature of the steel strip. Throughout the process, the rate of change of gas flow is dynamically matched with the rate of temperature drop, and the PID control algorithm ensures that the two are always in optimal coordination.

[0095] From a technical effect point of view, this intelligent exit mechanism realizes three breakthroughs: first, it avoids the surface carbon concentration fluctuation caused by sudden gas cut-off; second, the methane priority exit strategy eliminates the free carbon deposition caused by the decomposition of residual hydrocarbons; and finally, the design of argon protection to a safe temperature can control the generation of surface oxide layer, greatly reducing the workload of subsequent cleaning process.

[0096] Referring to Figure 7 During the stress relief stage, a set of precise and controllable gradient heating and stress regulation methods are constructed, and through multi-stage temperature control and real-time feedback adjustment, accurate organization regulation of the steel strip after recarburization and heat treatment is realized. This technical method combines zoned induction heating, gradient heating and dynamic stress monitoring technology, solving the problems of temperature unevenness and stress concentration caused by traditional overall heating.

[0097] In the specific implementation process, first, a plurality of groups of independent temperature-controlled induction coil arrays are arranged in the width direction of the steel strip, each group of coils is equipped with a dedicated power regulation module, and the steel strip transverse temperature distribution is scanned at a frequency of 50 frames per second by a high-resolution infrared thermal imager. When the temperature of any area deviates from the set value by more than ±15°C, the temperature difference gradient is immediately calculated and the power output of the corresponding position coil is adjusted. This real-time compensation mechanism is based on the skin effect principle of electromagnetic induction heating, and by changing the frequency and power, the depth of heat penetration in different areas can be accurately controlled, thereby controlling the steel strip transverse temperature uniformity within ±10°C.

[0098] The heating process adopts a three-stage gradient heating strategy: in the initial stage, the steel strip quickly passes through the low-temperature brittle zone at a rapid heating rate of 30-50°C / s to avoid the risk of hydrogen embrittlement caused by long-term residence below 300°C; in the middle stage, the speed is reduced to 15-20°C / s to pass through the medium temperature zone, at this time the plasticity of the steel strip increases, and appropriate control of the heating rate can reduce the accumulation of thermal stress; in the final stage, the speed is reduced to 5-10°C / s to approach the target temperature, ensuring smooth completion of the organization transformation. This variable heating curve design conforms to the law that the thermal expansion coefficient of steel changes with temperature, so that the development of thermal stress in different temperature zones is always controllable.

[0099] When the temperature reaches the target interval of 550-600℃, the laser ultrasonic detection device starts to work, and the internal stress state is inverted in real time by measuring the change of surface acoustic wave propagation speed. The holding time is dynamically adjusted according to the stress decay curve, and the residual stress can be reduced below the safety threshold (<50MPa) within 30-60 seconds. This process utilizes the principle of metal creep at high temperature, and the stress relaxation is achieved through atomic diffusion and recombination.

[0100] When the cooling process starts, a micro-tension of 10-15N / mm² is applied to both ends of the steel strip. This controlled tensioning state can effectively offset the shrinkage stress during cooling and prevent warping deformation. The entire cooling process can be divided into two stages: first, a high wind speed is used to quickly pass through the pearlite transformation zone, and then the cooling rate is reduced to pass through the bainite transformation zone, so that the microstructure can obtain the ideal proportioning.

[0101] From the technical mechanism, this method has three core advantages: first, the combination of zoned induction heating and real-time temperature control solves the problem of uneven heat treatment caused by edge effect of wide steel strip; second, the gradient heating strategy matches the change of material thermal physical properties in different temperature intervals through rate optimization; finally, the synergistic effect of stress monitoring and tension control ensures the dimensional stability of the steel strip during the whole heat treatment process.

[0102] Obviously, the above embodiments are only examples for clarity and do not limit the embodiments. Based on the above description, other different forms of changes or variations can be made by those skilled in the art. Here, it is not necessary and impossible to enumerate all the embodiments. The obvious changes or variations derived therefrom are still within the protection scope of the present invention.

Claims

1. An online detection and compensation method for localized decarburization of high-strength spring steel strip, characterized in that, Includes the following steps: Multiple oxygen content sensors are arranged in the soaking and slow cooling sections of the continuous annealing furnace to monitor the oxygen concentration in each area of ​​the furnace in real time. When the oxygen concentration of any set of oxygen content sensors exceeds the threshold, the coordinates of the steel strip in that area are recorded and marked as a potential decarburization risk area. Infrared thermal imaging scans were performed on the surface of the steel strip located in the potential decarburization risk zone after it exited the furnace. The difference in thermal radiation between the decarburized and non-decarburized zones was used to generate a surface carbon distribution map to locate the position and range of the actual decarburized zone. For the identified decarburized areas, a pulsed laser beam is used to locally heat them to the austenitizing temperature, while a methane-argon mixture is introduced to cause an in-situ carburizing reaction in the decarburized areas, restoring the surface carbon content to the level of the steel strip matrix. The carbonized steel strip is preheated rapidly as a whole using a high-frequency induction heating device to eliminate localized thermal stress caused by laser carbonization.

2. The online detection and compensation method for localized decarburization of high-strength spring steel strip according to claim 1, characterized in that: The oxygen content sensor is arranged as follows: The spacing between the multiple sets of oxygen content sensors is determined according to the length of each section of the annealing furnace. The spacing between two adjacent sets of oxygen content sensors in the soaking heat section shall not exceed 1 / 5 of the length of the section, and the spacing between two adjacent sets of oxygen content sensors in the slow cooling section shall not exceed 1 / 3 of the length of the section. Each set of oxygen content sensors covers the entire width of the steel strip and has at least three detection points in the width direction; When two or more adjacent detection points in the width direction simultaneously detect that the oxygen concentration exceeds the threshold, the marking area in the length direction is extended to a region that is 1 / 8 of the distance between the upstream and downstream of the detection range of the oxygen content sensor group, and the steel strip at the corresponding position in this region is marked as a potential decarburization risk section.

3. The online detection and compensation method for localized decarburization of high-strength spring steel strip according to claim 2, characterized in that: After identifying potential decarburization risk sections, a color-marked laser marking device is used to mark the starting position of the risk section on the edge of the steel strip.

4. The online detection and compensation method for localized decarburization of high-strength spring steel strip according to claim 1, characterized in that: The specific implementation methods of the infrared thermal imaging scanning include: Multiple infrared thermal imager arrays are set up along the running direction of the steel strip. Each array contains three thermal imagers at different angles, which simultaneously scan from directly above the steel strip, 45 degrees to the left, and 45 degrees to the right. The data collected by each thermal imager are fused in three dimensions to generate a surface carbon distribution map, and the thermal radiation differences are determined based on the surface carbon distribution map. Establish a model relating thermal radiation differences to decarburization depth. When a thermal radiation difference exceeds a set threshold, it is marked as a decarburization zone. Calculate the area and depth of the decarburization zone and determine the decarburization level. Edge recognition and contour extraction are performed on the marked decarburized areas to generate accurate decarburized area contour maps.

5. The online detection and compensation method for localized decarburization of high-strength spring steel strip according to claim 4, characterized in that: Determining the methane-argon mixture ratio based on the decarbonization level includes the following steps: The decarburization level is divided into three levels: light decarburization: decarburization depth ≤ 0.1 mm, moderate decarburization: 0.1 mm < decarburization depth ≤ 0.15 mm, and heavy decarburization: decarburization depth > 0.15 mm. For different decarbonization levels, the methane-argon mixing ratio is adjusted as follows: a 1:9 methane-argon mixing ratio is used for mild decarbonization, a 1:4 methane-argon mixing ratio is used for moderate decarbonization, and a 1:2 methane-argon mixing ratio is used for severe decarbonization.

6. The online detection and compensation method for localized decarburization of high-strength spring steel strip according to claim 4, characterized in that: Based on the area and depth of the decarburized zone, the laser spot diameter and power density are adjusted, where: For decarburization zones with an area less than 10 mm², a high power density mode with a small spot size of 1-2 mm is used. For decarburized zones with an area of ​​10-50 mm², a medium spot scanning mode with a diameter of 3-5 mm is used. For decarbonization zones with an area greater than 50 mm², a multi-spot collaborative processing mode with different regions is adopted.

7. The online detection and compensation method for localized decarburization of high-strength spring steel strip according to claim 1, characterized in that: The temperature of the pulsed laser beam is set to 50–80°C above the austenitizing temperature. The real-time temperature of the steel strip during the heating process is monitored. The flow rate of the methane-argon mixture is adjusted according to the real-time temperature of the steel strip. When the steel strip is heated to the austenitizing temperature, the flow rate of the methane-argon mixture reaches its maximum value.

8. The online detection and compensation method for localized decarburization of high-strength spring steel strip according to claim 1, characterized in that: During the in-situ carburizing reaction in the decarburization zone, the surface carbon concentration change is monitored using an online spectrometer. When the carbon concentration reaches 95% of the matrix level, the process is switched to the heat preservation stage, and the local heating of the pulsed laser beam and the supply of methane-argon mixed gas are stopped. Among them, the heat preservation time is calculated based on the area of ​​the decarburized zone at 5s / mm², and the surface carbon concentration change value is continuously detected until the surface carbon content reaches the level of the steel strip matrix.

9. The online detection and compensation method for localized decarburization of high-strength spring steel strip according to claim 8, characterized in that: When stopping the supply of methane-argon gas mixture, the gas flow rate is gradually reduced to stop the gas supply, and the ratio of methane-argon gas mixture is gradually adjusted to maintain argon protection until the temperature drops to a safe range.

10. The online detection and compensation method for localized decarburization of high-strength spring steel strip according to claim 1, characterized in that: The specific process steps for overall rapid preheating using a high-frequency induction heating device include: Multiple sets of induction coils are arranged in the width direction of the steel strip. The power of each set of coils is independently adjustable. The transverse temperature distribution of the steel strip is monitored in real time by an infrared thermal imager. When the temperature deviation exceeds ±15℃, the power of the coil at the corresponding position is adjusted. In the initial stage, the temperature is increased to 300-350℃ at a rate of 30-50℃ / s; in the middle stage, the temperature is increased to 450-500℃ at a rate of 15-20℃ / s; and in the final stage, the temperature is increased to the target temperature of 550-600℃ at a rate of 5-10℃ / s. The target temperature is maintained for 30-60 seconds to allow thermal stress to be fully released. Stress changes are monitored in real time using a laser ultrasonic testing device. When the residual stress drops below the safety threshold, the cooling process begins. During the cooling process, the steel strip is stretched under tension.

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