Spring steel fracture reason diagnosis process based on metallographic and stereoscopic analysis

Abstract

The invention relates to the technical field of spring steel, and discloses a spring steel fracture reason diagnosis process based on metallographic and stereoscopic analysis. According to the spring steel fracture reason diagnosis process based on metallographic analysis and stereoscopic analysis, S1, sample selection and preparation, S2, stereoscopic analysis (macroscopic morphology observation, S3, metallographic analysis, S4, metallographic observation and analysis, and S5, comprehensive analysis and conclusion drawing, the fracture root is accurately positioned through the process; the fracture characteristics of the spring steel are comprehensively analyzed from the macroscopic level and the microcosmic level, the macroscopic morphology of a fracture is observed in detail through stereoscopic analysis, and obvious defects such as mechanical damage, pits and scabs on the surface can be rapidly found; the internal structure is deeply explored by means of metallographic analysis, microdefects such as stress cracks, segregation, decarburization and cold deformation can be accurately identified, the root cause of fracture can be accurately positioned through combination of the two, and a reliable basis is provided for formulation of subsequent improvement measures.

Description

Technical Field

[0001] The present invention relates to the technical field of spring steel, and specifically to a diagnostic process for the fracture cause of spring steel based on metallographic and stereoscopic analysis. Background Art

[0002] In modern industrial production, as a key mechanical component, springs are widely used in many fields such as automobiles, mechanical manufacturing, aerospace, etc., undertaking important functions such as energy storage, buffering, and shock absorption. Spring steel, as the main material for manufacturing springs, its quality and performance directly determine the reliability and service life of the springs. However, during the production and actual use of springs, the fracture problem of spring steel occurs from time to time. This not only leads to failures of related equipment, affects the normal progress of production, increases maintenance costs and downtime, but may also cause safety accidents and threaten the lives of personnel.

[0003] In the past, when analyzing the fracture cause of spring steel, there was often a lack of a systematic and comprehensive method. Some detection means can only observe the macroscopic surface phenomena of the material, and it is difficult to deeply explore the internal microstructural defects; while some microscopic analysis methods are not effectively combined with macroscopic characteristics, resulting in inaccurate and incomplete judgment of the fracture cause. For example, relying solely on simple naked-eye observation, it is impossible to detect defects such as segregation and microcracks inside the material; when using metallographic analysis alone, without combining macroscopic morphological characteristics, it is also difficult to accurately determine the source of the defects and their relationship with the fracture. This situation makes it difficult for production enterprises to take effective measures to improve the production process and product quality, and there is an urgent need for a scientific, systematic and accurate diagnostic process to solve this problem. Summary of the Invention

[0004] (1) Technical Problems to be Solved Aiming at the deficiencies of the prior art, the present invention provides a diagnostic process for the fracture cause of spring steel based on metallographic and stereoscopic analysis, which has the advantages of accurately positioning the fracture root cause, improving product quality and reliability, etc., and solves the problem that there is often a lack of a systematic and comprehensive method when analyzing the fracture cause of spring steel. Some detection means can only observe the macroscopic surface phenomena of the material, and it is difficult to deeply explore the internal microstructural defects.

[0005] (2) Technical Solutions To achieve the above purposes of accurately positioning the fracture root cause, improving product quality and reliability, the present invention provides the following technical solutions: A diagnostic process for the fracture cause of spring steel based on metallographic and stereoscopic analysis, including the following process steps, S1 Specimen Selection and Preparation: Select multiple representative specimens from the fractured spring steel products. Select six specimens from different fracture positions and different batches of products, and number the specimens for easy subsequent distinction and recording. Use suitable cutting methods such as wire cutting and grinding wheel cutting to cut the specimens into appropriate sizes according to the analysis requirements. Generally, the size of the longitudinal section or cross-section is more suitable at 10 - 20 mm; After cutting, polish the cutting surface of the specimen. Use sandpapers with different mesh numbers in sequence, starting from coarse sandpaper (120 mesh) to fine sandpaper (1000 mesh) for polishing until the cutting surface is flat and smooth without obvious scratches; After polishing, polish the specimen. Adopt mechanical polishing or electrolytic polishing methods to make the surface of the specimen reach a mirror effect for subsequent metallographic observation and analysis; S2 Stereoscopic analysis (macroscopic morphology observation): Place the prepared specimen under a stereoscopic microscope and conduct a comprehensive observation at a low magnification (5 - 10 times). Focus on observing the overall morphology of the specimen fracture surface, record the shape, color, and texture trend characteristics of the fracture surface, carefully check whether there are obvious mechanical damages, scratches, and indentations on the fracture surface, as well as the position, depth, and scope of the damages; For specimens with mechanical damages, describe the characteristics of the damages in detail, such as whether the damaged area shows metallic luster and whether there are signs of deformation; Observe whether there are other defects at the fracture surface, such as pits, scabs, and foreign objects. If pits are found, measure the size of the pits, including diameter and depth, and record the number and distribution of the pits; For areas suspected of scab or foreign object pressing in, observe the deformation of the surrounding matrix; S3 Metallographic analysis: Metallographic specimen preparation: For specimens that have undergone stereoscopic analysis, select the parts that need to be subjected to metallographic analysis, such as the area near the fracture surface. Adopt the method of embedding to fix the specimen in a suitable embedding material, such as thermosetting plastic or epoxy resin, to ensure the stable position of the specimen during subsequent processing. Re-polish and polish the embedded specimen to make the metallographic observation surface reach a higher flatness and smoothness. During the polishing process, polishing paste auxiliary materials can be used to further improve the polishing effect; S4 Metallographic observation and analysis: Observation of unetched metallography: Place the prepared metallographic specimen under a metallurgical microscope. First, observe the overall tissue morphology in the area near the fracture surface at a low magnification (50X) to check for cracks. If cracks are present, record the number, orientation, distribution, and approximate depth of the cracks. If the crack depth is found to be between 100 - 250um, carefully observe the morphological characteristics of the cracks to determine if they are stress cracks. For example, stress cracks usually exhibit a sharp and straight shape. Switch to a higher magnification (100X) to conduct a more detailed observation of the area near the fracture surface to check for other microdefects such as pores and inclusions, and record their characteristics and distribution. Observation of etched metallography: Corrode the metallographic specimen using a suitable etchant such as nitric acid alcohol solution. Control the etching time according to the material and tissue characteristics of the specimen, generally between 10 - 30 seconds. After etching, rinse the specimen with water, then dehydrate it with alcohol and dry it. Observe the etched specimen under a 50X metallurgical microscope to check for abnormal tissues on the surface such as white bright bands, and record the position, width, and morphological characteristics of the white bright bands. S5 Comprehensive analysis and conclusion drawing: Based on the results of stereoscopic analysis and metallographic analysis, comprehensively judge the fracture cause of the spring steel. If mechanical damage is found on the specimen surface during stereoscopic analysis, and stress cracks and abnormal tissues are found near the fracture surface in metallographic analysis, it can be inferred that the fracture may be caused by stress concentration induced by surface mechanical damage during subsequent processing or use, leading to crack initiation and propagation, and ultimately resulting in fracture. If pits, scabs, or foreign object indentation defects are found on the surface during stereoscopic analysis, and decarburization is found at the bottom of the pits and cold deformation exists in the matrix in metallographic analysis, the fracture may be caused by uneven stress on the matrix due to these original defects during processing, resulting in cold deformation and then fracture.

[0006] Preferably, during the cutting process, pay attention to controlling the cutting speed and cooling conditions to prevent changes in the specimen tissue due to overheating or excessive force.

[0007] Preferably, maintain the stability of the specimen during grinding to avoid deformation or damage to the specimen surface.

[0008] Preferably, take photos of the observed macroscopic morphological characteristics to ensure that the photos are clear and complete and can accurately reflect the actual situation of the fracture surface. At the same time, mark the specimen number, magnification, and observation date information on the photos for convenient subsequent analysis and reference.

[0009] Preferably, for the sample with the pit defect, the microstructure at the bottom of the pit is observed under a 100X metallographic microscope to determine whether decarburization occurs. Decarburization is manifested as a lighter color of the structure at the bottom of the pit, which is significantly different from the matrix structure. The magnification is increased to 500X to observe the microstructure of the matrix at the pit to determine whether cold deformation occurs.

[0010] Preferably, the characteristics of the cold deformation include grain distortion and elongation. For samples that are broken from the inside, the organization of the crack origin zone is observed under a 50X and 100X metallographic microscope to determine whether there is segregation. The color of the organization in the segregation area is different from that in the normal organization, and it usually appears black or shiny. If segregation exists, the range and distribution characteristics of the segregation area are observed. Under a 500X metallographic microscope, the organization composition of the crack origin zone and the extension zone is analyzed in detail, such as which phases are mainly composed of, the proportion and morphological characteristics of each phase. It is observed that the crack origin zone is mainly troostite + a small amount of pearlite, with basically no ferrite, and the organization of the crack extension zone is troostite + pearlite + ferrite.

[0011] Preferably, for the internally fractured sample, when metallographic analysis finds severe positive segregation in the crack origin zone, and negative segregation rings and positive segregation points are found under low-magnification observation, it can be judged that the fracture is due to the uneven internal structure of the material caused by segregation, and during the processing or use of the spring, the deformation of the segregation area is not coordinated, thereby causing cracking. Based on the results of the comprehensive analysis, a detailed diagnostic report is written, and the report content includes the selection of the sample, the specific results of the stereoscopic analysis and metallographic analysis, the inference of the cause of the fracture, and improvement suggestions for the fracture problem, such as optimizing the processing technology and strengthening the inspection of raw materials.

[0012] (III) Beneficial effects Compared with the prior art, the present invention provides a spring steel fracture cause diagnosis process based on metallographic and stereoscopic analysis, which has the following beneficial effects: 1. The diagnosis process of the cause of spring steel fracture based on metallographic and stereoscopic analysis can accurately locate the root cause of fracture: This diagnostic process uses stereoscopic analysis and metallographic analysis technology to comprehensively analyze the fracture characteristics of spring steel from both macroscopic and microscopic levels. By observing the macroscopic morphology of the fracture in detail through stereoscopic analysis, it can quickly discover obvious defects such as mechanical damage, pits, and scars on the surface; with the help of metallographic analysis, the internal organization can be deeply explored, and microscopic defects such as stress cracks, segregation, decarburization, and cold deformation can be accurately identified. The combination of the two can accurately locate the root cause of the fracture and provide a reliable basis for the formulation of subsequent improvement measures.

[0013] 2. The diagnosis process for the fracture cause of spring steel based on metallographic and stereoscopic analysis can improve product quality and reliability. After accurately determining the fracture cause, the manufacturing enterprise can optimize the production process according to specific problems. For example, if it is found that the fracture is caused by surface mechanical damage, the protective measures during processing can be improved to avoid surface damage. If the fracture is caused by segregation problems, the smelting and processing processes can be optimized to reduce segregation. This series of targeted improvement measures can effectively improve the quality of spring steel, enhance the reliability and stability of spring products, and reduce the fracture risk during use.

[0014] 3. The diagnosis process for the fracture cause of spring steel based on metallographic and stereoscopic analysis can reduce production costs. Through this diagnosis process, potential problems can be detected in a timely manner during product R & D and production, avoiding the generation of a large number of defective products caused by spring steel fractures, reducing waste of raw materials and production costs. At the same time, due to the improvement of product quality, the number of equipment failures and repairs is reduced, lowering equipment maintenance costs and downtime losses, thus improving the economic efficiency of the enterprise as a whole.

[0015] 4. The diagnosis process for the fracture cause of spring steel based on metallographic and stereoscopic analysis can ensure production safety. The fracture of spring steel may cause serious safety accidents, especially in some key fields such as automobiles and aerospace. This diagnosis process can effectively prevent the occurrence of such problems. By ensuring the quality and reliability of spring products, it provides strong guarantee for the safe operation of related equipment, reduces the probability of safety accidents, and protects the lives of personnel and the property safety of the enterprise.

[0016] 5. The diagnosis process for the fracture cause of spring steel based on metallographic and stereoscopic analysis can promote technological innovation and industry development. The application of this diagnosis process helps to promote the innovation and development of spring steel production technology. During the process of solving the fracture problem of spring steel, enterprises will continuously explore new processing technologies, material treatment methods and quality detection means, which will promote the improvement of the technical level of the entire spring steel industry and drive the sustainable and healthy development of the industry. Detailed implementation mode

[0017] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0018] This solution provides a technical solution, specifically, a diagnosis process for the fracture cause of spring steel based on metallographic and stereoscopic analysis, including the following process steps: S1 Specimen selection and preparation: Select multiple representative specimens from the fractured spring steel products. Select six specimens from different fracture positions and different batches of products, and number the specimens for subsequent distinction and recording. Use suitable cutting methods such as wire cutting and grinding wheel cutting to cut the specimens into appropriate sizes according to the analysis requirements. Generally, the size of the longitudinal section or cross section is preferably 10 - 20 mm; During the cutting process, pay attention to controlling the cutting speed and cooling conditions to prevent changes in the specimen structure due to overheating or excessive stress; After cutting, polish the cutting surface of the specimen. Use sandpapers with different mesh numbers in sequence, from coarse sandpaper (120 mesh) to fine sandpaper (1000 mesh) for polishing until the cutting surface is flat and smooth without obvious scratches; During polishing, maintain the stability of the specimen to avoid deformation or damage on the specimen surface; After polishing, polish the specimen. Use mechanical polishing or electrolytic polishing methods to make the specimen surface reach a mirror effect for subsequent metallographic observation and analysis; S2 Stereoscopic analysis (macroscopic morphology observation): Place the prepared specimen under a stereoscopic microscope and observe it comprehensively at a low magnification (5 - 10 times). Focus on observing the overall morphology of the specimen fracture surface, record the shape, color, and texture direction characteristics of the fracture surface, carefully check whether there are obvious mechanical damages, scratches, and indentations on the fracture surface, as well as the location, depth, and scope of the damages; For specimens with mechanical damages, describe the characteristics of the damages in detail, such as whether the damaged area shows metallic luster and whether there are signs of deformation; Observe whether there are other defects at the fracture surface, such as pits, scabs, and foreign objects. If pits are found, measure the size of the pits, including diameter and depth, and record the number and distribution of the pits; For areas suspected of scab or foreign object indentation, observe the deformation of the surrounding matrix; Among them, take photos and record the observed macroscopic morphology characteristics to ensure that the photos are clear and complete and can accurately reflect the actual situation of the fracture surface. At the same time, mark the specimen number, magnification, and observation date information on the photos for convenient subsequent analysis and reference, S3 Metallographic analysis: Metallographic specimen preparation: For the specimens that have undergone stereoscopic analysis, select the parts that need to be subjected to metallographic analysis, such as the area near the fracture surface. Use the embedding method to fix the specimens in suitable embedding materials, such as thermosetting plastics or epoxy resins, to ensure the stability of the specimens during subsequent processing. Re-polish and polish the embedded specimens to make the metallographic observation surface reach a higher flatness and smoothness. During the polishing process, polishing paste auxiliary materials can be used to further improve the polishing effect; S4 Metallographic Observation and Analysis: Unetched Metallographic Observation: Place the prepared metallographic specimen under the metallographic microscope. First, observe the overall microstructure morphology of the area near the fracture surface at a low magnification (50X) to check for the presence of cracks. If cracks are found, record the number, orientation, distribution, and approximate depth of the cracks. If the crack depth is found to be between 100 - 250 um, carefully observe the morphological characteristics of the cracks to determine if they are stress cracks. For example, stress cracks usually exhibit a sharp and straight shape. Switch to a higher magnification (100X) to conduct a more detailed observation of the area near the fracture surface to check for other microdefects such as pores and inclusions, and record their characteristics and distribution. Etched Metallographic Observation: Conduct an etching treatment on the metallographic specimen using a suitable etchant such as nitric acid alcohol solution. Control the etching time according to the material and tissue characteristics of the specimen, generally between 10 - 30 seconds. After etching, rinse the specimen with clean water, then dehydrate it with alcohol, and dry it. Observe the etched specimen under a 50X metallographic microscope to check for abnormal microstructures on the surface such as white bright bands, and record the position, width, and morphological characteristics of the white bright bands. Among them, for specimens with pit defects, observe the microstructure at the bottom of the pits under a 100X metallographic microscope to determine if decarburization has occurred. Decarburization is manifested as a lighter color of the microstructure at the bottom of the pits, which is significantly different from the matrix microstructure. Increase the magnification to 500X to observe the microstructure of the matrix at the pits to determine if cold deformation has occurred. Among them, the characteristics of cold deformation include grain distortion and elongation. For specimens that fracture from the inside, observe the microstructure in the crack origin area under 50X and 100X metallographic microscopes to determine if segregation has occurred. The microstructure color in the segregation area is different from the normal microstructure, usually showing a darker or brighter color. If segregation exists, observe the range and distribution characteristics of the segregation area. Under a 500X metallographic microscope, conduct a detailed analysis of the microstructure composition in the crack origin area and propagation area, such as which phases mainly compose it, the proportion and morphological characteristics of each phase. It is observed that the crack origin area is mainly composed of sorbite + a small amount of pearlite, and there is basically no ferrite, and the microstructure in the crack propagation area is sorbite + pearlite + ferrite. S5 Comprehensive Analysis and Conclusion Drawing: Combined with the results of stereoscopic analysis and metallographic analysis, a comprehensive judgment is made on the cause of the fracture of the spring steel. If mechanical damage is found on the surface of the sample in the stereoscopic analysis, and the metallographic analysis shows stress cracks and abnormal structures (such as white bright bands) near the fracture, it can be inferred that the fracture may be caused by the surface mechanical damage causing stress concentration during subsequent processing or use, resulting in crack initiation and expansion, and ultimately causing fracture. If the stereoscopic analysis finds pits, scars or foreign body indentation defects on the surface, and the metallographic analysis shows decarburization at the bottom of the pit and cold deformation of the matrix, the fracture may be caused by these original defects causing uneven stress on the matrix during processing, resulting in cold deformation, and then causing fracture; Among them, for samples with internal fractures, when metallographic analysis finds severe positive segregation in the crack origin zone, and negative segregation rings and positive segregation points are found under low-power observation, it can be judged that the fracture is due to the uneven internal structure of the material caused by segregation. During the processing or use of the spring, the deformation of the segregation area is not coordinated, thus causing cracking. Based on the results of the comprehensive analysis, a detailed diagnostic report is written. The report content includes the selection of samples, the specific results of stereoscopic analysis and metallographic analysis, the inference of the cause of the fracture, and improvement suggestions for the fracture problem, such as optimizing the processing technology and strengthening the inspection of raw materials.

[0019] Furthermore, the process can accurately locate the root cause of the fracture: This diagnostic process uses a combination of stereoscopic analysis and metallographic analysis techniques to comprehensively analyze the fracture characteristics of spring steel from both macroscopic and microscopic levels. By observing the macroscopic morphology of the fracture in detail through stereoscopic analysis, it can quickly discover obvious defects such as mechanical damage, pits, and scars on the surface; with the help of metallographic analysis, the internal structure can be deeply explored, and microscopic defects such as stress cracks, segregation, decarburization, and cold deformation can be accurately identified. The combination of the two can accurately locate the root cause of the fracture and provide a reliable basis for the formulation of subsequent improvement measures; This process improves product quality and reliability: after accurately determining the cause of the fracture, the manufacturer can optimize the production process according to the specific problem. For example, if it is found that the fracture is caused by surface mechanical damage, the protective measures during the processing can be improved to avoid surface damage; if the fracture is caused by segregation, the smelting and processing technology can be optimized to reduce the segregation phenomenon. This series of targeted improvement measures can effectively improve the quality of spring steel, enhance the reliability and stability of spring products, and reduce the risk of fracture during use; This process reduces production costs: Through this diagnostic process, potential problems can be discovered in a timely manner during product development and production, avoiding the generation of large amounts of waste due to spring steel breakage, reducing the waste of raw materials and production costs. At the same time, due to improved product quality, equipment failures and maintenance times are reduced, reducing equipment maintenance costs and downtime losses, and improving the overall economic benefits of the enterprise; This process ensures production safety: The fracture of spring steel may trigger serious safety accidents, especially in some key fields such as automotive, aerospace, etc. This diagnostic process can effectively prevent the occurrence of such problems, provide strong guarantee for the safe operation of relevant equipment by ensuring the quality and reliability of spring products, reduce the probability of safety accidents, and protect the lives of personnel and the property safety of enterprises; This process promotes technological innovation and industry development: The application of this diagnostic process helps to promote the innovation and development of spring steel production technology. In the process of solving the problem of spring steel fracture, enterprises will continuously explore new processing techniques, material treatment methods and quality inspection means, which will promote the improvement of the technical level of the entire spring steel industry and drive the sustainable and healthy development of the industry.

[0020] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A process for diagnosing the fracture cause of spring steel based on metallographic and stereoscopic analysis, characterized in that: It includes the following technological steps. S1 Specimen selection and preparation: Select multiple representative specimens from the fractured spring steel products. Select six specimens from different fracture positions and different batches of products, number the specimens for subsequent distinction and recording. Use suitable cutting methods such as wire cutting and grinding wheel cutting to cut the specimens into appropriate sizes according to the analysis requirements. Generally, the size of the longitudinal section or cross-section is more suitable at 10 - 20mm; After cutting, polish the cutting surface of the specimen. Use sandpapers with different mesh numbers in turn, from coarse sandpaper (120 mesh) to fine sandpaper (1000 mesh) for polishing until the cutting surface is flat and smooth without obvious scratches; After polishing, polish the specimen. Adopt mechanical polishing or electrolytic polishing methods to make the surface of the specimen reach a mirror effect for subsequent metallographic observation and analysis; S2 Stereoscopic analysis (macroscopic morphology observation): Place the prepared specimen under a stereoscopic microscope and conduct a comprehensive observation at a low magnification (5 - 10 times). Focus on observing the overall morphology of the specimen fracture surface, record the shape, color, and texture trend characteristics of the fracture surface, carefully check whether there are obvious mechanical damages, scratches, indentations on the fracture surface, and the position, depth, and range of the damages; For specimens with mechanical damages, describe the characteristics of the damages in detail, such as whether the damaged area shows metallic luster and whether there are signs of deformation; Observe whether there are other defects at the fracture surface, such as pits, scabs, foreign objects. If pits are found, measure the size of the pits, including diameter and depth, and record the number and distribution of the pits; For areas suspected of scab or foreign object pressing in, observe the deformation of the surrounding matrix; S3 Metallographic analysis: Metallographic specimen preparation: For the specimens after stereoscopic analysis, select the parts that need metallographic analysis, such as the area near the fracture surface. Adopt the embedding method to fix the specimen in a suitable embedding material, such as thermosetting plastic or epoxy resin, to ensure the stable position of the specimen during subsequent processing. Polish the embedded specimen again to make the metallographic observation surface reach a higher flatness and smoothness. During the polishing process, polishing paste auxiliary materials can be used to further improve the polishing effect; S4 Metallographic observation and analysis: Uncorroded metallographic observation: Place the prepared metallographic specimen under a metallographic microscope. First, observe the overall tissue morphology of the area near the fracture surface at a low magnification (50X), observe whether there are cracks. If there are cracks, record the number, trend, distribution of the cracks, and the approximate depth of the cracks. If the crack depth is found to be between 100 - 250um, carefully observe the morphological characteristics of the cracks to judge whether they are stress cracks. For example, stress cracks usually show a sharp and straight shape. Switch to a higher magnification (100X) to conduct a more detailed observation of the area near the fracture surface to check whether there are other microscopic defects, such as pores and inclusions, and record their characteristics and distribution; Etching Metallographic Observation: The metallographic specimen is etched using a suitable etchant, such as nitric acid alcohol solution. The etching time is controlled according to the material and tissue characteristics of the specimen, generally between 10 - 30 seconds; After etching, the specimen is rinsed with clean water, then dehydrated with alcohol, dried, and observed under a 50X metallographic microscope to check if there is any abnormal tissue on the surface, such as white bright bands. Record the position, width, and morphological characteristics of the white bright bands; S5 Comprehensive Analysis and Conclusion Drawing: Combining the results of stereoscopic analysis and metallographic analysis, comprehensively judge the fracture cause of the spring steel. If mechanical damage is found on the specimen surface during stereoscopic analysis, and metallographic analysis shows stress cracks and abnormal tissue near the fracture surface, it can be inferred that the fracture may be caused by stress concentration induced by surface mechanical damage during subsequent processing or use, leading to crack initiation and propagation, and ultimately resulting in fracture. If pits, scabs, or foreign object indentation defects are found on the surface during stereoscopic analysis, and metallographic analysis shows decarburization at the bottom of the pits and cold deformation in the matrix, the fracture may be caused by uneven stress on the matrix due to these original defects during processing, resulting in cold deformation and then fracture.

2. The process for diagnosing the fracture cause of spring steel based on metallographic and stereoscopic analysis according to claim 1, characterized in that: During the cutting process, pay attention to controlling the cutting speed and cooling conditions to prevent changes in the specimen tissue due to overheating or excessive force.

3. The diagnostic process for the fracture cause of spring steel based on metallographic and stereoscopic analysis according to claim 1, characterized in that: When grinding, maintain the stability of the specimen to avoid deformation or damage on the specimen surface.

4. The process for diagnosing the fracture cause of spring steel based on metallographic and stereoscopic analysis according to claim 1, characterized in that: Take photos of the observed macroscopic morphological characteristics, ensuring that the photos are clear and complete, accurately reflecting the actual situation of the fracture surface. At the same time, mark the specimen number, magnification, and observation date information on the photos for convenient subsequent analysis and reference.

5. The fracture cause diagnosis process of spring steel based on metallographic and stereoscopic analysis according to claim 1, characterized in that: For specimens with the said pit defects, observe the tissue condition at the bottom of the pits under a 100X metallographic microscope to judge if there is decarburization. Decarburization is manifested as a lighter color of the tissue at the bottom of the pits, with an obvious difference from the matrix tissue. Increase the magnification to 500X to observe the microstructure of the matrix at the pits to judge if there is cold deformation.

6. The process for diagnosing the fracture cause of spring steel based on metallographic and stereoscopic analysis according to claim 1, wherein: The characteristics of the said cold deformation include grain distortion and elongation. For specimens fractured from the inside, observe the tissue in the crack origin area under 50X and 100X metallographic microscopes to judge if there is segregation. The tissue color in the segregation area is different from the normal tissue, usually showing blackening or brightening. If there is segregation, observe the range and distribution characteristics of the segregation area. Under a 500X metallographic microscope, detailedly analyze the tissue composition in the crack origin area and propagation area, such as which phases mainly compose it, the proportion and morphological characteristics of each phase. It is observed that the crack origin area is mainly composed of sorbite + a small amount of pearlite, with basically no ferrite, and the tissue in the crack propagation area is sorbite + pearlite + ferrite.

7. The process for diagnosing the fracture cause of spring steel based on metallographic and stereoscopic analysis according to claim 1, characterized in that: For the internally fractured specimens, when metallographic analysis finds severe positive segregation in the crack origin zone, and negative segregation rings and positive segregation points are found under low-power observation, it can be judged that the fracture is due to the uneven internal structure of the material caused by segregation. During the processing or use of the spring, the deformation of the segregation area is not coordinated, thus causing cracking. Based on the results of the comprehensive analysis, a detailed diagnostic report is written. The report content includes the selection of the specimen, the specific results of the stereoscopic analysis and metallographic analysis, the inference of the cause of the fracture, and the improvement suggestions for the fracture problem, such as optimizing the processing technology and strengthening the inspection of raw materials.