Early fatigue damage detection and identification method based on microstructure difference of rare earth steel rail

Abstract

The invention discloses an early fatigue damage detection and identification method based on rare earth steel rail microstructure difference. A high-sensitivity ultrasonic probe is used for carrying out three-dimensional positioning on a suspected fatigue damage area of a steel rail; the suspected area is cut and sampled, a 3mm groove is formed in the rail bottom, then a press machine is used for breaking, and a crack source area is fully exposed; performing high-magnification scanning observation on the fracture of the sample, analyzing the types of inclusions, and distinguishing the existence characteristics of rare earth oxides, sulfides or composite inclusions; a metallographic microscope is adopted to analyze the microstructure around the fracture, abnormal structures such as grain distortion, a precipitated phase and a deformation zone are evaluated, a multi-step microscopic analysis means is adopted to identify a nuclear injury source, and a correlation mechanism between rare earth inclusions and fatigue crack formation is disclosed.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of metallurgy and rail transit material detection technology, and particularly relates to an early fatigue damage detection and identification method based on microstructure differences of rare earth steel rails. BACKGROUND

[0002] With the continuous improvement of the use conditions of steel rails by rail transit development, the problem of early fatigue damage of steel rails is increasingly prominent. Current detection technologies for nuclear damage are mostly based on online non-destructive detection methods such as ultrasonic waves, which can achieve preliminary positioning, but are still insufficient in analyzing the damage formation mechanism and material intrinsic factors. Traditional steel rails are mostly made of high-carbon steel, and internal inclusions and abnormal structures are common sources of fatigue crack initiation. In recent years, rare earth elements (such as La and Ce) have been gradually introduced into steel rail alloys to purify inclusions and refine grains in order to improve strength and toughness.

[0003] However, the introduction of rare earth elements also brings non-uniformity in microstructure and mechanical properties, which may become a new inducement for crack initiation and propagation. There is a lack of systematic detection and analysis methods for the formation mechanism of early damage in rare earth-containing steel rails in existing literature. Therefore, there is an urgent need for a scientific and systematic method to qualitatively and quantitatively identify fatigue damage in such steel rails, providing a basis for optimizing formulations and service safety evaluation. SUMMARY

[0004] The present application provides a method for detecting and identifying early fatigue damage based on microstructure differences of rare earth steel rails and a preparation method thereof, which uses microstructure analysis and hardness gradient evaluation methods to identify potential fatigue nuclear damage in rare earth steel rails in multiple dimensions.

[0005] The present application aims to provide a method for detecting and identifying early fatigue damage based on microstructure differences of rare earth steel rails, which includes the following steps:

[0006] First, use an ultrasonic probe to locate;

[0007] Second, cut and sample the suspected area;

[0008] Third, perform CT imaging and quantitative analysis;

[0009] Fourth, observe the metallographic structure;

[0010] Fifth, perform microhardness testing.

[0011] Further, in the first step, use a single-crystal multi-angle probe to detect defects, and after an alarm is detected, use a mirror to inspect the reflective surface of the alarm to exclude external influencing factors.

[0012] The rail and non-rail area are distinguished, the rail surface area is extracted, the rail top surface is long-term rubbed by the wheel, the rail top surface area is separated by using the brightness difference between the rail top surface and the non-rail area, and the suspected fatigue damage area of the rail is positioned in three dimensions by using a high-sensitivity ultrasonic probe.

[0013] Further, after a 3mm groove is formed on the rail bottom, a press is used to implement fracture, so that the crack source area is fully exposed.

[0014] Further, two-dimensional slice information is obtained by CT imaging in the third step, the two-dimensional slice information is three-dimensionally reconstructed for internal inclusions, and size information such as length, width, surface area and volume of the internal inclusions of the sample is obtained from the three-dimensionally reconstructed image.

[0015] By means of micro-CT imaging, the fracture of the sample is scanned at a high magnification, the type of inclusion and the distribution rule of the inclusion are analyzed, and the existence characteristics of rare earth oxides, sulfides or composite inclusions are distinguished.

[0016] Further, the microstructure structure around the fracture is analyzed by using a metallographic microscope, and the organization abnormalities such as grain distortion, precipitated phase and deformation band are evaluated.

[0017] Further, high-density hardness testing is performed on the crack source and the adjacent area, and the correlation between the hardness distribution abnormality induced by rare earth and the fatigue crack initiation is analyzed.

[0018] Further, the two-dimensional gray slice data obtained after scanning is three-dimensionally reconstructed by using Avizo, a 3D data visualization, analysis and modeling system, to extract and three-dimensionally visualize the inclusion information, and the inclusion information is quantitatively analyzed by using different part algorithm modules in the Avizo software.

[0019] Further, the suspected area is cut and sampled to form a sample, and a crack source caused by stress concentration caused by inclusions forms a core damage, and the core damage morphology is divided into black core and white core.

[0020] Compared with the prior art, the beneficial effects of the present application are:

[0021] The present application can realize the precise positioning and analysis of the early crack source of the rare earth rail, and can distinguish different types of rare earth inclusions.

[0022] The present application can realize the precise positioning and analysis of the early crack source of the rare earth rail, and can distinguish different types of rare earth inclusions.

[0023] The influence mechanism of fatigue damage formation; through hardness and tissue analysis, the scientificity and repeatability of diagnosis are improved; it can be used for transverse comparison analysis of rare earth steel rails under different steel plants or formula processes, supporting composition optimization and failure prediction. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 The typical core damage morphology of the application is a white core schematic diagram;

[0025] Figure 2 The typical core damage morphology of the application is a black core schematic diagram;

[0026] Figure 3 The schematic diagram of the fracture morphology observed by the scanning electron microscope of the application. DETAILED DESCRIPTION

[0027] In order to make the person skilled in the art better understand the technical solutions in the embodiments of the application, and make the above-mentioned purposes, characteristics and advantages of the application more obvious and easy to understand, the specific embodiments of the application will be further described below.

[0028] The technical solutions in the embodiments of the application will be described clearly and completely below by combining the drawings in the embodiments of the application. Obviously, the described embodiments are only part of the embodiments of the application, not all the embodiments. Based on the embodiments in the application, all other embodiments obtained by the person skilled in the art without creative labor belong to the protection scope of the application.

[0029] A method for detecting and identifying early fatigue damage of rare earth steel rails based on microstructure differences, comprising the following steps:

[0030] First, use an ultrasonic probe to locate;

[0031] Second, cut and sample the suspected area;

[0032] Third, CT imaging quantitative analysis;

[0033] Fourth, metallographic structure observation;

[0034] Fifth, microhardness test.

[0035] In the first step, the flaw detection uses a single crystal multi-angle probe to detect. After the alarm is found, the surface of the alarm is checked using a mirror surface to exclude external influencing factors;

[0036] The rail and non-rail area are distinguished, and the rail surface area is extracted. The long-term friction between the wheel and the top surface of the rail makes the top surface of the rail bright. The brightness difference between the top surface of the rail and the non-rail area is used to segment the top surface area of the rail. A high-sensitivity ultrasonic probe is used to three-dimensionally locate the suspected fatigue damage area of the rail.

[0037] After the 3mm groove is opened on the rail bottom, the press is used to implement fracture, so that the crack source area is fully exposed.

[0038] In the third step, two-dimensional slice information is obtained by CT imaging, and the two-dimensional slice information is three-dimensionally reconstructed for internal inclusions. The length, width, surface area, and volume of the internal inclusions are obtained from the three-dimensionally reconstructed image.

[0039] By means of micro-CT imaging, high-magnification scanning of the sample fracture is performed, and the inclusion type and inclusion distribution rule are analyzed to distinguish the existence characteristics of rare earth oxides, sulfides, or composite inclusions.

[0040] The microstructure structure around the fracture is analyzed by means of a metallographic microscope, and the grain distortion, precipitated phase, deformation band, and other abnormal structures are evaluated.

[0041] High-density hardness testing is performed on the crack source and adjacent area, the correlation between the hardness distribution abnormality induced by rare earth and the fatigue crack initiation is analyzed, the scientificity and repeatability of the diagnosis are improved by combining the hardness gradient and the structure analysis, which can be used for transverse comparison and analysis of rare earth steel rails in different steel plants or under different formula processes, and can support composition optimization and failure prediction.

[0042] Microhardness testing method: three groups of samples are taken at different positions in the direction of the crack source and adjacent area on the section surface, the hardness values of the three positions are measured by using a Rockwell hardness tester, at least 3 points are measured at each position, the average value is taken, and the Rockwell hardness is converted into Vickers hardness.

[0043] The two-dimensional gray slice data obtained after scanning is extracted and three-dimensionally reconstructed by using Avizo, a 3D data visualization, analysis and modeling system three-dimensionally reconstructing software, and the inclusion information is quantitatively analyzed by using different part algorithm modules in the Avizo software.

[0044] The inclusion distribution rule is analyzed by fracture and three-dimensional visualization processing, the distribution rule of inclusions existing in the fracture source (developing from the external micro-crack to the inside), the fracture source is generated at the internal inclusion of the steel rail, and then the core damage is formed. Two inclusions are found in the fracture source area, and the main components of the inclusions are C (5.64%), O (41.51%), Na (7.20%), Mg (7.20%), S (7.93%), Ca (13.18%), and Fe (12.35%).

[0045] The suspected area is cut and sampled to show that the crack source caused by stress concentration caused by inclusions forms a black core and a white core. The black core and the white core formed by stress concentration caused by inclusions can obtain the distribution rule of the number and size of internal inclusions after three-dimensional reconstruction.

[0046] It will be apparent to those skilled in the art that the application is not limited to the details of the above-exemplified embodiments and that the present application can be implemented in other particular forms without departing from the spirit or essential characteristics of the present application. The presently disclosed embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, the scope of the application being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

[0047] Furthermore, it should be understood that although the description is made on embodiments, not every embodiment contains only one independent technical solution, and the description is made in this way only for the sake of clarity, and those skilled in the art should consider the description as a whole, and the technical solutions in each embodiment can also be combined appropriately to form other embodiments that those skilled in the art can understand.

Claims

1. A method for detecting and identifying early fatigue damage based on differences in the microstructure of rare-earth steel rails, characterized in that, Includes the following steps; The first step is to locate the target using an ultrasonic probe; The second step is to cut and sample the suspected areas; The third step is quantitative analysis of CT imaging. The fourth step is metallographic observation; Step 5: Microhardness test.

2. The method for early fatigue damage detection and identification based on microstructure differences in rare earth rails according to claim 1, characterized in that: In the first step, flaw detection is performed using a single-crystal multi-angle probe. After an alarm is detected, a mirror is used to inspect the surface of the alarm's reflective surface to eliminate external influencing factors. The rail and non-rail areas are separated, and the rail surface area is extracted. The long-term friction between the wheel and the top surface of the rail makes the top surface of the rail bright. The top surface area of ​​the rail is segmented by utilizing the difference in brightness between the top surface of the rail and the non-rail area. A high-sensitivity ultrasonic probe is used to perform three-dimensional positioning of the suspected fatigue damage area of ​​the rail.

3. The method for early fatigue damage detection and identification based on microstructural differences in rare earth rails according to claim 2, characterized in that: After cutting a 3mm groove at the bottom of the rail, a press is used to fracture the crack, so that the crack initiation area is fully exposed.

4. The method for early fatigue damage detection and identification based on microstructure differences in rare earth rails according to claim 2, characterized in that: In the third step, CT imaging obtains two-dimensional slice information, and the two-dimensional slice information is used to reconstruct the three-dimensional inclusions inside the sample. The dimensional information such as the length, width, surface area and volume of the inclusions inside the sample is obtained through the three-dimensional reconstructed image. Using micro-CT imaging, the fracture surface of the sample is scanned at high magnification to analyze the type and distribution of inclusions, and to distinguish the presence characteristics of rare earth oxides, sulfides or complex inclusions.

5. The method for early fatigue damage detection and identification based on microstructure differences in rare earth rails according to claim 4, characterized in that: Metallurgical microscopy was used to analyze the microstructure around the fracture surface and to evaluate structural anomalies such as grain distortion, precipitates, and deformation zones.

6. The method for early fatigue damage detection and identification based on microstructure differences in rare earth rails according to claim 5, characterized in that: High-density hardness tests were conducted in the crack initiation and adjacent areas to analyze the correlation between rare earth-induced hardness distribution anomalies and fatigue crack initiation.

7. The method for early fatigue damage detection and identification based on microstructure differences in rare earth rails according to claim 6, characterized in that: The two-dimensional grayscale slice data obtained after scanning is used to extract and visualize inclusion information using the Avizo 3D data visualization, analysis and modeling system 3D reconstruction software, and the inclusion information is quantitatively analyzed using different algorithm modules in the Avizo software.

8. The method for early fatigue damage detection and identification based on microstructure differences in rare earth rails according to claim 7, characterized in that: The sample is cut from the suspected area to form a specimen. The crack source caused by stress concentration due to inclusions forms a nuclear injury. The morphology of the nuclear injury is divided into black nucleus and white nucleus.

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