Hypoeutectoid steel fracture metallographic analysis method
By combining metallographic etching and scanning electron microscopy technology, the microstructure and fracture texture analysis of the fracture of the subeutectomy steel is solved, and the problem of independence of microstructure and fracture analysis in traditional methods is achieved, achieving more accurate fracture mechanism analysis.
Patent Information
- Application Number
- CN202510143316.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-02-10
- Publication Date
- 2025-05-13
AI Technical Summary
Microstructure analysis and fracture analysis of traditional subeutectoid steels are two relatively independent processes, which cannot accurately reflect the direct correspondence between the fracture crack initiation area and the crack expansion area. It depends on people's subjective thinking and experience, which can easily lead to irrational analysis errors.
Metallurgical etchant was used to etch the fracture of the subeutectomy steel, and then the fracture texture of the fracture, the microstructure structure of the crack source area, and the microstructure structure of the crack expansion area were characterized by using a scanning electron microscope to establish the correspondence between the microstructure and the fracture texture at the fracture.
Through this method, the microstructure factors of crack initiation and crack propagation during fracture of subeutectoid steel are accurately obtained, which improves the accuracy and reliability of the analysis, reduces costs, and simplifies operation.
Smart Images
Figure CN119985583A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the field of metallographic analysis of metal material fracture, and in particular relates to a method for metallographic analysis of hypoeutectoid steel fracture. Background Art
[0002] Hypoeutectoid steel is an iron-carbon alloy with a carbon content of less than 0.77%. Hypoeutectoid steel is widely used in the field of mechanical manufacturing, such as in the preparation of train wheels in the field of rail transportation. The structure of hypoeutectoid steel is mainly composed of proeutectoid ferrite and pearlite. The lower the carbon content, the higher the proeutectoid ferrite content and the lower the pearlite content; on the contrary, the higher the carbon content, the lower the proeutectoid ferrite content and the higher the pearlite content; under actual use conditions, hypoeutectoid steel metal parts are often subjected to static tensile load, static impact load and alternating load. Fracture is its main failure mode.
[0003] When a hypoeutectoid steel metal component breaks under actual service conditions, fracture analysis is an important means of determining the nature of the fracture, which is equivalent to the "fingerprint" characteristics of the person at the crime scene in a criminal case. The fracture characteristics of a hypoeutectoid steel metal component that has failed are an important basis for determining the nature and mechanism of the fracture. In addition, in scientific research, when performing performance tests on hypoeutectoid steel metal samples, including tensile tests, impact tests, and fatigue tests, the results will all yield the fracture surface of the hypoeutectoid steel metal sample. Characterizing the fracture surface is also an important basis for analyzing its fracture mechanism under specific test conditions.
[0004] In the past, the determination of fracture properties or fracture mechanism analysis of hypoeutectoid steel metal parts or metal samples often involves cutting metallographic samples near the fracture surface of metal parts or metal samples by wire cutting or other means, and then characterizing the microstructure of the metallographic sample. Combined with the characterization of the fracture surface, the microstructure of the hypoeutectoid steel is linked to the fracture surface by relying on the subjective analysis of scientific and technological personnel, and the role of the metal microstructure in the fracture process of hypoeutectoid steel is analyzed, and then the fracture mechanism of the hypoeutectoid steel is confirmed. It should be noted here that in the field of metal materials, the composition and organization of the metal are one factor that affects the fracture of metal parts and samples. In fact, environmental temperature and load are also another factor that affects the fracture of metal parts and samples. The interaction between environmental factors and the organization of metal materials ultimately leads to the fracture failure of metal parts or samples. Therefore, when determining the fracture properties and analyzing the fracture mechanism of metal parts or samples, the relationship between the organization of metal materials and the fracture characteristics must be established. Traditionally, the microstructure analysis and fracture analysis of metal materials are two relatively independent steps. On the one hand, it cannot accurately reflect the direct correspondence between the crack initiation zone and the crack propagation zone of the fracture. On the other hand, the characteristics of the organization at the fracture position are accidental. Cutting samples away from the fracture to obtain the microstructure of the metal material cannot accurately present the accidental factors of the organization. For example, the entire material organization is normal, but the only organizational defect appears in the crack initiation zone of the fracture site. Although the microstructure characterization and fracture analysis of metal materials still use the method of two independent steps, this method has obvious disadvantages. For this reason, how to combine metallography with fracture, open up metal fracture metallography methods, and accurately analyze the microstructure factors that cause crack initiation and crack propagation of hypoeutectoid steel metal parts or samples has become a technical problem that traditional technology needs to solve urgently.
[0005] Since the fracture of hypoeutectoid steel parts or sample fractures are usually obtained in the actual service environment or in the test environment, the fracture surface is often contaminated, which makes the fracture metallographic corrosion very difficult. In addition, fracture analysis is a niche business, and there are very few people who can engage in this business, because it requires knowledge of fracture science. Therefore, few people have tried to link fracture science with metallographic analysis methods to break through the last bottleneck of accurately analyzing the relationship between fracture and microstructure. The present invention organically combines the fracture science analysis method with the microstructure analysis method, and finds a new method for accurately establishing the relationship between fracture characteristics and the microstructure of hypoeutectoid steel. This method has important application value and very broad application prospects in the field of metal parts failure analysis in the fields of national defense, military industry, mechanism manufacturing, high-end equipment manufacturing, etc. If nothing unexpected happens, it should be an important beginning for the development of metal fracture metallography in my country. Because no such information was found in either literature search or invention patent search.
[0006] The present invention relates to a hypoeutectoid steel fracture metallographic analysis method. Traditionally, the characterization of the microstructure and fracture of hypoeutectoid steel are two independent processes. The fracture mechanism analysis of hypoeutectoid steel relies on people's subjective thinking and experience to link the organization with the fracture problem and obtain the fracture mechanism of hypoeutectoid steel. The traditional method has irrational analysis errors caused by factors such as insufficient experience of analysts, imperfect knowledge structure, and lack of knowledge. The method uses a metallographic etchant to etch the hypoeutectoid steel fracture, and then uses a scanning electron microscope to characterize the fracture texture of the fracture, the microstructure of the crack source area, and the microstructure of the crack extension area, thereby establishing a corresponding relationship between the microstructure and the fracture texture on the hypoeutectoid fracture, and accurately obtaining the microstructure factors that cause crack initiation and crack extension in the fracture process of hypoeutectoid steel through analysis. The method has the advantages of simple operation, low cost, high accuracy, etc., and is easy to promote and apply. Summary of the invention
[0007] The present invention proposes a hypoeutectoid steel fracture metallographic analysis method. The method uses a metallographic etchant to etch the hypoeutectoid steel fracture, and then uses a scanning electron microscope to characterize the fracture texture, the microstructure of the crack source area, and the microstructure of the crack extension area of the fracture, thereby establishing a corresponding relationship between the microstructure and the fracture texture on the hypoeutectoid fracture, and accurately obtaining the microstructure factors that cause crack initiation and crack extension in the hypoeutectoid steel fracture process through analysis. The method solves the irrational problem that traditional microstructure analysis and fracture analysis are independent of each other, and rely on human subjective thinking and experience to establish the corresponding relationship between the microstructure of hypoeutectoid steel and the fracture characteristics.
[0008] To achieve the above object, the technical solution adopted by the present invention comprises the following steps:
[0009] The first step is to physically clean the metal fracture. Use a soft brush to gently remove dust, sand and other attachments on the fracture surface. The brush should be perpendicular to the fracture surface and sweep back and forth on the fracture surface 3 to 5 times. Avoid using a hard brush, which will damage the fracture surface and lead to errors in fracture analysis.
[0010] The second step is to clean the fracture surface. Use 75-100% ethanol solution to clean the fracture surface. When the sample is small, ultrasonic assistance can be used. The cleaning time is 2-5 minutes, and then use cold air to dry.
[0011] The third step is metallographic etching of the fracture. The etching solution is 1-3% nitric acid alcohol solution. Place the fracture surface parallel to the desktop, use a pipette to absorb 2-5 ml of etching solution, and drop the etching solution on the fracture surface. After etching for 3-5 seconds, use a rapid water flow to quickly wash away the etching solution, then use anhydrous ethanol to clean the fracture surface to remove moisture from the fracture surface, and then use cold air to blow the fracture dry.
[0012] The fourth step is low-magnification characterization of the fracture. Low-magnification characterization of the fracture should be carried out using the secondary electron mode of a scanning electron microscope, with a voltage of 10 to 20 kV, a working distance of 8 to 25 mm, and a magnification of 200 to 1000 times, in order to clearly present the fracture texture and obtain fracture photos.
[0013] The fifth step is to analyze the crack source. The cleavage fracture surface confirms the crack source location based on the river pattern; the fatigue fracture surface confirms the crack source location based on the center of the curvature radius of the fatigue striation arc.
[0014] The sixth step is to characterize the microstructure of the crack source area. The microstructure of the fracture crack source area should be characterized by using the secondary electron mode of the scanning electron microscope, with a voltage of 10-20 kV, a working distance of 8-15 mm, and a magnification of 2000-20000 times to characterize the microstructure of the fracture crack source area.
[0015] The seventh step is to establish the correspondence between the microstructure and the crack source area. The microstructure of the crack source area is the weakest organizational factor that causes the fracture of hypoeutectoid steel. The fracture texture characteristics on the fracture surface are combined with the microstructure to obtain the correspondence between the microstructure of hypoeutectoid steel and crack initiation and crack propagation.
[0016] Preferably, the first step is physical cleaning of the metal fracture. Use a soft brush instead of a hard brush, which will damage the fracture and cause errors in fracture analysis. The soft brush is perpendicular to the fracture surface and is swept back and forth on the fracture surface 5 times to remove dust, sand and other attachments on the fracture surface.
[0017] Preferably, the second step is to clean the fracture surface by using anhydrous ethanol solution to clean the fracture surface. When the sample is small, ultrasonic wave can be used to assist. The cleaning time is 5 minutes, and then the sample is dried by cold air.
[0018] Preferably, the third step is metallographic etching of the fracture. The etching solution is a 3% nitric acid alcohol solution, the fracture surface is placed parallel to the desktop, 5 ml of etching solution is sucked with a pipette, and the etching solution is dropped on the fracture surface to ensure that the etching solution completely covers the fracture surface, and the etching is performed for 3 seconds, and the etching solution is quickly washed away with a rapid water flow, and then the fracture surface is washed with anhydrous ethanol to remove the moisture on the fracture surface, and then the fracture is blown dry with cold air.
[0019] Preferably, the fourth step is low-magnification characterization of the fracture. The low-magnification characterization of the fracture is preferably performed using a scanning electron microscope secondary electron mode, with a voltage of 20 kV, a working distance of 20 mm, and a magnification of 500 times, to clearly present the fracture texture and obtain a fracture photograph.
[0020] Preferably, the fifth step is to analyze the crack source. The cleavage fracture surface determines the crack source location according to the river pattern; the fatigue fracture surface determines the crack source location according to the center of the radius of curvature of the fatigue striation arc.
[0021] Preferably, the sixth step is characterizing the microstructure of the crack source area. The microstructure of the fracture crack source area is characterized by using a scanning electron microscope secondary electron mode, with a voltage of 20 kV, a working distance of 8 mm, and a magnification of 10,000 times, and focusing on capturing images of the crack source area and the crack extension area.
[0022] Preferably, the correspondence between the microstructure and the crack source region is established. The microstructure of the crack source region is the weakest organizational factor leading to the fracture of hypoeutectoid steel. The fracture texture characteristics on the fracture surface are combined with the microstructure to accurately obtain the correspondence between the microstructure of hypoeutectoid steel and crack initiation and crack propagation.
[0023] Traditionally, the characterization of the microstructure and fracture of hypoeutectoid steel are two independent processes. The analysis of the fracture mechanism of hypoeutectoid steel relies on people's subjective thinking and experience to link the organization with the fracture problem and obtain the fracture mechanism of hypoeutectoid steel. The traditional method has irrational analysis errors caused by factors such as insufficient experience, imperfect knowledge structure, and lack of knowledge of analysts. This method uses metallographic etchants to etch the fracture of hypoeutectoid steel, and then uses a scanning electron microscope to characterize the fracture texture of the fracture, the microstructure of the crack source area, and the microstructure of the crack extension area, and then establishes the correspondence between the microstructure and the fracture texture on the hypoeutectoid fracture. Through analysis, the microstructure factors that cause crack initiation and crack extension in the fracture process of hypoeutectoid steel are accurately obtained. This method has the advantages of simple operation, low cost, high accuracy, etc., and is easy to promote and apply.
[0024] Beneficial effects of the present invention: The present invention combines the traditional metallographic analysis method with the fractographic analysis method, and proposes a fractographic metallurgical analysis method. Traditionally, the characterization of the microstructure and the fractographic characterization of hypoeutectoid steel are two independent processes. The analysis of the fracture mechanism of hypoeutectoid steel relies on people's subjective thinking and experience to link the organization with the fracture problem and obtain the fracture mechanism of hypoeutectoid steel. The traditional method has irrational analysis errors caused by factors such as insufficient experience of analysts, imperfect knowledge structure, and lack of knowledge. The method uses a metallographic etchant to etch the fracture of hypoeutectoid steel, and then uses a scanning electron microscope to characterize the fracture texture of the fracture, the microstructure of the crack source area, and the microstructure of the crack extension area, and then establishes the corresponding relationship between the microstructure and the fracture texture on the hypoeutectoid fracture, and accurately obtains the microstructure factors that cause crack initiation and crack extension in the fracture process of hypoeutectoid steel through analysis. The method has the advantages of simple operation, low cost, high accuracy, etc., and is easy to promote and apply. BRIEF DESCRIPTION OF THE DRAWINGS
[0025] Figure 1 Conventional scanning electron microscopy secondary electron image characterization of the fracture surface of hypoeutectoid steel impact specimen.
[0026] Figure 2 Characterization of the crack source area of the hypoeutectoid steel impact specimen fracture using scanning electron microscope secondary electron image.
[0027] Figure 3 Fracture metallographic characterization of hypoeutectoid steel impact specimen using scanning electron microscope secondary electron image. DETAILED DESCRIPTION
[0028] The present invention will be further described in the following examples, but the present invention is not limited thereto.
[0029] Example 1 A method for metallographic analysis of hypoeutectoid steel impact fracture.
[0030] (1) Physical cleaning of hypoeutectoid steel impact fracture. Use a soft brush to gently remove dust, sand and other attachments on the surface of the hypoeutectoid steel impact fracture. The brush is perpendicular to the fracture surface and sweeps back and forth on the fracture surface 5 times. Avoid using a hard brush, which will cause fracture damage and lead to fracture analysis errors.
[0031] (2) Hypoeutectoid steel impact fracture surface cleaning: Add 100 ml of anhydrous ethanol to a 200 ml beaker, use tweezers to gently place the hypoeutectoid steel impact fracture sample in the anhydrous ethanol solution, and clean it for 5 minutes. Then use tweezers to clamp and take out the sample. During the removal process, the tweezers should not touch the fracture surface of the sample, and then use cold air to blow dry.
[0032] (3) Metallographic etching of hypoeutectoid steel impact fracture. Use a 3% nitric acid alcohol solution, place the hypoeutectoid steel impact fracture surface parallel to the desktop, use a pipette to absorb 5 ml of etching solution, and drop the etching solution on the fracture surface. This process needs to be completed quickly so that the etching solution completely covers the sample surface. After etching for 3 seconds, use a rapid water flow to quickly wash away the etching solution, then use anhydrous ethanol to clean the fracture surface to remove moisture from the fracture surface, and then use cold air to blow the fracture dry.
[0033] (4) Low-magnification characterization of hypoeutectoid steel impact fracture. Low-magnification characterization of fracture should be carried out using the secondary electron mode of a scanning electron microscope, with a voltage of 20 kV, a working distance of 13.68 mm, and a magnification of 3630 times, in order to clearly present the fracture texture, obtain fracture photos, and compare the traditional fracture characterization results with the fracture metallographic characterization results, as shown in the attached figure. Figure 1 shown.
[0034] (5) Analysis of crack source by impact fracture of hypoeutectoid steel. Judging from the texture of the hypoeutectoid steel impact fracture, the fracture is a typical brittle fracture, which is mainly composed of a large number of cleavage planes. The crack source position is determined according to the extension direction of the fracture ridge. The hypoeutectoid steel has a typical fan-shaped cleavage crack, and the crack source is located at the center of the "fan", such as Figure 2 shown.
[0035] (6) Characterization of the microstructure of the crack source area. The microstructure of the fracture crack source area should be characterized by using the secondary electron mode of the scanning electron microscope, with a voltage of 20 kV, a working distance of 14.39 mm, and a magnification of 5000 times. Figure 2 shown.
[0036] (7) Establish the corresponding relationship between microstructure and crack source area. The microstructure of the crack source area is the weakest organizational factor that causes the fracture of hypoeutectoid steel. The fracture texture characteristics on the fracture surface are combined with the microstructure to obtain the corresponding relationship between the microstructure of hypoeutectoid steel and crack initiation and crack propagation. Figure 2 As shown in the figure, this fracture texture is a typical fan-shaped cleavage, and the "fan" is the starting point of the crack, that is, the crack source. According to the fracture metallographic method proposed by the present invention, the microstructural characteristics of the crack source center can be observed intuitively and accurately. The center of the crack source area is a proeutectoid ferrite phase. It is determined that the fracture crack of the hypoeutectoid steel impact specimen starts at the junction of proeutectoid ferrite and pearlite, and the fracture is caused by proeutectoid ferrite as the weakest point. The crack propagates along the length direction of the pearlite layer, such as Figure 3 As shown, the longer the pearlite lamellae, the larger the fan-shaped cleavage plane, and the worse the impact properties of the material.
Claims
1. A method for metallographic analysis of hypoeutectoid steel fracture, characterized in that: The method includes the following steps: first, physical cleaning of the metal fracture; second, cleaning of the fracture surface; third, metallographic etching of the fracture; fourth, low-magnification characterization of the fracture; fifth, analysis of the crack source; and sixth, characterization of the microstructure of the crack source area. The seventh step is to establish the correspondence between the microstructure and the crack source area.
2. A hypoeutectoid steel fracture metallographic analysis method according to claim 1, characterized in that: The first step is to physically clean the metal fracture. Use a soft brush to gently remove dust, sand and other attachments on the fracture surface. The brush should be perpendicular to the fracture surface and sweep back and forth 3 to 5 times.
3. A hypoeutectoid steel fracture metallographic analysis method according to claim 1, characterized in that: The second step is to clean the fracture surface by using 75-100% ethanol solution to clean the fracture surface. The sample can be cleaned or assisted by ultrasonic wave for 2-5 minutes, and then blow-dried with cold air.
4. A hypoeutectoid steel fracture metallographic analysis method according to claim 1, characterized in that: The third step is metallographic etching of the fracture. The etching solution is 1-3% nitric acid alcohol solution. Place the fracture surface parallel to the table, use a pipette to absorb 2-5 ml of etching solution, and drop the etching solution on the fracture surface. After etching for 3-5 seconds, use a rapid water flow to quickly wash away the etching solution, then use anhydrous ethanol to clean the fracture surface to remove moisture from the fracture surface, and then use cold air to blow the fracture dry.
5. The method for analyzing hypoeutectoid steel fracture metallography according to claim 1, characterized in that: The fourth step is low-magnification characterization of the fracture. The low-magnification characterization of the fracture adopts the secondary electron mode of the scanning electron microscope, with a voltage of 10-20 kV, a working distance of 8-25 mm, and a magnification of 200-1000 times, aiming to clearly present the fracture texture and obtain fracture photos.
6. A hypoeutectoid steel fracture metallographic analysis method according to claim 1, characterized in that: The fifth step is to analyze the crack source. The cleavage fracture surface confirms the crack source location based on the river pattern; the fatigue fracture surface confirms the crack source location based on the center of the curvature radius of the fatigue striation arc.
7. A hypoeutectoid steel fracture metallographic analysis method according to claim 1, characterized in that: The sixth step is to characterize the microstructure of the crack source area. The microstructure of the fracture crack source area is characterized by using the secondary electron mode of a scanning electron microscope with a voltage of 10 to 20 kV, a working distance of 8 to 15 mm, and a magnification of 2000 to 20,000 times to characterize the microstructure of the fracture crack source area.
8. The method for analyzing hypoeutectoid steel fracture metallography according to claim 1, characterized in that: The seventh step is to establish the correspondence between the microstructure and the crack source area. The microstructure of the crack source area is the weakest organizational factor that causes the fracture of hypoeutectoid steel. The fracture texture characteristics on the fracture surface are combined with the microstructure to obtain the correspondence between the microstructure of hypoeutectoid steel and crack initiation and crack propagation. That is, the microstructure at the crack source is the main factor causing cracking, and the organizational characteristics on the crack propagation path are the organizational factors that lead to the preferred path of crack propagation.