Method for detecting non-metallic inclusions in steel

Abstract

The invention provides a method for detecting nonmetallic inclusions in steel, which comprises the following steps: placing a steel material in ethanol, cleaning with an ultrasonic cleaner, and drying to obtain steel to be detected; acquiring a detection surface of the steel to be detected; according to the method, the SEM is adopted to observe the morphology of the non-metallic inclusions on the detection surface, the sizes of the non-metallic inclusions are measured and counted, and the EDS is adopted to detect the components of the non-metallic inclusions, so that accurate positioning and qualitative analysis of the non-metallic inclusions can be realized, and the accuracy of the detection result is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of physical detection, and in particular relates to a method for detecting non-metallic inclusions in steel. Background Art

[0002] Non-metallic inclusions are an important factor affecting the quality of steel products and are also the focus of research in the field of steelmaking. Accurately and completely characterizing the shape, quantity, distribution, size, morphology and other characteristics of non-metallic inclusions in steel is particularly important for improving the quality of steel products.

[0003] At present, the inspection of non-metallic inclusions is carried out according to the method specified in the current standard GB / T 10561-2005 "Standard Rating Chart Microscopic Inspection Method for Determination of Non-metallic Inclusion Content in Steel". Generally, the inspection sample needs to be selected from the middle position between the center of the material and the surface, which takes a lot of man-hours to cut the sample, especially for spherical or nearly spherical particles such as DS inclusions. Because of their large particle size and random distribution, there are uncertain factors such as easy peeling, deformation, and polishing surface finish of inclusions during the grinding and polishing process. These influencing factors are the key steps that restrict the detection cycle and the accuracy of the results. In addition, the current detection of non-metallic inclusions mainly uses optical microscopes. Since the imaging principle of optical microscopes is plane reflection, the cutting depth of DS spheres is different during the sample preparation process, and the detection results are also different, which cannot accurately reflect the actual size of the inclusions; at the same time, the detection surface can only show a cross-section of the inclusions, and cannot characterize its surface characteristics, overall morphology and distribution.

[0004] At present, the morphology and chemical composition of DS inclusions are analyzed by combining SEM scanning electron microscope images and EDS energy spectrum. Generally, the sample is first ground and polished, and then placed under SEM for observation, to obtain "eye-shaped" inclusions. This method can characterize the inclusions to a certain extent. However, DS inclusions mainly exist in the matrix structure in the form of single spherical particles. Conventional metallographic inspection sample preparation uses grinding, polishing and other processes, which destroy the morphology and surface characteristics of the inclusions and the continuity of the organization; second, it is difficult to find inclusions, and third, conventional metallographic microscopes cannot determine the actual size of the inclusions. As a result, the analysis of chemical components cannot fully represent the composition of the inclusion body, making it difficult to accurately locate and qualitatively analyze, affecting the accuracy of the test results. Summary of the invention

[0005] The invention provides a method for detecting non-metallic inclusions in steel, which can realize accurate positioning and qualitative analysis of non-metallic inclusions and improve the accuracy of detection results.

[0006] The method for detecting non-metallic inclusions in steel provided by the present invention comprises the following steps:

[0007] The steel material is placed in ethanol, cleaned with an ultrasonic cleaning machine, and dried to obtain the steel to be tested;

[0008] Acquire the inspection surface of the steel to be inspected;

[0009] The SEM is used to observe the morphology of the non-metallic inclusions on the detection surface, the maximum size of the non-metallic inclusions is measured and statistically analyzed, and the EDS is used to detect the composition of the non-metallic inclusions.

[0010] In the detection method as described above, the detection surface of the steel to be detected is obtained by a method comprising the following process:

[0011] When the steel material to be tested is a failed part due to fracture during service, the crack source or the area with obvious macroscopic defects is selected as the test surface according to the cross-sectional characteristics;

[0012] When the inspection needs to occur before use, it is necessary to cut out the parts that can represent the fracture characteristics as the inspection surface. The specific parts are as follows:

[0013] When the diameter or side length of the steel material to be tested is ≤25mm steel bar, the steel material to be tested is subjected to stretching or impact treatment, and then cut to obtain a stretching fracture or impact fracture as the test surface;

[0014] When the diameter or side length of the steel material to be tested is within the range of 25mm to 40mm, the part is directly processed into a tensile or impact specimen, and the entire section is selected as the test surface;

[0015] When the diameter or side length of the steel material to be tested is ≥40mm, cut the tensile or impact specimen along 1 / 4 of the diameter of the bar or 1 / 4 of the side length from the edge source, and select the entire section as the test surface.

[0016] In the detection method as described above, the cutting process is performed by a cold cutting method.

[0017] In the detection method as described above, the cold cutting method includes at least one of electric spark wire cutting and liquid nitrogen brittle breaking.

[0018] In the detection method as described above, the detection surface is a characteristic area with macroscopic defects, a crack source area, or the entire cross-section of a fractured and failed part, or a tensile or impact fracture.

[0019] In the detection method as described above, when observing the morphology of non-metallic inclusions, the non-metallic inclusions detected by the detection surface to be detected are the number and size of DS-type inclusions.

[0020] In the detection method as described above, when measuring the size of non-metallic inclusions, the diameter of the largest spherical non-metallic inclusion in the detection surface to be detected is detected and recorded, and the diameter and number of all DS-type non-metallic inclusions on the detection surface are recorded.

[0021] The detection method as described above, wherein, when measuring the size of non-metallic inclusions, the scanning voltage is set to 20 kV, the beam current size is 100 pA, the magnification is 2 KX, the non-metallic inclusions are observed, the size is measured and the image is derived;

[0022] DS-type non-metallic inclusions are rated based on the size of the exported image.

[0023] In the detection method as described above, when counting the sizes of non-metallic inclusions, the proportion of DS type non-metallic inclusions with sizes i in the range of i<13μm, 13μm≤i<19μm, 19μm≤i<27μm, 27μm≤i<38μm, 38μm≤i<53μm, and i≥53μm are counted respectively, and the inclusions are graded according to the standards of i<13μm as level 0.5, 13μm≤i<19μm as level 1, 19μm≤i<27μm as level 1.5, 27μm≤i<38μm as level 2.0, 38μm≤i<53μm as level 2.5, and i≥53μm as level 3.0.

[0024] In the detection method as described above, EDS is used to analyze the composition of DS type non-metallic inclusions in each size segment.

[0025] The implementation of the present invention has at least the following beneficial effects:

[0026] The detection method of non-metallic inclusions in steel provided by the present invention can remove organic matter and impurities that are easy to fall off on the surface by pre-treating the detection surface, thereby avoiding the influence of impurities on the detection results. The detection method of the present invention can more comprehensively understand the morphology and distribution of non-metallic inclusions in steel, which is helpful to study the influence of non-metallic inclusions on steel performance; at the same time, the present invention uses SEM to observe the morphology of non-metallic inclusions in the detection surface, which can realize direct observation of the morphology of inclusions, and can also directly measure the size of inclusions. EDS can analyze the corresponding inclusion components and statistically analyze the inclusion components of each size segment, thereby realizing comprehensive detection of non-metallic inclusions in steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a SEM image of a detection section at a first angle in one embodiment of the present invention;

[0028] Figure 2 is a SEM image of a detection cross section at a second angle in one embodiment of the present invention;

[0029] Figure 3 is a SEM image of a detection cross section at a third angle in one embodiment of the present invention;

[0030] Figure 4 is a SEM image of a detection cross section at a fourth angle in one embodiment of the present invention;

[0031] Figure 5 is an EDS image of a non-metallic inclusion detected at a fourth angle in an embodiment of the present invention;

[0032] Figure 6 is a SEM image of a non-metallic inclusion in a detection section in one embodiment of the present invention;

[0033] Figure 7 is a SEM image of another non-metallic inclusion in the detection section in one embodiment of the present invention;

[0034] Figure 8 is a SEM image of another non-metallic inclusion in the detection section in one embodiment of the present invention;

[0035] Fig. 9 1 is a SEM image of another non-metallic inclusion detected in the cross section in one embodiment of the present invention. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] The invention provides a method for detecting non-metallic inclusions in steel, comprising the following steps: placing a steel material in ethanol, cleaning it with an ultrasonic cleaning machine, and obtaining the steel to be detected after drying; obtaining a detection surface of the steel to be detected; using SEM to observe the morphology of non-metallic inclusions on the detection surface, measuring the maximum size of the non-metallic inclusions and making statistics, and using EDS to detect the composition of the non-metallic inclusions.

[0038] Non-metallic inclusions are formed when a small amount of slag, refractory materials and smelting reaction products enter the molten steel during the steelmaking process. Non-metallic inclusions in steel refer to oxides, sulfides, silicates and nitrides that do not have metallic properties in steel. The type, composition, form, content, size, distribution, etc. of these non-metallic inclusions are one of the important indicators affecting steel quality.

[0039] The invention places the steel material in ethanol and uses an ultrasonic cleaning machine to clean it, thereby removing organic matter and large impurities that are easy to fall off on the surface, and obtaining the steel to be tested after drying.

[0040] The present invention does not limit the drying process. For example, a hair dryer may be used to quickly dry the surface of the steel material.

[0041] Among them, inclusion measurement is graded according to the maximum size, so it is the maximum size.

[0042] According to the research of the present invention, the above-mentioned detection method of non-metallic inclusions in steel is used to detect steel materials, which can realize accurate positioning and qualitative analysis of non-metallic inclusions. This is because, on the one hand, by pre-treating the detection surface, the organic matter and impurities that are easy to fall off on the surface can be removed, avoiding the influence of impurities on the detection results; on the other hand, the present invention uses SEM to observe the morphology of non-metallic inclusions in the detection surface, which can realize direct observation of the morphology of inclusions, and can also directly measure the size of inclusions. EDS can analyze the corresponding inclusion composition and statistically analyze the inclusion composition of each size segment, thereby realizing comprehensive detection of non-metallic inclusions in steel.

[0043] The present invention does not limit the specific process of obtaining the detection surface of the steel to be detected, and it can be obtained by conventional methods in the field. For example, in some embodiments, the detection surface of the steel to be detected is obtained by a method including the following process: when the fracture failure of the steel material part to be detected occurs during the service period, the area with obvious macroscopic defects or the crack source area of ​​the cross section of the steel material to be detected is selected as the detection surface. When the steel material detection demand occurs before the part is put into service, and when the diameter or side length of the steel material to be detected is ≤25mm steel bar, the steel material to be detected is subjected to stretching or impact treatment, and then cut to obtain a stretching fracture or impact fracture as the detection surface; when the diameter or side length of the steel material to be detected is within the range of 25mm to 40mm, the part is directly processed into a stretching or impact specimen, and the entire cross section is selected as the detection surface; when the diameter or side length of the steel material to be detected is ≥40mm, a stretching or impact specimen is cut along 1 / 4 of the diameter of the bar or 1 / 4 of the side length from the edge source, and the entire cross section is selected as the detection surface.

[0044] The detection surface is the characteristic area with macroscopic defects on the cross section of the fractured and failed parts, the crack source area, the entire cross section of the tensile fracture or the entire cross section of the impact fracture.

[0045] In some embodiments, when observing the morphology of non-metallic inclusions, the non-metallic inclusions to be detected by the detection surface are the number and size of DS-type inclusions.

[0046] Among them, when the size of the steel material to be tested is ≥40mm and the steel material to be tested has no natural cross-section, the tensile specimen or impact specimen can be prepared in accordance with the specifications of standard GB / T 2975-2018 "Sampling location and specimen preparation for mechanical properties test of steel and steel products", and then the fracture of the tensile specimen or impact specimen is cut as the test surface for observation.

[0047] The present invention does not limit the specific process of the above-mentioned cutting process, as long as a fracture can be obtained. For example, in some embodiments, a cold cutting method is used for cutting.

[0048] The present invention does not limit the specific operation steps of the cold cutting method, and conventional cold cutting methods in the art can be used. For example, the cold cutting method includes at least one of electric spark wire cutting and liquid nitrogen brittle fracture. In some embodiments, the cold cutting method includes: using liquid nitrogen to reduce the temperature of the part, and then using a hammer to fracture the part to produce a test surface; using a DK7255-2 electric spark wire cutting machine to cut the cross section of the fractured and failed part as the test surface.

[0049] The present invention does not limit the size of the detection surface. For example, in some embodiments, the area of ​​the detection surface is based on the area of ​​the cross section of the steel tensile test specimen, which is about 19 mm. 2 .

[0050] The present invention performs scanning electron microscope (SEM) detection on the detection surface, measures the size of non-metallic inclusions according to the SEM image and performs statistics, and uses EDS to detect the composition of the non-metallic inclusions. In this way, the size distribution and number density of non-metallic inclusions in steel are inferred by SEM, and the element composition of the corresponding non-metallic inclusions is analyzed by energy dispersive spectrometer (EDS), thereby ensuring the effectiveness and accuracy of the detection.

[0051] The present invention does not limit the number of inclusions detected by the detection surface, which depends on the actual situation. For example, in some embodiments, when observing the morphology of non-metallic inclusions, the number of non-metallic inclusions detected by the detection surface to be tested is 4, which exist in an aggregated state.

[0052] The present invention does not limit the specific operation steps when measuring the size of non-metallic inclusions, and conventional statistical methods in the art can be used. For example, in some embodiments, when measuring the size of non-metallic inclusions, the diameter of the largest spherical non-metallic inclusion in the test surface to be tested is detected and recorded, and the diameter and number of all DS-type non-metallic inclusions on the test surface are recorded. Among them, DS-type non-metallic inclusions are spherical, and by measuring the diameter and number of DS-type non-metallic inclusions, it is helpful to further grade DS-type non-metallic inclusions.

[0053] The present invention does not limit the parameters for measuring the size of non-metallic inclusions. For example, in some embodiments, when measuring the size of non-metallic inclusions, the scanning voltage is set to 20 kV, the beam current size is 100 pA, and the magnification is 2KX. The non-metallic inclusions are observed, the size is measured, and the image is exported; according to the size of the exported image, the DS type non-metallic inclusions are rated.

[0054] The present invention does not limit the specific parameters of the rating, and the conventional rating method in the art can be used, and the rating can be specifically based on the size. For example, in some embodiments, when the size of non-metallic inclusions is counted, the proportion of DS-type non-metallic inclusions with a size i in the range of i<13μm, 13μm≤i<19μm, 19μm≤i<27μm, 27μm≤i<38μm, 38μm≤i<53μm, and i≥53μm are counted respectively, and the rating is performed according to the standards of i<13μm as 0.5 level, 13μm≤i<19μm as 1 level, 19μm≤i<27μm as 1.5 level, 27μm≤i<38μm as 2.0 level, 38μm≤i<53μm as 2.5 level, and i≥53μm as 3.0 level. By dividing the size into the above-mentioned size segments, it is beneficial to analyze the distribution of DS-type non-metallic inclusions.

[0055] The present invention is not limited to the detection of DS non-metallic inclusions by EDS. For example, in some embodiments, EDS is used to analyze the composition of DS non-metallic inclusions of each size segment. By analyzing the distribution and composition elements of DS non-metallic inclusions of each size segment, it is helpful to further locate and qualitatively analyze non-metallic inclusions in steel.

[0056] The present invention will be further described below by means of specific examples and comparative examples.

[0057] Example 1

[0058] (1) Sample preparation: A 5 mm thick sample was cut from the fractured end of a locomotive water pump shaft that failed during service using a DK7255-2 wire-cut electric discharge machine. The sample was placed in an anhydrous ethanol solution and cleaned for 300 seconds using an ultrasonic cleaner to remove organic matter and other impurities that are easily detached from the surface. The sample was then quickly dried using a hair dryer for later use.

[0059] (2) The prepared sample is clamped under a scanning electron microscope and the parameters are set so that the image is clear and a single spherical particle embedded in the dimple can be observed, such as Figure 1 As shown; some spherical particles fall off and are free on the cross section, such as Figure 2 As shown in the figure; on the secondary cracks and some quasi-dissociation surfaces, there are spherical objects of different sizes in a clustered state, such as Figure 3As shown in the figure, DS non-metallic inclusions are spherical under an electron microscope, and neatly arranged and compact structures can be identified on the surface, such as Figure 4 As shown;

[0060] (3) Set the scanning voltage to 20KV, the beam current to 100pA, and the magnification to 2KX, observe the inclusions, measure the size, and export the image, such as Figure 6 , 7 , 8, 9;

[0061] According to the size of the exported image, the rating pattern is specified in accordance with the GB / T 10561-2005 standard for the rating requirements of DS inclusions, with sizes of 0.5 (i<13μm), 1 (13μm≤i<19μm), 1.5 (19μm≤i<27μm), 2.0 (27μm≤i<38μm), 2.5 (38μm≤i<53μm) and 3 (i≥53μm). Figure 6 The non-metallic inclusion size shown is D = 11.28 μm, with a grade of 0.5. Figure 7 The non-metallic inclusion size shown is D = 16.58 μm, with a grade of 1.0. Figure 8 The non-metallic inclusion size shown is D = 26.46 μm, with a grade of 1.5. Fig. 9 The non-metallic inclusion size shown is D = 34.89 μm, with a grade of 2.0;

[0062] (4)Select Figure 4 The chemical composition of the particles in the sample is mainly composed of Mg, Al, Ca, S and O elements through EDS spectrum analysis. Figure 5 shown.

[0063] The preferred specific embodiments of the present invention and the verification of the experiments are described in detail above. It should be understood that ordinary technicians in the field can make many modifications and changes based on the concept of the present invention without creative work. Therefore, all technical solutions that can be obtained by technicians in the technical field based on the concept of the present invention through logical analysis, reasoning or limited experiments on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. A method for detecting non-metallic inclusions in steel, characterized in that: The following steps are involved: The steel material is placed in ethanol, cleaned with an ultrasonic cleaning machine, and dried to obtain the steel to be tested; Acquire the inspection surface of the steel to be inspected; The SEM is used to observe the morphology of the non-metallic inclusions on the detection surface, the maximum size of the non-metallic inclusions is measured and statistically analyzed, and the EDS is used to detect the composition of the non-metallic inclusions.

2. The detection method according to claim 1, characterized in that: The detection surface of the steel to be detected is obtained by a method including the following process: When the steel material to be tested is a failed part due to fracture during service, the crack source or the area with obvious macroscopic defects is selected as the test surface according to the cross-sectional characteristics; When the inspection needs to occur before use, it is necessary to cut out the parts that can represent the fracture characteristics as the inspection surface. The specific parts are as follows: When the diameter or side length of the steel material to be tested is ≤25mm steel bar, the steel material to be tested is subjected to stretching or impact treatment, and then cut to obtain a stretching fracture or impact fracture as the test surface; When the diameter or side length of the steel material to be tested is within the range of 25mm to 40mm, the part is directly processed into a tensile or impact specimen, and the entire section is selected as the test surface; When the diameter or side length of the steel material to be tested is ≥40mm, cut the tensile or impact specimen along 1 / 4 of the diameter of the bar or 1 / 4 of the side length from the edge source, and select the entire section as the test surface.

3. The detection method according to claim 2, characterized in that: The cutting process is performed by a cold cutting method.

4. The detection method according to claim 3, characterized in that: The cold cutting method includes at least one of electric spark wire cutting and liquid nitrogen brittle cutting.

5. The detection method according to claim 2, characterized in that: The detection surface is a characteristic area with macroscopic defects on the cross section of the fractured and failed part, a crack source area, the entire cross section of the tensile fracture or the entire cross section of the impact fracture.

6. The detection method according to any one of claims 1 to 5, characterized in that: When observing the morphology of non-metallic inclusions, the non-metallic inclusions to be detected on the test surface are the number and size of DS type inclusions.

7. The detection method according to claim 6, characterized in that: When measuring the size of non-metallic inclusions, detect and record the diameter of the largest spherical non-metallic inclusion in the test surface to be tested, and record the diameter and number of all DS-type non-metallic inclusions on the test surface.

8. The detection method according to claim 6, characterized in that: When measuring the size of non-metallic inclusions, set the scanning voltage to 20kV, the beam current to 100pA, the magnification to 2KX, observe the non-metallic inclusions, measure the size and export the image; DS-type non-metallic inclusions are rated based on the size of the exported image.

9. The detection method according to claim 7, characterized in that: When counting the sizes of non-metallic inclusions, the proportion of DS non-metallic inclusions with sizes i in the range of i<13μm, 13μm≤i<19μm, 19μm≤i<27μm, 27μm≤i<38μm, 38μm≤i<53μm, and i≥53μm are counted respectively, and they are graded according to the standards of i<13μm as level 0.5, 13μm≤i<19μm as level 1, 19μm≤i<27μm as level 1.5, 27μm≤i<38μm as level 2.0, 38μm≤i<53μm as level 2.5, and i≥53μm as level 3.

0.

10. The detection method according to claim 9, characterized in that: EDS was used to analyze the composition of DS non-metallic inclusions in each size segment.

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